Getting Entangled with Sean Hodgman

Summary

StarTalk Radio: "Getting Entangled with Sean Hodgman"

Host: Neil deGrasse Tyson
Co-host: Chuck Nice
Guest: Dr. Sean Hodgman (Experimental Physicist, Australian National University)
Release Date: July 14, 2026

Episode Overview

In this Cosmic Queries edition of StarTalk, Neil deGrasse Tyson and Chuck Nice are joined by physicist Dr. Sean Hodgman to explore the mysterious and fascinating world of quantum entanglement. The discussion covers the fundamentals, history, experiments, applications, limitations, and philosophical implications of entanglement, with Dr. Hodgman illuminating these complex topics via his pioneering research with ultra-cold helium atoms. The episode features audience questions, clarifies much-misunderstood concepts, and delivers memorable science comedy moments.

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Main Discussion Points & Insights

1. Introduction to Quantum Entanglement

• The Appeal & Mystique: Quantum entanglement is one of the most captivating phenomena in quantum physics, intriguing both scientists and the general public.
• Key Concept: Entangled particles have connected quantum states such that measuring one instantly gives information about the other, regardless of the distance between them.
• Why It’s Weird: This instantaneous "connection" appears to violate the light-speed limit set by relativity, something Einstein famously disliked, calling it "spooky action at a distance."
  • (Neil, 08:40) “So Einstein was wrong in his assumption that it's incomplete, I guess. Or maybe it's still incomplete philosophically, but everything works.”

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2. Dr. Hodgman’s Research: Ultra-cold Helium & Bose-Einstein Condensates

• Experimental Platform: Hodgman’s group chills helium gas to nearly absolute zero, creating a Bose-Einstein Condensate (BEC)—a state where atoms merge into a single quantum entity.
  • (Sean, 03:04) “We take them and we cool them down to almost absolute zero... a millionth of a degree above absolute zero.”
• Purpose: The BEC provides a source for studying quantum phenomena, including momentum entanglement between entire atoms.
• Mental Picture: In a BEC, atoms lose individuality and become a “smooth blob.”
  • (Sean, 06:27) “It's basically just one state that just looks a very smooth, smooth sort of blob... there’s no random motion.”

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3. Entangling Whole Atoms

• A Step Beyond Photons: Most entanglement experiments historically focus on photons. Dr. Hodgman’s work involves entangling composite particles—specifically, helium atoms (including their nuclei and electrons).
  • (Sean, 11:35) “Most entanglement so far has been done with things like photons... but a helium atom is quite complicated... and now we're taking two of these, and we're entangling them together.”
• How It's Done:
  • The team splits the condensate and collides the parts, producing pairs of atoms whose motion directions (momentum states) are entangled.
  • (Sean, 10:50) “…when they do the collision, they go this way and they go this way at the same time.”
• Key Challenge: Maintaining entanglement is hard; in their setup, states remain entangled for a millisecond.
  • (Sean, 13:20) “Our whole experiment's about a millisecond that we do this entanglement for a millisecond.”

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4. Types of Entanglement

• Various Quantum Properties: You can entangle photons (in polarization), atoms (in spin or momentum), and, in theory, any property with distinct quantum states.
  • (Sean, 29:48) “…pretty much any quantum property can be entangled. You just have to be able to put it into a superposition of those states.”
• Momentum Entanglement: Their experiment demonstrates “external” entanglement—particles are literally moving in superposed directions.

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5. Testing Entanglement: Bell Inequality and Experiments

• Historical Context:
  • Einstein, Podolsky, and Rosen challenged entanglement’s implications, seeing them as evidence quantum theory was incomplete.
  • John Bell formalized a test (“Bell’s inequality”) that could distinguish quantum superpositions from classical correlations.
    • (Sean, 23:06) “John Bell...came up with an experiment where you could actually measure this...and show that it is actually violated.”
• Experimental Evidence:
  • Repeated experiments with photons—and now with atoms—violate Bell’s inequality, confirming quantum predictions and ruling out local classical alternatives.

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6. Nature & Limits of Entanglement

• Can Anything Be Entangled?: In principle, yes—not limited to “identical” particles.
  • (Sean, 26:01) "You just need some way that those particles can be identical...if you had non-identical particles, you could just collide them off each other..."
• Size Limit: Researchers are probing ever-larger objects; molecules and collections of atoms have been entangled, but there’s likely a fuzzy quantum/classical boundary.
  • (Sean, 37:08) “There have been people that have entangled collections of atoms and molecules...I believe it's of order, a thousand atoms.”

