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.

[jno]

I think there used to be one that expanded and contracted, but I believe it fell out of favour.

[ToraToraTora]

I'm aware of 2 main theories:
1) continual expansion - leading to heat death or possibly big rip.
2) expansion halt + collapse + big bang -> repeat

Current calculations are un clear entirely but 1) seems to be favoured based on current estimates of matter/ dark matter/ dark energy etc.

[New Judge]

We need to differentiate between the space in the Universe and the matter within it. The matter may well have started as a big lump which exploded, but the space it occupies must be infinite. I'm uncomfortable with the concept but there can be no other explanation. Space simply goes on forever. Any other explanation (however complex or convoluted - and I've heard of the "finite but unbounded" theory) necessitates a boundary of some sort. And if there is a boundary there must be something beyond it.

[jim360]

"And if there is a boundary there must be something beyond it."

Too late for me to answer this as fully as I'd like -- I'll come back tomorrow. Just wanted to note, though, that while what NJ is saying makes intuitive sense this isn't actually true. There's no requirement for a bounded Universe to exist inside something else. (In a similar way, an infinite universe can still have things "outside" it, but that would mean that an extra dimension existed.)

Also note that an infinite universe can also expand, because what really changes is the distance between things. Hence, again, the idea of the Big Bang as "a Big Lump [of matter] that exploded" isn't quite right.

[ToraToraTora]

judge the space is also created at the instant of the big bang. I know it's counter intuitive but it's 0 size and infinite density at the start of the universe as we know it.

[naomi24]

Interesting to toss ideas around but since no one knows, current scientific understanding isn’t really relevant at all.

[ToraToraTora]

naomi: "current scientific understanding isn’t really relevant at all. " - it is the best attempt we have so it's relevant.

[jim360]

What TTT said.

[naomi24]

TTT, it can only be a best guess - and anyone with an interest in it can have a best guess.

[jno]

relevant or not, it's what nailit has asked for.

[Peter Pedant]

// but the space it occupies must be infinite. //

I find it very difficult to get my head around that - our space is expanding but isnt expanding into anything - kinda like a balloon being blown up is a two d surface expanding in 3-space. kinda not like that

but as my nephew ( Maff : Cambridge ) said - if you look at the equations - it is obvious that isnt true - he might have said - 'that isnt the case.'

that was me told then.

[ I then said: oh it is like the kidney. If the kidney worked like the physiologists say it works: it wouldnt work - and he said - no that is not helpful]

[naomi24]

jno at 23:00, it is - but I don't see that all the other responses here conform so I'm happy with my answer.

[Peter Pedant]

// Interesting to toss ideas around but since no one knows, current scientific understanding isn’t really relevant at all.//

yikes Jim you have your work cut out tomorrow in your crusade against ingrained ignorance.....

Einstein said to LeMaitre the jesuit who came up with an early big bang theory "Vos calculs sont corrects, mais votre physique est abominable"[14] ("Your calculations are correct, but your physics is atrocious.") Einstein later called this the greatest mistake of his life

I would put that as 'your maff is boodifoll but your physique, eed eez like a peeg'

Sorry readers - bit of forrin there

[ToraToraTora]

naomi: "it can only be a best guess - and anyone with an interest in it can have a best guess. " - yes but the scientific community will quickly refute anything refutable. What is left us what the combined might of the scientific community cannot refute and also fits all known observations. More or less all scientific theories are the same, ie they are in a state of awaiting disproving .

[Peter Pedant]

// so I'm happy with my answer.// someone

I'm very happy with that answer

[naomi24]

TTT, //the scientific community will quickly refute anything refutable.//

But it's not always right because the fact is no one knows. I think we are in for a lot of surprises - but I like the discussion anyway.

[jim360]

It's technically speaking impossible to "know" that the Universe is infinite in space, as it's now understood to have a definite beginning, which means that you would have to wait around literally for ever to see the light from stars infinitely far away (this is a variation of what's called "Olber's Paradox", which asks why the night sky is dark if the Universe is infinite).

There are other, more exciting reasons than this. Assuming the Universe expands for ever then some parts of the Universe can never be seen because they are simply moving away from us too quickly for light emitted from them to ever reach us. That means that it will almost certainly be literally impossible to tell if the Universe is infinite or not.

The best we can do is to show, continually, that it is at least bigger than what we can see. In that sense, at least, current understanding certainly *is* relevant because the current understanding is that the question is open (but that it's probably infinite, for the moment).

[Peter Pedant]

// TTT, it can only be a best guess - and anyone with an interest in it can have a best guess.//

o god this is late night AB craziness

so my best guess is that the earth is flat ( or God created it in 4004BC) and so that should be given prominence in schools along with Darwin and Lyell ? -as all theories are equally valid. Oh Dear

[New Judge]

Since it's late and since nobody knows the real answer it's best to keep it simple:

There always has been and always will be a set amount of matter/energy (the two being interchangeable) in the universe, although its composition and density will have varied. It has always existed in an infinite space.

There's no real need to make it any more complex than that.

[ToraToraTora]

no one is saying it's right they are saying it's the best explanation we have that fits the observations.