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<v Speaker 1>Welcome to the quark Side. Quantum Physics podcast, an exploration

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<v Speaker 1>of the fundamental structure of reality, where quantum laws govern matter, energy,

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<v Speaker 1>and information. Here, uncertainty is a feature, not a flaw,

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<v Speaker 1>and understanding begins at the smallest scales.

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<v Speaker 2>Imagine you are holding your mourning coffee mug like you

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<v Speaker 2>can actually feel the weight of it right, the heat

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<v Speaker 2>of the ceramic, the handle against your fingers. It's solid,

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<v Speaker 2>and it's right there in.

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<v Speaker 3>Your hands, right, totally normal morning, exactly.

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<v Speaker 2>But now try to imagine that exact same coffee mug

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<v Speaker 2>simultaneously sitting on the kitchen counter, I don't know, ten

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<v Speaker 2>feet away, and not a copy of the mug, but

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<v Speaker 2>the actual mug itself existing in two entirely different places

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<v Speaker 2>at the exact.

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<v Speaker 3>Same time, which just sounds completely absurd. It goes against

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<v Speaker 3>literally everything we experience.

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<v Speaker 2>On a daily basis totally. But if we zoom in

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<v Speaker 2>far enough down to the microscopic world, a particle existing

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<v Speaker 2>in two different places at once isn't just some weird

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<v Speaker 2>thought experiment. It's a proven reality. In quantum mechanics. It's

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<v Speaker 2>called superposition, and it is.

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<v Speaker 3>Arguably the most jarring disconnect in all of science, honestly,

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<v Speaker 3>because we know for a fact that the foundational building

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<v Speaker 3>blocks of our universe electrons, photons, quirks, they exist in

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<v Speaker 3>this blurry state of multiple possibilities at once.

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<v Speaker 2>Yeah, but we don't. We live in a macroscopic world

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<v Speaker 2>of definite singular states. Your coffee mug is either in

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<v Speaker 2>your hand or on the counter, I mean it is

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<v Speaker 2>never both exactly, which brings us to the core mission

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<v Speaker 2>the really massive mystery we are exploring today, the measurement problem.

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<v Speaker 2>At some point between that microscopic realm of infinite possibilities

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<v Speaker 2>and the macroscopic realm of everyday life reality, just well.

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<v Speaker 3>It collapses, It snaps into place.

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<v Speaker 2>Right the moment a quantum system is measured or even

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<v Speaker 2>just interacts with this environment, all those blurry possibilities collapse

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<v Speaker 2>into a single fixed state. And today we are exploring

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<v Speaker 2>how scientists are actively trying to catch that exact microscopic

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<v Speaker 2>moment of collapse, like they are using a massive subterranean

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<v Speaker 2>dark matter detector in Italy to do it.

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<v Speaker 3>And we really need to emphasize the stakes here solving

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<v Speaker 3>this measurement problem. It isn't just about particle physics or

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<v Speaker 3>tying up some mathematical loose end. It's the key to

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<v Speaker 3>bridging the seemingly impassable gulf between quantum mechanics and general relativity,

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<v Speaker 3>which is basically gravity, right right gravity. Finding the mechanism

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<v Speaker 3>behind this collapse, it could honestly give us the holy

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<v Speaker 3>grail of modern physics, which is a unified theory of

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<v Speaker 3>quantum gravity.

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<v Speaker 2>Okay, let's unpack this because before we go a kilometer

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<v Speaker 2>underground to look at this Italian detector, we need to

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<v Speaker 2>understand exactly what scientists are trying to catch. So quantum superposition,

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<v Speaker 2>we're talking about a particle not sitting in a neat spot,

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<v Speaker 2>but existing as a wave function.

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<v Speaker 3>Yeah, it's essentially smeared out across space. It's representing a

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<v Speaker 3>probability of being in multiple places simultaneously.

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<v Speaker 2>Then it interacts with something and boom, that smeared out

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<v Speaker 2>wave function abruptly collapses. The particle snaps into a single location.

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<v Speaker 2>And for what nearly a century, the question has been why?

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<v Speaker 2>What physically causes that snap?

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<v Speaker 3>Well, early on, some theorists actually propose that the act

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<v Speaker 3>of observation by a conscious mind triggered the collapse.

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<v Speaker 2>Which is, come on, that feels way too mystical for physics,

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<v Speaker 2>the idea that human consciousness dictates physical reality.

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<v Speaker 3>Oh, most modern physicists are very uncomfortable with that leap.

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<v Speaker 3>It's exactly that discomfort that drove the development of theoretical

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<v Speaker 3>models to explain the collapse without needing an observer at all.

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<v Speaker 3>The two big ones are the continuous spontaneous localization model

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<v Speaker 3>or the CSL model, and the Doc Penrose model.

