Speaker 1: Welcome to the quark Side. Quantum Physics podcast, an exploration
Speaker 1: of the fundamental structure of reality, where quantum laws govern matter, energy,
Speaker 1: and information. Here, uncertainty is a feature, not a flaw,
Speaker 1: and understanding begins at the smallest scales.
Speaker 2: Imagine you are holding your mourning coffee mug like you
Speaker 2: can actually feel the weight of it right, the heat
Speaker 2: of the ceramic, the handle against your fingers. It's solid,
Speaker 2: and it's right there in.
Speaker 3: Your hands, right, totally normal morning, exactly.
Speaker 2: But now try to imagine that exact same coffee mug
Speaker 2: simultaneously sitting on the kitchen counter, I don't know, ten
Speaker 2: feet away, and not a copy of the mug, but
Speaker 2: the actual mug itself existing in two entirely different places
Speaker 2: at the exact.
Speaker 3: Same time, which just sounds completely absurd. It goes against
Speaker 3: literally everything we experience.
Speaker 2: On a daily basis totally. But if we zoom in
Speaker 2: far enough down to the microscopic world, a particle existing
Speaker 2: in two different places at once isn't just some weird
Speaker 2: thought experiment. It's a proven reality. In quantum mechanics. It's
Speaker 2: called superposition, and it is.
Speaker 3: Arguably the most jarring disconnect in all of science, honestly,
Speaker 3: because we know for a fact that the foundational building
Speaker 3: blocks of our universe electrons, photons, quirks, they exist in
Speaker 3: this blurry state of multiple possibilities at once.
Speaker 2: Yeah, but we don't. We live in a macroscopic world
Speaker 2: of definite singular states. Your coffee mug is either in
Speaker 2: your hand or on the counter, I mean it is
Speaker 2: never both exactly, which brings us to the core mission
Speaker 2: the really massive mystery we are exploring today, the measurement problem.
Speaker 2: At some point between that microscopic realm of infinite possibilities
Speaker 2: and the macroscopic realm of everyday life reality, just well.
Speaker 3: It collapses, It snaps into place.
Speaker 2: Right the moment a quantum system is measured or even
Speaker 2: just interacts with this environment, all those blurry possibilities collapse
Speaker 2: into a single fixed state. And today we are exploring
Speaker 2: how scientists are actively trying to catch that exact microscopic
Speaker 2: moment of collapse, like they are using a massive subterranean
Speaker 2: dark matter detector in Italy to do it.
Speaker 3: And we really need to emphasize the stakes here solving
Speaker 3: this measurement problem. It isn't just about particle physics or
Speaker 3: tying up some mathematical loose end. It's the key to
Speaker 3: bridging the seemingly impassable gulf between quantum mechanics and general relativity,
Speaker 3: which is basically gravity, right right gravity. Finding the mechanism
Speaker 3: behind this collapse, it could honestly give us the holy
Speaker 3: grail of modern physics, which is a unified theory of
Speaker 3: quantum gravity.
Speaker 2: Okay, let's unpack this because before we go a kilometer
Speaker 2: underground to look at this Italian detector, we need to
Speaker 2: understand exactly what scientists are trying to catch. So quantum superposition,
Speaker 2: we're talking about a particle not sitting in a neat spot,
Speaker 2: but existing as a wave function.
Speaker 3: Yeah, it's essentially smeared out across space. It's representing a
Speaker 3: probability of being in multiple places simultaneously.
Speaker 2: Then it interacts with something and boom, that smeared out
Speaker 2: wave function abruptly collapses. The particle snaps into a single location.
Speaker 2: And for what nearly a century, the question has been why?
Speaker 2: What physically causes that snap?
Speaker 3: Well, early on, some theorists actually propose that the act
Speaker 3: of observation by a conscious mind triggered the collapse.
Speaker 2: Which is, come on, that feels way too mystical for physics,
Speaker 2: the idea that human consciousness dictates physical reality.
Speaker 3: Oh, most modern physicists are very uncomfortable with that leap.
Speaker 3: It's exactly that discomfort that drove the development of theoretical
Speaker 3: models to explain the collapse without needing an observer at all.
Speaker 3: The two big ones are the continuous spontaneous localization model
Speaker 3: or the CSL model, and the Doc Penrose model.
