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Can you entangle three particles? · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: It sure feels like a classical universe out there. Things
• 0:11
  Speaker 1: move in paths, they don't seem to be uncertain. Everything
• 0:15
  Speaker 1: I know about has a location and a velocity, and
• 0:18
  Speaker 1: there doesn't seem to be any weird quantum mechanical effects
• 0:22
  Speaker 1: going on. And yet we're told that's wrong. We're told
• 0:26
  Speaker 1: that the deeper substrate of reality operates according to different rules,
• 0:31
  Speaker 1: that things are not determined until you measure them, that
• 0:34
  Speaker 1: they can be in a superposition, and that there's a
• 0:36
  Speaker 1: true randomness to the universe. That feels weird, that feels alien,
• 0:41
  Speaker 1: that feels counterintuitive. And so, as curious people, we want
• 0:46
  Speaker 1: to know, how do you know? How could you tell?
• 0:49
  Speaker 1: Often these things are hidden behind weird obstacles. Like, you
• 0:53
  Speaker 1: can't see things when they're superpositioned. You could just measure
• 0:56
  Speaker 1: them and get an outcome. That's unsatisfying. And the usual
• 1:00
  Speaker 1: story is a series of experiments thought up by John
• 1:03
  Speaker 1: Bell to prove that particles actually are determined randomly. that
• 1:08
  Speaker 1: there's no local hidden information carried along with the particles
• 1:12
  Speaker 1: that quietly determines what happens. But even these are still
• 1:16
  Speaker 1: quite unsatisfying, because the answer to those experiments is in
• 1:21
  Speaker 1: the patterns and the correlations. There's no smoking gun that says, here,
• 1:25
  Speaker 1: this one experiment proves that quantum mechanics is a description
• 1:29
  Speaker 1: of reality. And today on the pod, we're going to
• 1:32
  Speaker 1: talk about an even more subtle, more complicated experiment that
• 1:36
  Speaker 1: requires entangling three particles simultaneously and trying to get them
• 1:42
  Speaker 1: to flash a series of lights in a certain pattern,
• 1:45
  Speaker 1: which actually does definitively prove that quantum mechanics is the
• 1:50
  Speaker 1: way our universe works. It provides the smoking gun you've
• 1:54
  Speaker 1: always wanted. Welcome to Daniel and Kelly's Extraordinarily Quantum Universe.
• 2:13
  Speaker 2: Hello, I'm Kelly Wiener-Smith. I study parasites and space and
• 2:18
  Speaker 2: topics like entanglement make me wonder if physicists have the
• 2:21
  Speaker 2: best slash worst pickup lines.
• 2:25
  Speaker 1: Hi, I'm Daniel. I'm a particle physicist who likes to
• 2:28
  Speaker 1: think about alien minds. And I also like to get
• 2:31
  Speaker 1: tangled up in quantum mechanics, though I don't think that's
• 2:34
  Speaker 1: a good pickup line.
• 2:35
  Speaker 2: Okay, so here is, I was going to ask you
• 2:37
  Speaker 2: about the worst physicist pickup lines, but I'm actually not
• 2:40
  Speaker 2: sure that our audience wants to hear that. So when
• 2:42
  Speaker 2: physicists have a party, what are physicist parties like?
• 2:47
  Speaker 1: What are physicist parties like? Well, I can't generalize, but
• 2:50
  Speaker 1: I can tell you my experience. Katrina and I were
• 2:53
  Speaker 1: in grad school at the same time, and I went
• 2:55
  Speaker 1: to a poor public school, Berkeley, and she went to
• 2:58
  Speaker 1: a fancy private school, University of Chicago, and her department
• 3:01
  Speaker 1: was flush with cash, which meant that if you threw
• 3:04
  Speaker 1: a party at your house and invited the whole department
• 3:06
  Speaker 1: of grad students, they would pay for the alcohol. What?
• 3:09
  Speaker 1: So several times they gave us like $ 500 to throw
• 3:13
  Speaker 1: a party, and of course we invited all the biologists,
• 3:16
  Speaker 1: and then I invited all the physicists. So the physicists
• 3:20
  Speaker 1: crashed all those biology parties. And it was fascinating to
• 3:23
  Speaker 1: see the sort of cultural clash between the physics crew
• 3:27
  Speaker 1: and the bio crew. Yeah, it was interesting. You know,
• 3:30
  Speaker 1: we got some physics bio connections happening. You know, Katrina
• 3:34
  Speaker 1: and I are one example. So, yeah, it was interesting
• 3:37
  Speaker 1: to see how those folks approach a party differently. Right.
• 3:40
  Speaker 2: So physicist parties are only good if they're organized by
• 3:42
  Speaker 2: biologists is what I'm hearing.
• 3:43
  Speaker 1: That's the story. Yes, exactly. And funded by the biologists. Right.
• 3:49
  Speaker 1: Thank you, University of Chicago. We had some good times.
• 3:53
  Speaker 2: Amazing. All right. Well, today we're not talking about entangling
• 3:56
  Speaker 2: graduate students. We're talking about entangling particles.
• 3:59
  Speaker 1: Yes, we are. And I got a question from Roger
• 4:02
  Speaker 1: in Boston who heard about a fascinating set of experiments
• 4:07
  Speaker 1: and wanted them explained. Here's his question. Hello, Daniel and Kelly.
• 4:12
  Speaker 3: My name is Roger and I am reaching out from Boston, Massachusetts.
• 4:18
  Speaker 3: I discovered your podcast a little while ago and I
• 4:22
  Speaker 3: cannot get enough. Even though there's tons of stuff in there,
• 4:27
  Speaker 3: I just don't seem to be able to wrap my
• 4:30
  Speaker 3: head around. Fascinating stuff nonetheless. With a touch of makes
• 4:36
  Speaker 3: my skin crawl. Down to my question now. Would you
• 4:40
  Speaker 3: please explain how the Green Burger Horn Salinger Multi-particle entanglement
• 4:45
  Speaker 3: experiment proves quantum entanglement. Please explain the hows and the
• 4:51
  Speaker 3: whys of the experiment. I look forward to be blown
• 4:55
  Speaker 3: away by your explanation. Thank you kindly and keep up
• 5:00
  Speaker 3: the good work, guys.
• 5:02
  Speaker 2: Greenberger, Horn, Zillinger. That's a mouthful.
• 5:05
  Speaker 1: It's a mouthful. There's three smart guys who tangle themselves
• 5:09
  Speaker 1: up thinking about triples of particles. And I started digging
• 5:13
  Speaker 1: into this to answer Roger's question over email. And I
• 5:15
  Speaker 1: was like, this is way too much for an email.
• 5:17
  Speaker 1: Let's do a whole episode. Amazing. Yes, exactly. Because it
• 5:21
  Speaker 1: also gives me an opportunity to talk again about some
• 5:24
  Speaker 1: of my favorite experiments and then to talk about a
• 5:26
  Speaker 1: super version of those experiments that's much cleaner, much crisper,
• 5:30
  Speaker 1: sort of confusing in a different way about quantum mechanics. Oh, good.
• 5:34
  Speaker 2: Layers of confusion.
• 5:36
  Speaker 1: Yes.
• 5:36
  Speaker 2: Fantastic. Entanglement is definitely one of those topics where every
• 5:39
  Speaker 2: time I hear it, I'm still like, I think you
• 5:42
  Speaker 2: guys are getting something wrong. But then you'd always tell me, no,
• 5:48
  Speaker 2: we use this to predict other things and those predictions
• 5:50
  Speaker 2: come true. This is useful information. And anyway, but it
• 5:53
  Speaker 2: breaks my brain every time.
• 5:54
  Speaker 1: But that's the point of experiment, right? Is that you
• 5:57
  Speaker 1: go out and explore the universe so that it can
• 5:59
  Speaker 1: change your intuition. So it can teach you how the
• 6:01
  Speaker 1: universe actually works instead of how we think it might
• 6:04
  Speaker 1: or the way we hope it should work. The universe
• 6:08
  Speaker 1: follows its rules and the only way to learn it
• 6:10
  Speaker 1: is to follow the data. And so today we're going
• 6:12
  Speaker 1: to talk about that and we're going to talk about
• 6:13
  Speaker 1: some fascinating entanglement experiments that rely on entangling three particles
• 6:18
  Speaker 1: at the same time. Because entangling two is not complicated enough. No, no.
• 6:22
  Speaker 1: We are going to three particles.
• 6:25
  Speaker 2: Okay, but we're starting at two. But all right, keep going.
• 6:26
  Speaker 1: We're starting at two. We're going to work up to it, yeah.
• 6:29
  Speaker 1: But before we get there, I wanted to know what
• 6:31
  Speaker 1: people thought about entangling three particles and where their sort
• 6:34
  Speaker 1: of mental potholes were. So I went out and I
• 6:37
  Speaker 1: asked our group of extraordinaries, can you entangle three particles?
• 6:41
  Speaker 1: What is involved? Here's what folks had to say. But
• 6:45
  Speaker 1: I'm suspecting it's a trick question and three can actually
• 6:49
  Speaker 1: be entangled. Yes, you can, in fact, entangle multiple particles.
• 6:55
  Speaker 1: That's what they're trying to do in quantum computing. I
• 6:59
  Speaker 1: think we can somehow.
• 7:01
  Speaker 3: Actually, I have no idea at all, but I also
• 7:05
  Speaker 3: don't fully understand what quantum entanglement is.
• 7:09
  Speaker 1: So I'll let Daniel take this one. I would think
• 7:12
  Speaker 1: that you would need a particle with three different states,
• 7:16
  Speaker 1: like spin.
