Time Is Just F(r)iction

For decades, one of physics' strangest open questions has been whether time is fundamental at all — or whether it only emerges once you stop looking at the whole universe and start looking at how its parts talk to each other. 

In this episode of Heliox, we dig into a real 2026 paper out of the University of Birmingham, where physicist Giovanni Barontini built a working miniature universe from 24,000 ultracold rubidium atoms, split it in two with a wall of light, and used the flow of entropy across that wall to build a working clock — one that kept perfect time even when the lab's own stopwatch couldn't.

We walk through the Wheeler-DeWitt equation, why time vanishes from it, the "movie reel in a sealed tin" analogy for a static universe, and how this experiment translated 60-year-old theoretical debates into something you can photograph in a lab. And we end somewhere unexpectedly tender: on what it might mean, for you personally, if time really is just the record of things exchanging information with each other.

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References

Testing the problem of time with cold atoms

This is Heliox: Where Evidence Meets Empathy

Independent, moderated, timely, deep, gentle, clinical, global, and community conversations about things that matter.  Breathe Easy, we go deep and lightly surface the big ideas.

Transcript

Speaker 1: 0:25

This is Heliox, where evidence meets empathy. Independent, moderated, timely, deep, gentle, clinical, global, and community conversations about things that matter. Breathe easy. We go deep and lightly surface the big ideas. I want you to take a second and just pay attention to your immediate surroundings right now. Like maybe you can hear the hum of your refrigerator in the background or a clock ticking on the wall. Or, you know, maybe you can just feel your own pulse beating in your chest.

Speaker 2: 1:02

Yeah, just that steady rhythm.

Speaker 1: 1:04

Right. Think about the calendar sitting on your desk or the schedule app on your phone blocking out your entire day in these neat little 30-minute increments. We all have this deeply ingrained, I mean, completely undeniable feeling of time flowing. It moves from the past, which we remember but obviously can't change, through this infinitesimally tiny window we call the present. And it just flows steadily into the future, which is, you know, unwritten. It feels like the absolute most fundamental rule of reality. Like if there is one single thing you can trust, it is that time passes.

Speaker 2: 1:40

Oh, for sure. I mean, it is the backdrop against which our entire lives, our biology, our evolution, and frankly, our entire understanding of classical physics plays out. We experience time as this unstoppable forward marching river. You know, it carries us along whether we actually want it to or not.

Speaker 1: 1:59

So prepare yourself because we are going to spend this deep dive completely dismantling that intuition.

Speaker 2: 2:05

We really are.

Speaker 1: 2:06

We are going to look at some of the most advanced fundamental equations in theoretical physics specifically, something called the Wheeler-DeWitt equation. This is the math that physicists use when they try to describe the entire universe at a quantum level. And when you look at that math, time just drops out completely.

Speaker 2: 2:22

It really does.

Speaker 1: 2:22

It simply does not exist.

Speaker 2: 2:24

It remains one of the most profound, unsettling, and honestly, fiercely debated discoveries in the history of theoretical physics. I mean, when you attempt the ultimate goal of modern physics, which is merging the quantum mechanics of the very small with the general relativity of the very large, to describe the cosmos as a single, unified whole, the variable for time literally vanishes from the fundamental equation of the universe.

Speaker 1: 2:52

Which sounds completely absurd to anyone who's ever been like five minutes late for a meeting. Right, exactly. How can time not exist when my boss is clearly angry that I'm tardy? I mean, what does it actually mean for time to be an illusion and how could we possibly prove that?

Speaker 2: 3:06

Well, that's what we're going to get into.

Speaker 1: 3:07

Right. That is our mission today. We have our hands on a truly groundbreaking physics paper. It's titled Testing the Problem of Time with Cold Atoms. And we are going to explore how a team of scientists didn't just, you know, write more equations on a chalkboard, but literally built a miniature isolated universe in a laboratory to solve this exact problem.

Speaker 2: 3:28

Yeah, they engineered a physical experiment to demonstrate that time, as we intimately know it, might just be an emergent property, like an illusion created by the messy statistical flow of entropy. And they proved this by manipulating a microscopic universe of supercooled atoms.

Speaker 1: 3:45

We are going on a massive journey today. Like we are going to start in the absolute most abstract realms of quantum cosmology, talking about the state of the entire universe. And then we are going to zoom all the way down to a tangible laboratory bench where scientists are physically pausing and restarting the passage of time.

Speaker 2: 4:05

It's wild.

Speaker 1: 4:05

It really is. So to really grasp the magnitude of this experiment, I think we need to start with the core dilemma. Like why did time go missing from physics in the first place?

Speaker 2: 4:14

Yeah. So to understand the missing time, we have to look at how physics has historically treated the concept, right? If we go back to Isaac Newton in the 17th century, time is this absolute external parameter. Newton basically viewed time as a universal metronome sitting completely outside the universe, just ticking away at a constant unyielding rate.

Speaker 1: 4:32

Unaffected by anything.

Speaker 2: 4:34

Exactly. It was completely independent of whatever the planets or stars or people were actually doing.

Speaker 1: 4:39

Sort of like a stage for the universe. Like the universe is the play happening on the stage, but the stage itself doesn't care what the actors are doing.

Speaker 2: 4:46

That's a great way to put it.

