Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: Imagine standing in front of a mirror, just, you know,
Speaker 2: looking at your normal.
Speaker 3: Reflection, right, just checking your hair, yeah.
Speaker 2: Exactly, adjusted to your collar. But suddenly the glass shifts,
Speaker 2: and instead of just showing your face, the reflection starts playing.
Speaker 3: Backwards, like a movie on rewind.
Speaker 2: Yes, and not just by a few hours or like
Speaker 2: a few days, yep. Imagine the reflection rewinds faster and faster,
Speaker 2: dissolving the room right behind.
Speaker 3: You, just completely falling away, right.
Speaker 2: The walls fall away, the city outside dissolves into this wilderness,
Speaker 2: and the earth itself literally unforms. It turns back into
Speaker 2: a swirling disc of dust. The sun breaks apart.
Speaker 3: You're going back to the very beginning.
Speaker 2: All the way back. The mirror pulls back, accelerating through
Speaker 2: deep time, billions of years, just collapsing in seconds, retreating
Speaker 2: to a time of absolute, just unimaginable density. Everything you
Speaker 2: ever known shrinks into a blinding, searing point of heat,
Speaker 2: and then the mirror just pauses.
Speaker 3: It hits play, hits play.
Speaker 2: You are suddenly watching the entire thirteen point eight billion
Speaker 2: year history of the cosmos play out and fast forward
Speaker 2: right there in the glass.
Speaker 3: Which I mean, it sounds like pure unadulterated science fictionally,
Speaker 3: but the crazy thing is humanity is essentially building that
Speaker 3: exact mirror right now.
Speaker 2: It's wild to even think about. We are currently undertaking
Speaker 2: one of the most ambitious computational projects ever attempted in
Speaker 2: the history of our species. Oh, without a doubt, recreating
Speaker 2: the formation of the universe itself from its very first
Speaker 2: breath inside.
Speaker 3: The sheer audacity of the project is what makes it
Speaker 3: so compelling, honestly, because when we talk about these computational reconstructions,
Speaker 3: we really have to strip away the idea that these
Speaker 3: are just high definition animations.
Speaker 2: No, it's not a Pixar movie exactly.
Speaker 3: We aren't painting pretty pictures of stars and galaxies on
Speaker 3: a digital canvas just so someone can use them as
Speaker 3: a desktop wallpaper.
Speaker 2: Though they do make great wallpapers.
Speaker 3: They do, But we are constructing immense dynamic physical laboratories
Speaker 3: in silicon. These are mathematical reconstructions built rigorously, I mean
Speaker 3: line of code by line of code, from the.
Speaker 2: Ground up, driven by the actual math.
Speaker 3: Yes, they are governed by the precise, unrelenting equations of gravity, thermodynamics,
Speaker 3: radiation transfer, fluid motion, all of it cosmic expansion.
Speaker 2: So by taking the absolute limits of observational astronomy infusing
Speaker 2: them with the bleeding edge of supercomputing architecture, we're attempting
Speaker 2: to mathematically weave reality together just to see if we
Speaker 2: trulyunderstand how it works exactly. So today we are going
Speaker 2: to explore exactly how scientists are building these dynamic reconstructions
Speaker 2: of reality. You listening to this right now are about
Speaker 2: to see how the invisible forces that shape literally everything
Speaker 2: around us are being mapped and tested and ultimately understood.
Speaker 3: It's a huge undertaking, it really is.
Speaker 2: We're going to dive into the actual mechanics of how
Speaker 2: you take the raw, chaotic math of the cosmos and
Speaker 2: turn it into a breathing, evolving universe inside a machine.
Speaker 2: Because honestly, there's a profound philosophical weight.
Speaker 3: To this there is. It forces a real reckoning with
Speaker 3: our own place in the grand scheme of things. I mean,
Speaker 3: think about it. We are a temporary biological species residing
Speaker 3: on a tiny rock, a very tiny rock, attempting to
Speaker 3: mathematically model our own origins. We are building virtual universes
Speaker 3: to understand the singular physical universe that gave.
Speaker 2: Birth to us, which is just wow.
Speaker 3: It forces us to confront the deepest questions about the
Speaker 3: nature of reality and how unbelievable complexity like galaxies, stars, planets, biology,
Speaker 3: consciousness itself, how all of that emerges from incredibly simple
Speaker 3: initial conditions.
Speaker 2: But let's look at the immense roadblock right at the
Speaker 2: starting line. Because the fundamental challenge of understanding the cosmos,
Speaker 2: and therefore, you know, the very first challenge of simulating it,
Speaker 2: is deeply frustrated.
Speaker 3: It is a massive headache.
Speaker 2: It's the fact that the vast, overwhelming majority of the
Speaker 2: universe is completely utterly invisible to us. The stuff we know,
Speaker 2: ordinary matter, the atoms that make up the stars, the planets,
Speaker 2: the glowing gas clouds, the device you're listening to this
Speaker 2: on in our own biological bodies, that constitutes just a
Speaker 2: tiny almost negligible fraction of.
Speaker 3: Cosmic reality around five percent.
Speaker 2: Five percent. That is nothing.
Speaker 3: It really isn't, which means if you want to build
Speaker 3: a universe in a computer, you absolutely cannot start with ordinary.
Speaker 2: Matter because it just wouldn't work right.
Speaker 3: If you build a universe using only atoms, your simulation
Speaker 3: will fail catastrophically. It won't look anything like the night sky.
Speaker 3: The universe is completely dominated by two deeply mysterious, totally
Speaker 3: invisible components, dark matter and dark energy, the Big Two.
Speaker 3: The Big Two. Dark matter acts as the vital gravitational scaffolding.
Speaker 3: It is the structural foundation that actually allows galaxies and
Speaker 3: massive galaxy clusters to form in the first place.
Speaker 2: And then dark energy.
Speaker 3: Dark energy is the enigmatic force driving the accelerating expansion
Speaker 3: of space itself.
Speaker 2: And we can't see either of them.
Speaker 3: No, we cannot hold either of these in a jar.
Speaker 3: We don't even have a standardized particle model for dark
Speaker 3: matter yet. But their silent, invisible influence dictates absolutely everything,
Speaker 3: both the structure and the ultimate destiny of the cosmos.
Speaker 2: So I want to focus on the mechanics of getting
Speaker 2: this started. If you are a computational astrophysicist, sitting at
Speaker 2: a supercomputer terminal and you want to simulate this invisible universe.
Speaker 2: Where do you even begin?
Speaker 3: You definitely don't just write a command prompt that says
Speaker 3: run universe dot xe and walk away wish.
Speaker 2: Is that easy?
Speaker 3: Me too? But no, you have to give the computer
Speaker 3: a highly specific starting state, initial conditions, and those initial
Speaker 3: conditions are drawn from something called the cosmic microwave background
Speaker 3: or the CMB.
Speaker 2: Right, So, the CMB is what like the baby picture
Speaker 2: of the universe.
Speaker 3: Basically, it is the Rosetta stone of cosmology. Massive cosmological
Speaker 3: simulations must begin with the conditions inferred from that early universe.
Speaker 3: The cosmic microwave background is the ancient relic radiation left
Speaker 3: over from the Big Bang. So it's light, yes, yes,
Speaker 3: specifically it is the light emitted roughly three hundred and
Speaker 3: eighty thousand years after the Big Bang during an event
Speaker 3: called recombination.
