What You'd Find Before the Big Bang?

[00:00:00]So, you came from the Big Bang, or at least that's where the molecules that make you up and everything else came from. But, where did the Big Bang come from? Well, your scientists have some theories, and we're going to explore 10 of them. Oh, Billy.

[00:00:16]Physicist Lee Smolin proposed in 1992 that your universe was born inside a black hole. When matter collapses into a singularity, rather than being crushed out of existence, it may undergo a bounce, similar to the quantum bounce in the Big Bounce, and generate a new expanding space-time on the other side of the event horizon. A new universe, casually disconnected from the parent, unreachable, invisible, running its own physics independently. This is called the Fecund Universes Hypothesis. Fecund, meaning productive, fertile. In this model, the universe is not just a place where things happen, it's a reproduction mechanism. Each new universe inherits slightly mutated physical constants from its parent, as biological offspring inherit slightly different traits from their parents. Universes that produce many black holes produce many offspring universes. Universes that cannot produce black holes produce none. Over many generations of universes, the ones that survive and reproduce are the ones whose physical constants favor black hole formation. Your universe, with its specific values for gravity, electromagnetism, and the nuclear forces, may not be arbitrary. It may be the product of cosmic selection pressure acting across generations of universes, each born from the collapse of a star in the previous one. In this model, what came before your Big Bang was a parent universe, a universe with its own stars, its own black holes, its own history.

[00:01:40]One of those black holes collapsed, becoming your beginning. And right now, in your universe, black holes are forming. Inside those black holes, if Smolin is correct, new Big Bangs are happening. New expansions, new stars, new planets, new species sitting somewhere on their equivalent of a couch being told the same thing you're hearing right now.

[00:02:01]In 1982, physicist Alexander Vilenkin proposed something that sounds like a philosophical stunt, but was peer-reviewed and published in the physics literature. The universe may have tunneled into existence from literally nothing. Nothing in the absolute sense. No space, no time, no matter, no energy, no quantum fields, no probability. In quantum mechanics, particles are not bound by the same rules as large objects. A particle encountering a barrier that it classically should not be able to cross can, with some calculable probability, appear on the other side. This is quantum tunneling. Vilenkin applied this to cosmology. In this model, a universe can quantum tunnel into existence from a state of absolute nothingness. The probability is not zero. And in a framework where time may not have existed before the tunnel event, the phrase waiting for the probability to occur is meaningless. There is no waiting. There is simply an event that emerges without a prior moment. There is a further detail worth noting. The total energy of the universe is approximately zero. The negative energy of gravity exactly balances the positive energy from matter and radiation. The universe is, in total, a zero energy system.

[00:03:15]Creating a zero energy system from nothing does not violate conservation of energy. The universe costs nothing because it came from nothing and it sums to nothing. But it produced everything, which is either the most efficient use of resources in history or just unnecessarily complicated.

[00:03:34]String theory requires more spatial dimensions than you can currently see or use. Most of those extra dimensions are compactified, curled up so small that your entire life will pass without you detecting them. In certain versions of string theory, the universe exists on something called a brane, short for membrane. Think of it as a three-dimensional surface floating inside a higher-dimensional space called the bulk. You are on one of those surfaces right now. You have always been on one of those surfaces. You cannot leave it because you are physically incapable of moving in the extra dimensions.

[00:04:08]In the brane world model developed by Justin Khoury, Burt Ovrut, Paul Steinhardt, and Neil Turok in 2001, your brane had a neighbor. Another brane parallel to yours is also floating in the bulk. Over an immense span of time, gravitational forces caused the two branes to drift toward each other. Then, they collided. The collision released an enormous amount of energy across the entire surface of both branes simultaneously. That energy became the matter and radiation of the early universe. That collision was the Big Bang. Before the Big Bang in this model, there was no time as you know it. Two branes were drifting through the bulk in something that loosely functions like time, but follows different rules. The branes are now separating again. In some versions of this model, they'll eventually drift back together and collide a second time. The universe was created by a cosmic fender bender. Your entire existence is the aftermath of an interdimensional traffic incident. No one had right of way. The concept had not yet been invented. It required branes with opinions, which took several billion years to develop.