Speaker 1: 4:47

And even when Einstein came along and complicated things by showing that time gets flexible like that, it bends and warps with gravity and speed. It's still fundamentally part of the stage, right? It's woven into space time.

Speaker 2: 4:59

That is the crucial distinction. Yeah. For Einstein, space time is a dynamic fabric. But time is still a fundamental geometric dimension of reality. However, the Wheeler-DeWitt framework of quantum cosmology forces this radical, almost terrifying shift in perspective. It was formulated in the 1960s by physicists John Wheeler and Bryce DeWitt. And this equation attempts to describe the quantum state of the entire closed universe. And here is the logical trap that caught them. If you are mathematically describing the total state of the entire universe, by definition, there is no outside.

Speaker 1: 5:36

Right, because if there were an outside, you'd have to include that in your equation of the universe, too. I mean, the universe is, by definition, everything there is.

Speaker 2: 5:44

Precisely. Therefore, there is no room for a metronome sitting on the nightstand. There is no external clock to measure the universe against. Because in standard quantum mechanics, equations describe how a system changes over time, usually measured by an observer sitting outside the system in a laboratory. But in quantum cosmology, the observer is inside the system. Furthermore, in this framework, the total overall state of the universe is considered pure.

Speaker 1: 6:13

Hold on, let's define that. When you say the universe is in a pure state, what does that actually mean? Because I usually associate pure with, like, filtered water or something.

Speaker 2: 6:21

Right, right. In quantum mechanics, a pure state means you have maximal possible knowledge about the system. There is no fundamental uncertainty in the total overarching system itself, and its fine-grained entropy is perfectly conserved. It just doesn't change.

Speaker 1: 6:35

Okay, I'm going to need you to unpack fine-grained entropy because I know entropy is the general tendency for things to get messy, like a shattered glass on the floor or a messy bedroom. What is the fine-grained part?

Speaker 2: 6:47

Sure. Think of fine-grained entropy as the exact microscopic accounting of every single piece of quantum information in a system.

Speaker 1: 6:55

Every single piece?

Speaker 2: 6:56

Every single one. If you know the precise state of every particle, where it is, how it's moving, and how it's entangled with everything else, that information is never lost in fundamental physics. It just gets scrambled. And because that total information is conserved in a closed universe, the fine-grained entropy of the whole universe remains completely static. Oh. So we arrive at the Wheeler-DeWitt paradox if there's no external clock, and the overall quantum state of reality is completely static and unchanging, Well, where does our vivid, undeniable experience of the flow of time actually come from?

Speaker 1: 7:29

So I was wrestling with this concept, trying to visualize a totally static universe, and I came up with an analogy. Tell me if this works.

Speaker 2: 7:36

Let's hear it.

Speaker 1: 7:36

Think of the Wheeler-DeWitt universe like a feature-length movie reel sitting inside a sealed metal tin. Every single frame of that movie, the opening credits, the climax, the ending, it all exists simultaneously inside that dark box.

Speaker 2: 7:50

Yes. The entire timeline is just a single static object.

Speaker 1: 7:55

Yeah.

Speaker 2: 7:55

Past, present and future are all just physical locations on that strip of celluloid.

Speaker 1: 7:59

But for the movie to actually play for an audience, like for there to be a flow of events from one scene to the next, you need a projector. The projector pulls the frames out one by one, shines a light through them and creates the illusion of passing time. The projector is the external time parameter. Right. But the Wheeler-Dewitt equation is telling us there is no projector. There is no audience outside the box. There is only the tin box itself. So without a projector, how does the movie actually play for us, the characters trapped inside the film? How do we experience a present moment?

Speaker 2: 8:30

That analogy captures the dilemma perfectly. To find the internal projector that's powering our experience of time, physicists had to scour the laws of nature for the one and only thing in fundamental physics that actually has a built-in direction. Okay. Because here's the secret about the laws of physics. Newtonian mechanics, general relativity, standard quantum mechanics, their equations work just as well backwards as they do forwards. They have no inherent temporal orientation.

Speaker 1: 8:59

You mean like you could run the math in reverse, sort of like watching a video of two billiard balls bouncing off each other backwards and the laws of physics wouldn't be violated. It would look perfectly natural.

Speaker 2: 9:08

Exactly. The only robust asymmetry in fundamental physics, the only physical law that actually mans a before and after, is the second law of thermodynamics.

Speaker 1: 9:17

This is where we get into entropy.

Speaker 2: 9:18

Yes. The arrow of time always points toward larger, coarse-grained entropy. Things go from ordered to disordered. An egg shatters. It doesn't spontaneously unshatter and jump back up onto the counter. Heat flows from your hot cup of coffee into the cold room. The room doesn't spontaneously suck heat out of the air to boil your coffee.

Speaker 1: 9:40

But wait, you just told me a few minutes ago that in the Wheeler-DeWitt universe, the total fine-grained entropy is conserved. Like, it's perfectly static. So how can entropy be increasing if it's supposed to be static?

Speaker 2: 9:52

You're hitting on the core problem. The difference lies between the fine-grained entropy, we discussed the exact microscopic information of the whole universe, which is static and coarse-grained entropy, which is what we actually experience.

Speaker 1: 10:06

Okay, what's coarse-grained entropy?

