Beyond Einstein: The Reality of Quantum Entanglement

<v Speaker 1>Welcome to the quart Side Quantum Physics Podcast, an exploration
<v Speaker 1>of the fundamental structure of reality, where quantum laws govern matter, energy,
<v Speaker 1>and information. Here, uncertainty is a feature, not a flaw,
<v Speaker 1>and understanding begins at the smallest scales.
<v Speaker 2>You know, when we think about twentieth century science, we
<v Speaker 2>almost automatically picture Albert Einstein. Oh absolutely, he's the icon, right,
<v Speaker 2>the wild hair, the Nobel Prize. I mean, the guy
<v Speaker 2>literally rewrote gravity and time. He just seems like this
<v Speaker 2>ultimate victor, the person who cracked the code.
<v Speaker 3>And for a long time he really was. I mean,
<v Speaker 3>for the first half of his career he was the revolutionary, right,
<v Speaker 3>but there's this this almost tragic second act to his
<v Speaker 3>life that, you know, it often gets a little glossed
<v Speaker 3>over in the history.
<v Speaker 2>Book the Princeton years. Right, became the old Guard.
<v Speaker 3>Worse than the old Guard. He became sort of an
<v Speaker 3>outsider in his own field. He spent decades, literally decades,
<v Speaker 3>waging this intellectual war against a theory he had helped create,
<v Speaker 3>quantum mechanics, and he was haunted by one specific part
<v Speaker 3>of it, a phenomenon so bizarre, so deeply counterintuitive, that
<v Speaker 3>it really offended his entire sense of cosmic order, and he.
<v Speaker 2>Came up with that amazing phrase for it.
<v Speaker 3>He did. He dismissed it as spooky action at a distance.
<v Speaker 2>Which I mean it sounds like something out of a
<v Speaker 2>ghost story or b movie.
<v Speaker 3>Yeah, but he wasn't talking about ghosts. He was talking
<v Speaker 3>about quantum entanglement. And for him, this wasn't just some
<v Speaker 3>technical quibble about Adams.
<v Speaker 2>Yeah, it was fundamental.
<v Speaker 3>It was a philosophical cage match, a battle for the
<v Speaker 3>very soul of physics, about the nature of reality itself.
<v Speaker 2>And that's really what we want to unpack today, because
<v Speaker 2>this isn't just about weird little particles doing weird things.
<v Speaker 2>It's about the very thing that kept Albert Einstein awake
<v Speaker 2>at night. This idea that the universe might not be local,
<v Speaker 2>that it might not even be real in the everyday
<v Speaker 2>way we think about it, and everything is connected in
<v Speaker 2>this way that just seems to defy all logic.
<v Speaker 3>It really pits our intuition, and I mean the intuition
<v Speaker 3>of arguably the smartest person who ever lived, against the
<v Speaker 3>raw experimental facts of how the universe actually works.
<v Speaker 2>So the spoiler here is pretty clear.
<v Speaker 3>The universe won the universe always wins.
<v Speaker 2>And Einstein in this one particular battle lost, But how
<v Speaker 2>he lost and why he lost. I mean, that's a
<v Speaker 2>story that actually leads us directly to the technologies that
<v Speaker 2>are building our future.
<v Speaker 3>It's an incredible story. Yeah, So to really get it,
<v Speaker 3>we need to sort of walk through that battlefield, understand
<v Speaker 3>what entanglement is, why it seemed to break all the rules,
<v Speaker 3>and then how we proved it was real, and.
<v Speaker 2>What we're doing with all that spookiness today.
<v Speaker 3>Right, But before we get to the disruption, we have
<v Speaker 3>to understand what was being disrupted. We need to look
<v Speaker 3>at the world Einstein was fighting so hard to.
<v Speaker 2>Protect, classical world.
<v Speaker 3>The world of Isaac Newton and James Clerk Maxwell. The
<v Speaker 3>physics that you know just feels right, it feels comfortable.
<v Speaker 2>It's the physics of common sense.
<v Speaker 3>It really is. And that common sense worldview is built
<v Speaker 3>on two main pillars, and they seem so obvious that
<v Speaker 3>you don't even think to question them. The first one's
<v Speaker 3>called realism.
<v Speaker 2>And in physics that doesn't just mean being practical. It
<v Speaker 2>has a very specific.
<v Speaker 3>Meaning it does. Realism is the basic assumption that objects
<v Speaker 3>in the physical world have definite properties, whether you're looking
<v Speaker 3>at them or not.
<v Speaker 2>The classic if a tree falls in the forest argument,
<v Speaker 2>or you know, the moon is still there even when
<v Speaker 2>I'm not looking at it.
<v Speaker 3>Exactly that. If I take a coin and I see
<v Speaker 3>it in a box, that coin is either heads or
<v Speaker 3>its tails. It has a definite state. Now I might
<v Speaker 3>not know what that state is, but it exists. My
<v Speaker 3>ignorance doesn't change the physical reality inside the box.
<v Speaker 2>That seems like a pretty non negotiable starting point for
<v Speaker 2>doing science. Right. If things don't have definite proper is,
<v Speaker 2>what are you even measuring?
<v Speaker 3>That was precisely Einstein's point of view. He believed in
<v Speaker 3>an objective reality that exists independent of us. So that's
<v Speaker 3>pillar number one. The second pillar is locality.
<v Speaker 2>Locality this is all about the speed limit of cause
<v Speaker 2>and effect.
<v Speaker 3>Yeah, you could put it that way. It's the principle
<v Speaker 3>that any object can only be influenced by its immediate surroundings.
<v Speaker 3>If I want to move this coffee cup, I have
<v Speaker 3>to touch it, or I have to push arrogance it,
<v Speaker 3>throw something at it. I can't just snap my fingers
<v Speaker 3>here in this room and make a cup fall over in.
