A Brief History of the Universe, Part I
Time is a tricky thing. The idea of the Big Bang has become common knowledge, but a question many still have as to the birth of the universe is what came "before" it, or indeed what was the "cause" of the Big Bang. While one might answer these questions with "nothing," that's not really correct, because the answer is actually much simpler and at the same time so much harder to grasp in any intuitive sense. The answer, which I understand intellectually but still makes no sense to me in an intuitive way, is that there was no before, nor a cause, because time itself, which the idea of before and causation is predicated upon, began its existence synchronously with the Big Bang. I find this nearly impossible to grasp in a fundamental way, because our entire existence is based around and upon a notion of time as a strict linear progression of one thing to another, with every event having a causation and time preceding it. But, as I've covered before, we can see that time itself is not a constant, and, indeed, it had to have a beginning. Of course, a "beginning" to time still makes little intuitive sense, but we have to accept it based upon time being a product and property of the universe, and the universe itself came into existence with the Big Bang, so time could not exist until that point (I'm struggling with even basic wording here, because so much of our language to describe this implies time. Even "until" is a terrible word, but I can't think of another). While this understanding is not completely necessary to cover the early history of the universe, it's a rather important point that gets glossed over far too often, so I figured I'd lead with it, then move on to the easier stuff. So, let's begin.
In the very first second after the Big Bang, a whole lot of stuff happened. Our models have a lot of trouble predicting how the very, very early universe would behave, but it's theorized that in the very beginning, the temperature of the early universe was so high that all fundamental forces (gravity, electromagnetism, and the strong and weak nuclear forces) hadn't yet separated. At about 10-43 (that's 0.000000000000000000000000000000000000000001) seconds after the Big Bang, those forces began to separate as the universe was able to cool due to its incredible rate of expansion. First gravity separated from the pack, then the strong nuclear force, and finally the remaining force, called the "electroweak" force, separated into the more well-known forces of electromagnetism and the weak nuclear force. And after a lengthy amount of time, we begin to enter a period, known as inflation, that we understand better.
When I said lengthy, I was of course being relative. In fact, the period known as inflation ended a mere 10-32 (0.0000000000000000000000000000001) seconds after the Big Bang. But, during that period, the universe expanded at an alarming (and constantly accelerating) rate. This expansion would account for the current homogeneity (rather even distribution of matter) of the universe at a large scale, even if the universe at the moment of the Big Bang was highly disordered. This is important, as the Cosmological Principle states that the universe suffers from such homogeneity when viewed at a large enough scale. Currently, there are astronomers looking for gravitational waves which would be an aftereffect of such rapid inflation though luck on that front has been slim.
At around 10-6 (0.00001) seconds, we finally see the matter that we know and understand begin to form. Before now, the universe was mainly energy, with quarks making an appearance later on, and finally we now get hadrons forming, like those baryons familiar to use all, protons and neutrons (baryons are a form of hadron composed three primary quarks, which are the building blocks of subatomic particles the same way protons, neutrons, and electrons are the building blocks of atoms and atoms are the building blocks of molecules). Finally at about one second after the Big Bang, the universe as we know and understand it begins to emerge, as most of the matter formed in the early universe manages to annihilate itself (matter-antimatter annihilation) leaving an asymmetry in the favor of matter and a lot more leptons (like the electron) than hadrons.
Remember when I said that the universe as we understand it begins to emerge? The important word there was "begins." At the ten-second mark we enter a period known as the Photon Epoch, where photons (light) are the dominating particle in the universe. This stretches on for several hundred thousand years, even though atomic nuclei start forming by the three-minute mark (as the universe continues to cool). However, it takes over three-hundred thousand years before we actually see the first atoms. Up until that point, the universe was actually more or less translucent, due to the high energy plasma that matter was composed of, and it wasn't until the cooling caused those nuclei to snag electrons and become real atoms that the universe become transparent. The light from that point on is what makes up the Cosmic Microwave Background Radiation. This means, that no matter how hard or far we look, we can never see past this point in our universe's history using only light (hence, for example, the gravitational wave search to confirm inflation). But it will still take hundreds of millions years before we can get that fundamental part of our present-day universe: stars.
An important question to look at here is why matter took so long to condense from the early universe (so long being relative in some ways). The key is temperature. The early universe was hot. And by that I mean hot. The hotter matter is, the more energy it has, the more it vibrates, and, as we know from examples like nuclear power plants, the more likely it is to split itself apart. And while we can attain energies to split molecules into their constituent atoms, or even some atoms into smaller atoms, if you put enough heat into a system, those atoms are going to fall right apart, and they won't be able to recombine, because there's just too much energy. Add some more heat, and now even those pieces that make up atoms won't be able to hold together. This sort of behavior is actually theorized to exist in some of the more extreme places in the universe, such as the quark-gluon plasma in the heart of a white dwarf star. once you cool things down, which the early universe did by expanding (the more you expand, the more spread-out everything becomes, the cooler it becomes, like how decreasing the pressure of a gas while retaining the same volume will cause it to cool (for you chemistry fans, the Ideal Gas Law)), the matter we know and love will begin condensing out of that high-energy plasma. And the universe will continue to cool until its final energy state, as I'll get to in later parts of this series.
See you next time, when we move from stars to getting caught up at present day.