• 7:17
  Speaker 2: The idea of quantum entanglement always seemed to me to
• 7:20
  Speaker 2: be binary.
• 7:21
  Speaker 1: A left spin and a right spin, up or down, whatever.
• 7:24
  Speaker 1: So having a threesome would be very odd. This almost
• 7:28
  Speaker 1: broke my brain, but I guess.
• 7:30
  Speaker 2: If there's a particle with a superposition that has three
• 7:33
  Speaker 2: possible outcomes, then theoretically, yes, is how my logic would work.
• 7:38
  Speaker 1: But quantum physics is not logic.
• 7:40
  Speaker 2: There might be some super clever way you can entangle
• 7:43
  Speaker 2: three together all at once, where some of them has
• 7:47
  Speaker 2: to equal something, but you're not sure how it's distributed. Hmm.
• 7:51
  Speaker 2: I've only heard of entanglement of a pair of particles.
• 7:56
  Speaker 2: So I would say that doing it with three particles
• 7:59
  Speaker 2: is not possible. Nice mix of answers here.
• 8:04
  Speaker 1: Yeah. So there are definitely some misunderstandings here about entanglement
• 8:08
  Speaker 1: and how it works and the limitations. And we're going
• 8:10
  Speaker 1: to dig into all of that today. So thanks very
• 8:13
  Speaker 1: much to The Extraordinaries for giving me clues as to
• 8:16
  Speaker 1: where we need to go in this episode if you
• 8:18
  Speaker 1: would like to participate for future episodes we would love
• 8:20
  Speaker 1: to hear from you Please don't be shy. Write to
• 8:22
  Speaker 1: us to questions at danielandkelly.org. And you too can get
• 8:27
  Speaker 1: tough physics questions in your inbox. Didn't you always dream
• 8:30
  Speaker 1: of that?
• 8:30
  Speaker 2: The list is going to be a million people long, Daniel.
• 8:33
  Speaker 2: What are we going to do?
• 8:36
  Speaker 1: Email all at earth.
• 8:38
  Speaker 2: That's right.
• 8:38
  Speaker 1: That's right. All right.
• 8:41
  Speaker 2: Well, let's start at the very beginning. Forget entangling three particles.
• 8:45
  Speaker 2: Let's just entangle two. What is going on when two
• 8:49
  Speaker 2: particles are entangled?
• 8:50
  Speaker 1: Yeah. So first, what is entanglement anyway, right? Let's focus
• 8:54
  Speaker 1: with two particles and understand what it is we're talking about.
• 8:58
  Speaker 1: What entanglement is not is some magical connection between distant
• 9:02
  Speaker 1: particles that binds their fate together. I think some people
• 9:06
  Speaker 1: imagine entanglement the way it's often seen in science fiction.
• 9:09
  Speaker 1: It's like you have a particle here and a particle there,
• 9:12
  Speaker 1: and they have some connection. And anything you do to
• 9:14
  Speaker 1: one particle affects the other one. And that sounds awesome,
• 9:17
  Speaker 1: but that's not what entanglement is at all. That's like
• 9:21
  Speaker 1: Bad pop-sci version, that's the science fiction version that allows
• 9:24
  Speaker 1: you to communicate information across space and time instantly. If
• 9:29
  Speaker 1: you had such a particle, like if I had one
• 9:31
  Speaker 1: and Kelly had one and I could poke it and
• 9:33
  Speaker 1: then Kelly's particle got poked, then yeah, I could send
• 9:35
  Speaker 1: information along that wire, right? Because I could do stuff
• 9:38
  Speaker 1: to my particle that would happen to her particle and
• 9:40
  Speaker 1: she could read it out. That would be incredible. That
• 9:42
  Speaker 1: is not what entanglement is at all, unfortunately, right? Physics
• 9:47
  Speaker 1: as the wet blanket.
• 9:48
  Speaker 2: Well, longtime DKEU listeners will not be laboring under that
• 9:52
  Speaker 2: misconception because we have talked about this a few times.
• 9:55
  Speaker 2: but let's definitely do it again to make sure it's fresh.
• 9:57
  Speaker 1: The way you should think about entanglement is that you
• 10:00
  Speaker 1: have to think about the two particles together. It's a
• 10:03
  Speaker 1: correlation in the outcomes because it's really a single state.
• 10:07
  Speaker 1: It's always created locally. Two particles are entangled when they interact,
• 10:12
  Speaker 1: and then they maintain that correlation even if you separate them.
• 10:16
  Speaker 1: And that's not too hard to understand. You know, Let's
• 10:21
  Speaker 1: say you have two particles, and there's one property you
• 10:23
  Speaker 1: want to measure about them, their spin. It's either up
• 10:25
  Speaker 1: or it's down. So particle one can be up or down.
• 10:28
  Speaker 1: Particle two can be up or down, right? So then
• 10:31
  Speaker 1: how many possible outcomes are there for your measurement, Kelly?
• 10:34
  Speaker 3: Four.
• 10:34
  Speaker 1: Four, exactly.
• 10:35
  Speaker 2: Thanks for making an outline ahead of time.
• 10:38
  Speaker 1: Don't tip them off that you cheated. I wanted to
• 10:40
  Speaker 1: give you some points there.
• 10:42
  Speaker 2: I think I could have figured that one out. It's
• 10:43
  Speaker 2: a small number of options, but thanks.
• 10:45
  Speaker 1: So two for particle one, two for particle two. And
• 10:47
  Speaker 1: you can enumerate them. It's up, up, down, down, up, down,
• 10:50
  Speaker 1: or down, up. Those are the possible outcomes, right? If
• 10:53
  Speaker 1: the particles are totally free to do whatever they like.
• 10:56
  Speaker 1: Entanglement says, let's only allow some of those outcomes. We
• 11:00
  Speaker 1: have some physics process that has created these particles in
• 11:04
  Speaker 1: such a way that only some outcomes are allowed. For example,
• 11:07
  Speaker 1: maybe there's a conservation of spin. And so we need
• 11:10
  Speaker 1: zero spin for the whole state because it was made
• 11:12
  Speaker 1: from a zero spin state and spin is conserved. And
• 11:15
  Speaker 1: so the spin has to be zero afterwards, which means
• 11:17
  Speaker 1: you either need up-down or down-up. The up-up would have
• 11:21
  Speaker 1: too much spin and the down-down would have too much
• 11:22
  Speaker 1: negative spin. So they're not allowed. So if instead of
• 11:26
  Speaker 1: just having two particles free and willy-nilly to have any spin,
• 11:29
  Speaker 1: if instead you create them together in a correlated way, right,
• 11:33
  Speaker 1: from some interaction, and then separate them, then you know
• 11:37
  Speaker 1: that they're either in up-down or in down-up. So entanglement
• 11:40
  Speaker 1: is just those correlations. It just says, of the matrix
• 11:43
  Speaker 1: of possibilities, you're going to cross some out. And you're
• 11:46
  Speaker 1: imposing a condition that say only some of them are allowed, right? Mm-hmm. Now,
• 11:50
  Speaker 1: that seems very obvious. You're like, hold on a second.
• 11:52
  Speaker 1: Where's all the quantum weirdness, right? And the quantum weirdness
• 11:56
  Speaker 1: comes in when you add superposition. When you say, well,
• 11:59
  Speaker 1: which of those states are we in? In a classical
• 12:02
  Speaker 1: version of this problem, say you have like a bag
• 12:06
  Speaker 1: with two balls in it and one is labeled up
• 12:08
  Speaker 1: and one is labeled down. And I take a ball
• 12:10
  Speaker 1: and Kelly takes a ball and we go 10 miles
• 12:12
  Speaker 1: apart and we haven't looked at our balls, right? Then
• 12:15
  Speaker 1: if you look at your ball, you could say, oh,
• 12:16
  Speaker 1: I have the up ball. Cool. That means I know
• 12:19
  Speaker 1: instantly already that Daniel has the down ball because there
• 12:22
  Speaker 1: was one up and there was one down. There's a correlation.
• 12:25
  Speaker 1: So I know mine, therefore I know yours.
• 12:27
  Speaker 3: Okay.
• 12:28
  Speaker 1: And in that classical version, it's still not mysterious because
• 12:32
  Speaker 1: you know how it happened. You know that the fact
• 12:34
  Speaker 1: that you have up and I had down was determined
• 12:37
  Speaker 1: when we pulled the balls out of the bag, right?
• 12:39
  Speaker 1: So the fact that we walked 10 miles away, nothing
• 12:41
  Speaker 1: interesting happens there, nothing special. This is predetermined by some
• 12:46
  Speaker 1: properties on the ball. We call that hidden local variables.
• 12:49
  Speaker 1: There's some feature of the ball that is literally the
• 12:52
  Speaker 1: U on it or the D on it It tells
• 12:55
  Speaker 1: you which one it's going to be, right? It's determined
• 12:57
  Speaker 1: in advance. So that's the classical version of entanglement. Still
• 13:00
  Speaker 1: with me?
• 13:01
  Speaker 2: Yeah, I'm still with you. The whole time, the ball
• 13:03
  Speaker 2: was either up or down.
• 13:04
  Speaker 1: Exactly. Yes. And all that makes sense, right? So now
• 13:08
  Speaker 1: let's get to the quantum version. We have the whole
• 13:10
  Speaker 1: setup ready. So in the quantum version, there is no
• 13:13
  Speaker 1: local hidden information that determines whether the ball is up
• 13:16
  Speaker 1: or down. It's in a superposition, which is a fancy
• 13:20
  Speaker 1: quantum word for saying there's two possibilities in and neither
• 13:24
  Speaker 1: are determined yet. So both possibilities are live. The up
• 13:27
  Speaker 1: and the down are live on my ball until I look.