<v Speaker 2>Tokyo unless there's some kind of signal some connection between them.
<v Speaker 3>And that's the key. That signal has to travel through
<v Speaker 3>the space in between. It can't just happen magically instantly
<v Speaker 3>across a distance.
<v Speaker 2>And this is actually where Newton got into a bit
<v Speaker 2>of trouble, wasn't it. I Mean, we think of Newtonian
<v Speaker 2>gravity as this perfect clockwork system, but it had this
<v Speaker 2>huge locality problem.
<v Speaker 3>It did, and he knew it. In Newton's equations, gravity
<v Speaker 3>was instantaneous. If the Sun were to just vanish right now,
<v Speaker 3>poof Newton's math said the Earth would instantly fly out
<v Speaker 3>of its orbit at that exact moment, which implies that
<v Speaker 3>the Earth somehow knows the Sun is gone instantly across
<v Speaker 3>ninety three million miles of empty space.
<v Speaker 2>Which is well, it's spooky action at a distance, it's magic.
<v Speaker 3>Newton hated it. He called it so great an absurdity,
<v Speaker 3>but he didn't have a way to fix it.
<v Speaker 2>It just it worked till Einstein came along.
<v Speaker 3>Until Einstein fixed it. That's a huge part of what
<v Speaker 3>his nineteen oh five paper on special relativity was all about.
<v Speaker 3>He established the cosmic speed limit.
<v Speaker 2>The speed of light.
<v Speaker 3>Exactly nothing, not matter, not energy, and crucially not information.
<v Speaker 3>Can travel faster than light.
<v Speaker 2>So in Einstein's universe, if the sun vanishes, we're fine.
<v Speaker 2>For about eight minutes.
<v Speaker 3>We keep orbiting blissfully unaware.
<v Speaker 2>We don't know it's gone until that last bit of
<v Speaker 2>gravitational news arrives at light speed.
<v Speaker 3>He saved locality, He got rid of the magic. He
<v Speaker 3>built this beautiful, sensible universe that was local, that was real,
<v Speaker 3>and that was deterministic. Causes always precede effects. The cosmic
<v Speaker 3>timeline is safe.
<v Speaker 2>It's a very neat and tidy picture of reality.
<v Speaker 3>It is.
<v Speaker 2>And then almost immediately he and his colleagues started digging
<v Speaker 2>into the atom, and they found something that threatened to
<v Speaker 2>just tear that entire safety net to pieces.
<v Speaker 3>The quantum disruption. As soon as physicists started to describe
<v Speaker 3>the world of electrons and photons, they realized the rules
<v Speaker 3>of our big, comfortable world just didn't apply down there.
<v Speaker 2>So let's take those pillars one by one. How did
<v Speaker 2>quantum mechanics attack realism? First, this is the idea of superposition, right.
<v Speaker 3>Yes, superposition, and it's a concept that directly assaults realism.
<v Speaker 3>It says that before you measure it, a quantum particle
<v Speaker 3>does not have a definite state.
<v Speaker 2>And we have to be so careful with the language
<v Speaker 2>here because this is the first big hurdle for most people.
<v Speaker 2>This doesn't mean it has a state, but we just
<v Speaker 2>don't know what it is.
<v Speaker 3>Correct, This is not the coin in the box. It
<v Speaker 3>is a fundamental built in uncertainty. An electron has a
<v Speaker 3>property called spin, and just for simplicity, you can think
<v Speaker 3>of it an arrow pointing either up or down. Okay,
<v Speaker 3>in superposition, the electron isn't secretly up or secretly down.
<v Speaker 3>It is, in a very real mathematical sense, a combination
<v Speaker 3>of both up and down at the same time.
<v Speaker 2>This is described by the wave function.
<v Speaker 3>The wave function describes this quantum blur, this cloud of probabilities.
<v Speaker 3>The particle itself has no real spin until it interacts
<v Speaker 3>with something.
<v Speaker 2>Until you measure it right.
<v Speaker 3>The active measurement forces the universe too well to make
<v Speaker 3>a choice. The wave function collapses, and boom, the particle
<v Speaker 3>is suddenly definitely spin up or spin down.
<v Speaker 2>You can see why this drove Einstein crazy. It suggests
<v Speaker 2>that reality is somehow fuzzy or incomplete until an observer
<v Speaker 2>comes along and forces its hand. It just shatters the
<v Speaker 2>principle of realism.
<v Speaker 3>He absolutely hated it. This is where he famously debated
<v Speaker 3>with Neil's Borr, asking, do you really believe the moon
<v Speaker 3>is not there when you're not looking at it?
<v Speaker 2>It's a great question, it is.
<v Speaker 3>But then the rabbit hole got so much deeper, because
<v Speaker 3>what happens if you take this weirdness of superposition and
<v Speaker 3>you apply it to two particles at once, Well, then
<v Speaker 3>you get entanglement.
<v Speaker 2>And this is where the second pillar locality starts to crumble.
<v Speaker 3>This is where it gets truly spooky.
<v Speaker 2>Okay, so walk us through the basic setup for entanglement.
<v Speaker 3>Imagine we have a process that creates a pair of
<v Speaker 3>particles from a single source. Let's say a specific atom
<v Speaker 3>decays and spits out two electrons. Because of certain fundamental
<v Speaker 3>laws like the conservation of the momentum, we know their properties
<v Speaker 3>have to be linked. They have to be opposite.
<v Speaker 2>So if one is measured to be spin up, the.
<v Speaker 3>Other one absolutely must be spinned down. They're born as
<v Speaker 3>a correlated pair. They're linked, They're entangled, and in the
<v Speaker 3>language of quantum mechanics, this is more than just being linked.
<v Speaker 3>They are no longer two separate objects. They are described
<v Speaker 3>by a single shared wave function a single quantum existence,
<v Speaker 3>even if you separate them, even if you separate them.
