that would seem to explain the "big bang" :) an explosion from an infinitely dense point that is ever-growing, which began in a higher-order universe as a black hole that we now inhabit.

(of course I know nothing of science, this is all just pop-sci in my head, but boy is it fun to think about)

One very important difference between the big bang and the interior of the black hole: Within the event horizon of a black hole, there is always a singularity in your future. In our universe, that singularity is in our past.

One interpretation: the big bang theory describes a white hole -- the time-reversed version of a black hole.

Einstein-Cartan Theory (https://en.m.wikipedia.org/wiki/Einstein%E2%80%93Cartan_theo...) introduces a torsion term to General Relativity’s field equations that is not incompatible with observations and provides both an avenue for explaining the cosmological constant (https://arxiv.org/abs/1607.01128) and “big bounce” motivation for the beginning of our current universal epoch (https://arxiv.org/abs/1512.06074).

Imagine our universe is contained within a blackhole.

If time and space invert at the event horizon, could it be that the Big Bang was the event horizon of our black hole, that we are forced forward through time by the pull of our black hole interior, and that the expansion of the universe is actually just metatime passing, and as we move through space we are actually moving forward and back in metatime, with the expansion of our universe being an expression of increasing constraints due to metatime’s metaspace as we get closer to the center of our blackhole?

I could imagine that the “Big Rip” is what we experience when we asymptotically approach the singularity. The strangeness of black holes could mean that falling into a single point is actually experienced as space flying apart faster than light.

Yes.

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.

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'.

Turtles all the way down?