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7. Practical Applications

• Quantum Communication & Security:
  • While entanglement can’t be used for faster-than-light communication (the “no communication theorem”), it enables fundamentally secure quantum encryption.
    • (Sean, 41:24) “You can use entanglement for encrypted message sending…if anyone’s been eavesdropping…you could just abort the communication.”
• Quantum Computing:
  • Leveraging “qubits”—entangled quantum bits—for potentially revolutionary computing, though useful, large-scale quantum computers remain in development.
    • (Sean, 64:52) “A lot of current quantum research is going into how we do something useful with entanglement...quantum computing...and so there’s a lot of work going into building these processes.”

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8. Everyday Implications & Philosophical Questions

• Natural Entanglement: Happens continuously at the microscopic level, but is invisible in our macroscopic day-to-day world.
  • (Sean, 33:00) “Entanglement can happen all the time. It’s just that it’s...at such a small scale, we normally don’t see the effects of it.”
• Is Distance Fundamental?: Audience asks whether space and time could be emergent from quantum entanglement networks—a topic at the cutting edge of theoretical physics.
  • (Sean, 44:21) “[That’s] a bit beyond what we’re working on. It certainly sounds like an interesting take, but I’m not really sure unfortunately. Sorry.”

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9. Experimental Challenges & Scientific Method

• Experimental Loopholes: Addressing concerns about inadvertently biasing results in Bell tests, especially with atoms versus photons.
  • (Sean, 56:53) “A lot of these, all these loopholes have been closed with photons. For our particular experiment, we didn’t close all these loopholes...it would be a good area of future work for groups like us.”
• Theory vs. Experiment: Both progress together; new phenomena need theoretical frameworks and experiments need theory for context.
  • (Sean, 62:21) “There’s a lot of back and forth...we tried to do it the way [the theorists] proposed, and it didn’t work. So then we came up with a slightly different way.”

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10. The “Shut Up and Calculate” Attitude

• Theory or Philosophy?: Dr. Hodgman supports focusing on what can be calculated and tested, but values philosophy for conceptual exploration.
  • (Sean, 60:40) “I’m a big fan of shut up and calculate...If you can’t actually make predictions...that’s basically philosophy, and I think there’s definitely a role for that.”

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Notable Quotes & Memorable Moments

• On Bose-Einstein Condensates
  • Neil: “Helium, we're familiar as a gas that you can inhale out of a balloon in a birthday party.” (03:51)
  • Chuck: “Listen man, you're almost there, okay? Keep at it, man.” (03:40)
• On Einstein and Quantum Mechanics
  • Sean: “Einstein...essentially was one of the inventors of quantum physics...he really struggled with a little bit, some of the things such as entanglement.” (07:32)
  • Chuck: “He was just upset because it made his suppositions look stupid. That's what was wrong.” (08:51)
• On Entanglement Duration
  • Neil: “A millisecond is not a millionth of a second, even though it sounds like it should be.” (13:38)
  • Chuck: “So these are eternity on a quantum scale.” (13:50)
• On the Quest for Faster Than Light Communication
  • Sean: “There’s a theorem called the no communication theorem which basically says that, yeah, you can’t use entangled states to communicate faster than the speed of light.” (40:03)
  • Chuck: “I believe that's what many women call their husbands. No communication theorem.” (40:11)
• On the Value of Saying "I Don't Know" in Science
  • Sean: “It's a big part of being a scientist—you’ve got to learn to know what don’t you know. It's kind of the reverse Dunning-Kruger effect.” (44:54)
  • Chuck: “Dunning and Kruger, I know them, we have a great relationship. They told me I do the best Dunning and the best Kruger.” (45:15)
• On U.S. Investment in Basic Science
  • Neil: “I mean, the work...my group does, we don’t know what that is anymore in the United States. We don’t do research here anymore.” (67:41)
  • Chuck: “We run on vibes.” (68:02)

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Key Audience Questions (With Timestamps)

• What other types of entanglement are there besides momentum? (29:44)
  • [See section: Types of Entanglement]
• Can entanglement be used for long-distance, instant communication? (36:39; 39:03)
  • [See section: Practical Applications]
• Can macroscopic objects ever be entangled? (36:39)
  • [See section: Nature & Limits of Entanglement]
• Could switching off entanglement affect nature? (51:08)
  • Birds’ navigation, DNA stability, and photosynthesis may depend on it, but evidence is still emerging.
• Does the act of measurement destroy entanglement?
  • (Melanie Stickler’s question; 62:44)
  • Interaction with a quantum system typically collapses the superposition, but interference experiments (à la Bell) can demonstrate entanglement's effects.
• Limits of Theory vs. Experiment in Future Breakthroughs (59:43)
  • Dr. Hodgman: “Experiments are hard enough as is...the maths tells us the results that give us predictions of our experiments.”