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<v Speaker 2>So starting with CSL, the name kind of gives it away.

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<v Speaker 2>Continuous meaning it's happening all the time, spontaneous meaning no

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<v Speaker 2>conscious human observer is needed, and localization because it forces

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<v Speaker 2>that smearreed out particle into a local, definite spot right.

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<v Speaker 3>And the CSL model proposes that this collapse is driven

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<v Speaker 3>by a constant random background noise in the universe, like

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<v Speaker 3>a universal jitter that occasionally forces a particle to localize.

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<v Speaker 2>But then you have the Doc Penrose model, which is wild.

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<v Speaker 2>It looks at gravity as the trigger because if a

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<v Speaker 2>particle is in superposition, it mathematically exists in two places

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<v Speaker 2>at once, right exactly, which means it has mass in

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<v Speaker 2>two different places at.

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<v Speaker 3>Once, And that is the core gravitational contradiction. General relativity

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<v Speaker 3>tells us mass bends space time, but space time is rigid.

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<v Speaker 3>It cannot sustain two conflicting gravitational curvatures generated by the

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<v Speaker 3>very same object.

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<v Speaker 2>So the sheer physical strain of that contradiction builds up

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<v Speaker 2>until spacetime just forces the particle to pick a lane.

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<v Speaker 2>Gravity itself is the observer precisely.

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<v Speaker 3>But here is the critical part. Both the CSL and

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<v Speaker 3>the doc Penrose models share one highly testable prediction. When

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<v Speaker 3>this spontaneous collapse happens, it shouldn't be totally silent.

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<v Speaker 2>It leads a footprint.

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<v Speaker 3>Yes, specifically, the collapse should emit a very faint burst

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<v Speaker 3>of X ray radiation. It's a phenomenon called Bremstralung, or

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<v Speaker 3>breaking radiation. When a charged particle suddenly decelerates or localizes,

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<v Speaker 3>it has to shed excess energy.

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<v Speaker 2>It's like a magician making a balloon pop, but instead

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<v Speaker 2>of a loud bang, the universe emits a tiny, incredibly

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<v Speaker 2>faint X ray flash.

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<v Speaker 3>That's a great way to visualize it. And what's fascinating

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<v Speaker 3>here is how these models take a purely abstract mathematical mystery,

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<v Speaker 3>the wave function collapse, and turn it into a physical,

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<v Speaker 3>measurable event that we can actually build a trap for right.

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<v Speaker 2>If there's a flash, we can catch it. But that

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<v Speaker 2>brings up a massive problem. These theoretical X ray flashes

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<v Speaker 2>are incredibly faint. How do you build a trap sensitive

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<v Speaker 2>enough to catch one?

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<v Speaker 3>You don't build one from scratch, You borrow a trap

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<v Speaker 3>built for something else entirely, which.

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<v Speaker 2>Leads us to Grand Sasso, Italy. Deep underground tell us

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<v Speaker 2>about xxinon.

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<v Speaker 3>So Xenon is a highly sensitive detector located inside the

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<v Speaker 3>INFN Grand Sasso National Laboratory, protect did by roughly a

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<v Speaker 3>kilometer of solid rock which shields it from cosmic rays.

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<v Speaker 2>And the machine itself is just massive. It's a huge

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<v Speaker 2>cylinder filled with a liquid xenon, almost six tons of it, right.

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<v Speaker 3>Nearly six tons, yes, cooled to minus ninety five degrees celsiu.

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<v Speaker 3>So it becomes this ultrapure dense liquid, and floating right

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<v Speaker 3>at the top is a thin layer of xenon gas.

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<v Speaker 2>Okay, so how does it work as a trap? Say

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<v Speaker 2>a quantum collapse happens inside the liquid xenon and emids

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<v Speaker 2>that tiny X ray.

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<v Speaker 3>So if an X ray hits the xenon, it excites

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<v Speaker 3>the atoms. Those atoms instantly produce an initial flash of light.

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<v Speaker 3>We call that signal one or S one, with.

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<v Speaker 2>A quick prompt flash exactly.

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<v Speaker 3>But the X ray also knocks a few electrons completely free,

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<v Speaker 3>and there is a strong electric field running through the

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<v Speaker 3>liquid that acts like a current, pushing those loose electrons.

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<v Speaker 2>Upward, up toward the gas layer, right.

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<v Speaker 3>And by measuring how long they take to rise, we

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<v Speaker 3>know the exact depth of the event. Once they hit

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<v Speaker 3>the gas layer, a second electric field accelerates them, violently,

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<v Speaker 3>creating a second, brighter flash of light signal two or sne.

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<v Speaker 2>So you combine the S one flash and the S

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<v Speaker 2>two flash, and you know the exact energy and the

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<v Speaker 2>precise three D location of the pod.