Speaker 2: Recombination, what's happening there?
Speaker 3: That's when the universe finally cooled down enough for the
Speaker 3: first stable atoms to form, which meant light could finally
Speaker 3: travel freely through space without just smashing into a dense
Speaker 3: soup of particles.
Speaker 2: Ah, so it cleared up exactly.
Speaker 3: It's the oldest light we can possibly see, and preserved
Speaker 3: within that ancient light kind of like insects trapped in amber,
Speaker 3: are tiny, almost imperceptible density fluctuations from when the universe
Speaker 3: was extremely young.
Speaker 2: Let's talk about the scale of those fluctuations, because it's
Speaker 2: really hard to wrap your head around. When we say tiny,
Speaker 2: we really mean miniscus.
Speaker 3: It's absolutely tiny.
Speaker 2: The differences in density across that early universe were smaller
Speaker 2: than one part in one hundred thousand.
Speaker 3: Yeah, just barely there.
Speaker 2: Imagine a perfectly smooth, vast ocean and the only waves
Speaker 2: on it are microscopic ripples.
Speaker 3: Great analogy.
Speaker 2: Yet those incredibly faint quantum fluctuations, which were blown up
Speaker 2: to macroscopic size during an early period of rapid inflation,
Speaker 2: those are the seeds of absolutely everything that exists today.
Speaker 3: Every galaxy, every star, You and me.
Speaker 2: We all trace our physical lineage back to those microscopic
Speaker 2: density irregularities.
Speaker 3: And the physics of why those specific tiny seeds grew
Speaker 3: is the entire foundation of the simulation. Gravity is the
Speaker 3: ultimate patient sculptor here, how so well, under the influence
Speaker 3: of gravity, those slightly denser regions of that prime soup.
Speaker 3: The regions that were just a fraction of a percent
Speaker 3: denser than the average, they exerted a slightly stronger gravitational
Speaker 3: pull than the less dense regions around them.
Speaker 2: Because more mass equals more gravity exactly.
Speaker 3: So what happens. They gradually attract more matter. It is
Speaker 3: a compounding runaway effect. Over hundreds of millions and then
Speaker 3: billions of years, those one in one hundred thousand irregularities
Speaker 3: undergo what we call nonlinear gravitational collapse.
Speaker 2: Nonlinear gravitational collapse, right.
Speaker 3: They draw in more and more dark matter, pulling it
Speaker 3: out of the surrounding boyds and weaving it into these
Speaker 3: enormous DNSE structures.
Speaker 2: I always think of the CMB as this blurry static
Speaker 2: ultrasound of the infant universe. It gives us that initial snapshot,
Speaker 2: and the dark matter acts like an invisible, ghostly skeleton
Speaker 2: growing out of that snapshot.
Speaker 3: I like that, the skeleton holding it all together.
Speaker 2: Yeah, we can't see the bones directly, but we know
Speaker 2: exactly how they are shaping the glowing flesh of the
Speaker 2: galaxies resting on top of them. We know the skeleton
Speaker 2: is there because we see the exact shape of the
Speaker 2: body it supports.
Speaker 3: And historically this was a massive revelation back in the
Speaker 3: nineteen seventies and eighties when cosmologists first started running these
Speaker 3: primitive N body simulations.
Speaker 2: Wait, what's an N body simulation?
Speaker 3: Ah, there are computer algorithms that calculate the gravitational forces
Speaker 3: between thousands or millions of individual particles. So when they
Speaker 3: started running these, they realized that without dark matter, there
Speaker 3: simply hadn't been enough time since the Big Bang for
Speaker 3: ordinary matter to clump together and form the galaxies we see.
Speaker 3: It was too slow, way too slow. Ordinary matter is
Speaker 3: coupled to radiation in the early universe, so it just
Speaker 3: gets pushed around. It couldn't start collapsing until that three
Speaker 3: hundred and eighty thousand year.
Speaker 2: Mark, but dark matter could.
Speaker 3: Yes, dark matter doesn't care about light. It is collisionless.
Speaker 3: It started collapsing much earlier, creating these really deep gravitational wells.
Speaker 3: So by the time ordinary matter was free to collapse,
Speaker 3: the dark matter foundations were already laid out, just waiting
Speaker 3: for the gas to fall in.
Speaker 2: Wait. I want to pause there, because you just mentioned
Speaker 2: that dark matter is collisionless.
Speaker 3: I did, Yes, what does.
Speaker 2: That actually mean in the context of coding a simulation,
Speaker 2: how do you code a collisionless fluid?
Speaker 3: It is a brilliant mathematical abstraction. Honestly, in a computer,
Speaker 3: we don't simulate individual dark matter particles because if dark
Speaker 3: matter is composed of sub atomic particles, there would be
Speaker 3: an impossibly large number of them in even a cubic
Speaker 3: millimeter of space.
Speaker 2: Right the computer would just explode.
Speaker 3: Instantly, So instead we use macro particles. A single particle
Speaker 3: in the simulation might actually represent the mass of a
Speaker 3: million suns worth of dark matter, And because it is collisionless,
Speaker 3: it means these particles don't experience friction or pressure when
Speaker 3: they pass through each other.
Speaker 2: They just phase through.
Speaker 3: Exactly. If two clouds of ordinary gas collide, they heat up,
Speaker 3: they slow down, they emit X rays. If two clouds
Speaker 3: of dark matter collide, they literally pass right through each other,
Speaker 3: like ghosts, interacting only via their mutual gravitational pull.
Speaker 2: Eerie.
Speaker 3: It is so the code simply has to solve Quasslan's
Speaker 3: equation for gravity. It calculates the gravitational force every particle
Speaker 3: exerts on every other particle, moves them a tiny step
Speaker 3: forward in time, and then recalculates.
Speaker 2: But calculating the gravity of every particle pulling on every
Speaker 2: other particle, if you have billions of particles, doesn't the
Speaker 2: math get exponentially out of control?
Speaker 3: Yes, highly out of control.
Speaker 2: I mean I remember from high school physics. The gravitational
Speaker 2: force between two objects is easy. But if you have
Speaker 2: ten billion objects, calculating the distance and pull between every
Speaker 2: single combination of two objects sounds like it would melt
Speaker 2: a computer.
Speaker 3: You've hit on the exact computational bottleneck that plagued all
Speaker 3: those early simulations. If you use a naive brute force calculation,
Speaker 3: what we call an O N squared algorithm, the time
Speaker 3: it takes to compute grows with the square of the
Speaker 3: number of particles. So for billions of particles, for billions
Speaker 3: of particles, the universe would end before the simulation finished.
Speaker 3: That's a problem, a huge one. So computational astrophysicists had
Speaker 3: to invent these brilliant shortcuts, and one of the most
Speaker 3: famous is the tree algorithm, which was originally adapted from
Speaker 3: methods in plasma physics.
Speaker 2: How does that work?
Speaker 3: Well, imagine you are looking at a forest from say
Speaker 3: ten miles away. Do you need to calculate the gravitational
Speaker 3: pull of every individual leaf on you.
Speaker 2: No, obviously not right.