• 13:31
  Speaker 1: So I pick out the ball from the bag. It
• 13:33
  Speaker 1: can be up or down. I haven't looked yet. I
• 13:35
  Speaker 1: walk 10 miles. It can still be up or down.
• 13:37
  Speaker 1: I haven't looked yet. Kelly's ball can still be up
• 13:40
  Speaker 1: or down. She hasn't looked yet, right? So that's the
• 13:43
  Speaker 1: difference between the quantum version and the classical version. The
• 13:46
  Speaker 1: classical version is local information that's encoded in the ball.
• 13:49
  Speaker 1: It's predetermined. You learn about the other person's ball, but
• 13:53
  Speaker 1: it was determined in advance. And the quantum version, it's uncertain.
• 13:57
  Speaker 1: So what happens when I look is my ball goes
• 13:59
  Speaker 1: from either up or down, from being in an uncertain
• 14:02
  Speaker 1: state of those two, to being specifically up or specifically down, right?
• 14:06
  Speaker 1: Whatever the universe chooses. And then the weird quantum part
• 14:09
  Speaker 1: is the same thing has to happen to your ball, right? Now,
• 14:12
  Speaker 1: we had two possibilities. Either I have up and you
• 14:15
  Speaker 1: have down, or I have down and you have up.
• 14:17
  Speaker 1: One of those has gotten crossed off the list, right?
• 14:20
  Speaker 1: So now we only have one possibility. So just like
• 14:22
  Speaker 1: in the classical version, seeing mine means I know yours, right?
• 14:26
  Speaker 1: The fascinating thing is that when I measure mine, it's
• 14:30
  Speaker 1: the same quantum state as yours. It's just non-local, it's extended.
• 14:33
  Speaker 1: So the whole quantum state collapses from being in both
• 14:36
  Speaker 1: options to being one specific option where I have up
• 14:39
  Speaker 1: and you have down. So you haven't looked at your
• 14:41
  Speaker 1: ball yet, but me looking at mine collapses your state also.
• 14:46
  Speaker 1: That's the weird quantum thing, that over space and time,
• 14:49
  Speaker 1: your state also collapses when I look at mine. Does
• 14:52
  Speaker 1: that make sense?
• 14:53
  Speaker 2: Yeah, I think so. I'm going to hopefully not get
• 14:55
  Speaker 2: us too far off track with this question, okay? So
• 14:57
  Speaker 2: when you said it's a superposition of up and down,
• 15:00
  Speaker 2: that made me think about Schrodinger's cat, which is a
• 15:03
  Speaker 2: superposition of alive and dead. Whereas I think in PopSci,
• 15:07
  Speaker 2: they're usually like, it's dead until you take it out
• 15:08
  Speaker 2: of the box and then maybe it's alive or something
• 15:10
  Speaker 2: like that.
• 15:10
  Speaker 1: No, they say it's both alive and dead. Right.
• 15:13
  Speaker 2: It's a superposition.
• 15:14
  Speaker 1: Okay.
• 15:14
  Speaker 2: But so the difference is there, you're talking about one
• 15:17
  Speaker 2: cat that's in a box, but that's what superposition is.
• 15:19
  Speaker 2: And entanglement is when you have two things in superposition,
• 15:22
  Speaker 2: but what happens to them is correlated.
• 15:24
  Speaker 1: Yes, that's exactly right. Ding, ding, ding. You're a quantum mechanic. Yeah, exactly. Exactly.
• 15:29
  Speaker 1: And the thing that often trips people up is this
• 15:32
  Speaker 1: feeling like I've done something to my ball. I've measured
• 15:35
  Speaker 1: my ball. I've seen that it's up. And that does
• 15:38
  Speaker 1: something to your ball over there. And that's true. Your
• 15:40
  Speaker 1: ball goes from in a superposition to only in one state, right?
• 15:45
  Speaker 1: And so that feels like you should be able to
• 15:48
  Speaker 1: use that somehow to send information. I am affecting your ball.
• 15:52
  Speaker 1: I measure my ball. It affects your ball. Can I
• 15:55
  Speaker 1: use that to do something? Answer, no. Because you can't
• 15:59
  Speaker 1: tell that I've done that. You have your ball. You
• 16:01
  Speaker 1: haven't looked at it. All you can do is look
• 16:03
  Speaker 1: at it and measure up or down. When you look
• 16:05
  Speaker 1: at it and measure down, you don't know if I've
• 16:08
  Speaker 1: already collapsed it into down by looking at mine or
• 16:11
  Speaker 1: if by measuring it, you collapsed it. There's no test
• 16:13
  Speaker 1: you can do to say like, hey, are you collapsed
• 16:15
  Speaker 1: or not? Did Daniel collapse it? And that's the loophole
• 16:18
  Speaker 1: people usually try to use to build some device that
• 16:21
  Speaker 1: can send information across space and time. But you can't, unfortunately.
• 16:25
  Speaker 2: Boo.
• 16:25
  Speaker 1: It's also unsatisfying because you don't sort of see the
• 16:28
  Speaker 1: magic happening. Like, all you do is you look at
• 16:30
  Speaker 1: your ball and you see up or you see down. Okay,
• 16:33
  Speaker 1: but how do you know that it wasn't determined, right?
• 16:36
  Speaker 1: How do you know that it wasn't? How do you
• 16:37
  Speaker 1: know that there isn't some piece of information that's hidden
• 16:40
  Speaker 1: from you you just didn't know about, some feature of
• 16:43
  Speaker 1: this electron and that electron that really did determine it?
• 16:46
  Speaker 1: Like you can't tell that it was in superposition, can you?
• 16:50
  Speaker 1: That's the big puzzle, right? How do you know that
• 16:52
  Speaker 1: this story we're telling about how the universe keeps both
• 16:54
  Speaker 1: options live until you look, how do we know? And
• 16:57
  Speaker 1: that's Bell's experiment, which we've talked about before. I'm going
• 16:59
  Speaker 1: to get into again today. But Bell's experiment is unsatisfying, right?
• 17:03
  Speaker 1: It's a statistical pattern. You measure these things, you count
• 17:06
  Speaker 1: the numbers. There's no smoking gun.
• 17:08
  Speaker 2: But it's clever.
• 17:09
  Speaker 1: Oh yeah. Oh, it's genius. Absolutely.
• 17:11
  Speaker 3: No, no.
• 17:12
  Speaker 1: I don't mean to say, you know, the guy's not
• 17:14
  Speaker 1: a smart person. It's just like, As somebody who's learning
• 17:17
  Speaker 1: physics and wanting to see a clear and crisp smoking
• 17:20
  Speaker 1: gun example of how there can't be local hidden information,
• 17:24
  Speaker 1: how things really are random, it's a little unsatisfying. And
• 17:27
  Speaker 1: that's where three-particle entanglement comes in. So these guys, Greenberger, Horn, Zellinger...
• 17:34
  Speaker 1: came up with a way by entangling three particles together
• 17:39
  Speaker 1: to make a smoking gun experiment showing that no set
• 17:42
  Speaker 1: of pre-written local answers can reproduce the results. It just
• 17:46
  Speaker 1: absolutely cannot be in a single result from the experiment.
• 17:50
  Speaker 1: So that's exciting.
• 17:51
  Speaker 2: Hold on, hold on. So how can you entangle three particles?
• 17:54
  Speaker 2: I can imagine how like you can have an up
• 17:56
  Speaker 2: and a down and the other.
• 17:57
  Speaker 1: Yeah.
• 17:58
  Speaker 2: Do you have to have three options for their states
• 18:00
  Speaker 2: in order for this to work?
• 18:01
  Speaker 3: Right.
• 18:01
  Speaker 1: And this was the kind of thing that the listeners
• 18:03
  Speaker 1: were confused about. So I want to explain it briefly
• 18:05
  Speaker 1: before we get into the experiments. You know, there's the
• 18:08
  Speaker 1: number two in this example. You have two states and
• 18:11
  Speaker 1: you have two particles. But that's a coincidence. The fact
• 18:14
  Speaker 1: that there are two states doesn't limit you to having
• 18:17
  Speaker 1: two particles. You know, in that example, you had the
• 18:20
  Speaker 1: initial state with spin zero and it turned into two
• 18:23
  Speaker 1: particles with spin up and down and up plus down
• 18:26
  Speaker 1: equals zero. So it all worked out. But you could
• 18:28
  Speaker 1: very easily extend that to three particles. you could start
• 18:31
  Speaker 1: with an initial state that was up instead of zero,
• 18:34
  Speaker 1: and then turn that into three particles, and then you'd
• 18:37
  Speaker 1: have to require that the three particles were up, down, up,
• 18:40
  Speaker 1: so they all added up to the initial state. So
• 18:42
  Speaker 1: there's no limit to the number of particles you can entangle,
• 18:45
  Speaker 1: and you can just keep interacting. Entanglement comes from interactions.
• 18:49
  Speaker 1: So you have a two-particle system, you interact it with
• 18:51
  Speaker 1: another particle, now you have three particles entangled. Or you
• 18:54
  Speaker 1: can create the entanglement from a single interaction from the beginning.
• 18:58
  Speaker 1: And you can also... have particles with multiple spin states.