Speaker 2: 10:08

Coarse-grained entropy is our blurry macroscopic perspective. It ignores the microscopic details and just looks at the overall messiness of a subsystem.

Speaker 1: 10:17

So even if the whole universe is technically a perfectly conserved block of information, the pieces inside it can get messy relative to each other.

Speaker 2: 10:24

Exactly. And this introduces a crucial cosmological concept mentioned in our sources called the past hypothesis.

Speaker 1: 10:31

The past hypothesis.

Speaker 2: 10:33

Yes. This is the idea that our universe, at the moment of the Big Bang, began in an exceptionally, almost unfathomably low entropy macrostate.

Speaker 1: 10:43

Like a perfectly ordered, pristine deck of cards freshly opened from the factory where all the suits and numbers are perfectly aligned.

Speaker 2: 10:50

Yes, a highly concentrated, incredibly ordered state. And because it started so highly ordered, it has the capacity to shuffle. It allows for coarse-grained entropy to grow over billions of years. Even if the fundamental total quantum state of the whole universe is pure and static, the macroscopic subsystems within it, the galaxies, the stars, your coffee cup, can interact, get entangled, share information. and become disordered relative to one another.

Speaker 1: 11:15

That is fascinating. And our sources actually reference a paper from way back in 1929 by a physicist named Neville Mott that acts as a prototype for this idea. He was looking at cloud chambers.

Speaker 2: 11:24

An absolute classic experiment. And a really perfect illustration of how time and history emerge from a static quantum state.

Speaker 1: 11:31

Let me set this up because I found it super interesting. A cloud chamber is basically a glass box filled with super saturated alcohol vapor. It's right on the edge of condensing into liquid. When a radioactive particle, like an alpha particle, flies through it, it ionizes the vapor and leaves a visible track of little condensation droplets, kind of like a miniature contrail from an airplane. Mott was trying to solve a paradox. A quantum particle exists as a spread out fuzzy wave of probabilities. It doesn't actually have a specific location until it's measured. So how does a fuzzy wave of probability leave a single, classical, straight-line track of droplets that we can plainly see?

Speaker 2: 12:13

Yeah, and what Mott realized is that the classical record, the straight track you see with your physical eyes, arises because the quantum particle becomes heavily entangled with the many atoms of vapor in the chamber.

Speaker 1: 12:23

So they interact.

Speaker 2: 12:24

Exactly. The global quantum state of the whole room, the alpha particle plus all the vapor, is still mathematically pure and spread out. But if you only look at the macroscopic droplets, which is the coarse-grained perspective, they have formed a permanent record. The entropy of that specific subsystem has drastically increased.

Speaker 1: 12:43

The interaction, the relationship between the particle and the vapor, creates a history. It writes a timeline of events into the droplets, even if the overriding quantum math says everything is just a static wave.

Speaker 2: 12:55

Precisely.

Speaker 1: 12:55

Which leads us perfectly into how modern physicists try to fix the Wheeler-DeWitt problem. If the whole universe is a static tin box of film, how do we find time?

Speaker 2: 13:05

By taking a scalpel to reality and cutting the universe into pieces. A scalpel. Well, mathematically speaking. In theoretical physics, they use a strategy called mini-superspace models. You partition the universe. You basically divide it into subsystems. Once you do that, one part of the universe can act as an entropy sink or an entropy source for the other part.

Speaker 1: 13:24

Wait, so you're telling me that to find time, we have to deliberately stop looking at the whole picture? We have to put blinders on, completely ignore the rest of the universe, and just look at the relationship between two separate pieces. Are you saying time is literally just a relationship?

Speaker 2: 13:39

That is the logical leap at the heart of this entire field of physics. In these models, time is not a fundamental property of reality. It is emergent. It is purely relational. If you take one dynamic variable in your subsystem and promote it to be your clock, you can express all the other variables in relation to it.

Speaker 1: 13:57

Oh, wow.

Speaker 2: 13:58

The flow of entropy, the transfer of heat or information between the pieces, that becomes the tick of the clock.

Speaker 1: 14:04

That is incredibly counterintuitive. I mean, time isn't a thing itself. It's the friction of the universe interacting with its own parts.

Speaker 2: 14:11

It is a beautiful concept on paper. But for decades, this was purely theoretical math. I mean, the Wheeler-Dewitt equation describes the whole cosmos. We obviously cannot step outside our actual universe, slice it in half with some galactic scalpel, and rewind it to see what happens.

Speaker 1: 14:27

Which brings us to the absolute genius of the paper we're diving into today. If you can't rewind the actual universe, you just build a tiny one of your own. Precisely.

Speaker 2: 14:36

We are moving from the philosophical chalkboard of theoretical cosmology to the literal workbench of a laboratory.

Speaker 1: 14:43

Let's set the scene for this experiment because it's just a marvel of modern engineering. The scientists in this paper decided to create a physical analog for this quantum cosmology problem. To do that, they use something called a Bose-Einstein condensate.

Speaker 2: 14:57

Yeah, made of approximately 24,000 atoms of an isotope called rubidium-87.

Speaker 1: 15:02

24,000 atoms. That is our entire mini-universe for this deep dive. Now, a Bose-Einstein condensate, or a BEC, is a very specific, bizarre state of matter. It's what happens when you cool a cloud of atoms down to just a tiny fraction of a degree above absolute zero.

