Quantum Information meets Cosmology with Dr Aditya Iyer

From the Big Bang puzzles to testing if the early universe was quantum entangled — physicist Dr Aditya Iyer, from the University of Oxford, explains how quantum phenomena are key to understanding cosmology, gravity and even how it's possible we exist at all.

Episode Transcript

(00:00):
This should be strange to a quantum physicist because nothing can travel faster than the speed of light.

(00:04):
Except the expanding universe.
The fact that particle creation comes from something as algebraic as this is mind blowing.
When it's quantum, it's so beautiful because you get structure formation for free.
The uncertainty principle is the reason for you and me to be in existence, basically.
We are nothing but fluctuations, quantum fluctuations.

(00:24):
There was some dramatic process that happened in those 10 to the negative 34 seconds, which explains not only why the universe is so big today, but paradoxes of standard big bang cosmology.
This is the amazing thing.
That we see quantum mechanics expressed at all levels.
As we go further back in time, the universe was much smaller, that's the regime where quantum mechanics is king and also general relativity becomes very prominent because you have a lot more mass.

(00:50):
This is something that puzzled physicists for hundreds of years.
Einstein worked on this for a long period of time.
Why doesn't the electron emit gravitational waves? And why doesn't it collapse into the nucleus? it's about the interpretation of what it means for this entanglement to be created in the first place.
There are experimental predictions where quantum gravity becomes very important.
If you prove that the inflationary field is quantum some people actually say that gravity could be the inflaton.

(01:17):
With all of these things together, it becomes more and more difficult to refute that gravity is quantum.
That's what we're doing with quantum information theory and gravity.
Two disciplines that kind of evolve separately and are now starting to converge.
They're actually called the Big Bang Puzzles.
It's a good name.
It's a good name.
.000000001What's special about a flat universe? That's the first puzzle. 23 00:01:37,525.000000001 --> 00:01:37,945.000000001 Mm-hmm. 24 00:01:38,370.000000001 --> 00:01:42,666.66666667 And are you puzzled? Hello, welcome back to the Quantum Foundations Podcast. 25 00:01:43,56.66666667 --> 00:01:44,16.66666667 I'm Maria Vlo. 26 00:01:44,46.66666667 --> 00:01:59,256.66666667 I'm finishing my PhD here at Oxford, and today I'm joined by Adia Aya, who also did his PhD here at Oxford in the same group as as me with Blood Care Federal and is now doing a postdoc here. 27 00:02:00,306.66666667 --> 00:02:02,616.66666667 So the. 28 00:02:03,261.66666667 --> 00:02:13,341.66666667 Idea of this podcast is that we discuss interesting topics to do with the foundations of quantum visits, and there are two parts to it. 29 00:02:13,761.66666667 --> 00:02:15,861.66666667 One part is aimed at. 30 00:02:16,671.66666667 --> 00:02:18,681.66666667 Anyone who is interested. 31 00:02:18,741.66666667 --> 00:02:25,191.66666667 So this should be accessible for anyone and we will not be using technical jargon. 32 00:02:25,191.66666667 --> 00:02:29,211.66666667 We'll be explaining things in in an accessible but detailed way. 33 00:02:29,211.66666667 --> 00:02:31,461.66666667 So that's what this episode will be. 34 00:02:31,971.66666667 --> 00:02:34,791.66666667 And the other part is a technical part. 35 00:02:35,511.66666667 --> 00:02:47,331.66666667 Which is aimed at people that have some background in quantum mechanics have done some introductory course in quantum mechanics, and that will be more mathematical in a separate part two of each installment. 36 00:02:48,171.66666667 --> 00:02:56,151.66666667 So today we're going to be talking about the topic of quantum and cosmology, which is the focus of aias research. 37 00:02:56,931.66666667 --> 00:03:13,761.66666667 But before we dive into the interesting topics of your research, could you tell us a bit about how you ended up interested in these topics and how you ended up doing your PhD and postdoc research here? Yeah, absolutely. 38 00:03:13,761.66666667 --> 00:03:15,111.66666667 Thank you very much for having me. 39 00:03:15,651.66666667 --> 00:03:21,291.66666667 Um, well what's, what's not there to be interested in physics? I, I was very interested in physics since high school. 40 00:03:21,621.66666667 --> 00:03:21,711.66666667 Mm-hmm. 41 00:03:21,951.66666667 --> 00:03:24,741.66666667 Um, actually I was quite interested in chemistry. 42 00:03:25,341.66666667 --> 00:03:25,371.66666667 Oh. 43 00:03:25,371.66666667 --> 00:03:26,361.66666667 Um, and I. 44 00:03:26,706.66666667 --> 00:03:35,376.66666667 Was told by my chemistry instructors a number of times when I asked them, why is this like this? Or why, why is that like that? And they'd say, oh, that's just because it, it is. 45 00:03:35,376.66666667 --> 00:03:45,516.66666667 Or Why is the atomic structure of tungsten, um, five, D five instead of, why does the orbital fit like this? And they'd always say, oh, that's an exception. 46 00:03:45,816.66666667 --> 00:03:50,136.66666667 Um, but nature doesn't have any exceptions that are well-defined rules. 47 00:03:50,406.66666667 --> 00:03:51,906.66666667 Uh, it follows the laws of physics. 48 00:03:51,906.66666667 --> 00:03:56,346.66666667 As I later understood, and I wanted to dig deeper and understand the foundations of these things. 49 00:03:57,6.66666667 --> 00:03:58,566.66666667 Um, and that's how I got interested. 50 00:03:58,566.66666667 --> 00:04:13,776.66666667 It is in physics, uh, found many applications in a variety of different things, right? From why this table that, uh, we're sitting in front of is hard all the way to why planets form, why stars glow, and why the universe exists as, as we see today. 51 00:04:13,921.66666667 --> 00:04:14,341.66666667 Mm-hmm. 52 00:04:15,11.66666667 --> 00:04:15,301.66666667 Yeah. 53 00:04:15,571.66666667 --> 00:04:15,861.66666667 Cool. 54 00:04:16,476.66666667 --> 00:04:22,926.66666667 And then I think you, you, your research started off more in the cosmology direction Yes. 55 00:04:22,926.66666667 --> 00:04:24,126.66666667 Then became quantum. 56 00:04:24,216.66666667 --> 00:04:24,486.66666667 Yes. 57 00:04:24,486.66666667 --> 00:04:26,21.66666667 Could you tell us a bit about that? I. 58 00:04:27,36.66666667 --> 00:04:27,336.66666667 Yeah. 59 00:04:27,576.66666667 --> 00:04:28,656.66666667 Yeah, absolutely. 60 00:04:28,656.66666667 --> 00:04:39,731.66666667 So, um, as with many people enamored by physics, I was enamored by the universe like stars, um, their place in the universe, um, the age of the universe, why is it so old? Mm-hmm. 61 00:04:39,816.66666667 --> 00:04:45,6.66666667 And what astronomical objects can tell us about, about, about those, those questions. 62 00:04:45,516.66666667 --> 00:04:50,496.66666667 Um, and naturally, uh, cosmology was one such topic that could answer these questions. 63 00:04:50,501.66666667 --> 00:04:50,811.66666667 Mm-hmm. 64 00:04:51,36.66666667 --> 00:04:54,996.66666667 Um, so I became interested in cosmology, particularly early universe cosmology. 65 00:04:55,371.66666667 --> 00:05:05,241.66666667 Which is going as far back in time as we possibly can, uh, even further back than the things that we currently can see as signals from when the universe was conceived. 66 00:05:05,781.66666667 --> 00:05:16,41.66666667 Uh, and I realized that a lot of the phenomena that we can only hypothesize and not see, uh, today our test in the laboratory have something to do with quantum mechanics. 67 00:05:16,41.66666667 --> 00:05:22,341.66666667 It's a dramatic interplay, uh, of quantum mechanics and gravity at its finest in very extreme conditions. 68 00:05:22,791.66666667 --> 00:05:30,531.66666667 Um, and it's an inescapable fact to end up in quantum mechanics after having seen so much about early universe as, as, as I have. 69 00:05:30,771.66666667 --> 00:05:30,891.66666667 Mm-hmm. 70 00:05:31,971.66666667 --> 00:05:32,481.66666667 Interesting. 71 00:05:32,481.66666667 --> 00:05:32,601.66666667 Yeah. 72 00:05:32,901.66666667 --> 00:05:33,381.66666667 Cool. 73 00:05:33,861.66666667 --> 00:05:39,141.66666667 Well, yeah, hopefully our viewers will be convinced of that as well by the, the end of this episode. 74 00:05:39,141.66666667 --> 00:05:39,801.66666667 I sure hope so. 75 00:05:41,661.66666667 --> 00:05:42,81.66666667 Cool. 76 00:05:42,321.66666667 --> 00:05:51,22.66666667 So, um, yeah, so could you tell us a bit about what kind of things, um, you've been doing in your research in mm-hmm. 77 00:05:51,61.66666667 --> 00:05:52,131.66666667 Your PhD and then. 78 00:05:52,776.66666667 --> 00:05:55,896.66666667 Uh, more recently in your postdoc as well? Yeah, absolutely. 79 00:05:55,896.66666667 --> 00:06:04,146.66666667 So I started off my PhD and trying to answer this question like what signatures do we have? Uh, that gravity is indeed quantum. 80 00:06:04,146.66666667 --> 00:06:09,486.66666667 For over a hundred years, we've tried to unify quantum mechanics and gravity. 81 00:06:09,576.66666667 --> 00:06:13,776.66666667 Uh, the theory of gravity is general relativity, which is an entirely classical theory. 82 00:06:13,776.66666667 --> 00:06:15,156.66666667 There's nothing quantum about it. 83 00:06:15,456.66666667 --> 00:06:18,156.66666667 It says, um, space time is a manifold. 84 00:06:18,576.66666667 --> 00:06:22,236.66666667 Uh, when you put matter on that manifold, it curves in response to that matter. 85 00:06:22,506.66666667 --> 00:06:30,336.66666667 And the path matter takes is nothing but, um, following geodesics, which are straight line parts along that curved surface. 86 00:06:30,636.66666667 --> 00:06:34,141.66666667 Nothing quantum mechanical about this and a manifold fur. 87 00:06:34,601.66666667 --> 00:06:41,886.66666667 Um, a manifold is, you can think of it as a piece of cloth that can be stretched in any way, any shape or form that you like. 88 00:06:42,36.66666667 --> 00:06:42,156.66666667 Mm-hmm. 89 00:06:42,396.66666667 --> 00:06:45,636.66666667 Except this is paste time, so it's an infinitely large cloth. 90 00:06:45,726.66666667 --> 00:06:45,786.66666667 Mm. 91 00:06:46,716.66666667 --> 00:06:47,16.66666667 Yeah. 92 00:06:47,16.66666667 --> 00:06:51,576.66666667 So General Relativity gives us this, uh, space time cloth. 93 00:06:51,636.66666667 --> 00:06:51,936.66666667 Yes. 94 00:06:52,386.66666667 --> 00:07:13,86.66666667 And then what's the problem with, uh, yes, with gravity? Um, and it tells us, it tells us very well that if you put a particle or a star on this cloth, how is it going to move? Um, and it does this really well to the extent that, um, general, one of the earliest proofs that general Relativity was the theory of gravity. 95 00:07:13,371.66666667 --> 00:07:19,941.66666667 And not Newton mechanics was this guy Edington going on a boat and observing a solar eclipse to calculate the procession of mercury. 96 00:07:20,331.66666667 --> 00:07:27,51.66666667 Uh, so if Newtonian mechanics, which is the classical theory of gravity were true, he would've observed something. 97 00:07:27,381.66666667 --> 00:07:32,31.66666667 Uh, but actually in reality, he observed a very tiny deviation of 0.81 98 00:07:32,31.66666667 --> 00:07:41,661.66666667 arc seconds, which is a very, very tiny deviation in from the orbital pathic mercury processing, uh, which suggested that that correction had to come from somewhere, which is general activity. 99 00:07:41,691.66666667 --> 00:07:44,841.66666667 Uh, so yes, general relativity is a tested theory. 100 00:07:45,171.66666667 --> 00:07:48,801.66666667 Uh, it can tell you how things move in the presence of a gravitational traction. 101 00:07:48,801.66666667 --> 00:07:51,981.66666667 In the case of Mercury is that, is the planet Mercury responding to the sun. 102 00:07:52,611.66666667 --> 00:07:57,591.66666667 But there's also another theory, the theory of quantum mechanics that tells us matter is quantum. 103 00:07:57,951.66666667 --> 00:07:58,41.66666667 Mm-hmm. 104 00:07:58,281.66666667 --> 00:08:00,416.66666667 So, going back to the example of why this table is hard. 105 00:08:01,101.66666667 --> 00:08:02,811.66666667 It's because of the exclusion principle. 106 00:08:03,201.66666667 --> 00:08:07,641.66666667 Um, the poly exclusion principle tells us that no two Ians can occupy the same energy level. 107 00:08:07,641.66666667 --> 00:08:10,41.66666667 So my hand and my hand can't penetrate this table. 108 00:08:10,71.66666667 --> 00:08:10,371.66666667 Mm-hmm. 109 00:08:10,611.66666667 --> 00:08:19,671.66666667 So that's quantum mechanics, a bunch of spooky, um, laws, um, which I, which we actually quite understand really well. 110 00:08:19,881.66666667 --> 00:08:20,61.66666667 Yeah. 111 00:08:20,61.66666667 --> 00:08:23,421.66666667 That give rise to macroscopic properties, like the hardness of substances. 112 00:08:23,661.66666667 --> 00:08:23,751.66666667 Mm-hmm. 113 00:08:23,991.66666667 --> 00:08:28,671.66666667 Um, and if you take it to, to the next level, it can even explain the origin of the universe. 114 00:08:29,61.66666667 --> 00:08:31,551.66666667 Uh, which is what we will be covering in this podcast. 115 00:08:31,731.66666667 --> 00:08:33,861.66666667 So two very seemingly disconnected theories. 116 00:08:33,861.66666667 --> 00:08:39,411.66666667 One that tells you how matter how spacetime responds to matter when put on it, which is general relativity. 117 00:08:39,411.66666667 --> 00:08:39,531.66666667 Mm-hmm. 118 00:08:39,771.66666667 --> 00:08:43,101.66666667 And another which tells you how matter itself interacts with its surroundings. 119 00:08:43,101.66666667 --> 00:08:43,191.66666667 Mm-hmm. 120 00:08:43,641.66666667 --> 00:08:44,901.66666667 Which is quantum mechanics. 121 00:08:45,51.66666667 --> 00:08:45,141.66666667 Mm-hmm. 122 00:08:45,381.66666667 --> 00:08:54,141.66666667 So, um, when I shine a laser, the photons that are sent out of the laser, they're quantum, um, the electron, uh, bound to the hydrogen atom. 123 00:08:54,141.66666667 --> 00:08:54,921.66666667 That's quantum. 124 00:08:54,921.66666667 --> 00:08:55,11.66666667 Mm-hmm. 125 00:08:55,406.66666667 --> 00:08:57,291.66666667 And the interaction that's mediating this. 126 00:08:57,666.66666667 --> 00:09:02,496.66666667 Uh, the cool potential or, um, the electromagnetic force is also a quantum field. 127 00:09:02,766.66666667 --> 00:09:02,856.66666667 Mm-hmm. 128 00:09:03,96.66666667 --> 00:09:05,526.66666667 So everything matter in its interactions are quantum. 129 00:09:05,796.66666667 --> 00:09:05,946.66666667 Yeah. 130 00:09:05,946.66666667 --> 00:09:08,616.66666667 But seemingly gravity, this cloth does not seem to be. 131 00:09:10,86.66666667 --> 00:09:10,506.66666667 Yeah. 132 00:09:10,896.66666667 --> 00:09:18,126.66666667 So what's the, what's the problem where, so yeah, we have these two theories. 133 00:09:18,156.66666667 --> 00:09:18,246.66666667 Mm-hmm. 134 00:09:18,486.66666667 --> 00:09:24,996.66666667 So they're both very good space, time, cloth and quantum matter. 135 00:09:25,1.66666667 --> 00:09:25,191.66666667 Yeah. 136 00:09:26,196.66666667 --> 00:09:26,256.66666667 Um. 137 00:09:28,26.66666667 --> 00:09:42,666.66666667 What happens when, well, I guess what situations do we need to consider both of these, and then what's the issue? Why is this a, why is there a problem? Yeah. 138 00:09:43,86.66666667 --> 00:09:47,766.66666667 The fact that we can't, uh, treat gravity in this quantum as quantum. 139 00:09:48,936.66666667 --> 00:09:49,866.66666667 Yeah, absolutely. 140 00:09:49,866.66666667 --> 00:09:53,106.66666667 So, um, some people would say, actually there is no problem. 141 00:09:53,541.66666667 --> 00:09:55,401.66666667 Um, so let's address that first. 142 00:09:55,431.66666667 --> 00:09:55,611.66666667 Yeah. 143 00:09:56,31.66666667 --> 00:10:12,51.66666667 Um, so we, why do we know that the electromagnetic field is quantum? Well, there are many reasons, but one of the earliest signs was, um, the Rutherford model of the atom, where there's a nucleus and an electron spinning around that nucleus. 144 00:10:12,441.66666667 --> 00:10:15,291.66666667 Um, this would be a highly unstable system. 145 00:10:15,786.66666667 --> 00:10:17,106.66666667 Where the electron would start. 146 00:10:17,166.66666667 --> 00:10:28,896.66666667 According to Maxwell's theory of electromagnetic radiation, a moving charge should generate an electromagnetic wave, uh, which means our charge is losing energy, so it has no choice but to collapse and fall into the nucleus. 147 00:10:29,76.66666667 --> 00:10:29,166.66666667 Mm-hmm. 148 00:10:29,406.66666667 --> 00:10:30,936.66666667 And we know this is not true. 149 00:10:31,506.66666667 --> 00:10:38,436.66666667 Uh, things don't just, uh, you know, disintegrate in front of us spontaneously, and in fact, matter is very stable. 150 00:10:38,766.66666667 --> 00:10:41,436.66666667 And the solution was Bo's model of the atom, which said no. 151 00:10:41,436.66666667 --> 00:10:42,276.66666667 In fact, these things. 152 00:10:42,831.66666667 --> 00:10:49,371.66666667 Are quantum and the, the orbits that the electrons take have quantized energies and you can only make quantized jumps. 153 00:10:49,371.66666667 --> 00:10:51,831.66666667 You cannot lose continuous amounts of energy. 154 00:10:52,11.66666667 --> 00:10:52,431.66666667 Mm-hmm. 155 00:10:52,476.66666667 --> 00:10:55,191.66666667 So that was, so here quantum is kind of breaking it into chunks. 156 00:10:55,221.66666667 --> 00:10:59,601.66666667 Discreet chunks is where the quantum ness exactly is coming. 157 00:10:59,601.66666667 --> 00:11:06,771.66666667 So from a continuous thing to these discreet energy levels that we learn in high school chemistry. 158 00:11:06,776.66666667 --> 00:11:07,761.66666667 Yeah, yeah, yeah, exactly. 159 00:11:07,761.66666667 --> 00:11:09,501.66666667 And that's like one of the, um. 160 00:11:09,936.66666667 --> 00:11:12,246.66666667 Let's say base manifestations of quantum mechanics. 161 00:11:12,246.66666667 --> 00:11:12,336.66666667 Mm-hmm. 162 00:11:12,336.66666667 --> 00:11:19,446.66666667 As quantum information theorists, we know that there are many other expressions that quantum mechanics takes, but this is one of those things that quantum mechanics gives us. 163 00:11:19,476.66666667 --> 00:11:19,566.66666667 Mm-hmm. 164 00:11:19,866.66666667 --> 00:11:22,836.66666667 Uh, now the same argument can be made for gravity. 165 00:11:23,136.66666667 --> 00:11:28,296.66666667 So, uh, there are, uh, systems that are gravitationally bound. 166 00:11:28,296.66666667 --> 00:11:28,386.66666667 Mm-hmm. 167 00:11:28,896.66666667 --> 00:11:35,676.66666667 Uh, if these are quantum objects, uh, why, and a similar argument can be made that gravity is not quantum. 168 00:11:36,36.66666667 --> 00:11:37,836.66666667 Then they should be emitting gravitational waves. 169 00:11:37,836.66666667 --> 00:11:42,156.66666667 So imagine two, um, two stars that are gravitationally bound. 170 00:11:42,456.66666667 --> 00:11:42,576.66666667 Mm-hmm. 171 00:11:43,716.66666667 --> 00:11:44,946.66666667 As they revolve around each other. 172 00:11:44,946.66666667 --> 00:11:48,336.66666667 They should be emitting gravitational waves, which they do, and then they collapse into each other. 173 00:11:48,576.66666667 --> 00:11:51,426.66666667 But when you break, break it down into smaller and smaller parts. 174 00:11:51,426.66666667 --> 00:11:52,776.66666667 Go back to the hydrogen atom. 175 00:11:53,256.66666667 --> 00:11:53,346.66666667 Mm-hmm. 176 00:11:53,586.66666667 --> 00:11:57,666.66666667 Uh, proton has mass, the electron has mass and the electron is revolving around the proton. 177 00:11:58,56.66666667 --> 00:12:06,186.66666667 Why doesn't the electron emit gravitational waves? And why doesn't it collapse into the nucleus? Well, the argument there is gravity is such a weak force. 178 00:12:06,306.66666667 --> 00:12:06,396.66666667 Mm-hmm. 179 00:12:06,636.66666667 --> 00:12:11,136.66666667 Its 10 to the negative 34 times, um, weaker than the electromagnetic force. 180 00:12:11,136.66666667 --> 00:12:14,946.66666667 So maybe if you wait that long, all the atoms will start collapsing into each other. 181 00:12:14,946.66666667 --> 00:12:16,206.66666667 So that's a grim reality. 182 00:12:16,206.66666667 --> 00:12:19,626.66666667 Do we want to wait that long and watch our universe collapse into itself? Mm-hmm. 183 00:12:19,866.66666667 --> 00:12:20,256.66666667 Uh, no. 184 00:12:20,256.66666667 --> 00:12:23,316.66666667 So that could be a motivation for why we want gravity to be quantum. 185 00:12:24,276.66666667 --> 00:12:25,506.66666667 Uh, another motivation is. 186 00:12:26,46.66666667 --> 00:12:34,86.66666667 Everything that we just described, all the matter that we see around us is quantum, the electromagnetic field radioactivity, which is the weak force. 187 00:12:34,146.66666667 --> 00:12:37,686.66666667 The strong force which binds together, quarks into a proton. 188 00:12:38,16.66666667 --> 00:12:41,16.66666667 All of these things have successful quantum mechanical descriptions. 189 00:12:41,316.66666667 --> 00:12:48,606.66666667 Why is gravity, uh, the only thing that does not have, uh, quantum mechanical description? This is something that puzzled physicists for hundreds of years. 190 00:12:48,606.66666667 --> 00:12:51,246.66666667 Einstein worked on this for a long period of time. 191 00:12:51,546.66666667 --> 00:12:53,886.66666667 The idea that was perpetrated was that. 192 00:12:54,276.66666667 --> 00:13:04,116.66666667 Gravity would eventually be unified into unified quantum theory of fields where gravity would be yet another field that is unified with, um, with every other field that we know of. 193 00:13:04,581.66666667 --> 00:13:06,576.66666667 Quantum and quantum. 194 00:13:06,636.66666667 --> 00:13:11,77.66666667 Because since every other field is quantum and you want gravity to be unified with these quantum things mm-hmm. 195 00:13:11,151.66666667 --> 00:13:19,896.66666667 And there's a well known, uh, series of arguments that can be made that you can't have classical things interact with quantum mechanical things in a consistent way. 196 00:13:20,481.66666667 --> 00:13:23,61.66666667 Um, again, this is only a theoretical argument. 197 00:13:23,61.66666667 --> 00:13:32,331.66666667 It could be that we haven't found the right theory, uh, and in the future someone might find a theory where the classical gravity works and quantum mechanical fields have a place in such a classical theory. 198 00:13:32,691.66666667 --> 00:13:34,251.66666667 I cannot tell you that's not possible. 199 00:13:34,311.66666667 --> 00:13:34,401.66666667 Mm-hmm. 200 00:13:34,641.66666667 --> 00:13:39,591.66666667 But with all that we know now, and all the tools that we have available to us is just inconsistent. 201 00:13:39,591.66666667 --> 00:13:40,791.66666667 It feels very inconsistent. 202 00:13:40,911.66666667 --> 00:13:41,1.66666667 Mm-hmm. 203 00:13:41,241.66666667 --> 00:13:43,251.66666667 So that's another reason to quantize gravity. 