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Important Timestamps

• [01:03]—Episode topic introduction: quantum entanglement
• [03:04]—Research on ultra-cold helium atoms
• [07:32]—Einstein’s issues with quantum physics
• [11:35]—How do you entangle entire atoms?
• [13:20]—Challenges of maintaining entanglement
• [21:59]—Bell's inequality and quantum tests
• [37:08]—Entangling larger and larger objects
• [41:24]—Quantum encryption
• [44:21]—Philosophical questions about spacetime and entanglement
• [56:53]—Experimental loophole discussion
• [60:40]—"Shut up and calculate" philosophy
• [67:23]—Quantum computing and its unknown potential

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Episode Takeaways

• Quantum entanglement is fundamental but mind-bendingly strange.
• The best evidence supports nonlocal quantum connections: Bell’s experiment violations confirm that entanglement is a true feature of nature, not a classical illusion.
• Entanglement isn’t (yet) a pathway to instant messaging but is already revolutionizing encryption and may power new forms of computing.
• There is no clear quantum-classical boundary; current research pushes to scale up entanglement and understand its limits.
• Science marches forward with measured humility: As Dr. Hodgman illustrates, sometimes “I don’t know” is the most honest (and scientific) answer.
• Basic research, even without immediate "use," drives transformative innovation—quantum physics being a century-long example, with surprises still ahead.

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Final Thought:
Neil deGrasse Tyson: “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. We’ll look for our invitation to Stockholm in the mail.” (68:09)

Sean Hodgman: “Thanks for having me on your show.” (68:38)

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For curious minds: Keep looking up—and keep questioning quantum reality.

Transcript

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[Neil deGrasse Tyson]

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

[Chuck Nice]

I'll say some of the best questions we received on quantum entanglement. Yeah.

[Neil 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. Welcome to StarTalk, your place in the universe where science, pop culture collide. StarTalk begins right now. This is StarTalk Cosmic Queries Edition. What is the subject? Quantum entanglement. Chuck, are you ready for this?

[Chuck Nice]

Never. Let's be. I'm just going to be honest.

[Neil deGrasse Tyson]

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

[Chuck Nice]

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

[Neil 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 at the research school of physics there. And that would be Sean Hodgman. Sean, welcome to StarTalk.

[Sean Hodgman]

Thanks a lot for having me.

[Neil deGrasse Tyson]

Yeah, this is everybody. Nobody doesn't like quantum entanglement. Everybody's into it. 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?

[Sean Hodgman]

Yeah. So 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.

[Neil deGrasse Tyson]

I'd say that's cold.

[Chuck Nice]

It's super cold, Sean. Listen, man, you're almost there, okay?

[Neil deGrasse Tyson]

Keep at it. Keep trying.

[Chuck Nice]

Keep at it, man. Keep at it. You're almost there, man.

[Neil deGrasse Tyson]

Helium, we're familiar as a gas that you can inhale out of a balloon in a birthday party. Remind me. It liquefies around 3 degrees, is that correct?

[Sean Hodgman]

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

[Chuck Nice]

Whoa. Cool.

[Neil deGrasse Tyson]

Okay. And so why the hell do you do that?

[Sean Hodgman]

Yes, well, we ask ourselves that question too sometimes.

[Chuck Nice]

Yeah.

[Sean Hodgman]

So 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 quantum mechanically at low temperatures, so really cold. And when atoms are moving really slowly, they don't, 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.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Exactly, yeah.

[Neil 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?

[Sean Hodgman]

Definitely. 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 wavelengths are actually. It's macroscopic. So it's inside the trap. It's maybe 100 micrometers. So 0.1 of a millimeter. I'm not great on inches. So for your American, I'm not quite sure.

[Neil deGrasse Tyson]

Well, it's.

[Chuck Nice]

Interview's over.

[Sean Hodgman]

You don't know inches. But yeah. And 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.

[Chuck 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?

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Yeah, 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 really bouncing around off each other. There's just essentially one smooth blob.

[Neil 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's an Indian physicist. Right. And we credit him for the word we use for bosons, the particles. Is that right?

[Sean Hodgman]

Yeah, exactly. So the particles we cool down are bosons. We can also cool fermions. And they do a whole completely different set of physics.