Speaker 2: 15:19

And to understand why they used a BEC, you really have to understand how weird atoms get at that temperature.

Speaker 1: 15:23

They get weird.

Speaker 2: 15:24

Very weird. Normally, in a gas at wrong temperature, atoms are zipping around like angry bees, bouncing off each other. They have a lot of thermal energy, which means a lot of classical noise. But when you use advanced laser cooling techniques to strip almost all that kinetic energy away, dropping them to billions of a degree above absolute zero, their quantum nature takes over completely.

Speaker 1: 15:46

Right. I read that their quantum wavelengths actually start to stretch out as they get colder.

Speaker 2: 15:51

They do. In quantum mechanics, particles act like waves. As they lose momentum, those waves get longer and longer until the quantum waves of all 24,000 rubidium atoms physically overlap and merge. They literally lose their individual identities. They begin to act like one single macroscopic super atom, all occupying the exact same quantum state.

Speaker 1: 16:13

That's wild.

Speaker 2: 16:13

It is a state of matter that is incredibly pristine, completely devoid of classical thermal noise.

Speaker 1: 16:18

So it's the perfect blank slate, a pure unified quantum system just like the Wheeler-DeWitt universe is supposed to be. But obviously, you can't just leave a super chilled cloud of quantum rubidium sitting on a lab bench. It would instantly heat up and vanish. You have to contain it. So they trapped this mini-universe in an optical dipole trap.

Speaker 2: 16:38

This is where we get into the how of the experiment. An optical dipole trap is essentially a cage made of pure light. They take two extremely powerful focused laser beams. One operates at a wavelength of 1070 nanometers, the other at 1550 nanometers. They cross these two beams, and where they intersect, they create what physicists call a radially symmetric potential well.

Speaker 1: 16:59

Okay. Radially symmetric potential well. Sounds very technical. What is the light actually doing to the atoms, and why those specific numbers, half 170 and 1550 nanometers?

Speaker 2: 17:09

It comes down to how light interacts with the electrons orbiting the rubidium atoms. Rubidium atoms like to absorb light at a very specific wavelength, around 780 nanometers. If you hit them with 780 nanometer light, they absorb it, get excited, and scatter it. This creates heat. You definitely don't want that. So you use lasers that are red detuned, meaning their wavelengths, 1070 and 1550 nanometers, are longer or redder than what the atom naturally wants to absorb.

Speaker 1: 17:36

The atoms just ignore the light.

Speaker 2: 17:38

Not quite. They don't absorb the light, but the intense oscillating electric field of the laser beam still pulls on the atom's electron cloud. It induces a dipole moment, basically turning the atom into a tiny electromagnet that gets attracted to the brightest part of the laser beam.

Speaker 1: 17:52

Oh, I see.

Speaker 2: 17:53

So where those two lasers cross and the light is most intense, it acts like a gravitational valley. A bowl of light that holds the 24,000 atoms perfectly suspended in a vacuum.

Speaker 1: 18:03

I want you to picture this. A microscopic, invisible bowl of laser light suspended in a vacuum chamber holding a super chilled glowing droplet of quantum reality. It's beautiful. but a bowl is just a whole universe. It's a single tin box. To test the Wheeler-DeWitt problem, remember, we have to cut the universe into pieces. We need those mini super space models.

Speaker 2: 18:23

And this is where the experimental design gets truly brilliant. Let there be light and let there be dark. They took another laser, this one operating at 675 nanometers, and they used it

Speaker 1: 18:33

to project a microscopic wall right down the middle of the bowl. A potential barrier. Let's atom wants to absorb. It's blue detuned. You're catching on perfectly. Thanks. Because it is blue

Speaker 2: 18:50

detuned, the physics works in reverse. Instead of being attracted to the brightest part of the light, the atoms are repelled by it. This laser acts as a literal wall pushing the rubidium atoms away. And when we say microscopic, we mean it. This barrier is incredibly thin. It's only eight micrometers wide. That's about a tenth of the width of a human hair. But for a super cooled

Speaker 1: 19:11

cloud of atoms, it is a massive defining partition. This simple line of light splits their tiny bowl into two distinct sectors. The researchers arbitrarily detonate one side as the dark sector. This means it is unobserved. We put our blinders on and we don't mathematically track what happens there. The other side is the bright sector, the part of the mini universe that is being observed,

Speaker 2: 19:34

measured, and tracked. It perfectly mimics the theoretical mini superspace models we discussed earlier. You have a whole universe that is perfectly isolated from the outside laboratory, but internally it is partitioned into two distinct subsystems. You have a system and you have an

Speaker 1: 19:50

environment for it to interact with. And the isolation from the actual laboratory room is key,

Speaker 2: 19:55

right? Absolutely vital. The researchers note in the paper that on the timescale of the experiment, there is no measurable dissipation, no heat leaking in, and no particle loss to the outside world. None. It is a closed, unitary system with a time-independent Hamiltonian.

Speaker 1: 20:10

A time-independent Hamiltonian, meaning the total energy of the 24,000 atoms isn't changing over time. It's completely self-contained.

Speaker 2: 20:18

Exactly. It is the perfect, rigorous, physical analog for the isolated, static, Wheeler-DeWitt universe.

