- #1

- 70

- 0

I hope i'm making some sense, I didn't get much sleep last night

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter deltabourne
- Start date

- #1

- 70

- 0

I hope i'm making some sense, I didn't get much sleep last night

- #2

jcsd

Science Advisor

Gold Member

- 2,090

- 12

Imagine the universe as an infinitely large piece of square paper, when the paper universe expands the squares on the paper get bigger.

- #3

- 70

- 0

Hmm.. seems to make sense, except that what do the squares that get bigger represent? It isn't planets or celestial bodies, since those aren't getting bigger (are they?). However we know they are moving apart from blue shift, but that doesn't necessarily mean the universe is expanding. It's already large enough to have all the planets infinite distances away from each other (since the universe is infinitely large).Originally posted by jcsd

Imagine the universe as an infinitely large piece of square paper, when the paper universe expands the squares on the paper get bigger.

meh, I may be talking nonsense/semantics here, but it's just a little quirky idea that was bugging me today

- #4

jcsd

Science Advisor

Gold Member

- 2,090

- 12

Something is redshifted when it moves away from us (compared to blueshifted when it moves towrads us) and yes it does mena that the universe is expanding.

- #5

- 841

- 1

Originally posted by deltabourne

Hmm.. seems to make sense, except that what do the squares that get bigger represent?

Regions of space.

However we know they are moving apart from blue shift, but that doesn't necessarily mean the universe is expanding. It's already large enough to have all the planets infinite distances away from each other (since the universe is infinitely large).

When we say that the universe expands, we mean that all the galaxies are getting farther away from each other. That can happen whether the universe is finite or infinite. Any two galaxies are always a finite distance from each other, though that distance may increase with time.

Last edited:

- #6

- 362

- 0

So we're looking at finite space and saying that finite space is expanding. Overall is the universe getting larger? Or is just the space between things in the universe getting larger?

- #7

- 841

- 1

Originally posted by StephenPrivitera

Among infinities, isn't it the case that some infinities are larger than others? I remember hearing something along these lines before. Something like the set of reals is a larger infinity than the set of integers.

When we talk about an infinite universe expanding, no new points are being added: the set of points is always the same order of infinity, the cardinality of the reals.

So we're looking at finite space and saying that finite space is expanding. Overall is the universe getting larger? Or is just the space between things in the universe getting larger?

Both. The universe gets larger because the distances between all points in space get larger.

- #8

- 66

- 0

The application when it comes to these symbols and concepts when it comes to reality becomes somewhat stickier. If the universe is infinite how can it be expanding? What is it expanding into? Thats the kicker

The universe "makes" it own space as it expands it does not expand into anything =) counter intuitive but correct. You may use a sheet of paper as an example but there is nothing outside the sheet of paper . If you finally come to the accommodation , however unreasonable it seems, that there is no outside, you have it . The question on peoples minds is what is it expanding into? The answer is nothing, not really nothing because even nothing is something.. There is no there there, you have to use a Zen mindset to come to grips with it If that happens some of the other weirder concepts of QM and even Relitivistic physics becomes less a mind stunner.

- #9

- 841

- 1

Originally posted by TillEulenspiegel

The universe is considered to be infinite because all that exists is contained within it's limits.

We don't actually know whether the universe is infinite. "All that exists" could be contained within the universe, but the universe could still be finite in size.

- #10

- 66

- 0

Of course we won't know till the SNAP and Planck probes go up will we?

- #11

- 362

- 0

- #12

- 841

- 1

Originally posted by TillEulenspiegel

Well much is not certain, but recent evidance seems to point to omega as ~1 so if correct that means a flat, open , infinite universe dosn't it?

Well, that's if Omega is exactly equal to 1. But we can never know if that's true... the universe could be finite, but inflated so much that it's just under 1...

Originally posted by StephenPrivitera

Didn't the universe start out finite?

No, not necessarily. If the universe is infinite, then the universe started out infinite. (It's only the finite

- #13

- 66

- 0

- #14

- 362

- 0

Ow... my brain hurts.Originally posted by Ambitwistor

(It's only the finiteobservableuniverse that has to start out as a point.)

What nonsense is this? So every finite element of the universe started out as a point. And to sum all these points an infinite amount of times we get an infinite space. Sounds like 0 times infinity = infinity to me.

- #15

- 841

- 1

Share:

- Replies
- 4

- Views
- 2K