November 12, 2019 • 42 mins
With vast distances between habitable planets how will we eventually communicate with aliens?
Learn more about your ad-choices at https://www.iheartpodcastnetwork.com
See omnystudio.com/listener for privacy information.
Mark as Played
Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:08):
Hey, Daniel, I have a question for you that you
might not like. Oh, what is it? It's about aliens,
your favorite topic. I love it already. What is it? Okay? So,
if we can't send messages faster than light, right, all
the other planets are light years away, wouldn't any communication
or messages exchanged with aliens take years or decades? Ah,
(00:32):
you're right, I don't like that question. Hi. I'm or Hamming,
cartoonists and the creator of PhD comics. Hi. I'm Daniel.
(00:56):
I'm a particle physicist and the co author of our
book We Have No Idea, a guide to the Unknown
Universe that tells you all the things we don't know
about the universe. Yeah. It's a great book, which also
functions as a nice quantum banana stand or in anything
stand really, once you're done reading it. It's multi purpose.
You could buy thousands of copies and build a house
(01:16):
out of them. But welcome to our podcast, Daniel and
Jorge Explain the Universe, a production of My Heart Radio
in which we try to find amazing and crazy and
fascinating things about our universe and explain them to you.
We want to take you to the cutting edge of
science and break it down so that you have a
working understanding of it. Science is not something meant just
for a few people in an ivory tower. Sciences by
(01:38):
the people of the people and for the people. That's right.
It's a constitutional right to know your science and to
have physicists explained it to you. That's right. It doesn't
make it democratic, but it should be accessible. Do you
think is physics governed by democratic principles? Daniel? Maybe awesome
if we could change the laws of the universe by
(01:59):
voting on it, like he who wants to have faster
and light travel me, and we all vote on it,
and then it's possible. That would be pretty awesome, And
the universe has to follow the rules. Hey, if it's
a democracy, right, then we could like amend the laws
of physics. Right well, if if our government is any
indication that I think would be in deep trouble, I
think Mitch McConnell would stand in the way of any
(02:19):
uh any revolution we want in the laws of physics. Yeah,
I think would probably splinter into different universes. That's right.
I would have people arguing for these set of laws
and other people saying no, we want this to be possible.
Maybe we should not wish to have that kind of power. Yeah, yeah,
let's take to the undemocratic universe in which we actually
live in the dictatorial um quantum universe. That's right. So yeah,
(02:43):
so today on the program, we'll be talking about a
problem that a lot of people see if we ever
do find other life in the universe, right, Yeah, there
are certain things about the laws of physics which are
fascinating but also frustrating that put limits on us. And
you know, if we did find aliens, even in one
(03:03):
of the nearby stars that are light years and light
years away, it would be difficult to have a conversation
with them because light or anything else takes years to
get there in years to get back. Yeah, it would
be a really awkward conversation. Right, You'd be like, hey,
how's it going, and then you have to wait twenty
years or more maybe to get an answer that says
(03:24):
pretty good you they have like a revolution since then,
or have evolved into something else or whatever. How do
you have a conversation? Yeah, you might not even be alive, right, Like,
if we talked, we're trying to talk to another civilization
that's a hundred light years away, it would take two
hundred years to get a response, just to get a response,
and then imagine what that conversation would be like. You know,
(03:47):
the first statements of that conversation would be like, huh,
what were you? Wait? Can you hear me? Is this
being on? You know that's a thousand years right there,
you know, just to decode our language to right? Would
it would be kind of awkward? Would be like talking
to my nine year old right like, hey, can you
pick up your shoes? Hey? Can you pick up your shoes?
Twenty years later? Would be like what it would be
(04:09):
like having any video conferencing meeting. You know, the first
ten minutes of every video conferencing meeting between humans who
speak the same language, use the same technology. It's still
I can't hear you? What what was that? No, this
is not working, like the ultimate nightmare conference call, wouldn't it?
We would waste years just to say you're on speaker
phone or you're muted, or sorry I thought I was muted,
(04:33):
or hey, you're in the bathroom and you're not muted, right,
Although actually I would like to hear what it's as
sound like when the alien goes to the bathroom. Oh really,
that would be your opening question. No, but if that's
if that audio was just delivered to me somehow, Yeah,
I would like to hear that. That would be fascinating.
What if that's the only thing we ever learned about
aliens is that they accidentally but dialed us when they
(04:55):
were in the bathroom and we got to hear it.
I see you, assuming they have a butt, or they
might only they have m I'd have multiple buds. You
don't know. So many questions could be answered by that
accidental phone call. Yeah, you might get like two separate
calls on your phone. But hey, your left button your right,
but are both calling me? I gotta go? And maybe
(05:17):
they must have a whole different call waiting system depending
on the number of butts they have. But you know,
this is a fun topic to explore, But I read
a lot of science fiction, and in science fiction they
often have this same problem. Like, let's say it's a
million years in the future and humans have colonized the
galaxy and have a galaxy spanning empire. How do you
even govern an empire if it takes a thousand years
(05:39):
to send a message from one side of it to
the other, Right, Like, if you think about it. One
fact that always blows my mind is that the United States,
it's only like two fifty years old or less. So
imagine having a conversation in between the declaration of independence
and now it's a whole different country. Absolutely, it's a
(06:00):
whole different country. And I think there's also something interesting there.
I think something about the size of nations was determined
basically by the speed of information transit at the time
that you know, nation states came to be. And the
reason we don't have globe spanning empires might also be
because we didn't have instantaneous communication until fairly recently. Oh,
(06:21):
I see, like your furthest calling. You could be like, hey,
I am peace out, I'm leaving, and by the time
you get the message and say no way, dude, they're gone.
Tighter coordination between the UK and the American colonies might
have prevented the American Revolution, right, and England could still
be a globe spanning empire anyway. That's um ridiculous speculation
on a topic I have no expertise in. But that's
(06:44):
a that's a different topic. That's uh. Dano and j
confuse History another production of I Heart Radio. That's right,
but I think this is a really interesting one. And
in those books and science fiction novels, they often try
to avoid this problem them by inventing some way for
these people to communicate faster than light. They have some
(07:05):
clever ways, some telephone that communicates instantly from galaxy to
galaxy or even inside the galaxy's so that they can
talk to their subjects and their political connections and a
reasonable time, right, so that each page of the science
fiction story, it doesn't go two hundred years later or
it's like three next thing, Bob's great grant. If you
(07:26):
answered the phone, it says, what who's Who's this phone?
It wouldnt be a fun thing to get in the
wheel from your grandpa, Like, hey, I put a call
into some aliens. If you they call back. This is
what I wanted to know. Here's the conversation tree I started. Yeah, exactly,
but yeah, it's it's a big problem with the idea
(07:49):
of a connected universe. I think, right, like you can
imagine a galactic empire or you know, just getting to
know our neighbors. It would be a problem. It would
be a problem. And in a lot of these science
fiction novels and they try to solve this problem by
sort of painting over it with a magic phrase and said, well,
you know, maybe scientists in the future have figured out
(08:09):
where to use. Here, I'm doing air quotes quantum entanglement,
and that just sort of solves the problem. That's a
popular solution in science fiction to this problem. Yes, exactly,
quantum entanglement. Quantum entanglement sort of solves the problem of
faster and light communication. All right, So then today we're
going to answer the question can we use quantum entanglement
(08:35):
to send messages faster than light? Because I would love
to talk to the aliens more rapidly. I would love
to download their physics library and not have to take
a billion years. And so I want this to be true.
I want us to be able to send messages fast
and like using quantum entanglement or anything. Well, I think,
like any any phrase in science fiction, just put the
word quantum in it, and it sounds both magical and plausible.
(08:58):
Do you think that's going to be true for ever? Like,
won't that trope get tired? Won't people to be like yawn? Quantum?
The new thing is I don't know what is the
new thing? Dark matter, dark quantum, nous dark matter. Oh
my gosh, you're right, and there is even that novel.
Have you read that novel called dark Matter by Blake Crouch? No,
I haven't, very popular. I think was the best seller.
It's actually about quantum mechanics. But the title of it
(09:21):
is dark Matter, which is very confusing and has nothing
to do with dark matter except I think that dark
matter is a sexy, buzz worded physics that they were
there him or his agent or his publishing house we're
trying to latch onto. Well there you go. That should
be the title of our next book, dark Quantum, Dark Quantum, Yeah, exactly.
Maybe we can use dark matter for faster than light
communication Quantum after hours cinemas dark Matterez. Well, anyways, um, Yeah,
(09:50):
the idea is like in science fiction, can we actually
use quantum, this idea of quantum entanglement to send messages
faster than light? And so, as usual, we were wondering
if anyone had even heard of flantum entanglement or how
to pronounce it, or whether it could it could even
be used to send messages faster than light. So, as usual,
(10:11):
I walked around the campus have you see Irvine? And
I was grateful as always that they were willing to
answer a random question about a random topic. And so,
before you hear these answers, think to yourself, do you
think quantum entanglement can be used to send messages across
the universe faster than the speed of light? Here's what
people had to say. I don't know enough to answer
that question. I don't know now, I have not I
(10:35):
don't know, but I hope he can. I'm not sorry, No,
I'm not I do know what that is to do. Yeah,
do you think it can be used to send messages
faster than the speed of light? That is correct? Do
you think you can? So what do you think of
those answers? Jorge? All right, Well, I think they're probably
pretty common answers. And I don't think up until a
couple of years ago, I would have known what quantum
(10:55):
entanglement was. Yeah, a lot of people have never heard
of it. Um though, why guy was like, Oh, yeah,
that's in this guy's company. This Wow? What does he
know that we don't know? I don't know. I didn't
spend it time to dig into it with him. Was
he an alien? Possibly? Probably? Oh my gosh, I met
(11:18):
an alien. I didn't even realize it. After rewind back
in time, remember what that person looked like if you
can rewind back in time, Daniel, that's what do you know?