• 19:02
  Speaker 1: There are particles with three spin states, like the W
• 19:04
  Speaker 1: boson can be up, down, or zero, right? So you
• 19:08
  Speaker 1: have all that freedom.
• 19:10
  Speaker 2: Are you limited by features of the things that you're
• 19:15
  Speaker 2: working with? Like, do they have to have three spin states?
• 19:17
  Speaker 2: Or how the heck do you tell particles that we're
• 19:21
  Speaker 2: starting with up and you have to equal zero at
• 19:24
  Speaker 2: the end? And like, how do you convey that information
• 19:27
  Speaker 2: to particles?
• 19:29
  Speaker 1: You don't convey to the particles the rules of physics
• 19:32
  Speaker 1: limit you to certain outcomes. You know, like when a
• 19:36
  Speaker 1: photon decays to an electron and positron, the rules of
• 19:40
  Speaker 1: angular momentum say that some of those spin states are
• 19:43
  Speaker 1: allowed and some of them are not. And so some
• 19:44
  Speaker 1: of them just never appear because they would violate a
• 19:47
  Speaker 1: law of physics. And so if you create... three particles
• 19:50
  Speaker 1: at once from a single state, then some of the
• 19:53
  Speaker 1: spin outcomes just are not allowed. They will never happen
• 19:56
  Speaker 1: because they violate some law of physics. And that's something
• 19:59
  Speaker 1: we've reverse engineered. We've like watched this happen and we'd notice, huh,
• 20:03
  Speaker 1: this never happens. That never happens. There must be some
• 20:06
  Speaker 1: rule that prevents it. And we've reverse engineered that and
• 20:08
  Speaker 1: now we call that a law of physics. But the
• 20:11
  Speaker 1: reality is you just don't see that in the universe.
• 20:13
  Speaker 1: And we describe that with our laws.
• 20:15
  Speaker 2: So then it sounds like features of the particles determine
• 20:20
  Speaker 2: how many combinations of particles you could have.
• 20:22
  Speaker 1: Yeah, but particles have lots of features. You know, we're
• 20:24
  Speaker 1: talking about spins, but also they can be entangled in
• 20:27
  Speaker 1: their like linear momentum. You know, for example, if you
• 20:30
  Speaker 1: have a Higgs boson at rest and then it turns
• 20:33
  Speaker 1: into two particles flying off in either direction... then their
• 20:37
  Speaker 1: linear momentum has to sum to the original Higgs boson momentum. So,
• 20:41
  Speaker 1: you know, they have to be like going in opposite directions,
• 20:43
  Speaker 1: which makes sense intuitively. Like if a particle explodes into two,
• 20:46
  Speaker 1: they're back to back, which means you measure the direction
• 20:49
  Speaker 1: of one, you automatically know the direction of the other,
• 20:52
  Speaker 1: even if the direction of one has some randomness to it, right?
• 20:55
  Speaker 1: And so that's another example of a correlation between the
• 20:57
  Speaker 1: outcomes that really is a quantum superposition. It's because those
• 21:01
  Speaker 1: two particles are entangled. And so they're entangled in many ways,
• 21:05
  Speaker 1: not just their spin, also their momentum and all sorts
• 21:07
  Speaker 1: of stuff. Yeah. So entanglement is no limitations, basically. Wow.
• 21:12
  Speaker 2: Awesome. I have absorbed that, but I would still like
• 21:15
  Speaker 2: to hear more about Bell's experiment to make sure I'm
• 21:18
  Speaker 2: really following everything. So let's take a break. And when
• 21:20
  Speaker 2: we get back, we're going to dig into Bell's experiment
• 21:22
  Speaker 2: with two particles and then expand your mind out to
• 21:24
  Speaker 2: three particles. Okay, we're back. We are talking about entanglement today.
• 21:48
  Speaker 2: We have managed to mostly keep away from physicist pickup lines.
• 21:51
  Speaker 2: I'm very proud of us. Let's go ahead and jump
• 21:54
  Speaker 2: into Bell's experiments.
• 21:56
  Speaker 1: Yeah, but I consider today's episode basically a party between
• 21:59
  Speaker 1: physics and biology because here we are, right?
• 22:01
  Speaker 2: That's right. That's right.
• 22:02
  Speaker 1: It's a Friday morning coffee party.
• 22:05
  Speaker 2: That's right. Parties don't have to have pickup lines. In fact,
• 22:08
  Speaker 2: they're much better when they don't have pickup lines. So
• 22:11
  Speaker 2: let's party the particle way.
• 22:13
  Speaker 1: That's right. Let's pick up Bell's experiment. So the idea
• 22:16
  Speaker 1: here is to figure out how do we know that
• 22:19
  Speaker 1: the universe really is random, that it's not predetermined in
• 22:24
  Speaker 1: some way we couldn't tell in advance. And that sounds
• 22:26
  Speaker 1: like a tall order because you're trying to rule out
• 22:30
  Speaker 1: basically not just a specific theory for like how the
• 22:34
  Speaker 1: particles could be predetermined, what could be fixing their outcome,
• 22:39
  Speaker 1: but any theory, any theory which ever could have the
• 22:43
  Speaker 1: local information that would determine the outcome of your experiment, right?
• 22:47
  Speaker 1: And so that seems like a tall order, like how
• 22:50
  Speaker 1: do you tell if the universe was random and how
• 22:52
  Speaker 1: do you rule out every possible theory? And so Bell's
• 22:55
  Speaker 1: experiment is really genius. This guy invented this way of
• 22:59
  Speaker 1: distinguishing between these two outcomes. And it's very clever, but
• 23:02
  Speaker 1: it's also complicated and a little hard to follow. And
• 23:06
  Speaker 1: the outcome is not really a smoking gun. But as
• 23:10
  Speaker 1: a way to contrast it with a three-particle experiment, I
• 23:13
  Speaker 1: think it's a useful warm-up.
• 23:15
  Speaker 2: After that intro, I can't wait. Let's dig in.
• 23:19
  Speaker 1: It's really worth understanding. And all the nuances are really fun.
• 23:23
  Speaker 1: So the idea is, just like the example we started
• 23:26
  Speaker 1: with before... you have two entangled electrons, right? That means
• 23:30
  Speaker 1: if one is spin up in one direction, the other
• 23:32
  Speaker 1: one has to be spin down in that same direction. Okay,
• 23:35
  Speaker 1: but now we're gonna complicate things a little bit because
• 23:37
  Speaker 1: before we were talking about the electrons having spin up
• 23:40
  Speaker 1: and spin down as if there's only one kind of
• 23:42
  Speaker 1: spin they can have, right? Just like spin up or
• 23:44
  Speaker 1: spin down. But the truth is electrons are three-dimensional objects.
• 23:48
  Speaker 1: And so when you measure their spin, you have to
• 23:50
  Speaker 1: ask in which direction, right? Like think about the earth.
• 23:54
  Speaker 1: The Earth is spinning around its axis, right? But it
• 23:56
  Speaker 1: could have been spinning around a different axis. In fact,
• 23:59
  Speaker 1: because there are three dimensions of space, you can imagine
• 24:01
  Speaker 1: three different ways the Earth could be spinning, right? It
• 24:04
  Speaker 1: could be spinning around the axis that goes between the
• 24:06
  Speaker 1: North and the South Pole, like it does. Or you
• 24:08
  Speaker 1: could stick an axis through the equator, right? And it
• 24:12
  Speaker 1: could spin that way. Or another axis through the equator
• 24:14
  Speaker 1: at 90 degrees to that, and it could spin that way.
• 24:16
  Speaker 1: It's not, right? There are three different ways that the
• 24:18
  Speaker 1: Earth could spin. Or in reality, it could be any
• 24:21
  Speaker 1: mixture of those three, right? So the Earth is spinning
• 24:24
  Speaker 1: around one axis, but there are more complicated ways to spin.
• 24:28
  Speaker 1: And the same is true also for quantum particles. When
• 24:30
  Speaker 1: you measure their spin, you have to say, I'm measuring
• 24:33
  Speaker 1: your spin along this axis or along that axis or
• 24:35
  Speaker 1: along the other axis. And the weird thing about quantum
• 24:39
  Speaker 1: spin is that no matter what you ask, you either
• 24:42
  Speaker 1: get up or down. There's no intermediate values. Like if
• 24:46
  Speaker 1: you try to measure the Earth's spin using an axis
• 24:48
  Speaker 1: that was not aligned with the North and South Pole axis,
• 24:51
  Speaker 1: you would get some intermediate value. Say, oh yeah, it's
• 24:53
  Speaker 1: spinning along that axis a little bit. It's also spinning
• 24:56
  Speaker 1: along another axis a little bit. But that's not true
• 24:58
  Speaker 1: for quantum particles. You either just get up or down.
• 25:01
  Speaker 1: The answers are related, but they're always either up or down.
• 25:05
  Speaker 2: Can I back you up real quick?
• 25:06
  Speaker 1: Yeah, please.
• 25:06
  Speaker 2: I'm not sure the Earth thing was helping. I think
• 25:08
  Speaker 2: it might've confused me. So you've said there's three ways
• 25:09
  Speaker 2: that it could spin. So say you've got an axis.
• 25:12
  Speaker 2: Earth can spin the way it's spinning now. It could
• 25:15
  Speaker 2: go exactly backwards from the way that it's going, like
• 25:18
  Speaker 2: spin in the opposite direction. And then what is the
• 25:19
  Speaker 2: third way that it could spin?
• 25:21
  Speaker 1: Oh, I see. Spinning the opposite direction is still spinning
• 25:24
  Speaker 1: around the same axis.
