(Note: I’ve posted a follow up to this post here: https://physicalism.wordpress.com/2013/04/17/spacetime-singularities-and-the-origin-of-the-universe/ )
I was taking a break and watching Mr. Deity on YouTube, and a video caught my eye; it’s titled “Explain this to me Atheist” and it poses a question you see raised frequently in debates over theism (even occasionally by some bright kids):
Where did the universe come from?
Now that’s a reasonable question, and the most honest answer is that we don’t really know for sure because the conditions at the beginning of the universe are such that our current physics is inadequate for describing it (we’d need a full theory of quantum gravity, which we don’t yet have). Further, there are several speculative theories in cosmology that offer different answers to the question.
But it’s worth pointing out that if we turn to our best theory of spacetime, General Relativity, which has proved itself fantastically successful over the past century, there is a straightforward answer to this question:
The universe has always been here.
In General Relativity, the Big Bang is a spacetime singularity. What that means is that as you go backwards in time, you eventually run out of time (or, more accurately, out of spacetime). The path back in time cannot be extended beyond 13.7 billion years or so. There is no time before this.
What this means is that there was never a time when the universe didn’t exist. It has always been here.
It’s tempting to think, “Ah, but what about before the Big Bang — say 14 billion years ago — then there was nothing, not even the universe!” But this is mistake. According to General Relativity, there is no 14 billion years ago. There is no “before the Big Bang.” Time doesn’t extend beyond the universe. Anytime there was time, there was a universe to go with it.
So (on this account, at least) it really doesn’t make sense to ask “where” the universe came from, because there is no “where” or “when” apart from the universe. Likewise, it doesn’t make sense to ask what happened “before” there was time, because “before-ness” requires time. It’s difficult for us to wrap our heads around, but we need to recognize the limitations of our concepts. And our concepts of space, time, and cause do not extend beyond spacetime singularities.
Now that I think of it, it occurs to me that Mr. Deity covered this one too: