This synthesis masterfully reframes the Big Bang from a mystical genesis into a rigorous phase transition, grounding speculative cosmology in the mechanics of inflation. It offers a lucid map of our current epistemic limits without oversimplifying the profound complexity of pre-inflationary models.
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What Existed Before The Big Bang?Added:
In 1964, two engineers standing in a field in New Jersey accidentally found the oldest light in the universe while trying to clean pigeon droppings off the inside of a giant horn-shaped antenna. They were not looking for it. They thought it was a malfunction in the wiring. They thought the birds were the problem. What they had actually stumbled into was a faint, steady hum arriving from every direction at once at almost exactly 3° above absolute zero. The cooled afterglow of creation itself. It became almost overnight the single strongest piece of evidence that the big bang ever happened. And here is the part that makes this even stranger. In 2024, 60 years after that accidental discovery, in a quiet conference room in Copenhagen, somewhere around 80 of the world's working cosmologists were asked one simple question. Was the Big Bang the beginning of time? The majority of them said no. Not maybe. Not. We're still figuring it out. No. The story you were taught in school, the one with the glowing dot and the explosion blooming into stars, is no longer believed by most of the people who study it for a living. The very same people who can point to that hum from New Jersey and tell you with mathematical certainty that the Big Bang was real have quietly stopped believing it was the beginning.
Tonight, we are going to find out why.
Hit subscribe, settle in somewhere comfortable, and stay with me because the real story starts before the bang.
Part one, the universe that should have glowed white.
Isaac Newton when he gave us his theory of universal gravitation in 1687 did something that on the surface looked like victory. He took the heavens which had been the domain of theology and mystery for thousands of years and he reduced them to a tidy equation that you can fit on a coffee mug. Two masses, the distance between them squared, a constant, and gravity falls out the other side. Apples fall, planets orbit, moons swing around their parent worlds.
The universe in Newton's hands became a clockwork, predictable, mechanical, beautiful. But there was a quiet problem hiding in his picture. And Newton himself knew about it, even if he never quite found a satisfying answer. If gravity is universal and every massive object in the universe pulls on every other massive object, then any finite collection of stars should, given enough time, fall in on itself. The mutual attraction would crush everything together into a single enormous lump.
So, how do we have a universe at all?
Why hasn't gravity already won? Newton's answer, the one he wrote about in his correspondence with the theologian Richard Bentley, was that the universe must be infinite. If you spread stars out evenly across an infinite volume, then for any given star, there is no center for everything to fall toward.
The poles in every direction cancel out.
Infinity in Newton's cosmos was a structural necessity. Without it, the whole system collapses. But infinity is one of those words that sounds harmless until you actually start chasing what it implies. And in the early 1800s, a German astronomer named Heinrich Olers articulated a paradox that other thinkers had hinted at before, but that came to bear his name. The argument is so simple a child can follow it, and yet it quietly demolishes the entire Newtonian picture. If the universe is infinite and if it is filled more or less uniformly with stars and if it has been around forever, then no matter what direction you look in the night sky, your line of sight must eventually somewhere out there terminate on the surface of a star. There is no escape route. Every gap between every visible star, if you zoom in far enough, must contain another more distant star and beyond that another and another forever.
Which means the entire celestial sphere should be from your perspective blanketed in stellar surface. The night sky should not be black. It should not have stars sprinkled across darkness. It should glow, every point of it, as bright as the surface of the sun. And yet you can step outside tonight, anywhere on Earth, far enough from city lights, and look up, and the sky is dark, velvet dark, black between the stars. The contradiction is not subtle.
The reality of what you see when you look up directly contradicts what an infinite eternal static universe predicts. Something has to give. Either the universe is not infinite or it is not eternal or it is not static. One of those three assumptions, the assumptions Newton's cosmos rested on has to be wrong. And whichever one you abandon, you've made room for a very different kind of story about where everything came from. The unsettling part when you sit with this is that paradox was telling people something deep about the structure of reality more than a century before anyone built a telescope capable of confirming it. The dark night sky, the most ordinary feature of human existence, was a quiet message from the cosmos saying that the simple eternal universe story does not work. And this is what I want you to hold on to because it connects directly to where we're going. Even our earliest models of the universe failed to describe its actual structure. The Newtonian picture was incomplete and the night sky itself was the evidence. So when we get to the Big Bang model and we find that it too has gaps, that it too can't quite explain everything we observe, we should not be surprised. We should be patient. The history of cosmology is the history of incomplete pictures. Each one a little better than the last. Each one revealing the cracks in the previous one. The big bang is not exempt from that pattern. It might just be the latest, most accurate, but still incomplete picture in a long line of them. Which raises an obvious next question. If Newton's universe was wrong, what came next? Who took the next swing at it? And the answer takes us into the early 20th century, into the mind of a Swiss patent cler who would do something even Newton hadn't dared. He'd rewrite gravity itself.
Part two, Einstein's fix that broke everything. Albert Einstein published the field equations of general relativity in 1915. And what he gave us was not just a better theory of gravity.
It was a completely different way of thinking about what gravity is. Newton had treated gravity as a force, an invisible pull reaching across space between any two masses. Einstein said, "No, that's not what's happening. Mass and energy actually warp the geometry of space and time around them. And what we feel as gravity is just the local curvature of that geometry. A planet orbiting the sun is not being pulled. It is rolling freely along a curved groove in spaceime that the sun's mass has carved. The picture is so far beyond Newton's that they almost don't belong in the same conversation. Except that Einstein's equations reduce to Newton's in the limit of weak gravity and slow speeds, which is why apples still fall the way Newton said they would. But here's the thing about Einstein's equations. When you write them down and you start asking them questions about the universe as a whole, they say something Einstein himself was deeply uncomfortable with. They say spacetime is dynamic. The universe as a global thing cannot just sit there. It has to be either expanding or contracting. A static universe, the kind Newton imagined and the kind that everybody in 1915 still assumed was the right picture, is not a stable solution to general relativity. It would collapse.
And so Einstein, being human, did what any of us might do when our beautiful new theory predicts something that contradicts what we think we already know. He fudged it. He added a term to his equations, a constant he called lambda, the cosmological constant whose only purpose was to act as a kind of anti-gravity, a repulsive force built into the fabric of space itself, just strong enough to balance against the inward pull of all the matter and keep the universe sitting still. In 1917, he published his static universe model with the cosmological constant in place. And for a while, it seemed fine. The universe was eternal. It wasn't going anywhere. Newton would have approved.
And then, of course, the universe turned out not to be static. We'll get to Hubble in a minute. But when the evidence came in that galaxies were actually moving away from each other, that the cosmos was in fact expanding, Einstein's beautiful balancing act became unnecessary. The cosmological constant was a fix for a problem that didn't exist. Einstein, by his own later admission to the physicist George Gamo, called the introduction of lambda his greatest blunder. He pulled it out of his equations and tried to forget about it. But here is where the story gets interesting and where it loops back to the central thread of what we're chasing tonight. Lambda, the blunder, the embarrassment, the extra term Einstein tried to bury has come roaring back into modern physics. In 1998, two independent teams studying distant supernova discovered that the expansion of the universe is not just continuing, it's accelerating. Something is pushing space apart harder and harder against the inward pull of gravity. We don't know what that something is. We call it dark energy because we have to call it something. But the simplest mathematical description of dark energy is a cosmological constant. The same lambda Einstein invented and discarded. It is now back in the equations, not as a fudge, but as a real measured feature of the cosmos. And here's the part that should make the hair on the back of your neck stand up. The energy of empty space, the very same kind of energy that lambda describes, is exactly the kind of energy that in modern theories of inflation drove what we call the big bang. What Einstein dismissed as a mistake may be the most fundamental thing about reality. The repulsive energy of vacuum, of nothing, of the empty space between particles may be both the engine that started the cosmic expansion in the first place and the engine that is accelerating it now 14 billion years later. Same mechanism, different epoch. There is one further wrinkle that I want to plant in your mind because it'll come up again later.
When physicists try to calculate from first principles using quantum field theory what the value of the cosmological constant ought to be, the number they get is wrong. Not a little wrong, not off by a factor of 10. They get a number that is roughly 10 to the 120th power times larger than what we actually measure. That is the worst theoretical prediction in the history of physics. It's a number so absurd it has its own name. The cosmological constant problem. We have no idea why the energy of empty space is what it is. Only that it is. And that without it none of this works. So here is the irony. The one I want you to carry with you. The same vacuum energy Einstein introduced to keep the universe still may in fact be the very mechanism by which the universe banged into existence. The blunder was not a blunder. It was the fingerprint of the thing we don't yet understand. It was a clue sitting in the equations the whole time. And the universe was about to give us another clue, a much louder one. Because while Einstein was trying to keep the cosmos frozen, somebody far away from him was about to look up at a faint smear of light in a telescope and noticed that it was moving. Part three, the moment the universe became a process. Henrietta Swan Levit was a so-called computer at the Harvard College Observatory in the early 1900s, which in those days meant she was one of a group of women hired to do the painstaking work of measuring stellar positions and brightnesses on photographic plates. She was paid less than the men. Her work was not at first considered groundbreaking, and she went on to discover something that quietly opened up the entire universe. Levit was studying a particular kind of star called a sephiid variable which is a star that pulses brightening and dimming on a regular cycle of days or weeks. And what she noticed looking at thousands of these stars in the melanic clouds was that the period of pulsation, how long the cycle took, was directly related to the actual brightness of the star. If you knew how fast a sephiid was pulsing, you could figure out how luminous it really was. And if you know how luminous something really is, and you measure how bright it appears from Earth, you can calculate exactly how far away it must be. This is what's called a standard candle. And it gave astronomers for the first time a reliable yard stick for measuring distances across the cosmos, not just within our galaxy, but to other galaxies entirely. Although in 1912 nobody yet knew that other galaxies existed. Around the same time an American astronomer named Vesto Slifer working at Lel Observatory in Arizona was carefully measuring the spectra of what were then called spiral nebula fuzzy pinwheelshaped objects that nobody quite knew what to make of. And Slifer noticed something strange. The light from these objects was systematically shifted toward the red end of the spectrum. The wavelengths were stretched. By the early 1920s, he had measured the red shift of dozens of these nebula, and the pattern was unmistakable. Almost all of them were moving away from us, not toward, away.