• 25:25
  Speaker 2: Oh, but you said direction matters, but that doesn't count
• 25:29
  Speaker 2: as changing direction?
• 25:31
  Speaker 1: Right. So, you know, imagine spinning the way that we're
• 25:34
  Speaker 1: spinning around the north-south pole. Call that, you know, positive.
• 25:38
  Speaker 2: Yeah, okay.
• 25:38
  Speaker 1: Yeah. And spinning the other direction around that same pole,
• 25:42
  Speaker 1: that would be negative. But it's around the same axis.
• 25:44
  Speaker 1: I'm talking about measuring its spin along a different line. Like,
• 25:48
  Speaker 1: is it spinning around a line that goes through the equator? So, like,
• 25:51
  Speaker 1: take your Earth and stick a bar through it horizontally.
• 25:55
  Speaker 1: And imagine the Earth spinning around that line instead of
• 25:57
  Speaker 1: spinning around a vertical line. That would be a different axis.
• 26:00
  Speaker 2: But then couldn't you have infinite kinds of spin then?
• 26:03
  Speaker 2: Because that axis could be anywhere?
• 26:05
  Speaker 1: Yes, absolutely. There's infinite number of axes you could choose.
• 26:09
  Speaker 1: And if you have a 3D physical classical object, then
• 26:12
  Speaker 1: as you change the axis, you get more or less
• 26:14
  Speaker 1: of that spin captured by that axis, right?
• 26:16
  Speaker 2: Okay, I'm with you now.
• 26:17
  Speaker 3: Mm-hmm.
• 26:18
  Speaker 1: Okay. All right. Thanks. And so you can also do
• 26:20
  Speaker 1: that for an electron. So for example, if you have
• 26:23
  Speaker 1: two electrons and I measure mine to be up and
• 26:27
  Speaker 1: you measure yours to be down and we could say, well,
• 26:29
  Speaker 1: let's flip the axis we're measuring, right? Let's just turn
• 26:32
  Speaker 1: it 180 degrees. Then we're going to get the opposite results.
• 26:35
  Speaker 1: If I got up and you got down, then I'll
• 26:37
  Speaker 1: now get down and you'll get up, right? Okay. That's easy. Now,
• 26:41
  Speaker 1: if we flip the axis a little bit, like by
• 26:44
  Speaker 1: some angle, instead of all the way, 180 degrees, then
• 26:47
  Speaker 1: we get some different results up and down, but it
• 26:49
  Speaker 1: depends on the angle. And so Bell's axis does this.
• 26:54
  Speaker 1: It says, let's pick three spin directions in advance at random.
• 26:58
  Speaker 1: We'll call them A, B, and C, okay? And then
• 27:02
  Speaker 1: I'm gonna choose randomly which axis to measure my electron,
• 27:05
  Speaker 1: and you're gonna choose randomly which axis to measure your electron.
• 27:08
  Speaker 1: And then we're gonna ask, how often do we get
• 27:11
  Speaker 1: the opposite spin? Now, if we choose the same axis,
• 27:14
  Speaker 1: We get the opposite spin because one has to be up,
• 27:16
  Speaker 1: the other one has to be down. If we choose
• 27:19
  Speaker 1: axes that are upside down, then we'll always get the
• 27:21
  Speaker 1: same spin, right? I'll measure up and you're measuring down
• 27:25
  Speaker 1: along my axis. But if your axis is reversed, you're
• 27:28
  Speaker 1: going to get an up also. And if you choose
• 27:30
  Speaker 1: an axis that's like at some weird crazy angle, you're
• 27:33
  Speaker 1: sometimes going to get up, sometimes going to get down.
• 27:36
  Speaker 1: So you do this a bunch of times and you
• 27:38
  Speaker 1: measure how often do we get opposite spins, right? A
• 27:43
  Speaker 1: third of the time, you use the same axis, so
• 27:45
  Speaker 1: you're going to get opposite spins. And this is where
• 27:48
  Speaker 1: the two ideas separate. Remember, we're trying to distinguish between
• 27:51
  Speaker 1: quantum mechanics that says, look, everything is random and it's
• 27:54
  Speaker 1: determined only when you measure it, and the hidden variable
• 27:57
  Speaker 1: theory that says, no, it's predetermined. There's some information on
• 28:01
  Speaker 1: the particles that tells you all along which one was
• 28:04
  Speaker 1: up and which one was down. And so the hidden
• 28:07
  Speaker 1: variable theory says, well, We know the answer is all
• 28:10
  Speaker 1: in advance. We can just make a table of the outcomes.
• 28:13
  Speaker 1: And if you do that calculation, you can see that
• 28:15
  Speaker 1: you can't get the same spin more than two thirds
• 28:18
  Speaker 1: of the time. Like one third, you're going to get
• 28:20
  Speaker 1: the same spin because we flip axes. And then sometimes
• 28:25
  Speaker 1: you get the same axis because the angles. But if
• 28:28
  Speaker 1: you do the math, you get the same spin less
• 28:31
  Speaker 1: than two thirds of the time. But quantum mechanics disagrees.
• 28:34
  Speaker 1: Quantum mechanics says, no, you can get the same spin
• 28:36
  Speaker 1: up to 75% of the time. because of the correlations
• 28:41
  Speaker 1: between these two particles. And so this feels a little fuzzy.
• 28:45
  Speaker 1: I just sort of like said that and it is
• 28:47
  Speaker 1: a little bit fuzzy. It comes out of the math
• 28:49
  Speaker 1: and I've never found a great like intuitive way to
• 28:51
  Speaker 1: explain like why the quantum mechanics predicts something different from
• 28:55
  Speaker 1: the hidden variables. It just sort of comes out of
• 28:57
  Speaker 1: the math and you do the experiment and you get
• 29:00
  Speaker 1: an answer that's like 75% and that tells you, okay,
• 29:03
  Speaker 1: it's quantum mechanics. And you can't point to any individual
• 29:06
  Speaker 1: experiment and say, like, look, this one was up and
• 29:08
  Speaker 1: that one was down, and that's impossible by hidden variables.
• 29:11
  Speaker 1: It's just the pattern of the measurements that you've made
• 29:14
  Speaker 1: that tells you you've seen them get opposite spin more
• 29:16
  Speaker 1: often than you would expect from hidden variables. And it's
• 29:19
  Speaker 1: just the rate you would expect from quantum mechanics. Okay.
• 29:22
  Speaker 2: And so just to confirm, so you're measuring, for example,
• 29:26
  Speaker 2: are the particles up or down? And the only thing
• 29:28
  Speaker 2: that's changing is the axis along which you make that measurement.
• 29:31
  Speaker 3: Yes.
• 29:32
  Speaker 2: So you're not measuring multiple things about these particles. You're
• 29:35
  Speaker 2: just looking at it from a different like angle.
• 29:37
  Speaker 1: That's right. Yeah. Okay. And in the case of. quantum
• 29:40
  Speaker 1: mechanics like if you adjust the angles correctly so the
• 29:43
  Speaker 1: angles are like all 120 degrees apart then you get
• 29:46
  Speaker 1: this weird behavior and you know i can give a
• 29:49
  Speaker 1: little bit more intuition the reason that quantum mechanics gives
• 29:51
  Speaker 1: a different prediction from hidden variables is comes from the
• 29:54
  Speaker 1: interference of the possibilities, right? Which is something that quantum
• 29:57
  Speaker 1: mechanics has and the hidden variables theory doesn't. Hidden variables
• 30:00
  Speaker 1: is just like, look, everything's determined in advance. You can
• 30:03
  Speaker 1: write down before you look at the particles, the possible
• 30:06
  Speaker 1: outcomes and know which ones are going to happen. Quantum
• 30:09
  Speaker 1: mechanics says you can't, there are these various possibilities and
• 30:12
  Speaker 1: they interfere with each other. The way you see like
• 30:15
  Speaker 1: interference in the double slit experiment, right? If you do
• 30:18
  Speaker 1: not collapse the possibilities, then those various possibilities can interfere
• 30:22
  Speaker 1: with each other and give a change in the actual prediction.
• 30:24
  Speaker 1: And that's what's happening here. But again, it's kind of subtle, right?
• 30:28
  Speaker 1: It does tell you something amazing about the universe. It
• 30:30
  Speaker 1: tells you that it really is quantum mechanical. There isn't
• 30:33
  Speaker 1: any secret information that fixes the outcome, right? That this
• 30:38
  Speaker 1: really does happen at a distance. Quantum mechanics is non-local.
• 30:42
  Speaker 1: Like you measure one particle over here, And it determines,
• 30:46
  Speaker 1: it helps cross things off the list for the other particle.
• 30:49
  Speaker 1: And in that sense, determines stuff that's happening far away.
• 30:52
  Speaker 1: And that's fascinating and bizarre. And there's all sorts of
• 30:56
  Speaker 1: weird puzzles there about how to incorporate that with special relativity. Remember,
• 31:00
  Speaker 1: special relativity tells us that what I mean by now
• 31:04
  Speaker 1: and what somebody else means by now are different. And
• 31:07
  Speaker 1: simultaneity is not guaranteed in special relativity. So if you're
• 31:10
  Speaker 1: talking about two particles simultaneously collapsing over space-time, Then like, well,
• 31:15
  Speaker 1: how does that simultaneous for me and simultaneous for Zach,
• 31:19
  Speaker 1: who's flying by us at half the speed of light?