Speaker 3: You group the entire forest into one massive object and
Speaker 3: calculate the pull from its center of mass. The tree
Speaker 3: algorithm divides the simulated universe into a hierarchical grid. Okay,
Speaker 3: if a group of dark matter particles is far enough
Speaker 3: away from the particle you are currently calculating, the computer
Speaker 3: just treats that distant group as a single combined mass.
Speaker 2: Oh, that's smart.
Speaker 3: It drastically reduces the number of calculations required, changing the
Speaker 3: computing time from o n square to oen logan. And
Speaker 3: later they combine this with mesh grids, where you calculate
Speaker 3: the gravitational field on a three D grid and interpolate
Speaker 3: the forces resulting in three PM or tree particle mesh
Speaker 3: algorithm article mesh.
Speaker 2: Got it.
Speaker 3: That breakthrough is exactly what allowed us to scale up
Speaker 3: from simulating a few thousand particles in the eighties to
Speaker 3: literally trillions of particles today.
Speaker 2: That's incredibly elegant. We're using computational geometry to sort of
Speaker 2: cheat the math just enough to make it run without
Speaker 2: losing the macro accuracy precisely. Okay, so we have this
Speaker 2: optimized collisionless ghost skeleton of dark matter forming in the computer.
Speaker 2: But if we run this simulation, what does it actually
Speaker 2: look like? Because it's not just a random scattering of
Speaker 2: spherical blobs, right, it has a very specific, almost biological architecture.
Speaker 3: It does, and it is arguably one of the most
Speaker 3: stunning discoveries verified by these simulations. The dark matter organizes
Speaker 3: into what we call the cosmic web cladma. We imagine
Speaker 3: vast interconnected filaments of dense matter stretching across unimaginable distances
Speaker 3: of space. Where these filaments intersect, you get these massive,
Speaker 3: hyperdense knots called halos halos okay. And between these luminous
Speaker 3: threads light enormous, terrifying void regions of space millions of
Speaker 3: light years across that contain almost nothing at all, just
Speaker 3: dead space exactly. And this weblike structure wasn't programmed into
Speaker 3: the computers directly. It arises naturally, inevitably, just from the
Speaker 3: gravitational evolution of those tiny CMB fluctuations.
Speaker 2: I want to make sure I'm visualizing this correctly. It's
Speaker 2: like watching water trickle down a bumpy windshield. It naturally
Speaker 2: pools into streams and droplets leaving empty spaces between.
Speaker 3: That's a really good way to picture it. The process
Speaker 3: is often described by the Zeldovitch approximation. Initially, a matter
Speaker 3: collapses along one axis, forming vast flattened structures we call pancakes.
Speaker 2: Pancakes cosmologists are great at naming things.
Speaker 3: They really are. Then it collapses along a second axis,
Speaker 3: forming the long, stringy filaments. Finally, matter flows along those
Speaker 3: filaments and collapses along the third axis into the dense nodes,
Speaker 3: those dark matter.
Speaker 2: Halos, and the voids.
Speaker 3: The voids are just the regions that lost the gravitational
Speaker 3: tug of war, slowly empty out as all their material
Speaker 3: is pulled toward the filaments.
Speaker 2: So in our supercomputer, we now have this beautiful, twisting
Speaker 2: skeleton of dark matter. We have these dense halos acting
Speaker 2: as massive gravitational sinks. But we are missing the stars.
Speaker 3: We are missing the light, right.
Speaker 2: We are missing the galaxies. We need to introduce ordinary
Speaker 2: baryonic matter the gas. But wait, if gravity alone creates
Speaker 2: this beautiful dark matter web, why can't we just stop there?
Speaker 2: What goes wrong in the simulation if we hit play
Speaker 2: with only gravity and no ordinary gas.
Speaker 3: Well, if you only simulate gravity you get a highly
Speaker 3: accurate map of where galaxies should be, but you don't
Speaker 3: actually get galaxies. You just get cold, dark, gravitational wells,
Speaker 3: empty bowls. Exactly to understand the actual universe, you have
Speaker 3: to throw gas into those wells. You have to introduce hydrodynamics.
Speaker 3: And this is where the simulation goes from being a
Speaker 3: relatively clean, elegant mathematical exercise into an absolute nightmare of complexity.
Speaker 2: I find this historically fascinating. It's so counterintuitive that the
Speaker 2: stuff we understand best, ordinary matter, the gas, the stuff
Speaker 2: you and I are made of, is actually the hardest
Speaker 2: thing to mathematically simulate, oh without a doubt. Meanwhile, the
Speaker 2: dark matter, that we fundamentally don't understand at a quantum
Speaker 2: level is computationally much simpler because it's a one trick pony.
Speaker 2: It just does gravity. But ordinary gas gas is a diva.
Speaker 3: A diva is putting it mildly. Gas dynamics involve massive
Speaker 3: chaotic turbulence. When ordinary gas falls into a dark matter halo,
Speaker 3: it accelerates, and as it accelerates, it heats up to
Speaker 3: millions of degrees, creating supersonic shock waves that just ripple
Speaker 3: out through the space.
Speaker 2: That sounds intense. It is.
Speaker 3: You have incredibly complex magnetic fields twisting, snapping, and reconnecting.
Speaker 3: You have to calculate the cooling functions because gas can't
Speaker 3: form stars unless it cools down, and it cools by
Speaker 3: emitting radiation, which requires tracking this specific atomic transitions of
Speaker 3: elements like hydrogen, helium, and oxygen.
Speaker 2: That sounds computationally You can't just use those dark matter
Speaker 2: macro particles for gas, can you?
Speaker 3: You can, but you have to modify them entirely. There
Speaker 3: are two main approaches to handling the gas. One is
Speaker 3: grid based, where you divide the universe into millions of
Speaker 3: tiny cubic cells and calculate the flow of gas between
Speaker 3: the cells using the oiler equations of fluid dynamics DEMI other.
Speaker 3: The other is particle based. It's called smooth particle hydrodynamics
Speaker 3: or SPH. In SPH, the gas is represented by particles
Speaker 3: that carry properties like temperature, density, and entropy, and the
Speaker 3: computer essentially blurs them together to calculate fluid pressure.
Speaker 2: And both are hard.
Speaker 3: Both methods are computationally brutal, and it's.
Speaker 2: Not just the fluid dynamics right, because once the gas
Speaker 2: does cool down and form stars, those stars start fighting back.
Speaker 3: Yes, that is the crucial concept of baryonic feedback. In
Speaker 3: the late nineties and early two thousands, cosmologists ran these
Speaker 3: early hydrodynamics simulations and they ran into a massive problem
Speaker 3: called the overcooling problem.
Speaker 2: Cooling, what did that look like?
Speaker 3: Basically, the gas and the simulations cooled too efficiently. It
Speaker 3: fell into the center of the dark matter halos and
Speaker 3: formed stars at a ridiculous rate. The simulated galaxies ended
Speaker 3: up being way too massive, way too compact, and formed
Speaker 3: far too many stars compared to what we actually observed
Speaker 3: through telescopes.
Speaker 2: There were just star factories on overdrive exactly.
Speaker 3: The simulations were completely failing to match reality because.
Speaker 2: They were missing the explosions. They were modeling the stars
Speaker 2: being born, but they weren't modeling what happens when the
Speaker 2: massive ones die.