Speaker 1: 20:25

Okay, so the stage is set. We have the bowl of light, we have the dark sector, the bright sector, and the repulsive laser barrier between them. Now, it's time to start the clock. What actually happens when they run this experiment?

Speaker 2: 20:37

The whole dynamic action of this experiment takes place over a mere 120 milliseconds.

Speaker 1: 20:42

Wow, that's fast.

Speaker 2: 20:43

Just over a tenth of a second in our normal everyday laboratory time. They manipulate the shape of the trap slightly so that the atomic cloud starts to oscillate. It basically sloshes back and forth inside the bowl.

Speaker 1: 20:56

And when that cloud of atoms hits the light barrier and crosses over from the unobserved dark sector into the observed bright sector, The researchers call that the Big Bang for that sector.

Speaker 2: 21:06

Yeah, it is the moment the observed universe springs into existence. The atomic cloud enters the bright sector and it expands. It grows to its maximum physical extension. This is our universe expanding after the Big Bang. But because it's oscillating in this goal-shaped trap, the optical potential of the lasers pulls it back toward the center.

Speaker 1: 21:24

It contracts. The atoms rush back toward the barrier. And when the bright sector completely empties out, retreating entirely back into the dark sector, that's it, the big crunch.

Speaker 2: 21:33

The mini universe is born, it expands, it collapses, and it dies, all in a fraction of a heartbeat. And then, because it's still oscillating back and forth in the bowl, it crosses the barrier again. Another big bang, another big crunch. It cycles over and over, pulsing in and out of the bright sector.

Speaker 1: 21:50

So if you are a scientist standing in the lab holding a highly accurate stopwatch, you can just time this. You can say, okay, the first big crunch happened at 40 milliseconds, the next big bang happened at 55 milliseconds.

Speaker 2: 22:02

You certainly can. But remember the mission. The entire point of solving the Wheeler-DeWitt problem is that in the ultimate reality of the real cosmos, you do not have a stopwatch. There is no external lab. There is no scientist in a white coat looking down at the universe.

Speaker 1: 22:18

Right, right. We have to forget our stopwatch. We have to figure out how time works for the atoms inside the bright sector using only what is available inside the bright sector. We have to find an internal clock built out of the universe itself.

Speaker 2: 22:30

And this leads us to a fascinating theoretical hurdle that physicists call the non-monotonic clock problem.

Speaker 1: 22:36

I loved this part because my first thought reading the setup was, well, why not just use the size of the atomic cloud as the clock? Like if the mini universe is expanding, you just use a ruler. You say, OK, a bigger universe means more time has passed.

Speaker 2: 22:51

It seems like a perfectly logical solution.

Speaker 1: 22:53

Yeah.

Speaker 2: 22:54

In classical cosmology, the scale factor of the universe, basically how big it is, is frequently used as a stand-in for time in mathematical models.

Speaker 1: 23:03

But if you use the size of the cloud in this specific mini-universe as a clock, you run into a massive, hilarious problem. The bright sector expands, so your size clock ticks forward, but then it reaches its peak expansion in gravity, or the laser potential pulls it back. It starts to shrink back toward the big crunch.

Speaker 2: 23:22

Right. And if physical size is your clock, then as the universe shrinks, time would literally be ticking backwards.

Speaker 1: 23:28

It would be like having a wall clock in your kitchen that tells you it's 5 p.m., but it could actually be 9 a.m. on the return trip. It's completely ambiguous. You can't sequence events with a clock that goes up and then comes back down. You wouldn't know if an event happened during the expansion phase or the contraction phase. The paper notes that in re-collapsing models, the clock field is non-monotonic. It goes up and then it goes down. It doesn't have a single unified arrow spanning from the Big Bang to the Big Crunch.

Speaker 2: 23:54

Which means we cannot use the simple physical dimensions of the universe as our clock. We need something that only goes in one direction. We need an arrow of time that continually pushes forward, regardless of whether the physical space is getting bigger or smaller.

Speaker 1: 24:08

Enter the brilliant solution from the researchers, entropic time.

Speaker 2: 24:12

Yes, they realized they had to invent a completely new mathematical variable for this universe. They denoted it with the Greek letter tau, representing entropic time. Instead of looking at a physical ruler or the size of the atomic cloud, they looked at the thermodynamics of the bright sector.

Speaker 1: 24:29

They tracked the entropy, but how do you actually calculate the entropy of a cloud of atoms crossing a laser beam?

Speaker 2: 24:35

They went back to foundational thermodynamics. They defined this new time variable mathematically using Boltzmann's constant, which relates the average kinetic energy of particles in a gas with the temperature of the gas, and they multiplied it by the entropy per atom. Now here is the crucial conceptual leap. Remember that the total system, the whole 24,000 atoms in both the dark and bright sectors combined, is perfectly isolated in that vacuum chamber. Its total entropy is fundamentally constant.

Speaker 1: 25:04

The tin box of the movie reel is sealed. The total information is conserved.

Speaker 2: 25:08

Exactly. So if the total entropy of the whole bowl is constant, The only way the entropy in the bright sector can change is if atoms, and therefore the entropy they carry with them, physically flow across that 8 micrometer light barrier.

Speaker 1: 25:21

So it's less like a clock on the wall and more like an hourglass. But instead of sand falling steadily with gravity, the sand is entropy carried by the atoms moving from the unobserved dark sector to the observed bright sector.