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<v Speaker 3>You've perfectly mapped it.

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<v Speaker 2>Okay, but wait, xi and is a dark matter detector.

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<v Speaker 2>That's what it was built for. Isn't using a dark

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<v Speaker 2>matter detector to look for quantum collapse, like, I don't know,

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<v Speaker 2>using a telescope to look for a microbe? It just

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<v Speaker 2>seems like the wrong tool.

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<v Speaker 3>I get why you'd think that, But there is this

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<v Speaker 3>concept we call Moore's law of xenon detectors. They started

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<v Speaker 3>out using just a few kilograms of xenon. Now they

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<v Speaker 3>are up to multiple tons.

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<v Speaker 2>They just keep scaling up.

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<v Speaker 3>Exponentially, and because they've grown so massive while also keeping

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<v Speaker 3>background noise incredibly low, they have extremely low energy thresholds.

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<v Speaker 3>They've essentially evolved into the Swiss Army Knives of astroparticle physics.

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<v Speaker 3>They can detect things they were never originally designed to see.

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<v Speaker 2>That is wild. Okay, so we have the Swiss Army knife,

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<v Speaker 2>but having the trap is only half the battle. If

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<v Speaker 2>you're a scientist looking at the monitors, you have to

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<v Speaker 2>know what that quantum X ray flash actually looks like.

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<v Speaker 2>Otherwise it's just background noise.

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<v Speaker 3>Absolutely, and this is where the theorists come back in. Initially,

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<v Speaker 3>they had done all their math for these collapse models

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<v Speaker 3>using germanium atoms because older detectors use solid germanium.

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<v Speaker 2>But xenon T is liquid xenon. That's a totally different

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<v Speaker 2>atomic structure exactly.

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<v Speaker 3>So theoretical physicists had to completely recalibrate their math for xenon,

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<v Speaker 3>and the breakthrough they had was stunning. They calculated that

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<v Speaker 3>a quantum collapse in xenon wouldn't just produce a flat,

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<v Speaker 3>smooth energy.

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<v Speaker 2>Signal because of the atomic effects.

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<v Speaker 3>Right, Yes, the specific arrangement of electron shells and xenon

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<v Speaker 3>means the signal would have very distinct bumps at specific

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<v Speaker 3>low energies.

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<v Speaker 2>Here's where it it's really interesting. Instead of looking for

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<v Speaker 2>a needle in a massive haystack, the theoretical physicists basically

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<v Speaker 2>painted the exact needle they were looking for neon pink like.

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<v Speaker 2>Having those predictable bumps makes the statistical analysis so much

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<v Speaker 2>more powerful, and.

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<v Speaker 3>This raises an important question about how science actually gets done.

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<v Speaker 3>Neither side could make this sleep alone. The theorists provided

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<v Speaker 3>the exact neon pink map, and the experimentalists provided the

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<v Speaker 3>ultra quiet hardware to actually find it.

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<v Speaker 2>But getting that ultra quiet hardware is a nightmare. They

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<v Speaker 2>are a kilometer underground, but they still have to deal

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<v Speaker 2>with trace radioactivity, specifically rate on gas. Right.

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<v Speaker 3>Radon is the eternal enemy of underground physics. It seeps

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<v Speaker 3>out of the rock, decays into an isotope called lead

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<v Speaker 3>two fourteen, and causes background noise inside the detector.

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<v Speaker 2>So how did they fix that?

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<v Speaker 3>Through a technique called fiducialization. They didn't analyze the whole

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<v Speaker 3>five point nine ton tank. They only looked at the

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<v Speaker 3>innermost four point three seven ton subvolume.

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<v Speaker 2>Oh, they used the outer layers of the liquid xenon

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<v Speaker 2>as a radiation shield for the center. That is so smart. Okay,

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<v Speaker 2>So the trap is set, the background noise is handled,

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<v Speaker 2>the neon pink signal is defined. What happened in the

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<v Speaker 2>twenty twenty one science campaign.

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<v Speaker 3>They analyzed data from July sixth to November tenth, and

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<v Speaker 3>the result was definitive. They didn't find the predicted X ray.

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<v Speaker 2>Burs nothing at all.

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<v Speaker 3>Nothing.

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<v Speaker 2>So what does so all mean? I mean they spent

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<v Speaker 2>months looking, built this massive subterranean trap, mapped out the

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<v Speaker 2>exact signal, and found absolutely nothing. How is that not

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<v Speaker 2>a massive failure.

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<v Speaker 3>Because in experimental physics, finding nothing is extremely powerful. By

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<v Speaker 3>not finding the signal, they proved it doesn't exist within

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<v Speaker 3>those specific energy ranges. They constrained the continuous spontaneous localization

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<v Speaker 3>model to be more than one hundred times more sensitive

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<v Speaker 3>than previous leading experiments.