<v Speaker 3>So we send one particle to Alice, Let's say she's
<v Speaker 3>in New York, and we send the other particle to Bob,
<v Speaker 3>who's in Los Angeles.
<v Speaker 2>But all this time they're still in superposition. Neither every
<v Speaker 2>one has decided yet whether it's up or down exactly.
<v Speaker 3>They're both still in that quantum blur of up and downness. Now,
<v Speaker 3>Alice decides to megger her particle.
<v Speaker 2>Okay, she looks at it, she forces a collapse.
<v Speaker 3>She measures it, and the wave function collapses. She gets
<v Speaker 3>the result spin up at that exact instant, and I
<v Speaker 3>mean instantly, Bob's particle in Los Angeles, without anyone touching
<v Speaker 3>it becomes spin down.
<v Speaker 2>No signal passed between them, no little message saying hey
<v Speaker 2>I'm up, so you be down.
<v Speaker 3>None. The collapse of the wave function is global. The
<v Speaker 3>distance is completely irrelevant. It could be New York and
<v Speaker 3>Los Angeles, or it could be Earth in the Andromeda Galaxy.
<v Speaker 3>The moment Alice's result is determined, Bob's is too.
<v Speaker 2>And that is the spooky action. It looks for all
<v Speaker 2>the world like information is teleporting across space.
<v Speaker 3>It looks like a bleat and violation of Einstein's own
<v Speaker 3>cosmic speed limit. It looks like the universe is fundamentally
<v Speaker 3>non local.
<v Speaker 2>So Einstein sees this implication in the math and he
<v Speaker 2>basically decides, no, absolutely not, I need to kill this idea.
<v Speaker 3>He can't accept a universe that plays that fast and
<v Speaker 3>loose with his most cherished principles.
<v Speaker 2>So in nineteen thirty five he gets together with two
<v Speaker 2>colleagues and drops what is basically an intellectual bomb, the
<v Speaker 2>EPR paper.
<v Speaker 3>Yes, Einstein, Putolski and Rosen Yeah, and it is, without
<v Speaker 3>a doubt, one of the most important scientific papers ever written.
<v Speaker 3>Not because it was right it wasn't, but because of
<v Speaker 3>how profoundly productively wrong it was.
<v Speaker 2>So what was their central argument? They weren't saying the
<v Speaker 2>math of quantum mechanics was incorrect, were they? No?
<v Speaker 3>Not exactly. They admitted that the theory's predictions, the probabilities
<v Speaker 3>were correct, the math worked. What they argued was that
<v Speaker 3>the theory must.
<v Speaker 2>Be incomplete, that the spookiness was just an illusion, a
<v Speaker 2>magic trick caused by something we were missing.
<v Speaker 3>Precisely, this leads directly to their counterproposal which is usually
<v Speaker 3>called the theory of hidden variables.
<v Speaker 2>This was Einstein's way out, This was his escape patch,
<v Speaker 2>and the best way to understand it is with the
<v Speaker 2>famous gloves analogy. Okay, let's hear it.
<v Speaker 3>So imagine I have a pair of gloves, a left
<v Speaker 3>handed one and a right handed one. I put each
<v Speaker 3>one into an identical sealed box. I shuffle them up,
<v Speaker 3>I mail one box to you, and I keep the other.
<v Speaker 3>Right now, I open my box and I see a
<v Speaker 3>left handed glove. What do you instantly know about the
<v Speaker 3>glove in your box?
<v Speaker 2>I know I have the right handed one instantly.
<v Speaker 3>But did any spooky action take place? Did any information
<v Speaker 3>travel faster than light from my glove to yours?
<v Speaker 2>No, of course not. The outcome was decided from the
<v Speaker 2>very beginning. The gloves are always a left and right
<v Speaker 2>from the moment you pack them in the boxes.
<v Speaker 3>Exactly. The state of the gloves was determined at the source.
<v Speaker 3>My discovery didn't cause your glove to become a rity.
<v Speaker 3>It just revealed a pre existing fact.
<v Speaker 2>And Einstein argued that entangled particles were just like the gloves.
<v Speaker 3>That's it. He believed they weren't in some fuzzy superposition.
<v Speaker 3>He argued, they carried a set of hidden instructions, hidden variables,
<v Speaker 3>from the moment they were created.
<v Speaker 2>So when Alice measures her particle and gets up, that
<v Speaker 2>particle was always destined to be up. It didn't just
<v Speaker 2>decide on the spot. It had its marching orders from
<v Speaker 2>the get go.
<v Speaker 3>If that's true, then there's no spooky action, there's no
<v Speaker 3>FTL communication. Locality is saved, realism is saved. The universe
<v Speaker 3>makes sense again.
<v Speaker 2>It's an incredibly powerful and honestly, a much more comfortable argument.
<v Speaker 2>Why didn't people just accept it? Why did Neils bore
<v Speaker 2>and the quantum camp push back so hard?
<v Speaker 3>Because Borr was a purist about the theory. He looked
<v Speaker 3>at the equations of quantum mechanics and said, there are
<v Speaker 3>no hidden variables in this math, so why are you
<v Speaker 3>trying to add them. He believed you had to take
<v Speaker 3>the theory at face value. The particles really are undefined
<v Speaker 3>until measured.
<v Speaker 2>He famously told Einstein to stop telling God what to do.
<v Speaker 3>He did, but for decades this was just a war
<v Speaker 3>of words. It was pure philosophy. There was no experiment
<v Speaker 3>you could do to crack open an electron and look
<v Speaker 3>for a hidden instruction card inside.
<v Speaker 2>It was an impasse. For what thirty years, you were
<v Speaker 2>either on TM Einstein or Team Bor and basically just
<v Speaker 2>a matter of philosophical taste.
<v Speaker 3>It was a complete stale maid until nineteen sixty four.
