Getting Entangled with Sean Hodgman

How do you get entangled particles? Neil deGrasse Tyson and comic co-host Chuck Nice unpack the experimental side of entanglement, superposition, and the quantum underpinnings of our universe with experimental physicist, Sean Hodgman.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Neil deGrasse Tyson?

  Chuck, love me some quantum physics and apparently so does everybody else, especially when we're talking about quantum entanglement.

• 0:07Chuck Nice?

  I'll say some of the best questions we've received on quantum entanglement, yeah.

• 0:10Neil deGrasse Tyson?

  One of the world's experts, we went down under to Canberra, Australia. Sean Hodgman coming right up, a physicist on top of the situation.

• 0:22Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now.

• 0:37Neil deGrasse Tyson?

  This is StarTalk Cosmic Queries Edition. What is the subject? Quantum entanglement. Chuck, are you ready for this?

• 0:48Chuck Nice?

  Never.

• 0:51Chuck Nice?

  Let's be, I'm just gonna be honest.

• 0:54Neil deGrasse Tyson?

  Haven't you and I been a quantum entangled for a while?

• 0:56Chuck Nice?

  Yes, without a doubt. Anytime you feel pain, Neil, I feel it immediately.

• 1:02Neil deGrasse Tyson?

  That's how that works, you see? You see? Now, I have like a storybook understanding of quantum entanglement. So to really get to the bottom of this, we combed the world to find somebody who actually works in the field. And we found a physicist at the Australian National University, ANU. Research School of Physics there. And that would be Sean Hodgman. Sean, welcome to StarTalk.

• 1:31Speaker 02

  Thanks a lot for having me.

• 1:32Neil deGrasse Tyson?

  Yeah, this is, this is everybody, nobody doesn't like quantum entanglement. Everybody's into it. And we have a million questions before we even get to the queries part of this episode. We have questions of our own. I have questions of my own. And so let's just, let's just come right out of the box and tell me what you publish papers on. What is it you do?

• 2:02Speaker 02

  Yeah, so my, my group works on a whole range of experiments. Our particular apparatus that we work on involves making helium atoms really cold. So we take them and we cool them down to almost absolute zero. So absolute zero is as cold as you can get when there's essentially no motion in the system. Again, remembering that thermal temperature is basically just random thermal motion. We take all the motion out of the system and we make it really cold. The temperatures we get to are a millionth of a degree above absolute zero.

• 2:34Neil deGrasse Tyson?

  I'd say that's cold.

• 2:37Speaker 02

  It's, it's super cold.

• 2:38Chuck Nice?

  Sean, listen, man, you're, you're almost there, okay?

• 2:43Neil deGrasse Tyson?

  Keep at it, keep trying.

• 2:44Chuck Nice?

  Yeah, keep, keep at it, man, keep at it. No, almost there, man.

• 2:48Neil deGrasse Tyson?

  Helium, we're familiar as a gas that you can inhale out of a balloon in a, in a, in a birthday party. Remind me, it liquefies around three degrees, is that correct?

• 3:00Speaker 02

  So normally, at normal pressure it would, but because we do it in a vacuum system, we keep it at a, in the gaseous phase. So it's still, it's still a gas at these really cold temperatures, just at really low density.

• 3:12Chuck Nice?

  Whoa, cool.

• 3:14Neil deGrasse Tyson?

  Okay, and so why the hell do you do that?

• 3:19Speaker 02

  Well, I mean, we, we ask ourselves that question too sometimes.

• 3:23Speaker 02

  But, um, yeah, so the, uh, the purpose of this, at these cold temperatures, all the atoms will form a single coherent quantum state, called a Bose-Einstein condensate. So that's where, um, uh, quantum mechanically, at low temperatures, so really cold and when atoms are moving really slowly, they don't, uh, they don't behave like these little billiard ball situations that we like to think of. What they actually behave like is they become these fuzzy smeared out quantum blobs. And at these temperatures, they all become essentially an identical quantum state, which is very similar to a laser, where a laser is the same for photons.

• 4:02Neil deGrasse Tyson?

  Is this the same thing as, as you cool it down, its effective wavelength increases?

• 4:08Speaker 02

  Exactly, yeah.

• 4:09Neil deGrasse Tyson?

  Is that a fair way to say that? And so that the wavelength is so long, they're all just sharing the same wavelength? And so they all, they have a hive mind at that point? Is that a fair way to characterize this?

• 4:19Speaker 02

  Definitely. So, so the reason we don't see these quantum effects of particles behaving like waves at normal temperatures is because their wavelength is too small to actually see. Once you get to the temperatures that we cool them down to, then they form this single quantum state and their, their wavelengths are actually, it's, it's macroscopic. So it's inside the trap, it's maybe a hundred micrometers, so point one of a millimeter. I'm not great on inches, so for your American use, I'm not quite sure.

• 4:48Speaker 02

  But yeah, and, and when we, when we drop the atoms from the trap and release them onto our detector, so they fall nearly a meter. And in that distance, they expand. And so by the time they hit the detector, they're actually sort of centimeters big. And so we have a quantum object that is on the centimeter scale by the time it hits the detector.

• 5:04Chuck Nice?

  That's amazing. And when you say blob, what, what kind of structure? Because in a gas, it's almost random, like, you know, they're just sliding around everywhere. But, you know, in a structure, sometimes it's like a lattice or, but, so what does the quantum state look like?

• 5:22Neil deGrasse Tyson?

  Yeah, how do they look like compared to each other? Yeah.

• 5:25Speaker 02

  So because they're all identical, they're essentially an identical particle. So it's basically just one, one state that just looks a very smooth, smooth sort of blob essentially. There's no random motion, so they're not, not really bouncing around off each other. There's just essentially one smooth blob.

• 5:42Neil deGrasse Tyson?

  I remember first reading about this many years ago and was just totally impressed. And it's got Einstein's name on it and Bose, who was an Indian physicist, right? And we, it's, we credit him for the word we use for bosons, the particles, is that right?

• 5:59Speaker 02

  Yeah, exactly. So, so the particles we cool down are bosons. We can also cool fermions and they do a whole completely different set of physics. But yeah, um, the, there's the, the two types of elementary particles are bosons and fermions. And for Bose-Einstein condensates, we use bosons, which yeah, were named after the Indian physicist Bose, who came up with the statistics to describe them and, and to describe this state of Bose-Einstein condensation.

• 6:22Neil deGrasse Tyson?

  No, Einstein was not a fan of quantum physics. So why did he get something named after him? What's up with that?

• 6:29Speaker 02

  Yeah, I mean, it, it's kind of funny that, that Einstein, he essentially was one of the inventors of quantum physics. It was his, um, his black body radiation paper that, um, that, that came up with a lot of the initial physics stuff. What he had a problem with was some of the aspects of physics and kind of the interpretations of quantum, quantum physics were what he really struggled with a little bit, some of the things such as entanglement. So he didn't like the fact that when you have an entangled system, if you have two particles, it essentially means that if you take two particles and you separate them, if you measure one of them, you'll instantaneously know the state of the other. And this is what Einstein didn't like because that implies that something travels faster than the speed of light,

• 7:11Speaker 02

  which famously violates one of his other famous, um, uh, works on relativity. Um, and so he, he really didn't like that. And, um, uh, yeah, so he, he worked hard to sort of say that, well, quantum mechanics must be incomplete. There must be a way that, there must be some information that we're missing here. And it was only sort of, um, maybe thirty, forty, fifty years after that, that we're actually able to prove that, no, that really is how the world seems to work.