Speaker 3: Precisely. They were missing supernova and they were missing super
Speaker 3: massive black holes. A galaxy is not just a passive
Speaker 3: collection of stars. It is a highly volatile, finely balanced ecosystem.
Speaker 3: When a massive star dies in a supernova, it doesn't
Speaker 3: just disappear quietly. It detonates with unimaginable energy, violently heating
Speaker 3: the surrounding gas and physically blowing it out of the galaxy.
Speaker 3: In massive galactic.
Speaker 2: Winds, It's like the galaxy is an engine and the
Speaker 2: supernova is an exploding pistol, and that blows the fuel
Speaker 2: line apart. If the gas gets blown away, the galaxy
Speaker 2: is suddenly out of fuel, so it stops making new stars. Yeah,
Speaker 2: star formation shuts.
Speaker 3: Down perfect analogy. And if supernovae weren't enough, you have
Speaker 3: to model agn feedback AGM active galactic nuclei. At the
Speaker 3: center of almost every galaxy is a super massive black hole.
Speaker 3: As gas falls into the black hole, it forms an
Speaker 3: accretion disk that gets so incredibly hot it outshines the
Speaker 3: entire galaxy.
Speaker 2: Wow.
Speaker 3: It generates colossal jets of high energy particles that blast
Speaker 3: out into space, heating up the gas in the dark
Speaker 3: matter halo and preventing it from ever cooling down to
Speaker 3: form stars. Injecting that kind of localized, extreme violent energy
Speaker 3: into a massive, large scale cosmological simulation requires a level
Speaker 3: of computational finesse that we have only recently begun.
Speaker 2: To master, which brings us to the hardware. Because capturing
Speaker 2: the sheer explosive chaos of a single galaxy is hard enough.
Speaker 2: Trying to mathematically calculate the shock wave of a dying
Speaker 2: star or the jet of a black hole requires solving
Speaker 2: differential equations over incredibly tiny time steps, very tiny, but
Speaker 2: doing that simultaneously for tens of thousands of galaxies across
Speaker 2: a massive chunk of the observable universe, we are talking
Speaker 2: about true computational leviathans. I mean, my laptop fan sounds
Speaker 2: like a jet engine taking off just because I have
Speaker 2: too many browser tabs open.
Speaker 3: We've all been there.
Speaker 2: I literally cannot fathom the it infrastructure required to run
Speaker 2: a virtual universe.
Speaker 3: The computational scale is difficult to properly articulate modern cosmological projects,
Speaker 3: like the ILLUSTRISTMG project or the Egle simulation, they are
Speaker 3: not run on desktop computers. They run on the world's
Speaker 3: most powerful supercomputing clusters like warehouse sized things. Yes, we
Speaker 3: are talking about machines utilizing tens of thousands, sometimes millions,
Speaker 3: of CPU and GPU cores operating in perfect tandem. A
Speaker 3: single large scale simulation can take months of continuous uninterrupted operation. Months,
Speaker 3: and if a single node in the supercomputer fails, the
Speaker 3: code has to be robust enough to recover from the
Speaker 3: last save state without corrupting the entire virtual universe.
Speaker 2: And the data output. We aren't talking about a gigabyte
Speaker 2: file you can put on a thumb drive. The data
Speaker 2: sets they produce reach petabyte scales.
Speaker 3: It's astonishing.
Speaker 2: For context, for you listening, one petabyte is roughly the
Speaker 2: equivalent of a quarter of a million high definition movies.
Speaker 2: You would have to sit in front of a television
Speaker 2: twenty four hours a day for over fifty years just
Speaker 2: to watch that much data.
Speaker 3: And that's just to watch it. Scientists have had to
Speaker 3: invent entirely new database architectures and visualization software just to
Speaker 3: store and navigate these immense virtual environments. You literally can't
Speaker 3: load the whole simulation into memory at once. You have
Speaker 3: to stream it piece by piece just to look at it.
Speaker 2: That is insane.
Speaker 3: And yet, despite utilizing the most powerful machines ever constructed,
Speaker 3: there is a profound fundamental limitation. We have to face.
Speaker 3: These simulations, as incredibly detailed as they are, remain coarse
Speaker 3: grained approximate.
Speaker 2: They're still approximations.
Speaker 3: Computers, no matter how powerful, cannot mathematically model every single atom,
Speaker 3: or even every single sar individually across an entire observable
Speaker 3: volume of the universe. Consider the dynamic range required. You
Speaker 3: are trying to simulate a cosmic web that is hundreds
Speaker 3: of millions of light years across, while simultaneously trying to
Speaker 3: resolve a supernova shockwave that is a fraction of a
Speaker 3: light year across.
Speaker 2: You just can't do both.
Speaker 3: It is computationally impossible to resolve both scale simultaneously.
Speaker 2: So if the computer can't see the individual stars or
Speaker 2: the individual supernovae because they are smaller than the smallest
Speaker 2: pixels in the simulation, how do they run the feedback?
Speaker 2: How do they get the supernova to blow the gas away?
Speaker 2: If the simulation doesn't even know the supernova exists.
Speaker 3: They rely on what is arguably the most controversial and
Speaker 3: essential technique in computational astrophysics subgrid physics.
Speaker 2: Okay, we you just spend some time on subgrid physics.
Speaker 2: Because this feels like a massive conception leap it is.
Speaker 2: I like to think of it like trying to predict
Speaker 2: traffic in a massive city like Tokyo or New York.
Speaker 2: You don't need a supercomputer to track every single turn
Speaker 2: signal where every time a driver hits the brake, pedal
Speaker 2: or the rpm of every individual engine to know that
Speaker 2: there's a massive traffic jam forming on the main highway
Speaker 2: at five zero pm.
Speaker 3: Right, you don't make that.
Speaker 2: You don't need the micro details. You approximate the local
Speaker 2: chaos to understand the macro flow.
Speaker 3: That is an incredibly apt analogy. Subgrid physics utilizes statistical
Speaker 3: models to represent those smaller scale processes that occur strictly
Speaker 3: below the simulation's resolution limit the Greed size. For instance,
Speaker 3: the simulation might have a spatial resolution of one thousand
Speaker 3: light years, it cannot track the fiery mechanics of one
Speaker 3: specific star going supernova because that star is completely sub resolution.
Speaker 2: It's invisible to the grid.
Speaker 3: Yes. However, based on theoretical physics and smaller scale high
Speaker 3: resolution models, the developers know that a certain amount of
Speaker 3: gas of a certain dense and temperature will produce a
Speaker 3: specific number of supernovae over a specific period of time.
Speaker 2: So instead of simulating the bomb exploding, they just mathematically
Speaker 2: inject the heat of the explosion into that one thousand
Speaker 2: light year cell exactly.
Speaker 3: The code essentially says, ugh, this cell has met the
Speaker 3: conditions for star formation. Statistically, x number of supernovae just occurred. Here. Therefore,
Speaker 3: I will artificially inject why amount of thermal energy and
Speaker 3: Z amount of momentum into the surrounding gas cells.
Speaker 2: It just cheats the physics a little bit.
Speaker 3: It averages out the unobservable microphysics to faithfully reproduce the
Speaker 3: macroscale effects on the galaxy.