<v Speaker 2>Enter John Bell John.
<v Speaker 3>Stuart Bell, a physicist from Northern Ireland working at CERN,
<v Speaker 3>and he's the guy who managed to drag this argument
<v Speaker 3>out of the philosophy department and into the physics lab.
<v Speaker 3>He turned it into arithmetic.
<v Speaker 2>He was actually sympathetic to Einstein's view, wasn't he He
<v Speaker 2>wanted to see if hidden variables could work.
<v Speaker 3>He did. He wanted to find a way to make
<v Speaker 3>it work. But in the process he found a way
<v Speaker 3>to test it.
<v Speaker 2>So how on earth do you design a test for
<v Speaker 2>something that is, by its very definition hidden.
<v Speaker 3>That's the genius of it. You don't look for the
<v Speaker 3>variables themselves, You look at their consequences. You test the correlations.
<v Speaker 2>Okay, this is Bell's theorem. It's famous but notoriously tricky.
<v Speaker 2>Let's try and unpack it. How does the math set
<v Speaker 2>a trap for these hidden variables?
<v Speaker 3>Okay, let's go back to Alis and Bob, but this time,
<v Speaker 3>instead of just measuring spin as up or down. Let's
<v Speaker 3>say they can measure it at a few different angles.
<v Speaker 3>Let's three angles for their detectors, setting A, setting B,
<v Speaker 3>and setting C.
<v Speaker 2>Okay, so three possible questions I could ask their particle exactly.
<v Speaker 3>Now, let's assume Einstein is right and the particles are
<v Speaker 3>like the gloves. That means each particle leaves the source
<v Speaker 3>carrying a hidden instruction card that tells it how to
<v Speaker 3>answer for every possible question.
<v Speaker 2>So a card might say, if asked A, say up.
<v Speaker 2>If asked B, say down, If asked C, say.
<v Speaker 3>Up, precisely a pre written answer for every possible measurement.
<v Speaker 3>Now Bell's insight was this, if those pre written instruction
<v Speaker 3>cards exist, then just by simple logic and statistics, there
<v Speaker 3>is a strict mathematical limit to how strongly Alis and
<v Speaker 3>Bob's results can be correlated when they choose their settings randomly.
<v Speaker 2>It's like a probability limit.
<v Speaker 3>It's a logic limit.
<v Speaker 2>Yeah.
<v Speaker 3>Think about it with a simple example. If you survey
<v Speaker 3>a population about three yes no questions, do you like coffee, tea,
<v Speaker 3>and juice? There are mathematical limits on how the answers
<v Speaker 3>can overlap. You can't have eighty percent like coffee eighty
<v Speaker 3>percent like T and have only ten percent who like both.
<v Speaker 3>The logic doesn't work.
<v Speaker 2>I see there's constraint.
<v Speaker 3>There is a constraint. Bell wrote it down in a
<v Speaker 3>formula and inequality. Any theory based on local, pre existing properties,
<v Speaker 3>any hidden variable theory must obey this inequality. The correlations
<v Speaker 3>cannot be stronger than a certain amount.
<v Speaker 2>So Bell's inequality becomes the test. You run the experiment
<v Speaker 2>thousands of times with random settings. If the correlation rate
<v Speaker 2>stays below that limit, Einstein and his hidden variables could
<v Speaker 2>still be right correct.
<v Speaker 3>But here's the kicker. The established theory quantum mechanics itself
<v Speaker 3>predicted something different. It predicted that entangled particles would coordinate
<v Speaker 3>their answers better than the hidden instruction cards would allow.
<v Speaker 2>They would be more in sync than the gloves could
<v Speaker 2>ever logically be.
<v Speaker 3>Yes, quantum mechanics predicted the correlations would be so strong
<v Speaker 3>that they would violate Bells in equality, which would mean
<v Speaker 3>it would be mathematical proof that there are no pre
<v Speaker 3>written instruction cards. It would prove the particles are making
<v Speaker 3>up their answers on the fly in perfect spooky coordination.
<v Speaker 2>So Bell designs the trap in sixty four, but the
<v Speaker 2>technology to actually build the trap and run the experiment
<v Speaker 2>didn't exist yet.
<v Speaker 3>Right, We had to wait for lasers, for fast electronics.
<v Speaker 3>We had to wait until the early nineteen eighties. For
<v Speaker 3>a French physicist named Elaine Aspect.
<v Speaker 2>The Aspect experiment in nineteen eighty two. This is the
<v Speaker 2>moment of truth.
<v Speaker 3>This is the smoking gun. There had been some earlier
<v Speaker 3>attempts that were suggestive, but they all had potential loopholes,
<v Speaker 3>little ways that Einstein's view could sneak back in. Aspect
<v Speaker 3>designed an experiment to be as watertight as possible.
<v Speaker 2>So he generated pairs of entangled photons sent them off
<v Speaker 2>to two detectors. What was the crucial addition?
<v Speaker 3>He introduced ultra fast switches that could change the measurement
<v Speaker 3>angle the setting while the photons were in mid flight.
<v Speaker 2>Why is that timing so incredibly important.
<v Speaker 3>It's to close what's called the locality loophole. The fear was,
<v Speaker 3>what if the detectors could somehow communicate with each other,
<v Speaker 3>or what if the particles could somehow know in advance
<v Speaker 3>what setting they were going to be measured at.
<v Speaker 2>Kind of conspiracy between the particles and the detectors.
<v Speaker 3>Exactly, but aspect switches changed the settings in a few nanoseconds.
<v Speaker 3>It happened so fast that by the time a photon
<v Speaker 3>arrived at Alice's detector, there hadn't been enough time for
<v Speaker 3>any signal, even one traveling speed of light, to get
<v Speaker 3>from Bob's detector to Alice's to tell it what setting
<v Speaker 3>Bob was using.