[Neil deGrasse Tyson]

But, yeah,

[Sean Hodgman]

the two types of elementary particles are bosons and fermions. And for Bose, Einstein condensates, we use bosons, which were named after the Indian physicist Bose, who came up with the statistics to describe them and to describe this state of Bose Einstein condensation.

[Neil deGrasse Tyson]

Now, Einstein was not a fan of quantum physics, so why does he get something named after him? What's up with that?

[Sean Hodgman]

Yeah, I mean, it's kind of funny that Einstein, he essentially was one of the inventors of quantum physics. It was his black Body radiation paper 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 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, which famously violates one of his other famous works on relativity. And so he really didn't like that. And, yeah, so 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 maybe 30, 40, 50 years after that that we were actually able to prove that. No, that really is how the world seems to work.

[Neil 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.

[Chuck Nice]

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

[Neil deGrasse Tyson]

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

[Sean Hodgman]

The Bose Einstein condensate we essentially just use as a source for our experiments on entanglement. So what we do is 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 just focus on two of the directions they could go. So if you have two atoms, I can probably do it with. I normally do this with a couple of coins. So if you have a couple. 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 either this way or that way. And classically, if we think of them as little billiard balls, they could either go this sort of up or down. It doesn't. 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.

[Chuck Nice]

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

[Sean Hodgman]

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 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 what? Entanglements.

[Chuck Nice]

That's the entanglement. Oh, my God.

[Neil 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 fricking atom here. And are you saying you're entangling atoms?

[Chuck Nice]

Wow.

[Sean Hodgman]

Yes, exactly. Most entanglement so far has been done with things like photons, which is a very elementary particle. It's just an excitation of light. But like you said, Neil, I mean, a 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.

[Chuck Nice]

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

[Sean Hodgman]

now you're starting to see where Einstein was coming from.

[Chuck Nice]

I am.

[Neil deGrasse Tyson]

Oh, you're a good company, Chuck. Okay. Yeah.

[Chuck Nice]

Damn. I mean, that's kind of insane, you know? So now, all right, here's how long.

[Neil deGrasse Tyson]

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 one 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 make sure it stays isolated. What are the conditions to sustain this?

[Sean Hodgman]

Yeah, that's pretty much all correct. So you can. So in our case, we're entangling our particles in momentum or in the path that they travel. So the direction they go. And 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 now gone on a different path, and you'll.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

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

[Neil deGrasse Tyson]

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

[Sean Hodgman]

correct thousandth of a second. Exactly. Yes.

[Neil deGrasse Tyson]

Right. Like a millimeter is a thousandth of a meter. So a millisecond is a thousandth of a second. Okay.

[Chuck Nice]

So these are eternity on a quantum scale.

[Sean Hodgman]

It all depends on your perspective.

[Additional Sponsor Announcer]

Right?

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Yes. So this particular experiment that we did, it was kind of a demonstration that we could do this.

[Chuck Nice]

Have.

[Sean Hodgman]

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. 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 the 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.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

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

[Chuck Nice]

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[Sean Hodgman]

I'm Joel Cherico, and I support StarTalk on Patreon.

[Neil deGrasse Tyson]

This is StarTalk with Neil DeGrasse Tyson.

[Chuck Nice]

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

[Neil deGrasse Tyson]

Because if China has a particle in orbit and a particle in the lab, that sounds like they're on different paths. So where does the sensitivities come from for changing what one particle does relative to the other?

[Chuck Nice]

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

[Sean Hodgman]

In our case, it's the fact that it's the momentum states of the atom. So it's the direction it's traveling that is the entanglement. So if you imagine sort of north, south, sorry, northeast, southwest, northwest, southeast, pairs, then you can imagine that 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'll 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. Yes. It might be orbiting the Earth. It might be sitting in a lab, which is, of course, rotating. So it is moving, but it's not the motion that's entangled. That motion doesn't change.

[Chuck Nice]

So the momentum is really the key here. I got it. Okay? I got it. Right.

[Neil 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.

[Sean Hodgman]

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

[Neil deGrasse Tyson]

No, no, I meant for the other case. In the other case. Yeah, yeah. Okay. Got it, got it, got it. Okay. All right. So this is so. So I have it in my notes here to inquire with you about the Bell inequality theorem. Is that. How is that relevant to what's going on here?

[Sean Hodgman]

Yeah, so historically, if we're going back to Einstein and what he didn't like about entanglement. So 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 was that?