Speaker 2: 25:33

That is a phenomenal analogy. Every time an atom crosses that 675 nanometer light barrier, a grain of sand falls through the neck of the hourglass. The clock of this mini-universe ticks forward. Time is literally defined by the exchange of information and entropy between the unobserved environment and the observed system.

Speaker 1: 25:53

That makes so much sense.

Speaker 2: 25:55

Yeah, when entropy transfers into or out of the bright sector, this internal entropic time flows.

Speaker 1: 26:00

And if no atoms are crossing the barrier, if the sand just stops falling.

Speaker 2: 26:05

then time, from the perspective of the bright sector, completely pauses, even if the external lab stopwatch held by the scientists is still taking away the milliseconds.

Speaker 1: 26:14

That is deeply mind-bending. I mean, time isn't a constant speed. It isn't a relentless river. Time flows faster when entropy transfers quickly, and it stops when the transfer stops. It's a completely relational construct. It only exists when pieces of the universe are talking to each other.

Speaker 2: 26:29

It is a radical departure from how we normally experience reality, but it's exactly what the quantum cosmology theories demand. But of course, theoretical math is one thing. Building an hourglass out of atoms on a chalkboard is easy. The real question is, does this actually work in the physical lab? Can you use this invented entropic time to successfully sequence reality without breaking the laws of physics?

Speaker 1: 26:53

So the researchers put it to the test. They ran their 120 millisecond experiment and they used a technique called absorption imaging to take a picture of the atomic cloud every two milliseconds, basically shining a light on the atoms and seeing how much of a shadow they cast to count them. They essentially took 60 snapshots of this miniature universe being born, expanding, contracting and collapsing.

Speaker 2: 27:15

Right. And initially they plotted this data against the external lab time, the stopwatch time. And you see exactly what you'd expect to see a series of oscillations. Big bang, big crunch, big bang, big crunch, like a pendulum swinging back and forth.

Speaker 1: 27:26

But then they threw out the lab time. They took all those physical snapshots and they reordered them mathematically based solely on their newly calculated entropic time, tau. They basically asked the atoms what time it was instead of asking the lab clock.

Speaker 2: 27:42

And when they plotted the data against entropic time, the results were just stunning. The data ordered perfectly. The non-monotonic clock problem completely vanished.

Speaker 1: 27:52

The kitchen clock didn't say 5 p.m. when it was actually 9 a.m.

Speaker 2: 27:56

Exactly. The arrow of time did not flip backwards during the big crunch.

Speaker 1: 27:59

Entropic time marched steadily, relentlessly forward, providing a robust one-way arrow to sequence the events of the mini-universe. It didn't matter if the physical space of the universe was expanding or collapsing. As long as entropy was being exchanged across the barrier, time moved forward.

Speaker 2: 28:16

It was a triumphant validation of the relational time hypothesis. The math worked. But what I found most fascinating diving into the deep cuts of the paper's data were the variations.

Speaker 1: 28:25

Oh, the wiggles.

Speaker 2: 28:26

Yes, the wiggles in the data, as the researchers call them, which revealed the profound weirdness of this thermodynamic clock.

Speaker 1: 28:33

Yes, let's talk about the Wiggles, because they reveal so much about how you can manipulate time once you realize what it's made of. The researchers realized they could actually control how hard it was for atoms to cross the barrier by changing the intensity of the blue detuned laser. They could literally change the height of the wall separating the two sectors.

Speaker 2: 28:53

When they kept the laser intensity low, the barrier was shallow. The atoms sloshed back and forth easily. The mini-universe rapidly cycled through its big bangs and big crunches. But during the big crunch, that specific moment when the bright sector was completely empty of atoms, having retreated entirely into the dark side, an incredible thing happened to the mathematics of the clock.

Speaker 1: 29:15

Because the bright sector was completely empty, no atoms were crossing the barrier. There was no sand left in the top of the hourglass to fall. No entropy was being exchanged.

Speaker 2: 29:24

And because we have just established that time is the exchange of entropy, And tropic time literally paused. Between the big crunch and the subsequent big bang, time just ceased to exist for that sector. Then, when the oscillations swung back and the next big bang started, time picked up exactly where it left off.

Speaker 1: 29:42

It's exactly like pressing pause on a video game. Like, the characters inside the game don't know they've been paused. To them, the timeline is perfectly continuous, perfectly seamless. Even if the player went and made a sandwich for 10 minutes, they don't experience the gap.

Speaker 2: 29:55

That is a very apt analogy. The lab time in the real world kept going, but the internal time of the isolated universe paused. But then the researchers decided to push the system to its absolute limits. They cranked up the barrier laser intensity to its maximum setting, a state they denoted mathematically as V1.

Speaker 1: 30:15

They built a massive, impenetrable wall of light between the dark and bright sectors.

Speaker 2: 30:19

And when they did that, the kinetic exchange of atoms and therefore the exchange of entropy was heavily restricted. the bright sector stopped its wild, bouncing cycling. It couldn't easily slosh back and forth anymore. Instead, the atoms that were trapped in the bright sector just settled down. The system evolved into a stable, stationary state.

Speaker 1: 30:39

And in the study of thermodynamics, a stationary state where everything is uniform and no more entropy can be meaningfully exchanged has a very specific, ominous name.