204 00:13:43,281.66666667 --> 00:13:54,621.66666667 How can we reconcile these inconsistencies to have theoretical consistency? Um, in our description of gravity and the matter that gravity generates, that's the gravity that matter. 205 00:13:54,621.66666667 --> 00:13:55,11.66666667 Generates Uhhuh. 206 00:13:56,176.66666667 --> 00:13:56,416.66666667 Yeah. 207 00:13:56,841.66666667 --> 00:13:59,811.66666667 Yeah, yeah. 208 00:13:59,901.66666667 --> 00:14:11,841.66666667 And then, um, yeah, so there were these inconsistencies with where it, it, yeah, kind of seems strange for gravity not to be quantum. 209 00:14:11,841.66666667 --> 00:14:14,631.66666667 'cause then we can't model it in the way that we're modeling everything else. 210 00:14:14,691.66666667 --> 00:14:14,871.66666667 Yeah. 211 00:14:15,171.66666667 --> 00:14:17,961.66666667 And then there's some particular. 212 00:14:20,961.66666667 --> 00:14:26,271.66666667 Situations where we, we really need both quantum mechanics and general relativity. 213 00:14:26,301.66666667 --> 00:14:26,571.66666667 Yes. 214 00:14:26,661.66666667 --> 00:14:33,111.66666667 And then things get weird 'cause we dunno what to, to do anymore. 215 00:14:33,231.66666667 --> 00:14:34,41.66666667 Yeah, absolutely. 216 00:14:34,41.66666667 --> 00:14:40,401.66666667 So there are many gray areas, um, one such, um, but let's, let's talk about what we can do in the laboratory. 217 00:14:40,731.66666667 --> 00:14:46,341.66666667 Uh, one such experiment, which my supervisor, our supervisor Lakora proposed was, uh. 218 00:14:47,31.66666667 --> 00:14:55,791.66666667 The B and b experiment that says if you have two masses in a super position, so imagine this is a mouse that's in a super position and this is a mouse in a super position. 219 00:14:56,331.66666667 --> 00:15:00,981.66666667 Uh, the different branches of the super position would have a different gravitational interaction between them. 220 00:15:01,311.66666667 --> 00:15:04,221.66666667 So these two being closer would interact differently. 221 00:15:04,491.66666667 --> 00:15:06,681.66666667 This, and this would interact differently. 222 00:15:07,41.66666667 --> 00:15:09,591.66666667 And as they evolve, they would pick up different phases. 223 00:15:09,681.66666667 --> 00:15:11,751.66666667 That depends on the nature of the interaction. 224 00:15:12,246.66666667 --> 00:15:22,416.66666667 So you can do an interference experiment in the laboratory as different branches of the superposition pick up different phases, uh, purely because their interaction is mediated by gravity. 225 00:15:22,896.66666667 --> 00:15:30,36.66666667 Uh, so that's something you can observe in the laboratory where a quantum mechanical object to masses in superposition, uh, interact through gravity. 226 00:15:30,396.66666667 --> 00:15:30,876.66666667 Mm-hmm. 227 00:15:30,966.66666667 --> 00:15:32,166.66666667 Uh, they get entangled. 228 00:15:32,616.66666667 --> 00:15:36,336.66666667 And when they get entangled, uh, the natural conclusion to come to. 229 00:15:36,711.66666667 --> 00:15:44,91.66666667 Is that the field which medias the intraction gravity must also be quantum in light of these inconsistencies that we wanted to avoid. 230 00:15:44,691.66666667 --> 00:15:51,261.66666667 Um, so that's, uh, that's one, one area where we can see an interplay between gravity and quantum mechanics. 231 00:15:51,321.66666667 --> 00:15:51,411.66666667 Mm-hmm. 232 00:15:51,711.66666667 --> 00:15:57,921.66666667 Um, and the, yeah, if, um, yeah. 233 00:15:57,921.66666667 --> 00:16:05,181.66666667 So in these kinds of experiments, no one can really predict exactly what would happen because of the fact that we don't know yet. 234 00:16:05,571.66666667 --> 00:16:06,51.66666667 Um, I. 235 00:16:06,351.66666667 --> 00:16:19,731.66666667 Well, because there's different theories proposed for how, um, how we should model gravity, then people will predict different things based on different theories about the outcomes of, of these experiments. 236 00:16:19,731.66666667 --> 00:16:23,871.66666667 So it's a kind of unknown, um, that that's one way to think about it. 237 00:16:23,871.66666667 --> 00:16:31,851.66666667 And the BMV experiment is a very simple experiment, so we can model it with classical gravity as well, and we can model it with quantum gravity as well. 238 00:16:32,241.66666667 --> 00:16:36,741.66666667 Um, and yes, surely depending on the corrections, you'll get different predictions. 239 00:16:37,71.66666667 --> 00:16:41,481.6666667 Uh, but this is a qualitative argument that goes beyond just observing different predictions. 240 00:16:41,811.6666667 --> 00:16:50,961.6666667 Uh, it's, it's about the interpretation of what, um, what it means for this entanglement to be created in the first place. 241 00:16:51,201.6666667 --> 00:16:52,926.6666667 Entanglement, as you know, is. 242 00:16:53,661.6666667 --> 00:16:56,121.6666667 A very quantum thing. 243 00:16:56,301.6666667 --> 00:17:00,591.6666667 Uh, and also it is qualitatively different from not being entangled. 244 00:17:00,596.6666667 --> 00:17:00,896.6666667 Mm-hmm. 245 00:17:00,981.6666667 --> 00:17:04,431.6666667 So you can, you can say that something is entangled and something's not entangled. 246 00:17:04,761.6666667 --> 00:17:11,421.6666667 And of course you can quantify to what extent that thing is entangled, which is the differences in experimental predictions as you've said. 247 00:17:11,661.6666667 --> 00:17:16,221.6666667 But the, the, but this experiment distinguishes between disentangled and entangled. 248 00:17:16,221.6666667 --> 00:17:20,31.6666667 So that is a qualitative difference between what, um. 249 00:17:20,91.6666667 --> 00:17:20,151.6666667 Wow. 250 00:17:20,871.6666667 --> 00:17:23,871.6666667 What you would likely observe in the laboratory when you did this experiment. 251 00:17:24,411.6666667 --> 00:17:25,971.6666667 Uh, so I'd say that's a signature. 252 00:17:25,971.6666667 --> 00:17:31,671.6666667 It's more than just an experimental prediction where we're trying to fit a curve, uh, to a set of dots. 253 00:17:31,671.6666667 --> 00:17:31,761.6666667 Mm-hmm. 254 00:17:32,391.6666667 --> 00:17:37,311.6666667 But is it entangled or is it not entangled? Uh, so that's, um, one, one test. 255 00:17:37,671.6666667 --> 00:17:37,761.6666667 Mm-hmm. 256 00:17:38,1.6666667 --> 00:17:41,616.6666667 Uh, but there are experimental predictions where quantum gravity becomes very important. 257 00:17:41,751.6666667 --> 00:17:49,371.6666667 So when we go to the early universe, uh, when things are very energetic, um, you have higher and higher energy skills. 258 00:17:49,851.6666667 --> 00:17:56,271.6666667 Uh, and as you know, when energy scales get higher and higher, you have particle production, you have, you're in the realm of quantum mechanics. 259 00:17:56,721.6666667 --> 00:17:57,351.6666667 Um, right. 260 00:17:57,351.6666667 --> 00:18:02,721.6666667 So there, these corrections that you're talking about due to quantum gravity will become very important. 261 00:18:03,531.6666667 --> 00:18:03,591.6666667 Hmm. 262 00:18:03,591.6666667 --> 00:18:03,711.6666667 Yeah. 263 00:18:04,196.6666667 --> 00:18:04,486.6666667 Cool. 264 00:18:05,481.6666667 --> 00:18:10,191.6666667 So can you tell us a bit more about the early universe? What happens when we Yeah, yeah. 265 00:18:10,281.6666667 --> 00:18:12,591.6666667 What of the, the questions and. 266 00:18:13,116.6666667 --> 00:18:19,416.6666667 Issues when we try to understand the early universe, what do we know and what do we not know? Yeah, absolutely. 267 00:18:19,746.6666667 --> 00:18:20,916.6666667 Big, big questions. 268 00:18:20,946.6666667 --> 00:18:21,186.6666667 Yeah. 269 00:18:22,626.6666667 --> 00:18:28,146.6666667 Much of particle physics has been devoted to understanding what happens to things as we go to higher and higher energy. 270 00:18:28,446.6666667 --> 00:18:28,596.6666667 Mm-hmm. 271 00:18:28,836.6666667 --> 00:18:34,751.6666667 Uh, a very good example is a large on collider in cer, which sends two photons at 99.9999%. 272 00:18:34,776.6666667 --> 00:18:37,206.6666667 The speed of light, they collide and. 273 00:18:37,731.6666667 --> 00:18:41,1.6666667 Uh, of course when they collide, they break and they give rise to particles. 274 00:18:41,1.6666667 --> 00:18:46,641.6666667 That then we try to characterize, uh, um, uh, through various in, in various ways. 275 00:18:47,61.6666667 --> 00:18:49,311.6666667 Uh, now we can do that up to certain energies on earth. 276 00:18:49,311.6666667 --> 00:18:55,551.6666667 We can do that up to one 10 te electron, te electron volts maybe, which is the energy scale that we are interested in. 277 00:18:56,61.6666667 --> 00:19:06,801.6666667 Uh, when you put that in perspective of the early universe, um, to reach those kind of energy skills, you need to go back to when the universe is very young, about 10 to the negative 10 seconds. 278 00:19:06,801.6666667 --> 00:19:06,861.6666667 I. 279 00:19:06,861.6666667 --> 00:19:09,426.6666667 So the universe was 0.0001. 280 00:19:09,966.6666667 --> 00:19:11,136.6666667 Um, yeah. 281 00:19:11,436.6666667 --> 00:19:14,616.6666667 10 zeros, one uhhuh, seconds old. 282 00:19:15,66.6666667 --> 00:19:19,326.6666667 Um, to witness the very same processes we can observe on Earth today. 283 00:19:19,626.6666667 --> 00:19:19,926.6666667 Yeah. 284 00:19:19,926.6666667 --> 00:19:25,176.6666667 Uh, at those energy scale naturally when the universe was a zoo, uh, of particles, um. 285 00:19:26,301.6666667 --> 00:19:32,331.6666667 Now what happens when we go earlier? So that's, that's, that's, that's the topic of my research. 286 00:19:32,331.6666667 --> 00:19:39,321.6666667 The very early universe, uh, which is actually 10 to the negative, 34 seconds to 10 to the negative 10 seconds. 287 00:19:39,351.6666667 --> 00:19:46,191.6666667 What happened? Uh, and why do we want to answer that question? Uh, is because there are things that we see today mm-hmm. 288 00:19:46,971.6666667 --> 00:19:53,421.6666667 That actually, um, uh, invoke physics from that era. 289 00:19:53,841.6666667 --> 00:19:55,11.6666667 Um, so one very. 290 00:19:55,596.6666667 --> 00:19:58,656.6666667 Um, striking example is the Cosmic Microwave background. 291 00:19:58,656.6666667 --> 00:20:06,246.6666667 So for the viewers, um, the Cosmic Microwave background is, as the name suggests, microwave radiation that you can see in the Skype. 292 00:20:06,666.6666667 --> 00:20:09,786.6666667 It was discovered by two people, Penza and Willem. 293 00:20:10,566.6666667 --> 00:20:19,386.6666667 Who took an antenna out into the sky, uh, and on, on top of a roof and observed that there was noise in the sky, and how much ever they tried to filter away this noise. 294 00:20:19,416.6666667 --> 00:20:20,256.6666667 It didn't work. 295 00:20:20,376.6666667 --> 00:20:21,786.6666667 Uh, the noise still existed. 296 00:20:22,146.6666667 --> 00:20:22,266.6666667 Mm-hmm. 297 00:20:22,506.6666667 --> 00:20:28,716.6666667 Uh, and the conclusion they came into was that this is, this is relic radiation, uh, that's coming from the universe. 298 00:20:28,746.6666667 --> 00:20:31,806.6666667 It's a, it's, it's radiation that the universe is sending to us. 299 00:20:32,46.6666667 --> 00:20:33,756.6666667 There's no way we can filter this thing out. 300 00:20:33,816.6666667 --> 00:20:37,356.6666667 We're always gonna see it, regardless of how good we make our antenna. 301 00:20:37,806.6666667 --> 00:20:46,491.6666667 Uh, how is this radiation formed? Um, it was formed when, so as, as I told you, when you go earlier and earlier in the universe, it becomes hotter and hotter. 302 00:20:47,1.6666667 --> 00:20:51,411.6666667 Uh, why does it become hotter and hotter? Because the universe was smaller and smaller. 303 00:20:51,681.6666667 --> 00:20:53,661.6666667 We know that the universe expands today. 304 00:20:53,991.6666667 --> 00:20:54,81.6666667 Mm-hmm. 305 00:20:54,321.6666667 --> 00:20:59,121.6666667 And how do we know the universe expands? Uh, there are these things called standard candles. 306 00:20:59,121.6666667 --> 00:21:04,641.6666667 If you look far enough in the sky, um, you'd see, um. 307 00:21:05,106.6666667 --> 00:21:07,296.6666667 That these standard candles are redshifted. 308 00:21:07,746.6666667 --> 00:21:13,26.6666667 Um, what are standard candles? It's things of a fixed brightness, right? Or like Yes. 309 00:21:13,26.6666667 --> 00:21:13,356.6666667 Events. 310 00:21:13,416.6666667 --> 00:21:14,736.6666667 Like a supernova or something. 311 00:21:14,736.6666667 --> 00:21:16,296.6666667 That's exactly, yes. 312 00:21:16,296.6666667 --> 00:21:18,966.6666667 I remember my, uh, high school astrophysics module. 313 00:21:19,296.6666667 --> 00:21:20,256.6666667 No, no, absolutely. 314 00:21:20,256.6666667 --> 00:21:31,386.6666667 There are things with fixed brightness and we know, we know that because, uh, uh, the, the production processes that lead to the explosion of the supernova, it's, it's a fixed mechanism. 315 00:21:31,596.6666667 --> 00:21:31,836.6666667 Yeah. 316 00:21:31,836.6666667 --> 00:21:33,936.6666667 So it's like these events that happen at a critical. 317 00:21:34,521.6666667 --> 00:21:34,701.6666667 Yes. 318 00:21:34,731.6666667 --> 00:21:35,91.6666667 Point. 319 00:21:35,91.6666667 --> 00:21:39,111.6666667 So we know that whenever they, whenever we spot them, it's a certain brightness. 320 00:21:39,141.6666667 --> 00:21:39,471.6666667 Yes. 321 00:21:39,561.6666667 --> 00:21:47,631.6666667 And then when we see things, then we can see how bright it looks to us and figure out how far away it is. 322 00:21:47,631.6666667 --> 00:21:47,676.6666667 Far away it is. 323 00:21:47,991.6666667 --> 00:21:48,261.6666667 Yeah. 324 00:21:48,321.6666667 --> 00:21:48,831.6666667 Exactly. 325 00:21:48,831.6666667 --> 00:21:54,156.6666667 So as, as you rightly said, when light travels to us, it's redshifted, it's more and more redshifted. 326 00:21:54,161.6666667 --> 00:21:55,101.6666667 Mm-hmm. 327 00:21:55,191.6666667 --> 00:21:57,21.6666667 And this is what they observed in the experiment. 328 00:21:57,471.6666667 --> 00:21:57,561.6666667 Mm-hmm. 329 00:21:57,891.6666667 --> 00:21:59,271.6666667 And that doesn't make sense. 330 00:21:59,601.6666667 --> 00:22:06,681.6666667 Unless the very space between us and the supernova was expanding, it was literally stretching the wavelength of light. 331 00:22:07,161.6666667 --> 00:22:10,911.6666667 Uh, why would, uh, we don't see this in everyday life, right? Mm-hmm. 332 00:22:11,151.6666667 --> 00:22:16,191.6666667 If you shine a blue laser at me from there, I would see it blue from here, blue from there, blue from anywhere. 333 00:22:16,491.6666667 --> 00:22:22,251.6666667 I would not see it red unless the very space between us was expanding and it stretched the wavelength of light. 334 00:22:22,671.6666667 --> 00:22:26,841.6666667 As you know, higher wavelengths are more blue and lower wavelengths are more red. 335 00:22:27,411.6666667 --> 00:22:27,681.6666667 Um. 336 00:22:28,221.6666667 --> 00:22:31,881.6666667 So from these candle standard candles, we concluded that the universe was expanding. 337 00:22:32,211.6666667 --> 00:22:36,861.6666667 Uh, and there are many other probes as well, but the standard candles are a famous example. 338 00:22:36,921.6666667 --> 00:22:37,161.6666667 Mm-hmm. 339 00:22:37,521.6666667 --> 00:22:40,221.6666667 Um, and it also told us how old the universe was. 340 00:22:40,791.6666667 --> 00:22:49,161.6666667 Um, now that we know the universe is expanding, it only stands to reason that as we go further, back in time, the universe was much smaller. 341 00:22:49,881.6666667 --> 00:22:55,941.6666667 Um, and when things, when you put so much mass in a confined space, things become hotter and hotter. 342 00:22:55,986.6666667 --> 00:23:07,896.6666667 Uh, so that's the regime where quantum mechanics is, you know, king and also general relativity becomes very prominent because you have a lot more mass So that's the regime of the early universe, which is very interesting. 343 00:23:08,61.6666667 --> 00:23:08,351.6666667 Yeah. 344 00:23:09,936.6666667 --> 00:23:10,176.6666667 Yeah. 345 00:23:10,176.6666667 --> 00:23:13,896.6666667 So 10 to the negative 34 seconds, it, it becomes very dramatic. 346 00:23:13,896.6666667 --> 00:23:17,406.6666667 But I'll pause at this point and, uh, let you ask any questions. 347 00:23:17,406.6666667 --> 00:23:17,736.6666667 Yeah. 348 00:23:18,306.6666667 --> 00:23:18,786.6666667 Um. 349 00:23:19,401.6666667 --> 00:23:28,611.6666667 So is there a reason that 10 to the minus 34 is the, that you're looking at this range of 10 to the minus 34 to 10 to the minus 10? Not at all. 350 00:23:28,641.6666667 --> 00:23:29,121.6666667 Not at all. 351 00:23:29,391.6666667 --> 00:23:30,501.6666667 Not at all actually. 352 00:23:30,831.6666667 --> 00:23:39,356.6666667 Um, the, the resolution of one of the paradoxes that I mentioned, the horizon problem, uh, that we will speak about, mm-hmm. 353 00:23:39,501.6666667 --> 00:23:42,471.6666667 Actually posture is that time can go to negative infinity. 354 00:23:42,831.6666667 --> 00:23:43,521.6666667 Now this. 355 00:23:43,911.6666667 --> 00:23:48,741.6666667 This is not the normal time that you and I, it's not the time we read from a clock. 356 00:23:48,741.6666667 --> 00:23:49,971.6666667 It's conformal time. 357 00:23:49,971.6666667 --> 00:23:55,941.6666667 It's a time we, we define relative to something, uh, that's accelerating along with the universe. 358 00:23:55,941.6666667 --> 00:23:56,211.6666667 Mm-hmm. 359 00:23:56,451.6666667 --> 00:23:57,711.6666667 Uh, so that's not this. 360 00:23:57,711.6666667 --> 00:24:00,411.6666667 10 to the ne negative 34 is not special yet. 361 00:24:00,441.6666667 --> 00:24:10,491.6666667 Uhhuh uh, it's only special in the sense that we needed the universe to expand for 10 to the negative 34 seconds to explain why it's so big today. 362 00:24:11,506.6666667 --> 00:24:11,796.6666667 Okay. 363 00:24:11,801.6666667 --> 00:24:11,991.6666667 Yeah. 364 00:24:11,991.6666667 --> 00:24:15,921.6666667 So from zero to 10 to the negative 34, the universe expanded this much. 365 00:24:16,641.6666667 --> 00:24:16,671.6666667 Oh. 366 00:24:16,671.6666667 --> 00:24:22,191.6666667 Uh, and there was some dramatic process that happened in those 10 to the negative 34 seconds, which explains mm-hmm. 367 00:24:22,641.6666667 --> 00:24:29,121.6666667 Not only why the universe is so big today, but a few other things, Uhhuh, uh, which are paradoxes of standard big bang cosmology. 368 00:24:29,631.6666667 --> 00:24:29,751.6666667 Mm-hmm. 369 00:24:30,381.6666667 --> 00:24:30,531.6666667 Mm. 370 00:24:30,746.6666667 --> 00:24:31,36.6666667 Okay. 371 00:24:31,701.6666667 --> 00:24:35,841.6666667 So, um, you've mentioned paradoxes and. 372 00:24:36,621.6666667 --> 00:24:39,681.6666667 Everyone that knows me knows that I love paradoxes. 373 00:24:39,771.6666667 --> 00:24:48,621.6666667 So could you, uh, tell me what are these paradoxes that emerge? The early universe, quantum, general relativity, crazy stuff happening. 374 00:24:48,891.6666667 --> 00:24:52,561.6666667 Uh, so they're, they're actually called the Big Bang Puzzles, it's a good name. 375 00:24:53,166.6666667 --> 00:24:54,96.6666667 it's, a good name. 376 00:24:54,141.6666667 --> 00:24:54,261.6666667 Yeah. 377 00:24:54,261.6666667 --> 00:24:54,921.6666667 Big Bang puzzles. 378 00:24:55,16.6666667 --> 00:24:55,306.6666667 Yeah. 379 00:24:55,341.6666667 --> 00:24:59,481.6666667 Um, and, uh, one such puzzle is the flatness problem. 380 00:24:59,721.6666667 --> 00:25:03,141.6666667 So, um, the flatness problem states that, uh. 381 00:25:03,936.6666667 --> 00:25:09,771.6666667 When we zoom out, when we look at the universe, uh, let's say the universe is a stable, and I'm looking at it from a zoomed out perspective. 382 00:25:09,791.6666667 --> 00:25:10,211.6666667 Mm-hmm. 383 00:25:10,356.6666667 --> 00:25:11,976.6666667 It looks surprisingly flat. 384 00:25:12,486.6666667 --> 00:25:14,316.6666667 Uh, it's a very boring universe. 385 00:25:14,496.6666667 --> 00:25:14,676.6666667 Mm-hmm. 386 00:25:14,916.6666667 --> 00:25:31,896.6666667 Um, now if the universe is so flat today, um, and we are going further back in time, it must have been more flat, um, to explain why it's so flat today. 387 00:25:32,16.6666667 --> 00:25:32,766.6666667 This is because. 388 00:25:33,156.6666667 --> 00:25:36,36.6666667 Gravity, as you know, brings things closer and closer together. 389 00:25:36,41.6666667 --> 00:25:36,401.6666667 Mm-hmm. 390 00:25:36,606.6666667 --> 00:25:39,156.6666667 And it's a natural tendency of gravity to attract. 391 00:25:39,756.6666667 --> 00:25:48,156.6666667 Um, if there was some in homogeneity in the universe early on, it would've been attracted by gravity. 392 00:25:48,216.6666667 --> 00:25:50,706.6666667 And when gravity attracts things, you no longer have flatness. 393 00:25:50,706.6666667 --> 00:25:54,246.6666667 You have some curvature, which is what general relativity tells us. 394 00:25:54,276.6666667 --> 00:25:57,786.6666667 So if it was curvy early on, it would get curvier from gravity. 395 00:25:57,876.6666667 --> 00:25:58,446.6666667 Exactly. 396 00:25:58,506.6666667 --> 00:26:00,6.6666667 So, yeah. 397 00:26:00,6.6666667 --> 00:26:00,996.6666667 So we generally. 398 00:26:01,671.6666667 --> 00:26:04,161.6666667 Expect gravity would make things curvier. 399 00:26:04,221.6666667 --> 00:26:04,491.6666667 Yes. 400 00:26:04,551.6666667 --> 00:26:07,41.6666667 Therefore, as you go forward in time it should get curvier. 401 00:26:07,101.6666667 --> 00:26:07,341.6666667 Yes. 402 00:26:07,401.6666667 --> 00:26:12,51.6666667 So if it looks pretty flat now, it must have been even more flat before because it's Yes. 403 00:26:12,291.6666667 --> 00:26:15,441.6666667 It must have got curvier from the gravity. 404 00:26:15,441.6666667 --> 00:26:15,771.6666667 Exactly. 405 00:26:15,771.6666667 --> 00:26:16,551.6666667 During this time. 406 00:26:16,671.6666667 --> 00:26:17,271.6666667 Exactly. 407 00:26:17,271.6666667 --> 00:26:21,171.6666667 So the universe must have been incredibly flat, uh, that early on. 408 00:26:21,411.6666667 --> 00:26:21,651.6666667 Mm-hmm. 409 00:26:21,891.6666667 --> 00:26:29,856.6666667 Um, and then you might ask, okay, I'm happy to accept that the universe is incredibly flat, but why? Mm, why was it incredibly flat? Mm-hmm. 410 00:26:29,857.6666667 --> 00:26:39,451.6666667 Uh, so that's the first Big Bang puzzle, the flatness problem, right? Which is, did the universe always start off flat? If so, what's special about a flat universe? Uh, and that's the first puzzle. 411 00:26:39,751.6666667 --> 00:26:40,171.6666667 Mm-hmm. 412 00:26:40,596.6666667 --> 00:26:42,876.6666667 And are you puzzled? I am puzzled. 413 00:26:42,876.6666667 --> 00:26:42,906.6666667 Okay. 414 00:26:42,936.6666667 --> 00:26:44,256.6666667 Because like, yeah. 415 00:26:44,256.6666667 --> 00:26:48,396.6666667 If it was even, I guess this is one of those things where if it was even a little. 