Expanding Universe Question..

[kevin1981]

I know there are ideas floating around about the possibility of other universes existing, but i don't know how i feel about this idea, it depends on the answer to my next question.

Our universe is expanding and so i would expect that another universe would do the same. What would happen if the two universe starting to overlap? Could two universes join up to become one or would there be disastrous results ?

If two universes are close together and both expanding then it would be a natural consequence that they would interfere with each other, but i am not talking about "branes" here.

[Cougar]

Vilenkin (http://en.wikipedia.org/wiki/Alexander_Vilenkin)'s "eternal inflation" idea imagines that superluminal inflation is essentially the "background" of the multiverse, and each separate "bubble universe" is a region that has decayed from that background inflation, similar to how "our" universe's vacuum decayed from the ultra-high energy inflation background to a very low energy vacuum. Other universes might have different vacuums, etc.

But with superluminal inflation going on "between" any two bubble universes, they will NEVER be expanding into each other.

All very speculative and conjectural. Questionable whether the multiverse idea can even be considered science.

[pzkpfw]

... If two universes are close together and both expanding then it would be a natural consequence that they would interfere with each other, but i am not talking about "branes" here.

That tends to make it sound like you think of the Universe as existing within some pre-defined "space", such that other Universes could also exist in that same "space" - so that they could come into physcial contact.

(Similar to how many people (contrary to mainstream science) think of the Big Bang as occuring in some pre-existing space and spreading stuff out into that space.)

That's not how it is. The Universe more or less is space and vice-versa, the Universe isn't just some (expanding) area of matter within an endless otherwise empty space.


So without branes or some other multidimensional kind of view of multiverses, how would two Universes come into contact? How do you define "close together"?

[kevin1981]

That tends to make it sound like you think of the Universe as existing within some pre-defined "space", such that other Universes could also exist in that same "space" - so that they could come into physcial contact.

I understand that the mainstream view is that our universe is all that there is. My question is a hypothetical one.

What if our universe and other ones were expanding in a 4th spatial dimension and came into contact with each other, what would happen ?

[Strange]

But with superluminal inflation going on "between" any two bubble universes, they will NEVER be expanding into each other.

Thanks for that insight...

[astromark]

This question and others very like it are seen here on a regular basses...

and the answers are usually of the quality like 'Cougar' offered.. very good.

Understanding the enormity of.. and the expansion apparent.. and just what forces are at work..

All come back at you with a big and clear ?

To the purest scientific mind this is not good enough...

What started it ? Why ? How ? Very good questions that have at this time no clear and accurate answer..

As a proponent of things of science I am sure that no omni present being of unknown origins started it.

" What would happen ? " I can not imagine that as ever possible, is as close as you get to a answer..

From me. I read these offerings with the aim of perhaps one day finding a answer. Not today... :)

[kevin1981]

But with superluminal inflation going on "between" any two bubble universes, they will NEVER be expanding into each other.

All very speculative and conjectural. Questionable whether the multiverse idea can even be considered science.

Ok, thanks Cougar. So the idea's where there could be other bubble universes state that there is faster than light expansion going on between them, thus, they will never have contact with each other, got you !

[Grey]

I understand that the mainstream view is that our universe is all that there is. My question is a hypothetical one.

What if our universe and other ones were expanding in a 4th spatial dimension and came into contact with each other, what would happen ?It's hard to answer this question. As a pure hypothetical, it depends on what nature of the universe you assume, so you can get different results depending on what you imagine. And we don't have enough information about what our universe is like to be able to constrain the answers. So, to some extent, the only possible answer is "it depends".

If you really want to try, though, there are only certain types of universes where this question even makes sense. We can try to imagine one of those, and see what the result would seem to be. For example, we could imagine that the universe is a finite but unbounded hypersphere. That's a reasonable model, permitted by our current cosmology, as long as the scale radius is large enough that it looks essentially flat even on large scales. We could subtract a dimension so that it's the two-dimensional surface of a normal sphere (so that we can visualize it), and then imagine it interacting with another similar sphere. So, where the two spheres intersect, you'd see first a dot, and then a growing ring of material from the other universe. Presumably, matter from that universe would interact normally with matter from our own where the two cross, unless you want to postulate that the other universe has different laws of physics than ours (which isn't necessarily a bad assumption).

[kevin1981]

Hi Grey. I know our universe looks flat, even on large scales, but i like to think that on the largest of scales it is a finite but unbounded hypersphere. It seems to make sense to me and is easy to visualize, i know that i could be wrong but also, i could be right !

So yes, I was thinking about two finite but unbounded hypersphere universes coming into contact with each other and the results of that happening. Of course, it is all hypothetical.

[Grey]

Hi Grey. I know our universe looks flat, even on large scales, but i like to think that on the largest of scales it is a finite but unbounded hypersphere. It seems to make sense to me and is easy to visualize, i know that i could be wrong but also, i could be right !

So yes, I was thinking about two finite but unbounded hypersphere universes coming into contact with each other and the results of that happening. Of course, it is all hypothetical.Yep. I picked that option largely because it's one of the easiest options to visualize. Of course, I then assumed that the two would pass through each other (which seemed like the most natural assumption). But I could also imagine that they bounce off (with various choices for elasticity), or that they just distort each other, or that they join and share a common surface (like bubbles do), or that they merge into a single larger universe. Imagine two hollow spheres colliding, and think about all the ways you can imagine them interacting depending on what they're made of, and probably any of those could be possible. Some possibilities that you can't imagine would probably be possible, too. :)

[Strange]

a finite but unbounded hypersphere ... is easy to visualize

Wow! I wish I could visualize such a thing :)

[kevin1981]

Wow! I wish I could visualize such a thing :)


hehe Well to be honest I just think of the outside of a ballon, then say to myself " but it is 3 dimensional" !

[caveman1917]

Wow! I wish I could visualize such a thing :)

Use time. Imagine looking at a spherical planet with some civilization on it, but they seem to be locked in a "time loop". Everything constantly repeats itself periodically. There you go, your own personal hypersphere ;)

[speedfreek]

How I try to visualise a hypersphere:

Look in any direction and then imagine the straight line you are looking along is actually a section of a great circle much larger than the observable universe. Call that direction x. Then look in the y and z directions and do the same thing. Rinse and repeat, trying to fill all the gaps, until you either realise that the combination of all those circles represents the 3D surface of a hypersphere, or your brain overheats and comes out of your ears.