Speaker 2: 30:48

Heat death.

Speaker 1: 30:49

The mini-universe reached its heat death. It reached maximum entropy for its specific configuration. And what happened to our newly invented entropic time when the universe hit heat death?

Speaker 2: 30:59

It flatlined completely. Because there was no more meaningful flow of entropy across the barrier, the internal clock of that universe ceased to tick forever. The external laboratory time on the scientist's stopwatch marched on indefinitely, but within the confines of the bright sector, time was dead.

Speaker 1: 31:14

Just let the weight of that sink in. They didn't just theorize about it. They physically proved in a lab that time requires thermodynamic openness. It requires a relationship, a constant shuffling of the deck between different parts of a system. When the shuffling stops, when the heat death arrives, time doesn't just lose its meaning. It physically stops existing.

Speaker 2: 31:37

It's a staggering experimental achievement. And incredibly, they didn't stop with just graphing the data. The researchers went a step further and achieved a massive mathematical triumph to back up the physical data. They wanted to see if they could literally rewrite the fundamental laws of quantum mechanics to run natively on this new entropic clock.

Speaker 1: 31:57

Right, because normally the Schrodinger equation, which is like the Holy Grail equation that dictates how all quantum waves evolve and change, is powered by that external Newtonian metronome. It literally uses the letter T in the math to represent external time.

Speaker 2: 32:09

Exactly. So they started with their completely time-independent Hamiltonian, the static tin box of reality where total energy doesn't change. To get time out of it, they used a highly complex mathematical technique called a Fischbach-Villers decomposition.

Speaker 1: 32:24

Okay, I have to stop you there. I hear decomposition, and I instantly think of rotting fruit or a compost pile. We cannot just name drop a Fischbach-Villers decomposition without explaining it. What are they actually breaking down or rotting in this math?

Speaker 2: 32:38

Fair point. Fair point. Let's untangle that. It has absolutely nothing to do with rotting. Think of the static mathematical state of the universe as a tightly braided rope. The rope contains all possibilities, but it's a mess to deal with, especially because equations dealing with relativity and quantum mechanics, like the Klein-Gordon equation, often spit out mathematical anomalies, like negative probabilities, which make absolutely no physical sense. You can't have a negative 30% chance of existing.

Speaker 1: 33:06

That makes sense. Nature doesn't deal in negative existence.

Speaker 2: 33:10

Right. So a Fischbach-Viller's decomposition is a mathematical tool that essentially unbraids the rope. It separates the equation into two distinct strands, the forward-in-time, physically meaningful solutions, and the backward-in-time, non-physical solutions. They kept the forward-moving strand, discarding the negative anomalies, and then they injected their new variable, entropic time, tau, directly into it in place of standard time.

Speaker 1: 33:34

They rebraided the rope, but this time they used their own homemade thermodynamic clock to hold it together.

Speaker 2: 33:40

Beautifully put. Practically speaking, it allowed them to derive a brand new version of the Schrodinger equation, one that is parameterized entirely by internal entropic time. The external lab time is completely scrubbed from the math. The equation now dictates that the quantum state of the atoms evolves, not because an external clock is ticking on a wall, but solely because entropy is flowing across the barrier.

Speaker 1: 34:04

Going back to our movie reel analogy, they prove that the projector doesn't need to be plugged into the wall of an external reality. It is powered by the friction of the film physically rubbing against itself inside the box.

Speaker 2: 34:15

That is precisely what the math shows. And the ultimate test of any theoretical physics equation is whether it can accurately predict physical reality. So they took this new entropic Schrodinger equation and they fed it into a computer simulation. To solve it, they used something called a split-step Fourier method.

Speaker 1: 34:35

Another hefty term. What does a split-step Fourier method actually do in this context?

Speaker 2: 34:41

Simulating the quantum interactions of 24,000 atoms is incredibly computationally heavy. A split-step Fourier method is a numerical trick to make it manageable. Instead of trying to calculate everything happening all at once, it breaks the evolution of the system into tiny discrete steps. In one step, it calculates how the atoms move through space. In the next step, it calculates how the lasers and atomic forces act upon them. It balances back and forth between calculating movement and calculating force, stepping through the simulation.

Speaker 1: 35:10

It's sort of like animating a flipbook. You draw one tiny change, then the next, to see how the whole wave behaves over time. So they ran this complex flipbook simulation using their brand new entropic time equation. How did the computer's prediction match up with the actual physical photographs they took of the glowing rubidium cloud in the lab?

Speaker 2: 35:31

It was a virtually flawless match. The dotted line trajectory generated from their computer simulation tracked flawlessly with the physical data points they measured in the experiment. The physical width of the condensate, the timing of the expansion, the timing of the big crunches, it all aligned perfectly with the math that was running solely on entropy.

Speaker 1: 35:49

That gives me literal chills. Like, they didn't just play with graphs or philosophical arguments. They demonstrated that the fundamental mathematical engine of quantum mechanics can run on emergent thermodynamic time just as well, if not better, than it runs on the illusion of an absolute external clock.

Speaker 2: 36:06

They proved beyond a shadow of a doubt in this specific system that time isn't a background stage. It isn't the metronome. It is an emergent property of thermodynamic openness. It is the footprint left behind by the universe constantly interacting with its own pieces.