416 00:26:49,521.6666667 --> 00:26:50,391.6666667 Not flat. 417 00:26:50,451.6666667 --> 00:26:50,811.6666667 Yes. 418 00:26:50,991.6666667 --> 00:26:55,611.6666667 It would like throw, throw things wildly out of control. 419 00:26:55,611.6666667 --> 00:26:58,581.6666667 Is it, what a, is it kind of quite sensitive to? Absolutely. 420 00:26:58,581.6666667 --> 00:27:03,681.6666667 So if you, if you were to, um, deviate, let's say even 0.0001% 421 00:27:03,831.6666667 --> 00:27:04,821.6666667 from flatness mm-hmm. 422 00:27:05,511.6666667 --> 00:27:14,31.6666667 In the positive directions when, so a flat direct, you have slightly curved universe like this, like the earth, and it'll collapse on itself in under 45 seconds. 423 00:27:14,421.6666667 --> 00:27:16,521.6666667 But our universe is 13 billion years old. 424 00:27:16,566.6666667 --> 00:27:19,596.6666667 Um, it's, it hasn't collapsed on itself yet. 425 00:27:20,136.6666667 --> 00:27:30,966.6666667 Um, so it must have been incredibly, it's, it's a fine tuning problem where the initial conditions must have been so precise to explain why it's so flat today and that puzzle physics this for a very long time, and it still does. 426 00:27:30,966.6666667 --> 00:27:33,996.6666667 Why was the, why did the universe start? Start off so flat. 427 00:27:34,146.6666667 --> 00:27:34,476.6666667 Yeah. 428 00:27:34,536.6666667 --> 00:27:38,136.6666667 So it's an unexplained special initial condition. 429 00:27:38,406.6666667 --> 00:27:38,496.6666667 Yes. 430 00:27:38,496.6666667 --> 00:27:41,466.6666667 And the, so that's the first puzzle, Uhhuh. 431 00:27:41,466.6666667 --> 00:27:46,626.6666667 And we, we wanted to resolve the puzzle, which is a theory of inflation, a few other cosmological theories. 432 00:27:47,46.6666667 --> 00:27:49,776.6666667 Uh, the second puzzle is the horizon problem. 433 00:27:50,196.6666667 --> 00:27:51,456.6666667 And now I told you when these. 434 00:27:51,696.6666667 --> 00:27:58,206.6666667 Uh, guys, these scientists were searching for microwave radiation and they found the cosmic microwave background in their antennas. 435 00:27:58,866.6666667 --> 00:27:58,956.6666667 Mm-hmm. 436 00:27:58,957.6666667 --> 00:28:04,986.6666667 Um, the cosmic microwave background is light that's transmitted to us very early on from very early on in the universe. 437 00:28:05,466.6666667 --> 00:28:12,691.6666667 Um, and when you look at two different patches of the sky today, um, they're really, really far apart. 438 00:28:13,356.6666667 --> 00:28:17,16.6666667 And so I could be looking at that direction and that direction. 439 00:28:17,376.6666667 --> 00:28:17,736.6666667 Um. 440 00:28:18,261.6666667 --> 00:28:21,321.6666667 And there are things that could have never spoken to each other until today. 441 00:28:21,351.6666667 --> 00:28:24,321.6666667 Like the, the signal from there is reaching me today, let's say. 442 00:28:24,681.6666667 --> 00:28:30,321.6666667 And when you say never spoken to each other before today, what do you mean? Yeah. 443 00:28:30,351.6666667 --> 00:28:33,621.6666667 How so? The, the two really, really far things in the sky. 444 00:28:33,861.6666667 --> 00:28:38,211.6666667 Can I conceive that they interacted in some way? If I send a signal from that patch mm-hmm. 445 00:28:38,451.6666667 --> 00:28:39,981.6666667 Uh, to that patch would. 446 00:28:40,581.6666667 --> 00:28:44,91.6666667 Would that sort of communication have been possible very early on? Mm-hmm. 447 00:28:44,391.6666667 --> 00:28:49,71.6666667 Would light have been able to traverse those astronomical cosmological distances? Yeah. 448 00:28:49,131.6666667 --> 00:28:52,221.6666667 Um, in the available time, which is 13.8 449 00:28:52,221.6666667 --> 00:28:54,891.6666667 billion years, would it have, would a signal mm-hmm. 450 00:28:55,131.6666667 --> 00:29:03,771.6666667 Have been, would it, would, would it traverse that, that distance? Um, and the answer is no, actually, you know, this is far too big for Right. 451 00:29:03,771.6666667 --> 00:29:07,581.6666667 Um, those regions to have been in causal contact, so it would be impossible. 452 00:29:07,586.6666667 --> 00:29:07,716.6666667 Mm-hmm. 453 00:29:08,31.6666667 --> 00:29:14,481.6666667 If the universe were always this big uhhuh, it would be impossible to send a signal from that side of the sky to the other side of the sky, uhhuh. 454 00:29:15,891.6666667 --> 00:29:24,651.6666667 But when we do OB and, and you can, there's nothing wrong with two parts of the universe being in causal contact, but what's not being in causal contact. 455 00:29:24,861.6666667 --> 00:29:25,71.6666667 Yeah. 456 00:29:25,101.6666667 --> 00:29:28,371.6666667 But what's striking about this is they look the same. 457 00:29:30,81.6666667 --> 00:29:31,791.6666667 They're correlated in the same way. 458 00:29:33,381.6666667 --> 00:29:35,301.6666667 And this is not just for two random patches. 459 00:29:35,301.6666667 --> 00:29:37,71.6666667 This is for every patch in the sky. 460 00:29:37,131.6666667 --> 00:29:37,191.6666667 Mm. 461 00:29:37,761.6666667 --> 00:29:39,801.6666667 360 degrees is correlated. 462 00:29:40,461.6666667 --> 00:29:40,551.6666667 Mm-hmm. 463 00:29:41,434.974919 --> 00:29:44,889.974919 so yeah, I've kind of heard this idea of everything looking the same Yes. 464 00:29:45,249.974919 --> 00:29:47,439.974919 Around in whatever direction you look kind of thing. 465 00:29:47,619.974919 --> 00:29:47,859.974919 Mm-hmm. 466 00:29:48,669.974919 --> 00:29:57,609.974919 What is it that we're actually looking at that looks the same? Like what property of the sky is it? It's, it's the temperature of the sky. 467 00:29:58,509.974919 --> 00:30:02,529.974919 Um, uh, it's a photo as you know, have wavelength. 468 00:30:03,129.974919 --> 00:30:03,219.974919 Mm-hmm. 469 00:30:03,459.974919 --> 00:30:05,139.974919 Um, and they're transmitted to us. 470 00:30:05,709.974919 --> 00:30:06,99.974919 Um. 471 00:30:06,504.974919 --> 00:30:16,824.974919 The sky has temperature, which is temperature of the radiation microwaves, um, are about two kelvin, which is the temperature that we are talking about. 472 00:30:16,944.974919 --> 00:30:17,34.974919 Mm-hmm. 473 00:30:17,274.974919 --> 00:30:19,794.974919 And the sky is roughly two, 2.75 474 00:30:19,794.974919 --> 00:30:20,244.974919 kelvin. 475 00:30:20,249.974919 --> 00:30:20,569.974919 Mm-hmm. 476 00:30:20,694.974919 --> 00:30:27,324.974919 So these correlations that you're observing are tiny fluctuations around this 2.7 477 00:30:27,324.974919 --> 00:30:27,774.974919 kelvin. 478 00:30:28,914.974919 --> 00:30:32,604.974919 So they're temperature fluctuations in the microwave background of the sky. 479 00:30:32,994.974919 --> 00:30:33,354.974919 Right. 480 00:30:33,354.974919 --> 00:30:33,714.974919 Yeah. 481 00:30:33,744.974919 --> 00:30:37,14.974919 So we see this microwave background. 482 00:30:37,134.974919 --> 00:30:37,314.974919 Yes. 483 00:30:38,334.974919 --> 00:30:39,594.974919 This 2.7 484 00:30:39,864.974919 --> 00:30:40,524.974919 kelvin. 485 00:30:40,524.974919 --> 00:30:40,614.974919 Yes. 486 00:30:41,544.974919 --> 00:30:43,524.974919 Looks the same wherever we look. 487 00:30:43,734.974919 --> 00:30:44,94.974919 Yes. 488 00:30:44,214.974919 --> 00:30:54,294.974919 And that's strange because we'd expect that two things that have two parts of the sky that have not been in causal contact ever. 489 00:30:54,354.974919 --> 00:30:54,444.974919 Mm-hmm. 490 00:30:55,614.974919 --> 00:30:55,944.974919 It would be. 491 00:30:56,934.974919 --> 00:30:59,544.974919 Strange for them to somehow be at the same temperature. 492 00:30:59,574.974919 --> 00:31:06,414.974919 'cause um, I'm, we're okay accepting that they're at the same temperature because I could say, well, the universe is always at this temperature. 493 00:31:06,414.974919 --> 00:31:06,954.974919 Mm-hmm. 494 00:31:07,79.974919 --> 00:31:07,969.974919 It's a hand wave. 495 00:31:08,119.974919 --> 00:31:10,614.974919 It's, I could always say the universe is always this flat. 496 00:31:10,824.974919 --> 00:31:11,4.974919 Yeah. 497 00:31:11,4.974919 --> 00:31:11,874.974919 And there is no puzzle. 498 00:31:11,874.974919 --> 00:31:15,24.974919 Uh um, so that's the first level of the puzzle. 499 00:31:15,174.974919 --> 00:31:15,324.974919 Right. 500 00:31:15,324.974919 --> 00:31:17,694.974919 But the second level is, it's not. 501 00:31:18,444.974919 --> 00:31:20,454.974919 You? Yes, they're all 2.7 502 00:31:20,454.974919 --> 00:31:24,24.974919 Kelvin, but actually they're 2.74 503 00:31:24,24.974919 --> 00:31:24,414.974919 zeros. 504 00:31:24,414.974919 --> 00:31:25,824.974919 One, 2.74 505 00:31:25,824.974919 --> 00:31:26,394.974919 zeros two. 506 00:31:26,394.974919 --> 00:31:29,754.974919 So if I take five points and from that region, the sky will be 2.7 507 00:31:29,754.974919 --> 00:31:31,464.974919 0, 0 0 1, 2 0.7 508 00:31:31,464.974919 --> 00:31:37,194.974919 0, 0 0, 2, 3, 4, whatever, like some small standard deviation around 2.7 509 00:31:37,239.974919 --> 00:31:37,589.974919 uhhuh. 510 00:31:37,704.974919 --> 00:31:39,984.974919 And this patch in the sky would also be. 511 00:31:40,419.974919 --> 00:31:43,599.974919 Some small variations around 2.7. 512 00:31:43,599.974919 --> 00:31:45,39.974919 So you see like little speckles. 513 00:31:45,39.974919 --> 00:31:46,599.974919 It's not exactly 2.7. 514 00:31:46,659.974919 --> 00:31:46,749.974919 Mm-hmm. 515 00:31:46,989.974919 --> 00:31:47,709.974919 It's 2.7 516 00:31:47,709.974919 --> 00:31:51,99.974919 plus 10 to the negative five times some epsilon, which is a small error. 517 00:31:51,969.974919 --> 00:31:52,179.974919 Okay. 518 00:31:52,179.974919 --> 00:31:53,979.974919 Now those errors are correlated. 519 00:31:54,639.974919 --> 00:32:01,449.974919 Um, the, the distribution of those, um, of those fluctuations is the same in both. 520 00:32:01,449.974919 --> 00:32:03,249.974919 But now that. 521 00:32:04,269.974919 --> 00:32:08,859.974919 I, that's not something that we can just hand wave and say, well, the distribution was always like this. 522 00:32:08,889.974919 --> 00:32:10,239.974919 That needs an explanation. 523 00:32:10,389.974919 --> 00:32:10,479.974919 Mm-hmm. 524 00:32:10,719.974919 --> 00:32:20,79.974919 So that's the horizon problem, right? Which is how did two parts of the sky communicate with you? They must have interacted in some way for them to have precisely the same. 525 00:32:20,469.974919 --> 00:32:20,919.974919 Yeah. 526 00:32:21,69.974919 --> 00:32:22,59.974919 Characteristics. 527 00:32:22,179.974919 --> 00:32:22,449.974919 Yeah. 528 00:32:22,449.974919 --> 00:32:26,919.974919 How did they communicate? So that's the, the horizon problem, right? Yeah. 529 00:32:26,919.974919 --> 00:32:31,179.974919 So we can't explain, um, yeah. 530 00:32:31,539.974919 --> 00:32:31,989.974919 Why these. 531 00:32:33,804.974919 --> 00:32:34,134.974919 Yeah. 532 00:32:34,164.974919 --> 00:32:36,804.974919 They have these correlated fluctuations around Yes. 533 00:32:36,834.974919 --> 00:32:37,734.974919 2.7. 534 00:32:37,734.974919 --> 00:32:38,4.974919 Yes. 535 00:32:38,484.974919 --> 00:32:43,674.974919 And that needs an explanation for how they, I should think so. 536 00:32:43,734.974919 --> 00:32:44,94.974919 Yeah. 537 00:32:45,129.974919 --> 00:32:45,924.974919 Yeah, yeah. 538 00:32:46,104.974919 --> 00:32:46,254.974919 Yes. 539 00:32:46,254.974919 --> 00:32:46,614.974919 Cool. 540 00:32:47,394.974919 --> 00:32:47,814.974919 Yeah. 541 00:32:47,994.974919 --> 00:32:54,84.974919 And do we have some answers to these puzzles? Um, yeah. 542 00:32:54,84.974919 --> 00:33:00,894.974919 So we tried, um, early eighties and nineties, and one of the for running candidates. 543 00:33:01,314.974919 --> 00:33:02,364.974919 It's a paradigm. 544 00:33:02,634.974919 --> 00:33:06,984.974919 We don't call it a theory because it hasn't been tested in that regime yet. 545 00:33:07,344.974919 --> 00:33:07,554.974919 Right. 546 00:33:07,644.974919 --> 00:33:09,534.974919 Um, the paradigm of inflation. 547 00:33:10,14.974919 --> 00:33:10,104.974919 Mm-hmm. 548 00:33:10,344.974919 --> 00:33:18,174.974919 Which tells you, ah, um, if you go, so remember this 10 to the negative 10 seconds that we spoke about. 549 00:33:18,504.974919 --> 00:33:25,284.974919 If you go further, further back, actually, the universe underwent a period of dramatic acceleration. 550 00:33:25,674.974919 --> 00:33:27,174.974919 Phenomenal acceleration. 551 00:33:27,594.974919 --> 00:33:29,124.974919 It was really, really tiny. 552 00:33:29,544.974919 --> 00:33:35,784.974919 Um, which means, uh, early on, and which means that part of the sky and this part of the sky were actually very close. 553 00:33:35,784.974919 --> 00:33:38,544.974919 They were probably on top of each other at, at some point. 554 00:33:38,754.974919 --> 00:33:38,844.974919 Mm-hmm. 555 00:33:39,294.974919 --> 00:33:51,264.974919 Um, but the universe expanded so dramatically in those 10 to the negative 34 seconds that, um, it became incredibly vast and gives you the illusion that this thing was not in causal contact. 556 00:33:51,269.974919 --> 00:33:51,359.974919 Mm-hmm. 557 00:33:51,439.974919 --> 00:33:52,639.974919 There is some unexplained physics. 558 00:33:52,859.974919 --> 00:33:53,279.974919 Mm-hmm. 559 00:33:53,459.974919 --> 00:33:54,639.974919 Uh, that actually. 560 00:33:55,344.974919 --> 00:33:58,614.974919 Causally disconnected, apparently causally disconnected. 561 00:33:58,824.974919 --> 00:33:58,914.974919 Mm-hmm. 562 00:33:59,154.974919 --> 00:34:02,844.974919 To, uh, this should be strange to a quantum physicist. 563 00:34:03,204.974919 --> 00:34:05,484.974919 Uh, because nothing can travel faster than the speed of light. 564 00:34:05,514.974919 --> 00:34:05,904.974919 Yeah. 565 00:34:05,994.974919 --> 00:34:07,854.974919 Except the expanding universe. 566 00:34:08,139.974919 --> 00:34:08,359.974919 Mm. 567 00:34:09,789.974919 --> 00:34:10,79.974919 Yeah. 568 00:34:11,139.974919 --> 00:34:12,639.974919 So, yeah. 569 00:34:12,699.974919 --> 00:34:20,904.974919 So saying that these regions of the sky could never be causally connected was based on the assumption that the expansion. 570 00:34:22,134.974919 --> 00:34:25,164.974919 That the universe was expanding, but never faster than light. 571 00:34:25,704.974919 --> 00:34:29,364.974919 And well, the universe expands at the edges of the universe today. 572 00:34:29,364.974919 --> 00:34:35,334.974919 It expands faster than light, but locally, the universe does not, you don't see the solar system being ripped into shreds. 573 00:34:35,334.974919 --> 00:34:35,424.974919 Mm-hmm. 574 00:34:35,844.974919 --> 00:34:39,54.974919 This does not happen, um, for good reason. 575 00:34:40,734.974919 --> 00:34:48,264.974919 But, um, if, if you trace back those observations naively to the furthest we can, which is about 10 to the negative 10 seconds. 576 00:34:48,324.974919 --> 00:34:48,654.974919 Yeah. 577 00:34:48,654.974919 --> 00:34:48,714.974919 Um. 578 00:34:50,604.974919 --> 00:34:56,94.974919 You'd come to the naive conclusion that the universe has a certain size, therefore, these two patches of the sky could have never talked. 579 00:34:56,274.974919 --> 00:34:56,364.974919 Mm-hmm. 580 00:34:56,604.974919 --> 00:35:00,114.974919 But it could be that beyond this realm of known physics mm-hmm. 581 00:35:00,354.974919 --> 00:35:03,474.974919 There exists a realm of unknown physics that you can only theorize about. 582 00:35:03,474.974919 --> 00:35:07,674.974919 That's why we get paid to think, to think about these things. 583 00:35:07,734.974919 --> 00:35:08,94.974919 Yeah. 584 00:35:08,184.974919 --> 00:35:10,14.974919 And one way to resolve that is to say. 585 00:35:10,479.974919 --> 00:35:15,129.974919 In those, in that tiny period, the universe underwent all sorts of crazy stuff. 586 00:35:15,129.974919 --> 00:35:16,359.974919 It expanded dramatically. 587 00:35:16,359.974919 --> 00:35:18,729.974919 Things that were not in, were in causal contact. 588 00:35:18,729.974919 --> 00:35:20,469.974919 Were not in causal contact anymore. 589 00:35:20,919.974919 --> 00:35:27,159.974919 Uhhuh and, and when the universe expand so dramatically, it means something must be giving you the pressure. 590 00:35:27,624.974919 --> 00:35:30,264.974919 For the, for the entire universe to expand. 591 00:35:30,444.974919 --> 00:35:30,534.974919 Mm-hmm. 592 00:35:30,774.974919 --> 00:35:33,324.974919 So what happened to that thing? Why don't we see it anymore? Mm-hmm. 593 00:35:33,654.974919 --> 00:35:47,329.974919 Um, and what are the relics of that field which caused inflation? How did it interact with gravity? Was that field a quantum field? And if it interacted with gravity, can that say something about the quantum nature gravity? Those are the questions that we are trying to answer. 594 00:35:47,989.974919 --> 00:35:48,409.974919 Mm-hmm. 595 00:35:48,519.974919 --> 00:35:48,809.974919 Yeah. 596 00:35:49,819.974919 --> 00:35:50,169.974919 Great. 597 00:35:52,349.974919 --> 00:35:52,569.974919 So. 598 00:35:54,459.974919 --> 00:36:01,359.974919 So you said in this early period there's this paradigm of expansion happening. 599 00:36:01,389.974919 --> 00:36:01,659.974919 Yes. 600 00:36:01,659.974919 --> 00:36:02,469.974919 Faster than light. 601 00:36:02,499.974919 --> 00:36:02,769.974919 Yes. 602 00:36:03,159.974919 --> 00:36:15,969.974919 Um, how much should we be worried about the physics of that? Like does it cause lots of strange things to happen or is it kind of, I dunno. 603 00:36:17,49.974919 --> 00:36:17,709.974919 Um. 604 00:36:18,459.974919 --> 00:36:23,439.974919 Is there a kind of boundary of the strangeness so that I don't need to worry about it too much? Yes. 605 00:36:23,499.974919 --> 00:36:28,254.974919 Well, since it has already happened and since you're alive today, maybe we shouldn't worry about it so much. 606 00:36:28,304.974919 --> 00:36:28,654.974919 Uhhuh. 607 00:36:28,929.974919 --> 00:36:38,619.974919 But, uh, I would be deeply worried because the, the field, uh, or whatever thing it is that caused, this is definitely not something that we've seen on earth today. 608 00:36:38,619.974919 --> 00:36:38,709.974919 Mm-hmm. 609 00:36:38,949.974919 --> 00:36:41,589.974919 It's not something we probed with particle based experiments. 610 00:36:41,739.974919 --> 00:36:41,949.974919 Mm-hmm. 611 00:36:42,189.974919 --> 00:36:44,289.974919 Uh, it displays very strange characteristics. 612 00:36:44,589.974919 --> 00:36:44,889.974919 Um. 613 00:36:45,249.974919 --> 00:36:47,289.974919 There's something called the strong energy condition. 614 00:36:47,289.974919 --> 00:36:51,484.974919 I'm not gonna tell you what it is, but it sounds pretty important, right? Yes. 615 00:36:51,609.974919 --> 00:36:53,739.974919 This thing violates the strong energy condition. 616 00:36:54,99.974919 --> 00:36:59,709.974919 So, and, and how is everything else not allowed to do this? And this thing can, it's, it's a special mm-hmm. 617 00:36:59,949.974919 --> 00:37:00,9.974919 Yeah. 618 00:37:00,9.974919 --> 00:37:00,939.974919 It's a special field. 619 00:37:01,419.974919 --> 00:37:05,404.974919 Um, so it violates some core, yes, it violates some core principles. 620 00:37:05,404.974919 --> 00:37:07,164.974919 Principles, indeed. 621 00:37:07,344.974919 --> 00:37:07,764.974919 Mm-hmm. 622 00:37:08,184.974919 --> 00:37:14,439.974919 Um, and we need it to violate these things, uh, for the universe to expand, right? And. 623 00:37:15,84.974919 --> 00:37:23,934.974919 How do we, so how do we explain that? Like what causes this? Well, it was postulated that this could be a field, a quantum field that we haven't observed. 624 00:37:23,934.974919 --> 00:37:25,854.974919 It's not light, it's not the SBO zone. 625 00:37:25,854.974919 --> 00:37:28,794.974919 It's not, uh, the strong force or the weak force. 626 00:37:28,794.974919 --> 00:37:29,574.974919 It's something else. 627 00:37:29,574.974919 --> 00:37:31,14.974919 It's a completely different field. 628 00:37:31,344.974919 --> 00:37:32,784.974919 Some field we've never seen before. 629 00:37:32,784.974919 --> 00:37:36,234.974919 It's some field that we haven't seen that plays a part in the early, very early universe. 630 00:37:36,234.974919 --> 00:37:36,744.974919 Exactly. 631 00:37:37,434.974919 --> 00:37:37,554.974919 Mm-hmm. 632 00:37:37,794.974919 --> 00:37:37,797.974919 Something that, mm-hmm. 633 00:37:37,797.974919 --> 00:37:39,759.974919 We probably will never see on earth Uhhuh. 634 00:37:39,909.974919 --> 00:37:43,239.974919 It could be something from string theory, we are not even going to get into that. 635 00:37:43,719.974919 --> 00:37:47,349.974919 Um, it could be something mysterious that we've never probed in that way before. 636 00:37:47,529.974919 --> 00:37:47,619.974919 Mm-hmm. 637 00:37:47,859.974919 --> 00:37:49,899.974919 But let's assume that it exists. 638 00:37:49,989.974919 --> 00:37:50,79.974919 Mm-hmm. 639 00:37:50,319.974919 --> 00:37:52,839.974919 And that it is capable of expanding the universe. 640 00:37:53,49.974919 --> 00:37:53,139.974919 Mm-hmm. 641 00:37:53,379.974919 --> 00:37:55,29.974919 Then a number of interesting questions arise. 642 00:37:55,149.974919 --> 00:38:02,829.974919 So if you have a field, is that field quantum? If that field causes the expansion of spacetime it must definitely interact with gravity. 643 00:38:03,414.974919 --> 00:38:07,104.974919 So you're immediately in the territory of what we call quantum physics. 644 00:38:07,104.974919 --> 00:38:10,644.974919 A quantum field theory In curved spacetime space time. 645 00:38:10,644.974919 --> 00:38:15,594.974919 is curved with gr, semi classical and, and a classical, sorry. 646 00:38:15,744.974919 --> 00:38:17,724.974919 And, uh, the field is quantum. 647 00:38:17,814.974919 --> 00:38:21,354.974919 Quantum put together quantum and a classical background. 648 00:38:21,354.974919 --> 00:38:29,904.974919 You have semi classical quantum field theory and curves based on, there are a number of interesting things that happen, um, when. 649 00:38:30,789.974919 --> 00:38:33,789.974919 Space time is curved and you try to put a quantum field on it. 650 00:38:34,359.974919 --> 00:38:37,149.974919 Uh, the most striking thing is spontaneous particle production. 651 00:38:37,599.974919 --> 00:38:39,969.974919 You probably know about the hawking radiation. 652 00:38:41,259.974919 --> 00:38:47,649.974919 Um, it's when a black hole, um, black holes radiate, um, energy. 653 00:38:48,159.974919 --> 00:38:50,349.974919 Um, it's in the form of thermal radiation. 654 00:38:50,769.974919 --> 00:38:53,769.974919 And the universe does something similar when it's curved. 655 00:38:53,769.974919 --> 00:38:59,829.974919 And when you put a quantum field on it, uh, it starts producing particles spontaneously, outta vacuum. 656 00:38:59,889.974919 --> 00:39:03,699.974919 Um, and this is not something we see happen in everyday life. 657 00:39:04,149.974919 --> 00:39:04,239.974919 Mm-hmm. 658 00:39:04,479.974919 --> 00:39:07,29.974919 Um, and this is a quantum mechanical phenomenon. 659 00:39:07,629.974919 --> 00:39:23,169.974919 Why is it quantum mechanical? Because the uncertainty principle tells us, um, that if you, if you zoom in, uh, closer and closer, like at smaller and smaller distance scales, the uncertainty and energy in those distance skills is very large. 