And then Edwin Hubble working with the 100in Hooker telescope on Mount Wilson in California put the two pieces together. He used Sephiid variables to measure the actual distances to these spiral nebula and proved definitively that they were not part of the Milky Way. They were entire other galaxies millions of light years away. Each one a swirling island of hundreds of billions of stars. And when he plotted the distance to each galaxy against the red shift Sliper had measured, the result was a clean straight line. The farther away a galaxy was, the faster it was receding. The relationship is now called Hubble's law. And what it implied was staggering. The universe was not static.
It was expanding. Every galaxy was rushing away from every other galaxy like raisins in a loaf of bread that was rising in the oven. And if the universe is expanding now, the obvious question, the one any kid would ask, is what was it like in the past? If you run the movie backward, the galaxies must have been closer together. The cosmos must have been smaller, denser, hotter. And if you keep rewinding far enough, you arrive at a state in which all the matter and energy in the universe was packed into something arbitrarily small and arbitrarily hot. a primeval atom as a Belgian Catholic priest and physicist named Gor Lamech first called it in 1927 two years before Hubble's data was even published. Lmetra had derived the expansion of the universe from Einstein's own equations equations Einstein himself was still trying to neutralize with his cosmological constant and Lmetra had taken the next almost theological step. He had suggested that if the universe is expanding then it must have started at some finite time in the past from a single dense primordial state the cosmic egg the seed. The reaction to Lmetra's idea was not warm. Einstein himself when lame met first presented it to him reportedly said your calculations are correct but your physics is abominable.
Other physicists were uncomfortable too.
The notion that the universe had a beginning sounded uncomfortably close to a creation story, and many felt it was importing theology into physics through the back door. Fred Hy, the British astronomer who actually coined the term Big Bang, did so as a kind of mockery on a BBC radio program in 1949. He preferred a steadystate model in which the universe had no beginning and matter was continually created to fill the gaps left by expansion. The name Big Bang meant as a sneer ended up sticking the way insults sometimes do. There was also a numerical embarrassment that nearly sank the whole idea. Early measurements of the Hubble constant, the rate of cosmic expansion, gave an age for the universe of around 2 billion years, which was a problem because geologists already knew from radioactive dating of rocks that the Earth was older than that. You cannot have a planet older than the universe it sits in. It took several decades and a careful recalibration of the cosmic distance scale by Walter Bard and others to resolve this. The distances had been underestimated. The actual age of the universe is closer to 13.8 billion years. The Earth at 4.5 billion fits comfortably inside. What I want you to take away from this stretch of history, the part that connects directly to the question of what came before the bang, is that expansion changed everything. It transformed the universe from a static thing into a process, a noun into a verb. The cosmos was not a place. It was a sequence. It had a past that was different from its present, which meant it had a story, which meant the story had somewhere a beginning or at least a deepest reachable past. But, and this is the crucial point, expansion only tells you that the universe was once dense. It tells you nothing about why it started expanding or what existed before that dense state or whether the dense state was the actual beginning or just the earliest moment. We can run the equations to expansion is the evidence of a past. It is not the evidence of an origin. We were going to need something more to even start to ask that question.
And as it happens, the universe was already broadcasting that something constantly in every direction. We just hadn't figured out how to hear it yet.
Part four, the signal no one meant to find. Ano Pensius and Robert Wilson were not looking for the afterglow of creation. Let me say that very plainly because it's one of my favorite facts in the history of science. The two of them working at Bell Labs in Holell, New Jersey in 1964 were trying to use a giant horn-shaped antenna originally built for satellite communications to do radio astronomy.
They wanted to measure radio emissions from the Milky Way. They wanted clean data and they kept running into a problem. There was a hiss, a persistent faint microwave noise around a wavelength of 7.35 cm that was coming in from every direction they pointed the antenna. It didn't matter where they aimed, up, sideways, toward the galactic plane, away from it. The noise was the same. It corresponded to a temperature of roughly 3° above absolute zero just sitting there in the data refusing to go away.
So they did what any good experimentalists do. They tried to find the source of the noise. They checked the receivers. They cooled the components further. They went over the wiring. And they discovered to their mild horror that a pair of pigeons had taken up residence inside the horn and had been generously coating the interior with what Penszers would later in scientific papers refer to with magnificent restraint as a white dialectric material. They evicted the pigeons. They cleaned the antenna. The hiss remained. Around the same time about 30 m away at Princeton, a group led by Robert Dick and including a young theorist named Jim Peebles was preparing to actually go look for exactly this kind of signal. They had calculated based on the big bang model that if the universe really had started in a hot dense state, it should have left behind a faint relic radiation cooled by billions of years of cosmic expansion to just a few degrees above absolute zero, filling all of space uniformly. They were literally building an antenna to find it. And then someone mentioned to them that two engineers at Bell Labs were complaining about a microwave noise. they couldn't get rid of. Dicki is reported to have put down the phone after the call from Pensas and said to his colleagues, "Well, boys, we've been scooped. The hiss in the Bell Lab's horn was the cosmic microwave background. It is the literal afterglow of the early universe." When the cosmos was about 380,000 years old, it had cooled enough to about 3,000 Kelvin that protons and electrons could finally bind together into neutral hydrogen atoms. Before that moment, the universe was a hot plasma and photons couldn't travel freely. They were constantly scattering off the free electrons like trying to see through fog. After what we call recombination, the fog cleared. The photons that were last scattered at that moment have been traveling freely ever since. As space expanded, those photons got stretched, redshifted until their wavelengths, originally in the visible and ultraviolet, are now in the microwave.
And they fill the entire sky. They are arriving at your face right now. about 411 of them per cubic cm passing through every cubic cm of your body every second. You are bathing in the cooled light of the early universe. You always have been. The discovery earned Pensius and Wilson the 1978 Nobel Prize and it transformed cosmology overnight. The big bang model which had been one option among several suddenly had a smoking gun. The steadystate model, which had no mechanism to predict this kind of relic radiation, was dead within a few years, and subsequent experiments only sharpened the picture. The COBE satellite in 1992 showed that the spectrum of the cosmic microwave background was a nearperfect black body, deviating from theoretical perfection by less than 50 parts per million, which is the most precise black body spectrum ever measured for anything anywhere. WAP and Plank, the satellites that followed, mapped the tiny temperature fluctuations across the sky at exquisite resolution.
The cosmic microwave background's temperature today is 2.725 Kelvin and its uniformity is staggering.
The hottest patches and the coldest patches across the whole sky differ by only one part in 100,000. And here is where I want to bring us back gently but firmly to the central question. The cosmic microwave background is the strongest single piece of evidence that the Big Bang model is correct. It confirms that the universe really was hot and dense and uniform in its early state. But, and you can probably feel where this is going, the cosmic microwave background does not tell us anything about what caused that hot dense state. It is a snapshot of the universe at 380,000 years old. The bang itself, whatever the bang was, happened earlier at energies and densities far beyond anything the photons of the cosmic microwave background can show us. The relic radiation is in a very real sense a wall. We cannot see past it with light, no matter how good our telescopes get.
The early universe before recombination is opaque. The cosmic microwave background is the surface of the fog.
Everything we think we know about what happened before that in the first 380,000 years comes from theory and from the indirect fingerprints those early epochs left on the patterns we see in the radiation. So we have confirmation that the aftermath was real. We have confirmation that the universe had a hot dense past. What we do not have and what the big bang model itself is silent about is any direct observation of what triggered any of it. The wall of photons is between us and the actual bang. Which means when we want to ask about what banged, we have to start examining the model itself, looking for the places where it strains against the data.
Looking for where the picture stops fitting smoothly. And in the late 1970s, three such places became impossible to ignore. Part five, the three cracks that should have killed it. By the mid 1970s, the Big Bang model was on the surface a triumph. Expansion confirmed, cosmic microwave background confirmed, light element abundances confirmed, the framework worked. And yet a small number of cosmologists, the kind of people who can't help picking at a thread once they've spotted it, were starting to notice that the model only worked if you were willing to swallow some absolutely outrageous initial conditions. The universe, in order to look the way it does today, would have had to start out in a configuration so improbable, so finely tuned that calling it luck would be an insult to luck. There were three of these problems specifically and any one of them taken seriously was enough to make a thoughtful physicist lose sleep. Together they amounted to a quiet crisis. The first was the horizon problem. When you look at the cosmic microwave background, what you see is a sky that is to a precision of one part in 100,000 the same temperature in every direction. Two patches of sky on opposite sides of you separated by 180° are the same temperature. This sounds harmless until you realize what it means. According to general relativity, no signal can travel faster than light.
Which means no two regions of space can be in thermal equilibrium with each other unless they have had time since the beginning of the universe to exchange light to come into contact to swap energy and even out their temperatures. And when you do the calculation for the early universe when the cosmic microwave background was being emitted, you find that two patches of sky separated by more than about one degree could not in principle have ever been in causal contact. The universe wasn't old enough. The light hadn't had time. And yet the entire sky, all 180° of it, is at the same temperature.
regions that should never have spoken to each other are agreeing on the temperature down to five decimal places.