I just used my quantum tango particles, right, that's everbody
science fiction problems, dark quantum phone, quantum foam perfect. I
(11:38):
think that is the perfect blend of buzzwords right there.
That solves any problem. There you go. I'm gonna suggest
that to my students next time, the every research problem.
Have you tried dark quantum foam. Many people haven't even
heard of quantum entanglement, much less the idea of using
it to talk over long distances. It's a topic that's
actually decades old, but I think only recently has it
entered any sort of the edges of the cultural ZiT guy, well,
(12:00):
I think I remember a couple of a year or
two ago there was a big news item saying that
um scientists had finally teleported something and they use quantum
entanglement it. Yeah, there was some very misleading science headlines
about how scientists teleported something into space. But yeah, they
hadn't actually leading headlines misleading science headlines. No, that was
(12:22):
I wanted you to click on it. That's sweet. Yeah,
they had used quantum entanglement. And we did a whole
episode actually about teleportation whether it's possible. And there is
one aspect of teleportation which is possible, which is teleporting
a quantum state. That is saying, here, we have some
particles and a quantum arrangement over here. Can we make
other particles not the same particles, other particles had the
(12:45):
same state over there. It's sort of like, uh, you know,
um copying something. It's like emailing something to somebody else,
but doing emailing a quantum state, and to do that
you do need to have quantum entanglement. Yes, quantum factsing.
That is not a phrase anybody has ever said out
loud before. I think right, and I lay my stake
(13:05):
on it. Yes, Yeah, they didn't actually move anything to space.
People think when they hear teleportation that you have disappeared
some that or somewhere and reappeared it somewhere else. That's
the common understanding of teleportation, which is why the headlines
for that article were so misleading. Um. But they did
use quantum entanglement in that experiment. Quantum entanglement is a
real thing. It can be used to do some interesting science. Right,
(13:28):
it can be used to quantum facts things, for example,
which is fascinating and useful, but not faster than the
speed of light in that case. But yeah, I think
I think that would be a more better name for it,
quantum faccing, because it's not really teleporting. It's more like faccing. Yes, exactly,
that is quantum facting, and it's it's it's sort of
related to this idea of using it to communicate faster
than light. Or is that totally different than quantum teleportation? No,
(13:51):
it's different. I mean the idea of quantum entanglement is
to have two things that are far apart, but they
have some connection to each other, and can you use
that to send some information? And you can use it
to send some information, but the question is can you
use to send information faster than the speed of light?
But maybe before we dig into that, we should talk
(14:11):
about what quantum entanglement is, so everybody has a clear
sense for what that means. Yeah, let's talk about quantum entanglement. Um,
So what what is quantum entanglement? I feel like I
know the word quantum sort of which means magic, and
entanglement means that two things are kind of like intertwined
or um, you know, kind of like one of them
depends on the other. Yeah, that's exactly what it is.
(14:33):
Entanglement means that this sort of a constraint on the pair.
So I think it's simplest if you think about just
two particles. Now it can apply to other things, and
just particles that can apply to quantum fields of quantum systems.
Just to have a visual thing to hang our our
mental hats on, let's talk about, for example, two electrons.
And electrons we know have these weird quantum states, like
they can be spin up or they can be spinned down.
(14:55):
And for an individual electron, before you've looked at it,
it could be either spin up or down, and sort
of like the Shorteninger's cat in the box, until you
ask the electron, are you spin up or down? It's
sort of both. It's not determined it's fifty fifty one
or the other until you like poke it right, until
you ask the electron whether it's spinning over the right.
And we did a whole episode on quantum spin. How
(15:17):
you can measure an electron spin. You pass it through
a magnet and either goes left or goes right and
that's how you're measuring it. You require it to make
a decision about whether it's up or down so that
it can interact with an experiment you've built in a
certain way. And that's useful for thinking about individual electron.
A quantum entanglement is about pairs of electrons because sometimes
you can arrange these electrons in a special way so
(15:38):
that they're not independent. They have a constraint on them,
like they have their spins have to be opposite. For example,
if one is up, the other one has to be down.
Like you put a rule that um says that they
they're not totally independent. Yeah, Like if you sort of
two dies, they can be whatever they want to be
each one, But if you put a constraint on them,
saying they both have to add up to seven, then
(15:59):
that that's a constraint between two things exactly. Because quantum
mechanics has a lot of weirdness and a lot of fuzziness,
but there are some rules even quantum mechanics can't break,
like conservation of momentum, and spin is a kind of momentum.
And so if these electrons, for example, came from another particle,
say a photon generated an electron and opositron. That's that
(16:20):
photon has an overall spin zero for example, then the electron,
if one of them has spin up, the other one
has to be spinned down in order to conserve overall momentum.
There's spins have to add up to zero, which is
the same original amount of spin that the photon had.
So that's how you do it physically. That's how you
apply a constraint to two electrons to say, you can't
both be up and you can't both be down. If
(16:42):
one of you is up, the other one has to
be down. So you maintain your compliance with this other
law of physics, right, and you can set that rule
to whatever you want to be. Like, you could also
say they both have to be up, or they both
have to be down, or they can't both be the
same thing. It's just kind of like like a rule. Right. Yeah,
if your photon has spin one in a certain direction,
then you know that both electrons have to be spin up.
(17:02):
And if it has been um minus one, which is
the same it's been one of the other direction, then yeah,
the same thing applies. But it's most interesting when this
constraint adds up to zero, because then each electron can
be up or down, and it's the combination of the
two that has the constraint, not the individual one. So
each one is free to be up or down. But
if as soon as you know that one is up,
the other one has to be down. Okay. So that's
(17:23):
the basic idea of entanglement. It's like two particles that
have some kind of they're both quantum, so they're both
weird and fuzzy, but there's some sort of constraint between them,
some sort of rule that says that that when you
open those two electrons, they need to follow certain rules.
That's right, and the magic there is what happens if
you open just one electron, so electron A and electron B.
(17:46):
So you open the box electron A, you interact with it,
you measure it's been it's been up. Now you know
something about electron B. Right, you've measured something about electron
A and learn something about electron B. That constraint allows
you to extrappolate your knowledge of the first electron onto
the second one. That's the magic, because the two have
this constraint, and that happens sort of instantaneously. As soon
(18:08):
as you measure it on one, you know something about
the other one, even if in the meantime you've taken
that other electron and moved it a light year away.
So that's where the communication part comes in, Right, that's
where the sort of magic faster than light tempting thing
comes in. You take these two electrons, they're quantum entangled,
you move them really far apart without breaking the entanglement somehow,
(18:30):
and then when you measure something about one electron, you
learn something about something really really far away, and you've
learned something faster than light can travel. All right, well,
let's get into the details here a little bit more,
and how this was actually one of Einstein's ideas, right,
it was sort of Einstein's big backfire. So let's get
into it. But first let's take a quick break. All right,
(19:04):
we're talking about quantum entanglement and how we could use
that to talk to aliens right faster than like that's right.
We're hoping their aliens, and we're hoping we could develop
this technology based on quantum entanglement to send the messages
that aren't accidental toilet butt dials, right, using my quantum facts,
which I just invented ten minutes ago. Okay, so let
(19:25):
me see if I got this straight. Didea between quantum
entanglement is that you take two electrons or two particles
that are quantum, and you you you mix them up
so that there's some kind of rule between them, so
that then if you separate them and you open one
of them, you know something about the other, even if
it's really far away. Precisely, you've learned something about something
(19:47):
far away faster than light could get there, right you.
If you if you want to know what is the
state of electron B, rather than going there and measuring
it coming back, you can do it instantaneously by measuring
electron A, and that tells you something a about what's
happening far away. And normally in this universe, to learn
something about an object that's really far away takes time.
(20:07):
If you want to know what's happening in the star
a light year away, you need to wait a year
for that light to get here. So this seems like
a tempting way to learn things, to about things that
are far away, and maybe even to send information. That's
sort of the idea. It's made the picture a little
bit maybe, Like so I take two electrons and let's
say I make the rule that when I make the
electrons and make the rule that they both had to
(20:27):
be the same spin. Like, that's a possible rule, right,
that is a possible rule. Yes, if your photon has
spin one, then the electrons, which have spin half each
could be both having a point in the same direction
to make that original spin one. Yes, So I kind
of I entangle these two electrons and then I send
one of them to another star proxim Centauri. Yeah, And
(20:48):
I wait a while for it to get there. It
gets there, And now I opened my electron, the one
I kept, and I see that it's pointing up. You're saying, instantaneously,
without having to wait to check on the other electron,
I know that the other electron out there is also
pointing up. Precisely, you now officially understand quantum entanglement. This
is the day forever after which you are an expert
(21:11):
in quant entanglement. Congratulations, right, But I guess what I
don't know is how how you can use that for communication.