• 7:37Neil deGrasse Tyson?

  Yeah, so Einstein was wrong in his assumption that it's incomplete, I guess. Or maybe it's still incomplete philosophically, but everything works, so no, right?

• 7:48Chuck Nice?

  He was just upset because it made him look, it made his suppositions look stupid. That's what was raw. He was like, don't you know I'm Einstein? Do you know how smart I am? This can't be the case because now everything that I've figured out in my physical representation of the universe can't be. So guess what? No, no.

• 8:10Neil deGrasse Tyson?

  The Chuck account of the, of the history there. So, so Sean, where does entanglement come in to this Bose-Einstein condensate?

• 8:20Speaker 02

  The Bose-Einstein condensate, we essentially just use as a source for our experiments on entanglement. So what we do is we take, we take our condensate, we split it in two, and we collide the two parts of the condensate together. So we basically give, give one half of it a kick with a laser beam and then it collides with the other half. And in those collisions, you get all these individual pairs of atoms from each of them will collide off each other. And they could go in all sorts of different directions. Let's, let's just focus on two of the directions they could go. So if you have two atoms, um, I can probably do it with, I, I normally do this with, um, a couple of coins. So if you have a couple of, imagine these, these coins are the atoms, you bounce off each other. They could either go that way or they could go that way. Okay, so you can do this way or that way.

• 9:05Speaker 02

  And classically, if, if we think of them as little billiard balls, they could either go this sort of up or down. It doesn't, uh, they do either of those. And you do the experiment, they go this way, you measure it, or they go this way and you measure it. Now, quantum mechanically, that's not what happens. What happens quantum mechanically is that when they do the collision, they go this way and they go this way at the same time.

• 9:27Chuck Nice?

  For those who might be listening without the benefit of YouTube, the, the, this way and this way is kind of northeast and northwest instead of northeast and southwest. And that, that's what you're saying.

• 9:46Speaker 02

  Quantum mechanically, both of those pairs, well, the atoms go both ways. However, when you measure it, there's only still two atoms in the system. We're not, we're not creating matter here. We're not creating anything. And so when you measure it, you'll only either get northwest, southeast or northeast, southwest. But until you measure it, the atoms have gone both paths. And that's, that's what entanglement is.

• 10:10Chuck Nice?

  Entanglement. Oh my God.

• 10:13Neil deGrasse Tyson?

  Okay, so now I've only ever heard of entanglement with regard to particles. And now you're describing an entire atom. At those temperatures, the hydrogen nucleus will have its complement of electrons. So you've got a whole frickin' atom here. And are you saying you're entangling atoms?

• 10:31Chuck Nice?

  Wow.

• 10:32Speaker 02

  Yes, exactly. So, so most, most entanglement so far has been done with things like photons, which is a, a very elementary particle. It's just a excitation of light. But like, like you said, Neil, I mean, uh, helium atom is quite complicated. It's got a nucleus which has two protons, two neutrons, it's got two electrons whizzing around that. And now we're taking two of these and we're entangling them together.

• 10:55Chuck Nice?

  First of all, that's crazy. Based on everything that, you know, so far.

• 11:03Speaker 02

  I'm starting to see where Einstein was coming from.

• 11:05Chuck Nice?

  Yeah, I am.

• 11:07Neil deGrasse Tyson?

  Oh, you're good company, Chuck, okay, yeah.

• 11:09Chuck Nice?

  Damn, I mean, that's, that's kind of insane. You know, so now, all right, here's

• 11:17Neil deGrasse Tyson?

  How long, how long do they stay entangled? Because that's a big contest out there, right? I mean, I remember reading some papers about what they were doing in China, where they had two entangled particles. One was in orbit and what was in a lab. And so it's like, how are they doing this? And what are they after? Is it distance or is it time? Or do you have to make sure nobody messes with one of the particles? So you have to, you have to make sure it stays isolated? What, what are the conditions to sustain this?

• 11:47Speaker 02

  Yeah, that's, that's pretty much all correct. So you can for, for, so, so in our case, we're entangling our particles in momentum that, or, or in the path that they travel. So the direction they go. And that's, that's really hard to keep your particles entangled because if they go slightly differently from that path, so instead of going northeast, southwest, they go slightly towards north, northeast, say, then you're no longer going to be entangled because you've, you've now gone on a different path and you'll

• 12:15Neil deGrasse Tyson?

  You've broken the symmetry of it, I guess.

• 12:17Speaker 02

  Yeah, you might, you might, you might collapse the entanglement or degrade it to an extent. Where, so our particles don't stay entangled for long. It's, it's our whole experiment's about a millisecond that, that we do this entanglement for.

• 12:34Neil deGrasse Tyson?

  A millisecond is not a millionth of a second, even though it sounds like it should be. Millisecond would be a thousandth of a second, correct?

• 12:40Speaker 02

  Thousands of a second, exactly, yes.

• 12:41Neil deGrasse Tyson?

  Right, like a millimeter is a thousandth of a meter. So millisecond is a thousandth of a second. Okay. So these are not very long.

• 12:48Chuck Nice?

  Eternity on a quantum scale.

• 12:54Speaker 02

  It all depends on your perspective.

• 12:55Neil deGrasse Tyson?

  Yeah. Is, is there a long-term goal for this experiment? Or is it sort of an existence proof that you can entangle atoms?

• 13:04Speaker 02

  Yes, so this particular experiment that we did, it was a kind of a demonstration that we could do this. So, so people have, there's been a lot of entanglement previously done with photons. There's been some entanglement done with atoms as well. But the entanglement that's been done with atoms hasn't involved external degrees of freedom. By external degrees of freedom, I mean basically the fact that it moves in different paths. So things like momentum. Previous experiments have just been things such as spin. So you might put it in a superposition of being in different states, but they stay at the same place. And so ours was the first experiment that showed momentum entanglement with atoms.

• 13:45Speaker 02

  And the reason why that's interesting is because one of the things you might want to look at atoms for over photons is that atoms interact much more strongly with a gravitational field. And so potentially we could look at effects such as how does gravity interact with entanglement? Down the track we're talking about. And so that might open up avenues to explore things such as quantum gravity theories.

• 14:11Neil deGrasse Tyson?

  It's not that gravity doesn't interact with the photons. It would just be much harder to measure, right? So with, whereas a tangible particle, you've got something whose path you can track, I guess. Is that, is that what's going on there?

• 14:23Speaker 02

  Yeah, exactly. It's a much stronger interaction.

• 14:40Speaker 03

  I'm Joel Cherico and I support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 14:58Chuck Nice?

  Hey Sean, can you help me out as, as I'm trying to wrap my head around this? With the undetermined state and the path? Because you said if it, if it goes on a different path, can you talk a little bit more about that? Because I'm, I'm not quite understanding the, you know, the superposition before the actual measurement.

• 15:22Neil deGrasse Tyson?

  Because if China has a particle in orbit and a particle in the lab, that sounds like they're on different paths.