<v Speaker 2>So there is absolutely no way for the particles to
<v Speaker 2>coordinate their answers beforehand using any known physical signal. They
<v Speaker 2>have to decide what to be right now in the moment.
<v Speaker 3>That's it. Scrap was set. So what was the.
<v Speaker 2>Result, the billion dollar question.
<v Speaker 3>The result was that Bell's inequality was shattered. It wasn't
<v Speaker 3>even close. The correlations were far far stronger than any
<v Speaker 3>local hidden variable theory could possibly explain. They matched the
<v Speaker 3>predictions of quantum mechanics perfectly.
<v Speaker 2>So the gloves analogy is wrong. The instruction cards don't exist.
<v Speaker 3>They do not exist. Saying Einstein was wrong, and I
<v Speaker 3>mean it's a monumental conclusion. Locality in the classical sense
<v Speaker 3>that he cherished is dead. The universe is fundamentally irreducibly
<v Speaker 3>non local. The state of a particle right here is
<v Speaker 3>in some deep, way instantaneously connected to the state of
<v Speaker 3>another particle way over there.
<v Speaker 2>That is just it's a hard pill to swallow. I'm
<v Speaker 2>sitting here, you're sitting there. We feel very local, very separate.
<v Speaker 3>We do. And that's why even after aspect, scientists are
<v Speaker 3>so cautious they spent the next thirty years designing even
<v Speaker 3>more sophisticated experiments to close every other conceivable.
<v Speaker 2>Loophole, right like maybe the detectors aren't efficient enough, or
<v Speaker 2>maybe the random number generators aren't truly random.
<v Speaker 3>All of that, and then in twenty fifteen, a series
<v Speaker 3>of loophole free bell tests were finally performed that closed
<v Speaker 3>all the major loopholes simultaneously. The results were the same,
<v Speaker 3>rock solid. The universe is officially weird. Deal with it.
<v Speaker 2>Okay, let's deal with it. We have to really dig
<v Speaker 2>into what this means. Because the moment you say instantaneous connection,
<v Speaker 2>the first place everyone's mind goes is faster than like communication.
<v Speaker 2>They think, great, we can build an answable a subspace rate.
<v Speaker 2>I can have a real time conversation with someone on Mars.
<v Speaker 3>And this is where I, unfortunately have to be the buzzkill.
<v Speaker 3>You absolutely cannot use entanglement to send a message faster
<v Speaker 3>than like.
<v Speaker 2>But why not? I mean, it seems so obvious. If
<v Speaker 2>I poke my particle here and your particle wiggles instantly
<v Speaker 2>over there, Isn't that a signal one or a zero?
<v Speaker 3>It seems like it should be. But nature has this
<v Speaker 3>incredibly clever failsafe built in. It's called the no signaling theorem,
<v Speaker 3>and it's what preserves causality. The problem, in a word,
<v Speaker 3>is randomness.
<v Speaker 2>Okay, let's go back to Alice and Bob. Alice wants
<v Speaker 2>to send the bit one to Bob. How does it fail?
<v Speaker 3>Okay, Alice has her particle particle A. She decides I'm
<v Speaker 3>going to measure it now and that will be my signal.
<v Speaker 3>So she megres it. She gets let's say spin.
<v Speaker 2>Up, and instantly Bob's particle, particle B becomes spin down.
<v Speaker 3>Correct, So Bob could measure his and see spin down.
<v Speaker 3>But here's the catch. Alice couldn't force her particle to
<v Speaker 3>be spin up. The outcome of her measurement is fundamentally
<v Speaker 3>irreducibly random. It's a fifty to fifty quantum coin flip.
<v Speaker 3>She has absolutely no control over the results she gets.
<v Speaker 2>Ah, so she can't control the message she's sending.
<v Speaker 3>She can't encode any information into it. And now look
<v Speaker 3>at it from Bob's side. He's just sitting there in
<v Speaker 3>Los Angeles measuring his particles. He gets a stream of
<v Speaker 3>results down, up, up, down, down down. It's completely random.
<v Speaker 2>Right, It just looks like noise.
<v Speaker 3>It is noise. How does he know that the down
<v Speaker 3>he just measured was because Alice just measured and up.
<v Speaker 3>He has no way of knowing. He has no baseline,
<v Speaker 3>no context. A random string of bits contains zero information.
<v Speaker 2>The only way he'd know it wasn't just noise is
<v Speaker 2>if they compared their notes later.
<v Speaker 3>Exactly. Alice has to pick of the phone, a normal
<v Speaker 3>slower than light phone and call Bob and say hey
<v Speaker 3>at twelve point eight zho, I got up, and Bob
<v Speaker 3>looks at his logbook and says wow at twelve point
<v Speaker 3>eight oh one, I got down. It worked.
<v Speaker 2>But the phone call itself travels at or below the
<v Speaker 2>speed of light.
<v Speaker 3>And that's how causality is saved. Yeah, the spooky correlation
<v Speaker 3>is real and it's instantaneous, but the information you can
<v Speaker 3>extract from it can only travel the old fashioned way.
<v Speaker 3>Nature lets non locality exist, but it cloaks it in randomness,
<v Speaker 3>so you can't use it to break the timeline.
<v Speaker 2>That is unbelievably clever. It's like the universe has its
<v Speaker 2>cake and eats it too. It's weird, but it's not paradoxical.
<v Speaker 3>It prevents those kill your own grandfather paradoxes. If you
<v Speaker 3>could send a signal faster than light, you could send
<v Speaker 3>the message into your own past, and then the whole
<v Speaker 3>structure of cause and effect just dissolves.
<v Speaker 2>We should probably also quickly bust the other big myth
<v Speaker 2>that always crops.
<v Speaker 3>Up with this stuff, the consciousness myth.