Speaker 2: I have a real problem with this Conceptually. I understand
Speaker 2: why it's necessary for the computers to not melt down.
Speaker 2: But if we're using approximations, if we're manually writing code
Speaker 2: that says, inject this much energy when this happens, aren't
Speaker 2: we just baking our own assumptions into the cake.
Speaker 3: That's the big question.
Speaker 2: How do we know the simulation is actually revealing the
Speaker 2: underlying truth of the universe rather than just spinning our
Speaker 2: own bias theories back at us. It sounds like tuning
Speaker 2: a guitar until it plays the note you want and
Speaker 2: then declaring you've discovered music.
Speaker 3: That is the precise epistemological paradox that critics of cosmological
Speaker 3: simulations frequently raise. Are these predictive scientific tools or are
Speaker 3: they highly sophisticated post talk fitting exercises?
Speaker 2: Exactly?
Speaker 3: It is a deeply valid critique if you manually tune
Speaker 3: the subgrid parameters for supernova feedback just to make sure
Speaker 3: you're simulating galaxies match the exact size of the Milky Way,
Speaker 3: you haven't necessarily proven how the Milky Way formed. You've
Speaker 3: just reverse engineered a specific result.
Speaker 2: Right, So how do the scientists defend against that? How
Speaker 2: do they prove this is actual science and not just
Speaker 2: cosmic video game design?
Speaker 3: By demanding predictive power across multiple distinct observational metrics. A
Speaker 3: robust simulation like ILLUSTRISTNG is calibrated. The team tunes the
Speaker 3: some grid parameters so that the simulation correctly matches a
Speaker 3: very specific baseline observation. Usually the stellar.
Speaker 2: Mass function was the stellar mass function.
Speaker 3: Which is simply the abundance of galaxies of different masses
Speaker 3: in the present day universe. They adjust the feedback dials
Speaker 3: until the simulation produces the right ratio of large galaxies
Speaker 3: to small galaxies.
Speaker 2: Okay, so they calibrate to one specific metric. They tune
Speaker 2: the guitar to one string.
Speaker 3: Yes, but here's the critical test. Once those parameters are
Speaker 3: locked in to match the mass function, they do not
Speaker 3: touch the dials again. They let the simulation run hands
Speaker 3: off the keyboard, hands off of it, And then they
Speaker 3: ask does this simulation, which was only tuned to match
Speaker 3: galaxy masses, naturally reproduce other completely unrelated phenomena, like what
Speaker 3: does it produce the correct clustering of galaxies across the
Speaker 3: cosmic web? Does it naturally produce the observed division between
Speaker 3: blue star forming spiral galaxies and red dead elliptical galaxies.
Speaker 3: Does it correctly map the distribution of heavy metals like
Speaker 3: oxygen and iron in the intergalactic medium? Does it reproduce
Speaker 3: the mysterious magnetic field topologies we see in galaxy clusters
Speaker 3: Moonishingly yes, wow, When the physics are implemented correctly, these
Speaker 3: simulations reproduce a staggering array of observational data that they
Speaker 3: were never explicitly tuned to match.
Speaker 2: The math checks out, that's incredible.
Speaker 3: They are generating mock telescope observations that perfectly mimic the
Speaker 3: large scale gravitational lensing patterns we see in the real sky.
Speaker 3: In many instances, if you take a simulated galaxy from
Speaker 3: the high resolution runs and apply synthetic telescope noise to it,
Speaker 3: it is virtually indistinguishable from a real image. Taken by
Speaker 3: the Hubble space telescope.
Speaker 2: You can't tell the difference.
Speaker 3: Even trained astronomers struggle to tell which is the mathematical
Speaker 3: abstraction and which is the real universe.
Speaker 2: That convergence between simulation and observation is wild because traditionally
Speaker 2: the scientific method is all about direct experimentation. You want
Speaker 2: to know what a chemical does, You put it in
Speaker 2: a beaker, you add a regent, you heat it up,
Speaker 2: you measure the reaction. But cosmology has a fundamental constraint.
Speaker 2: We only have one universe. We are stuck inside it.
Speaker 2: We can't put the Big Bang in a Petri dish,
Speaker 2: and we can't rewind the actual universe to see what
Speaker 2: would happen if things were different exactly.
Speaker 3: Astrophysics is traditionally an observational science, not an experimental one.
Speaker 3: We can only look at the history of the universe
Speaker 3: decided to give us until now right. These highly accurate,
Speaker 3: predictive simulations completely change that paradigm. They cease to be
Speaker 3: just sophisticated visual aids. They function as true, rigorous computational experiments.
Speaker 3: They become active laboratories where human researchers can test hypothetical
Speaker 3: physical laws and compare the outcomes against the reality we
Speaker 3: observe in the night sky.
Speaker 2: We are essentially allowing human beings to play god with
Speaker 2: the laws of physics. Inside a machine, we get to
Speaker 2: tweak the dials of reality. What happens if we run
Speaker 2: a simulation where we alter the properties of dark matter
Speaker 2: just a tiny bit?
Speaker 3: That is precisely how we test competing theories of physics.
Speaker 3: For example, let's take dark matter. The standard model assumes
Speaker 3: cold dark matter, meaning the particles move very slowly compared
Speaker 3: to the speed of light.
Speaker 2: Cold means slow.
Speaker 3: Yes, this allows them to clump together easily, creating small
Speaker 3: structures that merge into larger ones a bottom up formation.
Speaker 3: But what if dark matter is warm? What if the
Speaker 3: particles are lighter and move much faster.
Speaker 2: If they're moving faster, they wouldn't clump together as easily, right,
Speaker 2: It would buzz out of the small gravitational wells.
Speaker 3: Precisely so, researchers run the exact same massive simulation, but
Speaker 3: they change the fundamental velocity properties of the dark matter
Speaker 3: particles to match a warm dark matter theory. They hit
Speaker 3: play let thirteen billion years pass in the computer, and
Speaker 3: then look at the results. And what do they find
Speaker 3: in a warm dark matter universe, the massive filaments and
Speaker 3: large galaxies still form, but the thousands of tiny dwarf
Speaker 3: galaxies that usually swarm around massive galaxies like our Milky
Speaker 3: Way are completely wiped out. The fast moving dark matter
Speaker 3: simply smoothed out the small scale structure.
Speaker 2: So then you take that virtual output, you look at
Speaker 2: the real milk You and you say, well, the real
Speaker 2: Milkiya does have dozens of dwarf galaxies orbiting it exactly.
Speaker 3: Therefore, the worm dark matter model must be wrong or
Speaker 3: at least highly constrained. If a tweaked parameter causes the
Speaker 3: simulated universe to fundamentally break down, if galaxies fail to form,
Speaker 3: or the cosmic web looks entirely wrong compared to massive
Speaker 3: sky surveys like the Slorn Digital Sky Survey, then that
Speaker 3: specific theoretical model of particle physics is discarded.
Speaker 2: It just doesn't survive the test.
Speaker 3: It is a ruthless computational process of.
Speaker 2: Elimination and one of the biggest, most terrifying dials they
Speaker 2: are trying to figure out how to tune is dark energy.