660 00:39:23,649.974919 --> 00:39:28,359.974919 Therefore, and if that, if that uncertainty is large enough, uh. 661 00:39:28,989.974919 --> 00:39:32,889.974919 To be greater than the rest mass of two particles you can pair produce particles. 662 00:39:33,579.974919 --> 00:39:36,759.974919 Um, let's review this again. 663 00:39:36,759.974919 --> 00:39:36,849.974919 Yes. 664 00:39:37,329.974919 --> 00:39:37,659.974919 Okay. 665 00:39:37,839.974919 --> 00:39:39,369.974919 We have uncertainty principle. 666 00:39:39,399.974919 --> 00:39:39,789.974919 Yes. 667 00:39:40,149.974919 --> 00:39:43,479.974919 Which applied here tells us. 668 00:39:43,509.974919 --> 00:39:43,839.974919 Yes. 669 00:39:43,839.974919 --> 00:39:48,369.974919 So the uncertainty, what's the uncertainty between here we have, we have, we have lens scales. 670 00:39:48,399.974919 --> 00:39:48,489.974919 Mm-hmm. 671 00:39:48,729.974919 --> 00:39:50,424.974919 So as you get smaller and smaller mm-hmm. 672 00:39:50,799.974919 --> 00:39:53,49.974919 The uncertainty and energy is larger and larger. 673 00:39:53,379.974919 --> 00:39:54,159.974919 Mm-hmm. 674 00:39:54,160.974919 --> 00:39:57,759.974919 Um, and so at some point, um, I cannot. 675 00:39:58,104.974919 --> 00:40:05,394.974919 Consistently tell you what's the energy in this spot, right? It just has a very large Delta E and that's a real Delta E. 676 00:40:05,394.974919 --> 00:40:08,694.974919 It's not, it's not something statistical or something. 677 00:40:09,114.974919 --> 00:40:11,394.974919 Something that our instruments can't detect. 678 00:40:11,394.974919 --> 00:40:12,834.974919 We can't make detects precise. 679 00:40:12,834.974919 --> 00:40:14,544.974919 It's not that it's a real Delta E. 680 00:40:14,784.974919 --> 00:40:15,54.974919 Yeah. 681 00:40:15,84.974919 --> 00:40:17,964.974919 So that real Delta E produces real particles. 682 00:40:18,444.974919 --> 00:40:18,714.974919 Uh, yeah. 683 00:40:18,774.974919 --> 00:40:22,674.974919 If the delta is with Delta E being the energy uncertainty Yes. 684 00:40:22,764.974919 --> 00:40:25,854.974919 Is a real energy uncertainty that. 685 00:40:26,229.974919 --> 00:40:31,29.974919 If there's enough of it, particles will appear in pairs in thin air. 686 00:40:31,89.974919 --> 00:40:31,479.974919 Yes. 687 00:40:32,49.974919 --> 00:40:32,859.974919 From, from backyard. 688 00:40:32,859.974919 --> 00:40:34,449.974919 From this uncertainty? Yes. 689 00:40:34,509.974919 --> 00:40:35,709.974919 In space. 690 00:40:35,769.974919 --> 00:40:39,189.974919 Yes, because the rest mass E equals mc squared, as everybody knows. 691 00:40:39,489.974919 --> 00:40:44,439.974919 So you need mc squared amount of energy to create a particle of mass N. 692 00:40:44,444.974919 --> 00:40:44,784.974919 Mm-hmm. 693 00:40:45,4.974919 --> 00:40:49,389.974919 Now, if the uncertainty energy is larger than mc squared, you can create one particle. 694 00:40:49,424.974919 --> 00:40:49,744.974919 Mm-hmm. 695 00:40:49,869.974919 --> 00:40:54,969.974919 Particles comes in, comes particles come in, pears to protect some symmetries. 696 00:40:55,359.974919 --> 00:40:58,299.974919 Um, so for two particles, you need two mc squared. 697 00:40:58,299.974919 --> 00:40:58,389.974919 Mm-hmm. 698 00:40:58,809.974919 --> 00:41:03,39.974919 And that's what you see when delta E is that large, that uncertainty can produce particles, uhhuh. 699 00:41:03,609.974919 --> 00:41:12,939.974919 Um, so there's, there are several effects like the Cassie effect, which is an example of this, which is related to the vacuum zero point energy, which is what we are talking about. 700 00:41:13,299.974919 --> 00:41:16,479.974919 But when space time is curved, this happens spontaneously. 701 00:41:17,559.974919 --> 00:41:24,609.974919 Uh, and that's, uh, that's, that's, that's super interesting to say that particles are produced spontaneously. 702 00:41:25,269.974919 --> 00:41:26,469.974919 Out of, out of thin air. 703 00:41:27,129.974919 --> 00:41:35,679.974919 So this happens when space time is curved and we, we still talk about this inflation field. 704 00:41:36,39.974919 --> 00:41:38,919.974919 Uh, this can happen for any field, just generally a quantum field. 705 00:41:38,919.974919 --> 00:41:41,529.974919 We put any quantum field on correct space time. 706 00:41:41,709.974919 --> 00:41:50,919.974919 Then particles will be, particles will be produced, spontaneously produced because the quantum field is bringing the uncertainty principle. 707 00:41:50,919.974919 --> 00:41:51,9.974919 Yes. 708 00:41:51,729.974919 --> 00:41:52,389.974919 And then, yeah. 709 00:41:52,569.974919 --> 00:41:57,549.974919 So on small scales, small scales, we're gonna have these energy uncertainties producing particles. 710 00:41:57,669.974919 --> 00:41:58,329.974919 Exactly. 711 00:41:58,629.974919 --> 00:42:04,269.974919 Uh, and this can happen even in flat space time, what we just discussed, but in curve space time. 712 00:42:04,659.974919 --> 00:42:05,19.974919 Yeah. 713 00:42:05,499.974919 --> 00:42:08,19.974919 Uh, the, I I told you matter curve space mm-hmm. 714 00:42:08,20.974919 --> 00:42:11,314.974919 And space response to matter being placed on top of it. 715 00:42:11,314.974919 --> 00:42:11,714.974919 Mm-hmm. 716 00:42:11,799.974919 --> 00:42:20,19.974919 What is space but gravity? Um, so if you now tell me that, uh, I have a field which clearly has energy. 717 00:42:20,409.974919 --> 00:42:21,789.974919 I'm putting it on space time. 718 00:42:21,879.974919 --> 00:42:24,489.974919 Something with energy must curve that space time even more. 719 00:42:24,489.974919 --> 00:42:24,999.974919 Mm-hmm. 720 00:42:25,5.974919 --> 00:42:25,254.974919 Right. 721 00:42:25,389.974919 --> 00:42:27,189.974919 So this is now a feedback loop. 722 00:42:27,434.974919 --> 00:42:27,854.974919 Mm-hmm. 723 00:42:27,939.974919 --> 00:42:32,49.974919 And you have a field that has energy, it curves space time, and then it releases particles more. 724 00:42:32,139.974919 --> 00:42:37,599.974919 So there's, there's this feedback going on right where the space time reacts to the quantum field. 725 00:42:37,899.974919 --> 00:42:39,639.974919 Uh, and that's the problem of quantum gravity. 726 00:42:39,639.974919 --> 00:42:42,789.974919 That's the problem we haven't fixed in over a hundred years. 727 00:42:42,969.974919 --> 00:42:45,879.974919 Uhhuh quantum field theory and curse space time is by an approximation. 728 00:42:45,939.974919 --> 00:42:46,509.974919 This is not. 729 00:42:47,109.974919 --> 00:42:48,819.974919 It is not the theory of quantum gravity. 730 00:42:48,819.974919 --> 00:42:55,839.974919 None of us expect that it would be, but it is an approximation that has given us many interesting results like hawking radiation. 731 00:42:56,169.974919 --> 00:43:14,259.974919 And now as we're going to talk about inflation, where we use qft curve space time to, to describe inflation, right? So people are trying to explain, trying to model this very early universe with this quantum inflation field. 732 00:43:14,319.974919 --> 00:43:14,679.974919 Mm-hmm. 733 00:43:15,4.974919 --> 00:43:15,224.974919 And. 734 00:43:16,494.974919 --> 00:43:17,484.974919 Curved space time. 735 00:43:17,514.974919 --> 00:43:17,814.974919 Yeah. 736 00:43:19,374.974919 --> 00:43:28,429.974919 But no one really thinks that that's the correct description or uh, um, well, quantum field theory in curved space time, we think it's an approximation. 737 00:43:28,779.974919 --> 00:43:28,869.974919 Uh huh. 738 00:43:29,529.974919 --> 00:43:29,919.974919 Yes. 739 00:43:29,979.974919 --> 00:43:32,589.974919 And inflation is a theory, it is a paradigm. 740 00:43:32,919.974919 --> 00:43:33,39.974919 Mm-hmm. 741 00:43:33,279.974919 --> 00:43:38,230.974919 Um, where you postulate the existence of an imaginary field, which we've never seen before, the infl on. 742 00:43:38,235.974919 --> 00:43:38,544.974919 Mm-hmm. 743 00:43:38,629.974919 --> 00:43:43,989.974919 To explain why the universe underwent a period of accelerated expansion uhhuh to resolve those puzzles. 744 00:43:43,989.974919 --> 00:43:45,729.974919 The big bang problem and the horizon problem. 745 00:43:45,759.974919 --> 00:43:46,29.974919 Yeah. 746 00:43:46,59.974919 --> 00:43:48,549.974919 So notice how we started with something classical. 747 00:43:48,969.974919 --> 00:43:49,449.974919 Yeah. 748 00:43:49,749.974919 --> 00:43:50,49.974919 The. 749 00:43:50,469.974919 --> 00:43:51,879.974919 Horizon problem, flatness problem. 750 00:43:51,879.974919 --> 00:43:53,109.974919 They're classical problems. 751 00:43:53,169.974919 --> 00:43:53,259.974919 Yeah. 752 00:43:53,259.974919 --> 00:43:55,59.974919 They have nothing to do with quantum mechanics. 753 00:43:55,179.974919 --> 00:43:55,419.974919 Yeah. 754 00:43:55,419.974919 --> 00:43:58,419.974919 And now somehow we found our way to quantum mechanics. 755 00:43:58,569.974919 --> 00:43:58,899.974919 Yeah. 756 00:43:58,929.974919 --> 00:44:00,609.974919 To solve these classical problems. 757 00:44:00,699.974919 --> 00:44:01,29.974919 Yeah. 758 00:44:01,54.974919 --> 00:44:05,349.974919 Um, Uhhuh, right? So that's why we need quantum gravity. 759 00:44:05,464.974919 --> 00:44:05,754.974919 Yeah. 760 00:44:07,419.974919 --> 00:44:07,899.974919 Yeah. 761 00:44:08,469.974919 --> 00:44:14,379.974919 So do these, um, yeah. 762 00:44:14,379.974919 --> 00:44:17,709.974919 So we said that the, the. 763 00:44:18,564.974919 --> 00:44:20,64.974919 Accelerating? No. 764 00:44:20,64.974919 --> 00:44:24,324.974919 The, the regions of the sky having causal connections mm-hmm. 765 00:44:25,284.974919 --> 00:44:36,144.974919 Um, could be explained by having this, uh, this inflation field is what's helping us explain that. 766 00:44:36,174.974919 --> 00:44:36,264.974919 Yes. 767 00:44:36,264.974919 --> 00:44:45,924.974919 And what, where is the quantum less coming in, in explaining these problems? So. 768 00:44:46,539.974919 --> 00:44:56,649.974919 Um, do these particles being created, are they playing a role in the resolution to these two problems? In, in the explanation, no. 769 00:44:56,709.974919 --> 00:45:03,219.974919 So we don't need a quantum inlet on to ex to resolve the horizon problem and the flatness problem uhhuh. 770 00:45:03,249.974919 --> 00:45:09,129.974919 But um, you remember we said that those patches in the sky are not just 2.7 771 00:45:09,129.974919 --> 00:45:09,549.974919 kelvin. 772 00:45:09,969.974919 --> 00:45:11,829.974919 They have some noise, some speckles. 773 00:45:11,919.974919 --> 00:45:12,309.974919 Yeah. 774 00:45:12,399.974919 --> 00:45:13,839.974919 These correlated fluctuations. 775 00:45:13,839.974919 --> 00:45:14,289.974919 Yes. 776 00:45:14,559.974919 --> 00:45:17,49.974919 Where did those fluctuations come from? Mm-hmm. 777 00:45:17,289.974919 --> 00:45:26,949.974919 And the answer is if the inlet on were a quantum field, it would be quantum fluctuations of tho of that field stretched to super horizon scales. 778 00:45:27,219.974919 --> 00:45:27,249.974919 Ah. 779 00:45:28,269.974919 --> 00:45:30,399.974919 So because of this uncertainty principle Yes. 780 00:45:30,759.974919 --> 00:45:32,289.974919 Happening in the early universe. 781 00:45:32,289.974919 --> 00:45:32,499.974919 Yes. 782 00:45:34,269.974919 --> 00:45:38,79.974919 That then explains these correlated fluctuations. 783 00:45:38,589.974919 --> 00:45:41,169.974919 Yes, that explains the origin of the fluctuations Uhhuh. 784 00:45:42,399.974919 --> 00:45:42,759.974919 Yes. 785 00:45:42,759.974919 --> 00:45:45,519.974919 So that's, that's why we need the field to be quantum. 786 00:45:45,999.974919 --> 00:45:50,109.974919 And when it's quantum, it's so beautiful because you get structure formation for free. 787 00:45:50,559.974919 --> 00:45:56,49.974919 Uh, quantum mechanics, the uncertainty principle is the reason for you and me to be in existence. 788 00:45:56,49.974919 --> 00:45:58,929.974919 Basically, we are nothing but fluctuations, quantum fluctuations. 789 00:45:59,404.974919 --> 00:45:59,524.974919 Hmm. 790 00:45:59,524.974919 --> 00:46:01,479.974919 Uh, stretch to super horizon skills. 791 00:46:02,649.974919 --> 00:46:02,889.974919 Uhhuh. 792 00:46:02,889.974919 --> 00:46:05,979.974919 Uh, so the standard story of cosmology, the Carl Sagan stories. 793 00:46:05,979.974919 --> 00:46:06,759.974919 We are Stardust. 794 00:46:06,759.974919 --> 00:46:09,759.974919 Yes, we're stardust, but where did the stardust come from? Yeah. 795 00:46:09,759.974919 --> 00:46:10,959.974919 Quantum fluctuations. 796 00:46:10,984.974919 --> 00:46:12,369.974919 Mm, mm-hmm. 797 00:46:12,609.974919 --> 00:46:12,909.974919 Yes. 798 00:46:13,179.974919 --> 00:46:13,599.974919 Yeah. 799 00:46:13,689.974919 --> 00:46:17,889.974919 So we really need quantum in this model for, to explain. 800 00:46:18,714.974919 --> 00:46:19,914.974919 These observations? Yes. 801 00:46:19,914.974919 --> 00:46:21,534.974919 And I see it as a huge bonus. 802 00:46:21,534.974919 --> 00:46:27,204.974919 The fact that we can explain this by saying, I will promote this field to a quantum operator is fantastic. 803 00:46:27,594.974919 --> 00:46:27,684.974919 Mm-hmm. 804 00:46:27,924.974919 --> 00:46:42,414.974919 Now then you might ask me the question, how do I know it's quantum? And that's, can I observe something in the universe that will tell me this field is quantum uhhuh and it will showing that this field, the infl on mysterious infl is quantum, say something about gravity. 805 00:46:42,864.974919 --> 00:46:43,14.974919 Yeah. 806 00:46:43,14.974919 --> 00:46:44,724.974919 And those are very important questions. 807 00:46:44,754.974919 --> 00:46:45,114.974919 Yeah. 808 00:46:46,14.974919 --> 00:46:46,944.974919 And this is what. 809 00:46:47,514.974919 --> 00:46:49,404.974919 You've been working in your research? Yes. 810 00:46:49,404.974919 --> 00:46:54,114.974919 So among other things, my, my research as I told you was signatures, the quantum gravity. 811 00:46:54,504.974919 --> 00:47:00,804.974919 And we tried postulating tabletop experiments, for example, a b Einstein condensate in a well. 812 00:47:01,284.974919 --> 00:47:03,924.974919 Um, what is a bine Einstein condensate. 813 00:47:03,984.974919 --> 00:47:05,244.974919 Ah, when you cool. 814 00:47:05,484.974919 --> 00:47:07,289.974919 Uh, so we have boons and fermions. 815 00:47:07,789.974919 --> 00:47:08,209.974919 Mm-hmm. 816 00:47:08,294.974919 --> 00:47:10,584.974919 And when I told you this table was hard, eh. 817 00:47:11,124.974919 --> 00:47:12,474.974919 That's the poly excl exclusion print. 818 00:47:12,594.974919 --> 00:47:12,834.974919 Yeah. 819 00:47:13,194.974919 --> 00:47:14,184.974919 On table believe. 820 00:47:14,184.974919 --> 00:47:14,514.974919 Just checking. 821 00:47:16,584.974919 --> 00:47:26,724.974919 Um, it's because of a property ion that we call the exclusion principle, the poly excl exclusion principle that prohibits two ions from being at the same, occupying the same quantum state. 822 00:47:27,144.974919 --> 00:47:27,234.974919 Mm-hmm. 823 00:47:27,474.974919 --> 00:47:31,524.974919 Now, boons on the other hand are particles that don't obey. 824 00:47:31,524.974919 --> 00:47:32,964.974919 They're very friendly particles. 825 00:47:32,964.974919 --> 00:47:39,414.974919 They like being together in bunches and, and the reason they're not boons are not in bunches all the time is because. 826 00:47:39,924.974919 --> 00:47:44,634.974919 And the temperature of the universe or whatever, wherever the boons are, is usually too high. 827 00:47:44,724.974919 --> 00:47:49,344.974919 The thermal excitations just knock them, jiggle them apart, and they don't coalesce. 828 00:47:49,554.974919 --> 00:47:51,449.974919 But when you lower the temperature mm-hmm. 829 00:47:51,529.974919 --> 00:47:57,594.974919 Uh, of a system of boons lower and lower, they start coalescing and they form boin and condensates. 830 00:47:58,44.974919 --> 00:48:05,394.974919 Uh, technically what does that mean? It means, um, a collection of particles is occupying a single quantum state. 831 00:48:05,994.974919 --> 00:48:08,634.974919 Um, so everything is in the ground state of a system. 832 00:48:08,964.974919 --> 00:48:09,264.974919 Mm-hmm. 833 00:48:09,339.974919 --> 00:48:17,349.974919 So what, what kind of particles do people do this with? Um, it, in the laboratory it's typically atoms, boon atoms. 834 00:48:18,399.974919 --> 00:48:18,489.974919 Mm-hmm. 835 00:48:18,729.974919 --> 00:48:23,349.974919 But fundamental boons, like from elementary particle physics, we know are photons. 836 00:48:23,349.974919 --> 00:48:23,889.974919 Photons. 837 00:48:23,979.974919 --> 00:48:26,229.974919 A photon is a boon, like D one. 838 00:48:26,379.974919 --> 00:48:31,599.974919 The particle that holds, um, pro proton, uh, quarks together in a proton is a boon. 839 00:48:32,409.974919 --> 00:48:32,529.974919 Mm-hmm. 840 00:48:32,589.974919 --> 00:48:38,589.974919 Uh, that's in fact a very interesting thing in particle physics that says, uh, all matter. 841 00:48:38,934.974919 --> 00:48:39,354.974919 It's fer. 842 00:48:39,354.974919 --> 00:48:39,774.974919 Monic. 843 00:48:40,44.974919 --> 00:48:40,164.974919 Mm-hmm. 844 00:48:40,974.974919 --> 00:48:42,714.974919 And the force mediators are B. 845 00:48:43,194.974919 --> 00:48:43,224.974919 Mm. 846 00:48:44,844.974919 --> 00:48:44,994.974919 Yeah. 847 00:48:45,474.974919 --> 00:48:45,714.974919 Yeah. 848 00:48:45,714.974919 --> 00:48:47,244.974919 And I don't have an explanation for that. 849 00:48:47,244.974919 --> 00:48:50,439.974919 It's just an interesting observation, but yeah. 850 00:48:50,444.974919 --> 00:48:50,724.974919 Yeah. 851 00:48:50,724.974919 --> 00:48:58,524.974919 So BEC is these B Einstein condensates in the lab? Yeah, they are as quantum as you can get in the laboratory because you have. 852 00:48:58,914.974919 --> 00:49:04,674.974919 A single particle occupying a macroscopic, having macroscopic occupation of a single quantum state. 853 00:49:04,944.974919 --> 00:49:08,514.974919 So a number of particles have come together and said, I'm going to take the same quantum state. 854 00:49:08,514.974919 --> 00:49:08,844.974919 Mm-hmm. 855 00:49:09,204.974919 --> 00:49:13,884.974919 Um, now if you have a quantum system that's sufficiently massive mm-hmm. 856 00:49:14,124.974919 --> 00:49:17,244.974919 Nothing will stop it from gravitating, any massive system will gravitate. 857 00:49:17,694.974919 --> 00:49:23,214.974919 But at a certain, a certain mass, let's say 10 to the negative six grams in the laboratory mm-hmm. 858 00:49:23,454.974919 --> 00:49:26,604.974919 You can start observing a quantum mechanical system. 859 00:49:26,994.974919 --> 00:49:40,554.974919 Interact gravitationally with itself or with another quantum mechanism, another BEC, for example, these two could gravitate, interact, right? So the bcs are useful for helping us get a quantum object that's massive enough to. 860 00:49:41,574.974919 --> 00:49:42,714.974919 Think about these kind of things. 861 00:49:42,744.974919 --> 00:49:42,864.974919 Yes. 862 00:49:42,864.974919 --> 00:49:44,694.974919 Is that the kind of function of Exactly. 863 00:49:44,934.974919 --> 00:49:47,94.974919 Trying to use a BC Exactly. 864 00:49:47,94.974919 --> 00:49:51,114.974919 So when I guarantee to you that this both Einstein condensate is quantum mm-hmm. 865 00:49:51,354.974919 --> 00:49:56,394.974919 Then it would be very easy for you to say, okay, let me now imagine that the BC is in super position. 866 00:49:56,399.974919 --> 00:49:56,579.974919 Mm-hmm. 867 00:49:56,904.974919 --> 00:50:00,564.974919 Nobody can come and say to you, ah, but you know, this is not a quantum object. 868 00:50:00,564.974919 --> 00:50:04,914.974919 How can you put it in a super position? Well, you can say it's A, B, e, C, I've guaranteed that it's quantum. 869 00:50:05,4.974919 --> 00:50:05,274.974919 Yeah. 870 00:50:05,334.974919 --> 00:50:07,944.974919 Now I can, ima I can imagine that it's in a super position. 871 00:50:07,949.974919 --> 00:50:08,299.974919 Uhhuh. 872 00:50:08,514.974919 --> 00:50:09,204.974919 It could be. 873 00:50:09,384.974919 --> 00:50:10,224.974919 It probably could be. 874 00:50:10,704.974919 --> 00:50:10,974.974919 Um. 875 00:50:11,664.974919 --> 00:50:15,474.974919 Uh, and there are many interesting things that come as a result of us imagining that. 876 00:50:15,474.974919 --> 00:50:16,284.974919 Mm-hmm. 877 00:50:16,285.974919 --> 00:50:21,229.974919 Um, a quantum system interacting gravitationally with another quantum system mm-hmm. 878 00:50:21,309.974919 --> 00:50:25,194.974919 Or interacting with itself because this is a collection of particles. 879 00:50:25,224.974919 --> 00:50:27,294.974919 It's not a single particle that's tend to be Right. 880 00:50:27,354.974919 --> 00:50:27,534.974919 Yeah. 881 00:50:28,14.974919 --> 00:50:35,484.974919 So, and you get some special signatures, uh, when you, when you look at this quantum system and try to. 882 00:50:36,24.974919 --> 00:50:39,984.974919 Um, understand what quantum gravity would do to this quantum system. 883 00:50:40,644.974919 --> 00:50:40,824.974919 Hmm. 884 00:50:40,854.974919 --> 00:50:44,694.974919 So those are the differences in predictions that we talked about very early on. 885 00:50:44,699.974919 --> 00:50:48,984.974919 Uhhuh, if I were to describe this quantum system with classical gravity Yeah. 886 00:50:49,44.974919 --> 00:51:02,394.974919 How would it respond? What, what would an experiment I do on it look like? And if it were quantum, if the GRA gravitational field were quantum, how would this quantum BEC respond to that? And you type discrepancies, which you do better and better experiments to understand. 887 00:51:02,454.974919 --> 00:51:04,104.974919 So that was one strand of my research, right. 888 00:51:04,524.974919 --> 00:51:05,4.974919 Yeah. 889 00:51:05,244.974919 --> 00:51:08,994.974919 And so you did some proposals Yes. 890 00:51:09,24.974919 --> 00:51:10,224.974919 In your research? Yes. 891 00:51:10,434.974919 --> 00:51:19,134.974919 Um, and yeah, when you said that, so sometimes it's Einstein Condensates affecting each other. 892 00:51:19,224.974919 --> 00:51:19,314.974919 Mm-hmm. 893 00:51:19,824.974919 --> 00:51:22,74.974919 So that would be like you take two of them Yes. 894 00:51:22,164.974919 --> 00:51:23,394.974919 And look at the effects. 895 00:51:23,424.974919 --> 00:51:23,604.974919 Yes. 896 00:51:23,604.974919 --> 00:51:25,494.974919 And some, some of the time is with itself. 897 00:51:25,494.974919 --> 00:51:29,544.974919 So is that kind of when it's so big that the atoms. 898 00:51:30,234.974919 --> 00:51:33,234.974919 Over here and over here would affect each other with gravity kind of thing. 899 00:51:33,234.974919 --> 00:51:35,569.974919 Is that everywhere? So the atoms everywhere? Yeah. 900 00:51:35,574.974919 --> 00:51:36,894.974919 So the whole thing is kind of Yes. 901 00:51:36,894.974919 --> 00:51:38,94.974919 Self interacting. 902 00:51:38,94.974919 --> 00:51:38,214.974919 Yes. 903 00:51:38,214.974919 --> 00:51:38,994.974919 With gravity. 904 00:51:38,994.974919 --> 00:51:41,184.974919 Like atoms interacting between themselves. 905 00:51:41,184.974919 --> 00:51:41,514.974919 Yes. 906 00:51:41,634.974919 --> 00:51:43,434.974919 And that will have some effect. 907 00:51:43,494.974919 --> 00:51:43,704.974919 Yeah. 908 00:51:43,704.974919 --> 00:51:45,684.974919 That will have some effect on the distribution. 909 00:51:45,744.974919 --> 00:51:48,114.974919 Like let's say the wave function of the BEC. 910 00:51:48,534.974919 --> 00:51:49,14.974919 Right. 911 00:51:49,464.974919 --> 00:51:52,74.974919 And we came up with a proposal to say, okay, if. 912 00:51:52,479.974919 --> 00:51:57,279.974919 If the gravitational interaction in this self interacting, both signs and condensate mm-hmm. 913 00:51:57,519.974919 --> 00:52:01,869.974919 Were to be modeled with classical gravity, Newtonian gravity, there's particles interacting with each other. 914 00:52:01,989.974919 --> 00:52:02,79.974919 Mm-hmm. 915 00:52:02,469.974919 --> 00:52:04,929.974919 How would the way function look? Mm-hmm. 916 00:52:05,559.974919 --> 00:52:10,479.974919 And if it were quantum, how would the way function look after a certain amount of time? And it's different. 917 00:52:10,689.974919 --> 00:52:10,929.974919 Yeah. 918 00:52:10,929.974919 --> 00:52:11,439.974919 They're different. 919 00:52:11,439.974919 --> 00:52:13,209.974919 And that's a test for quantum gravity. 920 00:52:13,689.974919 --> 00:52:14,139.974919 Yeah. 921 00:52:14,199.974919 --> 00:52:14,649.974919 Cool. 922 00:52:15,249.974919 --> 00:52:22,584.974919 And are people, can it be implemented or is it too difficult? To do other, I'm quite optimistic. 923 00:52:22,584.974919 --> 00:52:24,654.974919 Maybe in the next 10 years we could mm-hmm. 924 00:52:25,129.974919 --> 00:52:26,904.974919 Uh, we could test this. 925 00:52:27,84.974919 --> 00:52:27,474.974919 Yeah. 926 00:52:27,474.974919 --> 00:52:31,794.974919 Um, we don't, we actually don't need that many atoms to do A BEC. 927 00:52:31,794.974919 --> 00:52:33,264.974919 That's 10 to the negative six grams. 928 00:52:33,354.974919 --> 00:52:33,444.974919 Mm-hmm. 929 00:52:33,924.974919 --> 00:52:42,324.974919 Um, and people have tried with comparable, um, so I think the record holders about 10 to the 10 sodium atoms, which is. 930 00:52:43,209.974919 --> 00:52:45,789.974919 10 to the minus seven or minus eight grams. 931 00:52:45,789.974919 --> 00:52:50,289.974919 So if we could just make it 10 times better or a hundred times better, we'd be there. 932 00:52:50,289.974919 --> 00:52:50,379.974919 Mm-hmm. 933 00:52:51,99.974919 --> 00:52:51,189.974919 Right. 934 00:52:51,189.974919 --> 00:52:57,669.974919 And that's not, yeah, that's a much easier ask than saying I can reach one te electron volt on cern. 935 00:52:58,29.974919 --> 00:52:58,119.974919 Mm-hmm. 936 00:52:58,359.974919 --> 00:53:02,79.974919 But the plank scale is 10 to the 15 giga electron volt. 937 00:53:02,139.974919 --> 00:53:02,439.974919 Yeah. 938 00:53:02,469.974919 --> 00:53:06,824.974919 Which is 10 to the 12 times higher, so 104, which is crazy. 939 00:53:07,174.974919 --> 00:53:07,984.974919 Yeah, that's crazy. 940 00:53:08,589.974919 --> 00:53:08,859.974919 Yeah. 941 00:53:08,859.974919 --> 00:53:11,589.974919 And that's the second test, which is the cosmological test. 942 00:53:11,949.974919 --> 00:53:15,309.974919 You cannot reach such high energy levels in a electric period. 943 00:53:15,309.974919 --> 00:53:18,459.974919 You need to build a collider that's the size of the solar system. 944 00:53:18,969.974919 --> 00:53:23,529.974919 Good luck building that, or even the Milky Way, depending on what particle you want to accelerate. 945 00:53:23,589.974919 --> 00:53:25,569.974919 Yeah, good luck with that. 946 00:53:25,569.974919 --> 00:53:30,514.974919 So maybe space travel one day we can get there, but right now, one day. 947 00:53:30,789.974919 --> 00:53:40,209.974919 One day, right now, the best test we have for those high energies is from cosmology, which is the second strand of my research, to look at those high energy levels, high energy skills. 948 00:53:40,449.974919 --> 00:53:40,539.974919 Mm-hmm. 949 00:53:41,934.974919 --> 00:53:42,354.974919 Yeah. 950 00:53:42,444.974919 --> 00:53:55,884.974919 So could you tell us a bit more about that? What are these tests with cosmology that we can do that can get, let us access these energy scales that certain type experiments can't really, really realistically get us to? Yes. 951 00:53:56,154.974919 --> 00:53:56,634.974919 Uh, yeah. 952 00:53:56,634.974919 --> 00:54:06,294.974919 So going back to inflation, when we said that the inflation field could be quantum and that, uh, the quantum fluctuations are what became structured today mm-hmm. 953 00:54:06,534.974919 --> 00:54:08,694.974919 We can characterize those fluctuations really well. 954 00:54:08,994.974919 --> 00:54:09,804.974919 I can tell you. 955 00:54:10,209.974919 --> 00:54:15,999.974919 And because I'm a theorist, I can mathematically model the inlet on the evolution of its fluctuations. 956 00:54:15,999.974919 --> 00:54:19,359.974919 I can tell you what the fluctuations looked like at the end of inflation. 957 00:54:19,839.974919 --> 00:54:28,344.974919 I can tell you how they evolved in a universe that was later filled with matter, radiation, light and all those things. 958 00:54:28,344.974919 --> 00:54:34,869.974919 How did they evolve and how did they come to be The spot that I see on the sky today, if I can trace, trace out that entire evolution for you? Mm-hmm. 959 00:54:36,189.974919 --> 00:54:37,454.974919 Now the more. 960 00:54:39,414.974919 --> 00:54:47,274.974919 Uh, the more complex, the distribution, the initial distribution of those fluctuations are, that complexity will be reflected in the sky. 961 00:54:47,694.974919 --> 00:54:47,814.974919 Mm-hmm. 962 00:54:48,54.974919 --> 00:54:58,14.974919 And, and what captures the complexity of the initial fluctuation distribution fluctuations? It's the various field interactions. 963 00:54:58,14.974919 --> 00:55:01,194.974919 What was the potential of that field, for example? Um. 964 00:55:02,289.974919 --> 00:55:06,549.974919 There are objects in our everyday world that are held together by potentials. 965 00:55:06,969.974919 --> 00:55:09,219.974919 A very simple example is the hydrogen atom. 966 00:55:09,244.974919 --> 00:55:09,644.974919 Mm-hmm. 967 00:55:09,729.974919 --> 00:55:10,569.974919 The hydrogen atom. 968 00:55:10,569.974919 --> 00:55:17,829.974919 The proton interacts with the electron through the cool potential, which is an inverse R squared reaction, uh, between charges. 969 00:55:18,309.974919 --> 00:55:21,459.974919 Um, and that gives you a stable bounce state called the hydro aam. 970 00:55:21,969.974919 --> 00:55:24,789.974919 Uh, but those are not the only potentials you can have in the un. 971 00:55:24,819.974919 --> 00:55:26,349.974919 You can have something wild. 972 00:55:26,709.974919 --> 00:55:31,149.974919 So, uh, the distribution of what we see in the sky today will characterize what. 973 00:55:31,869.974919 --> 00:55:33,639.974919 Mechanism underpinned inflation. 974 00:55:33,969.974919 --> 00:55:39,159.974919 What were the potentials? What were the interactions? Was it one field? Was it many fields? Did it in check with gravity? Mm-hmm. 975 00:55:39,399.974919 --> 00:55:48,759.974919 So the more we unravel the sky by sending telescopes, uh, and so right now we see about 10 to the six pixels, uh, compressed into a single pixel. 976 00:55:48,849.974919 --> 00:55:53,799.974919 When we send a telescope into the sky, you can't, your telescopes can't zoom in so much. 977 00:55:53,799.974919 --> 00:55:57,609.974919 I can't give you infinite resolution over every single patch. 978 00:55:58,254.974919 --> 00:55:58,824.974919 In the sky. 979 00:55:58,824.974919 --> 00:56:00,594.974919 So we have to do some sort of compression. 980 00:56:00,954.974919 --> 00:56:03,924.974919 The hope is, and we've been hoping for 20 years now. 981 00:56:04,374.974919 --> 00:56:04,854.974919 Yeah. 982 00:56:04,854.974919 --> 00:56:11,214.974919 Uh, that as you send better and better telescopes, we can blow this little pixel up and see it in all its glory. 983 00:56:11,604.974919 --> 00:56:15,174.974919 And that can tell you something about the in field and its interactions. 984 00:56:15,179.974919 --> 00:56:15,339.974919 Mm-hmm. 985 00:56:15,599.974919 --> 00:56:18,474.974919 And how's that been happening over the last 20 years? Yes. 986 00:56:18,474.974919 --> 00:56:20,454.974919 We've sent, we've sent several probes. 987 00:56:20,454.974919 --> 00:56:25,974.974919 We've sent, um, the, the earliest prob was Kobe, then you had W Map. 988 00:56:26,574.974919 --> 00:56:28,74.974919 Uh, then you have Plank. 989 00:56:28,434.974919 --> 00:56:32,694.974919 Uh, then right now we have the James Weber telescope. 990 00:56:32,694.974919 --> 00:56:32,784.974919 Mm-hmm. 991 00:56:33,24.974919 --> 00:56:38,154.974919 Which is not necessarily for this, but Uhhuh has some experiments that can detect what we're talking about. 992 00:56:38,784.974919 --> 00:56:38,874.974919 Oh, okay. 993 00:56:38,904.974919 --> 00:56:40,614.974919 So we, we have tried, yeah. 994 00:56:40,644.974919 --> 00:56:44,79.974919 To send more and more telescopes and we've kept building theories as well. 995 00:56:44,79.974919 --> 00:56:44,439.974919 Mm-hmm. 996 00:56:44,524.974919 --> 00:56:46,194.974919 As we send these telescopes to space. 997 00:56:46,199.974919 --> 00:56:46,479.974919 Mm-hmm. 998 00:56:46,699.974919 --> 00:56:46,919.974919 Um. 999 00:56:47,154.974919 --> 00:56:47,184.974919 Okay. 1000 00:56:48,264.974919 --> 00:56:50,454.974919 So yes, that's, that's one way of experimenting. 1001 00:56:50,604.974919 --> 00:56:50,694.974919 Mm-hmm. 1002 00:56:51,24.974919 --> 00:57:03,234.974919 Um, but showing that this is quantum, like how do we know that this is not just thermal noise and this is a quantum, we actually require a quantum field, uh, to explain these fluctuations, you mean? Yes. 1003 00:57:03,234.974919 --> 00:57:06,984.974919 So, uh, I've kind of convinced you that Yeah. 1004 00:57:07,644.974919 --> 00:57:10,914.974919 It's, it's a really cool idea to think about these fluctuations as quantum. 1005 00:57:11,4.974919 --> 00:57:11,274.974919 Yeah. 1006 00:57:11,334.974919 --> 00:57:14,124.974919 But you may, you may come to me and say, okay. 1007 00:57:14,694.974919 --> 00:57:23,664.974919 Maybe this was just some random noise planted by a very specially designed field and it need not be, um, quantum. 1008 00:57:24,294.974919 --> 00:57:24,384.974919 Mm-hmm. 1009 00:57:24,624.974919 --> 00:57:30,114.974919 It's very poetic to think about them as quantum fields, but somebody could have just crumpled a piece of paper and said, here you go. 1010 00:57:30,114.974919 --> 00:57:31,314.974919 These are the fluctuations. 1011 00:57:31,344.974919 --> 00:57:31,584.974919 Yeah. 1012 00:57:31,584.974919 --> 00:57:32,844.974919 And that's what we see in the sky. 1013 00:57:33,144.974919 --> 00:57:33,444.974919 Yeah. 1014 00:57:33,444.974919 --> 00:57:35,274.974919 Um, it could have been like that. 1015 00:57:35,994.974919 --> 00:57:36,24.974919 Okay. 1016 00:57:36,24.974919 --> 00:57:38,754.974919 Uh, so you might insist that I want to know that this is quantum. 1017 00:57:38,874.974919 --> 00:57:39,204.974919 Yeah. 1018 00:57:39,204.974919 --> 00:57:41,34.974919 And when we, when we insist. 1019 00:57:41,349.974919 --> 00:57:44,109.974919 Um, that we want something to know if something's quantum or not. 1020 00:57:44,109.974919 --> 00:57:47,949.974919 Usually in the lab we do inequalities, which are tests for Quantums. 1021 00:57:48,639.974919 --> 00:57:48,849.974919 Mm-hmm. 1022 00:57:48,849.974919 --> 00:57:50,529.974919 So as you, which got a Nobel price. 1023 00:57:50,619.974919 --> 00:57:52,329.974919 Yes, absolutely. 1024 00:57:52,629.974919 --> 00:57:56,109.974919 Was it 2022? I want to say two. 1025 00:57:57,159.974919 --> 00:57:58,599.974919 Yeah, but it could be one. 1026 00:57:59,79.974919 --> 00:57:59,859.974919 I think it was two. 1027 00:57:59,949.974919 --> 00:58:00,459.974919 Yeah, it's too. 1028 00:58:00,519.974919 --> 00:58:00,759.974919 Okay. 1029 00:58:01,89.974919 --> 00:58:01,359.974919 Yeah. 1030 00:58:01,389.974919 --> 00:58:02,289.974919 But very recently. 1031 00:58:02,294.974919 --> 00:58:02,564.974919 Mm-hmm. 1032 00:58:02,859.974919 --> 00:58:04,809.974919 Um, and they're completely local. 1033 00:58:04,929.974919 --> 00:58:05,199.974919 Uh. 1034 00:58:05,619.974919 --> 00:58:06,939.974919 Quantum mechanics is local. 1035 00:58:07,539.974919 --> 00:58:11,409.974919 See, episode one of the, the podcast to, to hear more about that. 1036 00:58:11,529.974919 --> 00:58:16,869.974919 In the first installment of the Quantum Foundations Podcast, I spoke with Vidal our. 1037 00:58:17,559.974919 --> 00:58:45,234.974919 Colleague who also did his PhD in our group about these Bella equality experiments and how the usual popular narrative of them being non-local, um, and showing that entanglement means there's instantaneous action across space, uh, is actually not needed and is actually forbidden by, um, taking quantum theory with different assumptions so that it's fully. 1038 00:58:46,569.974919 --> 00:58:47,949.974919 Fully local theory. 1039 00:58:47,949.974919 --> 00:58:55,959.974919 So do watch that, that episode, if you want to hear more about those issues of locality in, in more detail. 1040 00:58:56,19.974919 --> 00:58:56,649.974919 It's a good one. 1041 00:58:57,819.974919 --> 00:58:59,109.974919 Thanks for the endorsement. 1042 00:58:59,259.974919 --> 00:58:59,379.974919 Mm-hmm. 1043 00:58:59,624.974919 --> 00:58:59,634.974919 Yeah. 1044 00:59:00,684.974919 --> 00:59:06,759.974919 And uh, yeah, so what, where were we? We were saying Oh yeah. 1045 00:59:06,789.974919 --> 00:59:12,9.974919 About be inequality violations, um, sharing. 1046 00:59:12,159.974919 --> 00:59:12,279.974919 Mm-hmm. 1047 00:59:13,359.974919 --> 00:59:13,809.974919 Yes. 1048 00:59:13,809.974919 --> 00:59:19,839.974919 You, you insisted that you want, well, I, I presume that you will insist that you want some proof mm-hmm. 1049 00:59:20,79.974919 --> 00:59:23,799.974919 That the infl in, in the field that caused inflation was indeed quantum. 1050 00:59:23,889.974919 --> 00:59:23,979.974919 Mm-hmm. 1051 00:59:24,339.974919 --> 00:59:25,839.974919 And how could we do that? Mm-hmm. 1052 00:59:26,79.974919 --> 00:59:29,529.974919 One way it might be to propose a be inequality test. 1053 00:59:29,534.974919 --> 00:59:29,744.974919 Mm-hmm. 1054 00:59:30,879.974919 --> 00:59:30,880.974919 Which. 1055 00:59:31,164.974919 --> 00:59:34,614.974919 Um, standard Alice and Bob type experiments mm-hmm. 1056 00:59:34,854.974919 --> 00:59:40,464.974919 Where you set Alice and Bob off with, uh, two detectors and a set of instructions. 1057 00:59:40,884.974919 --> 00:59:50,334.974919 Alice chooses to configure her detector in say this way, where she measures, um, cubit along one direction and along another direction. 1058 00:59:50,339.974919 --> 00:59:50,559.974919 Mm-hmm. 1059 00:59:50,664.974919 --> 00:59:53,424.974919 And Bob does the same, but picks two different directions. 1060 00:59:53,429.974919 --> 00:59:53,639.974919 Mm-hmm. 1061 00:59:53,939.974919 --> 00:59:54,999.974919 Um, so you have four. 1062 00:59:55,809.974919 --> 00:59:57,39.974919 Things that have been measured. 1063 00:59:57,279.974919 --> 00:59:57,369.974919 Mm-hmm. 1064 00:59:57,609.974919 --> 00:59:59,199.974919 Two by Alice and two by Bob. 1065 00:59:59,259.974919 --> 01:00:00,9.974919 Mm-hmm. 1066 01:00:00,10.974919 --> 01:00:02,469.974919 Um, and you can use that to construct a bell inequality. 1067 01:00:03,159.974919 --> 01:00:10,899.974919 Um, you might have covered what a be inequality is, but to recap, um, essentially depending on what Alice and Bob measure mm-hmm. 1068 01:00:11,139.974919 --> 01:00:14,829.974919 When they run this experiment, many, many times they repeat the same thing again. 1069 01:00:14,829.974919 --> 01:00:19,749.974919 Again, do it many times, but the statistics of what they observe will be very different. 1070 01:00:20,259.974919 --> 01:00:20,649.974919 Um. 1071 01:00:22,434.974919 --> 01:00:30,324.974919 If they were measuring a classical object versus measuring a quantum object, um, the be inequality as a bound two. 1072 01:00:30,804.974919 --> 01:00:41,424.974919 Um, if this, if this bound is violated, which means the set of measurements and the correlation functions, whatever a bulb choose to compute, if that's greater than two, then it's a strong. 1073 01:00:42,9.974919 --> 01:00:45,819.974919 Uh, is in fact conclusive that the thing that they're measuring is indeed quantum. 1074 01:00:46,419.974919 --> 01:00:46,509.974919 Mm-hmm. 1075 01:00:46,749.974919 --> 01:00:50,259.974919 Uh, because classical mechanics does not allow you to go beyond this bound of two. 1076 01:00:50,889.974919 --> 01:00:51,69.974919 Mm-hmm. 1077 01:00:51,699.974919 --> 01:01:04,264.974919 Uh, so can we replicate that for the early universe? Can we tell Alice and Bob, who, well maybe not people at this stage, but some other field, uh, to measure, uh, the infl on mm-hmm. 1078 01:01:04,599.974919 --> 01:01:07,509.974919 In four different configurations many, many times. 1079 01:01:08,154.974919 --> 01:01:12,984.974919 Because usually we, we have these experiments in the lab where we'll have, yeah, yeah. 1080 01:01:12,984.974919 --> 01:01:24,564.974919 Some, well, initially people were doing them in one lab where they say, okay, I'm gonna yeah, do this and tangle em up between these qubits, do these measurements, and then I've violated my inequality. 1081 01:01:24,564.974919 --> 01:01:35,934.974919 Then they made these loophole free bell tests where they, um, trying to move Alice and Bob so far apart that there can be no way to have some. 1082 01:01:36,999.974919 --> 01:01:39,99.974919 Uh, speed of light information passing mm-hmm. 1083 01:01:39,339.974919 --> 01:01:42,339.974919 Between them and, um, yeah. 1084 01:01:42,339.974919 --> 01:01:44,109.974919 So these experiments have been done. 1085 01:01:44,439.974919 --> 01:01:44,589.974919 Yeah. 1086 01:01:44,589.974919 --> 01:01:49,179.974919 And I think they've, these kinds of things have been done in space as well, on these satellites and Yes. 1087 01:01:49,809.974919 --> 01:01:50,289.974919 Stuff. 1088 01:01:50,379.974919 --> 01:01:52,749.974919 I think we sent one to the moon, if I'm not wrong. 1089 01:01:52,749.974919 --> 01:01:57,189.974919 Or did we Uh, well, we sent some entangled pairs. 1090 01:01:57,309.974919 --> 01:01:57,639.974919 Yeah. 1091 01:01:58,599.974919 --> 01:02:00,249.974919 But definitely with the satellite. 1092 01:02:00,849.974919 --> 01:02:01,59.974919 Yeah. 1093 01:02:01,179.974919 --> 01:02:01,389.974919 Yes. 1094 01:02:01,389.974919 --> 01:02:01,629.974919 Cool. 1095 01:02:02,19.974919 --> 01:02:02,409.974919 Yeah. 1096 01:02:02,799.974919 --> 01:02:03,669.974919 But what you are. 1097 01:02:04,659.974919 --> 01:02:15,159.974919 Suggesting is somehow doing this with the early universe, which seems quite different to like a kind of step step up from what we've been talking about here. 1098 01:02:15,579.974919 --> 01:02:15,999.974919 Yes. 1099 01:02:15,999.974919 --> 01:02:19,539.974919 And, and, and the thing that we are trying to prove is also very different. 1100 01:02:19,539.974919 --> 01:02:19,540.974919 Mm-hmm. 1101 01:02:19,989.974919 --> 01:02:24,309.974919 So when you do bell inequalities in the lab, you have your photon in two different. 1102 01:02:24,744.974919 --> 01:02:26,754.974919 Um, polarizations, for example. 1103 01:02:27,324.974919 --> 01:02:30,624.974919 Um, and that's another exciting topic for another podcast. 1104 01:02:30,624.974919 --> 01:02:33,24.974919 A photon is actually supposed to have three degrees of freedom. 1105 01:02:33,24.974919 --> 01:02:35,364.974919 Why does it have two? Because it's massless. 1106 01:02:35,544.974919 --> 01:02:36,654.974919 I'm not gonna get into that too. 1107 01:02:36,954.974919 --> 01:02:36,984.974919 Mm. 1108 01:02:37,254.974919 --> 01:02:40,344.974919 Let's hold that for, for, that's for another video's a whole new thing. 1109 01:02:40,794.974919 --> 01:02:40,854.974919 Yeah. 1110 01:02:40,884.974919 --> 01:02:46,764.974919 Um, but we typically do it with photons in the lab or something else that can exist in an up and down state. 1111 01:02:46,914.974919 --> 01:02:47,4.974919 Mm-hmm. 1112 01:02:47,304.974919 --> 01:02:56,499.974919 Um, and what are we really proving there? Whether proving that polarization is a quantum degree of freedom or spin if you're doing it with an electron is a quantum degree of freedom. 1113 01:02:56,499.974919 --> 01:02:57,189.974919 Mm-hmm. 1114 01:02:57,249.974919 --> 01:03:03,849.974919 Um, and you're proving that for that particle, that that particle can exhibit a quantum degree of freedom. 1115 01:03:04,329.974919 --> 01:03:14,379.974919 When you say a quantum degree of freedom, um, what does that mean? That these things can be in superposition or is what's like the. 1116 01:03:15,639.974919 --> 01:03:15,969.974919 Yeah. 1117 01:03:16,479.974919 --> 01:03:18,159.974919 Uh, yeah, this is an excellent question. 1118 01:03:18,219.974919 --> 01:03:21,249.974919 As far as I'm concerned, quantum mechanics is two things. 1119 01:03:21,249.974919 --> 01:03:30,999.974919 One, things are allowed to exist in superposition, and two, you can, if you have, uh, two systems, they're allowed to be entangled if your theory allows this. 1120 01:03:31,479.974919 --> 01:03:41,379.974919 Um, it's a quantum theory and by degrees of freedom, it's just a fancy way of saying what are the properties of the two systems that are entangled. 1121 01:03:41,979.974919 --> 01:03:42,909.974919 Right? Yes. 1122 01:03:42,914.974919 --> 01:03:42,924.974919 Mm-hmm. 1123 01:03:43,34.974919 --> 01:03:43,324.974919 Yeah. 1124 01:03:43,389.974919 --> 01:03:45,129.974919 So we do Berlin and quality test. 1125 01:03:45,159.974919 --> 01:03:50,349.974919 If we violate the bound, it tells us that these systems have properties that can be entangled. 1126 01:03:50,409.974919 --> 01:03:50,529.974919 Yes. 1127 01:03:50,529.974919 --> 01:03:52,239.974919 So that quantum, yes. 1128 01:03:52,239.974919 --> 01:03:56,439.974919 So this, so we would, and now we synonymously say the system is quantum. 1129 01:03:56,519.974919 --> 01:04:08,639.974919 So let's go back to take a step back and now say if we want Alice and Bob to do this in the early universe, what must be they being measuring? What is that quantum property? Yeah. 1130 01:04:08,664.974919 --> 01:04:17,699.974919 And, and as you know, so you, you asked me this question, which is, what does it mean for things to be quantum? And I said super position entanglement. 1131 01:04:17,704.974919 --> 01:04:17,964.974919 Mm-hmm. 1132 01:04:18,264.974919 --> 01:04:18,484.974919 Um. 1133 01:04:19,574.974919 --> 01:04:23,174.974919 Entanglement is actually related to complementarity of observables. 1134 01:04:23,294.974919 --> 01:04:27,464.974919 When you, complementarity essentially means you have two observables that do not commute. 1135 01:04:28,34.974919 --> 01:04:36,944.974919 What does that mean in an experimental setting? It means that Alice can't measure, uh, observable A and B at the same time. 1136 01:04:36,944.974919 --> 01:04:37,604.974919 Mm-hmm. 1137 01:04:37,754.974919 --> 01:04:39,74.974919 So we have two properties. 1138 01:04:39,434.974919 --> 01:04:41,954.974919 Alice can't measure them both at the same time. 1139 01:04:42,74.974919 --> 01:04:42,404.974919 Yes. 1140 01:04:42,914.974919 --> 01:04:45,464.974919 It's kind of a version of house and bugs. 1141 01:04:45,464.974919 --> 01:04:46,844.974919 Uncertainty principle Exactly. 1142 01:04:46,934.974919 --> 01:04:47,354.974919 Of. 1143 01:04:48,404.974919 --> 01:04:48,704.974919 Yeah. 1144 01:04:48,704.974919 --> 01:04:50,714.974919 Which you can phrase in such a way of Yes. 1145 01:04:50,744.974919 --> 01:04:55,214.974919 Saying that a system can't have these two properties mm-hmm. 1146 01:04:56,234.974919 --> 01:05:00,104.974919 Um, at a definite value simultaneously. 1147 01:05:00,109.974919 --> 01:05:00,599.974919 Exactly. 1148 01:05:00,599.974919 --> 01:05:00,999.974919 Mm-hmm. 1149 01:05:01,84.974919 --> 01:05:02,804.974919 And so they can't measure the same thing. 1150 01:05:03,344.974919 --> 01:05:03,464.974919 Mm-hmm. 1151 01:05:03,704.974919 --> 01:05:14,564.974919 Um, um, and a quantum system must necessarily have two non-com commuting observables like you must be able to find two non-com muting observables. 1152 01:05:15,149.974919 --> 01:05:17,939.974919 And measure those two non-com computing observables to be able to do a well. 1153 01:05:17,939.974919 --> 01:05:18,449.974919 Inequality. 1154 01:05:18,899.974919 --> 01:05:19,199.974919 Yeah. 1155 01:05:19,259.974919 --> 01:05:22,649.974919 So quantum system must have, yeah. 1156 01:05:22,709.974919 --> 01:05:25,589.974919 These properties that you can do an uncertainty principle Yes. 1157 01:05:26,129.974919 --> 01:05:27,389.974919 With Yeah. 1158 01:05:27,449.974919 --> 01:05:27,659.974919 Yeah. 1159 01:05:27,659.974919 --> 01:05:28,289.974919 Precisely. 1160 01:05:28,289.974919 --> 01:05:28,559.974919 You. 1161 01:05:28,619.974919 --> 01:05:34,829.974919 So, because that's the thing that makes, uh, that's, that's the property that makes things quantum, the uncertainty principle. 1162 01:05:34,979.974919 --> 01:05:35,69.974919 Mm-hmm. 1163 01:05:35,309.974919 --> 01:05:37,229.974919 Uh, if you didn't have an uncertainty principle. 1164 01:05:37,754.974919 --> 01:05:40,214.974919 Uh, that is planks constant would be zero. 1165 01:05:40,304.974919 --> 01:05:43,129.974919 In the case of commuting, all these things are connected. 1166 01:05:43,129.974919 --> 01:05:43,449.974919 Mm-hmm. 1167 01:05:43,574.974919 --> 01:05:45,764.974919 The fact that planks constant is finite. 1168 01:05:46,64.974919 --> 01:05:54,614.974919 The fact that absorbers don't commute, um, and the fact that something like an uncertainty principle exists are all related, they're just different ways of saying the same thing. 1169 01:05:54,614.974919 --> 01:05:54,914.974919 Mm-hmm. 1170 01:05:55,544.974919 --> 01:06:03,344.974919 Um, so now that we've agreed you need to have non-com commuting observables, and we need to go and establish what they are for the early universe. 1171 01:06:03,884.974919 --> 01:06:06,434.974919 And position momentum are a very good example. 1172 01:06:06,434.974919 --> 01:06:13,964.974919 So when you have a, a simple system in the laboratory, uh, you can categorize its position, categorize. 1173 01:06:14,84.974919 --> 01:06:20,204.974919 No, you can categorize, you can categorize its position and its momentum. 1174 01:06:20,294.974919 --> 01:06:20,384.974919 Mm-hmm. 1175 01:06:20,774.974919 --> 01:06:22,874.974919 Um, not simultaneously, of course. 1176 01:06:22,874.974919 --> 01:06:24,734.974919 And then you can do interesting experiments. 1177 01:06:24,884.974919 --> 01:06:24,974.974919 Mm-hmm. 1178 01:06:25,394.974919 --> 01:06:31,724.974919 Now, quantum fields such as the infl on field, have their own version of position and momentum. 1179 01:06:32,609.974919 --> 01:06:35,549.974919 It's the field and it's conjugate momentum. 1180 01:06:36,599.974919 --> 01:06:39,689.974919 Uh, so that the field is the field, like the electromagnetic field. 1181 01:06:39,719.974919 --> 01:06:46,319.974919 And then there's conjugate momentum, which essentially is a prop with a momentum like quantity for the field. 1182 01:06:46,829.974919 --> 01:07:00,449.974919 Uh, when you write a lag grandon, which is something like Newton's laws for a field, and in Newton's laws you always have, uh, tic energy plus potential energy equals. 1183 01:07:00,839.974919 --> 01:07:03,119.974919 Something equals zero typically. 1184 01:07:03,119.974919 --> 01:07:08,789.974919 And concept systems, um, are a constant however you like to put your bound of energy. 1185 01:07:09,389.974919 --> 01:07:22,859.974919 Um, in, in, in quantum field theory, there's something like that where you have the field and it's conjugate momentum and you're allowed to write lag, which are laws of motion for those fields which describe the laws of motions for those fields. 1186 01:07:24,179.974919 --> 01:07:24,569.974919 Okay. 1187 01:07:24,989.974919 --> 01:07:26,639.974919 Um, so. 1188 01:07:31,679.974919 --> 01:07:36,89.974919 So right now we're talking about a field in general, or the universe. 1189 01:07:36,179.974919 --> 01:07:36,839.974919 Any field. 1190 01:07:36,839.974919 --> 01:07:38,549.974919 This is any field, uhhuh, any field. 1191 01:07:38,549.974919 --> 01:07:41,729.974919 The electromagnetic field, the strong force, uhhuh, the weak for any field. 1192 01:07:42,89.974919 --> 01:07:42,419.974919 Yeah. 1193 01:07:42,419.974919 --> 01:07:43,709.974919 Has a conjugate momentum. 1194 01:07:43,709.974919 --> 01:07:44,699.974919 Mm-hmm. 1195 01:07:46,199.974919 --> 01:07:46,529.974919 Yeah. 1196 01:07:46,589.974919 --> 01:07:55,199.974919 So the properties we're comparing our, the field measuring the value of the field and its conjugate momentum right. 1197 01:07:55,199.974919 --> 01:07:55,859.974919 At the same time. 1198 01:07:56,519.974919 --> 01:07:57,479.974919 Right? Yeah. 1199 01:07:57,989.974919 --> 01:07:59,249.974919 We can even take this. 1200 01:07:59,249.974919 --> 01:08:03,389.974919 So if you'll indulge me for a moment, we can go back to the notion of particle creation. 1201 01:08:03,509.974919 --> 01:08:03,599.974919 Mm-hmm. 1202 01:08:04,79.974919 --> 01:08:07,799.974919 And there are operators in quantum mechanics that describe particle creation. 1203 01:08:08,309.974919 --> 01:08:14,99.974919 So you have the vacuum state and you say, if I apply this operator to the vacuum state, you will generate one particle. 1204 01:08:14,909.974919 --> 01:08:15,59.974919 Mm-hmm. 1205 01:08:15,299.974919 --> 01:08:19,889.974919 Um, and this, the inverse operate sort of inverse operator, which is, if I. 1206 01:08:20,249.974919 --> 01:08:24,539.974919 Apply the inverse to the one particle state, I will get back vacuum. 1207 01:08:24,599.974919 --> 01:08:26,909.974919 So they're creation and annihilation operators. 1208 01:08:26,939.974919 --> 01:08:27,209.974919 Mm-hmm. 1209 01:08:27,539.974919 --> 01:08:39,599.974919 Um, so the field and its conjugate momentum are manifestations of the creation and annihilation operator at, at its fundamental level, the fact that you can create particles and quantum field theory mm-hmm. 1210 01:08:39,839.974919 --> 01:08:45,749.974919 Necessarily means you must have two non-com commuting observers, the field and this conjugate momentum. 1211 01:08:46,499.974919 --> 01:08:46,979.974919 Right. 1212 01:08:47,219.974919 --> 01:08:48,839.974919 So when we have these two. 1213 01:08:49,829.974919 --> 01:08:51,869.974919 Properties that have this uncertainty principle. 1214 01:08:51,929.974919 --> 01:08:52,259.974919 Yes. 1215 01:08:52,889.974919 --> 01:08:57,269.974919 Um, what is the value of the field and what is this other Yes. 1216 01:08:57,269.974919 --> 01:08:58,589.974919 Property, the conjugate momentum. 1217 01:08:58,649.974919 --> 01:08:58,889.974919 Yes. 1218 01:08:59,339.974919 --> 01:09:01,679.974919 Then we can get particles out of it. 1219 01:09:01,679.974919 --> 01:09:04,49.974919 We can, we can now have, yes. 1220 01:09:04,289.974919 --> 01:09:04,589.974919 Yeah. 1221 01:09:04,589.974919 --> 01:09:08,219.974919 From vacuum we can create particles and an IC particles. 1222 01:09:08,309.974919 --> 01:09:08,669.974919 Yes. 1223 01:09:08,669.974919 --> 01:09:09,779.974919 And yeah. 1224 01:09:09,809.974919 --> 01:09:12,839.974919 Have this kind of ladder of ladderal practical creation. 1225 01:09:12,899.974919 --> 01:09:13,259.974919 Yeah. 1226 01:09:13,649.974919 --> 01:09:15,59.974919 And this is the amazing thing. 1227 01:09:15,479.974919 --> 01:09:15,779.974919 Um. 1228 01:09:16,184.974919 --> 01:09:16,364.974919 Yeah. 1229 01:09:16,514.974919 --> 01:09:19,214.974919 That we see quantum mechanics expressed at all levels. 1230 01:09:19,214.974919 --> 01:09:24,794.974919 The fact that particle creation comes from something as algebraic as this is mind blowing. 1231 01:09:25,454.974919 --> 01:09:25,544.974919 Mm-hmm. 1232 01:09:25,814.974919 --> 01:09:30,524.974919 That it has nothing to do with somebody pumping in energy into space. 1233 01:09:30,674.974919 --> 01:09:30,824.974919 Mm-hmm. 1234 01:09:31,64.974919 --> 01:09:32,54.974919 Is, yeah. 1235 01:09:32,234.974919 --> 01:09:34,229.974919 It, it, it's, it's a very profound mm-hmm. 1236 01:09:34,379.974919 --> 01:09:35,469.974919 Insight into physics. 1237 01:09:36,49.974919 --> 01:09:36,469.974919 Mm-hmm. 1238 01:09:37,289.974919 --> 01:09:40,154.974919 And does this, um. 1239 01:09:42,494.974919 --> 01:09:42,974.974919 Yeah. 1240 01:09:43,484.974919 --> 01:09:50,834.974919 So before you were talking about uncertainty principle leading to big uncertainty and energy mm-hmm. 1241 01:09:51,524.974919 --> 01:09:52,844.974919 Causing particle creation. 1242 01:09:52,904.974919 --> 01:09:53,324.974919 Yes. 1243 01:09:53,834.974919 --> 01:09:56,804.974919 Are these related forms of Absolutely. 1244 01:09:56,804.974919 --> 01:09:59,864.974919 As I said, uh, particle creation? Absolutely. 1245 01:09:59,864.974919 --> 01:10:02,54.974919 They're the same, uh, as we just discussed. 1246 01:10:02,444.974919 --> 01:10:07,604.974919 Um, the fact that observers don't commute and the fact that there exists an uncertainty principle. 1247 01:10:08,144.974919 --> 01:10:09,674.974919 Plants constant is not zero. 1248 01:10:09,734.974919 --> 01:10:11,264.974919 These are all interconnected. 1249 01:10:11,264.974919 --> 01:10:14,714.974919 You can express these things in terms of each other. 1250 01:10:15,14.974919 --> 01:10:15,104.974919 Yeah. 1251 01:10:15,104.974919 --> 01:10:19,334.974919 And the leg that we are interested in is uncertainty principle and non-com UNItivity. 1252 01:10:20,54.974919 --> 01:10:20,414.974919 Yeah. 1253 01:10:20,504.974919 --> 01:10:24,194.974919 Uh, and as quantum mechanics stands on these two legs. 1254 01:10:24,434.974919 --> 01:10:24,524.974919 Mm-hmm. 1255 01:10:24,764.974919 --> 01:10:29,414.974919 And uncertainty principle implies something like non-com commuting, observables and vice versa. 1256 01:10:29,539.974919 --> 01:10:29,889.974919 Uhhuh. 1257 01:10:30,159.974919 --> 01:10:30,449.974919 Yeah. 1258 01:10:30,829.974919 --> 01:10:32,9.974919 And can I, they're the same thing. 1259 01:10:32,159.974919 --> 01:10:32,449.974919 Yeah. 1260 01:10:32,774.974919 --> 01:10:36,884.974919 Can I think of the energy and certainty in terms of the. 1261 01:10:37,424.974919 --> 01:10:40,484.974919 Uh, yeah. 1262 01:10:40,574.974919 --> 01:10:49,599.974919 In terms of the uncertainty principle of, 'cause we, we have this uncertainty principle of the value of mm-hmm. 1263 01:10:49,684.974919 --> 01:10:51,14.974919 The field and the conjugate momentum. 1264 01:10:51,74.974919 --> 01:10:51,494.974919 Yes. 1265 01:10:51,764.974919 --> 01:10:55,814.974919 And then we have like, let's scales and energy uncertainty. 1266 01:10:56,54.974919 --> 01:10:56,384.974919 Yes. 1267 01:10:56,684.974919 --> 01:10:57,314.974919 They're the same. 1268 01:10:58,364.974919 --> 01:10:58,724.974919 Right. 1269 01:10:58,724.974919 --> 01:10:59,954.974919 Man, expressions are the same. 1270 01:10:59,954.974919 --> 01:11:01,784.974919 But sorry, please finish your question. 1271 01:11:01,904.974919 --> 01:11:02,564.974919 Yeah, yeah, yeah. 1272 01:11:02,564.974919 --> 01:11:03,614.974919 That's kind of my question. 1273 01:11:03,614.974919 --> 01:11:04,724.974919 Like how can I. 1274 01:11:05,429.974919 --> 01:11:10,799.974919 See that these are the same in a way? Or like what's the connection? Uh, yes. 1275 01:11:10,799.974919 --> 01:11:15,479.974919 So, um, it's a very interesting question. 1276 01:11:15,749.974919 --> 01:11:21,89.974919 So one is, so the field is actually a quantum operator. 1277 01:11:21,634.974919 --> 01:11:26,519.974919 Um, um, whereas energy is not an operator. 1278 01:11:26,579.974919 --> 01:11:27,239.974919 It's, mm-hmm. 1279 01:11:27,479.974919 --> 01:11:33,179.974919 Well, the Hamiltonian is an operator, but when we talk about the Hamiltonian, which is the generator of, uh. 1280 01:11:34,289.974919 --> 01:11:36,629.974919 Time translations and the iGen states are the energy. 1281 01:11:36,629.974919 --> 01:11:37,889.974919 iGen states is an operator. 1282 01:11:37,889.974919 --> 01:11:47,759.974919 But when you talk about energy and length uncertainty, you're sort of talking about, um, things you measure with a ruler or with a meter that measures energy. 1283 01:11:47,764.974919 --> 01:11:48,44.974919 Mm-hmm. 1284 01:11:48,124.974919 --> 01:11:50,669.974919 It is the same with position, momentum and certain principle. 1285 01:11:50,789.974919 --> 01:11:51,149.974919 Yeah. 1286 01:11:51,299.974919 --> 01:11:56,879.974919 Uh, you're again talking about relationships between quantities and a device can measure. 1287 01:11:56,999.974919 --> 01:11:57,89.974919 Mm-hmm. 1288 01:11:57,329.974919 --> 01:12:00,299.974919 But the expression of that is a deeper algebra property. 1289 01:12:00,479.974919 --> 01:12:00,569.974919 Mm-hmm. 1290 01:12:00,814.974919 --> 01:12:02,969.974919 Which is the uncertainty principles in the operators. 1291 01:12:03,569.974919 --> 01:12:07,769.974919 So that's actually in terms of non-com, right? Yeah. 1292 01:12:07,769.974919 --> 01:12:15,124.974919 So when you go to the position and Momentum Uncertainty principle, you say Commutator XP is I IH Bar, whatever? Mm-hmm. 1293 01:12:15,304.974919 --> 01:12:16,439.974919 Um, yeah. 1294 01:12:16,439.974919 --> 01:12:19,619.974919 So the relation between Yeah. 1295 01:12:19,739.974919 --> 01:12:23,759.974919 These ideas of the uncertainty principles, is that, yeah. 1296 01:12:23,819.974919 --> 01:12:29,609.974919 In the Energy Less Scale case, we were talking about the uncertainty of these. 1297 01:12:30,14.974919 --> 01:12:31,59.974919 Values of mm-hmm. 1298 01:12:31,244.974919 --> 01:12:33,164.974919 The quantity that you measure. 1299 01:12:33,194.974919 --> 01:12:33,434.974919 Yes. 1300 01:12:33,854.974919 --> 01:12:42,254.974919 And when we talk about the field and the conjugate momentum, we talk about these operators that are kind of on a, uh, yeah. 1301 01:12:43,154.974919 --> 01:12:44,714.974919 Slightly more fundamental level. 1302 01:12:44,714.974919 --> 01:12:44,715.974919 Mm-hmm. 1303 01:12:44,779.974919 --> 01:12:47,744.974919 If you want to be more fundamental level Yeah. 1304 01:12:47,804.974919 --> 01:12:48,74.974919 Yes. 1305 01:12:48,74.974919 --> 01:12:51,944.974919 In the sense of the overall description of, of what's happening. 1306 01:12:52,4.974919 --> 01:12:59,204.974919 But it's kind of a unified thing of this is how particles emerges from these uncertainties. 1307 01:12:59,609.974919 --> 01:13:01,469.974919 Um, yeah, absolutely. 1308 01:13:01,469.974919 --> 01:13:03,959.974919 And as you know, quantum mechanics doesn't have so many axioms. 1309 01:13:03,959.974919 --> 01:13:05,219.974919 It has four axioms. 1310 01:13:05,669.974919 --> 01:13:11,99.974919 Uh, so there's no luxury to make one uncertainty principle more special than the other. 1311 01:13:11,99.974919 --> 01:13:11,129.974919 Uhhuh. 1312 01:13:11,429.974919 --> 01:13:13,169.974919 They're all manifestations on the same thing. 1313 01:13:13,404.974919 --> 01:13:14,534.974919 Yeah, yeah. 1314 01:13:15,4.974919 --> 01:13:15,294.974919 Cool. 1315 01:13:15,834.974919 --> 01:13:22,19.974919 So we have, yeah, when we have a field quantum field, yes. 1316 01:13:22,79.974919 --> 01:13:23,519.974919 We have an uncertainty principle. 1317 01:13:23,639.974919 --> 01:13:24,269.974919 Exactly. 1318 01:13:24,689.974919 --> 01:13:26,699.974919 We, we, we have that, and that means the field. 1319 01:13:27,254.974919 --> 01:13:29,954.974919 Uh, and the conjugate momentum, they do not commute. 1320 01:13:30,344.974919 --> 01:13:33,854.974919 They're non-compatible operators, whatever you like to call them, but aha. 1321 01:13:33,854.974919 --> 01:13:37,244.974919 That means you can use these guys to do be inequalities. 1322 01:13:37,394.974919 --> 01:13:37,484.974919 Mm-hmm. 1323 01:13:37,724.974919 --> 01:13:40,784.974919 So we can send Alice and Bob with a detector mm-hmm. 1324 01:13:41,234.974919 --> 01:13:44,474.974919 To measure the field and the conjugate momentum, whatever that means. 1325 01:13:44,479.974919 --> 01:13:44,679.974919 Mm-hmm. 1326 01:13:44,759.974919 --> 01:13:47,534.974919 So we should be able to test the quantum nature of inflation. 1327 01:13:47,534.974919 --> 01:13:47,864.974919 Right. 1328 01:13:48,194.974919 --> 01:13:53,174.974919 If somebody could measure the field, the inflationary field, and this conjugate momentum, unfortunately. 1329 01:13:54,664.974919 --> 01:13:58,169.974919 Um, as, as with some of the most beautiful theories. 1330 01:13:58,229.974919 --> 01:13:58,559.974919 Yeah. 1331 01:13:58,919.974919 --> 01:14:04,379.974919 The very thing that this theory tries to solve, which is the size of the universe. 1332 01:14:04,889.974919 --> 01:14:04,979.974919 Mm-hmm. 1333 01:14:05,219.974919 --> 01:14:08,939.974919 It sort of kills our attempt to test whether it's quantum or not. 1334 01:14:09,119.974919 --> 01:14:14,759.974919 Why do I say that? Um, when you solve for the field and the con, these are dynamical variables. 1335 01:14:14,759.974919 --> 01:14:16,379.974919 They, they evolve over time. 1336 01:14:16,739.974919 --> 01:14:17,669.974919 So, um. 1337 01:14:18,59.974919 --> 01:14:24,509.974919 They may have value whatever, uh, one and zero at, uh, the beginning of the universe. 1338 01:14:24,779.974919 --> 01:14:28,349.974919 And as they evolve, it may be completely different value, like 0.01 1339 01:14:28,409.974919 --> 01:14:29,819.974919 and 0.0, 1340 01:14:29,819.974919 --> 01:14:30,899.974919 0 0 1, whatever. 1341 01:14:30,989.974919 --> 01:14:31,649.974919 Two different values. 1342 01:14:32,459.974919 --> 01:14:32,549.974919 Yeah. 1343 01:14:32,549.974919 --> 01:14:38,579.974919 And now the conjugate momentum, which is the observable that we need so much mm-hmm. 1344 01:14:38,819.974919 --> 01:14:40,379.974919 To do our bi inequality. 1345 01:14:40,949.974919 --> 01:14:45,569.974919 Uh, because of the dynamics of the expanding universe, it decays exponentially. 1346 01:14:46,499.974919 --> 01:14:46,859.974919 Um. 1347 01:14:47,669.974919 --> 01:14:50,99.974919 Over the timescales of inflation. 1348 01:14:50,219.974919 --> 01:14:53,99.974919 Oh, so even if it had a well-defined value Yeah. 1349 01:14:53,189.974919 --> 01:14:57,869.974919 In the beginning of the universe, uh, because the universe expanded so rapidly mm-hmm. 1350 01:14:58,109.974919 --> 01:14:58,919.974919 It was suppressed. 1351 01:14:58,919.974919 --> 01:15:00,89.974919 It still has a value. 1352 01:15:00,149.974919 --> 01:15:00,239.974919 Mm-hmm. 1353 01:15:00,479.974919 --> 01:15:05,159.974919 It can still be measured, but that value is so incredibly small that you can't conceive. 1354 01:15:06,299.974919 --> 01:15:07,169.974919 A test to measure. 1355 01:15:07,169.974919 --> 01:15:07,229.974919 Yeah. 1356 01:15:07,229.974919 --> 01:15:08,609.974919 Ah, right. 1357 01:15:09,59.974919 --> 01:15:10,799.974919 So now you're stuck with just the field. 1358 01:15:10,949.974919 --> 01:15:11,249.974919 Yeah. 1359 01:15:11,249.974919 --> 01:15:13,919.974919 The conjugate momentum is far too small to be measured. 1360 01:15:13,919.974919 --> 01:15:14,99.974919 Okay. 1361 01:15:14,369.974919 --> 01:15:14,609.974919 Yeah. 1362 01:15:14,609.974919 --> 01:15:17,879.974919 So it's extremely difficult to do a be inequality Yeah. 1363 01:15:17,909.974919 --> 01:15:18,269.974919 Today. 1364 01:15:19,409.974919 --> 01:15:20,819.974919 Oh, or at the end of inflation. 1365 01:15:20,939.974919 --> 01:15:21,89.974919 Mm-hmm. 1366 01:15:21,779.974919 --> 01:15:23,129.974919 No, can we. 1367 01:15:24,824.974919 --> 01:15:28,754.974919 Can we come up with a nice proposal? Like we shouldn't stop here. 1368 01:15:28,754.974919 --> 01:15:29,474.974919 We are physicists. 1369 01:15:29,474.974919 --> 01:15:30,794.974919 We should keep, we should keep trying. 1370 01:15:30,944.974919 --> 01:15:33,14.974919 Yes, we should. 1371 01:15:33,14.974919 --> 01:15:36,224.974919 So what if I told you that, aha. 1372 01:15:36,224.974919 --> 01:15:45,164.974919 I could put another field that plays the role of Alice and Bob to measure my primordial field? The inflationary field very early on. 1373 01:15:45,164.974919 --> 01:15:50,564.974919 So there are, it's no longer one field Uhhuh, but another field that just serves as a detector. 1374 01:15:50,984.974919 --> 01:15:51,14.974919 Okay. 1375 01:15:51,14.974919 --> 01:15:52,334.974919 That's there to measure this field. 1376 01:15:53,294.974919 --> 01:15:53,354.974919 Ah. 1377 01:15:53,354.974919 --> 01:15:56,834.974919 And is there to measure it before the conjugate momentum got? Yes. 1378 01:15:56,834.974919 --> 01:15:58,709.974919 So when it's not that small mm-hmm. 1379 01:15:58,829.974919 --> 01:16:00,349.974919 I try to make a measurement uhhuh. 1380 01:16:00,494.974919 --> 01:16:10,64.974919 So that's, we're trying, uh, now with the Be Inequality podcast that you made, you said that it's local. 1381 01:16:10,634.974919 --> 01:16:17,54.974919 Um, everything is local about this, and one of the ingredients of constructing belt Inequ is that Alice must make a local measurement. 1382 01:16:17,564.974919 --> 01:16:19,334.974919 Bob must also make a local measurement. 1383 01:16:19,814.974919 --> 01:16:21,434.974919 Fields are delocalized objects. 1384 01:16:22,259.974919 --> 01:16:22,679.974919 Yeah. 1385 01:16:23,129.974919 --> 01:16:27,869.974919 Um, but you can decompose a field in terms of four year modes. 1386 01:16:28,319.974919 --> 01:16:45,899.974919 So what that means is, um, um, as you know from signal theory, like any signal, any wave form, if you have, uh, some wave, it can be decomposed into sign and cosine waves, the sum of, um, uh, sign and co-signs, which is the four year transform. 