• 15:28Chuck Nice?

  Right.

• 15:28Neil deGrasse Tyson?

  So what, what, where does the sensitivities come from for changing what one particle does relative to the other?

• 15:36Chuck Nice?

  Well, thank you, Neil. That was my question, Sean.

• 15:43Speaker 02

  In our case, it's the fact that it's the momentum states of the atoms. So it's the direction it's traveling that is the entanglement. So if, if, if you imagine sort of north, south, sorry, northeast, southwest, northwest, southeast pairs, then you can imagine that it's, it's, it's the fact that the atoms are either going northwest, southeast, or they're going northeast, southwest. And they're going those two directions at the same time. Now, what's happened with previous atoms is you'll have an atom sitting somewhere and then you have another atom sitting somewhere and you'll use photons to communicate between those two and to flip the atom into a particular state. So it's still sitting there. It's doing whatever it's doing. It, yes, it might be orbiting the earth.

• 16:28Speaker 02

  It might be sitting in a lab, which is of course rotating with the earth. So it is moving, but it's not the motion that's entangled. That motion doesn't change.

• 16:36Chuck Nice?

  So the in-momentum is really the, the key here. I got it. Okay. I got it.

• 16:42Neil deGrasse Tyson?

  And the photon is your measurement of the state, right? Because you can't measure it unless you interact with it in some way.

• 16:49Speaker 02

  For our atoms, it's actually slightly different. So

• 16:52Neil deGrasse Tyson?

  No, no, I meant for the other case.

• 16:53Speaker 02

  The other case, yeah, sorry.

• 16:55Neil deGrasse Tyson?

  Yeah, okay. Got it, got it, got it. Okay. All right. So this is, so, so I have in my notes here to inquire with you about the Bell inequality theorem. Is that, how's that relevant to what's going on here?

• 17:08Speaker 02

  Yeah. So historically, if we're going back to Einstein and what he didn't like about entanglement. So he, he didn't like the idea that you could be in these two states at once and then measure, and that would collapse your superposition so that you then know which

• 17:22Neil deGrasse Tyson?

  Was that, or was that not his invocation of the phrase spooky action at a distance?

• 17:27Speaker 02

  Yeah, that was exactly what he said. So he described it as spooky action at a distance. And he says, you can't have this, you can't have this, that you're collapsed to being in this state, but before you collapse it, you're in both states once. He didn't like that. He, he thought there must be something.

• 17:42Neil deGrasse Tyson?

  And am I correct in that, because I've heard two different answers, but you're the horse's mouth here, that the other particle knows of this not simply faster than light, but instantaneously?

• 17:57Neil deGrasse Tyson?

  Which of those is the right way to think about it?

• 18:00Speaker 02

  To the best of our knowledge, it seems to be instantaneous, but it's very hard to prove that it's exactly instantaneous.

• 18:07Neil deGrasse Tyson?

  Wow.

• 18:07Speaker 02

  People have proven that it's faster than, faster than speed of light, though.

• 18:12Neil deGrasse Tyson?

  So tell me about the, the inequality theorem?

• 18:15Speaker 02

  Yeah. So Einstein and his co-authors Podolsky and Rosen wrote this paper, which was the famous spooky action at a distance paper, saying that this can't be how the world works and there must be something in quantum mechanics that's incomplete. And everyone for sort of decades kind of thought, well, you're never going to be able to test this. So it's just a philosophical debate to an extent. And then fast forward sort of 30 years or so into the sixties and John Bell, there was another famous theorist, came up with a experiment where you could actually measure this. And because, because the problem is with entanglement, if you imagine that you're in this superposition of northeast, southwest, the northwest, southeast, but you only ever get one result out of the system.

• 18:58Speaker 02

  So it's very hard to prove the difference between being in that superposition and not being in that superposition. And so what John Bell said is, hang on, we'll take that superposition and we'll then interfere it back with itself. So if you imagine if you have the particles going northeast, southwest, northwest, southeast, you then take those two parts of the superposition and you reflect them back on each other so that you have particles that go like this and particles that go like that. And you end up, there's a spot where they overlap again. And because the halves of the superposition can overlap, you can then get quantum interference at that point. And so Bell came up with this inequality called the Bell inequality, which he said that if they really are in this superposition, you'll get this interference.

• 19:40Speaker 02

  And he, as far as we know, thought that his inequality would always hold. It would, that, i.e. that classical physics would be correct and that the quantum prediction, which predicts that his inequality is violated, wouldn't be correct. And then, yeah, a couple, couple of decades later, some physicists such as Alain Aspect and co-measured it and showed that it is, is actually violated.

• 20:09Neil deGrasse Tyson?

  So, so that was a thought experiment, not an actual experiment that he conducted?

• 20:13Chuck Nice?

  Wow.

• 20:14Neil deGrasse Tyson?

  Right, right.

• 20:15Chuck Nice?

  Look at that.

• 20:15Neil deGrasse Tyson?

  Let's go to our fan base, our Patreon supporters, each paying $5 a month to gain access to our guests in the form of a question.

• 20:24Chuck Nice?

  Yes. Let's start with John Mayer. And John Mayer says, Dear Doctors Tyson, Hodgman, and Lord Nice, I've been reading about entanglement for decades, but I have never felt I could understand its nature. So thank you for this episode. My question is three parts. So one, how do you entangle a particle? And two, how do we know they are entangled with spooky action and not just similarly related? So I love the show and bravo.

• 20:55Neil deGrasse Tyson?

  And let me jump in the middle and ask, can you just take two random particles and forcibly entangle them? Or must they be birthed together to be entangled in the way you describe?

• 21:09Speaker 02

  Um, so you you need to, just to Neil's, I'll go to Neil's point first. So um, you just need some way that those particles can be identical. So they don't, in our case, we used identical helium atoms, but you wouldn't, you wouldn't need to. For instance, if you had non-identical particles, you could just collide them off each other and one would go one way, the other would go the other way. And they'd be in a superposition of, say, let's, let's, again, we'll go back to my coins, say, we have sort of a red and a blue particle, you could collide, so red goes one way, blue goes the other way, or blue goes one way, red goes the other way. Um, that would be fine as well.

• 21:45Neil deGrasse Tyson?

  You can entangle a red and a blue particle?

• 21:47Speaker 02

  Yeah, yep.

• 21:48Neil deGrasse Tyson?

  Did not know that. I thought they had to be kind of, sort of symmetrically identical, you know, with just complementary uh elements like spin or whatever. So I did, that's interesting to me. Okay, so in practice, how are you entangling particles? That's the first question, right, Chuck? Yeah?

• 22:05Chuck Nice?

  Yep.

• 22:06Speaker 02

  Yep. Yep. So in practice, that's, that's, um, we, we take one, one particle and we give it a kick and we collide it with the other particle and they bounce off each other. And then you get in this superposition of, um, the particles going as we're talking about northeast, southwest, or northwest, southeast. And um, uh, so you're in these, these different momentum states and that's your, um, initial entangled state.

• 22:31Neil deGrasse Tyson?

  So the act of colliding them off each other

• 22:34Chuck Nice?

  Of one another entangles them.

• 22:37Neil deGrasse Tyson?

  brings their wave functions into harmony. So that what was two wave functions becomes one.