[Neil deGrasse Tyson]

Or was that not his invocation of the phrase spooky action at a distance?

[Sean Hodgman]

Yep, 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 thought there must be something.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

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

[Neil deGrasse Tyson]

Wow.

[Sean Hodgman]

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

[Neil deGrasse Tyson]

So tell me about the inequality theorem.

[Sean Hodgman]

Yeah. So Einstein and his co authors, Podolsky and Rosen, wrote this paper. Which was the famous spooky accusation 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 60s. And John Bell, who was another famous theorist. Came up with a experiment where you could actually measure this. And because the problem is with entanglement. If you imagine that you're in this superposition of northeast, southwest and northwest, southeast. But you only ever get one result out of the system. 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 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. 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 Espe and co. Measured it and showed that it is actually violated.

[Neil deGrasse Tyson]

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

[Chuck Nice]

Wow.

[Neil deGrasse Tyson]

Right?

[Chuck Nice]

Look at that.

[Neil 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.

[Chuck Nice]

Yes, let's start with John Mayer. And John Mayer says, dear doctors Tyson, Hodsman, 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 entang. Entangled with spooky etching and not just similarly related? So I love the show and bravo.

[Neil 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 burst together to be entangled in the way you describe?

[Sean Hodgman]

So you need to just to Neil's. I'll go to Neil's point first. So 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 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 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.

[Neil deGrasse Tyson]

That would define a red and a blue particle.

[Sean Hodgman]

Yeah, Yep.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Yep, yep, yep. So in practice, that's. That's. We take one particle and we give it a kick, and we collide. It with the other particle.

[Neil deGrasse Tyson]

And.

[Sean Hodgman]

And they bounce off each other. And then you get in this superposition of the particles going, as we're talking about northeast, southwest, or northwest, southeast. And so you're in these. These different momentum states, and that's your initial entangled state.

[Neil deGrasse Tyson]

So the act of colliding them off

[Chuck Nice]

each other one another entangles them, brings

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Yeah, yeah. I think that's a really good way to describe it. There's two separate wave functions that you can describe separately. 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.

[Neil deGrasse Tyson]

Wow.

[Chuck Nice]

Okay.

[Neil deGrasse Tyson]

And this is because the wave particle duality of nature at those smaller scales. This is quantum physics at its finest, right? Yep. Okay, so the second question was, what, Chuck?

[Chuck Nice]

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

[Sean Hodgman]

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'll be different outcomes. And so the particle can essentially interfere with itself. And we can show we'll get different outcomes to what you would get classically.

[Chuck Nice]

Wow.

[Neil deGrasse Tyson]

Man. That's all right.

[Chuck Nice]

That is some freaky stuff. I love it.

[Neil deGrasse Tyson]

It's Freaky Friday. Yeah.

[Chuck Nice]

So this is Hayden Gorringe. I think Gorringe, he says. Hey, Dr. Tyson, Dr. Hodgman. Lord. Nice. Hope you are all doing well. It's in the paper by Dr. Hodgman et al. That the helium atoms were momentum entangled? And I hadn't heard of sub types of entanglement before. What other types of entanglement are there? And why did the team opt to use momentum entanglement for the bec made of helium atoms? All the best, Hayden from London, England. Pip, pip.

[Neil deGrasse Tyson]

What is the inventory of entanglements that you have?

[Sean Hodgman]

Yeah, so there's lots of different types of entanglements. So if you have the original experiments with photons, it would often be something such as Polarization. So polarization is just. If you imagine a photon is 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 measure that. And. Yeah, and so that was a lot of the original experiments were done with photons, with things such as polarization atoms. Previous experiments have done things such as spin. So spin is just a fundamental property of atoms or charged particles that you can either have 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, pretty much any quantum property can be entangled. You just have to be able to put it into a superposition of those states.

[Neil 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?

[Sean Hodgman]

No, no, definitely not. As physicists, we tend to use a shorthand that if there's, if there's any system that is a two spin system, you'll call that spin up and spin down, because that's how we tend to learn about it in undergraduate physics. And we tend to just divide it all the way through. Yeah, yeah. So, for instance, 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,

[Neil deGrasse Tyson]

but

[Sean Hodgman]

we still call it spin up and spin down because it's just, it's shorthand that physicists understand easily.

[Neil 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.

[Sean Hodgman]

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 interfere them. So if you can't change, the coupling just means changing. So if 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 parameter is, or in our experiment, it's momentum. And so as long as you can change coherently between those states, you can get entanglement and show that you've show a bell inequality violation.

