Friar Bellows

DNAunion, almost anything earlier than about 30,000 years after the Big Bang confuses the hell out of me, so I wouldn't even touch that "false vacuum decay" stuff with a ten-foot-pole! But maybe when I understand all that happened after that moment, I'll have a go at it.

B. H. Manners

Maybe Jebus H. Christ will explain it all one day.

Wiploc

I ain't no expert, but the answer is momentum. The universe was expanding rapidly enough that it hasn't fallen back yet, and probably won't ever. We're at or near escape velocity.

This naturally gives rise to the question of where we got the momentum. I ain't no expert so my answer is going to be stupid and wrong, but maybe it will provide a glimmer of insight (at least enough for someone who knows more than me to make a correction).

Time zero:
Picture the universe as a singularity. All matter is at a single point in space, infinitely dense.

Time one:
One tick of the cosmic clock after Time Zero (I mean to suggest that there is a shortest possible unit of time, and that Time One is would be exactly that long after Time Zero if Time Zero had ever existed. But Time Zero didn't exist. The universe actually started at Time One.) At Time One, stuff is bursting out of the, out of the ... uh, out of where the singularity would have been if there had been a singularity which there wasn't because Time Zero never existed. (Okay, okay, I know that it's misleading to suggest that the cosmic egg was at any location other than everywhere. (It's just that "everywhere" was very teeny back then.))

Since then:
We've continued flying apart because we were flying apart so fast at the moment of origin.

That's my simplistic explanation. It naturally raises the question (pretty much the same question it's an attempt to answer) of where all that momentum came from. Why were we expanding at the moment of origin?

By way of pretending to answer that question, I am willing to take two stabs in the dark:

1. What makes you think expansion is unnatural? Why would it need an explanation more than if the universe began in a state of contraction or stasis? Since we started off expanding, we ask why we weren't contracting; but if we'd started off contracting, we'd be asking why we weren't expanding.

2. Here I invoke the anthropic principle (or something that I misname the anthropic principle). If the universe had started off contracting, we wouldn't be here to ask why it hadn't started off expanding, because the universe would have immediately disappeared toward the singularity, so we wouldn't be here to ask. This explains why we necessarily ask our questions from a universe that started out expanding at escape velocity.

This isn't a causal theory. It doesn't mean that the universe had to be expanding. It just means that we don't get to ask questions about it unless it was expanding.

Maybe not all "universes" are expanding. Maybe dark matter consists of instantly self-annihilating universes. (This is presumptively particularly stupid, since I just made it up.)
crc

Shake

wiploc said:It's my understanding that we can't even talk about "space" existing at Time Zero. At Time One there was more than just "stuff ... bursting out." Spacetime itself was expanding, and this became the Universe.

Also, AFAIK under the current state of quantum physics, the state of the Universe before 10^-34 seconds is unknowable. All current theories break down at that point, and much the same happens in the singularity of a black hole. We can only hypothesize.

Wiploc

I don't see why not. (Let me reaffirm that I
speak with no authority.) If there's a black
hole --- excuse me, I mean a singularity ---
won't there necessarily be gravitational effects
around it (that is, in the space around
it)?

Or, if we change paradigms so we quit believing
in gravity, and instead believe that mass
warps space, then doesn't the cosmic egg
get to warp the space around it? The egg
isn't so heavy that gravity can't escape,
is it? I don't know; I'm just asking; but that
would seem peculiar to me.





I don't see this as conflicting with what I said.
Stuff burst out, and space expanded. They
aren't exactly the same idea, but they do fit
together like hand and glove.





"Became?"


Okay.
crc

eh

You're thinking of blackhole singularities, wiploc. The BB singularity was unique in that there was no space "outside" even though the gravity (curvature) is said to be infinite in both. But I'm not sure anyone takes the ideas of singularities to be a reality outside of mathematics. Though even when speaking of finite BH centers, and planck size universes, physicists still refer to them as singularities.

Wiploc

Thanks. When you say space is infinitely curved, I can see how nothing could propagate beyond the singularity.
crc

Answerer

Perhaps, this is the minimum point in which our spacetime could compress itself to.

Shake

Space does not equal spacetime! Spacetime is a four-dimensional merger of 3D space and a time element as well. I think eh clarified the singularity issue rather nicely. I'll see if I can find some other sources to help you out on this. I'll be back to check on this thread later.

Friar Bellows

That's true, but in the context of the Big Bang model, it's accurate to say that space is expanding. The universe is homogenous and isotropic in space, but changing with time. In the technical terms of general relativity, the universe can be foliated into spacelike slices such that each slice is homogeneous and isotropic.