<v Speaker 2>Yeah, the idea that it takes a conscious human mind
<v Speaker 2>an observer to collapse the wave function. Ah.
<v Speaker 3>Yes, the sort of new age interpretation of quantum mechanics.
<v Speaker 3>It's a very romantic idea that our minds shape reality.
<v Speaker 2>But the physics doesn't really support that, does it.
<v Speaker 3>Not at all. A measurement in physics isn't about consciousness.
<v Speaker 3>It's about interaction. Any interaction with a large classical system
<v Speaker 3>is enough to cause a collapse.
<v Speaker 2>So if an entangled photon hits a piece of photographic
<v Speaker 2>film and makes a silver halide molecule change state that's
<v Speaker 2>it collapse over.
<v Speaker 3>That's the measurement. It doesn't matter if a human develops
<v Speaker 3>that film and looks at the spot one hundred years
<v Speaker 3>from now. The collapse happened at the moment of that
<v Speaker 3>physical interaction.
<v Speaker 2>So my cat is a valid observer. My toaster is
<v Speaker 2>a valid observer.
<v Speaker 3>If your toaster interacts with a quantum system in a
<v Speaker 3>way that records its state, then yes, your toaster is
<v Speaker 3>a perfectly valid observer.
<v Speaker 2>Okay, so we've set the ground rules. No faster than
<v Speaker 2>light radios, no mystical mind control. But the amazing thing
<v Speaker 2>is we've moved past just staring at this in wonder.
<v Speaker 2>We're actually building things with it. We are entering the
<v Speaker 2>age of quantum technology.
<v Speaker 3>This is the really exciting part. We've pivoted from is
<v Speaker 3>this real to Okay, it's real. Now what can we
<v Speaker 3>do with it?
<v Speaker 2>So let's start with the one that sounds like it's
<v Speaker 2>straight out of science fiction. Quantum teleportation.
<v Speaker 3>It's a terrible name, it is.
<v Speaker 2>Isn't it. It immediately makes you think of Star Trek.
<v Speaker 2>Beat me up, Scotty.
<v Speaker 3>And we have to be very clear. We are not
<v Speaker 3>disintegrating a person in one place and reassembling them somewhere else.
<v Speaker 3>We're not moving matter at all.
<v Speaker 2>So what exactly is being teleported.
<v Speaker 3>We are teleporting the quantum state of a particle, the
<v Speaker 3>complete set of information that defines that particle.
<v Speaker 2>How is that different from just you know, standing it
<v Speaker 2>and emailing the data.
<v Speaker 3>Because of another weird quantum rule called the no cloning theorem.
<v Speaker 3>It states that it is fundamentally impossible to create an
<v Speaker 3>identical copy of an arbitrary, unknown quantum state.
<v Speaker 2>You can't just quantum photocopy something.
<v Speaker 3>You can't. The moment you try to measure a quantum
<v Speaker 3>state to get all the information needed to make a copy,
<v Speaker 3>you inevitably disturb it. You destroy the original, so you
<v Speaker 3>can't make a backup.
<v Speaker 2>You can only move it, right, And.
<v Speaker 3>That's what teleportation does. So here's the setup. Alice has
<v Speaker 3>a particle whose state she wants to send to Bob.
<v Speaker 3>Let's call her message particle. She also has one particle
<v Speaker 3>from an entangled pair that she shares with Bob.
<v Speaker 2>Okay, So Alice has two particles in her lab, the
<v Speaker 2>message and her half of the entangled link. Bob has
<v Speaker 2>the other half.
<v Speaker 3>Correct. Alice then performs a special kind of joint measurement
<v Speaker 3>on her two particles. It's called a Bell state measurement.
<v Speaker 3>In essence, she entangles her message particle with her half of.
<v Speaker 2>The link, and according to the no cloning rule, that
<v Speaker 2>has to destroy the original state of her message particle.
<v Speaker 3>It does. The information vanishes from Alice's location. But because
<v Speaker 3>of that spooky link, the state of Bob's particle way
<v Speaker 3>over in his lab instantly changes. It becomes a scrambled
<v Speaker 3>version of Alice's original message.
<v Speaker 2>Why scrambled?
<v Speaker 3>It's sort of locked. Bob needs the key to unscramble it,
<v Speaker 3>and the key is the result of Alice's Bell measurement.
<v Speaker 3>So Alice sends that result. It's just two bits of
<v Speaker 3>regular classical information over a normal fiber optic cable to Bob.
<v Speaker 2>So Bob gets these two classical bits, he performs a
<v Speaker 2>corresponding operation on his particle to unlock it, and then.
<v Speaker 3>And then his particle becomes an exact replica of Alice's
<v Speaker 3>original message particle. The state has effectively jumped from Alice's
<v Speaker 3>lab to Bob's. The physical particle didn't move, but its
<v Speaker 3>quantum identity did.
<v Speaker 2>That's amazing, and we're doing this for real.
<v Speaker 3>Oh yeah, routinely in labs. Back in twenty twenty two,
<v Speaker 3>a team achieved it over a forty four kilometer fiber
<v Speaker 3>optic network. We are literally building the foundations of a
<v Speaker 3>quantum Internet where fragile quantum information can be moved around
<v Speaker 3>without ever having to physically travel through the intervening space.
<v Speaker 2>Which leads us right to the application that everyone is
<v Speaker 2>either terrified of or incredibly excited about. Quantum computing.
<v Speaker 3>Right. This is the big one, and it relies on
<v Speaker 3>both superposition and entanglement to do its work. Your laptop, MyPhone,
<v Speaker 3>they all run on classical bits.
<v Speaker 2>A bit is either a zero or one on or
<v Speaker 2>off simple, but.
<v Speaker 3>A quantum bit or equibit can be in a superposition.