• 22:44Speaker 02

  Yeah, it, yeah. I think that's a really good way to describe it. It's, it's, there's two separate wave functions that you can describe separately. Um, and then after you collide them, there's no way that you can describe them with two different wave functions. You have to use a single wave function.

• 22:58Chuck Nice?

  Ah, gotcha.

• 23:00Neil deGrasse Tyson?

  And this, and this is because the wave particle duality of nature at those smaller scales. This is quantum physics at its finest, right?

• 23:08Speaker 02

  Yep.

• 23:08Neil deGrasse Tyson?

  Okay. So the second question was what, Chuck?

• 23:11Chuck Nice?

  How do we know they are actually entangled with spooky action and not just similarly related? That seems to be the, uh, the real question there. Uh, yeah.

• 23:25Speaker 02

  Yeah. So I think that that kind of goes back to, again, if they were classical particles, you could put them in this, you could put them in kind of a superposition where they either go one way or the other way. But quantum mechanically, they go one way and the other way at the same time. And so the reason we can, and the way we can prove that, even though we only ever measure one outcome, is that if we then take the two halves of that superposition and we combine them back together and interfere them, then we can show that there will be different, um, outcomes. And so the particle can essentially interfere with itself and, um, uh, we can show we'll get different outcomes to what you would get, uh, classically.

• 24:05Chuck Nice?

  Wow, man. That's

• 24:07Neil deGrasse Tyson?

  All right.

• 24:08Chuck Nice?

  That is some freaky stuff. I love it.

• 24:09Neil deGrasse Tyson?

  It's Freaky Friday, yeah.

• 24:11Chuck Nice?

  So this is Hayden Goringe, I think, Goringe. He says, hey, Dr. Tyson, uh, Dr. Hozman, Lord Nice, hope you are all doing well. It's in the paper by Dr. Hozman et al. Uh, that the helium atoms were momentum entangled and I hadn't heard of subtypes of entanglement before. What other types of entanglement are there? And why did the team opt to use momentum entanglement for the BEC, uh, made of helium atoms? Uh, all the best, Hayden from London, England. Pip, pip.

• 24:53Neil deGrasse Tyson?

  What is the inventory of entanglements that you have?

• 24:57Speaker 02

  Yeah, so there's, there's, there's lots of different types of entanglement. So if you have, uh, the original experiments with photons, it would often be something such as polarization. So polarization is just, if you imagine a photon as a small particle of light, it's basically which way is the light vibrating? Is it vibrating this way or is it vibrating this way? So vertical or horizontal? And you might entangle your photons in that so that one of your photons has vertical polarization, one has horizontal. And so you could be in a superposition of vertical going right, horizontal going left, or horizontal going left, vertical going right. And then you could, um, measure that. And, yeah, and so that was a lot of the original experiments were, um, uh, done with photons with things such as polarization. Um, atoms, previous experiments have done things such

• 25:42Speaker 02

  as spin. So spin is just a, it's a fundamental, uh, property of, um, atoms or, or partner, uh, charged particles that you can either sort of spin up or spin down. And you could be in a superposition of spin up and spin down and entangled with that. And in our case, we did momentum. Um, pretty much any quantum property can be entangled. Um, you just have to be able to put it into a superposition of those states.

• 26:06Neil deGrasse Tyson?

  Well, let's get back to the spin. So in the two entangled spin particles, does one have to be spin up and the other has to be spin down?

• 26:15Speaker 02

  No, no, definitely not. Um, as physicists, we tend to use a shorthand that if there's, if there's any system that is a two-spin system, um, you'll call that spin up and spin down because that's how we tend to learn about it in, uh, undergraduate physics and we tend to just

• 26:32Speaker 02

  Yep, yep. So for instance, uh, in, in my lab, we've done previous experiments where we've used a spin one and a spin zero state of helium and we've entangled them. Um, and, uh, but we still call it spin up and spin down because it's just, it's shorthand that physicists understand easily.

• 26:48Neil deGrasse Tyson?

  Because when I think of quantum particles, I think they have complementary quantum states. But that's not the case. They can have any quantum state.

• 26:57Speaker 02

  You just have to be able to couple between those quantum states. If you can't couple between the quantum states, then you can't, uh, interfere them. So if you can't change the, coupling just means changing. So if I, I can't change controllably from spin one to spin zero, or spin up to spin down, or horizontal to vertical polarization, whatever your entanglement parameters are. In our experiment, it's momentum. Um, and so if, as long as you can change coherently between those states, you can, uh, get entanglement and show that you've, uh, show of Bell inequality violation.

• 27:30Neil deGrasse Tyson?

  Okay.

• 27:31Chuck Nice?

  Wow. Look at that. That is mind-bending stuff.

• 27:35Neil deGrasse Tyson?

  I did not know that. I did not know that. Okay. Bring on some more.

• 27:40Chuck Nice?

  He says, hello, Dr. Tyson, Dr. Hozman, this is, uh, Jonas Williams, uh, from New York City. Uh, my question for you, has the study of quantum entanglement and subatomic particles changed or influenced how you understand reality?

• 27:59Neil deGrasse Tyson?

  I like that. I like that. If you're not purposely entangling particles, is that something that could happen to them by natural causes?

• 28:09Speaker 02

  Oh, definitely. Yeah, yeah. Entanglement can happen, um, all the time. It's just that it's, because it happens on such a small scale, um, we normally don't see the effects of it. Um, and so, yeah, yeah. And, and I think that, so back to the question, for me, um, it's kind of, it's really weird. And I think a lot of us who have studied quantum mechanics, when you first encounter it, whether it's, uh, in an undergrad or high school or, um, through a podcast like this, when you first hear about these quantum features, you might think, yeah, that, that, that, that sounds, sounds really weird. That can't be how the world works. And then, because it's not how, it's not how our brains have evolved. Our brains have kind of evolved to, um, uh, be used to sort of, I guess,

• 28:53Speaker 02

  throwing, throwing things at animals, I guess, um, which is a very classical way of looking at the world. And if, if, if I throw a cricket ball, or what do you have, baseball in America? If I throw a baseball, let's say, um, and, uh, it's, it's not going to be in two places at once. It's not going to go two directions at the same time. And so when we read about quantum mechanically, that a small particle, which we like to think of as just a smaller, smaller ball, um, when we read that can go both directions at once, uh, we just sort of think, oh, well, it must be some mathematical trick. And the fact that we can actually do these experiments to show, no, no, at the very small scale or very cold, um, this is how the universe works, it's, yeah, it's a bit mind-bending, right?

• 29:33Chuck Nice?

  Yeah, without a doubt.

• 29:35Neil deGrasse Tyson?

  To summarize, uh, because it happens on these microscopic scales, there's no macroscopic manifestation of entanglement that we experience.

• 29:46Speaker 02

  Yeah, that's correct.

• 29:47Neil deGrasse Tyson?

  Because we're just trying to not get eaten by the lion and that doesn't require quantum physics to accomplish.

• 29:52Chuck Nice?

  Are they forever, forever separated, the quantum and the macrophysical? Or is there a possibility that there is a point of crossover?

