February 20, 2020 • 48 mins
Daniel and Jorge discuss loop quantum gravity with a special appearance from Bianca Dittrich, a PhD in gravitational physics and an expert in loop quantum gravity and spin foam.
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Speaker 1 (00:08):
Hey, Daniel, do you think physics is in a rut?
A rut like we've been solving deep problems and delivering
amazing technology for too long. You're getting tired of it? Yeah,
I mean it's getting a little repetitive, all these discoveries. No, No,
I mean, like, is it on the right track? You know?
Do you think it will it get to the final
deep questions about the universe? I don't know. Sometimes I
(00:30):
wonder if we need like a revolution in physics. Does
physics need to be disrupted? Somebody out there should start
uber for physics. I'm more of a lift person, to
be honest, I think they have a better outlook in
the world. But yes, that's what I mean. You know,
I want to be able to call a physicist anytime
in my with my phone. Um, well you already have that.
(00:51):
That's this podcast. Nice, I'll give you four stars. Daniel here.
(01:12):
Hi am Rhema cartoonist and the creator of PhD comics. Hi.
I'm Daniel Whitson. I'm a particle physicist, and I'm here
to answer any question of physics on your app anytime.
Welcome to our podcast. Daniel and Jorge invent new physics apps.
For people who need physics on demand. Daniel and Jorge
make up terrible business ideas and pretending they're awesome. Now
(01:35):
it's Daniel and Jorge Explained the Universe, a production of
Our Heart Radio, in which we talk about all the
things amazing and beautiful but crazy and bonkers about our
universe because the more we learn, the more it makes sense,
the more it seems surprising and amazing. You know, within
we joke about it. But I think it would be
kind of a useful app. Don't you think, like anytime
anyone has a question about anything, you could just request
(01:58):
a physicist on your phone own and the nearest or
the most available physicists would answer and then answer your question.
Do you think that would be used a lot? Like
what kind of questions would people ask? How do we
reconcile the different theories about quantum physics? Sure? I think
it's more prosaic. It's like can I build a force
field to keep my teenager in his bedroom all night long? Also?
(02:22):
How does my toaster work? Why doesn't my toaster work?
That's probably be the number one question again? Can you
come fix my toaster? No, we're not engineers. You need
a different Uber for that. Yeah, but think about all
those grad students and post talcs and physics who are
looking for a little extra money. You know, they would,
I'm sure they would sign up to answer people's questions. Yeah,
you know, there actually is a physics consulting service where
(02:44):
if you think you have the great next theory of
physics but you're not being taken seriously by the mainstream establishment,
there is a service where expert physicists will read your
theory and give you like top level criticism of it.
Why it's probably not the winner of the next year's
Nobel Prize. Yeah, it's called Daniel at Daniel and Jorge
(03:07):
dot com. It's true. There are people who send me
their theories two questions at Daniel and Jorge dot com,
and I try to take a look at them. But
there is a service which will spend you know, half
an hour or an hour actually digging into your theory. Yeah,
but they charge a lot, don't they don't They charge
you like fifty or something. You think that's a lot.
(03:27):
You think, like, you know, deep deep expertise of the
universe should coming like seven. Sure, I mean, you know,
I want to know how my toaster works. But not
for fifty dollars, buy any toaster Roman for fifty dollars. Well,
then I guess you don't really want to know how
it works. You just want to buy a new one.
I want to buy a transparent toaster so I can
(03:47):
see how it works. Well, that's the difference between the
scientists and the engineer. The engineer just wants to make
it work, and the scientist wants to know why it
doesn't work. Yeah, we we just want to eat toast.
That's the basic difference. But sometimes scientists also want a
theory that just works. And in physics we were making
progress towards sort of like answering those deep questions of
(04:08):
the universe, but we're not quite there yet. Yeah, you
guys have been pretty successful. You have a standard model
of the universe and some pretty good theories. You know,
you have the standard model, not the not the non
standard model. We should have called it something else, right,
Standard models just so boring. It's like the Beije model
of the universe. We should have called it the amazing model. Yeah,
but you have pretty much everything answered right, kind of,
(04:31):
except for some basic things about the universe. Yeah, we've
made a lot of progress, which is incredible. We've explained electromagnetism,
we've explained the weak foce, we've made a lot of
progress and understanding the strong nuclear force. And then, in
a totally different camp, with totally different people, using completely
different mathematics and ways of thinking, we've made some in
(04:53):
rows into understanding gravity. Yeah, but there are some You
have all these great theories, but there's something not wide
right right, Like it works, it's pretty successful for a
lot of things, but there's something kind of fundamentally almost
wrong with all of your theories. What did you say, Yeah,
the problem is we have no theory that describes sort
of all of it. We have people who started from
(05:14):
the quantum mechanical side of things understanding that building an
incredible mind bending theory of the universe that seems to
be like an accurate description of the way things actually are.
And then we have people working from the other side,
starting from gravity and saying like, let's understand gravity is
a bending of space man, and they're actually making progress. Also,
the problem is these two theories don't agree with each other.
(05:37):
They don't play well, they don't have completely different views
of how the universe actually is. They're sort of incompatible.
It's kind of like if you're building a bridge across
the Atlantic, and you know, you build one side starts
building a bridge, and the other side starts building a
bridge from their side, and you find out that you're
nowhere near each other in the middle. Yeah, exactly. Or
(05:57):
you're using technologies which just cannot fit to other and
that's the problem. Right. You're hoping that there is one
truth that you can start in different places in your
investigation and sort of work together to find the central truth.
But sometimes we wonder if these models just depend on
your perspective. There's different ways to look at the universe,
and some are successful and some are limited, and so
(06:18):
we don't know like which is the right way to
look at the universe, if if either of them are
even right, or we need something totally new, right, if
either of them right, because it almost sounds like maybe
both of them are not looking at the world, at
the universe and quite the right way, you know, if
you can't make them work together. Yeah, And there's a
lot of examples in history where physics has been like
(06:39):
very confidently almost wrapped everything up except for a couple
of little details which turn out when you pull on them,
unravel everything and reveal like a completely different view of
the universe that was quantum mechanics. You know, in the
late eighteen hundreds, people felt like we've almost got this
thing wrapped up except for like, you know, the photoelectric
effect and the black body radiation, which revealed, of course
(07:01):
that the universe is quantized on a fundamental scale, which
blew everybody's minds. Kind of makes you wonder if maybe
physics needs to be shaken up a little bit, you know,
kind of reset or you know, disrupted, or you know,
start from a totally needed perspective. Yeah, I think it's
possible physics today has all those elements of needing a
(07:22):
new idea, of needing a new perspective, of discovering, of
stumbling over something which shows us that we've just been
asking the wrong questions or starting our solutions from the
wrong point of view. And that's not embarrassing, you know.
That's the way we explore the world. We start from
our current understanding. We see how long it works, and
when it breaks, we think, can we just add another
little widget to it, or do we have to toss
(07:43):
everything out and build it from a different kind of
bit In today's episode, we'll be talking about one such
idea that might help bridge this connector gap between quantum
mechanics and gravity. And it's a pretty new theory when
you say, it's sort of it's come out in the
last maybe what ten years, twenty years. I think it
has its history in the eighties, but it's been picking
(08:06):
up steam in the last ten or fifteen years, and
it's sort of emerging as a dark horse. It was
like first was sort of laughed off as a fringe
theory and you know, not nearly this popular other theories
of everything in quantum gravity, and so I think it's
recently gaining some sort of respectability. It's like millennials, you know,
born in the eighties but kind of easily discounted, but
(08:27):
now they're taking over the world. Are millennials getting respectable?
When did that happen? When we died? There? I'm working
on my theory of quantum respectability and currently I have
zero there you go. So today we'll be talking about
what about that theory. And the theory is loop quantum gravity.
(08:51):
What is it? Why is it in a loop? And
will it solve all the problems in physics? And here
I have to make a shout out to one of
our listeners, Jim Milco. Jim has been sending me questions
for about as long as we've been doing this podcast,
and he has been consistently asking for a podcast episode
about loop quantum gravity. So thanks for your patients, Jim,
here's your episode. Awesome as he sent you, any idea
(09:13):
is worthy of a Nobel price yet, Jim has sent
a lot of ideas and they're always fun to read.
So if you have ideas about the universe, or just questions,
or there's something you really want to understand more deeply
and you think we might be able to break it down,
please send your questions, your suggestions, your fundamental new theories
of the universe to questions at Daniel and Jore dot com. Yeah,
(09:34):
thanks to Jim for listening and to everyone out there listening.
And so as usual, we were wondering how many people
out there know or have heard of loop quantum gravity.
It's sort of a it's sort of a it has
two sort of technical familiar words, but then a pretty
common word, which is loop. I was very curious in
these interviews to see if anybody had heard of this
(09:54):
thing and had any ideas. So I went in with
a completely open mind. So before you hear these answers,
think to yourself, do you know what Luke quantum gravity is?
Could you describe it? What would you answer? Here's what
people had to say. I mean, I would assume it
has something to do with gravity, nothing at all, nothing
at all. So I heard of quantum mechanics and read
(10:17):
like brief history of time. Okay, but I don't don't
know what loup quantum gravity could be. What came to
mind first was entanglement. But I don't think that necessarily
has anything to do with that. So it's just as
opposed to just making up something that I think it
might be. I don't know. I have not no no
idea that I'm not No, I have it nothing. I
(10:41):
don't know, all right, not a lot of penetration in
the public market. No, these folks have to work on
their pr for sure. String theory has them beat, for sure.
Maybe they need to get it mentioned in the next
Big Bang Theory episode. Oh maybe we should create a
setim called loop quantum gravity. I want to see you
(11:02):
pitching that, like, Hey, it worked for the Big Bang theory.
We just need another physics theory named titled sitcom that
makes fun of nerds. Yeah, well I'm in as long
as we have characters that both are smart and can
talk to human beings. Oh really yeah? Any Oh that hurts, man,
(11:29):
That hurts. So not. Not only a lot of people
seem to have heard of it. I mean I imagine
they most of them have heard of quantum mechanics or
have heard the word quantum if anything, from the Marvel movies,
and they surely have heard of gravity, but loop quantum
gravity is pretty pretty unknown. Yeah, it's a little bit esoteric,
but it's fascinating and it has really interesting ideas, and
(11:52):
those ideas could have really deep implications. It's the kind
of theory which, if it's correct, really changes the way
we think about the entire universe and the fundamental nature
of our relationship with it. So it's super fun to
think about. And it's also really complicated and very technical,
and there's a humongous amount of complicated math involved, none
(12:14):
of which none of which you will have to understand
to get the basic ideas today, which is why Daniel,
you went out there and found an expert to talk
to about this topic. Right, that's right, because I'm a
particle physicist and my expertise doesn't extend to theories of
quantum gravity. So I went and I talked to Bianca Dittrich.
She's a professor at the Perimeter Institute in Canada, and
(12:36):
she's an active researcher on the forefront of quantum gravity.
So here is Bianca. So my name is Bianca Ditwich,
originately from Germany. Also studied in Germany and then oscillated
between the Canada and Europe a number of times and
ended up at in Canada. It's a parameter institute, a faculty.
(13:00):
All right, cool, So Bianca explained to you what loop
quantum gravity is. Yeah. I had a long conversation with
Bianca about why we need loop quantum gravity, how it
solves the problems in physics, where the current criticisms of
it are, how we could test it, and of course
then I had to ask her at the end about
black holes. Of course, because every good conversation ends in
(13:22):
a black hole literally, right, maybe at the end of
the universe, all that every conversation, everyone will ever have,
all that information will end up maybe in a black hole. Well,
what happens if you take a black hole and you
put it in a toaster oven. There's a question nobody's
ever asked, if I need to ask that a crunchy
outside of the inside will still be cold black hole temperature. Yes,
(13:46):
So what if I put a black hole in a microwave?
Then do I heat up the inside of the black hole.
That's a question I've never thought of. That's really a
fun question. All right, Well, that step us through what
Bianca explained to you, Daniel was so first of all,
I guess what is the big problem in physics? Did
that needs to be fixing? The big problem is that,
as we said earlier, we have two different basic ideas
(14:07):
about sort of how the universe works at the smallest scale,
and they start from very different places, and as you
said that they when they come together across the Atlantic,
they just don't meet. And those two ideas are quantum
mechanics and general relativity of theory Einstein's theory of gravity.
It's weird to me that there would be too so
many so different theories about the universe. You know, wouldn't
(14:29):
they all sort of meet at the at the you know,
plus and minus mathematical level. Well, you'd hope so. And
this is sort of the way physics starts. You know,
if your caveman cave woman physicist, you begin building your
model of the universe by sort of looking at all
this stuff around you, cataloging what it can do, and
then saying, can I understand all of this stuff in
as simple as possible terms? And so you're like, all right,
(14:51):
there's the thing where things fall down, there's the thing
where lightning comes from the sky. You know, there's a
thing where there's wind. And then you have a very
long list of stuff and try to boil it down
and say, oh, you know, this lightning thing is the
same as this other thing where I get zapped, and
things falling down is actually the same thing as stars
moving through the sky. There's all these moments when we
sort of shrunk the list of ideas we need to
(15:12):
explain the universe. And so you hope that as this
list gets shorter and shorter, they fit together nicely. And
that's happened a lot of time so far. Electricity is
the same thing as magnetism, and it's all part of
this other thing called the electroweak force that has happened.
But sometimes you get, you know, you get two puzzle
pieces and they just don't fit together, all right. So
maybe step remind us Daniel, what each of these theories are, Like,
(15:35):
what's the what's the easy way to describe what general
relativity is, And what's the easy way to describe what
quantum mechanics is. So general relativity is a way to
try to understand what is gravity. And remember that Newton
said gravity is things pulling on each other, things that
have mass pull on each other. So take a force, yeah, Newton,
that was the old thinking. That was the old thinking.
(15:56):
Newton thought gravity is a force, and it seems kind
of like a force. It acts like a force, like
electricity and magnetism, and he was able to write down
an equation that described how the Earth moved around the
Sun and how to move the Moon moved around the Earth,
and it works pretty well. Now, Einstein came along and
he gave us general relativity, which is a complete reconception
of how gravity works. He said, no, no, gravity is
(16:19):
not a force. Gravity is a change in the shape
of space and time itself. Like you have a blob
of mass or blob of any kind of energy density,
it changes the shape of space and that's what makes
things move in curves. Rather than moving and what feels
like a straight line to us, things moved through bent space.
It's not like a mysterious invisible force that pulls things together.
(16:43):
It's more like when things exist, they distort, they bend
the space around them, and that's why they come together. Yeah.
And it's a beautiful idea and it's been tested exilient
ways and it works. It describes very tiny deviations in
Mercury's orbit. It describes how light bends around the Moon
during an eclipse. Big stuff, big stuff, Yeah, really thoroughly
(17:06):
extensively tested. It predicted gravitational waves, which we've actually seen
black holes to right and black holes. Yeah. And and
the thing to understand the things that that's going to
be make it in conflict with quantum mechanics is that
it's a classical theory meeting that it assumes that, like
you can describe everything perfectly, that everything has a position
(17:26):
and a direction and a location, right, and that the
space is operating in is smooth, Like you can subdivide
space as many times as you want between me and you.
There's an infinite possible locations for like a ball that
we're throwing back and forth. That's Einstein's vision of space. Right,
it assumes that everything is kind of smooth and continuous,
(17:49):
and there there are no bumps in the universe at
the microscopic level. That's right. You can zoom in forever
according to Einstein and general relativity, and things still stay
smooth and and everything has a fixed location. Right, the
ball is somewhere and space and time makes some sense.
There's no uncertainty or or weird or weirdness. That's right.
The world can be known, everything can be determined according
(18:12):
to general relativity. But then you have quantum mechanics, that's right.
And then on the other hand, building from the other
side of the ocean, you know, the toaster side of
the ocean instead of the microwave side of the ocean.
Um completely mixing metaphors, there is quantum mechanics. And quantum mechanics,
of course developed in the early part of this century
to explain some things that didn't make sense, some experiments
(18:32):
we saw which just could not be described using a
classical understanding of electromagnetism. It was really what was light
that gave us the first clues. We did a whole
podcast episode about the photoelectric effect and how we know,
the photon is a thing, and they did these experiments
that just didn't make sense unless you thought of light
as being made of tiny little packets of energy rather
(18:55):
than a smooth, continuous beam. You had to think about
it as these tiny packets. When you zoom in, things
don't behave nice and smooth and continuous there are sort
of lumpy and clumpy. Yeah, And there were also just
some problems with the theory, like there's a kind of
radiation in the universe called black body radiation, which is
just how things glow, Like everything in the universe has
(19:16):
a temperature and it glows with that temperature, and quantum
mechanics predicted that well. Classical theory electromagnetism predicted a certain spectrum,
like if you're this temperature, you should glow with this color.
If you're that temperature, you should glow with that other color.
The problem was that it predicted that for certain temperatures
you should glow at a crazy nonsensical color, like if
(19:37):
you get an infinite amount of radiation. The original theory,
the one before quantum mechanics, said that things that certain
temperatures should have an infinite amount of light at very
very low wavelengths, right, it really really sort of it's
called ultra violet light, and that they should have like
a ridiculous amount of infinite amount of ultra violet light,
which is nonsensical. So you can do an ex perament
(20:00):
basically that proves that general relativity doesn't work for all cases. Well,
you can do an experiment that proves that the old
theory of electricity and magnetism doesn't work. And we knew
that didn't work. We're like, okay, this theory is making
a prediction that just doesn't make sense. But if you
add quantum mechanics to it, quantum mechanics says, oh, that's
just because light is not continuous. If you make light
(20:22):
into chunks, then if you predict that, you don't see
this crazy behavior. And that's in fact what we saw
in nature. And so we needed to sort of change
the theory. The theory gave nonsensical results. I mean, I
have to add this bit to it to say bit
that says, okay, well there's a minimum size to a photon,
and that solved that problem. It said, okay, now you
can make realistic predictions. And so but the thing to
(20:44):
understand is that like quantum mechanics changes also the way
we think about the universe, right, it says things are uncertain,
things are fluctuating. This is like crazy randomness the heart
of the universe. All right. So those are the two
two big titans in physics theories, right, general activity and
quantum mechanics to try to explain the universe. And the
problem is that they don't play well together. So let's
(21:06):
get into a little bit of why they don't play
well together and whether this idea of loop quantum gravity
can help solve that. But first let's take a quick break,
(21:28):
all right, Daniel, So general relativity and quantum mechanics don't
play well together. Is it fair to say? Is it?
Is it kind of like I'm trying to think of
an analogy. Is it kind of like microeconomics and macro economics, Like,
you know, macro economics is good for you know, big
economies and countries and and micro economics is good for
like how people make decisions, but like somehow they don't always.
(21:50):
It's weird to think about where they meet in the middle. Perhaps,
but in those two cases, one should be an extreme
case of the other. Here it's really you have a
fundamental different view of how the universe works. You know,
it's it's more like totally different kinds of art, you know,
like figurative art versus symbolic art. Like what's a better
way to describe the human experience? You know? Is that
(22:12):
through abstract splashes of color or is it by you know,
depicting the things we see in interesting juxtapositions or something.
I don't know, it's right, right, it's like a totally
lens or you know, totally set of glasses. Yes, it's
a completely different way of thinking about the world. And
people have been trying for a long time to bring
them together to say, all right, are these things in
(22:35):
conflict or can we make a consistent sort of quantum
theory of gravity that brings it all together? Right? And
so here is Bianca talking about that question. It's one
of the really big outstanding questions and physics and and
my view it really means quantum gravity should include a
new notion of space time. We have to replace it, however,
(22:56):
with something completely new we expected that which change quite
dramatically as a foundation, so physics um and get very
interesting insights into you know, the nature of space and time.
All right, So it seems like we need something totally
new here um, And so Daniel, can you explain to
me kind of what the problem is, like why can't
(23:17):
they play well together? The ones that we have. Well,
people have been trying to bring these two things together
since basically they've existed. You know, people have been working
on making gravity into a quantum theory for a very
very long time. But you know, quantum theories traditionally thinking
about forces very differently than gravity does. They think about
forces is like ripples in a quantum field. You know,
(23:38):
you have like the electromagnetic field, and you think about
how do photons communicate the electromagnetic field. There are ripples
in this electromagnetic field, and you quantize those ripples. That's
how quantum mechanics thinks about forces. But in general, relativity
of force is really more like a bending out space.
That's right, And mostly you can do this. You can say, like,
all right, well, can I make a quantum theory of gravity?
(24:00):
Can I build a theory where I exchange where gravity
is a field and it has ripples and those ripples
are quantized, just like I can for electromagnetism, And mostly
you can, actually you can. It's mostly it works, but
it fails in some moments. Couldn't you just have quantum
fields in a general relativity you know world? You know, like,
(24:21):
couldn't you have quantum particles that bend space as well?
Like why can't I a quantum particle also bend space
like a planet? Well, but then gravity is coming from
something that's classical, that's smooth and continuous, and general relativity
is just not a quantum theory, right, Like it assumes
that you know everything about the location and the time
(24:43):
and the position. What couldn't you just make the bending
also kind of uncertain? I'm just trying to figure out
why why you can't marry the two, you know, why
can't these particles and these fields exist in a world
that is as Einstein envisioned with the bending and the
gravity that's exactly what Looke gravity is? Or hey, you
just basically invented the idea prize right now, Thank you
(25:07):
very much. That's right, And you know this other idea
that like, let's take the gravitational field and think about
as a quantum field that mostly works. The important thing
to understand is that it only fails when gravity gets
really really strong, right, things like inside a black hole,
and what happens is that it makes nonsense predictions like
(25:28):
it just like we saw for the black body radiation.
It predicts like infinite amount of energy will be released,
but we know that's not true. We know it doesn't happen.
And so the theories work except in extreme circumstances. And
that's what makes it really hard, is like it's easy
to fix the theory when you can see it breaking.
But these theories general relativity and quantum mechanics, they only
(25:49):
disagree about like what happens in the inside of a
black hole, and we can't see that. Why don't we
just like nor black hole? If we just like nor
black holes in the universe, wouldn't that make our there's
a lot wouldn't that make physics a little bit easier,
you know, because it's all it seems like it seems
like everything breaks in a black hole, and so why
don't It's like, you know, the mess in my closet.
(26:10):
Let's just ignore it's the engineering, you man, that's the engineering.
The scientist in me is desperate to know. You have
to know inside a black hole. Yes, if you have,
you created a black hole in your closet, because if
so I'm coming over and I want to check it out.
I think we're close to the singularity. To be honest,
in there, you don't want to go in there that
you may never come out like you have all these
(26:30):
rejected toaster microwave prototypes in there, that's right, all these
rejected app ideas as well. And so these two things
aren't working together. Well. People have tried, but they just
give nonsense predictions like the calculations you get suggested, you know,
infinite amount of energy in a radiated inside a black
hole when gravity gets really strong, And we can't easily
(26:52):
test that because we don't have a black hole and
and I don't have a galaxy sized particle collider. I
would need to create the sort of energy density in
order to break quantum gravity. And so what we need
is we need to see inside a black hole, or
we need a new idea, and so we need Jorge's
vision of quantum gravity. I have an idea. How about
something called loop quantum gravity. That's such a great name too.
(27:17):
All right, So we have these two fourth theories, and
you know, one of them has an h thunderbolt cable
connector and the other side is a mini USB cable connector,
and so they don't fit. And so that's what this
idea of loop quantum gravity is. It's like, maybe it's
like an adapter. That is it like an adapter that
makes it to work or is it a totally new
cabling system. Yeah, it says instead of trying to think
(27:40):
of gravity is like a Newtonian gravity as a force
um and and and quantizing that gravitational field directly. Instead
take Jorges idea, which is just takes space itself and
quantize that and say, well, maybe general relativity is basically right,
except that instead of working on a smooth continue in
US space, we work on a space that is quantized,
(28:03):
like there are pixels of space instead of space being
infinite and smooth, they are like little chunks of space.
It would explain how quantum particles move, or it would
explain how gravity can be quantized. It would allow us
to build a theory of quantum gravity that doesn't make
nonsense predictions, because it basically makes the places where those
(28:25):
predictions get nonsense impossible, like the predictions of quantum gravity
breakdown really high energies and really small distances. So the
idea is basically, well, what if really small distances aren't allowed,
like there's just nothing smaller than ten of the minus
thirty five where things break down, then there isn't the problem.
Let's just ignore the closet and assume that the closet
(28:48):
is QUANTIEDA it's just one thing, I see. Yeah, it's
it's not ignoring the closet. It's saying the closet doesn't exist.
You were so worried about the closet. It turns out
it's impossible. There is no clause it. But it sounds
like you're trying to make gravity quantized. You're not trying
to make quantum things the bendy like space. Well, if
(29:09):
space is bendy and quantized, then you quantum things move
through quantizes bend bendy space. So this would allow you
to bend space in a quantized way. Yeah, it would
allow you to bend space in a quantized way. And
it's it's kind of a beautiful idea because it's very
similar to the origin of quantum mechanics itself. Right, we
solve the problem of black body radiation, of this thermal
(29:31):
emission giving crazy numbers by saying, oh, maybe we can
just um quantize photons and that mathematically solves that problem. Here,
we're solving the problem of infinite emissions inside black holes
and really high energies and small distances by saying, oh,
maybe we quantize space, and so those small distances are impossible.
So there's there's a beautiful sort of analogy there to
(29:52):
previous structures of solutions that suggests like tensively like, oh,
maybe this is the right track because it feels like
nineteen fifteen a little bit. That's right. We're gonna party
like it's people are growing mustaches and wearing top hats,
and you're like, I like it. I like it, except
for the fact that like, no women are allowed to
(30:12):
do physics. That's the bad part, all right. So the
idea is that maybe space and time itself like space
and time like there are no there's no there's no
infinite as at least small second. That's right, And that's
a question people have been sending me over email many times.
If you quantize space, you also quantize time. And you know,
(30:33):
space time is a fabric in this theory and they're
deeply connected, and so if you're quantizing space, then yes,
you're also probably quantizing time. Well, it's like you're there's
actually a ticking clock to the universe. Maybe, yeah, there's
a minimum time that makes sense. You know, you can't
infinitely divide a second into arbitrarily tiny slices. There's a
minimum of time below which makes no sense. Okay, And
(30:56):
so what does that mean? I guess space is not
really like space. Space is more like a clump of
little spaces. Well, the reason it's called loop quantum gravity
is that the way to think about it is that
space is a bunch of these loops and they're sort
of woven together. And so think about spaces like chain mail.
If you're into D and D. You know, it's like
(31:18):
a bunch of links that are all connected to each other.
And space comes out of that, right spaces, There are
these The fundamental thing in the universe are these little loops,
and the loops are woven together. And the way that
things move through space, and the way that gravity happens
is how these little loops interact with each other and
pull on each other and are built together. To what
(31:40):
are these little loops? They're like little bits of the universe.
That's the next Nobel prize, man, you want to win
two Nobel prizes in a single podcast, in a single
let's do you have enough for this to be a physicist?
For the what do you call the hat the hat trick?
A hat trick? You're gonna go for three Nobel prizes.
That's when you get fifteen minutes off, Daniel, Let's do
(32:00):
it when you invent the perfect toaster microwave combination, that
definitely is worth a novel prize. Well, nobody knows what
these loops are, and you know that's sort of the
next question, Like if you can start from these loops
and build a theory that describes everything and predicts the
universe and it is consistent with everything we know, then
the next question is you're like, well, why these little loops?
(32:21):
What do they mean? How do we get those little
loops right? Where do they come from? Do they emerge
from something deeper? You know, physicists are great at making
answers that create more questions. But I guess why call
them loops? Are they actually like little rings that are
tied together? What does that? Why not call them I
don't know, bubbles or uh pixels or you know what
(32:42):
I mean? Like, what is it about the idea of
a loop that gives it the name loop quantum gravity. Well,
I guess bubbles would work also, But I think it's
just a visualization idea. You know that these things are
linked together um and it's sort of a mesh, and
you know there are also loops, like we're doing calculations
around in a circle. You have to avoid a sort
of trap, Like you can't think about these as loops
(33:03):
in space. They're not like um circles on some axis, right,
because when you have what is that access, we're talking
about the very nature of space itself. It's not like
these loops are somewhere and like this loop is at
this point in that loop is at that point. The
loops are the points like space is these this thing
we're talking about like the nature of space itself, which
(33:26):
is really hard to sort of wrap your mind around. Oh,
I see you. You were just looking at you guys
were just looking for like a word that implies that
space is made up of little things that are kind
of interconnected or overlapping, right, or like hooked together. M
m okay. And so you went with them loops. I
was like loops. They went with loops. I think it's
(33:48):
not a terrible idea, you know, they could have called
it the bubble quantum gravity, but hear it. But you know,
we talked about this another time in the podcast. You
can think of these things as little bubbles, and then
you get to talk about things like space foam and
quantum foam because these loops aren't fixed, right, they can
like fluctuate in and out of existence. I see. So
(34:08):
these are all related ideas loop quantum gravity, space foam,
quantum foam. They're all sort of coming at this idea
of a bubbly space and thinking about space not as
continuous and smooth but made up of little quantized bits,
like let's quantize space itself because general relativity is an
attempt to understand gravity in terms of the nature of space.
(34:31):
And so if we're gonna get a quantum theory of gravity,
the idea is, let's let's just quantize space itself, all right.
So that's quantum loop or loop quantum gravity, and so
we'll get into what are some of the open questions
and why people think it may or may not be
the ultimate answer to how the universe works. But first
let's take a quick break. Okay, Daniel, what does it
(35:04):
all mean? What does loop quantum gravity mean? If it's
true or if it's not true, and why do we
think it might not be true? All right, well here's
the big letdown. Right, So, so far it seems like
you're gonna break the loop. I'm gonna break the loop. Yeah.
It seems like a beautiful idea. It seems really promising.
It seems like dot dot dot the next obvious step
in physics. Right. The problem is there's a lot of
(35:27):
problems with it, and there's a lot of open questions.
And that doesn't mean it's not gonna work. It just
means it's far from clear that it is going to work. Well,
I see, there's a room for us skepticism. Yeah, and
even among physicists there's a lot of skepticism about loop
quantum gravity. It's a bit of a fringe theory. There
are a lot more people working, for example, on string theory,
(35:47):
which is a completely different attempt to unify gravity and
quantum mechanics and all of the other forces all at once.
String theories like a theory of everything, where loop quantum
gravity is like, let's just focus on make in gravity
of quantum theory. If you can do that, then that's
another way to unify these two big theories. Yeah, the
string theory is sort of a The other idea is
(36:09):
that the opponent of Looke quantum gravity, let's build a
tunnel under the Atlantic instead of trying to make these
two bridges work. And the string theory is a much
bigger community, has a lot more people working on it,
people are sort of more excited about it, whereas Looke
quantum gravity is like, you know, the younger sibling in
terms of theories of quantum the underdog exactly making me
(36:30):
like it more now, And one reason is that it
sort of hasn't yet delivered on its promise. Like, what
you want to do is start from this concept of
loops and from it should emerge Einstein's theory of relativity.
You should be like, I'm gonna have a completely different
picture of the world, but it's going to give the
same predictions sort of at my scale. I should still
(36:51):
describe how a ball flies over my neighbor's wall, and
how and gravitational waves and all of that stuff. You
should be able to sort of are from there and
build up to general relativity. You start off imagining the
world the universe is a mesh of of loops, but
it doesn't give you baseballs and fences. Yeah, not yet.
And it's not like they can't do it. It's just like,
(37:13):
well they haven't quite figured it out yet, and it's hard,
right this is are difficult things, and people are hacking
with their machetes through the jungle of mathematics that's involved,
and it's not always clear that we have the right tools,
and sometimes progress is paused for like a decade or
thirty years until somebody's like, hey, we've heard this new
idea from mathematics. Turns out that's exactly what we need
(37:35):
over here. That kind of thing has happened in physics
at a lot of times. And there are other sort
of really interesting problems with loop quantum gravity, which actually
conflict with relativity. Okay, so there's maybe something fundamentally wrong here,
you know, or not necessarily wrong, but it would again
change the way we think about the universe. Like, here's
the problem with quantizing space. Says there are space pixels, right,
(37:57):
that means that in some sense there's a minimum distance
to the universe. But what is that distance? Because we
know that distances depend on velocities, right, Like as you
move faster, things get shrunk, so do things that are
moving see smaller space pixels than things that are stationary,
And if so, it would mean that there is some
(38:19):
sort of absolute velocity to the universe. Right, if you
can measure your space pixel the size of your space pixels,
that tells you sort of what your absolute speed is.
But special relativity has always told us velocity is relative.
There is no absolute frame, and so this is sort
of conflict with a really really core concept and special relativity.
(38:40):
Couldn't it be like the speed of light, which like
it always looks the same no matter how fast you're going.
Couldn't these loops always look the same no matter how
fast you're going. Yeah, So there's a lot of ways
to try to solve this problem. One is to say,
you know, we have these weird space pixels which to
form under certain circumstances, and there's some very complicated mathematics
involved to do essentially what you just described. You're really
(39:02):
hidden out of the park today with like going for
the hat track here, wait wait till you see why
what I pull out at the last five minutes. And
the other is to accept it and to say, you
know what, maybe there is maybe there is an absolute
reference frame. Maybe special relativity is slightly wrong, But wouldn't
that throw the whole light speed thing off. Well, not
(39:25):
all of special relativity has to be wrong. The consequence
would be that light would travel at a slightly different
speed as a function of its frequency. So like high
frequency light would travel that is slightly different speed from
lower frequency light like X rays and UV light would
move faster than radio waves. But it'd be a really
(39:46):
small difference to be really hard to tell, all right,
So there's some skepticism or I guess some open questions
about it, because it's not quite hitting it out of
the ballpark, over your fence or not into your neighbors
house or not um And so I guess the question
is what does it all mean? I mean, what if
it happens to be true? And how are we even
(40:07):
going to know of something like this is true? Yeah,
so of course the deep question I have is what
does this mean for the nature of the universe? And
how could we see it? Right? Where would it manifest itself?
And as we talked about at the beginning of the episode,
the place this would really be important, the place you
would notice at difference, the place where it matters is
inside a black hole of course, of course, right, so
(40:29):
let's go there, Let's go into the closet there. That's right,
we're opening the closet and all who knows what's in
there and who knows what's been growing? And so I
asked Bianca the professor, because she thinks about this stuff, right,
she thinks about what happens inside black holes when gravity
gets really strong and space gets twisty. And I asked her, like,
(40:50):
what is your mental image of inside a black hole?
Because I want to know, right, I mean, there's a
black hole in her mind at least, and I want
to know what does it look like inside her mind?
Effects will be only important very near the singularity. There,
the space and coviatures really getting very large. And maybe
I'd like to think that there's a new universe which
(41:13):
opens up with each singularity, which gives us much more
universes than we know of. Yeah, she went there, she
went for there are new universes inside black holes. I
love it. There's a new universe in my closet. I
would believe that. And inside that closet there are other
closets with other closets inside them, I meaning meaning that's
(41:35):
kind of a consequence of quantum blue gravity is that
when you get to these extreme singularities, these loops kind
of what like open up or you know, become their
own little universes. Is that the idea, I will not
pretend to even understand what that means, because there's some
crazy consequences that like, if there's a universe inside every
(41:55):
black hole, is our universe inside a black hole? You know,
maybe who knows? It's crazy stuff? Yes, is your answer.
I go with the s and that's my third Nobel
Prize claim. Or is that the conclusion to your pitch
or your loop quantum gravity sitcom episode there Echo at
(42:16):
the end of season twenty, it turns out they're all
in a black hole. That's right, And you know, we
might be able to figure this out in ways other
than going to a black hole. We actually do have
ideas for how you could test this, and they revolve
around seeing whether we can tell the difference in the
speed of light from high frequency and low frequency light.
The speed of light changes, which we didn't think it did,
(42:39):
but if it changes with frequency, then that's an indication
maybe there's something loopy going on. Yeah, maybe there's something
loopy going on, And this would be a really small effect.
So what you need to do is like have a
race between photons of different frequencies high frequency versus low frequency,
and the race would have to be super long because
light goes super past of course, and it's different is
(43:00):
really small. And so what they do is they look
for light sources that are really really far away and
then try to measure see if there's a difference in
like the arrival time of photons. Would you would I
need to know where they're coming from, right, Yeah, So
we have these sources which are variable, like quasars and
pulsars that are really far away. You know, they pulse,
and so you can sort of line the two up
(43:21):
and say, well, we know these two were emitted at
the same moment because they are the top of the
pulse at the same time or something. And then you
can say, well, did they arrive in sync or are
they sort of out of sync? And so there's a
satellite which looked out and measured this and looked for this.
What did they find, Well, this is the integral satellite.
And that's some tortured acronym for I don't even know
what is it. Really, It's called integral up and what
(43:44):
they found they didn't see anything, right, They didn't see
any difference in the arrival times. I didn't see any loops.
And they were able to say that if there are loops,
they're smaller than ten to the minus forty eight meters.
What they can do that, that's by looking at two photons. Yeah,
by looking at these photons, because the photons come from
(44:05):
really really far away, and so the differences would be
added up across the universe. And they claim they should
have seen them. They saw that they were in sync.
They were in sync. Yeah, and this is thirteen orders
of magnitudes smaller than what we think the size of
the loops are. So like that seems pretty definitive. Yeah,
but what did the loop quantum gravity folks say, Well,
(44:26):
you know, there's only one branch of loop quantum gravity.
The people who say that maybe that's that special relativity
needs to be tweaked. Other people have solutions, as you say,
to make light travel the same speed no matter what,
by having you know, crazy deformations these things, and all
sorts of complicated interactions between light and space, and so
it just sort of rules out one branch of loop
(44:48):
quantum gravity. You can never kill these theories. Man, They're
like weeds. They always there's another version that crops up there,
like exide one head of But they're fascinating, you know.
Each one is a wonderful exploration and sort of the
intellectual space of like how could the universe work? What
possible universes might we live in? And the amazing thing
(45:10):
is that there is an answer, right, there is one
way that the universe actually works. And what's kind of
interesting I think is that it wouldn't affect your everyday life,
like things would still work the same way. But who
knows what's going on down at the fundamental level? Right,
it could be one of these crazy theoretical ideas. Yeah,
and it's important now to scientists, but it might eventually
(45:31):
be important to engineers. You know, knowledge that seems impractical
and useless but reveals the fundamental nature of reality could
eventually be useful and hate to me, that's fun anyway.
I don't really care if it's useful. I just gotta know, right, Yeah,
I mean I think that's how micro rays were invented,
actually by accident, by looking at something else. And where
(45:52):
would we be? Where would burritas be these days? That's right.
And you know, there have been actually fascinating advances in
microwave and the technology the engineer ring of microwaves. And
I guess, you know, if you can unlock kind of
the magic and the power that's happening at that microscopic level,
who knows what you could do, right, what kind of
energies you can get, or what kinds of warp drives
(46:13):
or microwave ovens. Yeah, microwave toaster opens powered by artificial intelligence. Yeah,
And so I have to give a shout out to Nico.
He's one of our listeners and he heard our episode
about microwave ovens actually, and he wrote to me and
told me that they have a new fancier AI powered
microwave oven um which can heat stuff up at different
(46:35):
temperatures and monitor to make sure the heating is all
smooth and fancy, and actually dropped by my house and
delivered one of these prototypes, which has been a lot
of fun. That's amazing that you let one of your
listeners into your house. Hey, he was offering a brand
new appliance, so I thought. And while he was there,
I asked him about Luke quantum gravity, but he didn't
have any ideas. Oh man, there's no setting on that
(46:56):
in the microwave, not yet. Um. The next in the
prototype will be quantum gravity powered, I'm sure. All right, Well,
it sounds like the answer is stay tuned. You know,
that's what we explain, what Luke. Quantum gravity is and
who knows, and maybe it is the way that the
universe works at that level, and we may find out
in the near future. That's right, And these are the
(47:17):
kinds of mysteries that are going to help us figure
out the deep nature of the universe. You know. It's
when things break that we have an opportunity to figure
out how things should work. And so it's exciting to
have these kind of problems. It's exciting to know sort
of where to work, even if we don't know what
the answer should look like. All right, well, we hope
you enjoyed that. Daniel. How much this podcast costs me
in terms of your physics time? One loop one? Let's
(47:42):
tend to the minus thirty five dollars, My tend to
the minus thirty one plank dollar? Yeah, pick up plank dollar.
Oh good, I gotta I got a couple here in
my pocket. Okay. Quantum of the mover to me all right.
We hope you enjoyed that. Thanks for joining us, and
as usual, thank you to everybody who wrote in with
your questions. See you next time. Before you still have
(48:09):
a question after listening to all these explanations, please drop
us the line. We'd love to hear from you. You
can find us on Facebook, Twitter, and Instagram at Daniel
and Jorge That's one Word, or email us at Feedback
at Daniel and Jorge dot com. Thanks for listening and
remember that Daniel and Jorge Explain the Universe is a
production of I Heart Radio. For more podcast from my
(48:31):
Heart Radio, visit the i Heart Radio, a Apple Podcasts,
or wherever you listen to your favorite shows.
Hey, Daniel, do you think physics is in a rut?
A rut like we've been solving deep problems and delivering
amazing technology for too long. You're getting tired of it? Yeah,
I mean it's getting a little repetitive, all these discoveries. No, No,
I mean, like, is it on the right track? You know?
Do you think it will it get to the final
deep questions about the universe? I don't know. Sometimes I
(00:30):
wonder if we need like a revolution in physics. Does
physics need to be disrupted? Somebody out there should start
uber for physics. I'm more of a lift person, to
be honest, I think they have a better outlook in
the world. But yes, that's what I mean. You know,
I want to be able to call a physicist anytime
in my with my phone. Um, well you already have that.
(00:51):
That's this podcast. Nice, I'll give you four stars. Daniel here.
(01:12):
Hi am Rhema cartoonist and the creator of PhD comics. Hi.
I'm Daniel Whitson. I'm a particle physicist, and I'm here
to answer any question of physics on your app anytime.
Welcome to our podcast. Daniel and Jorge invent new physics apps.
For people who need physics on demand. Daniel and Jorge
make up terrible business ideas and pretending they're awesome. Now
(01:35):
it's Daniel and Jorge Explained the Universe, a production of
Our Heart Radio, in which we talk about all the
things amazing and beautiful but crazy and bonkers about our
universe because the more we learn, the more it makes sense,
the more it seems surprising and amazing. You know, within
we joke about it. But I think it would be
kind of a useful app. Don't you think, like anytime
anyone has a question about anything, you could just request
(01:58):
a physicist on your phone own and the nearest or
the most available physicists would answer and then answer your question.
Do you think that would be used a lot? Like
what kind of questions would people ask? How do we
reconcile the different theories about quantum physics? Sure? I think
it's more prosaic. It's like can I build a force
field to keep my teenager in his bedroom all night long? Also?
(02:22):
How does my toaster work? Why doesn't my toaster work?
That's probably be the number one question again? Can you
come fix my toaster? No, we're not engineers. You need
a different Uber for that. Yeah, but think about all
those grad students and post talcs and physics who are
looking for a little extra money. You know, they would,
I'm sure they would sign up to answer people's questions. Yeah,
you know, there actually is a physics consulting service where
(02:44):
if you think you have the great next theory of
physics but you're not being taken seriously by the mainstream establishment,
there is a service where expert physicists will read your
theory and give you like top level criticism of it.
Why it's probably not the winner of the next year's
Nobel Prize. Yeah, it's called Daniel at Daniel and Jorge
(03:07):
dot com. It's true. There are people who send me
their theories two questions at Daniel and Jorge dot com,
and I try to take a look at them. But
there is a service which will spend you know, half
an hour or an hour actually digging into your theory. Yeah,
but they charge a lot, don't they don't They charge
you like fifty or something. You think that's a lot.
(03:27):
You think, like, you know, deep deep expertise of the
universe should coming like seven. Sure, I mean, you know,
I want to know how my toaster works. But not
for fifty dollars, buy any toaster Roman for fifty dollars. Well,
then I guess you don't really want to know how
it works. You just want to buy a new one.
I want to buy a transparent toaster so I can
(03:47):
see how it works. Well, that's the difference between the
scientists and the engineer. The engineer just wants to make
it work, and the scientist wants to know why it
doesn't work. Yeah, we we just want to eat toast.
That's the basic difference. But sometimes scientists also want a
theory that just works. And in physics we were making
progress towards sort of like answering those deep questions of
(04:08):
the universe, but we're not quite there yet. Yeah, you
guys have been pretty successful. You have a standard model
of the universe and some pretty good theories. You know,
you have the standard model, not the not the non
standard model. We should have called it something else, right,
Standard models just so boring. It's like the Beije model
of the universe. We should have called it the amazing model. Yeah,
but you have pretty much everything answered right, kind of,
(04:31):
except for some basic things about the universe. Yeah, we've
made a lot of progress, which is incredible. We've explained electromagnetism,
we've explained the weak foce, we've made a lot of
progress and understanding the strong nuclear force. And then, in
a totally different camp, with totally different people, using completely
different mathematics and ways of thinking, we've made some in
(04:53):
rows into understanding gravity. Yeah, but there are some You
have all these great theories, but there's something not wide
right right, Like it works, it's pretty successful for a
lot of things, but there's something kind of fundamentally almost
wrong with all of your theories. What did you say, Yeah,
the problem is we have no theory that describes sort
of all of it. We have people who started from
(05:14):
the quantum mechanical side of things understanding that building an
incredible mind bending theory of the universe that seems to
be like an accurate description of the way things actually are.
And then we have people working from the other side,
starting from gravity and saying like, let's understand gravity is
a bending of space man, and they're actually making progress. Also,
the problem is these two theories don't agree with each other.
(05:37):
They don't play well, they don't have completely different views
of how the universe actually is. They're sort of incompatible.
It's kind of like if you're building a bridge across
the Atlantic, and you know, you build one side starts
building a bridge, and the other side starts building a
bridge from their side, and you find out that you're
nowhere near each other in the middle. Yeah, exactly. Or
(05:57):
you're using technologies which just cannot fit to other and
that's the problem. Right. You're hoping that there is one
truth that you can start in different places in your
investigation and sort of work together to find the central truth.
But sometimes we wonder if these models just depend on
your perspective. There's different ways to look at the universe,
and some are successful and some are limited, and so
(06:18):
we don't know like which is the right way to
look at the universe, if if either of them are
even right, or we need something totally new, right, if
either of them right, because it almost sounds like maybe
both of them are not looking at the world, at
the universe and quite the right way, you know, if
you can't make them work together. Yeah, And there's a
lot of examples in history where physics has been like
(06:39):
very confidently almost wrapped everything up except for a couple
of little details which turn out when you pull on them,
unravel everything and reveal like a completely different view of
the universe that was quantum mechanics. You know, in the
late eighteen hundreds, people felt like we've almost got this
thing wrapped up except for like, you know, the photoelectric
effect and the black body radiation, which revealed, of course
(07:01):
that the universe is quantized on a fundamental scale, which
blew everybody's minds. Kind of makes you wonder if maybe
physics needs to be shaken up a little bit, you know,
kind of reset or you know, disrupted, or you know,
start from a totally needed perspective. Yeah, I think it's
possible physics today has all those elements of needing a
(07:22):
new idea, of needing a new perspective, of discovering, of
stumbling over something which shows us that we've just been
asking the wrong questions or starting our solutions from the
wrong point of view. And that's not embarrassing, you know.
That's the way we explore the world. We start from
our current understanding. We see how long it works, and
when it breaks, we think, can we just add another
little widget to it, or do we have to toss
(07:43):
everything out and build it from a different kind of
bit In today's episode, we'll be talking about one such
idea that might help bridge this connector gap between quantum
mechanics and gravity. And it's a pretty new theory when
you say, it's sort of it's come out in the
last maybe what ten years, twenty years. I think it
has its history in the eighties, but it's been picking
(08:06):
up steam in the last ten or fifteen years, and
it's sort of emerging as a dark horse. It was
like first was sort of laughed off as a fringe
theory and you know, not nearly this popular other theories
of everything in quantum gravity, and so I think it's
recently gaining some sort of respectability. It's like millennials, you know,
born in the eighties but kind of easily discounted, but
(08:27):
now they're taking over the world. Are millennials getting respectable?
When did that happen? When we died? There? I'm working
on my theory of quantum respectability and currently I have
zero there you go. So today we'll be talking about
what about that theory. And the theory is loop quantum gravity.
(08:51):
What is it? Why is it in a loop? And
will it solve all the problems in physics? And here
I have to make a shout out to one of
our listeners, Jim Milco. Jim has been sending me questions
for about as long as we've been doing this podcast,
and he has been consistently asking for a podcast episode
about loop quantum gravity. So thanks for your patients, Jim,
here's your episode. Awesome as he sent you, any idea
(09:13):
is worthy of a Nobel price yet, Jim has sent
a lot of ideas and they're always fun to read.
So if you have ideas about the universe, or just questions,
or there's something you really want to understand more deeply
and you think we might be able to break it down,
please send your questions, your suggestions, your fundamental new theories
of the universe to questions at Daniel and Jore dot com. Yeah,
(09:34):
thanks to Jim for listening and to everyone out there listening.
And so as usual, we were wondering how many people
out there know or have heard of loop quantum gravity.
It's sort of a it's sort of a it has
two sort of technical familiar words, but then a pretty
common word, which is loop. I was very curious in
these interviews to see if anybody had heard of this
(09:54):
thing and had any ideas. So I went in with
a completely open mind. So before you hear these answers,
think to yourself, do you know what Luke quantum gravity is?
Could you describe it? What would you answer? Here's what
people had to say. I mean, I would assume it
has something to do with gravity, nothing at all, nothing
at all. So I heard of quantum mechanics and read
(10:17):
like brief history of time. Okay, but I don't don't
know what loup quantum gravity could be. What came to
mind first was entanglement. But I don't think that necessarily
has anything to do with that. So it's just as
opposed to just making up something that I think it
might be. I don't know. I have not no no
idea that I'm not No, I have it nothing. I
(10:41):
don't know, all right, not a lot of penetration in
the public market. No, these folks have to work on
their pr for sure. String theory has them beat, for sure.
Maybe they need to get it mentioned in the next
Big Bang Theory episode. Oh maybe we should create a
setim called loop quantum gravity. I want to see you
(11:02):
pitching that, like, Hey, it worked for the Big Bang theory.
We just need another physics theory named titled sitcom that
makes fun of nerds. Yeah, well I'm in as long
as we have characters that both are smart and can
talk to human beings. Oh really yeah? Any Oh that hurts, man,
(11:29):
That hurts. So not. Not only a lot of people
seem to have heard of it. I mean I imagine
they most of them have heard of quantum mechanics or
have heard the word quantum if anything, from the Marvel movies,
and they surely have heard of gravity, but loop quantum
gravity is pretty pretty unknown. Yeah, it's a little bit esoteric,
but it's fascinating and it has really interesting ideas, and
(11:52):
those ideas could have really deep implications. It's the kind
of theory which, if it's correct, really changes the way
we think about the entire universe and the fundamental nature
of our relationship with it. So it's super fun to
think about. And it's also really complicated and very technical,
and there's a humongous amount of complicated math involved, none
(12:14):
of which none of which you will have to understand
to get the basic ideas today, which is why Daniel,
you went out there and found an expert to talk
to about this topic. Right, that's right, because I'm a
particle physicist and my expertise doesn't extend to theories of
quantum gravity. So I went and I talked to Bianca Dittrich.
She's a professor at the Perimeter Institute in Canada, and
(12:36):
she's an active researcher on the forefront of quantum gravity.
So here is Bianca. So my name is Bianca Ditwich,
originately from Germany. Also studied in Germany and then oscillated
between the Canada and Europe a number of times and
ended up at in Canada. It's a parameter institute, a faculty.
(13:00):
All right, cool, So Bianca explained to you what loop
quantum gravity is. Yeah. I had a long conversation with
Bianca about why we need loop quantum gravity, how it
solves the problems in physics, where the current criticisms of
it are, how we could test it, and of course
then I had to ask her at the end about
black holes. Of course, because every good conversation ends in
(13:22):
a black hole literally, right, maybe at the end of
the universe, all that every conversation, everyone will ever have,
all that information will end up maybe in a black hole. Well,
what happens if you take a black hole and you
put it in a toaster oven. There's a question nobody's
ever asked, if I need to ask that a crunchy
outside of the inside will still be cold black hole temperature. Yes,
(13:46):
So what if I put a black hole in a microwave?
Then do I heat up the inside of the black hole.
That's a question I've never thought of. That's really a
fun question. All right, Well, that step us through what
Bianca explained to you, Daniel was so first of all,
I guess what is the big problem in physics? Did
that needs to be fixing? The big problem is that,
as we said earlier, we have two different basic ideas
(14:07):
about sort of how the universe works at the smallest scale,
and they start from very different places, and as you
said that they when they come together across the Atlantic,
they just don't meet. And those two ideas are quantum
mechanics and general relativity of theory Einstein's theory of gravity.
It's weird to me that there would be too so
many so different theories about the universe. You know, wouldn't
(14:29):
they all sort of meet at the at the you know,
plus and minus mathematical level. Well, you'd hope so. And
this is sort of the way physics starts. You know,
if your caveman cave woman physicist, you begin building your
model of the universe by sort of looking at all
this stuff around you, cataloging what it can do, and
then saying, can I understand all of this stuff in
as simple as possible terms? And so you're like, all right,
(14:51):
there's the thing where things fall down, there's the thing
where lightning comes from the sky. You know, there's a
thing where there's wind. And then you have a very
long list of stuff and try to boil it down
and say, oh, you know, this lightning thing is the
same as this other thing where I get zapped, and
things falling down is actually the same thing as stars
moving through the sky. There's all these moments when we
sort of shrunk the list of ideas we need to
(15:12):
explain the universe. And so you hope that as this
list gets shorter and shorter, they fit together nicely. And
that's happened a lot of time so far. Electricity is
the same thing as magnetism, and it's all part of
this other thing called the electroweak force that has happened.
But sometimes you get, you know, you get two puzzle
pieces and they just don't fit together, all right. So
maybe step remind us Daniel, what each of these theories are, Like,
(15:35):
what's the what's the easy way to describe what general
relativity is, And what's the easy way to describe what
quantum mechanics is. So general relativity is a way to
try to understand what is gravity. And remember that Newton
said gravity is things pulling on each other, things that
have mass pull on each other. So take a force, yeah, Newton,
that was the old thinking. That was the old thinking.
(15:56):
Newton thought gravity is a force, and it seems kind
of like a force. It acts like a force, like
electricity and magnetism, and he was able to write down
an equation that described how the Earth moved around the
Sun and how to move the Moon moved around the Earth,
and it works pretty well. Now, Einstein came along and
he gave us general relativity, which is a complete reconception
of how gravity works. He said, no, no, gravity is
(16:19):
not a force. Gravity is a change in the shape
of space and time itself. Like you have a blob
of mass or blob of any kind of energy density,
it changes the shape of space and that's what makes
things move in curves. Rather than moving and what feels
like a straight line to us, things moved through bent space.
It's not like a mysterious invisible force that pulls things together.
(16:43):
It's more like when things exist, they distort, they bend
the space around them, and that's why they come together. Yeah.
And it's a beautiful idea and it's been tested exilient
ways and it works. It describes very tiny deviations in
Mercury's orbit. It describes how light bends around the Moon
during an eclipse. Big stuff, big stuff, Yeah, really thoroughly
(17:06):
extensively tested. It predicted gravitational waves, which we've actually seen
black holes to right and black holes. Yeah. And and
the thing to understand the things that that's going to
be make it in conflict with quantum mechanics is that
it's a classical theory meeting that it assumes that, like
you can describe everything perfectly, that everything has a position
(17:26):
and a direction and a location, right, and that the
space is operating in is smooth, Like you can subdivide
space as many times as you want between me and you.
There's an infinite possible locations for like a ball that
we're throwing back and forth. That's Einstein's vision of space. Right,
it assumes that everything is kind of smooth and continuous,
(17:49):
and there there are no bumps in the universe at
the microscopic level. That's right. You can zoom in forever
according to Einstein and general relativity, and things still stay
smooth and and everything has a fixed location. Right, the
ball is somewhere and space and time makes some sense.
There's no uncertainty or or weird or weirdness. That's right.
The world can be known, everything can be determined according
(18:12):
to general relativity. But then you have quantum mechanics, that's right.
And then on the other hand, building from the other
side of the ocean, you know, the toaster side of
the ocean instead of the microwave side of the ocean.
Um completely mixing metaphors, there is quantum mechanics. And quantum mechanics,
of course developed in the early part of this century
to explain some things that didn't make sense, some experiments
(18:32):
we saw which just could not be described using a
classical understanding of electromagnetism. It was really what was light
that gave us the first clues. We did a whole
podcast episode about the photoelectric effect and how we know,
the photon is a thing, and they did these experiments
that just didn't make sense unless you thought of light
as being made of tiny little packets of energy rather
(18:55):
than a smooth, continuous beam. You had to think about
it as these tiny packets. When you zoom in, things
don't behave nice and smooth and continuous there are sort
of lumpy and clumpy. Yeah, And there were also just
some problems with the theory, like there's a kind of
radiation in the universe called black body radiation, which is
just how things glow, Like everything in the universe has
(19:16):
a temperature and it glows with that temperature, and quantum
mechanics predicted that well. Classical theory electromagnetism predicted a certain spectrum,
like if you're this temperature, you should glow with this color.
If you're that temperature, you should glow with that other color.
The problem was that it predicted that for certain temperatures
you should glow at a crazy nonsensical color, like if
(19:37):
you get an infinite amount of radiation. The original theory,
the one before quantum mechanics, said that things that certain
temperatures should have an infinite amount of light at very
very low wavelengths, right, it really really sort of it's
called ultra violet light, and that they should have like
a ridiculous amount of infinite amount of ultra violet light,
which is nonsensical. So you can do an ex perament
(20:00):
basically that proves that general relativity doesn't work for all cases. Well,
you can do an experiment that proves that the old
theory of electricity and magnetism doesn't work. And we knew
that didn't work. We're like, okay, this theory is making
a prediction that just doesn't make sense. But if you
add quantum mechanics to it, quantum mechanics says, oh, that's
just because light is not continuous. If you make light
(20:22):
into chunks, then if you predict that, you don't see
this crazy behavior. And that's in fact what we saw
in nature. And so we needed to sort of change
the theory. The theory gave nonsensical results. I mean, I
have to add this bit to it to say bit
that says, okay, well there's a minimum size to a photon,
and that solved that problem. It said, okay, now you
can make realistic predictions. And so but the thing to
(20:44):
understand is that like quantum mechanics changes also the way
we think about the universe, right, it says things are uncertain,
things are fluctuating. This is like crazy randomness the heart
of the universe. All right. So those are the two
two big titans in physics theories, right, general activity and
quantum mechanics to try to explain the universe. And the
problem is that they don't play well together. So let's
(21:06):
get into a little bit of why they don't play
well together and whether this idea of loop quantum gravity
can help solve that. But first let's take a quick break,
(21:28):
all right, Daniel, So general relativity and quantum mechanics don't
play well together. Is it fair to say? Is it?
Is it kind of like I'm trying to think of
an analogy. Is it kind of like microeconomics and macro economics, Like,
you know, macro economics is good for you know, big
economies and countries and and micro economics is good for
like how people make decisions, but like somehow they don't always.
(21:50):
It's weird to think about where they meet in the middle. Perhaps,
but in those two cases, one should be an extreme
case of the other. Here it's really you have a
fundamental different view of how the universe works. You know,
it's it's more like totally different kinds of art, you know,
like figurative art versus symbolic art. Like what's a better
way to describe the human experience? You know? Is that
(22:12):
through abstract splashes of color or is it by you know,
depicting the things we see in interesting juxtapositions or something.
I don't know, it's right, right, it's like a totally
lens or you know, totally set of glasses. Yes, it's
a completely different way of thinking about the world. And
people have been trying for a long time to bring
them together to say, all right, are these things in
(22:35):
conflict or can we make a consistent sort of quantum
theory of gravity that brings it all together? Right? And
so here is Bianca talking about that question. It's one
of the really big outstanding questions and physics and and
my view it really means quantum gravity should include a
new notion of space time. We have to replace it, however,
(22:56):
with something completely new we expected that which change quite
dramatically as a foundation, so physics um and get very
interesting insights into you know, the nature of space and time.
All right, So it seems like we need something totally
new here um, And so Daniel, can you explain to
me kind of what the problem is, like why can't
(23:17):
they play well together? The ones that we have. Well,
people have been trying to bring these two things together
since basically they've existed. You know, people have been working
on making gravity into a quantum theory for a very
very long time. But you know, quantum theories traditionally thinking
about forces very differently than gravity does. They think about
forces is like ripples in a quantum field. You know,
(23:38):
you have like the electromagnetic field, and you think about
how do photons communicate the electromagnetic field. There are ripples
in this electromagnetic field, and you quantize those ripples. That's
how quantum mechanics thinks about forces. But in general, relativity
of force is really more like a bending out space.
That's right, And mostly you can do this. You can say, like,
all right, well, can I make a quantum theory of gravity?
(24:00):
Can I build a theory where I exchange where gravity
is a field and it has ripples and those ripples
are quantized, just like I can for electromagnetism, And mostly
you can, actually you can. It's mostly it works, but
it fails in some moments. Couldn't you just have quantum
fields in a general relativity you know world? You know, like,
(24:21):
couldn't you have quantum particles that bend space as well?
Like why can't I a quantum particle also bend space
like a planet? Well, but then gravity is coming from
something that's classical, that's smooth and continuous, and general relativity
is just not a quantum theory, right, Like it assumes
that you know everything about the location and the time
(24:43):
and the position. What couldn't you just make the bending
also kind of uncertain? I'm just trying to figure out
why why you can't marry the two, you know, why
can't these particles and these fields exist in a world
that is as Einstein envisioned with the bending and the
gravity that's exactly what Looke gravity is? Or hey, you
just basically invented the idea prize right now, Thank you
(25:07):
very much. That's right, And you know this other idea
that like, let's take the gravitational field and think about
as a quantum field that mostly works. The important thing
to understand is that it only fails when gravity gets
really really strong, right, things like inside a black hole,
and what happens is that it makes nonsense predictions like
(25:28):
it just like we saw for the black body radiation.
It predicts like infinite amount of energy will be released,
but we know that's not true. We know it doesn't happen.
And so the theories work except in extreme circumstances. And
that's what makes it really hard, is like it's easy
to fix the theory when you can see it breaking.
But these theories general relativity and quantum mechanics, they only
(25:49):
disagree about like what happens in the inside of a
black hole, and we can't see that. Why don't we
just like nor black hole? If we just like nor
black holes in the universe, wouldn't that make our there's
a lot wouldn't that make physics a little bit easier,
you know, because it's all it seems like it seems
like everything breaks in a black hole, and so why
don't It's like, you know, the mess in my closet.
(26:10):
Let's just ignore it's the engineering, you man, that's the engineering.
The scientist in me is desperate to know. You have
to know inside a black hole. Yes, if you have,
you created a black hole in your closet, because if
so I'm coming over and I want to check it out.
I think we're close to the singularity. To be honest,
in there, you don't want to go in there that
you may never come out like you have all these
(26:30):
rejected toaster microwave prototypes in there, that's right, all these
rejected app ideas as well. And so these two things
aren't working together. Well. People have tried, but they just
give nonsense predictions like the calculations you get suggested, you know,
infinite amount of energy in a radiated inside a black
hole when gravity gets really strong, And we can't easily
(26:52):
test that because we don't have a black hole and
and I don't have a galaxy sized particle collider. I
would need to create the sort of energy density in
order to break quantum gravity. And so what we need
is we need to see inside a black hole, or
we need a new idea, and so we need Jorge's
vision of quantum gravity. I have an idea. How about
something called loop quantum gravity. That's such a great name too.
(27:17):
All right, So we have these two fourth theories, and
you know, one of them has an h thunderbolt cable
connector and the other side is a mini USB cable connector,
and so they don't fit. And so that's what this
idea of loop quantum gravity is. It's like, maybe it's
like an adapter. That is it like an adapter that
makes it to work or is it a totally new
cabling system. Yeah, it says instead of trying to think
(27:40):
of gravity is like a Newtonian gravity as a force
um and and and quantizing that gravitational field directly. Instead
take Jorges idea, which is just takes space itself and
quantize that and say, well, maybe general relativity is basically right,
except that instead of working on a smooth continue in
US space, we work on a space that is quantized,
(28:03):
like there are pixels of space instead of space being
infinite and smooth, they are like little chunks of space.
It would explain how quantum particles move, or it would
explain how gravity can be quantized. It would allow us
to build a theory of quantum gravity that doesn't make
nonsense predictions, because it basically makes the places where those
(28:25):
predictions get nonsense impossible, like the predictions of quantum gravity
breakdown really high energies and really small distances. So the
idea is basically, well, what if really small distances aren't allowed,
like there's just nothing smaller than ten of the minus
thirty five where things break down, then there isn't the problem.
Let's just ignore the closet and assume that the closet
(28:48):
is QUANTIEDA it's just one thing, I see. Yeah, it's
it's not ignoring the closet. It's saying the closet doesn't exist.
You were so worried about the closet. It turns out
it's impossible. There is no clause it. But it sounds
like you're trying to make gravity quantized. You're not trying
to make quantum things the bendy like space. Well, if
(29:09):
space is bendy and quantized, then you quantum things move
through quantizes bend bendy space. So this would allow you
to bend space in a quantized way. Yeah, it would
allow you to bend space in a quantized way. And
it's it's kind of a beautiful idea because it's very
similar to the origin of quantum mechanics itself. Right, we
solve the problem of black body radiation, of this thermal
(29:31):
emission giving crazy numbers by saying, oh, maybe we can
just um quantize photons and that mathematically solves that problem. Here,
we're solving the problem of infinite emissions inside black holes
and really high energies and small distances by saying, oh,
maybe we quantize space, and so those small distances are impossible.
So there's there's a beautiful sort of analogy there to
(29:52):
previous structures of solutions that suggests like tensively like, oh,
maybe this is the right track because it feels like
nineteen fifteen a little bit. That's right. We're gonna party
like it's people are growing mustaches and wearing top hats,
and you're like, I like it. I like it, except
for the fact that like, no women are allowed to
(30:12):
do physics. That's the bad part, all right. So the
idea is that maybe space and time itself like space
and time like there are no there's no there's no
infinite as at least small second. That's right, And that's
a question people have been sending me over email many times.
If you quantize space, you also quantize time. And you know,
(30:33):
space time is a fabric in this theory and they're
deeply connected, and so if you're quantizing space, then yes,
you're also probably quantizing time. Well, it's like you're there's
actually a ticking clock to the universe. Maybe, yeah, there's
a minimum time that makes sense. You know, you can't
infinitely divide a second into arbitrarily tiny slices. There's a
minimum of time below which makes no sense. Okay, And
(30:56):
so what does that mean? I guess space is not
really like space. Space is more like a clump of
little spaces. Well, the reason it's called loop quantum gravity
is that the way to think about it is that
space is a bunch of these loops and they're sort
of woven together. And so think about spaces like chain mail.
If you're into D and D. You know, it's like
(31:18):
a bunch of links that are all connected to each other.
And space comes out of that, right spaces, There are
these The fundamental thing in the universe are these little loops,
and the loops are woven together. And the way that
things move through space, and the way that gravity happens
is how these little loops interact with each other and
pull on each other and are built together. To what
(31:40):
are these little loops? They're like little bits of the universe.
That's the next Nobel prize, man, you want to win
two Nobel prizes in a single podcast, in a single
let's do you have enough for this to be a physicist?
For the what do you call the hat the hat trick?
A hat trick? You're gonna go for three Nobel prizes.
That's when you get fifteen minutes off, Daniel, Let's do
(32:00):
it when you invent the perfect toaster microwave combination, that
definitely is worth a novel prize. Well, nobody knows what
these loops are, and you know that's sort of the
next question, Like if you can start from these loops
and build a theory that describes everything and predicts the
universe and it is consistent with everything we know, then
the next question is you're like, well, why these little loops?
(32:21):
What do they mean? How do we get those little
loops right? Where do they come from? Do they emerge
from something deeper? You know, physicists are great at making
answers that create more questions. But I guess why call
them loops? Are they actually like little rings that are
tied together? What does that? Why not call them I
don't know, bubbles or uh pixels or you know what
(32:42):
I mean? Like, what is it about the idea of
a loop that gives it the name loop quantum gravity. Well,
I guess bubbles would work also, But I think it's
just a visualization idea. You know that these things are
linked together um and it's sort of a mesh, and
you know there are also loops, like we're doing calculations
around in a circle. You have to avoid a sort
of trap, Like you can't think about these as loops
(33:03):
in space. They're not like um circles on some axis, right,
because when you have what is that access, we're talking
about the very nature of space itself. It's not like
these loops are somewhere and like this loop is at
this point in that loop is at that point. The
loops are the points like space is these this thing
we're talking about like the nature of space itself, which
(33:26):
is really hard to sort of wrap your mind around. Oh,
I see you. You were just looking at you guys
were just looking for like a word that implies that
space is made up of little things that are kind
of interconnected or overlapping, right, or like hooked together. M
m okay. And so you went with them loops. I
was like loops. They went with loops. I think it's
(33:48):
not a terrible idea, you know, they could have called
it the bubble quantum gravity, but hear it. But you know,
we talked about this another time in the podcast. You
can think of these things as little bubbles, and then
you get to talk about things like space foam and
quantum foam because these loops aren't fixed, right, they can
like fluctuate in and out of existence. I see. So
(34:08):
these are all related ideas loop quantum gravity, space foam,
quantum foam. They're all sort of coming at this idea
of a bubbly space and thinking about space not as
continuous and smooth but made up of little quantized bits,
like let's quantize space itself because general relativity is an
attempt to understand gravity in terms of the nature of space.
(34:31):
And so if we're gonna get a quantum theory of gravity,
the idea is, let's let's just quantize space itself, all right.
So that's quantum loop or loop quantum gravity, and so
we'll get into what are some of the open questions
and why people think it may or may not be
the ultimate answer to how the universe works. But first
let's take a quick break. Okay, Daniel, what does it
(35:04):
all mean? What does loop quantum gravity mean? If it's
true or if it's not true, and why do we
think it might not be true? All right, well here's
the big letdown. Right, So, so far it seems like
you're gonna break the loop. I'm gonna break the loop. Yeah.
It seems like a beautiful idea. It seems really promising.
It seems like dot dot dot the next obvious step
in physics. Right. The problem is there's a lot of
(35:27):
problems with it, and there's a lot of open questions.
And that doesn't mean it's not gonna work. It just
means it's far from clear that it is going to work. Well,
I see, there's a room for us skepticism. Yeah, and
even among physicists there's a lot of skepticism about loop
quantum gravity. It's a bit of a fringe theory. There
are a lot more people working, for example, on string theory,
(35:47):
which is a completely different attempt to unify gravity and
quantum mechanics and all of the other forces all at once.
String theories like a theory of everything, where loop quantum
gravity is like, let's just focus on make in gravity
of quantum theory. If you can do that, then that's
another way to unify these two big theories. Yeah, the
string theory is sort of a The other idea is
(36:09):
that the opponent of Looke quantum gravity, let's build a
tunnel under the Atlantic instead of trying to make these
two bridges work. And the string theory is a much
bigger community, has a lot more people working on it,
people are sort of more excited about it, whereas Looke
quantum gravity is like, you know, the younger sibling in
terms of theories of quantum the underdog exactly making me
(36:30):
like it more now, And one reason is that it
sort of hasn't yet delivered on its promise. Like, what
you want to do is start from this concept of
loops and from it should emerge Einstein's theory of relativity.