I mean, I feel like I just sent you a
package that I kind of already knew what was in it,
and before you open it, I know what's already in it.
But I'm the one who sent it, so I'm not
sure how that helps us communicate. That is the rub right,
that's exactly the issue, And but you don't exactly know
(21:32):
what's in it, right. I think in the case where
the photon has spin zero and so the electrons have
to be opposite, you don't know until you open it
which electron do you have. Do you have the one
that's beIN up or do you have the one that's
beIN down? And so you have learned something about something
that's really far away. Before you measure your close by electron,
it could be up or down, and the far away
(21:53):
electron could also be up or down. It's not determined yet.
There's still some randomness. But when you measure the spin
of the close by electron, then you instantly know the
spin of the far away electron instantly. The other way
to get that information is to let the people who
have the far away electron measure it's spin and then
tell you, But that would take time for them to
(22:14):
send you that information. So this is like a way
to instantly no information that is far away. Now, that's
not the same as communication, which requires controlling information. And
this is the part that science fiction novels never get
into how do you use quantum entanglement to send information
faster than light? They just sort of dot dot dot
(22:35):
from quantum entanglement to instantaneous communication. They never get into it.
Nobody actually knows. Nobody has worked it out. Nobody has
worked it out. I mean people have thought about it.
And you know, this font experiment came from Einstein because,
as you said before, Einstein was trying to show the
quantum mechanics was ridiculous. Einstein was trying to prove that
this new field of quantum mechanics makes no sense. So
(22:55):
he actually came up with this thought experiment, like, could
you do this in the scenario your proposed in the
quantum mechanics universe? If that was real, then you could
do this absurd thing like knowing something about something really
far away. And so he proposed this in a paper
and he said, look at this absurd outcome of your
predictions of quantum mechanics. Clearly you must reject this whole idea. Instead,
(23:16):
people were like, I could write a science fiction story
about that. No. Instead, people were like, that's a cool experiment,
let's go do it, and they did it, and it
turns out that the quantum mechanics predictions, absurd as they were,
were correct. That that's exactly what happens. What did they
prove that if you take two electrons, entangle them, and
then separate them, they're still entangled. Is that the experiment
(23:38):
they're still entangled, and that if you measure the first one,
the second one instantly collapses to being the opposite of
the first one. It collapses to to you, to to me,
but not to the person who's holding it out there. Yeah,
if you measure electron A, right, then electron B, which
can be really far away, it can be faster, it
can be far away than light can travel in the
time they can. They measure it, and they measure that
(24:01):
electron B also collapses at the same moment that electron
A collapses. That if they ask electron air you spin
up or spin down, then electron B goes from being
spin up to spin down to being either one or
the other, being the opposite of electron A. So they've
shown that this happens, that making a measurement in one
location changes the physics of the universe somewhere far away,
(24:23):
and it changes that the physics of the universe faster
than you could send information via light. It's not like
something is happening in electron A and it secretly sends
a message to electron be quick. I'm up, so you
have to be down. They've separated these particles far enough away,
like kilometers now kilometers and kilometers, so there's no way
for light to sneak that information. But what do you
(24:44):
mean it collapses on the other end, Like, but they
haven't opened it. You're saying inside the box it's in,
it's technically collapse. Or are you saying that when they
whenever they open that other box out there, they're going
to find that it's the It follows the rule. They
do open the box, and it follows the rule. Yeah. Like,
let's say I put two take two electrons, entangled them.
(25:06):
Let's say I make the rule that they both have
to be spinning the same direction. I think it's clearest
when they have to be spinning the opposite directions. Okay,
so let's have been make the rule that they have
to be spinning the opposite direction. Okay, I entangled them.
I keep one in my box and I sent the
other one to you in office Centari in a in
A box. I'm an Alpha centari. I have to go
(25:29):
to alpha centauri. I get to Alpha. Okay, I thought
you already were there. But all right, I'm an alpha
centauri with the other box. Okay, yeah, I sent you
my the B electron. I kept the A electron. I
sent you the B electron, and they're both entangled. And
now you're saying, if I opened my A electron and
(25:50):
I see that it's pointing up, I know that B
is pointing down, but you don't know that B is
pointing down to you. That's right. But I measure it
and it points down right when you measure it. But
up to the point that you measure it, you don't
know if it's pointing open down. That's right. But how
does how do they talk to each other? How do
they know that one can point up and then we
can point down. They're separated, all right. Say we make
(26:11):
our measurements at the same moment or within a bill
of second of each other. Okay, we are separated by
a light year. There's no time for for electron A
to tell electron B what decision it has made. Oh,
I see what you're saying. You're saying that my electron
my A electron the one I kept could could be
either one. It could be either one. Yes, If I
do this experiment, a lot sometimes will be up, sometimes
(26:34):
they'll be down. But the ones that it's up, then
yours will be down, and the ones that it's down,
yours will be up. Precisely, and before you measure any
of the particles, both could be up or down. They
have a fifty percent chance of being up in a
fifty percent chance of being down. When you measure electron
A to B up, then electron B a light year
(26:54):
way has to instantly change from having even odds of
being up or down to just being down. It has
to because electron A was up. But how does it
know that electron A was up. There's no way for
that information to get to electron B in time. Electron
A could have been down, forcing B to up. Electron
(27:14):
A spin could have been down, forcing B to be
spin up. Remember that both of them are undetermined until
you measure one of them, and then suddenly both are determined.
This is like you take two prisoners and you isolate
them so they don't get to talk about their story,
and you asked one you know who robbed the bank,
and you ask the other one who robbed the bank,
and their stories always agree, right, even though they could
(27:39):
have lied, either of them, either of them could have
lied exactly either what could have like either both lie
or they both not tell the truth. But some other
insane and it's physically impossible for them to communicate because
they are too far apart. When they first did these experiments,
they try to isolate the things, but they weren't actually
really that far apart. It's hard to get two quantumentango
particles actually far apart. But now they've done it. They've
(28:01):
quantum entangled particles between the surface of the Earth and
things on satellites for example. That's what that article was about,
what we're talking about earlier. They quantum entangled physics on
the Earth and physics in a satellite. Okay, so that's
the spooky thing. It's like some of the two prisoners
have their stories in sync, you know, the two White
House officials are somehow saying the same thing. How about
(28:24):
the text messages. But they never talked to each other,
and they couldn't possibly have coordinated. It couldn't. It's physically
impossible for them to coordinate. Yet somehow when electron A
collapses to up, electron B collapses to down, or the
other way around. How do I know they didn't coordinate
before I separated them. Yes, that is one of the
deepest questions about particle physics and quantum mechanics is that
(28:45):
is there a hidden variable. Maybe A wasn't actually both
up and down. Maybe there's some hidden variable there, something
that determines it forces A to be up, and so
of course B is down. It's no surprise you know
that you have half of the cake the other one.
It's the other half of the cake, because it's been
those halves the entire time. When while they were traveling
to be farther away, that's a really like they decided like, hey,
(29:06):
i'll be down, Okay, that means you have to be up,
and then they separated. You're saying, that's not that's not
what's happening. We know that's not what's happening. The explanation
for that, And I know people out there who are
desperately curious about quantum mechanics and skeptical of this. I
wanted to precisely the answer to that question because when
I was learning quantum mechanics, that's the thing I was
wondering about, how do you know there isn't some like
hidden variable, something we just haven't measured, some property the
(29:28):
electron which determines or forces want to be up in
the other one to be down. Now, the answer is
a bit frustrating. The answer is not a smoking gun.
It's a much more subtle experiment. It's called an It's
invented by a guy named Bell, and it's about measuring
the correlation between A and B. You can't prove that
there's no hidden variable for one experiment, but if you
do this over and over again and you sort of
(29:49):
rotate the spin of the electrons, you can prove that
there is no local hidden variable. It's really one of
the most beautiful and subtle pieces of physics I've ever learned.
So to show that there's no way for the two
electrons to have been determined in advance which one would
be up and which one would be down, that's what
we technically called the no local hidden variable. What Bell
(30:11):
did was used a second weird aspect of quantum mechanics
to help pin down this first weird aspect. On the
episode about spin, remember we talked about how you can't
know the spin in two directions at the same time.
It's just like how you can't know a particle's momentum
in position at the same time because of the uncertainty principle.
In the same way, measuring the spin in one direction
(30:31):
like X will re randomize the spin in the other
directions like why. So Bell used this to his advantage
to show that the spin really is randomized before it's measured.