• 31:22
  Speaker 1: And we have a whole episode digging into that and
• 31:23
  Speaker 1: like retro causal theories of quantum mechanics. We're not going
• 31:26
  Speaker 1: to get into that today, but it's amazing what it
• 31:29
  Speaker 1: tells you about the universe. But still, it's kind of
• 31:31
  Speaker 1: unsatisfying because like, yeah, you know, you're counting the numbers,
• 31:35
  Speaker 1: you're getting a seven. And you know that if you
• 31:38
  Speaker 1: get a seven, it's quantum mechanics. If you get a five,
• 31:40
  Speaker 1: it's hidden variables. But like, show me the experiment that
• 31:43
  Speaker 1: really proves it. And I always found this experiment to
• 31:46
  Speaker 1: be kind of unsatisfying. And I think a lot of
• 31:48
  Speaker 1: people did, which is why three smart folks came up
• 31:51
  Speaker 1: with a more complicated version of the experiment that is
• 31:54
  Speaker 1: more complex, but it does give a very crisp and
• 31:57
  Speaker 1: clear smoking gun of quantum mechanics.
• 32:00
  Speaker 2: But when Bell came up with this, did it, like,
• 32:03
  Speaker 2: make a big wave?
• 32:03
  Speaker 1: Oh, yeah. Absolutely, it did. But it took a little while.
• 32:07
  Speaker 1: I mean, Bell was, like, not a big name at
• 32:10
  Speaker 1: the time, and he published his theorem in in this
• 32:13
  Speaker 1: little journal that not a lot of people read. And
• 32:16
  Speaker 1: the reason he chose that is because it didn't charge
• 32:19
  Speaker 1: you to publish. Like a lot of times when you
• 32:21
  Speaker 1: submit a paper, they're like, great, we accept your paper.
• 32:25
  Speaker 1: Please pay $ 4, 000 of publishing fees. And it's like, what?
• 32:29
  Speaker 1: Oh my gosh. It's expensive to publish a paper.
• 32:31
  Speaker 3: Yeah.
• 32:31
  Speaker 1: But some journals are free. Like society journals tend to
• 32:34
  Speaker 1: not charge as much. And so he actually published in
• 32:37
  Speaker 1: a journal that paid the authors who published there. Amazing.
• 32:40
  Speaker 2: That happens?
• 32:41
  Speaker 1: Yeah.
• 32:41
  Speaker 2: Yeah.
• 32:42
  Speaker 1: But it also means that they were cheap in other ways.
• 32:44
  Speaker 1: They didn't provide free reprints of the article. This is
• 32:46
  Speaker 1: before you could just download any article online. And so
• 32:50
  Speaker 1: he used the money he was paid to publish the
• 32:53
  Speaker 1: article to buy copies of the article that he then
• 32:55
  Speaker 1: sent to other physicists. So it took a little while
• 32:57
  Speaker 1: for people to get the word. But once people read
• 32:59
  Speaker 1: the paper, they were like, oh my gosh, this is
• 33:02
  Speaker 1: a big deal. And then people went and did the experiments.
• 33:04
  Speaker 1: And there's been a whole series of these experiments over
• 33:07
  Speaker 1: the last few decades verifying Bell's predictions and closing loopholes.
• 33:11
  Speaker 1: There's a bunch of assumptions in this experiment, like you
• 33:15
  Speaker 1: have to get these particles far enough away that when
• 33:18
  Speaker 1: they collapse, information can't travel from one to the other
• 33:22
  Speaker 1: in time to communicate the collapse. So you have to
• 33:25
  Speaker 1: get them far enough away and measure them quickly enough
• 33:28
  Speaker 1: that you can verify that light doesn't have time to
• 33:30
  Speaker 1: go from one particle to the other. Because otherwise, maybe
• 33:32
  Speaker 1: somehow the information did sneak from one to the other.
• 33:35
  Speaker 1: So you got better and better versions of this experiment
• 33:38
  Speaker 1: that were further and further apart to close loopholes. And
• 33:41
  Speaker 1: there are still loopholes. The experiment relies on choosing these
• 33:45
  Speaker 1: axes randomly. And so what if you don't have a
• 33:48
  Speaker 1: real random number generator? What if your choice of those
• 33:52
  Speaker 1: axes is actually predetermined by some demon in the early
• 33:56
  Speaker 1: universe who set up the whole universe so that it
• 33:58
  Speaker 1: looks like it was quantum mechanical, but actually it's not?
• 34:01
  Speaker 1: That's called superdeterminism. And That's technically a live option to
• 34:06
  Speaker 1: explain this, though I find it kind of bonkers.
• 34:08
  Speaker 2: The demon thing is superdeterminism? Yes.
• 34:11
  Speaker 1: Superdeterminism says, let's set up the universe in advance in
• 34:15
  Speaker 1: a way so that when humans do these experiments, they
• 34:17
  Speaker 1: get results that look quantum mechanical, but we're just going
• 34:19
  Speaker 1: to predetermine the quantum mechanical appearing outcome.
• 34:23
  Speaker 3: Wow. Right?
• 34:24
  Speaker 1: By tweaking with the random numbers so they're not really random.
• 34:27
  Speaker 1: I mean, people think deeply about this stuff, and they should.
• 34:29
  Speaker 1: It's like... we're drawing bonkers conclusions about the natures of reality.
• 34:33
  Speaker 1: Let's make sure we didn't miss anything. You know, I
• 34:36
  Speaker 1: get it. And so people have been doing these experiments,
• 34:39
  Speaker 1: closing loopholes, winning Nobel prizes for that, and also inventing
• 34:43
  Speaker 1: more complicated versions that are clear and crisper proofs that
• 34:47
  Speaker 1: the universe really is quantum mechanical. All right.
• 34:50
  Speaker 2: Well, now that we've got Bell's experiment and two entangled
• 34:53
  Speaker 2: particles all entangled up in our brain, let's go ahead
• 34:57
  Speaker 2: and jump to three particles. And we're going to do
• 34:59
  Speaker 2: that after the break. So Welcome back to Daniel and
• 35:22
  Speaker 2: Kelly's Extraordinary Universe. We are going to talk about entangling
• 35:25
  Speaker 2: three particles now in the G-H-K experiment.
• 35:29
  Speaker 1: G-H-K. Kelly, come on.
• 35:32
  Speaker 2: All right.
• 35:35
  Speaker 1: So Bell's experiment, very cool, but there's no smoking gun there.
• 35:39
  Speaker 1: And so people were wondering, can we invent an experiment
• 35:43
  Speaker 1: where there's an outcome from a single run of the experiment?
• 35:46
  Speaker 1: that shows you that only quantum mechanics can explain this, right?
• 35:50
  Speaker 1: Can it do something which is impossible under hidden variables?
• 35:54
  Speaker 1: Bell's experiment does something which is like less likely under
• 35:57
  Speaker 1: hidden variables. And if you run it often enough, you
• 35:59
  Speaker 1: can exclude it and say, okay, the outcomes don't seem
• 36:02
  Speaker 1: like hidden variables, but it doesn't do something which is
• 36:05
  Speaker 1: impossible under hidden variables. So people are like, can we
• 36:08
  Speaker 1: come up with an experiment where the universe does something
• 36:11
  Speaker 1: which is just flat out impossible under hidden variables? And therefore,
• 36:16
  Speaker 1: there must be quantum mechanics. And to do that, you
• 36:19
  Speaker 1: need three entangled particles. And that's why we're doing this
• 36:22
  Speaker 1: whole episode about three entangled particles, because this is what
• 36:25
  Speaker 1: GHK came up with.
• 36:26
  Speaker 2: But the payoff is now, people.
• 36:29
  Speaker 1: All right. So thank you to everybody who's curious about
• 36:31
  Speaker 1: this topic and stayed with us so far. We're about
• 36:33
  Speaker 1: to get weirder, all right? Oh, yay. Yeah. And so
• 36:37
  Speaker 1: this is a really strange explanation. What we're going to
• 36:39
  Speaker 1: do is we're going to describe an experiment with detectors.
• 36:43
  Speaker 1: And we're not going to explain how those detectors work.
• 36:45
  Speaker 1: We're going to describe an experiment, and then we're going
• 36:47
  Speaker 1: to design an outcome to that experiment that's possible in
• 36:50
  Speaker 1: quantum mechanics and impossible in hidden variables, okay? Okay. Without
• 36:55
  Speaker 1: being specific about how the detectors work, because we don't care.
• 36:58
  Speaker 1: So imagine we have something which entangles three particles and
• 37:02
  Speaker 1: then shoots them out in three different directions, okay? Okay.
• 37:06
  Speaker 1: And those particles then hit detectors, and each detector has
• 37:10
  Speaker 1: a switch on it. one or two. So you have
• 37:12
  Speaker 1: like a switch on it. It can be either in
• 37:13
  Speaker 1: state one or state two. And it also has two lights,
• 37:17
  Speaker 1: red and green. So the particles are entangled. They shoot out,
• 37:22
  Speaker 1: they get to each detector. And then each detector has
• 37:25
  Speaker 1: some algorithm that says, based on how the switch is set,
• 37:28
  Speaker 1: I'm going to either flash red or I'm going to
• 37:30
  Speaker 1: flash green. Okay. Okay. So you might be wondering like,
• 37:33
  Speaker 1: how does this detector work? Is it as simple as like,
• 37:36
  Speaker 1: if the switch is set to one, it flashes green.
