Infinite Or Closed Universe

[nailit]

Can any of the scientific minds here please tell me what the current scientific understanding of the universe is at the present? (or at least the general consensus). Is it closed or infinite?
I have trouble wrapping my head around either model. Is there another one that I havnt heard about.
Thanks.

[davegosling]

"before" implies relative in time. There was no time before the Big Bang, which is why "before the Big Bang" is meaningless.

[jim360]

Well, the point is (surely) that the South Pole is, by definition, the most South you can be. So there can't be anything south of it. In the same sort of vein, the Big Bang is the beginning of time, so there can't be anything "before" it -- at least, not in the sense we would usually understand when we say "before".

[nailit]

Is the pub still open???
Parecetomol just arnt doing it anymore.....

[THECORBYLOON]

As far as I know, nothing travels faster than light. Why is the radius of the universe much greater than the distance light would have travelled since the Big Bang? The universe is thought to be about 13.8 billion years old but the radius is about 46 billion light years so how does that happen?

[Peter Pedant]

I think Jim and Kidas have done very well
( altho I am gonna have to leave the 4D lorentzian manifold until later)
and as for - "a mediaeval historian may have a better grasp of Hawking radiation than you two do" - how do you keep your faces straight when you read that sort of stuff ?

[jim360]

The statement that nothing travels faster than light only applies to actual matter (or, more generally, anything that carries meaningful "information"). Space isn't matter -- really, it's nothing more than a reference point that allows you to define where things are -- so it can "expand" as rapidly as you like. In the very early universe -- we are talking a stupidly tiny fraction of a second -- this is essentially what (we think) happened, the expansion of space running away with itself way, way faster than the speed of light would allow.

So there's no contradiction between, as you say, a 14 billion year-old Universe and a Universe (that we can see) that's about 90 billion light years across.

[THECORBYLOON]

If it is only "space" and not something material, how can they know where the extremities are to measure them? I don't understand how particles can have travelled about 13.8 billion miles across the universe yet there is said to be another 30 odd billion miles of nothing?

[jim360]

I am not sure if I know enough about Cosmology to be confident in this answer but I think the point is that we can actually see objects that are 46 billion light years away, rather than that there is 30 billion-odd light years of nothingness that we just say is there.

I'm struggling to articulate the next bit, but in rough summary:

-- The Universe is still expanding.
-- Objects we can see now were closer to us in the early Universe.
-- Light that they emitted back then will have been able to reach us.
-- Some properties of the light we observe tell us that the objects are *now* 46 billion light years away from us.

I think that's the point. At any rate, there is never a time when anything material travels faster than the speed of light, and all of this follows from the equations of General Relativity.

If this clears things up let me know -- if not, I'm afraid I'm not familiar enough with the specifics in this case to be able to clear up any further questions.

[Old_Geezer]

As I understand it, particles can be further away than 13.8 billion miles across the universe. Space is created wherever it is, not just at some kind of imagined edge. Particles can appear to be going faster than light when far enough away from you; which is why there is a boundary one can not see beyond. But much of the apparent speed will be down to space creation between you and the particles, not the actual speed of the particles.

[Old_Geezer]

When stood on the South Pole, which direction can you point to, to indicate south ? There is none; it's all north, in all directions.

[THECORBYLOON]

I understand the bit about the universe still expanding but if the objects are now 46 billion light years (bly) away, I can't see how that's possible if the universe is only 14 bly old and the objects can't travel faster than light.

[Old_Geezer]

Because new space has been created between you and them making them further away from you regardless what 'actual speed' they were travelling relative to you.

[jim360]

Basically what OG said. Nothing material is moving faster than the speed of light, but space can expand faster than that speed because it's not actually a material -- just a reference point.

A consequence of the expansion of space at a speed faster than light is that there are some objects that we will never be able to see, because they were always "too far away" for light to ever be able to reach us.

[Old_Geezer]

Go back to the baloon analogy. The dots on the surface don't move at all. They stay wherever they are inked on the surface. The distance between them grows because the distance stretches instead.