• 30:05Speaker 02

  Yeah, that's, that, that, that's a really good question. And that's, that's a really active area of research at the moment. Uh, because clearly at the small scale, quantum works. At the large scale, quantum doesn't. But there's got to be somewhere in between. There's either must be a hard point where they stop working, or maybe it's a fuzzy boundary. A lot of the research we're kind of seeing these days is that there might be a fuzzy boundary where you just kind of get less and less quantum and more and more classical.

• 30:28Chuck Nice?

  Wow. All right. God, how do you deal with this every day, man?

• 30:39Chuck Nice?

  All right, here we go.

• 30:40Neil deGrasse Tyson?

  This is Mike. Do you arrive at home at the end of the day depressed? Or jubilant?

• 30:47Speaker 02

  Normally depends on how much university bureaucracy I've had to deal with in a particular day. Depressed at home. The quantum physics is the easy part of the job some days.

• 30:56Neil deGrasse Tyson?

  As they say, the administration is a new kind of subatomic particle called the moron.

• 31:04Chuck Nice?

  Damn. Okay, this is Mike Parker. And Mike Parker says, Dr. Hodgman, Dr. Tyson, Lord Nice, Mike Parker from Virginia. It seems entanglement is observed in larger and larger particles. Is there an upper size limit to entanglement? Could there ever be a way to use particle entanglement for instant long distance communication or other practical purposes? This is the question that every sci fi fan wants to know, man. Can we have faster like communication like on Star Trek? Where Captain, there's a subspace communication waiting for you in your quarters.

• 31:47Neil deGrasse Tyson?

  Or can you entangle molecules? I mean, yeah, we're impressed with the atoms, but what have you done with us lately? Can you, can you entangle molecules, be they simple or complex?

• 31:59Speaker 02

  On the entangling larger particles, that's, that's another really active area of research. People keep pushing it further and further. There have been people that have entangled collections of atoms and molecules. And they sort of push, I believe, I believe it's of order a thousand atoms, but don't quote me on that because I could be, um, I could be wrong on that.

• 32:16Neil deGrasse Tyson?

  Within one is all I care about.

• 32:18Speaker 02

  It's more than, way more than one. Yep. Yep. And so, yeah, and trying to push this entanglement on the bigger scale and work out where it breaks down at some level, it clearly doesn't, uh, it doesn't work anymore. And so, yeah, where that transition is, is a really active area of research.

• 32:34Neil deGrasse Tyson?

  So maybe you were familiar with George Gamow's Mr. Tompkins in Wonderland. I don't know if you, I'm a little older than you, so I don't know if this was around in your day, but George Gamow, Mr. Wonderland was a place where the laws of physics were different simply by the physical constants being different. So in one of them, the speed of light is like 60 miles per hour, right? And so you're driving down the street and then you see these, these relativistic effects just by approaching the speed of light as your speed limit on the road. One of them was they changed the value of the Planck's constant so that macroscopic objects would feel a quantum phenomenon, that you'd walk through the door and you'd

• 33:18Neil deGrasse Tyson?

  like diffract as you went through the door. It's just, it's fun to think about what, how that, if you have a knob that could tune it, what different things would happen to you? Or we just simply develop a new sense of, of what the world is, right? Like you said, we throw the ball and it follows one arc. But if quantum rules were all around us at all times and you threw the ball and it split into two states, you would tell it's just splitting into two states. It wouldn't even be odd to watch that because it would happen so frequently. Is that a fair way to think about this?

• 33:58Speaker 02

  Yeah, I, I, I think so. Our brains are great at adapting and I'm pretty sure that if, if we'd had to evolve to live in a quantum world, I'm sure we'd just think it was normal.

• 34:06Neil deGrasse Tyson?

  It's just normal. That's right.

• 34:07Chuck Nice?

  That's cool. And what about the communication portion of Mike's question?

• 34:12Neil deGrasse Tyson?

  Oh, yeah, yeah, yeah, yeah.

• 34:13Chuck Nice?

  Would it ever be a viable use for long distance communication?

• 34:18Neil deGrasse Tyson?

  Is there a future in this?

• 34:20Speaker 02

  Yeah, so this, this is what everyone thinks as soon as you hear entanglement, you think there's instant, measuring one instantly changes the other. We could use that to communicate faster than the speed of light. Unfortunately, that doesn't seem to be the case. And essentially it's because the way you measure it, um, contains information. So if you make a measurement on that particle, um, yes, you'll, you will know what the other one is, but you won't be able to communicate that in a useful way unless you communicate it classically because you'll, you'll then, the other person would then have to, uh, make a particular measurement to get anything useful out of that. And so, um, yeah, you wouldn't, you, you can't actually use it to, uh, for faster than light communication.

• 35:03Speaker 02

  There's, there's a theorem called the no communication theorem, um, which basically says that, yeah, you can't, um, you can't use entangled states to communicate faster than the speed of light.

• 35:12Neil deGrasse Tyson?

  Really? That's the name of the theorem? The no communication theorem? That's the best name they can come up with?

• 35:19Chuck Nice?

  Yeah, that, I believe that's what many women call their husbands.

• 35:25Chuck Nice?

  The no communication theorem. But yeah, so, so basically what you're saying is the collapse of the superposition and once that information is set, you, you can't know it unless you're making the same measurement that the other person is making on the other side. And you wouldn't be able to know which position it is unless you were to call them and say, here's the position.

• 35:51Speaker 02

  Yeah, it's exactly because, because quantum measurement perturbs the state. If you, if, if you make your measurement in a way that could exploit that information, it will change the state of it. And so then that will change the state of the other one. And then when they make their measurement, they'll get a different result out of it.

• 36:07Chuck Nice?

  Different result.

• 36:08Speaker 02

  Unless you've called ahead and told them, hey, you need to make this particular measurement.

• 36:12Chuck Nice?

  Which by the way, is how you know that it's entangled.

• 36:17Chuck Nice?

  That's how you know it's entangled.

• 36:19Speaker 02

  Exactly. It's kind of frustrating. You're like, we should be able to do this, but yeah, we, we can't.

• 36:24Neil deGrasse Tyson?

  So we can't use it for, um, encrypted message sending?

• 36:32Speaker 02

  Uh, now that's, that's a completely different question. You can use entanglement for encrypted message sending. So that's, that's where you exploit the fact that if you measure one half of that, you will change the other half. And so if you encrypt your message on two, uh, photon pairs and you send one of them to the person that you want to, and you keep the other one yourself, then if you make measurements on that and compare the results with the person you've sent it to, you'll know if anyone's messed with your system because you'll get different results. And so you'll know if anyone's been eavesdropping on your messaging. And so there's, there's mathematically provably secure encryption protocols, uh, using quantum

• 37:13Speaker 02

  communication, which can be shown that, uh, you, you, you just can't break them because if you interfered with it, if you, you interfered with the state, if you listened to it, you interfered with the state and people would know you're eavesdropping and, um, you could just abort the communication.

• 37:28Neil deGrasse Tyson?

  So this is a pipe dream then? It's a pipe dream that people have for it.

• 37:32Speaker 02

  These things have been demonstrated, um, at, at, at various scales and, um, yeah, they're, they're essentially, um, it's, it's, it's almost an engineering problem at this stage to get it to work better.

• 37:46Chuck Nice?