• 37:38
  Speaker 1: And if a switch is set to two, it flashes red. Well,
• 37:41
  Speaker 1: we haven't set that up yet. We're going to start
• 37:43
  Speaker 1: instead from the outcome we want. We're going to devise
• 37:47
  Speaker 1: an outcome of this experiment, and then we're going to see,
• 37:50
  Speaker 1: can we build a hidden variables version that gives us
• 37:53
  Speaker 1: that outcome? And can we build a quantum mechanical version
• 37:56
  Speaker 1: that gives us that outcome? And somebody has already thought
• 37:58
  Speaker 1: about this and come up with an outcome that's impossible
• 38:02
  Speaker 1: for hidden variables and possible for quantum mechanics. That's where
• 38:05
  Speaker 1: we're going to walk through. And so we need to
• 38:07
  Speaker 1: think about what outcome do we want from this experiment?
• 38:11
  Speaker 1: given any of the settings of the switches. So like,
• 38:13
  Speaker 1: what if all the switches are one? What if all
• 38:15
  Speaker 1: the switches are two? What if two of the switches
• 38:18
  Speaker 1: are one and one of the switches is two? Okay,
• 38:20
  Speaker 1: so we're gonna design the outcome of the experiment so
• 38:23
  Speaker 1: that it's possible to do in quantum mechanics and not
• 38:25
  Speaker 1: possible to do in hidden variables. And we're gonna start
• 38:28
  Speaker 1: with what happens to this experiment. We have three detectors
• 38:31
  Speaker 1: and three switches. What happens to this experiment if one
• 38:34
  Speaker 1: detector has the switch set to one and two of
• 38:37
  Speaker 1: them have the switches set to two, okay? And what
• 38:40
  Speaker 1: we want is that in that scenario, we have three flashes, right?
• 38:44
  Speaker 1: Three detectors with three lights. We want an odd number
• 38:47
  Speaker 1: of them to be red. So we want like red, green, green,
• 38:52
  Speaker 1: or green, green, red, or red, red, red. Okay, that's
• 38:55
  Speaker 1: the possible outcomes. And then if all three switches are
• 38:58
  Speaker 1: set to one, like one on one, we want an
• 39:01
  Speaker 1: even number of reds. So if one of the detectors
• 39:03
  Speaker 1: has a switch at one, we want an odd number
• 39:05
  Speaker 1: of reds. If all three of them have switches at one,
• 39:09
  Speaker 1: We want an even number of reds. And the other
• 39:11
  Speaker 1: configurations don't matter. They're not interesting. So we've designed this outcome.
• 39:17
  Speaker 1: It feels kind of weird. We're thinking about how the
• 39:19
  Speaker 1: detectors will flash red and green given their lights, et cetera.
• 39:24
  Speaker 1: And so now let's think about, can we make this
• 39:27
  Speaker 1: happen in the hidden variables case? Can we design detectors?
• 39:31
  Speaker 1: Is it even possible to design detectors that respond in
• 39:34
  Speaker 1: this way if everything is predetermined? Remember, the particles can communicate.
• 39:39
  Speaker 1: They're entangled, so they can have some correlation between them.
• 39:42
  Speaker 1: And then they fly off to their detectors. And when
• 39:45
  Speaker 1: they get to the detector in the hidden variables version,
• 39:47
  Speaker 1: There has to be whatever information you need to flash
• 39:50
  Speaker 1: the right way based on whatever the particle has. So
• 39:53
  Speaker 1: in the hidden variables version, we can like write some
• 39:56
  Speaker 1: instructions into the particle. We can say like, all right,
• 39:59
  Speaker 1: if the switch is one, flash red. If the switch
• 40:01
  Speaker 1: is two, flash green, right? So we can give little
• 40:04
  Speaker 1: instructions to the particles. When they get to the detector,
• 40:06
  Speaker 1: they know which light to flash.
• 40:08
  Speaker 2: Sorry, I think I'm not totally following that. So the
• 40:10
  Speaker 2: particle arrives at the detector.
• 40:12
  Speaker 1: Yeah.
• 40:13
  Speaker 2: What is it doing to the detector to make it
• 40:14
  Speaker 2: flash a light?
• 40:15
  Speaker 1: It gets to decide. The particle arrives at the detector
• 40:17
  Speaker 1: and it gets to decide whether it flashes red or green.
• 40:20
  Speaker 2: And it doesn't matter if it's on one or two?
• 40:22
  Speaker 1: It decides based on whether the detector is at one
• 40:25
  Speaker 1: or two when it gets there. And it can't know
• 40:27
  Speaker 1: that in advance, right? Like, it gets to the detector
• 40:29
  Speaker 1: and it sees, okay, you're set one, I'm going to
• 40:32
  Speaker 1: flash red. Or set two, I'm going to flash green.
• 40:34
  Speaker 1: So each particle, you have to give a little instruction
• 40:36
  Speaker 1: set to say, when you get to the detector, here's
• 40:39
  Speaker 1: what to do depending on how the switch is set.
• 40:42
  Speaker 1: Here's which light to flash. Okay.
• 40:43
  Speaker 2: And so then just to be clear, we're doing like
• 40:45
  Speaker 2: a thought experiment that would help you understand what happened
• 40:49
  Speaker 2: in a more complicated experiment because you can't give particles
• 40:52
  Speaker 2: those kinds of instructions.
• 40:54
  Speaker 1: And we're not being specific about like, how would you
• 40:56
  Speaker 1: inscribe these instructions in the particle? Because we want to
• 40:58
  Speaker 1: be very general. We want this to apply to any
• 41:00
  Speaker 1: hidden variables theory, any way that you're inscribing this information.
• 41:04
  Speaker 1: That's why we're being sort of vague about it. Okay.
• 41:06
  Speaker 1: And so, you know, the particles don't know in advance,
• 41:09
  Speaker 1: is the detector set to one or two? They have
• 41:11
  Speaker 1: to be prepared for either outcome. And so they have
• 41:13
  Speaker 1: to know which light to flash when they arrive. And
• 41:17
  Speaker 1: so the question is, can you give each particle the
• 41:21
  Speaker 1: instructions it needs so that when it gets to the detector,
• 41:24
  Speaker 1: it satisfies our requirement? Our requirement was if only one
• 41:28
  Speaker 1: detector has switched one, you get an odd number of reds.
• 41:31
  Speaker 1: If all three have switched one, you get an even
• 41:33
  Speaker 1: number of reds. So let's consider the first case where
• 41:36
  Speaker 1: one detector is one and the other two are two.
• 41:39
  Speaker 1: So like the switches are like one, two, two, or two, two, one.
• 41:43
  Speaker 1: So you can devise a set of instructions to give
• 41:46
  Speaker 1: all your little particles so that when they get there,
• 41:49
  Speaker 1: they do the right thing. You know, for example, particle one,
• 41:52
  Speaker 1: you can say, flash me a red if you see
• 41:55
  Speaker 1: one and green if you see two. And the other
• 41:57
  Speaker 1: particles get the opposite instructions. Green if you see one,
• 42:00
  Speaker 1: red if you see two. And then for all the settings, one, two, two, two, one, two, two, two, one,
• 42:05
  Speaker 1: you always get an odd number of reds. And you
• 42:07
  Speaker 1: can sit down and work this out. And so that's cool.
• 42:10
  Speaker 1: You can actually inscribe the instructions into the particles in
• 42:12
  Speaker 1: the hidden variable theory. It works and you can get
• 42:15
  Speaker 1: the desired outcome for the case where one switch is
• 42:19
  Speaker 1: one and the other one are two. All right. Okay.
• 42:21
  Speaker 2: And the particle doesn't know what's happening at the other detectors.
• 42:24
  Speaker 1: That's right.
• 42:25
  Speaker 2: It only knows, yeah, what's happening at its detector and
• 42:27
  Speaker 2: you gave it instructions for what to do.
• 42:29
  Speaker 1: Exactly. We gave it instructions for what to do. So
• 42:31
  Speaker 1: we're devising some general hidden variable theory to give the
• 42:33
  Speaker 1: desired outcome for this case. The one of the switches
• 42:36
  Speaker 1: is one and the other two switches are two. And
• 42:39
  Speaker 1: there's exactly eight sets of instructions you can give that
• 42:43
  Speaker 1: make this work.
• 42:44
  Speaker 3: Okay.
• 42:44
  Speaker 1: And people went through and enumerated all of them. And like,
• 42:47
  Speaker 1: you know, the instructions are very simple. It's like red
• 42:50
  Speaker 1: if one, green if two or whatever. And you can
• 42:52
  Speaker 1: give different instructions to each of the three particles. And
• 42:54
  Speaker 1: so you have that freedom and there's eight different ways
• 42:56
  Speaker 1: to do it. That's cool. All right. Now, what about
• 43:00
  Speaker 1: the three switches or one case? Okay. Now the same
• 43:03
  Speaker 1: set of instructions have to work because you don't know
• 43:06
  Speaker 1: in advance how what the detectors are set to. And
• 43:08
  Speaker 1: somebody could even flip the switches after the particles have
• 43:12
  Speaker 1: been given their instructions and before they reach the detector.
• 43:14
  Speaker 1: So the instructions have to work for both cases, okay?