<v Speaker 3>It can be a zero in a one at the
<v Speaker 3>same time. But the real exponential power comes when you
<v Speaker 3>entangle them. Okay, you have one quibit, you have two
<v Speaker 3>possible states zero in one. If you're entangled too, quib
<v Speaker 3>you don't have two plus two. You have two to
<v Speaker 3>the power of two. You have four seats that exist
<v Speaker 3>simultaneously in this shared quantum space. Three entangled quivitz gives
<v Speaker 3>you eight states.
<v Speaker 2>So it scales exponentially. If you have say three hundred
<v Speaker 2>entangled covids.
<v Speaker 3>If you have three hundred perfectly stable entangled quibts, you
<v Speaker 3>can represent more simultaneous states than there are atoms in
<v Speaker 3>the entire observable universe.
<v Speaker 2>That number is just impossible to comprehend.
<v Speaker 3>It is, and it means a quantum computer doesn't solve
<v Speaker 3>problems by brute force trying one answer after another. It
<v Speaker 3>sets up this massively complex quantum state, this interference pattern
<v Speaker 3>where all the wrong answers are programmed to cancel each
<v Speaker 3>other out and the right answer is amplified.
<v Speaker 2>It's like finding the needle in a haystack by making
<v Speaker 2>all the hay instantly vanish.
<v Speaker 3>That is a fantastic analogy. Yes, and this isn't just
<v Speaker 3>theory anymore. In twenty twenty three, Google announced they had
<v Speaker 3>achieved quantum advantage using their Sycamore process or to do
<v Speaker 3>a calculation in seconds that they estimated would take the
<v Speaker 3>world's most powerful classical supercomputer something like forty seven years.
<v Speaker 2>And that's why all of our current encryption is potentially
<v Speaker 2>in jeopardy.
<v Speaker 3>A lot of it is. Yes, modern encryption relies on
<v Speaker 3>mathematical problems that are incredibly hard for classical computers to
<v Speaker 3>solve like finding the prime factors of a gigantic number.
<v Speaker 3>A large scale quantum computer could, in theory, slice through
<v Speaker 3>those problems like a hot knife through butter.
<v Speaker 2>So entanglement creates the threat, but it also provides the shield.
<v Speaker 3>It does, which brings us to quantum cryptography.
<v Speaker 2>Or QKD quantum key distribution.
<v Speaker 3>And this is probably the most mature and commercially available
<v Speaker 3>quantum technology right now. It uses the weirdness of measurement,
<v Speaker 3>the observer effect as the ultimate burglar alarm.
<v Speaker 2>So how does it work?
<v Speaker 3>It's quite elegant. Alice and Bob want to create a
<v Speaker 3>shared secret random key for encryption. They can do this
<v Speaker 3>by setting a stream of entangled photons over a fiber
<v Speaker 3>optic cable. Now, let's say a sky will call her
<v Speaker 3>Eve tries to tap into that cable read the key.
<v Speaker 2>To read the state of the photons, she has to
<v Speaker 2>measure them.
<v Speaker 3>In the moment she measures a photon, she forces its
<v Speaker 3>wave function to collapse. She fundamentally alters its state. She
<v Speaker 3>leaves a trace.
<v Speaker 2>She breaks the delicate entanglement exactly.
<v Speaker 3>When Alis and Bob are dune, they can publicly compare
<v Speaker 3>a small random sample of their key bits. If there's
<v Speaker 3>an eavesdropper on the line, they'll find a higher than
<v Speaker 3>expected error rate in that sample.
<v Speaker 2>The errors are Eve's fingerprints.
<v Speaker 3>You cannot observe a quantum system without disturbing it. That's
<v Speaker 3>a fundamental law of physics, which means you cannot wire
<v Speaker 3>tap a quantum channel without being detected. The laws of
<v Speaker 3>nature themselves guarantee the security, and this.
<v Speaker 2>Is already being deployed.
<v Speaker 3>Oh yeah. Banks are using it for secure transactions between
<v Speaker 3>data centers, and most famously, China launched the Musha satellite,
<v Speaker 3>which can beam entangled photons down to ground stations thousands
<v Speaker 3>of kilometers apart, creating unhackable communication keys from space.
<v Speaker 2>It's just incredible to go from Einstein calling it spooky
<v Speaker 2>action in nineteen thirty five to using that same spookiness
<v Speaker 2>to secure global financial networks. It's a breath taking pace.
<v Speaker 3>It just goes to show you that even the most
<v Speaker 3>abstract philosophical what is reality debates in physics can end
<v Speaker 3>up completely transforming technology and civilization.
<v Speaker 2>But speaking of those philosophical debates, they're not over. We
<v Speaker 2>may be using the technology, but we still argue ferociously
<v Speaker 2>about what it all means the measurement problem.
<v Speaker 3>We have the math and it works perfectly. We can
<v Speaker 3>build machines with it. But the story we tell ourselves
<v Speaker 3>about what the math is describing that is still very
<v Speaker 3>much up for grabs.
<v Speaker 2>These are the interpretations of quantum mechanics. Let's touch on
<v Speaker 2>the main contenders first. There's the standard textbook one, the
<v Speaker 2>Copenhagen interpretation, right.
<v Speaker 3>This is essentially the view of Neil's Bore and his group,
<v Speaker 3>and it's very pragmatic. It basically says, shut up and calculate.
<v Speaker 3>The wave function isn't a real thing. It's just a
<v Speaker 3>mathematical tool that tells us the probabilities of our measurements.
<v Speaker 3>Reality is created in the active measurement. Don't ask what
<v Speaker 3>was there before.
<v Speaker 2>It works, but it feels a little unsatisfying, like a
<v Speaker 2>cop out too many.
<v Speaker 3>Yes, it leaves the concept of measurement as this magical,
<v Speaker 3>undefined thing that sits outside the theory, which.
<v Speaker 2>Leads to the one that well, it either sounds brilliant
<v Speaker 2>or completely insane. The many World's interpretation.