Speaker 2: We mentioned it earlier, but it is such a profound mystery,
Speaker 2: a huge one for most of human history, we assume
Speaker 2: the expansion of the universe, which started with the Big Bang,
Speaker 2: would eventually be slowed down by the collective gravitational pull
Speaker 2: of all the matter inside it.
Speaker 3: Like tossing a ball in the air.
Speaker 2: Yeah, exactly, it has to come back down. But in
Speaker 2: the late nineteen nineties, observations of distant supernovae reveal the
Speaker 2: exact opposite. The expansion of the universe is actually accelerating.
Speaker 2: Space is pushing itself apart faster and faster.
Speaker 3: It was a Nobel Prize winning discovery that completely upended physics.
Speaker 3: In the standard cosmological model known as Lambda CDM, this
Speaker 3: dark energy is represented by Lambda, the cosmological constant.
Speaker 2: The cosmological constant.
Speaker 3: It acts as an intrinsic, pervasive repulsive energy of empty
Speaker 3: space itself. As space expands, there is more empty space,
Speaker 3: which means there's more repulsive energy, driving even faster expansion.
Speaker 3: What is it really The true physical nature of dark
Speaker 3: energy remains completely unexplained. Is it the vacuum energy of
Speaker 3: quantum fields. Is it a dynamic changing scalar field often
Speaker 3: called quintessence, or do we fundamentally misunderstand how gravity operates
Speaker 3: on colossal scales.
Speaker 2: So we put these different theories of dark energy into
Speaker 2: the supercomputer. What do the simulations tell us if we
Speaker 2: play with that specific dial. What happens if dark energy
Speaker 2: doesn't remain constant but actually gets stronger over time.
Speaker 3: If you program a simulation where the dark energy equation
Speaker 3: of state the dial dictating its strength, increases over time,
Speaker 3: you enter a scenario known as the Big Rip.
Speaker 2: The big rip that sounds bad it is.
Speaker 3: The simulation shows the repulsive force of space eventually overpowering everything. First,
Speaker 3: it pushes the galaxy clusters apart. Then the repulsive force
Speaker 3: grows so strong it overwhelms the gravity holding individual galaxies together,
Speaker 3: stripping stars away from the core.
Speaker 2: Oh wow.
Speaker 3: Eventually it overwhelms the gravity of planetary systems, tearing planets
Speaker 3: from their stars. In the final moments of the simulation,
Speaker 3: the expansion outpaces the electromagnetic and strong nuclear forces, and
Speaker 3: the very atoms themselves are ripped apart.
Speaker 2: Okay, that is deeply bleak, very bleak. But what if
Speaker 2: we just stick to the standard model. What if dark
Speaker 2: energy is just a constant, unchanging force exactly as Lamb
Speaker 2: to CDM suggests. The simulation must show us where our
Speaker 2: actual re universe is heading.
Speaker 3: It does, and the implications are haunting in a quieter way.
Speaker 3: How So, if dark energy remains constant, the accelerating expansion
Speaker 3: continues unchecked. The simulations reveal that the cosmic web as
Speaker 3: we see it today is a temporary structure. Over tens
Speaker 3: of billions of years, the gravitational bonds holding the larger
Speaker 3: web together will fail, The voids will expand relentlessly.
Speaker 2: Everything just drifts apart.
Speaker 3: Yes, galaxies that are not already bound together by local
Speaker 3: gravity will be pushed away from each other at speeds
Speaker 3: exceeding the speed of light.
Speaker 2: Wait, I thought nothing could move faster than the speed
Speaker 2: of light.
Speaker 3: Nothing can travel through space faster than the speed of light.
Speaker 3: But space itself has no such speed limit. It can
Speaker 3: expand at any rate. The simulations show that eventually distant
Speaker 3: galaxies will be pushed beyond our observable horizon. The light
Speaker 3: they emit will never be able to traverse the rapidly
Speaker 3: expanding space between us.
Speaker 2: That means that future civilizations, if biological or synthetic life
Speaker 2: manages to survive billions of years from now, are going
Speaker 2: to wake up in incredibly lonely universe, every lonely they
Speaker 2: might inhabit isolated galactic islands, just the merged remnants of
Speaker 2: their local group of galaxies. They would look out through
Speaker 2: their ultra advanced telescopes, expecting to see a vast cosmos,
Speaker 2: and they would see absolutely nothing.
Speaker 3: A completely black, empty sky.
Speaker 2: All the evidence of the Big Bang, the cosmic Web,
Speaker 2: the billions of other galaxies that we are privileged enough
Speaker 2: to observe and simulate today, will have been permanently erased
Speaker 2: from their observable horizon. They might falsely conclude that their
Speaker 2: single solitary galaxy is the entire universe.
Speaker 3: It is a profound existential insight derived directly from the
Speaker 3: numerical outputs of a supercomputer. We are living in a
Speaker 3: privileged observational epoch. We happen to exist at a time
Speaker 3: when the universe is old enough to have formed complex
Speaker 3: galaxies and conscious observers, but young enough that dark energy
Speaker 3: hasn't yet erased the evidence of our origins.
Speaker 2: And this brings up another existential revelation from these computational experiments,
Speaker 2: the sheer, terrifying fragility of our reality.
Speaker 3: It's a fine tuning problem. It is inescapable. When you
Speaker 3: work with these simulations, they prove mathematically that our universe
Speaker 3: is incredibly, almost absurdly sensitive to its initial conditions.
Speaker 2: The dials are very touchy.
Speaker 3: Exactly if you alter the parameters just a microscopic amount,
Speaker 3: if you change the initial expansion rate of the Big Bang,
Speaker 3: if you shift the density of dark matter by a
Speaker 3: tiny fraction, or if you make those primordial quantum fluctuations
Speaker 3: in the CMB just slightly smaller or larger, you produce
Speaker 3: dramatically different sterile universes.
Speaker 2: I read about one where they just slightly lowered the
Speaker 2: initial density fluctuations and what happened. The dark matter never
Speaker 2: gathered enough mass to overcome the expansion of space.
Speaker 3: Galaxies simply failed to form entirely. The universe remained a
Speaker 3: diffuse dark fog of hydrogen gas, forever expanding, forever cooling,
Speaker 3: no stars, no carbon, no biology.
Speaker 2: Or conversely, if you make gravity just slightly stronger or
Speaker 2: the expansion rate slightly slower, the entire universe collapses back
Speaker 2: in on itself in a big crow before stars even
Speaker 2: have time to ignite. Wow. The window of parameters that
Speaker 2: allows for the formation of stable cosmic web structures long
Speaker 2: lived stars, and the complex chemistry necessary for life is
Speaker 2: infinitesimally narrow.
Speaker 3: So how do scientists grapple with this? If tweaking the
Speaker 3: code just a tiny fraction ruins the whole simulation and
Speaker 3: prevents planets and humans from forming, does this suggest our
Speaker 3: existence hangs by a mere mathematical thread. Do we just
Speaker 3: accept that we got incredibly improbably lucky in a.
Speaker 2: Cosmic watery it's a huge debate.
Speaker 3: Or does this fine tuning point to something else? Does
Speaker 3: it imply there's a deeper, unifying physical law that naturally
Speaker 3: locks those dials into place, and we simply haven't discovered
Speaker 3: the math yet. That represents the very bleeding edge of
Speaker 3: modern theoretical physics. The simulations don't answer the why, they
Speaker 3: only illuminate the what. This immense fine tuning highlights how
Speaker 3: beautifully balanced cosmic evolution appears to be for some physicists.
