Expanding Universe

[Khandro]

If the universe is expanding, which seems to be the case, what is it expanding in to?

[jim360]

Incidentally, that also means that there are as many odd numbers as there are whole numbers, as many prime numbers, cubes, etc etc...

Why this relates to the Universe, then, is that if it's infinite to start with, then expansion takes the form of, say, doubling the distance between everything. After that, there's still exactly the same "amount" of Universe you had to start with, it's just that two points that were one light year apart before are now two lights years apart, say. The Universe as a whole isn't getting bigger, because it *can't* get bigger. It can just get more spread out.

[Old_Geezer]

Example ? Occurring all the time in "empty space".
It's what causes Hawking Radiation which is part of black hole "evaporation".

[Old_Geezer]

Still unconvinced that our universe is infinite.

[rockyracoon]

'The Universe as a whole isn't getting bigger, because it *can't* get bigger. It can just get more spread out.'

See, that makes absolutely no sense to me.

[Prudie]

Can I add that every single number is interesting. If you take out all the interesting numbers, be they perfect squares, cubes, days in a year whatever then you will be left with a list of boring numbers that have no claim to fame - however 2 of them will be the largest and the smallest boring number so now they too are interesting for that reason so you must remove them from the boring list. Having done that you will have 2 new largest and smallest etc etc ad infinitum (or is it ad nauseam). Anyway keep going and you will find nothing boring is left, all numbers are interesting. :-)

[Old_Geezer]

Well Rocky, it makes sense when you get a grasp on infinity and infinities. You can add as much as you like to an infinity and it remains an infinity.

So IF you decide that the universe is infinite then it's constellations can move apart as much as they like, but the universe simply remains infinite, the same as before.

There's some decent explanations on infinity on YouTube.

[Khandro]

I'd forgotten about that other topic (it's an age thing!), not quite the same as this though, and which I see I had myself responded re. the big bang;

'In simple terms, he (Penrose) believes that the singularity in Einstein's field equation at the Big Bang is only an apparent singularity, similar to the well-known apparent singularity at the event horizon of a black hole. The latter singularity can be removed by a change of coordinate system, and he proposes a different change of coordinate system that will remove the singularity at the big bang. One implication of this is that the major events at the Big Bang can be understood without unifying general relativity and quantum mechanics, and therefore we are not necessarily constrained by the Wheeler–DeWitt equation, which disrupts time. Alternatively, one can use the Einstein–Maxwell–Dirac equations.'
I really couldn't have put it better myself. :0)

[ToraToraTora]

how about this one, are all infinities the same size? NO! eg there are an infinite number of numbers between 1 and 2 so between 1 and 10 there must be 10 x infinity of numbers! (from Jim Al Khalili's maths program)

[jim360]

What is even the point of copy-pasting something like that? The aim ought to be to at least try to explain something, not to throw about technobabble in the hope of blinding people.

I may not have succeeded in explaining why an infinite Universe can still expand, either, but to be fair it's a tremendously hard concept and in practice I only understand it myself by pretending to.

[jim360]

Here's a video that may (or may not) be helpful about the weirdness of infinity when it comes to counting:

[jim360]

Possibly. It depends on what's causing the Universe to expand, and how much stuff there is inside it. Gravity would tend to want to bring things together, so it's a question of balance between these two.

[bazigi]

By the universe i would assume these people are talking about the actual matter in the universe and not the actual space that it frequents.

[bazigi]

I think that when scientists use the term expanding universe they are talking about the expanding of the matter in the universe and not space itself.

[Bazile]

5 in related question on expanding universe

What part of the subject is giving you lot a problem ?

[jim360]

Basigi -- are we? I would have said it was the other way round...

[Khandro]

//The aim ought to be to at least try to explain something, not to throw about technobabble in the hope of blinding people.//

Well, there's a lot of it (technobabble) about. The truthful answer is of course, that nobody knows. However my own view, for what its worth, and it is based purely on intuition, is that wherever I look in nature, everything moves and changes in cycles and circles (more accurately ellipsis) The seasons return, the planets return - never quite the same, but near enough. If I walk a straight line long enough I will return to the same place, - Newton said if he could throw a stone hard enough it would hit him on the back of his head.

I believe somehow that this would apply to space. Travel far enough and you will come back to the same place because space is curved. Therefore, there is no such thing as spatial infinity.

This is only a guess, but I read recently that Enrico Firmi was a great believer in guessing; arguably that's maybe all his amazing mind and mine have in common :0)

[Hopkirk]

It's expanding into next door's back yard.

[jim360]

I'm not quite sure that "Fermi Estimation" is the same thing as "guessing", but never mind.

Also, one should be careful to distinguish spacetime (eg, space and time tied together in the same object) from space. Gravity alone can't curve three-dimensional space without also involving a time dimension.

In the same vein, being obliged to travel in a loopy path through space and time doesn't rule out the possibility that space on its own is infinite.

In practice, of course, we can't ever know that space is infinite, because it is by definition too big to measure. But the best observations of our Universe support the idea that it is almost flat, infinitely big, but with a beginning in time.

[Zacs-Master]

Thanks, Jim. ;-)