This is the equivalent of finding 10,000 strangers scattered across continents that have never had any communication with each other, all wearing the same shade of paint on their walls to a precision of but it is so wildly improbable that any physicist looking at it has to wonder whether the model is missing something. The second problem was the flatness problem. The geometry of the universe on large scales can in principle be one of three shapes. It can be positively curved like the surface of a sphere in which parallel lines eventually meet and triangles have angles that add up to more than 180°. It can be negatively curved like a saddle in which parallel lines diverge and triangles have angles that add up to less. Or it can be flat, the boring uklidian case you learned about in school, where triangles add up to exactly 180. And which of these the universe is depends on a single parameter cosmologists call omega. The ratio of the actual density of matter and energy to a specific critical density. If omega is greater than one, the universe is positively curved, less than one, negatively curved, equal to one, flat.
And every observation we have ever made suggests that omega today is very very close to one. The universe is to within our ability to measure geometrically flat. The problem is that flatness is unstable. If you run the equations of cosmology backward, you find that omega is being driven away from one over time.
Any tiny deviation from perfect flatness in the early universe gets amplified as the cosmos expands. The way a pencil balanced on its tip gets more and more wobbly the longer it stands. For omega to be close to one today after 13.8 8 billion years of amplification. It would have had to be unbelievably surgically close to one in the very early universe.
Like one part in 10 to the 62nd close.
That is a level of fine tuning that beggars the imagination. It's the equivalent of balancing a pencil on its tip perfectly for billions of years and finding it still upright. There is no physical mechanism in the standard big bang model that would have made omega start out at exactly one. It just had to or there is no us. And the third problem was the monopole problem which is more technical but no less devastating. Many of the leading theories of how the fundamental forces of nature unify at high energies, the so-called grand unified theories, predict that the early universe should have produced enormous numbers of heavy exotic particles, magnetic monopoles in particular, particles with a single magnetic pole, north or south, but not both, which would be incredibly massive and incredibly stable, surviving from the early universe. to the present day.
According to the math, there should be loads of them. They should be detectable. They should leave signatures in cosmic ray experiments and dominate the matter budget of the universe. We have never confirmed seeing one, not a single one. There is a famous moment in the history of monopole searches on Valentine's Day in 1982 when a physicist named Blas Cabrera running a superconducting detector at Stanford recorded a single beautiful textbook event that looked exactly like a magnetic monopole passing through his apparatus just one. He has been running monopole detectors ever since in various forms and has never seen another candidate. So that one event is now generally treated as either a fluke, a glitch or charitably an unconfirmed sighting. Whatever it was, it has not been repeated. The monopoles that the early universe should have produced in vast quantities are simply not there.
And here is the pattern. All three of these problems, the horizon problem, the flatness problem, and the monopole problem share the same shape. They are all problems of initial conditions. They all require the very early universe to have started out in a state that the standard big bang model can't explain.
The universe had to have already been homogeneous across causally disconnected regions. It had to have already been almost perfectly flat. And whatever process generated heavy relic particles had to have been dramatically diluted.
The big bang model taken on its own has no mechanism for any of this. It just has to assume it. The finetuning is so extreme that some physicists started calling it a cosmic conspiracy. Either the universe was set up by some unknown agency in exactly the right configuration to produce the cosmos we see or and this is the thought that started keeping people up at night.
Something happened before the big bang that prepared those conditions.
Something earlier, something that in a single mechanism could smooth out the temperature, flatten the geometry and dilute the monopoles all at once. And in 1979 on a December night in California, a young posttock working on an entirely different problem was about to scribble two words in his notebook in capital letters that would change everything. He was going to find that mechanism part spectacular realization.
Alan Guth in 1979 was a 32-year-old particle physicist with no permanent academic job. bouncing between post-doal positions, trying to make himself useful in a field that hadn't quite figured out where to put him. He was working at SLAC, the Stanford Linear Accelerator Center, with a colleague named Henry Thai, on a deeply unsexy problem. They were trying to figure out why the universe wasn't full of magnetic monopoles, the same monopole problem we just talked about.
Tai had pushed him to think about how phase transitions in the early universe.
The kind of transitions where the laws of physics themselves shift as the temperature drops might affect the production rate of monopoles. Phase transitions in the everyday sense are familiar to you. Water freezing into ice, steam condensing into water. They happen at specific temperatures and they often involve a kind of sluggishness, a phenomenon called super cooling, where the substance can briefly persist in the wrong phase, water still liquid below freezing, before suddenly snapping into the new phase. Guth was thinking about what super cooling might do to a particular kind of field in the early universe, a scalar field that physicists associate with high energy phase transitions. And on the night of December 6th, 1979, working through equations in his notebook, he realized something. If a scalar field gets stuck in a high energy state, what physicists call a false vacuum while the universe is super cooling, the energy density of that field would behave mathematically exactly like a cosmological constant. a repulsive, anti-gravitational, push everything outward kind of energy.
And under those conditions, the equations of general relativity predict that the universe wouldn't just expand, it would expand exponentially, doubling and doubling and doubling in size on time scales of about 10 -35th seconds. A tiny region smaller than an atomic nucleus would in a fraction of a fraction of a fraction of a second balloon up to dwarf the entire observable universe. Guth opened his notebook and at the top of the page he wrote two words spectacular realization and then he doubleboxed them. Anyone who has seen a photograph of that notebook page and you can find it online will tell you that you can feel looking at it the moment somebody realized they had just touched the edge of something enormous. What Guth had stumbled onto was the mechanism we now call cosmic inflation. The idea is straightforward to state even if the physics behind it is dense. Sometime in the very early universe before the hot dense state we usually identify with the big bang a scalar field which we now call the inflaton got temporarily stuck in a high energy configuration. The energy density of that field acted like a cosmological constant driving exponential expansion for a tiny window of time somewhere between 10 - 36 and 10 -32 seconds after whatever the true beginning was. The universe doubled in size something like 60 times. The expansion factor was on the order of e to the 60th which is roughly 10 the 26th. A region the size of a proton became a region larger than the observable universe today. And what's beautiful, what made this idea spread through the physics community like fire is that this single mechanism in one stroke solves all three of the problems we just talked about. The horizon problem evaporates because the entire visible universe before inflation was a tiny causally connected region that had plenty of time to come into thermal equilibrium. Inflation then stretched that already equilibrated patch up to cosmic scales. The flatness problem evaporates because exponential expansion irons out any initial curvature. The way a wrinkled balloon becomes smooth as you inflate it.
Whatever omega started as by the end of inflation it is driven to within a hair's breadth of one no matter what.
And the monopole problem evaporates because any heavy relic particles produced before inflation get diluted spread out across the enormous new volume until their density is essentially zero. You'd be lucky to find one in the entire observable universe.
When inflation ends, when the inflaton field finally rolls down out of its false vacuum and into its true minimum, all that energy that had been stored in the field has to go somewhere. It dumps itself in a process called reheating into a hot bath of particles and radiation.
And that hot bath, that is the moment we usually call the big bang, the hot dense state. The starting condition for everything that comes after the Big Bang in this picture is not the beginning of the universe. It's the end of inflation.
It's the moment the engine that had been running on vacuum energy finally cuts out and the energy that had been pushing space apart gets converted into the matter and radiation that will eventually become galaxies and stars.
And you take a second to feel the shape of what this is saying. Everything you can see, every atom of every galaxy stretching out to the observable horizon, every photon arriving from the cosmic microwave background, every star and planet and rock and breath is in this picture the decay product of a temporary high energy configuration of an empty field. The universe was shaped by nothing. By the energy of a region of space with no particles in it, just a field sitting briefly in the wrong place. And this is not just speculation.
Inflation makes specific testable predictions. It predicts the spectrum of tiny temperature fluctuations in the cosmic microwave background. It predicts the distribution of those fluctuations on different scales. The spectral index, what physicists call n subs, should be close to but slightly less than one. The plank satellite measured it. It's about 0.965.
That matches inflation's predictions to a precision that in any other branch of science would be considered a solid confirmation. So inflation works. It plugs the holes in the big bang model.
It provides the mechanism that the original picture was missing. And it does so by reframing the entire question of what banged. Because in the inflation picture, what banged was not a singularity. What banged was the energy of empty space decaying into everything.
And once you accept that framing, you've opened a door. Because if vacuum energy can drive inflation in our universe, and if it once did, then the obvious next question, the one we have to chase, is what is that energy exactly? And what determines when it decays? And could it still be doing the same thing somewhere else? We are about to walk through that door. And on the other side, things get very strange very quickly. Part seven.
Nothing expanding into everything.
In 1964, two engineers standing in a field in New Jersey accidentally found the oldest light in the universe while trying to clean pigeon droppings off the inside of a giant horn-shaped antenna. They were not looking for it. They thought it was a malfunction in the wiring. They thought the birds were the problem. What they had actually stumbled into was a faint steady hum arriving from every direction at once at almost exactly 3° above absolute zero. The cooled afterglow of creation itself. It became almost overnight the single strongest piece of evidence that the big bang ever happened. And here is the part that should stop you cold. In 2024, 60 years after that accidental discovery, in a quiet conference room in Copenhagen, somewhere around 80 of the world's working cosmologists were asked one simple question. Was the Big Bang the beginning of time? The majority of them said no. Not maybe. Not. We're still figuring it out. No. The story you were taught in school, the one with the glowing dot and the explosion blooming into stars, is no longer believed by most of the people who study it for a living. The very same people who can point to that hum from New Jersey and tell you with mathematical certainty that the Big Bang was real have quietly stopped believing it was the beginning.