Speaker 2: So starting with CSL, the name kind of gives it away.
Speaker 2: Continuous meaning it's happening all the time, spontaneous meaning no
Speaker 2: conscious human observer is needed, and localization because it forces
Speaker 2: that smearreed out particle into a local, definite spot right.
Speaker 3: And the CSL model proposes that this collapse is driven
Speaker 3: by a constant random background noise in the universe, like
Speaker 3: a universal jitter that occasionally forces a particle to localize.
Speaker 2: But then you have the Doc Penrose model, which is wild.
Speaker 2: It looks at gravity as the trigger because if a
Speaker 2: particle is in superposition, it mathematically exists in two places
Speaker 2: at once, right exactly, which means it has mass in
Speaker 2: two different places at.
Speaker 3: Once, And that is the core gravitational contradiction. General relativity
Speaker 3: tells us mass bends space time, but space time is rigid.
Speaker 3: It cannot sustain two conflicting gravitational curvatures generated by the
Speaker 3: very same object.
Speaker 2: So the sheer physical strain of that contradiction builds up
Speaker 2: until spacetime just forces the particle to pick a lane.
Speaker 2: Gravity itself is the observer precisely.
Speaker 3: But here is the critical part. Both the CSL and
Speaker 3: the doc Penrose models share one highly testable prediction. When
Speaker 3: this spontaneous collapse happens, it shouldn't be totally silent.
Speaker 2: It leads a footprint.
Speaker 3: Yes, specifically, the collapse should emit a very faint burst
Speaker 3: of X ray radiation. It's a phenomenon called Bremstralung, or
Speaker 3: breaking radiation. When a charged particle suddenly decelerates or localizes,
Speaker 3: it has to shed excess energy.
Speaker 2: It's like a magician making a balloon pop, but instead
Speaker 2: of a loud bang, the universe emits a tiny, incredibly
Speaker 2: faint X ray flash.
Speaker 3: That's a great way to visualize it. And what's fascinating
Speaker 3: here is how these models take a purely abstract mathematical mystery,
Speaker 3: the wave function collapse, and turn it into a physical,
Speaker 3: measurable event that we can actually build a trap for right.
Speaker 2: If there's a flash, we can catch it. But that
Speaker 2: brings up a massive problem. These theoretical X ray flashes
Speaker 2: are incredibly faint. How do you build a trap sensitive
Speaker 2: enough to catch one?
Speaker 3: You don't build one from scratch, You borrow a trap
Speaker 3: built for something else entirely, which.
Speaker 2: Leads us to Grand Sasso, Italy. Deep underground tell us
Speaker 2: about xxinon.
Speaker 3: So Xenon is a highly sensitive detector located inside the
Speaker 3: INFN Grand Sasso National Laboratory, protect did by roughly a
Speaker 3: kilometer of solid rock which shields it from cosmic rays.
Speaker 2: And the machine itself is just massive. It's a huge
Speaker 2: cylinder filled with a liquid xenon, almost six tons of it, right.
Speaker 3: Nearly six tons, yes, cooled to minus ninety five degrees celsiu.
Speaker 3: So it becomes this ultrapure dense liquid, and floating right
Speaker 3: at the top is a thin layer of xenon gas.
Speaker 2: Okay, so how does it work as a trap? Say
Speaker 2: a quantum collapse happens inside the liquid xenon and emids
Speaker 2: that tiny X ray.
Speaker 3: So if an X ray hits the xenon, it excites
Speaker 3: the atoms. Those atoms instantly produce an initial flash of light.
Speaker 3: We call that signal one or S one, with.
Speaker 2: A quick prompt flash exactly.
Speaker 3: But the X ray also knocks a few electrons completely free,
Speaker 3: and there is a strong electric field running through the
Speaker 3: liquid that acts like a current, pushing those loose electrons.
Speaker 2: Upward, up toward the gas layer, right.
Speaker 3: And by measuring how long they take to rise, we
Speaker 3: know the exact depth of the event. Once they hit
Speaker 3: the gas layer, a second electric field accelerates them, violently,
Speaker 3: creating a second, brighter flash of light signal two or sne.
Speaker 2: So you combine the S one flash and the S
Speaker 2: two flash, and you know the exact energy and the
Speaker 2: precise three D location of the pod.