[Neil deGrasse Tyson]

Okay.

[Chuck Nice]

Wow, look at that. That is Mind bending stuff.

[Neil deGrasse Tyson]

I did not know that. I did not know that. Okay, bring on some more.

[Chuck Nice]

He says. Hello, Dr. Tyson, Dr. Hosman. This is Jonas Williams from New York City. My question for you. Has the study of quantum entanglement and subatomic particles changed or influenced how you understand reality?

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Oh, definitely. Yeah. Yeah. Entanglement can happen all the time. It's just that it's. Because it happens on such a small scale, we normally don't see the effects of it. And so. Yeah, yeah. And I think that. So back to the question for me, 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 in an undergrad or high school or through a podcast like this, when you first hear about these quantum features, you might think, yeah, that sounds really weird. That can't be how the world works. And then, because it's not how our brains have evolved, our brains have kind of evolved to be used to sort of, I don't know, throwing things at animals, I guess, which is a very classical way of looking at the world. And if I throw a cricket ball, what do you have baseball in America? If I throw a baseball, let's say, and 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, when we read that can go both directions at once, we just sort of think, oh, well, it must be some mathematical trick. And the fact that we can actually do these experiments that show. No, no, at the very small scale or very cold, this is how the universe works. It's. Yeah, it's a bit mind bending, right?

[Chuck Nice]

Yeah, without a doubt.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Yeah, that's correct.

[Neil deGrasse Tyson]

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

[Chuck Nice]

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

[Sean Hodgman]

Yeah, that's. That's a really good question. And that's. That's a really active area of research at the moment. That. 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.

[Chuck Nice]

Wow. All right. God, how do you deal with this? Every. All right, here we go. This is Mike.

[Neil deGrasse Tyson]

Do you arrive at home at the end of the day depressed or jubilant? Jubilant. Like what is your.

[Sean Hodgman]

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

[Neil deGrasse Tyson]

as they say, the administration is a new kind of subatomic particle called the morons. Oh, damn.

[Chuck Nice]

Okay, this is Mike Parker, and Mike Parker says Dr. Hodsman, 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 than light communication like on Star Trek where Captain, there's a subspace communication waiting for you in your quarters?

[Neil 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 entangle molecules, be they simple

[Sean Hodgman]

or complex, on the entangling larger particles, 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 it's of order, a thousand atoms. But don't quote me on that because I could be. I could be wrong on that.

[Neil deGrasse Tyson]

It's more than one is all I care about.

[Sean Hodgman]

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

[Neil deGrasse Tyson]

So maybe you were familiar with George Gamow' 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 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 quantum phenomena that you'd walk through the door and you'd like defract as you went through the door. It 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 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 say, oh, 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?

[Sean Hodgman]

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

[Neil deGrasse Tyson]

It's normal. That's right.

[Chuck Nice]

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

[Sean Hodgman]

Oh, yeah, yeah, yeah, yeah.

[Chuck Nice]

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

[Neil deGrasse Tyson]

Is there a future in this?

[Sean Hodgman]

Yeah. So 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 contains information. So if you make a measurement on that particle, yes, 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 the other person would then have to make a particular measurement to get anything useful out of that. And so, yeah, you wouldn't. You can't actually use it for faster than light communication. There's a theorem called the no communication theorem which basically says that, yeah, you can't use entangled states to communicate faster than the speed of light.

[Chuck Nice]

Really?

[Neil deGrasse Tyson]

That's the name of the theorem, the no communication theorem. That's the best name they can come up with.

[Chuck Nice]

I believe that's what many women call their husbands. No communication theorem, but yeah. So basically what you're saying is the collapse of the superposition. Once that information is set, 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.

[Sean Hodgman]

Yeah, exactly. Because quantum measurement perturbs the state. 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. Then when they make their measurement, they'll get a different result.

[Chuck Nice]

They'll get a different result.

[Sean Hodgman]

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

[Chuck Nice]

measurement, which, by the way, is how you know that it's entangled. That's how you know it's entangled.

[Sean Hodgman]

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

[Neil deGrasse Tyson]

So we can't use it for encrypted message sending.

[Sean Hodgman]

Now, that's a completely different question. You can use entanglement for encrypted message sending. So 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 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 mathematically provably secure encryption protocols Using quantum communication, which can be shown that you just can't break them. Because if you interfered with it, if you'd interfere with the state, if you listen to it, you'd interfere with the state, and people would know your eavesdropping. And you could just abort the communication.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

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

[Chuck 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 space time itself emerge from a vast network of entangled particles? In other words, and 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.