• 43:18
  Speaker 1: So in the three switches equals one case, you want
• 43:21
  Speaker 1: an even number of reds. Problem is that none of
• 43:25
  Speaker 1: the eight valid instructions that work for the other case
• 43:27
  Speaker 1: work for this case. So in the example I gave
• 43:29
  Speaker 1: you before where particle one gives a red, if you
• 43:32
  Speaker 1: see switch one and particles two and three give a
• 43:35
  Speaker 1: green if they see switch one, then that would give
• 43:37
  Speaker 1: you red, green, green, which is an odd number of reds,
• 43:40
  Speaker 1: which is wrong. We needed to give an even number
• 43:43
  Speaker 1: of reds for the three switches case. And there is
• 43:46
  Speaker 1: no way to write the instructions for the particles that
• 43:50
  Speaker 1: satisfies the one switch is set to one and the
• 43:53
  Speaker 1: three switches are set to one case. You can figure
• 43:55
  Speaker 1: out all the valid instructions for the one, two, two
• 43:58
  Speaker 1: case that works, but none of the valid instructions for
• 44:01
  Speaker 1: that case also work for the one, one, one case,
• 44:04
  Speaker 1: which means If you build this thing and you run
• 44:08
  Speaker 1: it and you set the switches to 1, 1, 1,
• 44:11
  Speaker 1: and you ever see an even number of reds, then
• 44:15
  Speaker 1: you know that it's not hidden variables because it's impossible
• 44:19
  Speaker 1: to write instructions for a hidden variable theory that ever
• 44:22
  Speaker 1: gives you an even number of reds when the detectors
• 44:25
  Speaker 1: are set to 1, 1, 1. It's just impossible. We
• 44:27
  Speaker 1: just proved it. There's no way to devise that experiment.
• 44:31
  Speaker 1: But fascinatingly, and this is why we started with this setup,
• 44:34
  Speaker 1: It is possible in quantum mechanics. You can organize your
• 44:39
  Speaker 1: particles and entangle them in the right way to maintain
• 44:43
  Speaker 1: superposition and correlations where you choose one and that affects
• 44:47
  Speaker 1: the other, right? The particles in the hidden variable theory
• 44:50
  Speaker 1: can't talk to each other at all. They have the
• 44:51
  Speaker 1: instructions and they go off and they do their thing.
• 44:53
  Speaker 1: But in quantum mechanics, what happens to one particle can
• 44:56
  Speaker 1: affect the other particles, right? Okay. So you can build
• 44:59
  Speaker 1: a quantum mechanical version of this, which does have this outcome.
• 45:03
  Speaker 1: which when you set all the detectors to 111, gives
• 45:05
  Speaker 1: you an even number of reds. And it works on
• 45:09
  Speaker 1: measuring particle spin in different directions. And you can have
• 45:12
  Speaker 1: like little devices that measure their spin. If it's spin up,
• 45:15
  Speaker 1: you get red. If it's spin down, you get green.
• 45:18
  Speaker 1: And the key to the quantum mechanical setup is how
• 45:20
  Speaker 1: you entangle those three particles. You have to create this
• 45:23
  Speaker 1: special state where you have the possibility of them being up, up, up,
• 45:27
  Speaker 1: and the possibility of them being down, down, down, but
• 45:30
  Speaker 1: you combine those two states with a minus sign instead
• 45:33
  Speaker 1: of a plus sign. And that gives you all the
• 45:36
  Speaker 1: exact correlations that you need and gives you exactly the
• 45:40
  Speaker 1: right behavior for all the conditions that we set up before,
• 45:42
  Speaker 1: no matter what the detector switches are set to. And
• 45:46
  Speaker 1: this was a theory first, like people came up with
• 45:48
  Speaker 1: this idea. They're like, okay, it's possible to do this
• 45:51
  Speaker 1: in quantum mechanics. It's impossible to do it with hidden variables.
• 45:56
  Speaker 1: But it was just like a thought experiment. So these guys, Greenberger, Horn,
• 46:01
  Speaker 1: and Zellinger are the first ones to think up this experiment.
• 46:04
  Speaker 1: And it was really complicated. It was really hard to understand.
• 46:06
  Speaker 1: A guy named David Merman, who's a physicist and an
• 46:09
  Speaker 1: expert in quantum mechanics, he simplified it. He came up
• 46:12
  Speaker 1: with this red-green detector switch one-two thing. And if you
• 46:17
  Speaker 1: can believe it, that's the simpler version of the description.
• 46:20
  Speaker 1: It's already like a lot to absorb. Then people actually
• 46:24
  Speaker 1: went and did it. They built these devices. So guys
• 46:27
  Speaker 1: named Pan, Baumister, Daniel, Weinfurter, and Zellinger of GHZ, who
• 46:32
  Speaker 1: came up with this, actually built this thing and they
• 46:34
  Speaker 1: made it work in the year 2000. And they got
• 46:37
  Speaker 1: that outcome. They got an even number of reds when
• 46:40
  Speaker 1: they set the detectors to 111, even though it's impossible
• 46:44
  Speaker 1: for that to happen in the hidden variables theory. And
• 46:47
  Speaker 1: then Zellinger won the Nobel Prize in 2022 for helping
• 46:51
  Speaker 1: close some of these hidden variable loopholes And that's because
• 46:55
  Speaker 1: of this smoking gun result. He made the universe do
• 47:00
  Speaker 1: something that's proven to be impossible with hidden variables and
• 47:04
  Speaker 1: only possible in quantum mechanics. And so you run the experiment,
• 47:08
  Speaker 1: you get an even number of flashes. It's definitely impossible
• 47:12
  Speaker 1: with hidden variables. That single run of the experiment shows
• 47:15
  Speaker 1: you that there can't be hidden variables there.
• 47:17
  Speaker 2: Was there a physics party when all the red lights
• 47:20
  Speaker 2: lit up?
• 47:23
  Speaker 1: I wonder what that moment was like because you've thought
• 47:26
  Speaker 1: about the theory. You already think quantum mechanics does describe
• 47:29
  Speaker 1: the universe. So this is just a demonstration. But to
• 47:32
  Speaker 1: actually see it happen, it must be really thrilling. Those
• 47:35
  Speaker 1: are the moments when you force the universe to reveal
• 47:38
  Speaker 1: an answer to you. You know, that's what experimental science
• 47:41
  Speaker 1: is all about. I think a lot of people underestimate
• 47:44
  Speaker 1: the creativity required in experimental physics. They think theory is
• 47:48
  Speaker 1: where the brains are at. But, you know, experiment requires
• 47:51
  Speaker 1: a different kind of creativity. You have to conduct these experiments.
• 47:55
  Speaker 1: You have to build these situations that force the universe
• 47:58
  Speaker 1: to reveal option A or option B, right? And boy,
• 48:02
  Speaker 1: this was complicated and creative. And I didn't think it
• 48:05
  Speaker 1: was even possible. I thought Bell's experiment was it, that
• 48:09
  Speaker 1: all we had was this sort of subtle pattern of correlations.
• 48:12
  Speaker 1: And so for somebody to come up with this convoluted
• 48:15
  Speaker 1: setup that's impossible for hidden variables, impossible for quantum mechanics,
• 48:19
  Speaker 1: and then you have this moment. When you're like, you
• 48:21
  Speaker 1: run the thing, you press the button, the lights flash,
• 48:24
  Speaker 1: the universe is telling you how it works. Wow, what
• 48:27
  Speaker 1: a thrill.
• 48:27
  Speaker 2: Yeah, that does sound amazing. And I'll note that you
• 48:30
  Speaker 2: might be able to force the universe to give up
• 48:32
  Speaker 2: her secrets, but you can't force Daniel and Kelly to
• 48:34
  Speaker 2: get names right. And so I'll note that we've referred
• 48:37
  Speaker 2: to this idea as the GHK and the GHZ experiment.
• 48:42
  Speaker 2: And I think it's the GHZ, right?
• 48:44
  Speaker 1: It's definitely the GHZ. Yes, exactly.
• 48:47
  Speaker 2: Okay.
• 48:48
  Speaker 1: That must just be a typo on my part. Sorry.
• 48:50
  Speaker 1: Apologies to Z and your Nobel Prize.
• 48:53
  Speaker 2: I'm guessing that Z is sleeping just fine at night. Yeah.
• 48:56
  Speaker 1: All right, everybody.
• 48:57
  Speaker 2: Thank you so much for listening. And thank you so
• 48:59
  Speaker 2: much for sharing your questions about the universe with us.
• 49:01
  Speaker 2: If you'd like to share a question with Daniel, you
• 49:03
  Speaker 2: can write at questions at danielandkelly.org. I will be taking
• 49:07
  Speaker 2: biology questions again. Not until 2027, though, because I've gotten
• 49:10
  Speaker 2: so many amazing questions from you all. I just need
• 49:12
  Speaker 2: a moment to catch up. But we look forward to
• 49:14
  Speaker 2: explaining another topic to you again next time.
• 49:24
  Speaker 1: Thanks everybody for listening. Please go and do us a
• 49:26
  Speaker 1: favor and rate the show on whatever podcast app you're using.
• 49:30
  Speaker 1: It really helps people find us.
• 49:32
  Speaker 2: Daniel and Kelly's Extraordinary Universe is edited by the amazing
• 49:36
  Speaker 2: Matt Kesselman.
• 49:37
  Speaker 1: He really is a wizard. You can also find us
• 49:40
  Speaker 1: online on Blue Sky, Instagram, and X, D & K Universe.
• 49:45
  Speaker 1: Come engage with us.
• 49:47
  Speaker 2: You can email us at questions at danielandkelly.org. We really
• 49:51
  Speaker 2: do want to hear from you.
• 49:52
  Speaker 1: And you can find our website, www.danielandkelly.org, where you'll also
• 49:57
  Speaker 1: find an invitation to join our Discord, where everybody comes
• 50:01
  Speaker 1: and talks about the amazing universe.
• 50:03
  Speaker 2: And we also have the most amazing moderators. This is
• 50:07
  Speaker 2: an iHeart podcast. Thanks for joining us.