<v Speaker 3>Proposed by Hugh Everett in nineteen fifty seven. He looked
<v Speaker 3>at the math and asked a very simple question, why
<v Speaker 3>do we have to add this messy collapse part to
<v Speaker 3>the equations. What if the wave function just never collapses.
<v Speaker 2>But if it never collapses, how do we ever get
<v Speaker 2>a single definite result. I measure the electron and I
<v Speaker 2>see up, not a blur.
<v Speaker 3>Everett's answer was that the wave function just continues to
<v Speaker 3>evolve smoothly. When you, the observer, interact with the particle,
<v Speaker 3>that's in a superposition of up and down. The entire universe,
<v Speaker 3>including U splits it br branches. In one branch of
<v Speaker 3>the universe, there's a version of you who just measured up,
<v Speaker 3>and in another completely separate branch, there's another version of
<v Speaker 3>you who just measured down.
<v Speaker 2>And both of these branches, both versions of me are
<v Speaker 2>equally real.
<v Speaker 3>Equally real, So in the entanglement experiment, there's no spooky action.
<v Speaker 3>When Alice measures her particle, the universe splits in the
<v Speaker 3>Alice measured up branch, Bob is now correlated to measure down.
<v Speaker 3>The correlation is just between the different branches of this
<v Speaker 3>universal wave function.
<v Speaker 2>It saves locality, but at the cost of creating an
<v Speaker 2>infinite number of parallel universes every single nanosecond.
<v Speaker 3>That's the trade off. It's a very high price to
<v Speaker 3>pay onto logically, but a lot of physicists love it
<v Speaker 3>because the underlying math is so clean and elegant. There's
<v Speaker 3>no arbitrary collapse rule.
<v Speaker 2>And just when that seems like the weirdest it can get,
<v Speaker 2>there's a newer, even wilder idea that tries to connect
<v Speaker 2>all this back to Einstein's other great theory gravity ER
<v Speaker 2>equals EPR.
<v Speaker 3>This is right at the cutting edge. For a century.
<v Speaker 3>We've had these two pillars of modern physics, quantum mechanics
<v Speaker 3>which describes the very small with things like EPR and entanglement,
<v Speaker 3>and general relativity, which describes the very large gravity space time,
<v Speaker 3>and they just do not get along.
<v Speaker 2>Their mathematics are incompatible totally.
<v Speaker 3>But EPR is a conjecture that suggests maybe there are
<v Speaker 3>two sides of the same coin. The ER stands for
<v Speaker 3>Einstein rosenbridge, which is the technical term for a wormhole,
<v Speaker 3>a tunnel, a shortcut through the fabric of space.
<v Speaker 2>Time, and EPR is the entanglement paradox we've been talking about.
<v Speaker 2>So the theory is that entanglement and wormholes are the
<v Speaker 2>same thing.
<v Speaker 3>The conjecture is that the spooky connection between two entangled
<v Speaker 3>particles is a microscopic wormhole connecting.
<v Speaker 2>Them, a literal physical tunnel through space time, a tiny.
<v Speaker 3>Non traversible quantum scale. One yes, And if this is true,
<v Speaker 3>it has a staggering implication. It implies that spacetime itself,
<v Speaker 3>the very geometry of our universe, might be an emergent property.
<v Speaker 3>It might be literally stitched together by a vast network
<v Speaker 3>of quantum entanglement.
<v Speaker 2>So space time isn't the stage that the play of
<v Speaker 2>physics happens on. Space time is the play. It's the
<v Speaker 2>actors holding hands.
<v Speaker 3>That's a beautiful way to put it. If you could
<v Speaker 3>somehow remove all the entanglement from the universe, space time
<v Speaker 3>itself might just dissolve into an unstructured mess. The concept
<v Speaker 3>of distance might be the illusion, and entanglement the deeper.
<v Speaker 2>Reality that brings us full circle right back to Einstein's nightmare.
<v Speaker 2>He was terrified that entanglement meant the breakdown of locality,
<v Speaker 2>the breakdown of the clear separation of space.
<v Speaker 3>And he might have been right, but in a way
<v Speaker 3>he never could have imagined. Entanglement doesn't break space. It
<v Speaker 3>might actually build space. The very thing he hated most
<v Speaker 3>might be the glue that holds his own theory of
<v Speaker 3>gravity together.
<v Speaker 2>That is the ultimate cosmic irony.
<v Speaker 3>It really is, and it's a profound reminder that the
<v Speaker 3>universe has absolutely no obligation to conform to our common sense.
<v Speaker 3>It's random, it's non local, and it's interconnected in ways
<v Speaker 3>that we're only just beginning to grasp.
<v Speaker 2>It really suggests that separation is the illusion. I mean,
<v Speaker 2>if everything in the universe erupted from a single point
<v Speaker 2>in the Big Bang.
<v Speaker 3>Then in some say sense, everything was entangled with everything
<v Speaker 3>else at the very beginning. We are, in a very real,
<v Speaker 3>physical way, all part of a single, vast quantum system.
<v Speaker 2>Now that is a thought that will keep me up tonight.
<v Speaker 3>It should keep us all up.
<v Speaker 2>We have gone from a simple analogy about gloves and
<v Speaker 2>boxes to the fundamental fabric of reality itself. I think
<v Speaker 2>my brain needs to cool down for a bit.
<v Speaker 3>I think we all do. It's a lot to take in.
<v Speaker 2>Well, thank you for being our guide through this quantum wilderness.
<v Speaker 2>It's been fascinating, my pleasure.
<v Speaker 3>It's the best story there is.
<v Speaker 2>And to all of you listening, we'll leave you with
<v Speaker 2>that thought, what if distance is just a stubborn illusion?
<v Speaker 2>Keep questioning reality? We'll see you on the next one.