Tonight, we are going to find out why.
Hit subscribe, settle in somewhere comfortable, and stay with me to the end. Because the real story starts before the bang. I want you to actually sit with that contradiction for a moment because it is one of the strangest pieces of intellectual ground in modern science and almost nobody outside the field knows about it. The Big Bang model is by every reasonable measure one of the most successful theories humans have ever produced. It correctly predicts the expansion of the universe, the relative abundances of the lightest chemical elements, and the precise temperature and uniformity of that cooled afterglow Pensas and Wilson stumbled into in their pigeon haunted antenna. Every observation we have made for the past 60 years, with every increasingly sensitive instrument, has confirmed the basic picture. The universe really was at one point hot and dense and uniform. The math works. The data fits. By any normal scientific standard, the case is closed.
And yet, when you walk into a room of the actual experts, the people who write the papers and teach the graduate students and review each other's work, and you ask them whether the Big Bang was the beginning, most of them now say no. Not because they think the model is wrong. They think the model is right.
They think the hot, dense early state really existed. What they have stopped believing is something subtler and in some ways more interesting. They have stopped believing that the hot, dense early state was the beginning of anything. They think it was a transition, a handoff, the end of an earlier process we are only just starting to understand. The bang, in other words, was not the moment everything came into existence. The bang was the moment something that already existed turned into the universe we see.
And the something that already existed, the thing that was there before the bang, is the part nobody has finished writing down yet. This is the gap I want us to walk into through tonight. Not as outsiders peering in, but as fellow explorers taking it slowly, one piece at a time, because the gap is not a small one. It contains, depending on which physicist you ask, the entire prehistory of reality, and the candidates for what is in it are some of the most spectacular ideas anybody has ever proposed in any field ever. We are going to look at all of them patiently. The way you look at a constellation on a cold night, letting your eyes adjust until the dimmer stars start coming out.
But before we do, I want to give you a sense of the journey ahead because this is not going to be a quick conversation and I think you deserve to know what you are signing up for. We are going to start of all places with Isaac Newton sitting in 17th century England building the first real model of a universe held together by gravity and quietly running into a problem he never solved. We are going to look at why the night sky, the most ordinary feature of human existence, is actually a piece of cosmological evidence so strange that it should have told us 300 years ago that the universe could not be eternal. We are going to follow the dark sky paradox named for an obscure German astronomer named all the way to its inescapable conclusion, which is that something about Newton's universe was missing. We are going to walk into the early 20th century with Albert Einstein who in 1915 rewrote gravity itself and who immediately ran into something almost nobody warns you about in popular science. His own equations told him the universe could not sit still. They predicted mathematically that spacetime had to be either expanding or contracting. And Einstein being human did what most of us would do when our beautiful new theory predicted something that contradicted what we already believed. He fudged it. He invented a number, called it the cosmological constant, and used it to glue the universe in place. He later called it the worst mistake of his career. We will see by the end of this video that the mistake was not a mistake at all. that the same number Einstein invented and discarded has come roaring back into modern physics and may in fact be the very thing that did the banging. We are going to meet a Belgian Catholic priest named Gor Lamett who working from Einstein's own equations dared to suggest in 1927 that the universe must have started from a single dense state, a primeval atom, a cosmic egg. The reaction from the scientific community was not warm. Einstein himself reportedly told him his physics was abominable. We are going to watch slowly as the evidence began to pile up against the doubters as Edwin Hubble measured galaxies receding from us at Mount Wilson. As the universe stopped being a thing and became a process, we are going to feel what it must have felt like sitting in the 1920s realizing for the first time in human history that the cosmos had a past that was different from its present. That it had in some real sense a story. We are going to walk into a field in New Jersey, and we are going to stand next to Arno Pensius and Robert Wilson while they argue with two pigeons about a noise they cannot explain. We are going to watch them realize with growing disbelief that the noise is the literal afterglow of the early universe. Photons that have been traveling for 13.8 8 billion years arriving at a giant horn-shaped antenna because of a young telecommunications company's frustration with bird droppings. We are going to talk about exactly how many of those photons are passing through your body right now at this very second and what that strange and quiet fact says about the world you actually live in. Then we are going to step into the late 1970s into the moment when the big bang model despite all of its triumphs started to develop cracks.
Three of them specifically. Three problems that taken seriously by anyone willing to look honestly at the math were enough to suggest the entire picture had to be either modified or replaced. We will look at each one carefully. The horizon problem in which patches of the sky agree on their temperature when they should never have been in contact. The flatness problem in which the geometry of the universe is balanced on a knife edge that no physical mechanism can explain. The monopole problem in which heavy exotic particles that should be everywhere are stubbornly nowhere. We will look at how these three problems hung over cosmology like a quiet storm cloud and how they pushed the field gradually toward a moment of breakthrough that nobody saw coming. We are going to spend a long careful evening with Alan Guth, the man we mentioned at the start on the night of December 6th, 1979. We are going to sit beside him as he scribbles in his notebook the words spectacular realization doubleboxed in capital letters. We are going to walk through what he saw on that page. The idea that would come to be called inflation and we are going to understand step by step how it solves all three of the problems we just talked about in a single elegant move. We are going to come to terms with what inflation actually says, which is that the energy of empty space, of vacuum, of a region with no particles in it, briefly drove the universe to expand exponentially, doubling and doubling on impossibly short time scales. And that everything we can see, every galaxy, every star, every atom of you, is the decay product of that process. nothing in the most literal sense possible expanding into everything and then we are going to face the consequence almost nobody who built the theory wanted because the math of inflation when you follow it honestly does not give you one universe. It gives you potentially infinitely many. We will walk into the strange territory of eternal inflation of pocket universes forming continuously in a vastly larger inflating bulk of a string theory landscape with around 10 to the 500th possible vacuum states each one with different physical laws. We will look at whether any of this can be tested, what the most serious objections are, and whether a strange cold patch in the cosmic microwave background near the constellation Erodis might, just possibly be the bruise left on our universe by the impact of a neighboring one. We are going to look at the menu of pre- Big Bang proposals that physicists are currently arguing about right now, this year, in journal papers and conference rooms around the world. The no boundary proposal of Hawking and Hartle in which time itself becomes spatial near the origin and there simply is no first moment. The tunneling from nothing of Valenin in which the universe quantum mechanically appears out of literal non-existence. The loop quantum bounce in which our big bang is the rebound of an earlier contracting cosmos. The cyclic epyrotic model of Steinhart and Churro in which entire universes collide along higher dimensions in an endless rhythm. The conformal cyclic cosmology of Roger Penrose in which our universe is one of an infinite chain of aons each one smoothly becoming the next. And we are going to look at the cracks in our current best picture. the tensions in the data that suggest to the people who study this for a living that something deeper is hiding underneath. The Hubble tension where the universe seems to be expanding at two different rates depending on how you measure it. The strange new results from Desi suggesting that dark energy may not be constant after all that the very thing driving the universe apart might be evolving with time. the cosmological constant problem where the energy of empty space is roughly 10 to the 120th times smaller than the simplest theory predicts. Any one of these is a clue. Together, they may be the first whispers of whatever larger system the big bang is embedded inside of. By the end of tonight, we will not have a final answer to the question we started with. I want to be honest with you about that upfront the way a good guide would be honest with you about how long the trail is. Nobody has the final answer. The frontier is still open, but we are going to walk all the way to where the frontier currently is together and we are going to look out at what lies beyond. And the view, I promise you, is worth the walk. So again, hit subscribe if you have not already and find a comfortable chair and turn off any notifications that might pull you out of this. Pour something warm. Settle in. We are about to start at the very beginning of how we got to this question 300 years ago with a quiet Englishman who looked up at the night sky and noticed it was darker than his own physics said it should be. Part eight. the consequence no one wanted. In 1983, the Russian-American physicist Andre Lindai took Guth's basic insight and pushed it further than Guth himself had been willing to go. Guth's original model, the one he had scribbled spectacular realization about in his notebook a few years earlier, what he later called old inflation, had a problem. It was, in Guth's own words, a model that worked beautifully right up until it had to end. The way he had set it up, with the inflaton field stuck in a metastable false vacuum and tunneling out into the true vacuum, was elegant in principle, but ungraceful in practice.
The bubbles of true vacuum that formed during this tunneling were supposed to expand and collide and merge smoothly stitching together into the hot uniform universe we now observe. But the math refused to cooperate. The bubbles when you ran the equations honestly did not merge cleanly. They formed pockets of empty space between them. The reheating, the conversion of vacuum energy into particles and radiation would happen unevenly. The result would be a universe that was lumpy, jagged, full of empty cavities and walls between bubble walls.
Nothing like the smooth, flat, uniform cosmos we actually see. Lindai working independently in Moscow proposed an alternative he called chaotic inflation and it was a kind of intellectual escape hatch. Instead of imagining the inflaton field stuck at a single high energy point and having to tunnel out, Lind said, "What if the field starts out in any of a wide range of possible high energy configurations? Different patches of the early universe might have the field at different values. And in each patch where the field happens to be high enough, the field rolls smoothly down its potential like a marble rolling slowly down the inside of a wide bowl, generating inflation as it goes. No tunneling required, no bubble collisions to worry about. The graceful exit problem simply dissolves because the end of inflation in each patch is a smooth continuous process rather than an abrupt phase transition. And it worked. Within a few years, chaotic inflation had become the dominant paradigm in cosmology and it remains in various refined forms the framework most working physicists rely on today. But then in 1986, Lind took a step that nobody, including arguably Lind himself, had been quite ready for. He showed that in chaotic inflation, the process never globally ends. He showed with the equations open in front of him that once inflation begins, it does not stop. Not anywhere, not ever. Locally, it can end. In any given patch, the inflaton field can roll down to its true minimum and reheat into a hot big bang. But globally, taken as a whole, the inflating volume of the cosmos always grows faster than the volume that has stopped inflating.