His experiment says, you should separate the particles, but then
measure the spin in other directions, not the one that
you have this quantum mechanical entanglement constraint on. And he
(30:52):
showed that if there is a local hidden variable, it
will affect not just the constraint direction, but also the
spins you measure in other directions. If there isn't a
local hidden variable, if the electrons really are undetermined until
you measure them, then you will not affect the randomness
in the other directions. So he was able to come
up with an experiment that gives different predictions if there's
(31:15):
randomness and if there's local hidden variables. And then they
did the experiment and boom, it showed that there really
is randomness, but we should dig into it further on
a whole separate podcast episode, because it's really fascinating. They
have proven that there is no local bit of information
that could be hiding inside those boxes to determine that
one electron actually is up and the other one actually
(31:37):
is down. We know that the that there really is
uncertainty there, that the electron could really be up or
down when you've entangled them and when when you've separated them,
and that that collapses the moment you measure one of them,
even if they're really far apart. Yeah, it's kind of
like if you do the experiment a bunch of times
and you you sort of know for sure that the
two prisoners couldn't have possibly God in their story straight
(31:59):
ahead of time. There's something weird going on. There is
something weird going on. Even just doing a lot of
times doesn't satisfactory resolve that question, because there could be
a hidden variable in each case, and so doing it
many many times just reinforces that. It has to do
with having with measuring these spins along different axes and
then rotating that access and you can show that as
(32:20):
a function of that rotation, things would act differently if
there is a hidden variable, then if there isn't a
hidden variable. But again it's a bit too subtle to
get into. I think on today's podcast it involves spinning prisoners,
which we can't get into. It's right. We tried to
file for research allow us to do that, and they said, no,
that's uh, that's not that's the violent human rights in
(32:41):
humane exactly. And then I tried to say, but it's
for black matter, quantum foam telephone, and we're doing it
in a Stanford basement. It's all right, at least, no,
it wasn't approved, all right. So so that's where this
idea that you could use this for faster than light
communication is that there's something something's going on faster than light,
and so could we use that to communicate faster than light? Right,
(33:04):
that's where the idea came from. Yes, something here is
happening faster than light, and so people thought, oh, maybe
we could communicate faster than light. That's the genesis of
the idea. All right, let's get into whether it is
possible to use this for faster than light communication. But
first let's take a quick break. All right. So we
(33:34):
talked about quantum entanglement and how there is something going
on with it that's faster than light. But the question
is can we use that to talk to aliens faster
than light or to you know, Daniel, who's an alpha
centry faster than light? And so what's the answer here, Daniel?
How how could we use could we use quantum entanglement
to violate the fundamental speed limit of the universe? Well, first,
(33:58):
I want to say that I think this is a
totally good idea to investigate because there's often loopholes, you know,
we talked about on the warp Drive episode, like yeah,
you can't travel faster than light through space, but just
change your definition of what you want to do and
don't say I want to go through space, so you
want to squeeze space so you can get somewhere faster
than light would have gotten. So it's a great sort
(34:18):
of avenue for exploration to look for loopholes and try
to find ways to accomplish what you want to do
without breaking the laws of physics. But in this case
it's not gonna work. And the reason is to go
back to what you were saying before, like say you
have these two electrons, let's try to dot the lines
to say, say you have these two electrons quantum entangled
between here and alpha centauri. How would you actually use
(34:40):
that to send information? Why would you build a communication system?
Say you want to send me a bit, right, you
want to send me a zero or a one. You
know you wanna tell me whether or not the apple
pie is ready to eat? One? Is apple pie is ready? Zeros? Noops,
I burned the apple pie or something. You want to
send me some I want to give you a thumbs
up or thumbs down. Yeah, how would you do that? Well?
(35:00):
In order to do one lamp if the British are coming,
two lamps if they're coming by spaceship. In order to
do that, you have to sort of control the information
you You might be tempted to say, Okay, what I'm
gonna do is I'm gonna force my electron to be
spin up in one case. I'm gonna force it to
be spin down in the other case, because that determines
(35:22):
what happens to Daniel's electron. And sort of like twiddle
Daniel's electron from really far away by twiddling mine, that's
the tempting way to thing to go right, and twangled
entanglement connects the two electrons and you're saying, like, if
I see the British coming by sea, I'll turn my
electron down, which makes your electron turn up, And somehow
(35:44):
I talked to you faster than like that's the idea.
But that doesn't work, right, That fundamentally doesn't work. And
the reason it's pretty simple is that you can ask
the electron what state is it, but you can't force
it to be in a particular state because if you do,
it breaks the tanglement. Right, the rules of the entanglement
are that the two have to be in opposite states
(36:05):
because you're preserving the Anglar momentum of the system that
created them. There's this law of physics that requires them
to still tally up in the end to have the
same Anglar momentum as the original system. But if you
interact with one of them, then you break that because
you're adding momentum or adding Anglard momentum to the system.
You've broken that quantum system. You made a new quantum
system and that doesn't have to follow the same rules
as the original. Oh, I see, so there's communication going on,
(36:29):
but there's no So it's like there's communication going on,
but there's no talking. Going on. The two electrons somehow
are coordinating, right, there's definitely collusion happening there, but you
can't force one electron to be in a certain state,
which is what you would need to do to send
information from one to the other. No, no, Daniel, no
collusion which hunt, No elect These electrons really do colue
(36:51):
this quantum collusion. See I invented the phrase. Also, all right,
quantum collusion good luck. Yeah, but that one you both
did it and are somehow not guilty of it at
the same time. Anyway. No, the possess the frustrating is
the problem is that this quantum entanglement thing really is real,
and it really does happen, and there is something weird
(37:12):
and fashion light happening, but we can't use it to
send information because you touch one of them, you basically
break the magic. Right. It's like, we can both learn
what each other has faster than light, but I can't
tell you about what. I can't tell you anything. We
just both learned faster than light. Precisely, we learn, we
learn about each other, but what we have, but we
(37:35):
can't tell each other something. Yeah, you're like, okay, I
did sent Daniel to Alpha Centauri he spent five years
of his life getting there, and now I know which
electronic has. Okay, what does that do for us? Nothing? Yeah,
it's like I opened my I opened my electron. It's like, oh,
it's pointing up. That means Daniels is pointing down and
that that doesn't help us at all. Talk that doesn't
help us at all. And so I spent ten years
(37:57):
of my life on an experiment we already knew was
doomed about what we've learned, and we just spanned forty
minutes on a podcast that's also doing Yeah, and so
you know, there are fascinating ideas there. There's amazing quandom,
magic seeming stuff happening. It seems like maybe quantum mechanics
could evade relativity somehow, but in the end, relativity is
(38:19):
hard and fast. There's no way to send information through
space faster than light. I mean, if you did, you
could break causality. And we're gonna have a whole podcast
episode about what it means to have things happening simultaneously
and causality and all that fun stuff maybe next week
or so. But the short version is that relativity is
the law. We're pretty sure cannot be broken. It can
be evaded. You can squeeze space instead of moving through it,
(38:42):
but you cannot break it. So the only way I
think to get messages to Alpha Centauri faster than light
would get there would basically be to warp there and
warp back. Well, there you go. Can I make a
warmhole telephone, like open a wormhole to you that somehow
I can, you know, transmit information through it? That is
totally theoretically allowed. Yes, so that doesn't require quantum entanglement.
(39:06):
It requires negative mass particles, which were not sure actually
exist in this universe. But theoretically there's nothing that prevents
you from opening a wormhole. It might also require as
much energy as is stored in the planet Jupiter, but hey,
that's an engineering problem, not physics problem. That's a small
price to pay to to tell you if the pie
(39:26):
is burned or not. You can just send me a
new pie for that price. I can just eat the
pie and forget about you. I'm never going to see
you again. Danny Dann won't be back for years. He's
stuck on Office Centauri and some wild quantum hip I
will be running, and only by the timing unless it's
a quantum pie. There we go. We're inventing phrases all
(39:48):
over the place. All right, Well, it sounds like the
answer to the question is not really, you can't use
quantum entanglement to talk to aliens faster than light. All
those science fiction novels, they're just fiction. They are just fiction,
after all. And I want to give props to science
fiction authors for trying, for actually thinking how could you
(40:08):
do this, and for getting a little bit into the
science from not just sort of brushing over like I
don't know, we just have some sort of answerable that
let's just talk magically across the universe. I like that
they dug into a little bit, and uh, you know,
so kudos to them. And science fiction often leads the
way in research and creates things which then scientists actually build.
So we certainly don't mean to criticize science fiction authors,
(40:30):
but in this case, that idea, as far as I understand,
will not work, which is a bummer. But hey, you know,
if you're writing a science fiction novel right now and
this episode frustrated to you, just remember that scientists have
not technically disproven quantum facting, which is not field yeah,
not yet, which you can use for your science fiction novels,
(40:54):
So there you go, send me the royalties. That's right.
And if you are writting a science fiction novel and
struggling a little bit with the science of it, hey
send me an email. I am happy to give you
consultation on how to devise your science fiction universe. Daniel
and Jorge fix your science fit your novel new podcast.
That's right, all right, Well, thank you for joining us.
(41:14):
We hope you found that interesting and um not didn't
get too entangled in your head there, that's right. We
hope we didn't entangle your neurons any further than they
already were, or that we gave it unnecessary spin to
the topic. As usual, Jorge spun it up and I
spun it down. Well, thanks for joining us, see you
next time. Thanks for tuning in. Before you still have
(41:42):
a question after listening to all these explanations, please drop
us a line. We'd love to hear from you. You
can find us at 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 Hey explain the universe is a
production of i heart Radio. For more podcast from my
(42:05):
heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yeah.
