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Comment by thechao | Hacker News Reader

Be wary of saying things like "from an infinitely dense point" because you might mistakenly think the universe is expanding from some distinguished point in our space. Instead, the infinitely dense position was in time, and the universe has always been (we think) infinitely big.

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Yeah it's like all points exploded at the same time, but we can only trace our light cone back to one of them.

Thanks for pointing this out. I've always thought about the initial singularity as a point in both time and space. Is it still correct to say all the matter that makes up our observable universe started out at a single point in space? Since the singularity was infinitely dense, this at least seems possible.

I'm about to do something terrible, but it helped me immensely to understand the Big Bang. Let's pretend we have a magic box that tells us how space expands over time:

    V(t)

So, t starts at '0', which we're gonna call 't0', and goes until 'now'. So V could be small, it could be big. We don't know, and it kinda doesn't matter. The reason is that the way the Big Bang works is like this:

    (t - t0) * V(t)

So, when t == t0 (the beginning of time), it doesn't matter what shape space (V) has, the size of the universe (spacetime) is '0'.

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