You should be like, I'm gonna have a completely different
picture of the world, but it's going to give the
same predictions sort of at my scale. I should still
(36:51):
describe how a ball flies over my neighbor's wall, and
how and gravitational waves and all of that stuff. You
should be able to sort of are from there and
build up to general relativity. You start off imagining the
world the universe is a mesh of of loops, but
it doesn't give you baseballs and fences. Yeah, not yet.
And it's not like they can't do it. It's just like,
(37:13):
well they haven't quite figured it out yet, and it's hard,
right this is are difficult things, and people are hacking
with their machetes through the jungle of mathematics that's involved,
and it's not always clear that we have the right tools,
and sometimes progress is paused for like a decade or
thirty years until somebody's like, hey, we've heard this new
idea from mathematics. Turns out that's exactly what we need
(37:35):
over here. That kind of thing has happened in physics
at a lot of times. And there are other sort
of really interesting problems with loop quantum gravity, which actually
conflict with relativity. Okay, so there's maybe something fundamentally wrong here,
you know, or not necessarily wrong, but it would again
change the way we think about the universe. Like, here's
the problem with quantizing space. Says there are space pixels, right,
(37:57):
that means that in some sense there's a minimum distance
to the universe. But what is that distance? Because we
know that distances depend on velocities, right, Like as you
move faster, things get shrunk, so do things that are
moving see smaller space pixels than things that are stationary,
And if so, it would mean that there is some
(38:19):
sort of absolute velocity to the universe. Right, if you
can measure your space pixel the size of your space pixels,
that tells you sort of what your absolute speed is.
But special relativity has always told us velocity is relative.
There is no absolute frame, and so this is sort
of conflict with a really really core concept and special relativity.
(38:40):
Couldn't it be like the speed of light, which like
it always looks the same no matter how fast you're going.
Couldn't these loops always look the same no matter how
fast you're going. Yeah, So there's a lot of ways
to try to solve this problem. One is to say,
you know, we have these weird space pixels which to
form under certain circumstances, and there's some very complicated mathematics
involved to do essentially what you just described. You're really
(39:02):
hidden out of the park today with like going for
the hat track here, wait wait till you see why
what I pull out at the last five minutes. And
the other is to accept it and to say, you
know what, maybe there is maybe there is an absolute
reference frame. Maybe special relativity is slightly wrong, But wouldn't
that throw the whole light speed thing off. Well, not
(39:25):
all of special relativity has to be wrong. The consequence
would be that light would travel at a slightly different
speed as a function of its frequency. So like high
frequency light would travel that is slightly different speed from
lower frequency light like X rays and UV light would
move faster than radio waves. But it'd be a really
(39:46):
small difference to be really hard to tell, all right,
So there's some skepticism or I guess some open questions
about it, because it's not quite hitting it out of
the ballpark, over your fence or not into your neighbors
house or not um And so I guess the question
is what does it all mean? I mean, what if
it happens to be true? And how are we even
(40:07):
going to know of something like this is true? Yeah,
so of course the deep question I have is what
does this mean for the nature of the universe? And
how could we see it? Right? Where would it manifest itself?
And as we talked about at the beginning of the episode,
the place this would really be important, the place you
would notice at difference, the place where it matters is
inside a black hole of course, of course, right, so
(40:29):
let's go there, Let's go into the closet there. That's right,
we're opening the closet and all who knows what's in
there and who knows what's been growing? And so I
asked Bianca the professor, because she thinks about this stuff, right,
she thinks about what happens inside black holes when gravity
gets really strong and space gets twisty. And I asked her, like,
(40:50):
what is your mental image of inside a black hole?
Because I want to know, right, I mean, there's a
black hole in her mind at least, and I want
to know what does it look like inside her mind?
Effects will be only important very near the singularity. There,
the space and coviatures really getting very large. And maybe
I'd like to think that there's a new universe which
(41:13):
opens up with each singularity, which gives us much more
universes than we know of. Yeah, she went there, she
went for there are new universes inside black holes. I
love it. There's a new universe in my closet. I
would believe that. And inside that closet there are other
closets with other closets inside them, I meaning meaning that's
(41:35):
kind of a consequence of quantum blue gravity is that
when you get to these extreme singularities, these loops kind
of what like open up or you know, become their
own little universes. Is that the idea, I will not
pretend to even understand what that means, because there's some
crazy consequences that like, if there's a universe inside every
(41:55):
black hole, is our universe inside a black hole? You know,
maybe who knows? It's crazy stuff? Yes, is your answer.
I go with the s and that's my third Nobel
Prize claim. Or is that the conclusion to your pitch
or your loop quantum gravity sitcom episode there Echo at
(42:16):
the end of season twenty, it turns out they're all
in a black hole. That's right, And you know, we
might be able to figure this out in ways other
than going to a black hole. We actually do have
ideas for how you could test this, and they revolve
around seeing whether we can tell the difference in the
speed of light from high frequency and low frequency light.
The speed of light changes, which we didn't think it did,
(42:39):
but if it changes with frequency, then that's an indication
maybe there's something loopy going on. Yeah, maybe there's something
loopy going on, And this would be a really small effect.
So what you need to do is like have a
race between photons of different frequencies high frequency versus low frequency,
and the race would have to be super long because
light goes super past of course, and it's different is
(43:00):
really small. And so what they do is they look
for light sources that are really really far away and
then try to measure see if there's a difference in
like the arrival time of photons. Would you would I
need to know where they're coming from, right, Yeah, So
we have these sources which are variable, like quasars and
pulsars that are really far away. You know, they pulse,
and so you can sort of line the two up
(43:21):
and say, well, we know these two were emitted at
the same moment because they are the top of the
pulse at the same time or something. And then you
can say, well, did they arrive in sync or are
they sort of out of sync? And so there's a
satellite which looked out and measured this and looked for this.
What did they find, Well, this is the integral satellite.
And that's some tortured acronym for I don't even know
what is it. Really, It's called integral up and what
(43:44):
they found they didn't see anything, right, They didn't see
any difference in the arrival times. I didn't see any loops.
And they were able to say that if there are loops,
they're smaller than ten to the minus forty eight meters.
What they can do that, that's by looking at two photons. Yeah,
by looking at these photons, because the photons come from
(44:05):
really really far away, and so the differences would be
added up across the universe. And they claim they should
have seen them. They saw that they were in sync.
They were in sync. Yeah, and this is thirteen orders
of magnitudes smaller than what we think the size of
the loops are. So like that seems pretty definitive. Yeah,
but what did the loop quantum gravity folks say, Well,
(44:26):
you know, there's only one branch of loop quantum gravity.
The people who say that maybe that's that special relativity
needs to be tweaked. Other people have solutions, as you say,
to make light travel the same speed no matter what,
by having you know, crazy deformations these things, and all
sorts of complicated interactions between light and space, and so
it just sort of rules out one branch of loop
(44:48):
quantum gravity. You can never kill these theories. Man, They're
like weeds. They always there's another version that crops up there,
like exide one head of But they're fascinating, you know.
Each one is a wonderful exploration and sort of the
intellectual space of like how could the universe work? What
possible universes might we live in? And the amazing thing
(45:10):
is that there is an answer, right, there is one
way that the universe actually works. And what's kind of
interesting I think is that it wouldn't affect your everyday life,
like things would still work the same way. But who
knows what's going on down at the fundamental level? Right,
it could be one of these crazy theoretical ideas. Yeah,
and it's important now to scientists, but it might eventually
(45:31):
be important to engineers. You know, knowledge that seems impractical
and useless but reveals the fundamental nature of reality could
eventually be useful and hate to me, that's fun anyway.
I don't really care if it's useful. I just gotta know, right, Yeah,
I mean I think that's how micro rays were invented,
actually by accident, by looking at something else. And where
(45:52):
would we be? Where would burritas be these days? That's right.
And you know, there have been actually fascinating advances in
microwave and the technology the engineer ring of microwaves. And
I guess, you know, if you can unlock kind of
the magic and the power that's happening at that microscopic level,
who knows what you could do, right, what kind of
energies you can get, or what kinds of warp drives
(46:13):
or microwave ovens. Yeah, microwave toaster opens powered by artificial intelligence. Yeah,
And so I have to give a shout out to Nico.
He's one of our listeners and he heard our episode
about microwave ovens actually, and he wrote to me and
told me that they have a new fancier AI powered
microwave oven um which can heat stuff up at different
(46:35):
temperatures and monitor to make sure the heating is all
smooth and fancy, and actually dropped by my house and
delivered one of these prototypes, which has been a lot
of fun. That's amazing that you let one of your
listeners into your house. Hey, he was offering a brand
new appliance, so I thought. And while he was there,
I asked him about Luke quantum gravity, but he didn't
have any ideas. Oh man, there's no setting on that
(46:56):
in the microwave, not yet. Um. The next in the
prototype will be quantum gravity powered, I'm sure. All right, Well,
it sounds like the answer is stay tuned. You know,
that's what we explain, what Luke. Quantum gravity is and
who knows, and maybe it is the way that the
universe works at that level, and we may find out
in the near future. That's right, And these are the
(47:17):
kinds of mysteries that are going to help us figure
out the deep nature of the universe. You know. It's
when things break that we have an opportunity to figure
out how things should work. And so it's exciting to
have these kind of problems. It's exciting to know sort
of where to work, even if we don't know what
the answer should look like. All right, well, we hope
you enjoyed that. Daniel. How much this podcast costs me
in terms of your physics time? One loop one? Let's
(47:42):
tend to the minus thirty five dollars, My tend to
the minus thirty one plank dollar? Yeah, pick up plank dollar.
Oh good, I gotta I got a couple here in
my pocket. Okay. Quantum of the mover to me all right.
We hope you enjoyed that. Thanks for joining us, and
as usual, thank you to everybody who wrote in with
your questions. See you next time. Before you still have
(48:09):
a question after listening to all these explanations, please drop
us the line. We'd love to hear from you. You
can find us on Facebook, Twitter, and Instagram at Daniel
and Jorge That's one Word, or email us at Feedback
at Daniel and Jorge dot com. Thanks for listening and
remember that Daniel and Jorge Explain the Universe is a
production of I Heart Radio. For more podcast from my
(48:31):
Heart Radio, visit the i Heart Radio, a Apple Podcasts,
or wherever you listen to your favorite shows.
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Daniel Whiteson
Kelly Weinersmith
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