1387 01:16:45,899.974919 --> 01:16:52,529.974919 So what, uh, what signs and co-sign must I put in to create this? Complex waveform that I observed. 1388 01:16:52,859.974919 --> 01:16:54,119.974919 So you can do a four year transform. 1389 01:16:54,359.974919 --> 01:17:03,269.974919 The advantage of doing a four year transform in cosmology is you can describe each field by a collection of four year modes that evolve independently. 1390 01:17:04,649.974919 --> 01:17:05,9.974919 Okay. 1391 01:17:05,99.974919 --> 01:17:07,799.974919 So we have these two fields that we're interested in. 1392 01:17:07,919.974919 --> 01:17:08,219.974919 Yes. 1393 01:17:08,549.974919 --> 01:17:17,159.974919 And each and them we can describe by these, uh, compositions of waves that are evolving independently. 1394 01:17:17,429.974919 --> 01:17:17,969.974919 Exactly. 1395 01:17:18,179.974919 --> 01:17:19,709.974919 So, um. 1396 01:17:20,159.974919 --> 01:17:20,609.974919 Yes. 1397 01:17:20,669.974919 --> 01:17:25,469.974919 So let's say the inflationary field is a very complex pattern across space. 1398 01:17:25,469.974919 --> 01:17:30,929.974919 I mean, it's high in one place, it's low in another place, it's flat in another place. 1399 01:17:31,19.974919 --> 01:17:34,919.974919 Uhhuh, I can deconstruct all of that in terms of four year modes. 1400 01:17:34,979.974919 --> 01:17:39,479.974919 I can say that's just because you're adding up these signs and cosign in this way. 1401 01:17:40,169.974919 --> 01:17:43,319.974919 Um, and you get the desired pattern, whatever you want, Uhhuh. 1402 01:17:43,769.974919 --> 01:17:48,419.974919 But this is an interesting mathematical trick, which will help us when we construct our be inequality. 1403 01:17:48,419.974919 --> 01:17:48,479.974919 Um. 1404 01:17:50,414.974919 --> 01:17:55,454.974919 So as with, so the moment you enter into the territory of signs and co-signs, you need to talk about wavelengths. 1405 01:17:55,454.974919 --> 01:17:58,604.974919 Right? The sign and co-sign have periodicity. 1406 01:17:58,604.974919 --> 01:18:00,134.974919 Some signs are very long. 1407 01:18:00,674.974919 --> 01:18:02,894.974919 Uh, sometimes some signs are compressed. 1408 01:18:02,894.974919 --> 01:18:03,674.974919 They're very close. 1409 01:18:03,674.974919 --> 01:18:10,694.974919 So you, you need to have an infinitely large number of these to completely do the four year transform of a system. 1410 01:18:10,784.974919 --> 01:18:10,874.974919 Mm-hmm. 1411 01:18:11,174.974919 --> 01:18:16,304.974919 With sign and cosign being these waves that are kind of face shifted. 1412 01:18:16,859.974919 --> 01:18:17,459.974919 From each other. 1413 01:18:17,699.974919 --> 01:18:20,369.974919 And then we, ah, so let's just say signs. 1414 01:18:20,369.974919 --> 01:18:20,729.974919 Okay. 1415 01:18:20,729.974919 --> 01:18:21,749.974919 Let's stick to signs. 1416 01:18:21,749.974919 --> 01:18:23,489.974919 You can do four transformer just signs. 1417 01:18:23,549.974919 --> 01:18:23,759.974919 Yeah. 1418 01:18:23,789.974919 --> 01:18:24,779.974919 Forget the co signs. 1419 01:18:25,559.974919 --> 01:18:25,864.974919 They're not, yeah. 1420 01:18:25,864.974919 --> 01:18:29,159.974919 It's just waves of different wavelength that we're gonna add. 1421 01:18:29,159.974919 --> 01:18:29,849.974919 Adapt with each other. 1422 01:18:29,939.974919 --> 01:18:30,29.974919 Yes. 1423 01:18:30,34.974919 --> 01:18:30,64.974919 Yeah. 1424 01:18:30,69.974919 --> 01:18:30,209.974919 Yeah. 1425 01:18:30,209.974919 --> 01:18:33,839.974919 So they, it's, it's even better to think they have all the same phase. 1426 01:18:33,869.974919 --> 01:18:33,959.974919 Mm-hmm. 1427 01:18:34,199.974919 --> 01:18:35,519.974919 But just different coefficients. 1428 01:18:35,579.974919 --> 01:18:35,759.974919 Mm-hmm. 1429 01:18:36,89.974919 --> 01:18:36,329.974919 Yeah. 1430 01:18:36,329.974919 --> 01:18:37,619.974919 So different coefficient. 1431 01:18:37,769.974919 --> 01:18:38,489.974919 Mm-hmm. 1432 01:18:38,729.974919 --> 01:18:42,239.974919 And so how does this help us? Mm-hmm. 1433 01:18:42,479.974919 --> 01:18:45,119.974919 Well, the four year transform is not just a mathematical trick. 1434 01:18:45,719.974919 --> 01:18:48,779.974919 Um, these four year modes are just as real as the field itself. 1435 01:18:48,839.974919 --> 01:18:51,714.974919 They're both mathematical objects, so they stand on mm-hmm. 1436 01:18:51,799.974919 --> 01:18:52,619.974919 On the same level. 1437 01:18:53,189.974919 --> 01:18:59,549.974919 So, um, and the advantage of a four year transform is before I was restricted to talking about my inflationary field. 1438 01:18:59,549.974919 --> 01:19:05,849.974919 Like, is it large in that spot? Is it low in this spot? Is it flat in this spot? And no longer talk about spots. 1439 01:19:06,149.974919 --> 01:19:11,459.974919 I just say, uh, it's a combination of a wave that has this amplitude. 1440 01:19:11,519.974919 --> 01:19:18,899.974919 Um, maybe this amplitude and this, so you no longer describe it with, uh, in position space, but in momentum space. 1441 01:19:19,319.974919 --> 01:19:20,339.974919 Mm, yes. 1442 01:19:20,339.974919 --> 01:19:20,429.974919 Mm-hmm. 1443 01:19:20,669.974919 --> 01:19:22,799.974919 So that's the, you change the representation. 1444 01:19:23,69.974919 --> 01:19:29,459.974919 Now, why is that good for the universe, um, is because, um, now you have a notion of scale. 1445 01:19:30,629.974919 --> 01:19:33,659.974919 Um, a long wavelength of four year mode. 1446 01:19:33,749.974919 --> 01:19:37,79.974919 A long sine wave can be as long as the horizon itself. 1447 01:19:37,904.974919 --> 01:19:40,694.974919 A short sine wave can be very short. 1448 01:19:40,694.974919 --> 01:19:41,294.974919 Mm-hmm. 1449 01:19:41,479.974919 --> 01:19:46,64.974919 And, and this can get us one step closer to constructing a be inequality. 1450 01:19:46,394.974919 --> 01:19:50,774.974919 I can tell you that I want my bell measurements by the second field that we introduced. 1451 01:19:50,779.974919 --> 01:19:50,979.974919 Mm-hmm. 1452 01:19:51,194.974919 --> 01:19:52,574.974919 To be done in a local way. 1453 01:19:53,234.974919 --> 01:19:59,24.974919 And for that to be done in a local way, I need to use a short wavelength mode because a long wavelength mode would. 1454 01:19:59,294.974919 --> 01:20:00,404.974919 Would be too long. 1455 01:20:00,404.974919 --> 01:20:03,344.974919 It would connect things that are as large as the horizon itself. 1456 01:20:03,464.974919 --> 01:20:03,494.974919 Oh. 1457 01:20:03,824.974919 --> 01:20:05,954.974919 So I'd use a short wavelength four year mode. 1458 01:20:06,134.974919 --> 01:20:06,404.974919 Yeah. 1459 01:20:06,464.974919 --> 01:20:08,84.974919 To do my experiment uhhuh. 1460 01:20:08,234.974919 --> 01:20:16,64.974919 Um, and then because the long wavelength mode actually, uh, connects two different patches of space time. 1461 01:20:16,94.974919 --> 01:20:16,184.974919 Mm-hmm. 1462 01:20:16,424.974919 --> 01:20:18,584.974919 You can say, oh, that must be a very quantum thing. 1463 01:20:18,614.974919 --> 01:20:22,994.974919 It, it must be, um, it must be super quantum. 1464 01:20:23,444.974919 --> 01:20:24,524.974919 Uh, and I can measure that. 1465 01:20:25,394.974919 --> 01:20:28,874.974919 Um, but unfortunately again. 1466 01:20:29,594.974919 --> 01:20:33,944.974919 As with most things that make our theory beautiful, that very same thing is killing our theory. 1467 01:20:34,574.974919 --> 01:20:41,894.974919 Um, when inflation happens, the universe grows so dramatically fast. 1468 01:20:41,984.974919 --> 01:20:42,74.974919 Mm-hmm. 1469 01:20:42,344.974919 --> 01:20:45,824.974919 That, um, it's even faster than light. 1470 01:20:46,274.974919 --> 01:20:48,439.974919 So these four year modes that you saw mm-hmm. 1471 01:20:49,64.974919 --> 01:20:56,924.974919 And they're not able to keep up with the expansion of the universe, and so they, at some point they have to exit the universe. 1472 01:20:57,344.974919 --> 01:20:57,734.974919 Right. 1473 01:20:58,154.974919 --> 01:21:02,84.974919 Because the universe just gets so big that it kind of throws out the four year modes. 1474 01:21:02,924.974919 --> 01:21:11,984.974919 Um, so that means the long wavelength modes, which are the first to exit the universe, they get stretched so much that they eventually leave the universe. 1475 01:21:12,554.974919 --> 01:21:17,894.974919 Um, they are no longer quantum because they've left the universe. 1476 01:21:18,704.974919 --> 01:21:21,959.974919 What do you mean so long that they leave the universe? Okay. 1477 01:21:21,959.974919 --> 01:21:25,999.974919 Like is it that they really, I. 1478 01:21:26,324.974919 --> 01:21:31,364.974919 It's small, like, okay, let's try to understand it from the inverse perspective. 1479 01:21:31,664.974919 --> 01:21:33,704.974919 Let's say that nothing is happening to the mode. 1480 01:21:33,824.974919 --> 01:21:34,184.974919 Yeah. 1481 01:21:34,424.974919 --> 01:21:37,664.974919 Um, and actually it's the size of the horizon that's shrinking. 1482 01:21:38,144.974919 --> 01:21:38,354.974919 Okay. 1483 01:21:38,354.974919 --> 01:21:39,584.974919 What does that mean? Well. 1484 01:21:40,634.974919 --> 01:21:42,284.974919 My universe is expanding today. 1485 01:21:42,434.974919 --> 01:21:42,764.974919 Yeah. 1486 01:21:42,929.974919 --> 01:21:45,464.974919 And, and it's expanding faster than the speed of light. 1487 01:21:45,644.974919 --> 01:21:45,734.974919 Mm-hmm. 1488 01:21:45,974.974919 --> 01:21:49,904.974919 Which means a signal that I'm able to get today from the most distant star. 1489 01:21:49,909.974919 --> 01:21:50,109.974919 Mm-hmm. 1490 01:21:50,294.974919 --> 01:21:53,954.974919 I'm not going to see tomorrow because that star is now outside mm-hmm. 1491 01:21:54,194.974919 --> 01:21:55,94.974919 My causal horizon. 1492 01:21:55,184.974919 --> 01:21:55,514.974919 Mm-hmm. 1493 01:21:55,844.974919 --> 01:22:00,944.974919 Uh, the universe has expanded so much that it's thrown that star outside where light can reach me. 1494 01:22:01,124.974919 --> 01:22:01,484.974919 Yeah. 1495 01:22:01,664.974919 --> 01:22:08,624.974919 And so effectively what that means is what I can see has become smaller uhhuh, uh, so. 1496 01:22:09,569.974919 --> 01:22:12,809.974919 Uh, from in this converse perspective Yeah. 1497 01:22:12,809.974919 --> 01:22:17,519.974919 Uh, the core moving horizon, which is what I can see the size of my observable universe Yeah. 1498 01:22:17,519.974919 --> 01:22:18,149.974919 Is shrinking. 1499 01:22:19,79.974919 --> 01:22:19,409.974919 Okay. 1500 01:22:19,409.974919 --> 01:22:19,679.974919 Right. 1501 01:22:19,829.974919 --> 01:22:20,39.974919 Yeah. 1502 01:22:20,39.974919 --> 01:22:20,249.974919 Yes. 1503 01:22:20,309.974919 --> 01:22:21,779.974919 So now this is much simpler. 1504 01:22:21,809.974919 --> 01:22:23,489.974919 Let's say nothing happened to four year modes. 1505 01:22:23,489.974919 --> 01:22:23,549.974919 Yeah. 1506 01:22:23,549.974919 --> 01:22:24,539.974919 They're all stationary. 1507 01:22:24,539.974919 --> 01:22:26,249.974919 Where in the reference frame where, yeah. 1508 01:22:26,249.974919 --> 01:22:28,289.974919 The four year modes are just doing their thing. 1509 01:22:28,379.974919 --> 01:22:28,469.974919 Mm-hmm. 1510 01:22:28,709.974919 --> 01:22:33,479.974919 But actually, because pace time is expanding so dramatically, the core moving horizon is shrinking. 1511 01:22:33,484.974919 --> 01:22:33,614.974919 Mm-hmm. 1512 01:22:33,754.974919 --> 01:22:38,369.974919 So the long wavelength modes leave the horizon because the core moving horizon is shrinking. 1513 01:22:38,369.974919 --> 01:22:38,729.974919 I see. 1514 01:22:38,729.974919 --> 01:22:39,29.974919 Yeah. 1515 01:22:39,29.974919 --> 01:22:39,179.974919 Yes. 1516 01:22:39,444.974919 --> 01:22:39,804.974919 Yeah. 1517 01:22:39,924.974919 --> 01:22:44,94.974919 Um, and the short wavelength modes, they're there for as long as the horizon comes for them. 1518 01:22:44,634.974919 --> 01:22:44,814.974919 Horizon. 1519 01:22:46,854.974919 --> 01:22:50,814.974919 So the moment a mode leaves the horizon, it behaves differently. 1520 01:22:50,814.974919 --> 01:22:52,164.974919 There's new dynamics. 1521 01:22:52,284.974919 --> 01:22:52,494.974919 Mm-hmm. 1522 01:22:52,734.974919 --> 01:22:54,444.974919 But we call this classical. 1523 01:22:55,14.974919 --> 01:23:01,164.974919 The mode is going to leave the horizon and that's when the conjugate momentum gets suppressed. 1524 01:23:01,164.974919 --> 01:23:01,944.974919 Ah, yes. 1525 01:23:02,34.974919 --> 01:23:02,394.974919 Okay. 1526 01:23:02,754.974919 --> 01:23:03,84.974919 Yeah. 1527 01:23:03,534.974919 --> 01:23:05,844.974919 So this is a problem for be inequalities. 1528 01:23:05,879.974919 --> 01:23:09,299.974919 Um, I want to measure a quantum system. 1529 01:23:09,479.974919 --> 01:23:09,599.974919 Yeah. 1530 01:23:09,599.974919 --> 01:23:13,439.974919 I just told you that Alice and Bob want to measure two things that are separated. 1531 01:23:13,499.974919 --> 01:23:13,829.974919 Yeah. 1532 01:23:13,979.974919 --> 01:23:17,879.974919 Um, and at those lens scales, the four year mode that matters is the long wavelength. 1533 01:23:17,884.974919 --> 01:23:22,979.974919 The four year mode Uhhuh, and I told you to do this experiment locally, I'm going to use a short wavelength four year mode. 1534 01:23:23,159.974919 --> 01:23:23,249.974919 Mm-hmm. 1535 01:23:23,489.974919 --> 01:23:26,9.974919 But I've just told you, because inflation is happening. 1536 01:23:26,129.974919 --> 01:23:26,249.974919 Mm-hmm. 1537 01:23:26,329.974919 --> 01:23:28,979.974919 The long wavelength mode leaves the horizon first. 1538 01:23:28,984.974919 --> 01:23:29,124.974919 Mm-hmm. 1539 01:23:29,309.974919 --> 01:23:30,839.974919 The conjugate momentum decays. 1540 01:23:30,929.974919 --> 01:23:31,49.974919 Mm-hmm. 1541 01:23:31,294.974919 --> 01:23:33,689.974919 It's the first thing that is no longer. 1542 01:23:34,64.974919 --> 01:23:34,844.974919 Quantum, yeah. 1543 01:23:34,844.974919 --> 01:23:36,344.974919 Is the first thing that becomes classical. 1544 01:23:36,584.974919 --> 01:23:39,614.974919 So you are trying to measure your alleged quantum system. 1545 01:23:39,674.974919 --> 01:23:39,854.974919 Yeah. 1546 01:23:39,854.974919 --> 01:23:41,234.974919 With a more quantum system. 1547 01:23:41,384.974919 --> 01:23:41,894.974919 Yeah. 1548 01:23:42,254.974919 --> 01:23:43,304.974919 And that's the problem. 1549 01:23:44,564.974919 --> 01:23:45,794.974919 Ah, yeah. 1550 01:23:46,214.974919 --> 01:23:51,554.974919 So your apparatus is more quantum in the system, and this does not happen laboratory physics. 1551 01:23:51,554.974919 --> 01:23:51,614.974919 Ah. 1552 01:23:52,484.974919 --> 01:23:56,654.974919 So now models of bell inequalities and cosmology are very contrived. 1553 01:23:56,714.974919 --> 01:23:57,554.974919 They need to make. 1554 01:23:58,154.974919 --> 01:24:06,224.974919 Some allowances for the thing that you want to measure to be quantum and you need to contrive a very contrived field, of course. 1555 01:24:06,344.974919 --> 01:24:06,584.974919 Mm-hmm. 1556 01:24:06,824.974919 --> 01:24:11,114.974919 Uh, that is sufficiently local and classical and yeah. 1557 01:24:11,774.974919 --> 01:24:15,584.974919 At that point I think you're just not doing good theoretical physics anymore. 1558 01:24:15,584.974919 --> 01:24:18,494.974919 You're just coming up with, uh, wacky ideas. 1559 01:24:18,914.974919 --> 01:24:19,334.974919 Yeah. 1560 01:24:19,934.974919 --> 01:24:21,404.974919 Um, so that's where we're at. 1561 01:24:21,404.974919 --> 01:24:23,984.974919 We we're not able to do bell inequality with the universe. 1562 01:24:24,74.974919 --> 01:24:24,224.974919 Mm-hmm. 1563 01:24:24,464.974919 --> 01:24:27,224.974919 Um, because the fields are not quantum at late times. 1564 01:24:27,239.974919 --> 01:24:27,959.974919 Mm-hmm. 1565 01:24:28,199.974919 --> 01:24:34,439.974919 And also when you try to do it early on in the universe, the is more quantum than the system itself. 1566 01:24:34,919.974919 --> 01:24:36,509.974919 But that should not discourage us. 1567 01:24:36,899.974919 --> 01:24:38,9.974919 There are still ways. 1568 01:24:38,399.974919 --> 01:24:38,669.974919 Mm-hmm. 1569 01:24:38,909.974919 --> 01:24:41,489.974919 Uh, to try to do a quantum be inequality. 1570 01:24:41,879.974919 --> 01:24:52,319.974919 They rely on other things like temporal witnesses of entanglement, and that's a whole new topic to get into. 1571 01:24:52,469.974919 --> 01:24:52,619.974919 Yeah. 1572 01:24:52,799.974919 --> 01:24:53,129.974919 Cool. 1573 01:24:53,879.974919 --> 01:24:56,639.974919 And that's the research you're doing. 1574 01:24:57,44.974919 --> 01:24:58,754.974919 With Eduardo and Yes. 1575 01:24:58,754.974919 --> 01:25:02,924.974919 Yeah, with Eduardo, with, that's the kind of research I'm doing now. 1576 01:25:03,164.974919 --> 01:25:11,144.974919 How do we get past this hurdle where you can no longer do two spatially separated Alice and Bob's? Mm-hmm. 1577 01:25:11,774.974919 --> 01:25:19,124.974919 And because of all the reasons I told you, and you're stuck with maybe Alice at time, T one and Alice at another time, T two. 1578 01:25:19,589.974919 --> 01:25:20,759.974919 That's the best you can do. 1579 01:25:20,759.974919 --> 01:25:23,264.974919 Can I construct a better inequality from that? Mm-hmm. 1580 01:25:23,404.974919 --> 01:25:26,879.974919 And, and hopefully the answer is yes, it's an active area of research. 1581 01:25:27,29.974919 --> 01:25:27,119.974919 Mm-hmm. 1582 01:25:27,359.974919 --> 01:25:28,949.974919 There's not no conclusion to this question. 1583 01:25:29,39.974919 --> 01:25:29,399.974919 Yeah. 1584 01:25:29,459.974919 --> 01:25:30,419.974919 We'll see where it goes. 1585 01:25:30,659.974919 --> 01:25:31,79.974919 Cool. 1586 01:25:31,559.974919 --> 01:25:31,799.974919 Yeah. 1587 01:25:31,799.974919 --> 01:25:38,519.974919 So hopefully whenever you figure this out, we'll we'll hear from you and your collaborators on Yes. 1588 01:25:38,819.974919 --> 01:25:38,999.974919 Yeah. 1589 01:25:39,59.974919 --> 01:25:40,949.974919 How we can, uh, yeah. 1590 01:25:40,979.974919 --> 01:25:44,759.974919 Do equality tests in time for cosmology Yes. 1591 01:25:45,359.974919 --> 01:25:46,349.974919 To answer these questions. 1592 01:25:46,349.974919 --> 01:25:46,859.974919 Absolutely. 1593 01:25:46,859.974919 --> 01:25:48,209.974919 And this is very important. 1594 01:25:48,704.974919 --> 01:25:57,224.974919 Uh, because not only can it tell us whether the inflationary field, which is this hypothetical field is quantum, it could also tell us if gravity is quantum. 1595 01:25:57,794.974919 --> 01:26:02,24.974919 Because gravity couples to the inflationary field, gravity couples to any field. 1596 01:26:02,24.974919 --> 01:26:02,834.974919 Mm-hmm. 1597 01:26:02,835.974919 --> 01:26:08,264.974919 And gravity couples very dramatically to the inflationary field because it's modifying the structure of spacetime Yeah. 1598 01:26:08,354.974919 --> 01:26:09,644.974919 So if you prove. 1599 01:26:10,19.974919 --> 01:26:11,849.974919 That the inflationary field is quantum. 1600 01:26:12,29.974919 --> 01:26:12,329.974919 Yeah. 1601 01:26:12,389.974919 --> 01:26:26,130.974919 Some people actually say that gravity could be the inflaton It's just a very peculiar, uh, whatever it may be, if you manage to prove the infl on, is whatever it is that costs infl on being the mediating the field that causes all of this. 1602 01:26:26,224.974919 --> 01:26:26,819.974919 Of this. 1603 01:26:26,909.974919 --> 01:26:27,179.974919 Yeah. 1604 01:26:27,239.974919 --> 01:26:28,499.974919 All of this is just. 1605 01:26:29,294.974919 --> 01:26:29,444.974919 Could. 1606 01:26:29,444.974919 --> 01:26:29,744.974919 Yeah. 1607 01:26:30,224.974919 --> 01:26:30,464.974919 Yeah. 1608 01:26:30,584.974919 --> 01:26:34,994.974919 So the infl on is the thing that composes the inflationary field? Yes. 1609 01:26:35,24.974919 --> 01:26:35,294.974919 Yeah. 1610 01:26:35,299.974919 --> 01:26:35,679.974919 Mm-hmm. 1611 01:26:35,764.974919 --> 01:26:42,404.974919 So, like we see, say, the Electrodynamic field, we have the inflationary field, which is, which is called the infl on, it's like a pet name for the field. 1612 01:26:42,404.974919 --> 01:26:42,614.974919 Yeah. 1613 01:26:43,274.974919 --> 01:26:46,94.974919 Like instead of a photon, it's the infl on. 1614 01:26:46,94.974919 --> 01:26:46,95.974919 Yes. 1615 01:26:46,100.974919 --> 01:26:46,679.974919 You have infl. 1616 01:26:46,829.974919 --> 01:26:47,119.974919 Yeah. 1617 01:26:47,324.974919 --> 01:26:47,714.974919 Yes. 1618 01:26:47,714.974919 --> 01:26:47,894.974919 Yeah. 1619 01:26:47,894.974919 --> 01:26:48,914.974919 You can think of it like that. 1620 01:26:49,4.974919 --> 01:26:49,34.974919 Uhhuh. 1621 01:26:49,34.974919 --> 01:26:49,154.974919 Yeah. 1622 01:26:50,504.974919 --> 01:26:50,804.974919 Yeah. 1623 01:26:50,864.974919 --> 01:26:54,44.974919 Um, this infl gravity mm-hmm. 1624 01:26:54,554.974919 --> 01:26:55,934.974919 Are coupled. 1625 01:26:56,159.974919 --> 01:27:06,444.974919 And you say something quantum about the inlet on, chances are you're also saying something quantum about gravity, which is yet another test except for the signature of quantum gravity. 1626 01:27:06,444.974919 --> 01:27:06,804.974919 Mm-hmm. 1627 01:27:07,194.974919 --> 01:27:08,324.974919 Yeah, that would be really cool. 1628 01:27:08,544.974919 --> 01:27:09,764.974919 Uh, it would, it would. 1629 01:27:09,864.974919 --> 01:27:14,909.974919 And, and as you know, gravity is a spin to field. 1630 01:27:15,299.974919 --> 01:27:21,719.974919 What does that mean? Um, your photon can exist in a state up or down. 1631 01:27:22,24.974919 --> 01:27:22,304.974919 Mm-hmm. 1632 01:27:22,559.974919 --> 01:27:25,289.974919 And your electron can exist in a state up or down. 1633 01:27:25,289.974919 --> 01:27:26,849.974919 So it has two degrees of freedom. 1634 01:27:27,89.974919 --> 01:27:27,179.974919 Mm-hmm. 1635 01:27:27,449.974919 --> 01:27:32,639.974919 And the gravitational field will have way more degrees of freedom because it has higher spin. 1636 01:27:33,389.974919 --> 01:27:35,309.974919 Um, and it's a massless field. 1637 01:27:35,309.974919 --> 01:27:40,949.974919 So we'll come to some other conclusion, but it definitely has more than two um, states. 1638 01:27:41,244.974919 --> 01:27:41,664.974919 Mm-hmm. 1639 01:27:42,539.974919 --> 01:27:45,359.974919 So by virtue of it being spin two. 1640 01:27:46,4.974919 --> 01:27:52,64.974919 Not only does it source a potential like your electromagnetic field, you can source an electric potential with a charge. 1641 01:27:52,424.974919 --> 01:27:55,334.974919 But if you start jiggling that charge, it creates a magnetic field. 1642 01:27:55,399.974919 --> 01:27:55,819.974919 Mm-hmm. 1643 01:27:55,934.974919 --> 01:28:03,584.974919 Which is a consequence of the electromagnetic field means uh uh uh, yeah. 1644 01:28:03,704.974919 --> 01:28:06,104.974919 Having two non-com commuting observers. 