[Neil deGrasse Tyson]

We've heard on another installment of StarTalk from one of our physicist friends, Brian Greene, that it might be that the virtual particles in the vacuum of space that are connected to each other by entanglement, they're entangled. That. That entangled gap between them may be a wormhole. And a wormhole would have the same property because you just step through and you're just there. Right. You're not moving faster than light. The whole enable that. And it's not because you had special rockets. So what is the latest thinking, other than what I just shared with you about what the entangled pathway actually is?

[Sean Hodgman]

Yeah. Wow. This is. You gotta remember, I'm only a dumb experimentalist. I basically make measurements.

[Neil deGrasse Tyson]

Dumbass experimentalist. Okay.

[Sponsor Announcer]

Yeah.

[Sean Hodgman]

I would certainly defer thinking on that to things such as to the experts like Brian and co. Because, yeah, that's kind of a bit beyond what we're working on. It certainly sounds like an interesting take, but I'm not really sure, unfortunately. Sorry.

[Chuck Nice]

Okay, but listen, we. We like that answer. You know, nowadays it's hard to get somebody to say, hey, I'm not that sure. Sorry. You know what I mean?

[Sean Hodgman]

Yeah, it's a really good point. I think 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. It's kind of the reverse. The more you know, the more you realize that, wow, there's heaps of stuff that I. I just don't know at all.

[Chuck Nice]

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

[Neil deGrasse Tyson]

You know, 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. Right.

[Chuck Nice]

And they're both the same for me,

[Sean Hodgman]

Whether physics itself knows. I think the answer's still out on that as well. I think there's still 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 some really interesting theories and the trick is going to be a bit like with Einstein's spooky action at a distance claim, coming up with an experiment to test it. That's what will be. Yeah, that would be a big Nobel Prize discovery.

[Chuck Nice]

Cool.

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[Sean Hodgman]

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[Sean Hodgman]

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[Chuck Nice]

All right, let's go to Alejandro Guardado

[Neil deGrasse Tyson]

and he says he's from Hackensack, New Jersey.

[Additional Sponsor Announcer]

No.

[Chuck Nice]

Where's he from?

[Neil deGrasse Tyson]

Where's he from?

[Chuck Nice]

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

[Neil deGrasse Tyson]

Oh, okay. He says he's from Monterrey.

[Chuck Nice]

No, at Washington State. I'm sorry, he does Washington State.

[Neil deGrasse Tyson]

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

[Chuck Nice]

Okay, that's my fantasy of Alejandro in Washington State. He says, hey, Dr. Tyson, Dr. Hodsman. 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.

[Neil 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 everything is always in motion. There's always some energy to the state. 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 in all systems?

[Sean Hodgman]

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.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

We're kind of reducing the classical fluctuation. So temperature is really 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 flex for our particular system, the quantum fluctuations don't really come into it. It's. There's. There's much larger things that cause the entanglement to decohere. Things such as our classical sort of magnetic. Stray magnetic fields and.

[Neil deGrasse Tyson]

Yeah, the, like your macroscopic disruptions to it. Yeah, okay.

[Sean Hodgman]

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

[Chuck Nice]

This is Mikael Boisvert who says hello, Guardians of the geeks. Mikael 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? Would we notice a change every day?

[Sponsor Announcer]

Life.

[Chuck Nice]

Wow.

[Neil deGrasse Tyson]

By the way, in the same spirit of that, I heard someone suggest that evidence we're 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.

[Chuck Nice]

The.

[Neil deGrasse Tyson]

The outer edge of.

[Chuck Nice]

Of those sets, of the television set.

[Neil deGrasse Tyson]

Of the set. Of the set. So, yeah. So what happened? Turn off quantum entanglement. What's different about the world?

[Sean Hodgman]

Yeah. So at the macroscopic level, I think probably. Probably not. Not a huge amount like entanglements, only at the 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, maybe 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.

[Neil deGrasse Tyson]

Migration. Migration of birds.

[Sean Hodgman]

Migration of birds.

[Chuck Nice]

Yeah.

[Sean Hodgman]

Navigation during migration is kind of what I mean. Like when they migrate, how do they know to go north? Yeah, how do they know which way to go? And so 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, it may actually be really important.

[Chuck Nice]

Okay, very cool. I love the idea of photosynthesis and quantum entanglement. That sounds so cool. All right, this is Bruce Lessee, And Bruce says Dr. Tysons and Hodgman. This is Bruce Lessee from Cripple creek, Virginia. My question is related to entanglement and spooky action at a distance, as Einstein phrased it, in space time. 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 a light, distance is non existent. 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.