  Okay, look at that. All right, this is William Warren and William says, hi, Dr. Tyson and Dr. Hodgman. This is William Warren from Abingdon, Maryland. If quantum entanglement is a fundamental feature of nature, could spacetime itself emerge from a vast network of entangled particles? In other words, is it possible that distance isn't fundamental, but rather a consequence of how information is connected at the quantum level? Thank you so much.

• 38:23Neil deGrasse Tyson?

  We've heard on another installment of StarTalk from one of our physicist friends, Brian Green, that it might be that the virtual particles in the vacuum of space that are connected to each other by entanglement, that they're tangled, that that entangled gap between them may be a wormhole. And a wormhole would have the same property because you just step through and it's, you're just there, right? You're not moving faster than light. The, the hole enabled that. And it's not because you had special rockets.

• 39:06Neil deGrasse Tyson?

  So, so what, what is the latest thinking, other than what I just shared with you, about what the entangled pathway actually is?

• 39:18Speaker 02

  Yeah, wow, this is, um, you've got to remember, I'm only a dumb experimentalist. I basically make measurements in the world, the world does.

• 39:25Neil deGrasse Tyson?

  You dumbass experimentalist, okay.

• 39:27Speaker 02

  Yeah, I, I, I probably, I would certainly defer, um, yeah, thinking on that to things such as to the experts like Brian and, um, and Co. Cause, um, yeah, that's, that's kind of a bit, a bit beyond, um, what, what we're working on. I, it certainly sounds like a, um, uh, interesting take, uh, but I'm, yeah, I'm not, not really sure, unfortunately, sorry.

• 39:51Chuck Nice?

  Okay, no, okay. But listen, we, we like that answer.

• 39:58Chuck Nice?

  You know, nowadays it's hard to get somebody to say, hey, I'm not that sure, sorry. You know what I mean?

• 40:03Speaker 02

  Yeah, it's really good point. I think it's a, it's a big part of being a scientist is you've got to learn to know what don't you know? And it's one of those things that the more you know, the less you know, you know? It's kind of the reverse Dunning Kruger effect, you know, the Dunning Kruger effect, that the less you know, the more you think you know. Um, it's kind of the reverse. The more you know, the more you realize that, wow, there's heaps of stuff that I just don't know at all. And, um, yeah.

• 40:25Chuck Nice?

  Dunning Kruger. We get along very well, very well. Dunning and Kruger. I know them. We have a great relationship. They told me I do the best Dunning and the best Kruger.

• 40:40Chuck Nice?

  All right. I think there's a, I think there's a value in, uh, saying, I don't know, and allowing people to understand that, that science is sometimes the answer is, well, we don't know. You know?

• 40:52Speaker 02

  Absolutely.

• 40:53Neil deGrasse Tyson?

  Him not knowing, they're two different. There's science doesn't know and there's this, I don't know. Those are two different things.

• 40:58Chuck Nice?

  Right, and they're both the same for me.

• 41:06Speaker 02

  Whether physics itself knows, I think the answer's still out on that as well. I think there's still, um, some open theories in that because again, you can come up with a theory, but you have to be able to prove it experimentally. And I think to prove something like that experimentally, it would be extremely hard. So there's, there's some really interesting theories and the trick is going to be a bit like with Einstein spooky action in a distance claim, coming out with an experiment to test it. That's, that's what will be, yeah, that, that would be a big Nobel Prize discovery.

• 41:35Chuck Nice?

  Cool.

• 41:59Chuck Nice?

  All right, let's go to Alejandro Guardado. And he says.

• 42:07Neil deGrasse Tyson?

  He's from Hackensack, New Jersey. No.

• 42:11Neil deGrasse Tyson?

  Where's he from?

• 42:13Chuck Nice?

  I don't think Alejandro says where he's from.

• 42:16Neil deGrasse Tyson?

  Oh, okay.

• 42:17Chuck Nice?

  He says.

• 42:18Neil deGrasse Tyson?

  He's from Monterey.

• 42:20Chuck Nice?

  No, and Washington State. I'm sorry. He did say Washington State.

• 42:24Neil deGrasse Tyson?

  Washington State speaks that way. I just want you to know.

• 42:27Chuck Nice?

  Okay. That's my fantasy of Alejandro in Washington's in Washington State.

• 42:36Chuck Nice?

  He says, Hey, Dr. Tyson, Dr. Hodgman, Lord Nice, Alejandro here from Washington State. My question is, what stabilizes quantum fluctuations when particles fuse or collide? How does this increasing proximity affect entanglement? More extremely, how would this work for particles in the singularity of a black hole? Thank you.

• 43:06Neil deGrasse Tyson?

  Yeah, so I want to reshape that just a little bit. So if I have two particles, we know that quantum physics says there's, everything is always in motion. There's always some energy to the state. Is, does that disrupt any attempt to entangle two particles? So in other words, can two particles natively break apart simply because of quantum fluctuations? That are inherent in all particles and all systems?

• 43:34Speaker 02

  Quantum fluctuations at some level will probably have an effect on entanglement, but it's normally at such a small scale that it won't stop entanglement happening, I think.

• 43:47Neil deGrasse Tyson?

  And in fact, when you cool down your helium atoms, you are reducing the quantum fluctuations by dropping the temperature, correct?

• 43:55Speaker 02

  We're kind of reducing the classical fluctuations. So temperature is, temperature is really a classical, a classical phenomenon. It's just random motion of particles. We're reducing the classical fluctuations to get to the scale where you can in principle, see quantum fluctuations. However, for our entanglement, the quantum fluctuation, for our particular system, the quantum fluctuations don't really come into it. It's that there's, there's much larger things that cause the entanglement to decohere. Things such as our classical, so magnetic stray magnetic fields and, yeah, the like.

• 44:29Neil deGrasse Tyson?

  Your macroscopic disruptions to it. Yeah, okay.

• 44:32Speaker 02

  Yeah, definitely. We're not really at a level where we're sensitive to the microscopic quantum fluctuations.

• 44:36Chuck Nice?

  This is Michael Boysevert, who says, Hello, Guardians of the Geeks. Michael here from Canada. I like that Guardians of the Geeks, right? How would the universe change if the programmer behind would suddenly toggle particle entanglement off?

• 45:01Chuck Nice?

  Would we notice a change in our everyday life?

• 45:06Chuck Nice?

  Wow.

• 45:06Neil deGrasse Tyson?

  By the way, in the same spirit of that, I heard someone suggest that evidence where in a simulation is that the programmer already put a limit to how fast things can go because they can't simulate it faster than that. So the speed of light is the programmer's limit that we've bumped up against. And it took a long time to get there, but we finally got there. So it's like in the Truman Show, he finally gets to the, the outer.

• 45:35Chuck Nice?

  Edge of the set, of the television set.

• 45:39Neil deGrasse Tyson?

  Of the set, of the set. So, yeah, so what happened to our quantum entanglement? What's different about the world?

• 45:47Speaker 02

  Yeah, so at the macroscopic level, I think probably, probably not, not a huge amount. Like entanglement's only at a very small scale. However, well, yeah, however, there are a range of processes that we're starting to have hints at that maybe really entanglement may be really important. There's some biological processes such as people are postulating the stability of DNA may be due to entanglement within the molecules itself. Navigation of birds, some birds use magnetic sensors. And there's hints that there's quantum elements of that that rely on entanglement.