Speaker 3: You've perfectly mapped it.
Speaker 2: Okay, but wait, xi and is a dark matter detector.
Speaker 2: That's what it was built for. Isn't using a dark
Speaker 2: matter detector to look for quantum collapse, like, I don't know,
Speaker 2: using a telescope to look for a microbe? It just
Speaker 2: seems like the wrong tool.
Speaker 3: I get why you'd think that, But there is this
Speaker 3: concept we call Moore's law of xenon detectors. They started
Speaker 3: out using just a few kilograms of xenon. Now they
Speaker 3: are up to multiple tons.
Speaker 2: They just keep scaling up.
Speaker 3: Exponentially, and because they've grown so massive while also keeping
Speaker 3: background noise incredibly low, they have extremely low energy thresholds.
Speaker 3: They've essentially evolved into the Swiss Army Knives of astroparticle physics.
Speaker 3: They can detect things they were never originally designed to see.
Speaker 2: That is wild. Okay, so we have the Swiss Army knife,
Speaker 2: but having the trap is only half the battle. If
Speaker 2: you're a scientist looking at the monitors, you have to
Speaker 2: know what that quantum X ray flash actually looks like.
Speaker 2: Otherwise it's just background noise.
Speaker 3: Absolutely, and this is where the theorists come back in. Initially,
Speaker 3: they had done all their math for these collapse models
Speaker 3: using germanium atoms because older detectors use solid germanium.
Speaker 2: But xenon T is liquid xenon. That's a totally different
Speaker 2: atomic structure exactly.
Speaker 3: So theoretical physicists had to completely recalibrate their math for xenon,
Speaker 3: and the breakthrough they had was stunning. They calculated that
Speaker 3: a quantum collapse in xenon wouldn't just produce a flat,
Speaker 3: smooth energy.
Speaker 2: Signal because of the atomic effects.
Speaker 3: Right, Yes, the specific arrangement of electron shells and xenon
Speaker 3: means the signal would have very distinct bumps at specific
Speaker 3: low energies.
Speaker 2: Here's where it it's really interesting. Instead of looking for
Speaker 2: a needle in a massive haystack, the theoretical physicists basically
Speaker 2: painted the exact needle they were looking for neon pink like.
Speaker 2: Having those predictable bumps makes the statistical analysis so much
Speaker 2: more powerful, and.
Speaker 3: This raises an important question about how science actually gets done.
Speaker 3: Neither side could make this sleep alone. The theorists provided
Speaker 3: the exact neon pink map, and the experimentalists provided the
Speaker 3: ultra quiet hardware to actually find it.
Speaker 2: But getting that ultra quiet hardware is a nightmare. They
Speaker 2: are a kilometer underground, but they still have to deal
Speaker 2: with trace radioactivity, specifically rate on gas. Right.
Speaker 3: Radon is the eternal enemy of underground physics. It seeps
Speaker 3: out of the rock, decays into an isotope called lead
Speaker 3: two fourteen, and causes background noise inside the detector.
Speaker 2: So how did they fix that?
Speaker 3: Through a technique called fiducialization. They didn't analyze the whole
Speaker 3: five point nine ton tank. They only looked at the
Speaker 3: innermost four point three seven ton subvolume.
Speaker 2: Oh, they used the outer layers of the liquid xenon
Speaker 2: as a radiation shield for the center. That is so smart. Okay,
Speaker 2: So the trap is set, the background noise is handled,
Speaker 2: the neon pink signal is defined. What happened in the
Speaker 2: twenty twenty one science campaign.
Speaker 3: They analyzed data from July sixth to November tenth, and
Speaker 3: the result was definitive. They didn't find the predicted X ray.
Speaker 2: Burs nothing at all.
Speaker 3: Nothing.
Speaker 2: So what does so all mean? I mean they spent
Speaker 2: months looking, built this massive subterranean trap, mapped out the
Speaker 2: exact signal, and found absolutely nothing. How is that not
Speaker 2: a massive failure.
Speaker 3: Because in experimental physics, finding nothing is extremely powerful. By
Speaker 3: not finding the signal, they proved it doesn't exist within
Speaker 3: those specific energy ranges. They constrained the continuous spontaneous localization
Speaker 3: model to be more than one hundred times more sensitive
Speaker 3: than previous leading experiments.