[Sean Hodgman]

Yeah. So 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, 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.

[Sponsor Announcer]

Per Second.

[Chuck Nice]

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

[Neil deGrasse Tyson]

for free in unix.

[Sean Hodgman]

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

[Chuck Nice]

Wow, that's really cool, man. Because, yeah, they have mass and. And, yeah, they're entangled at much, much, much slower speeds. So, yeah, that's really. That's what a. Well, it's still a good question.

[Sean Hodgman]

That's great question. Great question.

[Chuck Nice]

Yeah, really good question, Bruce. Thanks. All right, this is David Barlow. And David barlow says. Greetings, Dr. Hosman, 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. Love your fantastic science broadcast guy. So, so, yeah, how you know that you're not messing it up? Like,

[Sean Hodgman]

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 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, and 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 Bell experiments, there's these things called loopholes, which are basically ways that people come up to say, well, maybe to still preserve localities, 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 the observer is doing something, is communicating in a way. Maybe 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. 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 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.

[Chuck Nice]

That's a damn good question, Chuck.

[Neil deGrasse Tyson]

We have time for a couple more.

[Chuck Nice]

Cleo Fox, he says, hello, Dr. Tyson, my name is Cleo from Denver, Colorado. Modern quantum physics has achieved extraordinary predictive accuracy. 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? Put another way, are we currently limited by our theories or by the tools we use to test them?

[Neil deGrasse Tyson]

Yeah, so I was going to 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, in science in general, but especially in quantum physics where there's so much that makes no fricking 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 what was the final question there?

[Chuck Nice]

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

[Sean Hodgman]

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 is.

[Neil deGrasse Tyson]

Count me on that vote as well. Okay.

[Sean Hodgman]

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

[Neil deGrasse Tyson]

And it works.

[Sean Hodgman]

Yep, and it works. And so at that level, yeah, I'm happy with that. I'm happy to leave the questions 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, if you can't test these results, then you probably need to work harder on your theory.

[Neil deGrasse Tyson]

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

[Sean Hodgman]

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

[Chuck Nice]

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

[Neil deGrasse Tyson]

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

[Sean Hodgman]

Absolutely. 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.

[Chuck Nice]

Okay, cool, cool.

[Neil deGrasse Tyson]

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

[Chuck Nice]

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. Hodgman'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.

[Neil 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.

[Sean Hodgman]

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 a 0.1 of a millimeter. And yeah, 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 have a measure one result? And again, that really comes down to John Bell's work for how you can measure this Bell 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.

[Neil deGrasse Tyson]

Is there a quantum entanglement arms race in the world? 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 ahead and who's behind.

[Sean Hodgman]

It kind of depends what you're talking about. I mean, our experiments probing the fundamentals of entanglement, 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 1 and 0 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 of problems, you can probe, 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 large. 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. So 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. There's a lot of quantum computing startups

[Neil deGrasse Tyson]

all around the world on the assumption that whoever gets advances in it first might have a leg up either economically or, 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 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?

[Sean Hodgman]

Absolutely. It's still really an open question as to what the impact of quantum computing will be. Quantum computing could be anything from like you say, have massive economic implications, massive security implications. It could be used for 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.

[Neil deGrasse Tyson]

I bet people said the same thing about quantum physics a century ago. This is just a curiosity on the fringes of physics. We'll never have any use for this. It's still fun anyway. And now it's the foundation of our IT revolution.

[Chuck Nice]

Everything.

[Neil deGrasse Tyson]

Yeah, everything. Yeah.

[Sean Hodgman]

It's one of the reasons it's really important to invest in basic research. I mean the work be might my group does is where we don't know

[Neil deGrasse Tyson]

what that is anymore in the United States. We don't know what that is anymore.

[Chuck Nice]

Exactly. We don't do research here anymore. Okay.

[Neil deGrasse Tyson]

Will you hire, hire, hire.

[Sean Hodgman]

Australia's not much better, unfortunately.

[Chuck Nice]

We run on vibes.

[Neil deGrasse Tyson]

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

[Chuck Nice]

Oh yeah, unfortunately.

[Neil deGrasse Tyson]

Find out. Yeah, well Sean, that's all the time we have. I'm saddened by this because 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 condosit as a source of entanglement. Okay, we will look for our invitation to Stockholm in the mail.

[Sean Hodgman]

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

[Neil 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.

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[Sean Hodgman]

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