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<v Speaker 2>Oh so they didn't kill the theories, but they shrank

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<v Speaker 2>the wiggle room.

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<v Speaker 3>Drastically shrank it. They forced the models into a much

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<v Speaker 3>tighter mathematical corner.

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<v Speaker 2>But wait, if they just ran the machine longer, wouldn't

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<v Speaker 2>they eventually hear the pops. Why stop there?

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<v Speaker 3>Because they hit an unbeatable wall of background noise, the

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<v Speaker 3>ultimate background noise. Solar neutrinos own the neutrino fog. Right

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<v Speaker 3>our sun is constantly blasting out these ghostly particles. Right

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<v Speaker 3>now as we speak, roughly seventy billion solar neutrinos are

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<v Speaker 3>passing through an area the size of your thumbnail every

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<v Speaker 3>single second.

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<v Speaker 2>Seventy billion through a thumbnail every second. That is terrifying.

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<v Speaker 3>And they pass right through the rock, through the lead shielding,

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<v Speaker 3>straight into the xenon. Mostly they leave no trace, but

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<v Speaker 3>with a detector this sensitive, eventually a neutrino strikes a

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<v Speaker 3>xenon atom perfectly and it creates a flash that perfectly

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<v Speaker 3>mimics the exact X ray signal we are looking for.

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<v Speaker 2>Wow, so you can't shield against it. It's an irreducible

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<v Speaker 2>background noise, the neutrino fog. So how does science move forward?

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<v Speaker 2>Are we just stuck?

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<v Speaker 3>Not at all? The future is an upcoming detector called XLZD.

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<v Speaker 3>It's a mega collaboration merging the xinon LZ and Darwin teams.

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<v Speaker 3>They are going to pack five to ten times the

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<v Speaker 3>massive current detectors into.

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<v Speaker 2>One machine to push deep into the fog.

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<v Speaker 3>Exactly, if you have a mass of enough volume you

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<v Speaker 3>can precisely characterize the solar neutrino signature, model it and

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<v Speaker 3>then mathematically subtract it from your data.

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<v Speaker 2>That is brilliant. And this brings us back to the

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<v Speaker 2>Doc Penrose model and gravity because if they actually push

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<v Speaker 2>through the fog and find this collect as, it changes

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<v Speaker 2>how we view reality.

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<v Speaker 3>Right fundamentally, the Dooce Penrose model suggests that space time

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<v Speaker 3>might not be perfectly smooth. It implies a fundamental microscopic fuzziness,

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<v Speaker 3>an intrinsic limitation in the structure of reality.

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<v Speaker 2>Like space time is pixelated, yes.

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<v Speaker 3>Which is an idea of discreteness that dates all the

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<v Speaker 3>way back to the ancient Greek philosopher Democritus. He thought

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<v Speaker 3>everything was eventually made of discrete parts. If space time

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<v Speaker 3>is fundamentally pixelated, that fuzzy, uncertain texture might be exactly

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<v Speaker 3>what forces a quantum superposition to collapse. Spacetime just can't

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<v Speaker 3>handle the contradiction across its rigid pixels.

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<v Speaker 2>It's amazing to think that building massive vats of liquid

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<v Speaker 2>xenon underground is ultimately about gravitizing quantum mechanics, proving that

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<v Speaker 2>space and time are pixelated.

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<v Speaker 3>And if we connect this to the bigger picture, it

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<v Speaker 3>goes so far beyond quantum mechanics. It is our absolute

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<v Speaker 3>best pathway toward testing a unified theory of quantum gravity,

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<v Speaker 3>reconciling Newton's gravity with the quantum realm once and for all.

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<v Speaker 2>We have covered so much ground today, from the absolute

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<v Speaker 2>absurdity of a coffee mug being in two places at once,

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<v Speaker 2>down into a subterranean Italian vault filled with liquid xenon,

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<v Speaker 2>to hunting the neutrino fog, and finally arriving at the

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<v Speaker 2>pixelated fabric of space time itself.

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<v Speaker 3>It is a phenomenal time to be watching this field.

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<v Speaker 2>It really is. So next time you look at a

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<v Speaker 2>solid object, whether it's your coffee mug or the wall

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<v Speaker 2>next to you, consider this. Its stable, singular existence right

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<v Speaker 2>there in front of you might just be the result

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<v Speaker 2>of a microscopic, fuzzy texture of space time quietly measuring it.

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<v Speaker 2>It might be emitting an invisible chorus of tiny X

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<v Speaker 2>rays as it constantly forces itself into reality, and humanity

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<v Speaker 2>is finally on the absolute verge of being able to

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<v Speaker 2>hear it,