Speaker 3: It strongly implies the existence of a multiverse idea being.
Speaker 2: If you run infinite simulations with random parameters, most of
Speaker 2: them will be dead steril fogs, but simply by statistical inevitability,
Speaker 2: one of them will roll the exact right numbers to
Speaker 2: create stars in life and because we are alive, we
Speaker 2: must necessarily be in the one that worked the anthropic
Speaker 2: principle exactly.
Speaker 3: But for others, invoking a multiverse is an intellectually unsatisfying
Speaker 3: cop out. They believe that a future deeper fundamental theory,
Speaker 3: perhaps a complete theory of quantum gravity like string theory
Speaker 3: or loop quantum gravity, will eventually reveal that these parameters
Speaker 3: are not random dials that can be freely tweaked.
Speaker 2: They have to be what they are.
Speaker 3: A deeper theory might dictate mathematically that the universe must
Speaker 3: have exactly the dark matter density and dark energy values
Speaker 3: that we observe, but that remains completely unresolved. What is
Speaker 3: undeniably proven by these computational experiments is precisely how delicate
Speaker 3: and improbable the long chain of physical events was that
Speaker 3: allowed you and me to exist and have this conversation.
Speaker 2: To push these boundaries further, to try and solve these
Speaker 2: ultimate mysteries, we need to run more experiments. We need
Speaker 2: to test thousands of different dial tweaking scenarios, run higher resolutions,
Speaker 2: and resolve both the massive cosmic web and the individual
Speaker 2: supernovae simultaneously. We more power, right, but human minds and
Speaker 2: even our traditional algorithms are hitting a limit, so we
Speaker 2: are now enlisting the help of artificial minds. AI and
Speaker 2: machine learning are fundamentally rewriting how we simulate the universe.
Speaker 3: The integration of artificial intelligence into cosmological simulation represents a massive,
Speaker 3: necessary paradigm shift. Remember the petabyte scale data sets we discussed.
Speaker 2: The fifty years of movies.
Speaker 3: Yes, the sheer volume of output is overwhelming human beings,
Speaker 3: even teams of thousands of postdocs simply cannot comb through
Speaker 3: that much information efficiently. Machine learning systems, particularly convolutional neural networks,
Speaker 3: are incredibly adept at analyzing these massive, multidimensional data sets.
Speaker 3: They can identify deeply hidden nonlinear patterns in the cosmic
Speaker 3: web that human intuition would completely miss.
Speaker 2: The AI isn't just acting as a highly efficient data janitor.
Speaker 2: It's not just sweeping up the data after the simulation
Speaker 2: is done. AI is actively helping to build the virtual
Speaker 2: universes faster.
Speaker 3: Yes, through the development of AI surrogate models or emulators,
Speaker 3: we talked about how computationally expensive subgrid physics and fluid
Speaker 3: dynamics are. A high resolution simulation calculating every thermal shockwave
Speaker 3: can take months. But what if we don't have months.
Speaker 3: What if we want to test ten thousand different dark
Speaker 3: energy models. We can't wait ten thousand months. So researchers
Speaker 3: train an AI on a small, insanely detailed, high resolution simulation.
Speaker 3: The neural network learns the deeply complex physical mapping.
Speaker 2: It finds the shortcuts exactly.
Speaker 3: It learns ah when the dark matter density looks exactly
Speaker 3: like this, the resultant gas temperature and star formation rate
Speaker 3: will look exactly like that.
Speaker 2: It bypasses the traditional math. Instead of calculating the fluid
Speaker 2: dynamics step by step using the oiler equations, the AI
Speaker 2: just looks at the innatetion and immediately predicts the final
Speaker 2: state based on the patterns.
Speaker 3: It learned exactly. It emulates the physics. Once the AI
Speaker 3: is trained, they can deploy it across a massive scale,
Speaker 3: low resolution dark matter simulation. The AI instantly paints the
Speaker 3: highly complex, realistic buryonic gas and stars onto the dark
Speaker 3: matter skeleton in a fraction of the time.
Speaker 2: That is brilliant.
Speaker 3: It dramatically saves millions of hours of supercomputing time while
Speaker 3: rigidly preserving an astonishing degree of scientific accuracy. This allows
Speaker 3: us to run vast parameter sweeps that were literally impossible
Speaker 3: five years ago, and we're.
Speaker 2: Going to need that speed because the data pipeline from
Speaker 2: Rule World astronomy is about to explode and the simulations
Speaker 2: are going to have to keep up. We are looking
Speaker 2: at future computing horizons like exass scale architectures, machines like
Speaker 2: the Frontier supercomputer capable of performing over a quintillion calculations
Speaker 2: per second.
Speaker 3: A billion billion operations a second.
Speaker 2: We need that power because the telscoast are getting too good.
Speaker 3: Between observation and computation is entering an era of unprecedented
Speaker 3: tension and precision. The James Webb Space Telescope is currently
Speaker 3: peering further back in time than human eyes ever have,
Speaker 3: looking at the very dawn of galaxy formation, and it
Speaker 3: is finding massive, fully formed galaxies existing much earlier in
Speaker 3: the universe than our current simulations predicted.
Speaker 2: It's breaking the models.
Speaker 3: It is actively stressing our subgrid models of star formation.
Speaker 2: The model said those early galaxies shouldn't have had enough
Speaker 2: time to get that big. JWST is looking at the
Speaker 2: sky and saying your code is wrong.
Speaker 3: Precisely, and that is exactly how the science advances JWST
Speaker 3: provides the tension, and the computational astrophysicists must return to
Speaker 3: the supercomputers, refine their models of dark matter or early
Speaker 3: baryonic feedback, perhaps introduce new mechanics like birsty star formation
Speaker 3: or primordial black holes, and run the simulations again until
Speaker 3: the virtual universe matches the new reality.
Speaker 2: It's a constant feedback loop.
Speaker 3: Furthermore, we have the upcoming of v Uroc Reuben Observatory,
Speaker 3: which will map the entire Southern Sky every few nights,
Speaker 3: generating an absolute tsunami of data regarding dark matter lensing
Speaker 3: and cosmic expansion.
Speaker 2: The Vera Reuben is going to catalog billions of galaxies.
Speaker 2: To make sense of that, we need simulated universes that
Speaker 2: contain billions of simulated galaxies to compare them against.
Speaker 3: Exactly, as JWST and the Vera Ruben Observatory gather vastly
Speaker 3: more precise data, our simulations will become increasingly relentlessly constrained
Speaker 3: by reality. We will be forced to simulate magnetic fields,
Speaker 3: general relativistic effects, and complex chemical evolution with a resolution
Speaker 3: we previously thought impossible.
Speaker 2: That is going to get more more detailed.
Speaker 3: We are approaching an era where entire observable volume universes
Speaker 3: may be mathematically modeled at resolutions currently reserved for a
Speaker 3: single isolated galaxy.
Speaker 2: I want to take a step back from the terabytes
Speaker 2: and the algorithms for a moment and just look at
Speaker 2: the existential reality of what we have discussed today, because
Speaker 2: there is something deeply, overwhelmingly poetic about this higher endeavor.