Inflation once started is an eternal phenomenon. And here is the argument and I'll walk you through it carefully because it's the kind of thing that sounds insane until you follow the logic at which point it becomes something more disturbing than insane. It becomes terrifyingly reasonable. The inflaton field while it is rolling down its potential is not behaving like a smooth classical object. It is a quantum field and it is subject like any quantum field to fluctuations, random kicks up and down on top of its smooth classical descent. In any given region of space, in any given moment, the field can be jolted slightly higher or slightly lower than where it would otherwise be. In most regions, those fluctuations are small. The classical descent dominates.
The field continues rolling down.
Inflation eventually ends in those regions. The energy converts into particles and radiation and a hot big bang occurs and a universe much like ours forms. Standard story, tidy ending.
Galaxies, stars, planets, cosmologists arguing about pizza toppings at conferences. The whole familiar package.
But, and this is where everything starts to wobble. In some regions, by random chance, a quantum fluctuation will kick the field not down, but up back to a higher energy. And in those regions, inflation does not end. It continues.
The field now sitting at a higher value has more potential energy to burn through and the exponential expansion rolls onward. Now you might think fine eventually those regions will also roll down and inflation will end there too and it will in any individual region given enough time. But here is the kicker. Inflation is exponential. The volume of any still inflating region grows by enormous factors on impossibly short time scales. So even though some regions are constantly dropping out of inflation and forming hot big bangs, the regions that are still inflating are growing in volume so much faster that they always dominate. The total inflating volume is always increasing.
There is always more inflation happening than ending and it never ever stops.
This is the picture we now call eternal inflation. And I want you to actually sit with what it implies because it is a profound shift in what the word universe even means. The universe in this view is not a single thing that began at a single moment. It is not a finite closed bounded entity that came into existence and is now playing out its history. It is a vast eternally inflating bulk within which pocket universes like ours are constantly forming. Each pocket is a region where locally inflation ended and a hot big bang occurred. Each pocket has its own cosmic microwave background, its own galaxies, its own structure formation, its own potential for chemistry and biology and observers, if any of those things are possible there.
And between the pockets the bulk continues inflating forever. There is no global beginning. There is no global end. Inflation as a process is eternal in both directions or at least eternal into the future with the past structure depending on technical details that physicists are still vigorously arguing about. The Big Bang, our Big Bang, the one that gave rise to everything we can see, is not the beginning of anything.
It is one of countless local events. It is the moment our particular pocket cooled out of the bulk. It is, if you want a homely analogy, a single raindrop condensing out of a vast and indifferent atmosphere. And there is a further wrinkle, one that takes the picture from strange to almost unbearably strange. In string theory, which is currently the most developed candidate for a theory of quantum gravity, there are not just one or two possible vacuum states for the universe to settle into when inflation ends. There are not even thousands or millions. Some estimates suggest there are roughly 10 to the 500th distinct vacua in the so-called string landscape.
10^ the 500. I want you to actually sit with that number for a moment because I think we throw around large numbers in physics so casually that they stop landing. The number of atoms in the entire observable universe, every atom in every star in every galaxy out to our cosmic horizon is somewhere around 10 to the 80th. The number of possible vacuum configurations in string theory by these estimates exceeds the number of atoms in the observable universe not by a factor of 10 or a thousand or even a million but by hundreds of orders of magnitude.
There is no human intuition that can hold this number. We don't have a category for it. It is in a very literal sense beyond our cognitive equipment.
And in each of these different vacua the laws of physics would be different, not slightly different, substantially different. The values of the fundamental constants, the masses of the particles, the strengths of the four forces, the number of stable atomic configurations, the chemistry that's possible, if any chemistry is possible at all. Each pocket universe in eternal inflation might land by chance in a different vacuum out of that vast landscape. Each pocket might have its own physics, its own chemistry, its own possibilities or impossibilities for the kinds of structures we'd recognize as stars or planets or living things. This is the multiverse. And I want to be very precise about which multiverse we're talking about because the word has been thrown around so loosely in popular culture that it has lost most of its meaning. We are not talking about the comic book version with parallel timelines where you made different choices and there's a version of you who became a concert pianist instead of going to law school. That is a fun idea but it has nothing to do with what physicists are talking about. We are talking about the cosmological version which is a genuine mathematically consistent prediction of inflation combined with string theory. An infinite or near infinite collection of pocket universes embedded in an eternally inflating bulk with vastly different physical laws in each one. And our universe, the one we inhabit, with its specific values of the constants of nature, the ones that allow stable hydrogen atoms and longived stars, and the chemistry of carbon and water, and you sitting wherever you are listening to this, may simply be one of the lucky ones, one of the small subset where the conditions happen to allow stable atoms and stars and chemistry and consciousness. The other pockets where the constants are different may be sterile or short-lived or so structurally unlike anything we can imagine that the word universe barely applies. Empty cosmic basement, failed drafts, dead worlds where stars never formed and matter never condensed. This line of reasoning is what's called the anthropic argument. And it is frankly a kind of physics nobody really wanted.
The dream the one that goes back through Einstein and Newton and Kepler and beyond was that the laws of physics would turn out to be the only logically consistent laws possible that the values of the constants of nature would be determined by some deep beautiful principle and that one day a clever theorist would derive them from first principles. The way you derive the area of a circle from pi and the radius that the universe would be necessary in some philosophical sense that nothing about it could have been otherwise. The multiverse picture says sorry no the universe is not necessary. It is one of an enormous possibly infinite family.
The reason the constants have the values they do is not because they had to, but because in a multiverse with all possible values represented, observers like us only arise in the small subset of pockets where the values permit observers to exist in the first place.
We see the constants we see because we couldn't see anything else. We are not at the center of a uniquely tuned cosmos. We are at the bottom of a probability filter looking up. There is something almost humbling and something almost vertigenous about that. The criticism of this view and it is a serious criticism that you should take seriously even if you ultimately decide to accept the multiverse picture is that it appears to be untestable. We cannot even in principle travel to another pocket universe. The other pockets are causally disconnected from us. The space between them is inflating faster than light. And so there is no way for any signal, no light, no particle, no gravitational wave, no information of any kind to cross from one pocket to another. They are forever mathematically beyond reach. A theory that posits unobservable entities to explain the things we do observe is some philosophers of science argue not really a scientific theory at all. It is metaphysics dressed up in equations. It is the kind of thing that in another era would have been considered theology rather than physics. and reasonable physicists, the kind who take both math and method seriously, disagree about whether this is a fatal objection or merely an uncomfortable feature of where the equations have led us. There is though one possible exception, one tantalizing crack in the idea that we can never see other pockets. There is a region of the cosmic microwave background in the constellation Eridanis in the southern sky that is significantly colder than the surrounding sky and unusually large in extent. It is called with admirable bluntness by cosmologists the cold spot and it has been a puzzle since it was first identified clearly in the W map data and then confirmed in higher resolution by plank. There are conventional explanations having to do with a possible enormous void in the foreground galaxy distribution, a kind of cosmic cavity through which the microwave photons passed and lost a little bit of energy along the way. The conventional explanation is currently the favored one and I want to be honest about that. But there have also been speculative proposals, most famously by the cosmologist Laura Msini Hton, that the cold spot could be something else entirely. A bruise, a scar left on our cosmic microwave background by the impact of a neighboring pocket universe, brushing against ours during the inflationary epoch, leaving its faint imprint on the relic radiation we still measure today. I want to be very clear here. This is speculative. It is not confirmed. The data does not require this interpretation. The conventional explanation foreground voids is currently considered more likely by the majority of cosmologists working in the field. But it is the kind of thing that if it ever did get nailed down, if a direct, repeatable, independently verified observational signature of another pocket universe ever appeared in our data would be one of the most extraordinary discoveries in the history of science. A direct observational fingerprint of another universe. Proof that we are not alone in the bulk. proof that the multiverse is not just a logical consequence of equations but a real physical structure we have somehow glimpsed. What I want you to sit with before we move on is the emotional weight of where we have arrived. We started this video with a question. What banged at the big bang? And following the equations honestly with no particular agenda, neither religious nor atheistic nor mystical. just patient and careful and willing to go wherever the math led. We have ended up with a picture in which the bang was the local end of an episode of inflation in which inflation does not globally end anywhere. In which there are likely innumerable other pockets where inflation has ended differently and produced cosmic neighborhoods we can never see. And in which our universe, our entire observable universe, the one with 13.8 8 billion years of history and 100 billion galaxies and us in it is a small finite local feature in a much larger possibly infinite structure that is still going right now. Even as you listen to this, the bulk is still inflating. New pockets are still forming. The cosmos in the largest sense the word can carry is not winding down.
It is just starting. The hard limit of this picture, the thing nobody can promise you is that those other pockets are forever beyond our ability to reach.
We cannot visit them. We may never even confirm they exist with the kind of certainty we have for say the cosmic microwave background or the expansion of space. We can only follow the math and notice that if the math is right, they're there. So we are sitting inside a local event in a vastly larger system and what we call the universe is just our pocket, the neighborhood, the block.