Hey, Daniel, I have a question for you that you
might not like. Oh, what is it? It's about aliens,
your favorite topic. I love it already. What is it? Okay? So,
if we can't send messages faster than light, right, all
the other planets are light years away, wouldn't any communication
or messages exchanged with aliens take years or decades? Ah,
(00:32):
you're right, I don't like that question. Hi. I'm or Hamming,
cartoonists and the creator of PhD comics. Hi. I'm Daniel.
(00:56):
I'm a particle physicist and the co author of our
book We Have No Idea, a guide to the Unknown
Universe that tells you all the things we don't know
about the universe. Yeah. It's a great book, which also
functions as a nice quantum banana stand or in anything
stand really, once you're done reading it. It's multi purpose.
You could buy thousands of copies and build a house
(01:16):
out of them. But welcome to our podcast, Daniel and
Jorge Explain the Universe, a production of My Heart Radio
in which we try to find amazing and crazy and
fascinating things about our universe and explain them to you.
We want to take you to the cutting edge of
science and break it down so that you have a
working understanding of it. Science is not something meant just
for a few people in an ivory tower. Sciences by
(01:38):
the people of the people and for the people. That's right.
It's a constitutional right to know your science and to
have physicists explained it to you. That's right. It doesn't
make it democratic, but it should be accessible. Do you
think is physics governed by democratic principles? Daniel? Maybe awesome
if we could change the laws of the universe by
(01:59):
voting on it, like he who wants to have faster
and light travel me, and we all vote on it,
and then it's possible. That would be pretty awesome, And
the universe has to follow the rules. Hey, if it's
a democracy, right, then we could like amend the laws
of physics. Right well, if if our government is any
indication that I think would be in deep trouble, I
think Mitch McConnell would stand in the way of any
(02:19):
uh any revolution we want in the laws of physics. Yeah,
I think would probably splinter into different universes. That's right.
I would have people arguing for these set of laws
and other people saying no, we want this to be possible.
Maybe we should not wish to have that kind of power. Yeah, yeah,
let's take to the undemocratic universe in which we actually
live in the dictatorial um quantum universe. That's right. So yeah,
(02:43):
so today on the program, we'll be talking about a
problem that a lot of people see if we ever
do find other life in the universe, right, Yeah, there
are certain things about the laws of physics which are
fascinating but also frustrating that put limits on us. And
you know, if we did find aliens, even in one
(03:03):
of the nearby stars that are light years and light
years away, it would be difficult to have a conversation
with them because light or anything else takes years to
get there in years to get back. Yeah, it would
be a really awkward conversation. Right, You'd be like, hey,
how's it going, and then you have to wait twenty
years or more maybe to get an answer that says
(03:24):
pretty good you they have like a revolution since then,
or have evolved into something else or whatever. How do
you have a conversation? Yeah, you might not even be alive, right, Like,
if we talked, we're trying to talk to another civilization
that's a hundred light years away, it would take two
hundred years to get a response, just to get a response,
and then imagine what that conversation would be like. You know,
(03:47):
the first statements of that conversation would be like, huh,
what were you? Wait? Can you hear me? Is this
being on? You know that's a thousand years right there,
you know, just to decode our language to right? Would
it would be kind of awkward? Would be like talking
to my nine year old right like, hey, can you
pick up your shoes? Hey? Can you pick up your shoes?
Twenty years later? Would be like what it would be
(04:09):
like having any video conferencing meeting. You know, the first
ten minutes of every video conferencing meeting between humans who
speak the same language, use the same technology. It's still
I can't hear you? What what was that? No, this
is not working, like the ultimate nightmare conference call, wouldn't it?
We would waste years just to say you're on speaker
phone or you're muted, or sorry I thought I was muted,
(04:33):
or hey, you're in the bathroom and you're not muted, right,
Although actually I would like to hear what it's as
sound like when the alien goes to the bathroom. Oh really,
that would be your opening question. No, but if that's
if that audio was just delivered to me somehow, Yeah,
I would like to hear that. That would be fascinating.
What if that's the only thing we ever learned about
aliens is that they accidentally but dialed us when they
(04:55):
were in the bathroom and we got to hear it.
I see you, assuming they have a butt, or they
might only they have m I'd have multiple buds. You
don't know. So many questions could be answered by that
accidental phone call. Yeah, you might get like two separate
calls on your phone. But hey, your left button your right,
but are both calling me? I gotta go? And maybe
(05:17):
they must have a whole different call waiting system depending
on the number of butts they have. But you know,
this is a fun topic to explore, But I read
a lot of science fiction, and in science fiction they
often have this same problem. Like, let's say it's a
million years in the future and humans have colonized the
galaxy and have a galaxy spanning empire. How do you
even govern an empire if it takes a thousand years
(05:39):
to send a message from one side of it to
the other, Right, Like, if you think about it. One
fact that always blows my mind is that the United States,
it's only like two fifty years old or less. So
imagine having a conversation in between the declaration of independence
and now it's a whole different country. Absolutely, it's a
(06:00):
whole different country. And I think there's also something interesting there.
I think something about the size of nations was determined
basically by the speed of information transit at the time
that you know, nation states came to be. And the
reason we don't have globe spanning empires might also be
because we didn't have instantaneous communication until fairly recently. Oh,
(06:21):
I see, like your furthest calling. You could be like, hey,
I am peace out, I'm leaving, and by the time
you get the message and say no way, dude, they're gone.
Tighter coordination between the UK and the American colonies might
have prevented the American Revolution, right, and England could still
be a globe spanning empire anyway. That's um ridiculous speculation
on a topic I have no expertise in. But that's
(06:44):
a that's a different topic. That's uh. Dano and j
confuse History another production of I Heart Radio. That's right,
but I think this is a really interesting one. And
in those books and science fiction novels, they often try
to avoid this problem them by inventing some way for
these people to communicate faster than light. They have some
(07:05):
clever ways, some telephone that communicates instantly from galaxy to
galaxy or even inside the galaxy's so that they can
talk to their subjects and their political connections and a
reasonable time, right, so that each page of the science
fiction story, it doesn't go two hundred years later or
it's like three next thing, Bob's great grant. If you
(07:26):
answered the phone, it says, what who's Who's this phone?
It wouldnt be a fun thing to get in the
wheel from your grandpa, Like, hey, I put a call
into some aliens. If you they call back. This is
what I wanted to know. Here's the conversation tree I started. Yeah, exactly,
but yeah, it's it's a big problem with the idea
(07:49):
of a connected universe. I think, right, like you can
imagine a galactic empire or you know, just getting to
know our neighbors. It would be a problem. It would
be a problem. And in a lot of these science
fiction novels and they try to solve this problem by
sort of painting over it with a magic phrase and said, well,
you know, maybe scientists in the future have figured out
(08:09):
where to use. Here, I'm doing air quotes quantum entanglement,
and that just sort of solves the problem. That's a
popular solution in science fiction to this problem. Yes, exactly,
quantum entanglement. Quantum entanglement sort of solves the problem of
faster and light communication. All right, So then today we're
going to answer the question can we use quantum entanglement
(08:35):
to send messages faster than light? Because I would love
to talk to the aliens more rapidly. I would love
to download their physics library and not have to take
a billion years. And so I want this to be true.
I want us to be able to send messages fast
and like using quantum entanglement or anything. Well, I think,
like any any phrase in science fiction, just put the
word quantum in it, and it sounds both magical and plausible.
(08:58):
Do you think that's going to be true for ever? Like,
won't that trope get tired? Won't people to be like yawn? Quantum?
The new thing is I don't know what is the
new thing? Dark matter, dark quantum, nous dark matter. Oh
my gosh, you're right, and there is even that novel.
Have you read that novel called dark Matter by Blake Crouch? No,
I haven't, very popular. I think was the best seller.
It's actually about quantum mechanics. But the title of it
(09:21):
is dark Matter, which is very confusing and has nothing
to do with dark matter except I think that dark
matter is a sexy, buzz worded physics that they were
there him or his agent or his publishing house we're
trying to latch onto. Well there you go. That should
be the title of our next book, dark Quantum, Dark Quantum, Yeah, exactly.
Maybe we can use dark matter for faster than light
communication Quantum after hours cinemas dark Matterez. Well, anyways, um, Yeah,
(09:50):
the idea is like in science fiction, can we actually
use quantum, this idea of quantum entanglement to send messages
faster than light? And so, as usual, we were wondering
if anyone had even heard of flantum entanglement or how
to pronounce it, or whether it could it could even
be used to send messages faster than light. So, as usual,
(10:11):
I walked around the campus have you see Irvine? And
I was grateful as always that they were willing to
answer a random question about a random topic. And so,
before you hear these answers, think to yourself, do you
think quantum entanglement can be used to send messages across
the universe faster than the speed of light? Here's what
people had to say. I don't know enough to answer
that question. I don't know now, I have not I
(10:35):
don't know, but I hope he can. I'm not sorry, No,
I'm not I do know what that is to do. Yeah,
do you think it can be used to send messages
faster than the speed of light? That is correct? Do
you think you can? So what do you think of
those answers? Jorge? All right, Well, I think they're probably
pretty common answers. And I don't think up until a
couple of years ago, I would have known what quantum
(10:55):
entanglement was. Yeah, a lot of people have never heard
of it. Um though, why guy was like, Oh, yeah,
that's in this guy's company. This Wow? What does he
know that we don't know? I don't know. I didn't
spend it time to dig into it with him. Was
he an alien? Possibly? Probably? Oh my gosh, I met
(11:18):
an alien. I didn't even realize it. After rewind back
in time, remember what that person looked like if you
can rewind back in time, Daniel, that's what do you know?
