The purpose of this page is to provide an in-depth timeline of what is known, or at least strongly presumed, about the history of our universe. I'll try to paint the most accurate picture of the past that I can here. There'll be illustrations, too!

Well, let's start as far back as it goes.

Cosmic inflation (time: unknown)

At least 13.8 billion years ago, there was a universe. No one really knows where it came from.

This universe contained a rippling soup of some kind - each microscopic volume of space contained some varying amount of energy. There was a kind of subatomic white noise all over the Universe. For reasons unknown, this white noise expanded; the size of its features increased exponentially, doubling every tiny fraction of a second for an unknown length of time (10^-35 seconds at the very least). This cosmic inflation led to the Universe becoming a gazillion bajillion times less dense than it was before, smoothing out the white noise and locking in the amount of stuff in each little region. This was the beginning of the large-scale structure of our cosmos. Later on, regions that had more stuff in them would attract the surrounding matter as it formed, becoming even denser.

This process explains the overall structure of the Universe, since without it matter would remain perfectly uniform forever instead of forming galaxies, at least according to models of the Big Bang. The main hypothesis for what drove cosmic inflation is the so-called inflaton field - a primordial version of light, crudely speaking, that produced an enormous outward pressure that caused whatever existed back then to dilute tremendously. The density dropped so much that temperature ceased to have any meaning for a moment.

An unremarkable region somewhere containing about 10⁵³ kilograms of stuff would soon approach the size of a person, give or take. This was our current observable universe, the stuff that has since become trillions of galaxies, one of which now contains a G-type dwarf star orbited by at least eight planets, one of which is home to a grandiose ecosystem and a young, inexperienced civilization of curious bipedal mammals.

It's still unclear whether or not this inflation actually happened, but many cosmologists agree that it did, since there's a fair bit of evidence for it, which you can explore through the Wikipedia article. What happened before cosmic inflation remains a mystery, for there is no evidence for any events preceding it, not even indirect signs hidden within the cosmic microwave background. This is as far back as our knowledge goes. Basic extrapolation predicts that the Universe expanded into existence out of an infinitely dense singularity, but there's no solid reason to believe that was the case. Many different ideas exist for how our cosmos came to be. Many of them seem to inevitably imply the existence of other universes.

Birth of matter (time: still unknown)

At some point, matter as we know it was created in a process called reheating. It could have happened sometime during inflation or after it, or possibly even before it - we're still in the uncertain era where it's unclear what happened and in what order, we just suspect these things must have occurred at some point for the Universe to end up the way it is. As inflation stretched the Cosmos thin, the primordial radiation that drove it must have decayed into regular radiation, which back then included particles we usually understand as matter, such as electrons and quarks. Those particles zoomed around at the speed of light and smacked into each other with so much energy that it produced even more particles.

There are two main categories of particles - fermions and bosons. Fermions (like quarks and electrons) make up matter, while bosons (like gluons, photons or the famous Higgs) are little things they toss at each other in order to interact. In the early Universe bosons had such insane energies that they spontaneously turned into fermion-antifermion pairs - gluons became quarks and antiquarks, photons became electrons and positrons, etc. These particles and antiparticles annihilated each other, becoming their respective bosons again, which produced more fermion-antifermion pairs, and so on. The observable universe contains something like 10¹⁰⁰ fermions.

Note that by "observable universe" I mean "the sphere of space that would become our current observable universe". There was technically no observable universe up until some 380,000 years after inflation, given space was fully opaque, but even if there was, its size would be different from the sphere containing all currently visible matter.

Structures that existed before inflation were now drowned in an incredibly hot & dense quark-gluon plasma, but nevertheless slightly affected it with their gravity. The Universe continued to expand at a much slower, but still tremendous rate, driven by the pressure of radiation the plasma emitted into itself. Still quadrillions of degrees hot, the Universe continued to cool, at some point allowing some particles to begin interacting with Higgs bosons and thus acquiring mass.