In the beginning, there was a question mark. All else followed. The end.
We've all heard of the Big Bang theory (I'm talking about the cosmological model, not the TV show), but it's important to understand what that theory is and what it's not. Let me take this opportunity to be precisely, abundantly, emphatically, ridiculously, fantastically clear: The Big Bang theory is not a theory of the creation of the universe. Full stop. Done. Call it. Burn that sentence into your brain. Say it before you go to sleep, and first thing when you wake up.
The Big Bang theory is a model of the history of the universe, tracing the evolution of the cosmos to its very earliest moments. And that's it. Don't try to stuff anything else into that framework. Just stop. You can keep your meta safely away from my physics, thank you very much.
I'm emphasizing this because there is a lot of confusion from all sides, and it's best to keep it simple. The Big Bang theory is a scientific model, just like any other scientific model. We believe the theory is on the right track because it's — gasp — supported by extensive evidence.
You don't have to take my word for it. Since the idea was first cooked up, the Big Bang theory has survived decades of scientists fighting, scratching, backstabbing, criticizing, undermining, bickering, arguing and even name-calling, all in an attempt to crush their rivals and prove that their pet alternatives were superior. Why? Because whoever takes down a major scientific paradigm gets a free trip to Stockholm.
The further we push back in time, the stranger the universe gets — yes, even stranger than a plasma. Push back further, and stable nuclei can't form. Go even further back, and protons and neutrons can't stand the pressure and degenerate into their components: quarks and gluons. Push back even further and, well, it gets complicated.
The Big Bang theory can be summarized thusly: At one time, the entire universe — everything you know and love, everything on the Earth and in the heavens — was crushed into a trillion-Kelvin ball about the size of a peach. Or apple. Or small grapefruit. Really, the fruit doesn't matter here, OK?
That statement sounds absolutely ridiculous, and if you said it a few hundred years ago… Well, I hope you like barbecues, because you're about to be burned at the stake. But as crazy as this concept sounds, we can actually understand this epoch with our knowledge of high-energy physics. We can model the physics of the universe at this early stage and figure out the latter-day observational consequences. We can make predictions. We can do science.
At the "peach epoch," the universe was only a tiny fraction of a second old. In fact, it was even tinier than a tiny fraction — 10^-36 seconds old, or thereabouts. From there on out, we have a roughly decent picture of how the universe works. Some questions are still open, of course, but in general, we have at least a vague understanding.
The further along in age the universe gets, the more clear our picture becomes, but it's almost frightening to consider that our poor monkey brains are even contemplating such early epochs in the universe.
At even earlier times, though, our understanding of the universe gets … fuzzy. The forces, energies, densities and temperatures become too high, and the knowledge of physics we've cobbled together over the centuries just isn't up to the task. In the extremely early universe gravity starts to get very important at small scales, and this is the realm of quantum gravity, the yet-to-be-solved grand riddle of modern physics. We just flat-out don't have an understanding of strong gravity at small scales.
We. Just. Don't.
Earlier than 10^-36 seconds, we simply don't understand the nature of the universe. The Big Bang theory is fantastic at describing everything after that, but before it, we're a bit lost. Get this: At small enough scales, we don't even know if the word "before" even makes sense! At incredibly tiny scales (and I'm talking tinier than the tiniest thing you could possible imagine), the quantum nature of reality rears its ugly head at full strength, rendering our neat, orderly, friendly spacetime into a broken jungle gym of loops and tangles and rusty spikes. Notions of intervals in time or space don't really apply at those scales. Who knows what's going on?
There are, of course, some ideas out there — models that attempt to describe what "ignited" or "seeded" the Big Bang, but at this stage, they're pure speculation. If these ideas can provide observational clues — for example, a special imprint on the CMB, then hooray — we can do science!