I just used my quantum tango particles, right, that's everbody
science fiction problems, dark quantum phone, quantum foam perfect. I
(11:38):
think that is the perfect blend of buzzwords right there.
That solves any problem. There you go. I'm gonna suggest
that to my students next time, the every research problem.
Have you tried dark quantum foam. Many people haven't even
heard of quantum entanglement, much less the idea of using
it to talk over long distances. It's a topic that's
actually decades old, but I think only recently has it
entered any sort of the edges of the cultural ZiT guy, well,
(12:00):
I think I remember a couple of a year or
two ago there was a big news item saying that
um scientists had finally teleported something and they use quantum
entanglement it. Yeah, there was some very misleading science headlines
about how scientists teleported something into space. But yeah, they
hadn't actually leading headlines misleading science headlines. No, that was
(12:22):
I wanted you to click on it. That's sweet. Yeah,
they had used quantum entanglement. And we did a whole
episode actually about teleportation whether it's possible. And there is
one aspect of teleportation which is possible, which is teleporting
a quantum state. That is saying, here, we have some
particles and a quantum arrangement over here. Can we make
other particles not the same particles, other particles had the
(12:45):
same state over there. It's sort of like, uh, you know,
um copying something. It's like emailing something to somebody else,
but doing emailing a quantum state, and to do that
you do need to have quantum entanglement. Yes, quantum factsing.
That is not a phrase anybody has ever said out
loud before. I think right, and I lay my stake
(13:05):
on it. Yes, Yeah, they didn't actually move anything to space.
People think when they hear teleportation that you have disappeared
some that or somewhere and reappeared it somewhere else. That's
the common understanding of teleportation, which is why the headlines
for that article were so misleading. Um. But they did
use quantum entanglement in that experiment. Quantum entanglement is a
real thing. It can be used to do some interesting science. Right,
(13:28):
it can be used to quantum facts things, for example,
which is fascinating and useful, but not faster than the
speed of light in that case. But yeah, I think
I think that would be a more better name for it,
quantum faccing, because it's not really teleporting. It's more like faccing. Yes, exactly,
that is quantum facting, and it's it's it's sort of
related to this idea of using it to communicate faster
than light. Or is that totally different than quantum teleportation? No,
(13:51):
it's different. I mean the idea of quantum entanglement is
to have two things that are far apart, but they
have some connection to each other, and can you use
that to send some information? And you can use it
to send some information, but the question is can you
use to send information faster than the speed of light?
But maybe before we dig into that, we should talk
(14:11):
about what quantum entanglement is, so everybody has a clear
sense for what that means. Yeah, let's talk about quantum entanglement. Um,
So what what is quantum entanglement? I feel like I
know the word quantum sort of which means magic, and
entanglement means that two things are kind of like intertwined
or um, you know, kind of like one of them
depends on the other. Yeah, that's exactly what it is.
(14:33):
Entanglement means that this sort of a constraint on the pair.
So I think it's simplest if you think about just
two particles. Now it can apply to other things, and
just particles that can apply to quantum fields of quantum systems.
Just to have a visual thing to hang our our
mental hats on, let's talk about, for example, two electrons.
And electrons we know have these weird quantum states, like
they can be spin up or they can be spinned down.
(14:55):
And for an individual electron, before you've looked at it,
it could be either spin up or down, and sort
of like the Shorteninger's cat in the box, until you
ask the electron, are you spin up or down? It's
sort of both. It's not determined it's fifty fifty one
or the other until you like poke it right, until
you ask the electron whether it's spinning over the right.
And we did a whole episode on quantum spin. How
(15:17):
you can measure an electron spin. You pass it through
a magnet and either goes left or goes right and
that's how you're measuring it. You require it to make
a decision about whether it's up or down so that
it can interact with an experiment you've built in a
certain way. And that's useful for thinking about individual electron.
A quantum entanglement is about pairs of electrons because sometimes
you can arrange these electrons in a special way so
(15:38):
that they're not independent. They have a constraint on them,
like they have their spins have to be opposite. For example,
if one is up, the other one has to be down.
Like you put a rule that um says that they
they're not totally independent. Yeah, Like if you sort of
two dies, they can be whatever they want to be
each one, But if you put a constraint on them,
saying they both have to add up to seven, then
(15:59):
that that's a constraint between two things exactly. Because quantum
mechanics has a lot of weirdness and a lot of fuzziness,
but there are some rules even quantum mechanics can't break,
like conservation of momentum, and spin is a kind of momentum.
And so if these electrons, for example, came from another particle,
say a photon generated an electron and opositron. That's that
(16:20):
photon has an overall spin zero for example, then the electron,
if one of them has spin up, the other one
has to be spinned down in order to conserve overall momentum.
There's spins have to add up to zero, which is
the same original amount of spin that the photon had.
So that's how you do it physically. That's how you
apply a constraint to two electrons to say, you can't
both be up and you can't both be down. If
(16:42):
one of you is up, the other one has to
be down. So you maintain your compliance with this other
law of physics, right, and you can set that rule
to whatever you want to be. Like, you could also
say they both have to be up, or they both
have to be down, or they can't both be the
same thing. It's just kind of like like a rule. Right. Yeah,
if your photon has spin one in a certain direction,
then you know that both electrons have to be spin up.
(17:02):
And if it has been um minus one, which is
the same it's been one of the other direction, then yeah,
the same thing applies. But it's most interesting when this
constraint adds up to zero, because then each electron can
be up or down, and it's the combination of the
two that has the constraint, not the individual one. So
each one is free to be up or down. But
if as soon as you know that one is up,
the other one has to be down. Okay. So that's
(17:23):
the basic idea of entanglement. It's like two particles that
have some kind of they're both quantum, so they're both
weird and fuzzy, but there's some sort of constraint between them,
some sort of rule that says that that when you
open those two electrons, they need to follow certain rules.
That's right, and the magic there is what happens if
you open just one electron, so electron A and electron B.
(17:46):
So you open the box electron A, you interact with it,
you measure it's been it's been up. Now you know
something about electron B. Right, you've measured something about electron
A and learn something about electron B. That constraint allows
you to extrappolate your knowledge of the first electron onto
the second one. That's the magic, because the two have
this constraint, and that happens sort of instantaneously. As soon
(18:08):
as you measure it on one, you know something about
the other one, even if in the meantime you've taken
that other electron and moved it a light year away.
So that's where the communication part comes in, Right, that's
where the sort of magic faster than light tempting thing
comes in. You take these two electrons, they're quantum entangled,
you move them really far apart without breaking the entanglement somehow,
(18:30):
and then when you measure something about one electron, you
learn something about something really really far away, and you've
learned something faster than light can travel. All right, well,
let's get into the details here a little bit more,
and how this was actually one of Einstein's ideas, right,
it was sort of Einstein's big backfire. So let's get
into it. But first let's take a quick break. All right,
(19:04):
we're talking about quantum entanglement and how we could use
that to talk to aliens right faster than like that's right.
We're hoping their aliens, and we're hoping we could develop
this technology based on quantum entanglement to send the messages
that aren't accidental toilet butt dials, right, using my quantum facts,
which I just invented ten minutes ago. Okay, so let
(19:25):
me see if I got this straight. Didea between quantum
entanglement is that you take two electrons or two particles
that are quantum, and you you you mix them up
so that there's some kind of rule between them, so
that then if you separate them and you open one
of them, you know something about the other, even if
it's really far away. Precisely, you've learned something about something
(19:47):
far away faster than light could get there, right you.
If you if you want to know what is the
state of electron B, rather than going there and measuring
it coming back, you can do it instantaneously by measuring
electron A, and that tells you something a about what's
happening far away. And normally in this universe, to learn
something about an object that's really far away takes time.
(20:07):
If you want to know what's happening in the star
a light year away, you need to wait a year
for that light to get here. So this seems like
a tempting way to learn things, to about things that
are far away, and maybe even to send information. That's
sort of the idea. It's made the picture a little
bit maybe, Like so I take two electrons and let's
say I make the rule that when I make the
electrons and make the rule that they both had to
(20:27):
be the same spin. Like, that's a possible rule, right,
that is a possible rule. Yes, if your photon has
spin one, then the electrons, which have spin half each
could be both having a point in the same direction
to make that original spin one. Yes, So I kind
of I entangle these two electrons and then I send
one of them to another star proxim Centauri. Yeah, And
(20:48):
I wait a while for it to get there. It
gets there, And now I opened my electron, the one
I kept, and I see that it's pointing up. You're saying, instantaneously,
without having to wait to check on the other electron,
I know that the other electron out there is also
pointing up. Precisely, you now officially understand quantum entanglement. This
is the day forever after which you are an expert
(21:11):
in quant entanglement. Congratulations, right, But I guess what I
don't know is how how you can use that for communication.
I mean, I feel like I just sent you a
package that I kind of already knew what was in it,
and before you open it, I know what's already in it.
But I'm the one who sent it, so I'm not
sure how that helps us communicate. That is the rub right,
that's exactly the issue, And but you don't exactly know
(21:32):
what's in it, right. I think in the case where
the photon has spin zero and so the electrons have
to be opposite, you don't know until you open it
which electron do you have. Do you have the one
that's beIN up or do you have the one that's
beIN down? And so you have learned something about something
that's really far away. Before you measure your close by electron,
it could be up or down, and the far away
(21:53):
electron could also be up or down. It's not determined yet.
There's still some randomness. But when you measure the spin
of the close by electron, then you instantly know the
spin of the far away electron instantly. The other way
to get that information is to let the people who
have the far away electron measure it's spin and then
tell you, But that would take time for them to
(22:14):
send you that information. So this is like a way
to instantly no information that is far away. Now, that's
not the same as communication, which requires controlling information. And
this is the part that science fiction novels never get
into how do you use quantum entanglement to send information
faster than light? They just sort of dot dot dot
(22:35):
from quantum entanglement to instantaneous communication. They never get into it.
Nobody actually knows. Nobody has worked it out. Nobody has
worked it out. I mean people have thought about it.
And you know, this font experiment came from Einstein because,
as you said before, Einstein was trying to show the
quantum mechanics was ridiculous. Einstein was trying to prove that
this new field of quantum mechanics makes no sense. So
(22:55):
he actually came up with this thought experiment, like, could
you do this in the scenario your proposed in the
quantum mechanics universe? If that was real, then you could
do this absurd thing like knowing something about something really
far away. And so he proposed this in a paper
and he said, look at this absurd outcome of your
predictions of quantum mechanics. Clearly you must reject this whole idea. Instead,
(23:16):
people were like, I could write a science fiction story
about that. No. Instead, people were like, that's a cool experiment,
let's go do it, and they did it, and it
turns out that the quantum mechanics predictions, absurd as they were,
were correct. That that's exactly what happens. What did they
prove that if you take two electrons, entangle them, and
then separate them, they're still entangled. Is that the experiment
(23:38):
they're still entangled, and that if you measure the first one,
the second one instantly collapses to being the opposite of
the first one. It collapses to to you, to to me,
but not to the person who's holding it out there. Yeah,
if you measure electron A, right, then electron B, which
can be really far away, it can be faster, it
can be far away than light can travel in the
time they can. They measure it, and they measure that
(24:01):
electron B also collapses at the same moment that electron
A collapses. That if they ask electron air you spin
up or spin down, then electron B goes from being
spin up to spin down to being either one or
the other, being the opposite of electron A. So they've
shown that this happens, that making a measurement in one
location changes the physics of the universe somewhere far away,
(24:23):
and it changes that the physics of the universe faster
than you could send information via light. It's not like
something is happening in electron A and it secretly sends
a message to electron be quick. I'm up, so you
have to be down. They've separated these particles far enough away,
like kilometers now kilometers and kilometers, so there's no way
for light to sneak that information. But what do you
(24:44):
mean it collapses on the other end, Like, but they
haven't opened it. You're saying inside the box it's in,
it's technically collapse. Or are you saying that when they
whenever they open that other box out there, they're going
to find that it's the It follows the rule. They
do open the box, and it follows the rule. Yeah. Like,
let's say I put two take two electrons, entangled them.
(25:06):
Let's say I make the rule that they both have
to be spinning the same direction. I think it's clearest
when they have to be spinning the opposite directions. Okay,
so let's have been make the rule that they have
to be spinning the opposite direction. Okay, I entangled them.
I keep one in my box and I sent the
other one to you in office Centari in a in
A box. I'm an Alpha centari. I have to go
(25:29):
to alpha centauri. I get to Alpha. Okay, I thought
you already were there. But all right, I'm an alpha
centauri with the other box. Okay, yeah, I sent you
my the B electron. I kept the A electron. I
sent you the B electron, and they're both entangled. And
now you're saying, if I opened my A electron and
(25:50):
I see that it's pointing up, I know that B
is pointing down, but you don't know that B is
pointing down to you. That's right. But I measure it
and it points down right when you measure it. But
up to the point that you measure it, you don't
know if it's pointing open down. That's right. But how
does how do they talk to each other? How do
they know that one can point up and then we
can point down. They're separated, all right. Say we make
(26:11):
our measurements at the same moment or within a bill
of second of each other. Okay, we are separated by
a light year. There's no time for for electron A
to tell electron B what decision it has made. Oh,
I see what you're saying. You're saying that my electron
my A electron the one I kept could could be
either one. It could be either one. Yes, If I
do this experiment, a lot sometimes will be up, sometimes
(26:34):
they'll be down. But the ones that it's up, then
yours will be down, and the ones that it's down,
yours will be up. Precisely, and before you measure any
of the particles, both could be up or down. They
have a fifty percent chance of being up in a
fifty percent chance of being down. When you measure electron
A to B up, then electron B a light year
(26:54):
way has to instantly change from having even odds of
being up or down to just being down. It has
to because electron A was up. But how does it
know that electron A was up. There's no way for
that information to get to electron B in time. Electron
A could have been down, forcing B to up. Electron
(27:14):
A spin could have been down, forcing B to be
spin up. Remember that both of them are undetermined until
you measure one of them, and then suddenly both are determined.
This is like you take two prisoners and you isolate
them so they don't get to talk about their story,
and you asked one you know who robbed the bank,
and you ask the other one who robbed the bank,
and their stories always agree, right, even though they could
(27:39):
have lied, either of them, either of them could have
lied exactly either what could have like either both lie
or they both not tell the truth. But some other
insane and it's physically impossible for them to communicate because
they are too far apart. When they first did these experiments,
they try to isolate the things, but they weren't actually
really that far apart. It's hard to get two quantumentango
particles actually far apart. But now they've done it. They've
(28:01):
quantum entangled particles between the surface of the Earth and
things on satellites for example. That's what that article was about,
what we're talking about earlier. They quantum entangled physics on
the Earth and physics in a satellite. Okay, so that's
the spooky thing. It's like some of the two prisoners
have their stories in sync, you know, the two White
House officials are somehow saying the same thing. How about
(28:24):
the text messages. But they never talked to each other,
and they couldn't possibly have coordinated. It couldn't. It's physically
impossible for them to coordinate. Yet somehow when electron A
collapses to up, electron B collapses to down, or the
other way around. How do I know they didn't coordinate
before I separated them. Yes, that is one of the
deepest questions about particle physics and quantum mechanics is that
(28:45):
is there a hidden variable. Maybe A wasn't actually both
up and down. Maybe there's some hidden variable there, something
that determines it forces A to be up, and so
of course B is down. It's no surprise you know
that you have half of the cake the other one.
It's the other half of the cake, because it's been
those halves the entire time. When while they were traveling
to be farther away, that's a really like they decided like, hey,
(29:06):
i'll be down, Okay, that means you have to be up,
and then they separated. You're saying, that's not that's not
what's happening. We know that's not what's happening. The explanation
for that, And I know people out there who are
desperately curious about quantum mechanics and skeptical of this. I
wanted to precisely the answer to that question because when
I was learning quantum mechanics, that's the thing I was
wondering about, how do you know there isn't some like
hidden variable, something we just haven't measured, some property the
(29:28):
electron which determines or forces want to be up in
the other one to be down. Now, the answer is
a bit frustrating. The answer is not a smoking gun.
It's a much more subtle experiment. It's called an It's
invented by a guy named Bell, and it's about measuring
the correlation between A and B. You can't prove that
there's no hidden variable for one experiment, but if you
do this over and over again and you sort of
(29:49):
rotate the spin of the electrons, you can prove that
there is no local hidden variable. It's really one of
the most beautiful and subtle pieces of physics I've ever learned.
So to show that there's no way for the two
electrons to have been determined in advance which one would
be up and which one would be down, that's what
we technically called the no local hidden variable. What Bell
(30:11):
did was used a second weird aspect of quantum mechanics
to help pin down this first weird aspect. On the
episode about spin, remember we talked about how you can't
know the spin in two directions at the same time.
It's just like how you can't know a particle's momentum
in position at the same time because of the uncertainty principle.
In the same way, measuring the spin in one direction
(30:31):
like X will re randomize the spin in the other
directions like why. So Bell used this to his advantage
to show that the spin really is randomized before it's measured.