• 46:26Neil deGrasse Tyson?

  Migration, migration of birds.

• 46:28Speaker 02

  Migration of birds, yeah. Navigation during migration is kind of what I mean. Like when, when, when they migrate, how do they know to go north? Yeah, how do they know which way to go? And so there's, there's, there's thoughts of that. And even things such as, I think photosynthesis is the latest one that they're looking at that may have elements. Now, I think the jury's still out on all of these. Again, it's not quite my area of expertise, but I believe the jury is still out on all of these as to whether it's definitely quantum entanglement enhanced. But there's definitely some evidence that's starting to point towards some of these biological processes. Quantum physics is really important and entanglement in particular. And so, yeah, while at first glance, you might think that if the programmer of the universe turned off entanglement, we wouldn't see anything, any difference.

• 47:11Speaker 02

  It may actually be really important.

• 47:14Chuck Nice?

  Okay, very cool. I love the idea of photosynthesis and quantum entanglement. That sounds so cool. All right, this is Bruce Lessie. And Bruce says, Dr. Tyson's and Hodgman, this is Bruce Lessie from Cripple Creek, Virginia. My question is related to entanglement and spooky action at a distant, as Einstein phrased it. If spacetime for a photo traveling at the speed, he said photo, but I think he means photon, traveling at the speed of light represents zero time experienced by the photon. Because at the speed of light, distance is nonexistent.

• 47:55Chuck Nice?

  Why did Einstein have a problem with instantaneous communications between entangled particles? Nothing is at a distance for particles that travel at the speed of light.

• 48:08Speaker 02

  Yeah, so I'd, I'd say that's one of the reasons why it's really important to measure entanglement for things, not just that aren't photons. So, yeah, like, like because photons travel at the speed of light, if you just measure entanglement with that, you could perhaps come up with some sort of explanation like that. But in our system, we measure it with atoms. Our atoms move very slowly. We give them a kick and they move at several centimeters per second. Let's call it an inch per second for you Americans with your freedom units.

• 48:39Chuck Nice?

  Oh my God, freedom units. That's exactly what we use to measure the octagon on the White House lawn.

• 48:54Speaker 02

  So, yeah, so back, back to the atoms. So because they're moving relatively slowly, you can't come up with that sort of explanation to explain it. It really, and simultaneous, yeah, instantaneous communication suddenly becomes a problem again.

• 49:09Chuck Nice?

  Well, that's really cool, man, because, yeah, they have mass and, yeah, they're entangled at much, much, much slower speeds. So, yeah, that's really, that's, well, it's still a good question.

• 49:22Speaker 02

  That's a great question. Great question.

• 49:23Chuck Nice?

  Yeah, really good question, Bruce. Thanks. All right, this is David Barlow. And David Barlow says, Greetings, Dr. Hodgman, Dr. Tyson, Lord Nice. David Barlow from Chicago, Illinois here, a newly signed up Patreon supporter. Kudos to you, my friend. He says, I was wondering if, as an experimental physicist and an observer within the quantum field, you and your associates knew for a certain, for certain, that you were not affecting the results of your experiments in the Bell's theorem? What loophole prevention precautions were taken to negate your field collapse of the wave function when taking measurements?

• 50:06Chuck Nice?

  Love your fantastic science broadcast, guy. So, so, yeah, how you know this, that you're not messing it up, like?

• 50:20Speaker 02

  It could well be. That's that you always have a big doubt that, yeah, did we just do something wrong and measure something? That's why we have to do sort of rigorous and multiple tests and, and for the scientific method in general, it's part of the reason why you have to publish these papers that other scientists can then go, hang on, did you think about this? Did you try turning this off? Did you try turning that on? And, yeah, it's, it's, yeah, it's an important part of the process. For our particular experiment, so maybe I should just briefly cover what loopholes are that are referred to there. So with, with Bell, with Bell experiments, there's these things called loopholes, which are basically ways that people come up to say, well, maybe to still preserve locality,

• 51:02Speaker 02

  to still preserve the fact that you don't have instantaneous communication. And so it can be things such as, well, maybe, maybe the experiment's conspiring in a way such that it only lets certain results through. Or maybe your, maybe the observer is, is doing something, is communicating in a way. Maybe like, if you, if you set the interference on the two halves of the system and the measurement, if you don't set them after you've, if you set them in a way that they could communicate with each other, maybe there would be some really weird theory that could explain that.

• 51:38Speaker 02

  And so a lot of these, all these loopholes have been closed with the experiments on photons. For our particular experiment, we didn't close all these loopholes. So our experiment isn't loophole free. In principle, you could make some of these criticisms about our experiment. However, the fact that they've been closed with photons means that we probably expect that they should also be closed for atoms as well. And so, yeah. And, and part of the reason why we didn't close them was because a couple of them are technically extremely challenging to close with atoms, just because atoms move a lot slower than photons and they move over much smaller distances. And so, yeah, it's an ongoing area of work. It would be a good area of future work for groups like us.

• 52:18Chuck Nice?

  That's a damn good question.

• 52:19Neil deGrasse Tyson?

  Chuck, we have time for a couple more.

• 52:21Chuck Nice?

  Cleo Fox, he says, Hello, Dr. Tyson, my name is Cleo from Denver, Colorado. Modern quantum physics has achieved extraordinary predictive accuracy, but many of its foundational interpretations remain experimentally indistinguishable. Given recent advances in quantum information theory, weak measurements, quantum computing, and tests of non-locality, do you think the next major breakthrough in quantum physics is more likely to come from developing new mathematical frameworks? Or from entirely new experimental methodologies capable of probing quantum phenomena in ways we cannot currently access?

• 53:01Chuck Nice?

  Put another way, are, are we currently limited by our theories or by the tools we use to test them?

• 53:11Neil deGrasse Tyson?

  Yeah, so I was gonna say something similar to that in summary of that question. So Sean, there's, you know, philosophers like believing they have access to emerging truths in science in general, but especially in quantum physics, where there's so much that makes no freaking sense. So is there room for philosophers to guide the physicists through this and/or out of it? Or are we just stuck, just as they say, shut up and calculate? And so that's a nuanced way of saying, is it, what was the final question there?

• 53:51Chuck Nice?

  Are we currently limited by our theories and the tools we use to test them?

• 53:56Speaker 02

  On the shut up and calculate versus philosophy debate, I'm a big believer as an experimentalist, I'm a big fan of shut up and calculate, experiments are hard enough as it is.

• 54:06Neil deGrasse Tyson?

  Count me on that vote as well. Okay.

• 54:09Speaker 02

  Yeah, it's basically the maths tells us the results that give us predictions of our experiments.

• 54:13Neil deGrasse Tyson?

  And it works.

• 54:14Speaker 02

  Yeah, and it works. And so at that level, yeah, I'm happy with that. I'm happy to leave the questions to the, essentially to the realm of philosophy to an extent. If, if you, if you're, if you can't actually make predictions of what an experiment will give you, I think that's basically philosophy. And I think there's definitely a role for that. I mean, we've, we've seen that how brain bending some of these quantum effects are, and I think it's really interesting to probe that. I think it's really interesting to have philosophers and the like guide that and theorists and interact with quantum theorists. But I think it's also equally really important for experimentalists to actually test these results. And if you can, if you can't test these results, then you probably need to work harder on

• 54:59Speaker 02

  your theory, I think.

