There are many things that we can observe about the universe which lead us to assert that it all started with a Big Bang. There is the velocity of galaxies further away from us being faster, or the fact that when we look back to a younger universe we see more primitive structures that would precede what our universe looks like now. But probably the best evidence of the Big Bang is called the Cosmic Microwave Background Radiation. Which sounds really cool, and totally is. So what exactly is it?

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.