His experiment says, you should separate the particles, but then
measure the spin in other directions, not the one that
you have this quantum mechanical entanglement constraint on. And he
(30:52):
showed that if there is a local hidden variable, it
will affect not just the constraint direction, but also the
spins you measure in other directions. If there isn't a
local hidden variable, if the electrons really are undetermined until
you measure them, then you will not affect the randomness
in the other directions. So he was able to come
up with an experiment that gives different predictions if there's
(31:15):
randomness and if there's local hidden variables. And then they
did the experiment and boom, it showed that there really
is randomness, but we should dig into it further on
a whole separate podcast episode, because it's really fascinating. They
have proven that there is no local bit of information
that could be hiding inside those boxes to determine that
one electron actually is up and the other one actually
(31:37):
is down. We know that the that there really is
uncertainty there, that the electron could really be up or
down when you've entangled them and when when you've separated them,
and that that collapses the moment you measure one of them,
even if they're really far apart. Yeah, it's kind of
like if you do the experiment a bunch of times
and you you sort of know for sure that the
two prisoners couldn't have possibly God in their story straight
(31:59):
ahead of time. There's something weird going on. There is
something weird going on. Even just doing a lot of
times doesn't satisfactory resolve that question, because there could be
a hidden variable in each case, and so doing it
many many times just reinforces that. It has to do
with having with measuring these spins along different axes and
then rotating that access and you can show that as
(32:20):
a function of that rotation, things would act differently if
there is a hidden variable, then if there isn't a
hidden variable. But again it's a bit too subtle to
get into. I think on today's podcast it involves spinning prisoners,
which we can't get into. It's right. We tried to
file for research allow us to do that, and they said, no,
that's uh, that's not that's the violent human rights in
(32:41):
humane exactly. And then I tried to say, but it's
for black matter, quantum foam telephone, and we're doing it
in a Stanford basement. It's all right, at least, no,
it wasn't approved, all right. So so that's where this
idea that you could use this for faster than light
communication is that there's something something's going on faster than light,
and so could we use that to communicate faster than light? Right,
(33:04):
that's where the idea came from. Yes, something here is
happening faster than light, and so people thought, oh, maybe
we could communicate faster than light. That's the genesis of
the idea. All right, let's get into whether it is
possible to use this for faster than light communication. But
first let's take a quick break. All right. So we
(33:34):
talked about quantum entanglement and how there is something going
on with it that's faster than light. But the question
is can we use that to talk to aliens faster
than light or to you know, Daniel, who's an alpha
centry faster than light? And so what's the answer here, Daniel?
How how could we use could we use quantum entanglement
to violate the fundamental speed limit of the universe? Well, first,
(33:58):
I want to say that I think this is a
totally good idea to investigate because there's often loopholes, you know,
we talked about on the warp Drive episode, like yeah,
you can't travel faster than light through space, but just
change your definition of what you want to do and
don't say I want to go through space, so you
want to squeeze space so you can get somewhere faster
than light would have gotten. So it's a great sort
(34:18):
of avenue for exploration to look for loopholes and try
to find ways to accomplish what you want to do
without breaking the laws of physics. But in this case
it's not gonna work. And the reason is to go
back to what you were saying before, like say you
have these two electrons, let's try to dot the lines
to say, say you have these two electrons quantum entangled
between here and alpha centauri. How would you actually use
(34:40):
that to send information? Why would you build a communication system?
Say you want to send me a bit, right, you
want to send me a zero or a one. You
know you wanna tell me whether or not the apple
pie is ready to eat? One? Is apple pie is ready? Zeros? Noops,
I burned the apple pie or something. You want to
send me some I want to give you a thumbs
up or thumbs down. Yeah, how would you do that? Well?
(35:00):
In order to do one lamp if the British are coming,
two lamps if they're coming by spaceship. In order to
do that, you have to sort of control the information
you You might be tempted to say, Okay, what I'm
gonna do is I'm gonna force my electron to be
spin up in one case. I'm gonna force it to
be spin down in the other case, because that determines
(35:22):
what happens to Daniel's electron. And sort of like twiddle
Daniel's electron from really far away by twiddling mine, that's
the tempting way to thing to go right, and twangled
entanglement connects the two electrons and you're saying, like, if
I see the British coming by sea, I'll turn my
electron down, which makes your electron turn up, And somehow
(35:44):
I talked to you faster than like that's the idea.
But that doesn't work, right, That fundamentally doesn't work. And
the reason it's pretty simple is that you can ask
the electron what state is it, but you can't force
it to be in a particular state because if you do,
it breaks the tanglement. Right, the rules of the entanglement
are that the two have to be in opposite states
(36:05):
because you're preserving the Anglar momentum of the system that
created them. There's this law of physics that requires them
to still tally up in the end to have the
same Anglar momentum as the original system. But if you
interact with one of them, then you break that because
you're adding momentum or adding Anglard momentum to the system.
You've broken that quantum system. You made a new quantum
system and that doesn't have to follow the same rules
as the original. Oh, I see, so there's communication going on,
(36:29):
but there's no So it's like there's communication going on,
but there's no talking. Going on. The two electrons somehow
are coordinating, right, there's definitely collusion happening there, but you
can't force one electron to be in a certain state,
which is what you would need to do to send
information from one to the other. No, no, Daniel, no
collusion which hunt, No elect These electrons really do colue
(36:51):
this quantum collusion. See I invented the phrase. Also, all right,
quantum collusion good luck. Yeah, but that one you both
did it and are somehow not guilty of it at
the same time. Anyway. No, the possess the frustrating is
the problem is that this quantum entanglement thing really is real,
and it really does happen, and there is something weird
(37:12):
and fashion light happening, but we can't use it to
send information because you touch one of them, you basically
break the magic. Right. It's like, we can both learn
what each other has faster than light, but I can't
tell you about what. I can't tell you anything. We
just both learned faster than light. Precisely, we learn, we
learn about each other, but what we have, but we
(37:35):
can't tell each other something. Yeah, you're like, okay, I
did sent Daniel to Alpha Centauri he spent five years
of his life getting there, and now I know which
electronic has. Okay, what does that do for us? Nothing? Yeah,
it's like I opened my I opened my electron. It's like, oh,
it's pointing up. That means Daniels is pointing down and
that that doesn't help us at all. Talk that doesn't
help us at all. And so I spent ten years
(37:57):
of my life on an experiment we already knew was
doomed about what we've learned, and we just spanned forty
minutes on a podcast that's also doing Yeah, and so
you know, there are fascinating ideas there. There's amazing quandom,
magic seeming stuff happening. It seems like maybe quantum mechanics
could evade relativity somehow, but in the end, relativity is
(38:19):
hard and fast. There's no way to send information through
space faster than light. I mean, if you did, you
could break causality. And we're gonna have a whole podcast
episode about what it means to have things happening simultaneously
and causality and all that fun stuff maybe next week
or so. But the short version is that relativity is
the law. We're pretty sure cannot be broken. It can
be evaded. You can squeeze space instead of moving through it,
(38:42):
but you cannot break it. So the only way I
think to get messages to Alpha Centauri faster than light
would get there would basically be to warp there and
warp back. Well, there you go. Can I make a
warmhole telephone, like open a wormhole to you that somehow
I can, you know, transmit information through it? That is
totally theoretically allowed. Yes, so that doesn't require quantum entanglement.
(39:06):
It requires negative mass particles, which were not sure actually
exist in this universe. But theoretically there's nothing that prevents
you from opening a wormhole. It might also require as
much energy as is stored in the planet Jupiter, but hey,
that's an engineering problem, not physics problem. That's a small
price to pay to to tell you if the pie
(39:26):
is burned or not. You can just send me a
new pie for that price. I can just eat the
pie and forget about you. I'm never going to see
you again. Danny Dann won't be back for years. He's
stuck on Office Centauri and some wild quantum hip I
will be running, and only by the timing unless it's
a quantum pie. There we go. We're inventing phrases all
(39:48):
over the place. All right, Well, it sounds like the
answer to the question is not really, you can't use
quantum entanglement to talk to aliens faster than light. All
those science fiction novels, they're just fiction. They are just fiction,
after all. And I want to give props to science
fiction authors for trying, for actually thinking how could you
(40:08):
do this, and for getting a little bit into the
science from not just sort of brushing over like I
don't know, we just have some sort of answerable that
let's just talk magically across the universe. I like that
they dug into a little bit, and uh, you know,
so kudos to them. And science fiction often leads the
way in research and creates things which then scientists actually build.
So we certainly don't mean to criticize science fiction authors,
(40:30):
but in this case, that idea, as far as I understand,
will not work, which is a bummer. But hey, you know,
if you're writing a science fiction novel right now and
this episode frustrated to you, just remember that scientists have
not technically disproven quantum facting, which is not field yeah,
not yet, which you can use for your science fiction novels,
(40:54):
So there you go, send me the royalties. That's right.
And if you are writting a science fiction novel and
struggling a little bit with the science of it, hey
send me an email. I am happy to give you
consultation on how to devise your science fiction universe. Daniel
and Jorge fix your science fit your novel new podcast.
That's right, all right, Well, thank you for joining us.
(41:14):
We hope you found that interesting and um not didn't
get too entangled in your head there, that's right. We
hope we didn't entangle your neurons any further than they
already were, or that we gave it unnecessary spin to
the topic. As usual, Jorge spun it up and I
spun it down. Well, thanks for joining us, see you
next time. Thanks for tuning in. Before you still have
(41:42):
a question after listening to all these explanations, please drop
us a line. We'd love to hear from you. You
can find us at 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 Hey explain the universe is a
production of i heart Radio. For more podcast from my
(42:05):
heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yeah.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
Popular Podcasts
Stuff You Should Know
If you've ever wanted to know about champagne, satanism, the Stonewall Uprising, chaos theory, LSD, El Nino, true crime and Rosa Parks, then look no further. Josh and Chuck have you covered.
Dateline NBC
Current and classic episodes, featuring compelling true-crime mysteries, powerful documentaries and in-depth investigations. Follow now to get the latest episodes of Dateline NBC completely free, or subscribe to Dateline Premium for ad-free listening and exclusive bonus content: DatelinePremium.com
24/7 News: The Latest
The latest news in 4 minutes updated every hour, every day.