Speaker 2: Oh so they didn't kill the theories, but they shrank
Speaker 2: the wiggle room.
Speaker 3: Drastically shrank it. They forced the models into a much
Speaker 3: tighter mathematical corner.
Speaker 2: But wait, if they just ran the machine longer, wouldn't
Speaker 2: they eventually hear the pops. Why stop there?
Speaker 3: Because they hit an unbeatable wall of background noise, the
Speaker 3: ultimate background noise. Solar neutrinos own the neutrino fog. Right
Speaker 3: our sun is constantly blasting out these ghostly particles. Right
Speaker 3: now as we speak, roughly seventy billion solar neutrinos are
Speaker 3: passing through an area the size of your thumbnail every
Speaker 3: single second.
Speaker 2: Seventy billion through a thumbnail every second. That is terrifying.
Speaker 3: And they pass right through the rock, through the lead shielding,
Speaker 3: straight into the xenon. Mostly they leave no trace, but
Speaker 3: with a detector this sensitive, eventually a neutrino strikes a
Speaker 3: xenon atom perfectly and it creates a flash that perfectly
Speaker 3: mimics the exact X ray signal we are looking for.
Speaker 2: Wow, so you can't shield against it. It's an irreducible
Speaker 2: background noise, the neutrino fog. So how does science move forward?
Speaker 2: Are we just stuck?
Speaker 3: Not at all? The future is an upcoming detector called XLZD.
Speaker 3: It's a mega collaboration merging the xinon LZ and Darwin teams.
Speaker 3: They are going to pack five to ten times the
Speaker 3: massive current detectors into.
Speaker 2: One machine to push deep into the fog.
Speaker 3: Exactly, if you have a mass of enough volume you
Speaker 3: can precisely characterize the solar neutrino signature, model it and
Speaker 3: then mathematically subtract it from your data.
Speaker 2: That is brilliant. And this brings us back to the
Speaker 2: Doc Penrose model and gravity because if they actually push
Speaker 2: through the fog and find this collect as, it changes
Speaker 2: how we view reality.
Speaker 3: Right fundamentally, the Dooce Penrose model suggests that space time
Speaker 3: might not be perfectly smooth. It implies a fundamental microscopic fuzziness,
Speaker 3: an intrinsic limitation in the structure of reality.
Speaker 2: Like space time is pixelated, yes.
Speaker 3: Which is an idea of discreteness that dates all the
Speaker 3: way back to the ancient Greek philosopher Democritus. He thought
Speaker 3: everything was eventually made of discrete parts. If space time
Speaker 3: is fundamentally pixelated, that fuzzy, uncertain texture might be exactly
Speaker 3: what forces a quantum superposition to collapse. Spacetime just can't
Speaker 3: handle the contradiction across its rigid pixels.
Speaker 2: It's amazing to think that building massive vats of liquid
Speaker 2: xenon underground is ultimately about gravitizing quantum mechanics, proving that
Speaker 2: space and time are pixelated.
Speaker 3: And if we connect this to the bigger picture, it
Speaker 3: goes so far beyond quantum mechanics. It is our absolute
Speaker 3: best pathway toward testing a unified theory of quantum gravity,
Speaker 3: reconciling Newton's gravity with the quantum realm once and for all.
Speaker 2: We have covered so much ground today, from the absolute
Speaker 2: absurdity of a coffee mug being in two places at once,
Speaker 2: down into a subterranean Italian vault filled with liquid xenon,
Speaker 2: to hunting the neutrino fog, and finally arriving at the
Speaker 2: pixelated fabric of space time itself.
Speaker 3: It is a phenomenal time to be watching this field.
Speaker 2: It really is. So next time you look at a
Speaker 2: solid object, whether it's your coffee mug or the wall
Speaker 2: next to you, consider this. Its stable, singular existence right
Speaker 2: there in front of you might just be the result
Speaker 2: of a microscopic, fuzzy texture of space time quietly measuring it.
Speaker 2: It might be emitting an invisible chorus of tiny X
Speaker 2: rays as it constantly forces itself into reality, and humanity
Speaker 2: is finally on the absolute verge of being able to
Speaker 2: hear it,