Comment by doctorwho42 2 months ago
Actually, in theory there is one place denser but our models show it can never happen.
The moment right after the big bang. As energy can never be created nor destroyed, all the energy in the universe was practically in one point in space-time a femtosecond after the big bang.
My layman understanding is that we don't have the theories or math to try and understand this so it's just a black box that we pretend to understand
It wasn't an explosion. Space itself expanded, so there wasn't anything to expand into. https://en.wikipedia.org/wiki/Expansion_of_the_universe
I think there are some philosophical definitions in the way. The Universe is everything we know, it is made of space and time, so of course it cannot expand into any space as it contains all of it.
We don't know what's outside the Universe, so we can't say there is nothing, and we can't say there's anything, we don't know what it is expanding into, or if "expansion" even makes sense outside the Universe. If we somehow find out what's outside the known Universe, that will inevitably become part of the known Universe, so we will never know what's outside the Universe.
Consider a bubble rising to the surface of a pond. As the bubble breaches the surface, it extends beyond the surface and expands as the pressure reduces.
If you consider the surface of the water as a 2D plane, the bubble expands into a third dimension perpendicular to the others. The bubble's surface is made of the same water as the surface of the pond, and there is no hard boundary between them. The bubble pushes part of the 2D plane into the third dimension, which results in the water having more surface area than the total possible area of the 2D plane.
Area (space) has been created without creating matter or energy. The surface is simply extended into an extra spatial dimension.
The way I like to interpret the big bang is as a higher dimensional structure folding or knotting itself such that a bubble is forced into a 3D space. The bubble expands and thus creates more volume than is possible in the lower-dimensional surface the bubble was formed on. This is my ill-informed interpenetration of M-theory.
Dunno why, but much of mathematics and the universe in general makes much more sense to me when viewed in terms of dimensionality. Our universe is 'just' a 4D slice of a higher dimensional structure, and I find a certain kind of beauty in that. In another life, I'd have been a string theorist
Instead of thinking of it as a bang in an existing space-time, the way to conceptualize it is the collapsing of a universal wave function from a superposition of all possible universal states. Of which our universe is just one potential possibility. Space time is a function of the collapsing state.
I’m a layman but I think I’ve understood this enough to repeat. The early universe is hypothesized to have been so uniform (gravity pulling in every direction) there was no net direction for anything to collapse to. Because the expansion was so quick, before the uniformity could be ruined due to quantum randomness, it expanded away from there being tons of or one giant black hole.
You also must remember the universe was always infinite (in this model). So for every particle there were particles in every direction from them, ie the universe not a point or point like because points have edges. It was (much much) denser, but still infinite and expanding from all regions.
Since there are conserved quantities like energy and angular momentum it is impossible that everything just collapses. If something collapses, there is usually a large amount of matter which does not collapse to carry away the energy and momentum of the collapsing stuff.
This is a misunderstanding. All the energy in our « observable » universe was compressed in that small size. We do not have any estimates of the size of the actual universe now, nor at a time shortly after Big Bang. For all we know, the universe might be infinite, both now and back then.