The little finite plot of cosmic real estate that happens to be ours. Which raises finally the only question left worth asking. The question we have been circling all night. the question that the entire history of cosmology from Newton's static cosmos to the dark night sky to Einstein's blunder to Hubble's galaxies to Pensas and Wilson's pigeons to Goth's notebook to Linda's eternal inflation has been driving us toward if inflation isn't really the beginning either if even inflation is just a stage on top of something deeper then what is the actual bottom what is the universe we are ultimately ely sitting inside of part n if inflation isn't the beginning what is we have arrived you and I at the frontier this is the part of the conversation where the edges of certainty start dissolving where the data thins out where the equations stop giving you synjexes and start giving you menus the candidates for what came before inflation begin to multiply here and I want to walk you through the most serious of them not as a list of curiosities not as a tour through scientific exotica, but as competing answers to the question we have been chasing since the very first sentence of this video.
Because each of these proposals in its own way is a serious physicist's attempt to write the missing first chapter. To put words on the blank page to describe what is happening on the other side of the boundary we call the big bang. None of them is currently confirmed. None of them has crossed the line from speculation into established fact. All of them are mathematically consistent with what we currently know. And the discrimination between them, the moment when the data finally sharpens enough to tell us which one is right, if any of them are right, is going to require physics we don't yet have. Possibly instruments we haven't yet built.
Possibly entire theoretical frameworks that haven't yet been invented. So treat what follows the way you would treat a serious detective story where the suspect list has been narrowed but the case is still open. The first candidate and probably the most famous is the no boundary proposal developed in the early 1980s by Steven Hawking and James Hartell. It is a strange and beautiful idea and to understand it you have to be willing to let go of one of the most basic assumptions you carry around which is that time and space are different kinds of things. The idea in its essence is that if you go back far enough toward what we usually call the beginning, time itself stops behaving the way you think it does. In the no boundary proposal, time near the origin does not behave as a temporal dimension at all. It becomes mathematically a fourth spatial dimension, indistinguishable from the three you already move through every day. The up, the forward, the sideways.
The distinction between time and space dissolves.
There is no first moment. There is no edge, no boundary, no point at which you can stand and say this is where it all started. This is the moment before which there was nothing. Hawking liked to compare it to the surface of the earth and the analogy is the most useful one I have ever heard for grasping the idea.
So let me walk you through it slowly.
Imagine you are walking south. You can walk south from anywhere on the planet, anywhere at all. And as you walk, the latitude lines tick by and the climate gets colder. And eventually, after enough walking, you arrive at the South Pole. Stand there. Now ask yourself the obvious question. What is south of here?
The answer, of course, is nothing. Not because there is some mysterious wall blocking your path. Not because someone has put a fence around the south pole, but because the geometry of a sphere simply doesn't have a south of the south pole. There is no such direction. The question is malformed. It uses words that don't apply to the place you're standing. The no boundary proposal says exactly the same thing about time near the beginning of the universe. The question, what came before the universe?
Has no answer. Not because the answer is hidden. Not because we are too ignorant to know, but because the geometry doesn't have a before. There is no such direction. The universe is finite in time, but it has no first moment. It is bounded, but unbounded, compact, but without an edge. It is, in Hawkings own framing, a self-contained mathematical object that does not require anything outside of it to explain its existence.
And if Hawking and Hartle are right, then the question we have been asking all night, what existed before the Big Bang is the cosmic equivalent of asking what is south of the South Pole. The question is real. The answer is that there is no answer because the question is asking about a thing that does not exist. The second candidate is the tunneling from nothing proposal developed by Alexander Valenin working independently of Hawking and Hartle around the same time in the early 1980s.
Villain's idea is in some ways more radical than the no boundary proposal because it takes the word nothing more seriously than almost any physicist had taken it before. Valenin's claim is that the universe quantum mechanically tunnneled into existence from a state of literal nothingness. No space, no time, no matter, no fields, no laws of physics in the usual sense. A very specific kind of nothing. The kind that has no properties because there is nothing there to have properties. To understand why this is even a coherent idea, you have to know about quantum tunneling. In quantum mechanics, particles can do something that in classical physics would be flatly impossible. They can pass through energy barriers that by the rules of ordinary mechanics they should not have enough energy to cross. The particle does not climb over the barrier. It does not break through it.
It simply by virtue of the strange probabilistic rules of the quantum world has some chance of being found on the other side. This is not a thought experiment. Quantum tunneling is real, observable, and is the basis for things like nuclear fusion in the sun, the operation of certain types of microscopes, and the eventual decay of unstable nuclei. It happens. We have measured it. We have built devices that depend on it. Valenin proposed that the universe itself treated as a quantum object tunnneled from non-existence to a tiny inflating but nonzero state the universe was not and then with some calculable probability the universe was inflation took over from there and the entire history we have been describing the bang the cooling the structure formation all of it unfolded from that initial tunnneled state. The arithmetic of how nothing tunnels into something is predictably contentious. There are deep arguments about what the relevant probability calculations even mean, about what it means for nothing to have a probability of becoming something, about whether the words we are using have content or are just sounds we have arranged into mathematical syntax. Some physicists, Valenin among them, defend the calculations as well.
Others find the whole business philosophically suspect. But the idea has stayed alive in serious physics for 40 years. In part because it has the appealing feature of not requiring any prior structure, no preceding universe, no eternally inflating bulk, no previous eon, just a quantum origin from genuine emptiness. If Villenin is right, the universe really did come from nothing.
The question we have been asking what was there before has the answer that nothing was and the universe nevertheless found a way. The third candidate is the loop quantum bounce championed by Abhee Ashtikar and a community of theorists who have been working on it for several decades now.
To understand the loop quantum bounce, you have to know a little bit about the underlying theory called loop quantum gravity which is one of the leading attempts to construct a quantum theory of spacetime. It is in some ways an alternative to string theory and it takes a very different approach to the problem. In loop quantum gravity, space and time themselves are not smooth. They are made of discrete units like pixels on the smallest scales. There is a smallest possible volume of space. There is a smallest possible interval of time.
The continuous infinitely divisible spaceime of Einstein's general relativity is in this picture an approximation that breaks down when you zoom in far enough. The smooth fabric is on close inspection a fine mesh. And when you apply loop quantum gravity to cosmology, when you take the equations and run them backward toward what classical relativity calls the big bang singularity, something extraordinary happens. The singularity disappears. The infinite densities and infinite curvatures that signal the breakdown of classical general relativity simply do not occur in the loop quantum picture.
Instead, the discreetness of space introduces a kind of effective repulsive force at extreme densities. A quantum gravity pressure that turns on only when the density gets close to the plank scale. The contracting universe instead of collapsing to a point and producing the singularity bounces. It rebounds.
The contraction reverses. The cosmos snaps outward. And what we see as the big bang is in this picture that rebound, the hot dense state we observe is not a beginning. It is the moment a previous contracting cosmos hit its minimum size and bounced back outward into our expanding cosmos. Everything that happened before the bounce was the long death of a previous universe. A universe much like ours. billions of years of stars and galaxies and possibly observers. All of it contracting toward maximum density and then mediated by quantum gravity snapping outward into us. There was a before. The before was a universe just like this one, running backward, ending the way ours might one day end in a great convergent collapse that doesn't actually collapse, but rebounds. We are not the first cosmos.
We are the latest member of a much longer sequence and the bang at our beginning is the bounce at the end of someone else's. The fourth candidate is the epyotic or cyclic model developed primarily by Paul Steinhard and Neil Turo and rooted in string theory's concept of higher dimensional brains.
The word epyotrotic comes from a Greek term meaning out of fire. And the picture it describes is in its way the strangest one yet. In this model, our entire universe, every galaxy, every star, every cubic cm of space we have ever observed is a three-dimensional brain embedded in a higher dimensional space. And we are not alone in that higher dimensional space. Another parallel brain sits some small distance away from ours, separated by a tiny gap in the extra dimension. The brains are attracted to each other by something analogous to gravity acting through the higher dimensions. Every so often on a time scale of trillions of years, the brains drift toward each other and collide. The collision is what we experience as a big bang. The energy of impact deposited across the brain generates the hot, dense state that begins our cosmic history. The brains then separate, drifting apart again, and the matter on each brain proceeds through its own evolution of expansion and cooling. Galaxies form, stars burn.
Eventually, after enough time, the brain has expanded so much that everything is diluted to near nothing. The cosmos has cooled to nearly absolute zero. And the residents of that brain, if any are left, are watching their universe fade out. And then slowly the brains are drawn back together for the next collision. The cycle repeats forever, or at least for a very, very long time.
There is no first bang in this picture.
There have been infinitely many or close to it. We are simply living in the aftermath of the most recent. The big bang you have been taught about is just one collision in an unending series. The fifth candidate and this one is more elegant in a strange almost mystical way is conformal cyclic cosmology. The brainchild of Roger Penrose. Penrose noticed something that most physicists had not or had not taken seriously about the geometric structure of the very early universe and the very late universe. The very early universe just after a big bang has a particular property. It is dominated by radiation and the masses of particles are negligible compared to their energies which means there is no real notion of scale. There is nothing to measure distances against. The universe in those moments has a kind of geometric homelessness. And the very late universe, the one we are slowly heading toward, has the same property. After all stars have burned out, after all matter has decayed, after all the protons themselves have on time scales beyond comprehension dissolved into lighter particles, the cosmos is dominated by a thin gr of photons spreading through everexpanding space. No mass, no scale, just radiation. The two states, the very beginning and the very end, look from the right mathematical angle geometrically identical. Penrose argued that if you allow yourself to perform a mathematical transformation called a conformal rescaling, which essentially throws away information about absolute size while preserving angles and shapes, the late state of one universe and the early state of another are geometrically equivalent. They are the same object viewed from different scales. The end of one universe smoothly becomes the beginning of the next. The cosmos goes through infinite aons. Each one ending in an infinitely diluted radiation soup that geometrically becomes the hot dense start of the next aon. There is no first aon. There is no last. The universe is an infinite chain, an unending auraoros of cosmic generations. and our big bang is just the most recent link in it.