[00:05:12]General relativity, the theory that governs gravity and the large-scale structure of the universe, has an inconvenient flaw. When you trace the universe backward in time toward the Big Bang, the equations eventually produce a singularity, a point of infinite density, infinite temperature, and zero volume where the math breaks down. This is not considered a feature. It does suggest, however, that general relativity is not the final word on the subject. Loop quantum cosmology, or the Big Bounce, attempts to fix this by applying quantum mechanics directly to the structure of space-time itself. In Big Bounce, space is not continuous.

[00:05:49]It's made of discrete fundamental units called quanta of geometry. Below a certain scale, you cannot compress space further. Quantum effects push back. This means the Big Bang singularity does not exist. Instead of collapsing to an infinite point, the universe compressed to an incredibly small but finite volume, and then quantum pressure caused it to bounce and begin expanding again.

[00:06:11]The Big Bang was a bounce. In this model, before the Big Bang, there was a contracting universe. A prior universe governed by the same physics was collapsing through its own final moments until it reached the quantum bounce point and became your beginning. What caused that prior universe to collapse is a question the Big Bang does not fully resolve, which gets it something in common with most explanations of how things got this way.

[00:06:35]In 2010, physicist Roger Penrose published a theory called conformal cyclic cosmology. The universe, he proposed, is not the first universe.

[00:06:44]It's one chapter in an infinitely long book, and the book has no first page.

[00:06:49]Here's how each cycle works. Penrose calls it an eon. A universe begins with a Big Bang. It expands, stars form and burn out, galaxies scatter. Over an incomprehensible span of time, all matter either collapses into black holes or decays into its most fundamental components. Eventually, the black holes themselves evaporate through Hawking radiation, releasing their mass as a diffuse haze of photons and gravitons.

[00:07:15]Here's the strange part. Massless particles do not experience time. They cannot age or change. To a photon, the end of the universe and the beginning of the next one are the same instant. The cold, dark, sparse endpoint of one eon is mathematically identical to the explosive starting conditions of a new Big Bang. One eon transitions seamlessly into the next. The universe does not end. It reboots. Penrose believes this model leaves detectable imprints in the cosmic microwave background, faint circles, echoes of black hole collisions from a previous universe. If he's right, there is observational evidence of what came before the Big Bang, and it's a previous version of everything.

[00:07:58]In 1980, physicist Alan Guth proposed that the very early universe went through a period of exponential expansion called inflation, and not the kind that means you're down a kidney to afford groceries, something considerably more dramatic. In the first tiny fraction of a second after the Big Bang, space expanded faster than the speed of light, stretching outward in every direction at once. Here's where it gets interesting. The eternal inflation theory suggests that inflation never fully stopped, not everywhere at least.

[00:08:29]In most regions of space, inflation is still ongoing. The universe is not a finished product. Occasionally, in this eternally expanding ocean of inflating space, a small region stops inflating.

[00:08:40]Energy converts into matter and radiation. Local physics locks in. Stars form, planets form, and on at least one of those planets, things with opinions about their situation eventually develop and begin arguing about it on the internet. That pocket is called a bubble universe. You are currently inside one.

[00:08:58]The others are not accessible. This has been described as unfortunate, though by whom and from where remains unclear.

[00:09:05]There may be infinitely many of these bubbles, each one potentially running on different physical constants, different laws, different versions of chemistry, and different versions of time. Some may not allow stars. Some may not allow atoms.

[00:09:19]Before your bubble formed in this model, there was no emptiness. There was inflation. The question of what came before the Big Bang is therefore roughly equivalent to asking what came before Tuesday. It depends entirely on which bubble's calendar you're using.

[00:09:34]String theory is full of mathematical symmetries, places where two physically different sounding descriptions of a situation turn out to be the same situation written in different languages. One of the most significant is a symmetry between very large and very small scales. In string theory, a universe with a physical size of R is mathematically equivalent to a universe with a size of 1 / R. Large and small are not opposites, they're the same description translated. Physicist Gabriele Veneziano and Maurizio Gasperini used this symmetry to propose the pre-Big Bang model. In this framework, your universe has a mathematical mirror image. Before the Big Bang, a twin phase existed called the dilation-driven pre-Big Bang phase.

[00:10:18]A contracting universe running on the same string physics as yours, moving through the same equations in the opposite direction. This pre-Big Bang universe was large, cold, and weakly coupled. Gravity was weak, strings interacted slowly. A dilation field grew stronger as the universe contracted, driving the collapse. Eventually, the contraction reached such extreme conditions that string effects became dominant. The dilation reversed, and the contraction flipped into expansion. That flip was the Big Bang. What this implies is that the Big Bang was not an origin.

