How can an infinite universe expand?

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NewTime
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22 Jul 2015, 11:41 am

Really? If the universe is infinite, how can it get any bigger? If it's infinite, it can't be expanding.

starfox
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22 Jul 2015, 11:43 am

If its infinite it's just 'there'. Infinite can't be measured.

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22 Jul 2015, 1:38 pm

NewTime wrote:

Really? If the universe is infinite, how can it get any bigger? If it's infinite, it can't be expanding.

What happens when you add 1 to infinity? How about infinity plus infinity?

xenocity
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22 Jul 2015, 6:42 pm

Technically the universe is finite, not infinite.
Everything outside of the universe is nothingness on this plane (other universes is exist in parallel on other planes along side our universe).

They can measure how fast the universe is expanding, due to how fast everything is moving away from the center/each other.
If the universe was contracting, everything would be moving closer together, toward the center.

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naturalplastic
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22 Jul 2015, 9:03 pm

The universe is thought to be finite ( ninety billion light years across). But it might be infinite.

But even if it is infinite you can always add more to infinity.

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22 Jul 2015, 11:11 pm

Even though there are infinitely many rational numbers, they are vastly outnumbered by the number of irrational numbers.

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23 Jul 2015, 6:24 am

Another theory is that the Void is infinite, and that our universe is expanding into it. There may or may not be other universes in the same Void, but they are either too far away for their light to have reached us yet, or they had already decayed into nothingness before our universe came into being.

eric76
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23 Jul 2015, 12:49 pm

Fnord wrote:

By definition, if light or anything else can get from one universe to another, they are the same universe.

zer0netgain
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23 Jul 2015, 1:23 pm

Or the mindbender that a subset of infinity is itself infinite even though it's smaller.

Fnord
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23 Jul 2015, 1:54 pm

eric76 wrote:

Fnord wrote:

By definition, if light or anything else can get from one universe to another, they are the same universe.

True. The "Raisin Pudding" theory basically states that the infinite "Void" (e.g., the "Multiverse") is a vast volume of space in which a universe (e.g., a "Hubble Volume") might burst into existence at some random location, expand, evolve, die, and eventually decay into a dim mist of subatomic particles. Several universes may coexist in this "Void"; but because they are so far apart the light from our closest neighboring universe would not reach our universe until one or both universes have decayed to quark soup.

This is also called a Type 1 Multiverse in Max Tegmark's Taxonomy of Universes.

Wikipedia wrote:

"... an infinite universe will contain an infinite number of Hubble volumes, all having the same physical laws and physical constants. In regard to configurations such as the distribution of matter, almost all will differ from our Hubble volume. However, because there are infinitely many, far beyond the cosmological horizon, there will eventually be Hubble volumes with similar, and even identical, configurations. ... Given infinite space, there would, in fact, be an infinite number of Hubble volumes identical to ours in the Universe ..."

Source: Wikipedia Article on Multiverse

Jono
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23 Jul 2015, 7:49 pm

NewTime wrote:

Really? If the universe is infinite, how can it get any bigger? If it's infinite, it can't be expanding.

Actually, the simplest answer is that the size of the universe does not have to be finite in order to expand because doesn't mean that it's getting "bigger". Thinking that the universe has to expand into something is not really the right way to think about, it's more that empty space is "stretching". In other words, distances between galaxies are getting larger because the space between them is stretching but I can imagine this happening even for an infinite universe.

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23 Jul 2015, 8:02 pm

zer0netgain wrote:

Or the mindbender that a subset of infinity is itself infinite even though it's smaller.

The set of odd numbers is smaller than the set of whole numbers. But both are infinity.

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24 Jul 2015, 8:40 am

Fnord wrote:

This is also called a Type 1 Multiverse in Max Tegmark's Taxonomy of Universes.

Wikipedia wrote:

Source: Wikipedia Article on Multiverse

Which logically means an infinite number of Fnords and infinities of near-Fnord variants in nearly identical hubble volumes...

Something entertaining to think about.

Fnord
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24 Jul 2015, 8:45 am

Adamantium wrote:

Fnord wrote:

This is also called a Type 1 Multiverse in Max Tegmark's Taxonomy of Universes.

Wikipedia wrote:

Source: Wikipedia Article on Multiverse

Which logically means an infinite number of Fnords and infinities of near-Fnord variants in nearly identical hubble volumes ... Something entertaining to think about.

Somewhere out there may be a variant of me that is popular, incredibly wealthy, in perfect health, and has the physique of Clark Kent.

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24 Jul 2015, 8:50 am

xenocity wrote:

Technically the universe is finite, not infinite....

Then, what exists outside it?

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24 Jul 2015, 8:53 am

naturalplastic wrote:

zer0netgain wrote:

Or the mindbender that a subset of infinity is itself infinite even though it's smaller.

The set of odd numbers is smaller than the set of whole numbers. But both are infinity.

It is very easy to map the set of whole numbers onto the odd numbers and the odd numbers onto the whole numbers.

Therefore, there is a 1:1 correspondence between the two sets and thus both have the same number of elements.

Consider this:

The odd numbers are the positive integers not divisible by 2: { 1, 3, 5, 7, 9, ... }
The Whole numbers are the postive integers and 0: { 0, 1, 2, 3, 4, 5, ... }

Let O be the set of odd numbers and W be the set of whole numbers.

Define f :W->O by f(x)=2x+1 for all x in W. Since for every x in W, there is an f(x) in W, we have that |O| >= |W|.

Define g:O->W by g(y)=(y-1)/2 for all y in O. Since for every y in O, there is a g(y) in W, we have that |O|<=|W|.

Thus, |O|=|W|.

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