1645 01:28:06,224.974919 --> 01:28:15,284.974919 The ENB gravity has scalers, which is something like the electric field vectors, which is like the magnetic field and tensors. 1646 01:28:15,614.974919 --> 01:28:17,564.974919 Which give rise to gravitational waves. 1647 01:28:17,564.974919 --> 01:28:18,344.974919 Mm-hmm. 1648 01:28:18,434.974919 --> 01:28:22,544.974919 Gravitational waves we've observed already on earth from black holes merging. 1649 01:28:22,844.974919 --> 01:28:22,934.974919 Mm-hmm. 1650 01:28:23,174.974919 --> 01:28:27,44.974919 And we've seen them, but primordial gravitational waves. 1651 01:28:27,44.974919 --> 01:28:34,814.974919 Gravitational waves that are created from fluctuations and due to the gravitational sector in inflation. 1652 01:28:34,819.974919 --> 01:28:34,909.974919 Mm-hmm. 1653 01:28:35,29.974919 --> 01:28:35,984.974919 We have not seen yet. 1654 01:28:36,494.974919 --> 01:28:36,704.974919 Right. 1655 01:28:36,704.974919 --> 01:28:38,174.974919 And we are sending more telescopes. 1656 01:28:38,234.974919 --> 01:28:38,504.974919 Yeah. 1657 01:28:38,804.974919 --> 01:28:39,374.974919 To look for this. 1658 01:28:39,374.974919 --> 01:28:43,269.974919 In fact, in 2014 somebody had claimed that they solved this, but unfortunately, mm. 1659 01:28:43,679.974919 --> 01:28:45,389.974919 It was instrumental error. 1660 01:28:45,389.974919 --> 01:28:50,9.974919 It was some dust in the galaxy that could have been a landmark day for physics. 1661 01:28:50,99.974919 --> 01:28:50,489.974919 Yeah. 1662 01:28:51,329.974919 --> 01:28:54,179.974919 And that would tell us that there's quantum ness. 1663 01:28:54,329.974919 --> 01:28:56,69.974919 Uh, it would get us one step closer. 1664 01:28:56,159.974919 --> 01:28:58,979.974919 It wouldn't conclusively prove that gravity is quantum. 1665 01:28:59,339.974919 --> 01:29:04,379.974919 But with all of these things together, it becomes more and more difficult to refute that gravity is quantum. 1666 01:29:04,379.974919 --> 01:29:05,9.974919 Right? Yeah. 1667 01:29:05,129.974919 --> 01:29:07,109.974919 So it's kind of another piece to the Yes. 1668 01:29:07,289.974919 --> 01:29:07,919.974919 Kind of. 1669 01:29:08,909.974919 --> 01:29:14,489.974919 Implication that gravity should be quantum to explain everything that we're seeing Exactly. 1670 01:29:14,489.974919 --> 01:29:16,829.974919 And hopefully this will give us a new clue. 1671 01:29:16,979.974919 --> 01:29:17,69.974919 Mm-hmm. 1672 01:29:17,309.974919 --> 01:29:18,809.974919 Which can be the definitive proof. 1673 01:29:18,959.974919 --> 01:29:19,229.974919 Yeah. 1674 01:29:19,229.974919 --> 01:29:29,624.974919 A very simple example in the electromagnetic field, it's how do we know the electromagnetic field is quantum? Is, do you Well, um, tell me. 1675 01:29:30,254.974919 --> 01:29:36,209.974919 No, we, we've, like in from high school, we were told the photo electric effect uhhuh. 1676 01:29:36,404.974919 --> 01:29:38,954.974919 That's why the photon is quantum because you know Yeah. 1677 01:29:39,14.974919 --> 01:29:42,824.974919 High school quantum mechanics, high school quantum mechanic, H Stones, Nobel Prize. 1678 01:29:42,884.974919 --> 01:29:43,154.974919 Yeah. 1679 01:29:43,154.974919 --> 01:29:44,54.974919 High Nobel Prize. 1680 01:29:44,54.974919 --> 01:29:44,204.974919 Yeah. 1681 01:29:44,204.974919 --> 01:29:46,4.974919 He got for the photoelectric effect. 1682 01:29:46,9.974919 --> 01:29:46,249.974919 Mm-hmm. 1683 01:29:46,394.974919 --> 01:29:51,524.974919 But that was not, still not enough evidence to convince people that the electromagnetic field is quantum. 1684 01:29:52,234.974919 --> 01:29:54,394.974919 Um, so they went a step further. 1685 01:29:54,394.974919 --> 01:29:57,394.974919 They said, okay, maybe I can put these things in a super position. 1686 01:29:57,574.974919 --> 01:29:57,814.974919 Mm-hmm. 1687 01:29:58,54.974919 --> 01:30:00,244.974919 And you can put photons in a super position. 1688 01:30:00,244.974919 --> 01:30:00,664.974919 Great. 1689 01:30:00,994.974919 --> 01:30:02,674.974919 Still not quantum. 1690 01:30:03,184.974919 --> 01:30:07,504.974919 Um, but, uh, something like the lamb shift, which is. 1691 01:30:08,819.974919 --> 01:30:11,879.974919 Um, which is a property of the energy levels of the hydrogen atom. 1692 01:30:11,879.974919 --> 01:30:14,699.974919 They're not, we've calculated them to be something. 1693 01:30:14,699.974919 --> 01:30:15,389.974919 Mm-hmm. 1694 01:30:15,390.974919 --> 01:30:17,524.974919 Uh, they're not that something, they're slightly different. 1695 01:30:17,524.974919 --> 01:30:17,804.974919 Mm-hmm. 1696 01:30:17,884.974919 --> 01:30:22,409.974919 They're slightly shifted, and that shift can only be explained by the fact that. 1697 01:30:23,204.974919 --> 01:30:27,134.974919 The electromagnetic field is quantum and it is generating these particles mm-hmm. 1698 01:30:27,374.974919 --> 01:30:28,739.974919 Virtual particles that I told you about. 1699 01:30:28,739.974919 --> 01:30:29,99.974919 Mm-hmm. 1700 01:30:29,294.974919 --> 01:30:34,934.974919 The electromagnetic field was gen, which contribute to how the, the spectrum of the hydrogen atom looks uhhuh. 1701 01:30:35,264.974919 --> 01:30:39,344.974919 Um, so that was the nail in the coffin, right? For Yeah. 1702 01:30:39,554.974919 --> 01:30:41,564.974919 Um, to say that, yes. 1703 01:30:41,624.974919 --> 01:30:41,834.974919 Yeah. 1704 01:30:41,834.974919 --> 01:30:44,324.974919 I finally believe the electromagnetic field is quantum. 1705 01:30:44,444.974919 --> 01:30:44,534.974919 Mm-hmm. 1706 01:30:45,14.974919 --> 01:30:47,84.974919 Um, not bell inequalities. 1707 01:30:47,114.974919 --> 01:30:48,584.974919 You can do bell equality with. 1708 01:30:49,19.974919 --> 01:30:54,419.974919 Uh, the electromagnetic field as well, but this is what it took for people to say, yes, the electromagnetic field is quantum. 1709 01:30:54,539.974919 --> 01:30:54,749.974919 Yeah. 1710 01:30:54,779.974919 --> 01:30:56,459.974919 We will need something like that for gravity. 1711 01:30:56,459.974919 --> 01:30:56,549.974919 Right. 1712 01:30:56,549.974919 --> 01:30:57,869.974919 And it's gonna take a long time. 1713 01:30:58,64.974919 --> 01:30:58,304.974919 Yeah. 1714 01:30:59,219.974919 --> 01:30:59,579.974919 Yeah. 1715 01:30:59,759.974919 --> 01:31:01,619.974919 But we can do these kind of steps. 1716 01:31:01,679.974919 --> 01:31:01,889.974919 Yes. 1717 01:31:01,889.974919 --> 01:31:01,890.974919 Yeah. 1718 01:31:02,214.974919 --> 01:31:03,504.974919 Towards, yeah. 1719 01:31:03,509.974919 --> 01:31:03,989.974919 Yeah. 1720 01:31:04,499.974919 --> 01:31:05,819.974919 Pieces of quantum ness. 1721 01:31:05,849.974919 --> 01:31:06,209.974919 Yeah. 1722 01:31:06,299.974919 --> 01:31:09,89.974919 Or signatures of, but yeah. 1723 01:31:09,149.974919 --> 01:31:10,829.974919 Yes, we are taking those steps. 1724 01:31:11,414.974919 --> 01:31:14,354.974919 For gravity, but from an information theoretical perspective. 1725 01:31:14,594.974919 --> 01:31:14,684.974919 Mm-hmm. 1726 01:31:14,984.974919 --> 01:31:19,634.974919 And because now gravity is just proven immune to one of the tests Yeah. 1727 01:31:19,634.974919 --> 01:31:23,924.974919 That we now have to resort to clever and clever ways to test the quantum properties of gravity. 1728 01:31:23,954.974919 --> 01:31:24,254.974919 Yeah. 1729 01:31:24,314.974919 --> 01:31:27,14.974919 And the fundamental problem is gravity and tracks with everything. 1730 01:31:27,74.974919 --> 01:31:29,744.974919 So it's very difficult to separate gravity from everything else. 1731 01:31:30,194.974919 --> 01:31:33,434.974919 And gravity is also the very fabric of the space time we sit on. 1732 01:31:33,734.974919 --> 01:31:35,864.974919 So it responds to anything we do. 1733 01:31:36,239.974919 --> 01:31:41,129.974919 And when an experiment responds to the thing that you're trying to do to it, it's no longer an experiment. 1734 01:31:41,129.974919 --> 01:31:41,999.974919 There's a feedback. 1735 01:31:42,179.974919 --> 01:31:42,689.974919 Yeah. 1736 01:31:42,779.974919 --> 01:31:43,859.974919 So that's the hard part. 1737 01:31:44,69.974919 --> 01:31:44,609.974919 Yeah. 1738 01:31:44,609.974919 --> 01:31:44,669.974919 Yeah. 1739 01:31:46,79.974919 --> 01:31:46,499.974919 Cool. 1740 01:31:46,889.974919 --> 01:31:50,729.974919 Yeah, so we've really, um, it's quite cool how we've gone from the. 1741 01:31:51,434.974919 --> 01:31:53,264.974919 Um, yeah. 1742 01:31:53,294.974919 --> 01:31:56,279.974919 Kind of like you said before these very classical questions, but like mm-hmm. 1743 01:31:57,464.974919 --> 01:32:09,319.974919 What, what happened in the early universe and then we end up having to go into quantum theory and then we've actually ended up in this quantum information setting of thinking about inequalities and entanglement and this very, yeah. 1744 01:32:09,524.974919 --> 01:32:09,854.974919 Yeah. 1745 01:32:09,884.974919 --> 01:32:14,24.974919 Quantum information ideas have now become, uh. 1746 01:32:14,84.974919 --> 01:32:19,334.974919 Uh, significant for thinking about trying to solve these, these puzzles. 1747 01:32:19,364.974919 --> 01:32:19,844.974919 Exactly. 1748 01:32:19,844.974919 --> 01:32:20,984.974919 A hundred year old puzzle mm-hmm. 1749 01:32:21,224.974919 --> 01:32:26,114.974919 That has seen many, many interpretations over the last several decades that I've not been alive for. 1750 01:32:26,354.974919 --> 01:32:26,594.974919 Mm-hmm. 1751 01:32:26,834.974919 --> 01:32:32,84.974919 But this problem has been exploding, a variety of flavors, and we finally turned to quantum information for some answers. 1752 01:32:32,324.974919 --> 01:32:32,624.974919 Yeah. 1753 01:32:32,804.974919 --> 01:32:33,104.974919 Cool. 1754 01:32:33,104.974919 --> 01:32:37,409.974919 Well, hopefully it leads us to interesting directions, especially as. 1755 01:32:38,99.974919 --> 01:32:40,349.974919 So relatively recent field. 1756 01:32:40,409.974919 --> 01:32:40,739.974919 Yes. 1757 01:32:40,829.974919 --> 01:32:42,29.974919 So yeah. 1758 01:32:42,29.974919 --> 01:32:43,169.974919 It feels Yeah. 1759 01:32:43,199.974919 --> 01:32:44,249.974919 Intuitively like this. 1760 01:32:44,939.974919 --> 01:32:47,609.974919 Hopefully there's lots of interesting things for Yeah. 1761 01:32:47,969.974919 --> 01:32:51,689.974919 Uh, for you and us and everyone else to, to figure out. 1762 01:32:51,989.974919 --> 01:32:52,619.974919 Absolutely. 1763 01:32:52,769.974919 --> 01:32:53,219.974919 Yeah. 1764 01:32:53,849.974919 --> 01:32:54,239.974919 Yeah. 1765 01:32:54,299.974919 --> 01:33:00,89.974919 So yeah, I can try and do a, a summary of mm-hmm. 1766 01:33:00,389.974919 --> 01:33:03,184.974919 Where we've gone this, the excursion you've taken. 1767 01:33:03,614.974919 --> 01:33:03,904.974919 Yeah. 1768 01:33:03,929.974919 --> 01:33:06,629.974919 The excursion, um, this, uh. 1769 01:33:07,154.974919 --> 01:33:07,574.974919 Yeah. 1770 01:33:07,604.974919 --> 01:33:09,974.974919 Cosmological travels. 1771 01:33:11,24.974919 --> 01:33:22,484.974919 So we, we started talking about, um, yeah, I guess overarching theme has been we have this problem of, we have these very good theories, general relativity, quantum mechanics. 1772 01:33:22,514.974919 --> 01:33:22,604.974919 Mm-hmm. 1773 01:33:22,964.974919 --> 01:33:27,674.974919 Um, quantum mechanics describes matter as being quantum general. 1774 01:33:27,674.974919 --> 01:33:32,354.974919 Relativity describes gravity in the fabric of space time. 1775 01:33:32,359.974919 --> 01:33:32,549.974919 Mm-hmm. 1776 01:33:32,769.974919 --> 01:33:34,304.974919 But we have this, uh. 1777 01:33:34,379.974919 --> 01:33:40,769.974919 Uh, difficulty of, uh, it feels like gravity should be quantum. 1778 01:33:40,769.974919 --> 01:33:40,859.974919 Mm-hmm. 1779 01:33:40,859.974919 --> 01:33:47,879.974919 And then we have these situations where we want to think about both of these theories and we run into problems. 1780 01:33:48,209.974919 --> 01:33:48,689.974919 Mm-hmm. 1781 01:33:48,689.974919 --> 01:33:48,690.974919 Yeah. 1782 01:33:48,695.974919 --> 01:33:53,399.974919 And so that's huge open problem in, in physics mm-hmm. 1783 01:33:53,429.974919 --> 01:33:54,719.974919 In foundations of physics. 1784 01:33:55,199.974919 --> 01:34:03,149.974919 Um, and then we talked about in the very early universe, you have really high energies and very compressed. 1785 01:34:03,779.974919 --> 01:34:05,639.974919 Um, universe. 1786 01:34:05,639.974919 --> 01:34:09,299.974919 So quantum mechanics becomes significant in these regimes. 1787 01:34:09,329.974919 --> 01:34:09,419.974919 Mm-hmm. 1788 01:34:10,49.974919 --> 01:34:14,789.974919 And then we have these big bank puzzles that you mentioned. 1789 01:34:14,789.974919 --> 01:34:15,929.974919 We have the flatness problem. 1790 01:34:15,929.974919 --> 01:34:19,949.974919 How did the universe end up So specially flat at the beginning. 1791 01:34:19,979.974919 --> 01:34:20,69.974919 Mm-hmm. 1792 01:34:20,429.974919 --> 01:34:31,319.974919 Um, and also this issue with the causal connections of how did, when we look at different regions of the sky, they have these correlated fluctuations and mm-hmm. 1793 01:34:31,739.974919 --> 01:34:37,949.974919 Uh, according to a standard expansion, there wouldn't have been a way for them to be causally connected. 1794 01:34:37,949.974919 --> 01:34:48,584.974919 And then you have to introduce this, uh, inflationary feel at the very early universe, this super fast, the light expansion mm-hmm. 1795 01:34:48,839.974919 --> 01:34:50,579.974919 To explain how they could be causally connected. 1796 01:34:50,584.974919 --> 01:34:50,624.974919 Mm-hmm. 1797 01:34:51,59.974919 --> 01:34:57,689.974919 And it actually, not only that, it needs to be quantum to explain these correlated fluctuations. 1798 01:34:57,694.974919 --> 01:34:57,784.974919 Mm-hmm. 1799 01:34:58,124.974919 --> 01:34:58,344.974919 Um. 1800 01:35:00,164.974919 --> 01:35:01,694.974919 In these regions. 1801 01:35:01,754.974919 --> 01:35:01,844.974919 Mm-hmm. 1802 01:35:03,74.974919 --> 01:35:15,374.974919 And then we want to look for some ways to, so this is a kind of theory, a model approximation to, um, to what could be happening in the early universe. 1803 01:35:15,374.974919 --> 01:35:25,784.974919 So we wanna be able to do experiments that tell us something about these, this inflationary field, and if it's actually quantum and if gravity is quantum. 1804 01:35:25,784.974919 --> 01:35:25,844.974919 Yeah. 1805 01:35:27,104.974919 --> 01:35:46,544.974919 And then you mentioned these experiments that you've been looking at in your research, some of these kind of tabletop ideas of having these macroscopic quantum systems based on Einstein condensate that are so, um, macroscopic that gravity is actually playing a significant role. 1806 01:35:47,129.974919 --> 01:35:47,549.974919 Mm-hmm. 1807 01:35:47,555.974919 --> 01:35:50,714.974919 And then you can look at the role of gravity. 1808 01:35:50,834.974919 --> 01:35:54,704.974919 Um, you can look at the predictions of gravity being quantum and not quantum. 1809 01:35:54,704.974919 --> 01:35:55,4.974919 Mm-hmm. 1810 01:35:55,409.974919 --> 01:35:58,199.974919 To what they do to these Yes. 1811 01:35:58,199.974919 --> 01:35:59,69.974919 Quantum states. 1812 01:35:59,639.974919 --> 01:36:10,439.974919 Um, and then you have this maybe more, uh, dramatic idea of doing better in equality tests with the early universe. 1813 01:36:10,529.974919 --> 01:36:10,679.974919 Yes. 1814 01:36:11,39.974919 --> 01:36:17,489.974919 Where you, um, want to be able to, yeah. 1815 01:36:17,669.974919 --> 01:36:20,459.974919 Look at this Heisenberg Uncertainty principle property. 1816 01:36:20,519.974919 --> 01:36:20,609.974919 Mm-hmm. 1817 01:36:21,119.974919 --> 01:36:24,59.974919 Um, you kind of wanna find a signature that that's. 1818 01:36:25,664.974919 --> 01:36:29,69.974919 That the inflationary field has this Yes. 1819 01:36:29,289.974919 --> 01:36:30,434.974919 Un uncertainty principle. 1820 01:36:30,884.974919 --> 01:36:41,234.974919 And so you want to do this be inequality test, which if we get this statistical violation, it tells us that the field that you did it with has these properties. 1821 01:36:41,264.974919 --> 01:36:41,414.974919 Mm-hmm. 1822 01:36:41,654.974919 --> 01:36:42,884.974919 This uncertainty principle. 1823 01:36:43,244.974919 --> 01:36:50,714.974919 Um, but you explained that the standard way of trying to do such a test has various challenges. 1824 01:36:50,714.974919 --> 01:36:50,804.974919 Mm-hmm. 1825 01:36:51,74.974919 --> 01:36:52,274.974919 Because one of these. 1826 01:36:52,664.974919 --> 01:36:59,504.974919 Properties, the two uncertainty principal properties we wanna measure, one of them becomes really weak today. 1827 01:36:59,804.974919 --> 01:37:00,14.974919 Yes. 1828 01:37:00,14.974919 --> 01:37:08,384.974919 So then you wanna try and use this field from the past as a detector for where this property was stronger. 1829 01:37:08,444.974919 --> 01:37:08,564.974919 Mm-hmm. 1830 01:37:08,834.974919 --> 01:37:14,204.974919 But then there's issues with, uh, yeah. 1831 01:37:14,209.974919 --> 01:37:16,184.974919 Trying to detect the quantum ness Yes. 1832 01:37:16,424.974919 --> 01:37:16,994.974919 Of that. 1833 01:37:16,994.974919 --> 01:37:17,384.974919 And then. 1834 01:37:17,924.974919 --> 01:37:21,524.974919 Now you are thinking about further modifications of this proposal. 1835 01:37:21,524.974919 --> 01:37:21,614.974919 Yes. 1836 01:37:21,974.974919 --> 01:37:23,744.974919 Undeterred by these challenges. 1837 01:37:23,744.974919 --> 01:37:24,44.974919 Yes. 1838 01:37:24,194.974919 --> 01:37:27,374.974919 Thinking about doing entanglement across time. 1839 01:37:27,494.974919 --> 01:37:27,794.974919 Yeah. 1840 01:37:27,884.974919 --> 01:37:30,314.974919 Um, which Yeah. 1841 01:37:30,344.974919 --> 01:37:33,764.974919 Remains to be seen if, uh, can get some Yeah. 1842 01:37:33,764.974919 --> 01:37:34,934.974919 Nice experiments out of that. 1843 01:37:34,964.974919 --> 01:37:35,534.974919 Absolutely. 1844 01:37:35,534.974919 --> 01:37:35,714.974919 Yeah. 1845 01:37:35,714.974919 --> 01:37:43,424.974919 And I'm sure, um, if this is not it, there are other tools in quantum information theory and other avenues that will surely get us closer to quantum gravity. 1846 01:37:43,429.974919 --> 01:37:43,749.974919 Mm-hmm. 1847 01:37:43,939.974919 --> 01:37:44,229.974919 Yeah. 1848 01:37:44,579.974919 --> 01:37:44,869.974919 Yeah. 1849 01:37:45,159.974919 --> 01:37:45,509.974919 Great. 1850 01:37:46,79.974919 --> 01:37:47,39.974919 Okay, great. 1851 01:37:47,39.974919 --> 01:37:49,319.974919 So yeah, I think we've covered a lot. 1852 01:37:49,319.974919 --> 01:37:49,379.974919 Yeah. 1853 01:37:49,469.974919 --> 01:37:51,689.974919 And, uh, yeah, it's really interesting. 1854 01:37:51,749.974919 --> 01:37:54,299.974919 So thanks for, for explaining all of that. 1855 01:37:54,329.974919 --> 01:37:58,494.974919 Thank you for having me and indulging, uh, and thank you viewers for indulging me. 1856 01:37:58,494.974919 --> 01:37:59,99.974919 Yeah, thank you. 1857 01:37:59,99.974919 --> 01:38:02,459.974919 Yeah, so let us know if you have any, any comments. 1858 01:38:02,519.974919 --> 01:38:14,729.974919 Um, or if anything, did it make sense or if we accidentally use too much jargon or any feedback at all, put it in the comments and we'll take a look and, uh. 1859 01:38:15,719.974919 --> 01:38:16,79.974919 Yeah. 1860 01:38:16,79.974919 --> 01:38:38,69.974919 Is there anything you'd like to leave the viewers with? Any final comments on? Anything? Yeah, I think, uh, we've, we've been hearing that science is getting more complicated and that some parts of science have, are completely saturated. 1861 01:38:38,69.974919 --> 01:38:39,809.974919 Like no more progress can be made there. 1862 01:38:40,199.974919 --> 01:38:41,669.974919 I think both these views are wrong. 1863 01:38:42,179.974919 --> 01:38:44,789.974919 Um, it's important to have interdisciplinary. 1864 01:38:45,494.974919 --> 01:38:46,934.974919 And collaboration in science. 1865 01:38:46,934.974919 --> 01:38:49,304.974919 And that's what we're doing with Quantum information Theory and Gravity. 1866 01:38:49,304.974919 --> 01:38:53,924.974919 Two disciplines that kind of evolve separately and are now starting to converge. 1867 01:38:54,344.974919 --> 01:39:00,884.974919 And the other thing to say, uh, we've built the largest particle accelerators, how much further can we go? Uh, no. 1868 01:39:00,884.974919 --> 01:39:04,364.974919 We will find complementary avenues to do better and better science. 1869 01:39:04,364.974919 --> 01:39:10,4.974919 So there will always be problems to solve and there will always be more and more interesting solutions because the easy problems. 1870 01:39:10,514.974919 --> 01:39:14,204.974919 Are solved and now we have the more interesting problems that need to be solved. 1871 01:39:14,684.974919 --> 01:39:14,924.974919 Mm-hmm. 1872 01:39:15,584.974919 --> 01:39:16,544.974919 Yeah, I like that. 1873 01:39:16,544.974919 --> 01:39:19,124.974919 We'll keep, keep solving more and more interesting problems. 1874 01:39:19,124.974919 --> 01:39:19,424.974919 Yeah. 1875 01:39:19,604.974919 --> 01:39:26,504.974919 And we need to keep innovating new approaches to help us make this progress. 1876 01:39:26,564.974919 --> 01:39:27,134.974919 Absolutely. 1877 01:39:27,194.974919 --> 01:39:27,434.974919 Yeah. 1878 01:39:27,439.974919 --> 01:39:27,559.974919 Mm-hmm. 1879 01:39:27,644.974919 --> 01:39:28,454.974919 I completely agree. 1880 01:39:29,894.974919 --> 01:39:29,954.974919 Yeah. 1881 01:39:29,954.974919 --> 01:39:30,344.974919 Great. 1882 01:39:30,944.974919 --> 01:39:37,994.974919 Well thanks for joining us today and do join us for the next part, which will be more. 1883 01:39:39,104.974919 --> 01:39:47,264.974919 Mathematical exploration of some of these ideas for people that have some introductory background in quantum mechanics. 1884 01:39:48,164.974919 --> 01:39:51,764.974919 And yeah, we will see you next time. 1885 01:39:52,994.974919 --> 01:39:53,599.974919 Bye bye. 1886 01:39:55,694.974919 --> 01:39:56,384.974919 Excellent. 1887 01:39:56,444.974919 --> 01:39:56,864.974919 Done. 1888 01:39:59,61.7039892 --> 01:40:01,851.7039892 The spin degree of freedom or whatever it is that violated the. 1889 01:40:08,181.7039892 --> 01:40:14,416.7039892 This is the spin degree of Maybe this is not the most stable, uh, setup. 1890 01:40:14,806.7039892 --> 01:40:19,191.7039892 It's like everything's becoming chaotic, like with the rain pouring outside. 1891 01:40:20,381.7039892 --> 01:40:21,931.7039892 We're talking about the chaotic universe. 1892 01:40:21,931.7039892 --> 01:40:23,651.7039892 It's only expected, right? Yeah. 1893 01:40:28,366.4811733 --> 01:40:28,996.4811733 Bloopers. 1894 01:40:29,386.4811733 --> 01:40:30,46.4811733 Bloopers. 1895 01:40:30,136.4811733 --> 01:40:30,496.4811733 Yeah. 1896 01:40:30,951.4811733 --> 01:40:31,371.4811733 Mm-hmm. 1897 01:40:32,476.4811733 --> 01:40:35,386.4811733 Okay, so let's get ready. 1898 01:40:36,46.4811733 --> 01:40:36,256.4811733 Okay.