[00:10:52]It was a phase transition, a moment when one regime handed off to another in the same set of equations. The universe did not begin, it changed state.

[00:11:01]Before the Big Bang, on this model, there was a contracting universe with a history of its own. And if you apply the same logic to that universe, you get another pre-phase, and another before that. The symmetry does not terminate.

[00:11:15]Everything in the universe, at its most fundamental level, is not a particle or a wave or both. In string theory, everything is a string, infinitesimally small vibrating loops or strands of energy. Different vibration patterns produce different particles. Every force, every element, every interaction have ever had is the universe playing different notes on strings too small to ever be directly observed. Before the Big Bang, string theory suggests the universe existed in what is called a Hagedorn phase. Temperature, as you know it, measures how fast particles move.

[00:11:48]Heat something and the particles move faster. In string theory, there's a ceiling, the Hagedorn temperature. When you pump energy into a system of strings past a certain point, they don't move faster. They produce more strings. The energy goes into generating new string excitations rather than increasing temperature, and the system stabilizes.

[00:12:08]In string gas cosmology developed by Robert Brandenberger and Cumrun Vafa, the early universe existed in this stabilized state, a hot, dense, tangled gas of strings winding around compact extra dimensions and vibrating in place, a Hagedorn soup unable to get hotter, unable to collapse further, just sitting there in a state of maximum density like a traffic jam with no off-ramp. At some point, certain winding modes of the strings annihilated each other and released the constraint. Three spatial dimensions were free to expand. The other six or seven curled up too small to participate and have been in there ever since. Those three became the universe you currently occupy. In this model, the Big Bang was not a beginning.

[00:12:50]It was a phase transition, a moment when the Hagedorn tangle unlocked and space was finally allowed to grow. What the strings were before they were strings is not currently a question with an answer.

[00:13:01]What if the question what came before the Big Bang is not unanswerable, but meaningless?

[00:13:07]What if it's the cosmological equivalent of asking what's south of the South Pole? In 1983, Stephen Hawking and James Hartle proposed that the universe has no boundary in time. Not that the boundary is inaccessible. The universe doesn't have an edge in time anymore than the Earth has an edge in space. Their model uses a the technique called imaginary time. Not imaginary in the sense of pretend, imaginary in the precise mathematical sense. It involves the square root of -1, which you may remember from school as being the number that technically should not exist. It exists. It is also apparently load-bearing. In imaginary time, the universe has a shape similar to a sphere. A sphere has no edge, no boundary, no point where it starts or stops. At the South Pole of this sphere, the universe is at its smallest. As you move toward the equator, it expands.

[00:13:58]But, the South Pole is not a beginning, it's simply a point on a surface.

[00:14:02]Time, as you experience it, emerged along with the universe. Before that emergence, time didn't exist in any form that the word before can apply to.

[00:14:13]Everything so far has assumed that space-time is smooth, that space is continuous and unbroken, that time flows without interruption, and that the universe is, at its foundation, analog.

[00:14:24]Causal set theory disagrees. In causal set theory, space-time is not continuous, it's discrete, fundamentally, irreducibly made of individual elementary units, like pixels in an image or atoms in an object. These units are called causal sets, and each one is related to every other by a single rule, which came before which.

[00:14:45]There is no space between the causal atoms. There's nothing smaller. The universe, at the Planck scale, has a resolution limit. Reality is not infinitely detailed. It's the world's most complex finite bitmap, and you're a pattern of bits running on it. There is no zoom level below the pixel. This is maximum resolution. You are already at the sharpest version of real that's physically available. In this model, the Big Bang was not the beginning of space-time. It was a moment in a larger causal structure. The causal set that constitutes your observable universe grew from a pre-existing causal set through a process called sequential growth. New causal atoms were added to the existing network according to probabilistic rules derived from the network structure.

[00:15:29]What came before the Big Bang in causal set theory is more causal sets, an earlier network of discrete space-time events from which your universe's causal structure grew. And before those, more causal sets. The question is how far back the chain extends and whether it has a beginning. Current theory does not require it to. Discrete causal atoms, and before that, more. And before that, more. The chain extends without a confirmed floor. The theory does not require one.

[00:15:58]There you have it, 10 theories, one conclusion. The question of what came before the Big Bang still remains largely unanswered. Anyway, check out this video.