Penrose has even claimed controversially to see direct evidence for this picture in the cosmic microwave background. He and his collaborators have argued that there are concentric circles of low temperature varants in the relic radiation which they interpret as the imprints of super massive black hole collisions from the previous Aon leaking through the conformal boundary into ours. Most cosmologists disagree. The claim remains contested and the evidence is at best suggestive rather than conclusive. But it is the kind of claim that if it ever did get nailed down would be one of the most extraordinary discoveries in the history of science, a direct observational fingerprint of a previous universe. These five proposals, the no boundary, the tunneling from nothing, the loop quantum bounce, the epyotic cycle, and conformal cyclic cosmology are not the only candidates on the menu, but they are the most developed, the most thoroughly worked out, the ones with actual mathematical structure underneath them rather than just handwaving and hopeful adjectives.
And I want you to notice something about them, something that I think is more important than any of the individual proposals because it tells you something about where physics has actually arrived. They disagree wildly on what came before. They disagree on whether there was a before at all. They disagree on the geometry of time, on the discretetness of space, on the role of higher dimensions, on the nature of the cosmic cycle. But they all agree on one thing. None of them treats the singularity of classical general relativity as a real physical object.
None of them says yes, there really was an actual moment where density was infinite and time had a sharp boundary and reality just popped into existence at a single point. They all replaced that moment with something else. a smooth transition, a bounce, a tunneling event, a previous aon. Each one is a different first chapter, but they all agree that the first chapter exists. The boundary we used to call the beginning is in every one of these pictures just a chapter break in a longer story. The discrimination between these proposals is currently beyond our observational reach. They make different predictions.
In principle, they differ on the spectrum of primordial gravitational waves we should be able to detect with future instruments. They differ on the statistical properties of cosmic microwave background fluctuations at the very largest and very smallest scales.
They differ on the existence of certain rare features, certain kinds of cosmic relics, certain patterns in the distribution of matter on the sky. But the predictions are subtle, frustratingly subtle, and our instruments are not yet sensitive enough to tell them apart. We may in coming decades with better gravitational wave detectors like LISA and the next generation of groundbased observatories, with more sensitive cosmic microwave background experiments, with surveys mapping the largest scales of the cosmos in finer and finer detail, finally start to rule some of them out. Or just as likely, we may find that the data is consistent with several at once and that picking between them requires advances in theoretical physics that nobody has yet made. What I want you to take from this stretch of the conversation is the shape of where physics actually stands tonight on the actual question of what banged. We do not have an answer. We have a menu. The menu has at least five entre possibly more. All of them mathematically serious. All of them backed by working physicists with real reputations.
None of them confirmed. None of them refuted. We are at the same place in some ways that astronomers were before Hubble took his first photograph at Mount Wilson. We have models. We do not yet have decisive observations. And while we wait for the observations to catch up, the models keep getting more interesting, not less. The frontier is open. The frontier is being actively explored. We just have not yet built the instruments to map it. Part 10, the cracks in the modern picture. Before we close out this conversation, I want to bring you back from the frontier and into something more immediate. Because while cosmologists argue in journals and at conferences and over late night beers in physics departments about pre big bang models, the standard picture of cosmology, the one that includes inflation and dark matter and dark energy and the whole framework we've been carefully building up over the course of this video, is itself starting to show some cracks, anomalies, tensions, places where the data at the level of precision we now have, the precision that the satellites of the past two decades have given us, doesn't quite fit the model. The picture is straining at the seams. And these tensions matter, not just for their own sake, not just as technical curiosities for specialists, but because they may be the first whispers of whatever lies beneath, of whatever bigger system the Big Bang is embedded inside. They may be clues to the deeper picture. The one we have been chasing all night. The one whose first chapter is still missing. So let's look at three of them carefully because each of them is a thread and pulling on any of them might unravel something very large. The first is the Hubble tension and this one has been keeping cosmologists awake for several years now. It is the kind of thing that when you first hear it sounds technical and dry, but the more you sit with it, the more unsettling it becomes. The Hubble constant, the parameter that describes how fast the universe is expanding right now, can be measured in two very different ways. The first way, the local way, is to look at nearby galaxies and carefully calibrate their distances using a chain of standard candles. Starting with the Sephiid variable stars Henrietta Levit first cataloged a century ago, then climbing up the cosmic distance ladder through type supernova and seeing how fast each galaxy is receding from us. This is direct measurement. You look at the universe today. You measure what it is doing and you write down the answer. The team that does this most carefully, the SH0ES collaboration led by Adam Ree who won a Nobel Prize for the discovery of accelerating expansion in 1998 gets a value around 73 km/s per mega parc. The second way, the early universe way is completely different. You take the cosmic microwave background, the same fossil light Pensas and Wilson stumbled into in their pigeon haunted antenna, and you fit the standard cosmological model to the precise pattern of temperature fluctuations, the plank satellite mapped across the sky. The model tells you what the universe was doing 13.8 billion years ago, and then you let the equations evolve forward in time to figure out what the expansion rate should be today. That gives you a value around 67 km/s per mega parc.
These two numbers should agree. They are not measurements of two different things. They are measurements of the same physical quantity taken from two different ends of cosmic history. They are supposed to converge. They do not converge. The discrepancy is about five sigma which in physics speak means the probability of it being a statistical fluke is essentially zero. To put that in context, 5 sigma is the threshold physicists use to claim a new discovery.
It is the standard for something being officially real rather than a noise artifact. The two Hubble values, in other words, disagree at the level where if they were a new particle in a collider, we would already be holding press conferences and writing Nobel speeches. Something is off. Something is genuinely structurally off. There are essentially two possibilities. Either there is some unrecognized systematic error in one of the measurements, some subtle calibration issue that nobody has caught yet, some flaw in the chain of standard candles, or in the modeling of the cosmic microwave background, or the standard cosmological model is wrong in some way between the early universe and the late universe. And the second possibility is the one cosmologists are increasingly taking seriously because the systematics on both measurements have been audited and reodited and audited again by independent teams using different techniques and the disagreement persists. It does not go away. It has, if anything, gotten more solid as the data has improved. So the suspicion is growing that the model itself has a gap that something happened between the early universe and the late universe that we are not capturing. New physics possibly involving dark energy and how it has evolved. Possibly involving the very early universe before inflation ended. Possibly involving some entirely new component nobody has yet considered. It could be, in other words, a clue to the deeper picture. The Hubble tension may be the universe quietly informing us that the standard picture is incomplete, in exactly the way the dark night sky once informed Newton's contemporaries that the eternal static cosmos was incomplete. The second tension comes from Desi, the dark energy spectroscopic instrument perched on a telescope at Kit Peak in Arizona, whose results in 2024 and 2025 have been quietly seismic in the way certain results in physics are seismic before the popular press has noticed. Desi is mapping the positions of millions of galaxies with extraordinary precision, building a three-dimensional atlas of the cosmos at multiple distances in order to probe how dark energy has behaved over cosmic history. The technique is called barriion acoustic oscillation measurement and it uses faint pressure waves frozen into the distribution of galaxies, ancient ripples from the early universe that act as a kind of cosmic ruler. By measuring how those ripples appear at different distances, you can reconstruct how the expansion history of the universe has actually played out. And the data Desi has released suggests tentatively but strongly something that nobody really expected. Dark energy may not be a constant. The energy density of dark energy, the very thing driving the universe apart, may be evolving with time. It may have been somewhat denser in the past and may be decreasing now.
This is a problem and you can probably feel why if you have been paying attention because the simplest description of dark energy, the framework everyone has been using since the discovery of accelerating expansion is the cosmological constant. The same lambda Einstein invented to keep the universe still and then called his greatest blunder. The same lambda we resurrected when we discovered the universe was actually accelerating apart.
And a cosmological constant by definition has to be exactly constant.
It is built into the math. If dark energy is evolving, then the cosmological constant is not a constant.
Which means we are not dealing with the simple lambda picture anymore. We are dealing with something more complicated.
A dynamical scalar field perhaps very similar in structure to the inflaton field that drove inflation in the early universe but operating now at a much lower energy and a much slower pace.
Some physicists have started calling this idea quintessence after the fifth element of ancient cosmology. If Desi's results hold up and the next few years of additional data will tell us whether they do, it would mean something genuinely profound. It would mean that the dark energy of today and the inflationary energy of the early universe are not just analogous, not just two examples of the same general kind of vacuum energy. They might be the same kind of thing, the same scalar field behaving differently at different epochs, the same engine running at different speeds. Inflation in this picture would be one extreme of the phenomenon. And our current accelerating expansion would be another. The bang, in other words, and the slow tearing apart of the cosmos that we are living through right now might be two acts of a single underlying drama. The thing that drove the universe to inflate at the very beginning may be the same thing that is slowly and quietly driving it to accelerate. Now we may be watching in the data the long tail of whatever banged. The third tension is in a way an absence rather than a discrepancy. It is a thing we have been looking for and not yet finding and the not finding is itself becoming meaningful. We have been searching with increasingly sensitive experiments for a particular kind of fingerprint inflation should have left in the cosmic microwave background. It is called Bode polarization and it is the signature of primordial gravitational waves ripples in spaceime generated during inflation itself that should have polarized the cosmic microwave background photons in a very specific swirling twisting pattern across the sky. If you imagine a polarization map of the sky as a field of tiny arrows, the B modes are the curls in that field. the places where the arrows form little vortices and they are produced only by genuine gravitational waves not by any other effect we know of they are inflation's smoking gun the amplitude of these B modes characterized by a parameter called R the tensor to scalar ratio depends on the energy scale at which inflation occurred higher energy inflation produces stronger B modes the current upper limit from the bicep and kek array collaborations operating at the south pole is R less than 0.036.
We have not detected B modes. We have only set upper limits, increasingly tight upper limits that are now starting to constrain which kinds of inflation are possible. The simplest models of inflation, the ones theorists have favored for decades, predict our values right around where we are now starting to look. We are getting close. The instruments are nearly sensitive enough.
A detection in the next decade would be one of the most extraordinary discoveries in the history of physics.
It would be the strongest direct evidence of inflation we have. It would be the first time we had measured a direct signature of the bang itself rather than its aftermath. A nondetection or a detection at a much lower level than expected would force us to rethink which kind of inflation actually happened which would in turn affect every pre big bang model that depends on inflation as part of the picture. It would be another constraint another window into the bigger system.
The B mode search is one of the few experimental probes we have that reaches behind the cosmic microwave background behind the wall of photons into the inflationary epoch itself. Whatever it finds or fails to find will reshape the conversation and then hovering over all of these tensions like an ancient unsolved riddle is the cosmological constant problem. The same problem we mentioned earlier in this video. The energy density of empty space, which we measure to be very small but non zero, is roughly 120 orders of magnitude smaller than what the simplest quantum field theory calculation predicts. Let me try to convey what that number means because it has lost its sting through repetition.
120 orders of magnitude. The size of the observable universe in meters is about 10 27th. The size of an atomic nucleus is about 10 to the -15th.
The ratio between those two, the cosmos and the nucleus, is roughly 42 orders of magnitude. The discrepancy between predicted and measured vacuum energy is three times worse than that. It is so large it is almost a joke. We have no idea why empty space has the energy density it does. We have no derivation.
We have no first principles argument. We just have a measurement sitting there daring us to explain it. And the measurement disagrees with theory by a number so large it dwarfs almost any other gap between expectation and observation in the history of science.
What I want you to feel when you take these tensions together, the Hubble disagreement and the desi hint and the missing be modes and the absurd cosmological constant is a particular kind of intellectual queasiness.
Modern cosmology is a triumph in many ways. We have a picture of the universe that fits enormous amounts of data from the cosmic microwave background that the plank satellite mapped to a precision of micro Kelvin to the distribution of galaxies in three dimensions out to billions of light years to the abundances of the lightest elements that match our nucleiosynthesis predictions to within a fraction of a percent to the accelerating expansion confirmed across multiple independent techniques. The model called the lambda cold dark matter model works astonishingly well. It is one of the great intellectual achievements of the species. And yet at the level of precision we now have, the precision that has only become possible in the last decade or two, that picture is starting to fray. Not catastrophically, not in a way that overturns the fundamentals, but in a way that suggests there is something underneath, something we haven't seen yet. something that might explain why the two Hubble constants disagree. Why dark energy seems to be evolving rather than sitting still. Why the cosmological constant has the absurd value it does.
Why inflation looks the way it does. Why the universe is fine-tuned in the specific ways it is fine-tuned. The tensions could be all of them together.
The first hints of the deeper layer, the bigger system, the thing the Big Bang is embedded inside, the structure we have been trying to glimpse this entire conversation. We do not yet know what it is. We may not know in our lifetimes, but we know it is there because the cracks tell us so. The model is talking.
We just have to keep listening. Part 11.
What are we actually sitting inside of?
So, let me bring us all the way back back to the question we started with, which was what existed before the Big Bang and which I told you we wouldn't be able to fully answer, but which I promised we would walk to the edge of.
We are at the edge. Let me tell you what the view from here actually looks like.
The Big Bang, as you were taught it in school, almost certainly never happened in the way the textbook implies. There was no singular moment where everything came into existence from nothing. The hot dense state we call the big bang was real. But it was not the beginning. It was a transition. The end of an earlier process almost certainly inflation in which the energy of a scalar field decayed into the particles and radiation that became everything you can see. The bang, in other words, was the conversion of vacuum energy into matter. The thing that banged was empty space behaving in a specific way in a region we cannot directly observe billions of years ago.
And that vacuum energy did not come from nothing. It came from the conditions of an even earlier epoch. An epoch that is currently beyond our ability to probe.
What that earlier epoch was, what the universe looked like before inflation is what the menu of pre- Big bang proposals is trying to answer. It might have been the smooth boundaryless geometry of Hawking and Hartle where time near the origin becomes spatial and there is no first moment. It might have been the quantum tunneling from nothing of Valenin. It might have been the bounce of a previous contracting universe mediated by loop quantum gravity. It might have been the collision of higher dimensional brains in an endless cycle.
It might have been a previous aonom, an entire prior cosmos that in its asimtotic radiation dominated state smoothly became the hot dense start of ours. We do not know which. We may never know which in our lifetimes. But we are increasingly confident as a field that some kind of earlier epoch existed because the alternative that the universe popped into existence from absolutely nothing at a sharp moment in time is no longer the simplest or the best supported picture. And the big bang in this reframing is not really an event in the way you think of events. It is a boundary condition. It is the surface on which we set our initial data for the equations that describe everything since. It is the limit of what we can see directly. The wall behind which the cosmic microwave background hides. It is real. It is well confirmed in the sense that the conditions at that boundary are the ones that produce the universe we observe. But it is not the beginning. It is more accurately the end of our ignorance. the line beyond which our observational instruments fail and our theoretical knowledge thins out into competing speculations. There are philosophical implications to this that I want you to sit with because they are not small. If the big bang is not the beginning, then it is possible that the universe has no beginning at all. Time itself as a concept may not extend infinitely backward, but it also may not have a sharp first moment. The very category of beginning which feels so natural to us as creatures who are born and die and watch movies that have opening credits may not be the right framework for thinking about the cosmos.
The universe might be more like a mathematical structure eternal in some sense whose properties we describe but whose existence does not require a starting event. Or it might be infinite into the past with our region just one of many. Or it might be cyclical or it might have a structure of time so different from our experience that the words we use to describe it are inadequate. Whatever it is, the simple narrative of in the beginning there was nothing and then suddenly there was something is not where modern physics has landed. And while we are sitting here having this conversation, the universe is still doing what it has always been doing. It is still expanding. The galaxies you cannot see, the ones beyond our cosmic horizon, the ones whose light has not yet reached us, are still out there, sweeping outward, unaware of our existence. The cosmic microwave background photons that have been traveling for 13.8 billion years are arriving at this moment, right now, at the surface of your skin, 411 of them per cm/s.
You are being illuminated gently by the early universe every moment of your life. You always have been. You always will be. The universe is not a finished thing. It is still happening. Inflation may still be happening somewhere out there in regions that broke off from us long before our pocket cooled into ordinary cosmology. Other pocket universes may be forming even now in the eternally inflating bulk we cannot see.
We are inside a local event in a structure that is much larger than we can perceive. What we call the universe is almost certainly just our neighborhood, a finite observable region, a pocket, a piece. The larger structure, the bulk, the multiverse, the infinite chain of aons, whatever it is, extends beyond our horizon in space and possibly in time in directions we have no instruments to look. We are the equivalent of fish at the bottom of an ocean building elaborate theories about the surface never quite breaking through. We can tell from the equations and the data that the surface is there.
We cannot directly see it. The distinction matters. And yet, and this is the note I want to leave you on, none of this should feel like defeat. None of it should feel like ignorance. The fact that we can sit here, you and I, on a small wet rock in a quiet corner of an unremarkable galaxy and trace the logic of what came before the big bang and follow the equations honestly all the way to the edge of what they can say and recognize the place where they stop that is not nothing. That is the most extraordinary thing humans have ever done. We have built out of mathematics and observation and argument and the slow accumulation of confirmed pieces a picture of how the universe works that extends back nearly 14 billion years and forward into speculation about what lies beyond. We have used the cosmic microwave background, the literal fossil light of the early universe to test our models to absurd precision. We have followed the math from Newton's apple to Einstein's spaceime to Hubble's galaxies to Penzius and Wilson's hiss to Gth's notebook to Lind's eternal inflation to the menu of pre Big Bang proposals that physicists are arguing about right now this year while you are listening. The story is incomplete. Of course, it's incomplete. Every story we have ever told about the cosmos has been incomplete. The story is also in its incompleteness more astonishing than any complete story we could have invented.
The first chapter of the universe is still missing. We are still reading the second chapter, the one we are inside of, trying to deduce the first from the way the second begins. And what we are finding slowly, painfully, page by page is that the first chapter exists. There is something there. Whether it is a smooth quantum geometry or a bounce or a previous aon or an eternally inflating bulk full of pocket universes. The page is not blank. It is just written in a language we have not yet finished translating. The unknown in cosmology is not a wall. It is not a place where curiosity stops. It is not ignorance in the dismissive sense. The unknown is the frontier. It is the part of the map that has not yet been drawn. The part that the next generation of physicists and possibly some kid listening to this video on their phone tonight are going to draw. The Big Bang was not the beginning. It was a doorway. We are standing in it looking outward into a much older much stranger universe than the one we were taught about. And whatever is on the other side, whatever the universe is actually sitting inside of is patient. It has been there forever. It will still be there when we are ready to look. Good night and keep wondering.
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