Speaker 1: 36:21

And what's so thrilling about this paper is that this isn't just a one-off parlor trick to solve a 60-year-old cosmological debate. This paper opens up a whole new sandbox for experimental physics. The authors actually list a bunch of future playgrounds, specific experiments they want to run next using this cold atom setup because it's so versatile.

Speaker 2: 36:39

Yes, the experimental platform they've built here is incredibly robust. For example, they discussed the possibility of engineering analog black holes.

Speaker 1: 36:48

Wait, really? Analog black holes?

Speaker 2: 36:50

Yeah, by using arbitrarily shaped attractive laser potentials, basically using the optical traps to create very specific deep shapes of gravity wells, they can simulate the event horizons of black holes right there in the bright sector of their mini universe.

Speaker 1: 37:05

Imagine testing Stephen Hawking's theories of black hole radiation in a microscopic droplet of super cold rubidium. That's insane. They also mentioned testing something called the Lachmitt Echo. Let's unpack that. What is a Lachmitt Echo?

Speaker 2: 37:17

The Lachmitt Echo is a fascinating measure of quantum chaos and reversibility. It basically asks a profound question about the arrow of time. If you run a quantum system forward, letting it evolve and get messy, and then you perfectly reverse the Hamiltonians, like you reverse the forces acting on it, does it perfectly return to its exact starting state?

Speaker 1: 37:37

Does the shattered egg unshatter perfectly if you push all the pieces back together?

Speaker 2: 37:41

Exactly. Or does the tiny, inherent chaotic butterfly effect of quantum mechanics prevent it from ever perfectly going back? This cold atom platform, with its precise control over interactions and its new entropic clock, is perfect for testing the absolute physical limits of the reversibility of time.

Speaker 1: 38:00

They can also look at the Big Bang itself. They can adjust the interactions of the rubidium atoms to see if a collapsing universe hits a true singularity, a point of infinite density where all our mathematical equations break down and divide by zero, or if it experiences what physicists call a quantum bounce, where the universe squishes down to a certain microscopic limit and then elastically bounces back out into a new Big Bang.

Speaker 2: 38:20

It is genuinely a new frontier in physics. They've taken the absolute most abstract, untouchable concepts in theoretical cosmology ideas that scientists have argued about purely on chalkboards for decades and dragged them down to a physical workbench where we can literally poke them with lasers and measure them with cameras.

Speaker 1: 38:39

So bringing this all home, what does this mean for you, the listener, sitting in traffic right now or staring at a looming deadline on your calendar? The next time you look at a clock or feel frustrated by the relentless, unstoppable passage of your day, I want you to remember those 24,000 super cold rubidium atoms suspended in a bowl of laser light.

Speaker 2: 38:59

It's a profound shift in personal perspective, I think. The present you are experiencing right now, the moment you are listening to this sentence, isn't some magical cursor moving across an objective cosmic timeline.

Speaker 1: 39:09

No. Your present is just the continuous, messy reshuffling of entropy. It is the transfer of information from the unobserved, dark sectors of the universe, all the things you haven't seen or interacted with yet, into your personally observed bright sector. You are a macroscopic subsystem of the universe, and your entire psychological experience of time is just the friction of your relationship with the rest of reality.

Speaker 2: 39:34

We are, in a very real physical sense, writing the timeline of the universe just by being entangled with it, by breathing the air, by letting heat radiate from our skin.

Speaker 1: 39:43

Which leads me to one final, slightly terrifying, absolutely mind-bending thought to leave you with. If this paper is fundamentally right about the true nature of reality, if time is strictly defined by the flow of entropy, by the act of change in relationships between subsystems...

Speaker 2: 39:57

Then time is a finite resource. It is not eternal.

Speaker 1: 40:01

Exactly. Think about what happens trillions upon trillions of years from now when our actual universe reaches its own absolute heat death, when the last stars burn out and go dark, when the supermassive black holes evaporate into hawking radiation, and the entire cosmos reaches a state of maximum entropy. A perfectly uniform, lukewarm, static soup where everything is the exact same temperature. If there is no more entropy left to exchange between subsystems.

Speaker 2: 40:29

If the shuffling of the cosmic deck finally stops and there are no more grains of sand left in the hourglass.

Speaker 1: 40:35

Does time itself simply vanish? Does the universe freeze forever in an eternal, timeless snapshot, completely unmoving with no past to remember and no future to arrive? It's something to mull over while you're waiting in line for your morning coffee. Thank you so much for joining us on this massive journey today, for being willing to stretch your mind and explore the fundamental nature of reality with us. Until our next deep dive into the unknown, keep questioning the obvious, and remember that even time itself might just be a matter of perspective.

Speaker 2: 41:05

Heliox is produced by Michelle Bruecker and Scott Bleakley. It features reviews of emerging research and ideas from leading thinkers curated under their creative direction with AI assistance for voice, imagery and composition. Systemic voices and illustrative images of people are representative tools, not depictions of specific individuals. Thanks for listening today. Four recurring narratives underlie every episode. Boundary dissolution, adaptive complexity, embodied knowledge, and quantum-like uncertainty. These aren't just philosophical musings, but frameworks for understanding our modern world. We hope you continue exploring our other episodes, responding to the content, and checking out our related articles at helioxpodcast.substack.com.