• 55:00Neil deGrasse Tyson?

  I spent some time at Princeton where they're very theory based, although they do quite a bit of experiments there and they have a tokamak and fusion reactor. But there's a strong theoretical legacy in the department. And there's a sign up somewhere or someone's door, it says, never trust an observation unless it's backed up by a good theory.

• 55:24Speaker 02

  Yeah. Yeah. So I think, I think coming back to the question, it really is, it's both. There's, there's a lot of work on theory, but there's also a lot of work on experiments to cover that.

• 55:37Chuck Nice?

  Do they, do they inform one another, I think, is kind of also the, the spirit of the question.

• 55:44Neil deGrasse Tyson?

  Ideally, there you go. That's, that's the correct way to think about that, Chuck.

• 55:48Speaker 02

  Absolutely. There's, there's plenty of times, like our experiment on entanglement, that was originally proposed by some theorists. We tried to do it the way they proposed and it didn't work. So then we came up with a slightly different way and then we came back to them and then they helped analyze our results. And yeah, it's really, there's a lot of back and forth that.

• 56:06Chuck Nice?

  Okay, cool.

• 56:07Speaker 02

  Goes on in science.

• 56:08Chuck Nice?

  Cool.

• 56:09Neil deGrasse Tyson?

  Chuck, one more question. We got time for it.

• 56:11Chuck Nice?

  All right, let's close it out with Melanie Stickler. And Melanie says, hello, Dr. Tyson, I'm Melanie, originally from Austria, now in the Bay Area of California. My question is about Dr. Hozman's helium experiment. I understand massless photons have wave particle duality, but how does a massive particle like a helium atom, which is subject to gravity, function as a wave cloud? Furthermore, if measuring a quantum system collapses the wave function, how did the team measure the atoms in simultaneous momentum states without instantly destroying the superposition? I'm sure the paper covers this, but I'm having a hard time wrapping my head around it. So thank you.

• 56:55Neil deGrasse Tyson?

  Yeah, helium is a massive particle compared to stuff we're used to. And so there's a wave function associated with such a massive particle?

• 57:04Speaker 02

  Yeah, definitely. And I should say, great question. And yeah, the, there's a wave function associated with helium atoms, and that's why we need to cool them down to make it work, because otherwise at room temperature, the wave function is so small that you can't see it. But at these temperatures, the wave function is macroscopic. It's sort of in the order of tens to hundreds of micrometers. So that's 0.1 of a millimeter. And yeah, it's, it's quite large at that scale. The other part of the question, if I remember, if I'm getting it correctly, was how do you measure that they're in two different states at once when they're only ever going to be in, how do you prove they're in two different states at once when you can only ever measure one result? And again, that really comes down to John Bell's work for how you can measure this Bell

• 57:49Speaker 02

  inequality, where if you interfere those states, you can measure the results of that in the outcomes you get. You can interfere those states and you can get more probability of being in one than the other in your output, due to the fact that you were in this superposition of two states at the same time.

• 58:04Neil deGrasse Tyson?

  Is there a quantum entanglement arms race in the world? Like who's leading the quantum entanglement experiments? Because I don't think it's us, is it? Us Americans, you're in Australia, who's, who's ahead and who's behind?

• 58:18Speaker 02

  It kind of depends what you're talking about. I mean, our, our experiments proving the fundamentals of entanglement, there's, there's still work going on in that. But a lot of what current quantum research is going into is how we do something useful with entanglement. So how you can use it, so things such as quantum computing. So quantum computing is a computer that rather than using bits to encode information, so bits have to be one or zero, you use qubits, which can be in a superposition of one and zero at the same time. And then if you have multiples of these together, you can end up with, you can entangle the different qubits. And by the fact that you can have qubits in many states at once, for certain types

• 59:01Speaker 02

  of problems, you can probe many answers at once, even though you only ever get one result when you get out and so, when you do your final measurement. And so there's a lot, so in principle, it seems really promising that you should be able to do much faster calculations, much higher level computation with this. But the problem is that finding, there's only particular problems that we know of that this is true. That's, so there's, there's a lot of work going into that. Then the other problem is that quantum systems are really hard to get to work on a large scale, so have lots of qubits. And so there's a lot of work going into building these processes. And so, yeah, there really is, if you want to call it an arms race, there's a lot of government and private investment in this at the moment.

• 59:46Speaker 02

  There's a lot of quantum computing startups all around the world.

• 59:48Neil deGrasse Tyson?

  And the assumption that whoever gets advances in it first might have a leg up, either economically or with regard to security or computing. And so even if at the end of the day, it's just a pipe dream, because it's like, it's just a fun physics exercise, but it doesn't have any practical use, no one knows that yet. Is that a correct way to think about that?

• 1:00:16Speaker 02

  Absolutely. It's still, it's still really an open question as to what the impact of quantum computing will be. Quantum computing, it could be anything from, like you say, have massive economic implications, massive security implications. It could be used to things such as medical implications, like drug development, data processing, all these massive things. Or it could just be on a much smaller level and that it's kind of a toy physics system that helps us advance physics, but may not have quite such a wide economic implication. And I think it's a really, really exciting time.

• 1:00:51Neil deGrasse Tyson?

  I bet people said the same thing about quantum physics a century ago.

• 1:00:55Chuck Nice?

  Right.

• 1:00:56Neil deGrasse Tyson?

  This is just a curiosity on the fringes of physics. We'll never have any use for this, but it's still fun anyway. And now it's the foundation of our IT revolution.

• 1:01:06Chuck Nice?

  Everything.

• 1:01:07Neil deGrasse Tyson?

  And everything, yeah.

• 1:01:09Speaker 02

  It's one of the reasons it's really important to invest in basic research. I mean, the work, the work my group does is where.

• 1:01:15Neil deGrasse Tyson?

  We don't know what that is anymore. The United States, we don't know what that is anymore.

• 1:01:19Chuck Nice?

  Exactly. We don't, we don't do research here anymore.

• 1:01:21Neil deGrasse Tyson?

  Will you hire, hire, hire?

• 1:01:24Speaker 02

  Australia's not much better, unfortunately.

• 1:01:28Chuck Nice?

  We run on vibes.

• 1:01:30Neil deGrasse Tyson?

  Vibes. No, right now it's on physics fumes, that's all that's left.

• 1:01:36Chuck Nice?

  Unfortunately.

• 1:01:37Neil deGrasse Tyson?

  We'll find out. Yeah. Well, Sean, that's all the time we have. I'm saddened by this because this, this topic has no end of curious people out there thinking about it. They've read about it and it's not every day you get to bump into someone who gets paid for thinking about it. Congratulations on your Bose Einstein condensate as a source of entanglement. Okay, we will look for our invitation to Stockholm in the mail.

• 1:02:06Speaker 02

  Really good. Thanks, thanks a lot for the questions and yeah, thanks for having me on your show.

• 1:02:10Neil deGrasse Tyson?

  I am Neil deGrasse Tyson, your personal astrophysicist, finishing up a very special edition of Cosmic Queries specializing in quantum entanglement. Until next time, keep looking up.