Speaker 3: There really is.
Speaker 2: We are a biological species. We evolve to hunt, gather,
Speaker 2: and survive on a rocky planet orbiting a very average
Speaker 2: yellow star. We have possessed electricity for less than a
Speaker 2: couple of centuries. We have been looking through telescopes for
Speaker 2: a blink of a cosmic eye, just a blink. And
Speaker 2: yet somehow the physical matter inside our skulls has developed
Speaker 2: the mathematical capacity to reverse engineer and reconstruct the entire
Speaker 2: fourteen billion year history of the universe that created us.
Speaker 3: It is the most profound recursion imaginable in the natural world.
Speaker 3: Let us trace the physical path we've outlined today. The
Speaker 3: universe begins as incomprehensibly tiny random quantum fluctuations in a
Speaker 3: primordial soup, through entirely deterministic, unthinking physical laws gravity, thermodynamics,
Speaker 3: fluid dynamics operating silently over billions of years in the dark,
Speaker 3: those fluctuations evolve, They collapse into a dark matter web,
Speaker 3: they ignite into stars. Those stars forge heavy elements like
Speaker 3: carbon and iron in their cores and explode them out into.
Speaker 2: The void, spreading the seeds.
Speaker 3: That complex chemistry eventually coalesces into planets and ultimately generates
Speaker 3: conscious biological observers us.
Speaker 2: And then those conscious observers extract silicon from the Earth,
Speaker 2: constructs sophisticated mechanical brains out of it, and program those
Speaker 2: supercomputers to build internal mathematical models capable of perfectly reproducing
Speaker 2: the universe's on history right back to the quantum fluctuations.
Speaker 3: It is exactly as if the universe spent fourteen billion
Speaker 3: years growing a biological brain, just so that biological brain
Speaker 3: could build a mechanical brain, all to dream about how
Speaker 3: the universe was born in the first place.
Speaker 2: That is just beautiful.
Speaker 3: Through these computational laboratories, we are the cosmos performing self reflection.
Speaker 3: We are the universe trying to understand itself.
Speaker 2: And I think the visual beauty of these simulations completely
Speaker 2: reinforces this awe. When you look at the outputs of
Speaker 2: projects like Illustrious or the Millennium simulation, the vast twisting
Speaker 2: filaments of dark mans stretching across the blackness of space
Speaker 2: look remarkably undeniably like luminous neural networks.
Speaker 3: The resemblance is uncanny.
Speaker 2: The largest macro structures of the universe visually echo the
Speaker 2: microstructures of the human brain that is currently simulating them.
Speaker 2: The universe appears simultaneously intensely coldly mathematical and deeply beautifully organic.
Speaker 3: It completely changes how we view the very nature of
Speaker 3: reality itself. These simulations demonstrate unequivocally that staggering, our inspiring
Speaker 3: complexity naturally emerges from ultimate simplicity.
Speaker 2: Right, you don't need a complicated start now.
Speaker 3: You start with a few simple rules, a few basic
Speaker 3: fundamental forces, and a slight imbalance in density. You give
Speaker 3: it fourteen billion years of processing time, and you get everything,
Speaker 3: the cosmic web, the galaxies, the planets, and the mines
Speaker 3: capable of understanding the math.
Speaker 2: But despite all of this computing power, despite the AI
Speaker 2: and the EXAs scale machines, we have to remain humble
Speaker 2: because these simulations also explicitly define the bounce of human ignorance.
Speaker 3: Oh.
Speaker 2: Absolutely, the universe remains fundamentally mysterious. We can model dark
Speaker 2: matter flawlessly, but we have never directly detected a dark
Speaker 2: matter particle in a lab. We can code dark energy
Speaker 2: into the simulation, but it remains completely unexplained. In fundamental physics,
Speaker 2: the crucial unification of quantum mechanics and gravity, the very
Speaker 2: thing required to understand the literal instant of the Big Bang,
Speaker 2: remains unresolved.
Speaker 3: It's the holy grail of physics.
Speaker 2: Every single virtual universe we boot up inside a supercomputer
Speaker 2: is built upon a foundation that contains a vast ocean
Speaker 2: of known unknowns.
Speaker 3: That humility is essential. A simulation is only as good
Speaker 3: as the physics programmed into it, but the progress is undeniable.
Speaker 3: We are no longer just guessing at how the invisible
Speaker 3: shapes the visible. We are testing it.
Speaker 2: We are proving it.
Speaker 3: Yes, we are proving that our reality possesses a deep
Speaker 3: underlying order, an order capable of being represented mathematically across
Speaker 3: scales of time and space that utterly defy daily heute intuition.
Speaker 2: Let's bring this grand journey full circle. Think about the sheer,
Speaker 2: mind bending scale of what we've explored today. We started
Speaker 2: with microscopic one in one hundred thousand quantum ripples preserved
Speaker 2: in the ancient light of the CMB. The very beginning,
Speaker 2: we watch those ripples get magnified by gravity, pulled into
Speaker 2: an invisible, collisionless dark matter skeleton. We saw how chaotic, hot,
Speaker 2: turbulent ordinary gas falls into those structures, battles against the
Speaker 2: explosive feedback of supernovae and supermassive black holes to finally
Speaker 2: ignite the galaxies we know and love.
Speaker 3: It's a chaotic ballet, it really is.
Speaker 2: We talked about how computational astrophysicists are mathematically rebuilding all
Speaker 2: of this, using petabytes of data, running complex fluid dynamics
Speaker 2: on millions of processing cores, and tweaking the physical dials
Speaker 2: of reality to see what happens. All while artificial intelligence
Speaker 2: helps us untangle the unimaginable complexity of the results.
Speaker 3: It is a testament to the fact that profound intelligence
Speaker 3: can arise within a universe vast enough to contain both
Speaker 3: the crushing gravit of dark matter halos and the fragile
Speaker 3: biological minds capable of deciphering their equations.
Speaker 2: Which brings us to one final deeply provocative thought, something
Speaker 2: for you listening right now to ponder long after you
Speaker 2: stop the playback. Today, we have talked extensively about how
Speaker 2: our supercomputers are already generating entire observable universes. They're utilizing
Speaker 2: complex subgrid physics and AI emulators to produce simulated galaxies
Speaker 2: that are virtually indistinguishable from real telescope images. We've established
Speaker 2: that incredible organic complexity inevitably arises from simple mathematical rules
Speaker 2: executing over vast stretches of time. So if we can
Speaker 2: simulate a universe this accurately today, imagine what we will
Speaker 2: be able to simulate in one hundred years or one thousand.
Speaker 2: What happens when a simulation running inside one of our
Speaker 2: descendants machines becomes complex enough and operates at high enough
Speaker 2: quantum resolution to naturally develop its own simulated conscious observers.
Speaker 3: Observers who evolve on a simulated Rocky plan.
Speaker 2: Yes, who look up at their simulated stars, build their
Speaker 2: own simulated computers and try to mathematically model their own origins.
Speaker 2: And if that recursion is mathematically possible, if simulated universes
Speaker 2: can spawn their own simulated minds, how can we be
Speaker 2: absolutely fundamentally certain that we aren't already living inside one
Speaker 2: of those computational experiments right now,