# I'm sure this has been asked before, but: Universes colliding with each other

1. Oct 23, 2012

### mustang19

Forgive me for not being a professional cosmologist, but can't the universe collide with another universe? If similar instances of the universe's Hubble volume occur every so often, won't they eventually run up against each other and push each other around like giant jelly balls?

And can't our universe even get sandwiched between two other such universes, compressing ours down to a singularity?

I know I make no sense, but thanks for your patience.

2. Oct 23, 2012

### ImaLooser

Today anything outside our Universe is completely unknown, so who knows?

3. Oct 23, 2012

### Staff: Mentor

Universes (if there is more than 1) are not like balls in a 3- or 4-dimensional environment which could collide. They are not embedded in some space. They are space (with objects inside).

4. Oct 23, 2012

### mustang19

As good an answer as any.

I see. But they can still exert force against each others' volumes, I think. Doesn't the dark energy in one Hubble volume compress or act against the dark energy in the ones it collides with, or do both volumes keep on inflating regardless?

5. Oct 23, 2012

### Staff: Mentor

How do you define "force" without space(time)?

The Hubble volume is a part of our universe, and its "boundary" is not different from anything else in the universe (its position is just the result of a mathematical calculation). That is a completely different thing.

6. Oct 23, 2012

### mustang19

Alright, alright, I get it now.

Say you have three universes sitting in a row, with Universe A on the left and Universe C on the right, with universe B in the middle. As A and C expand and "sandwich" B, pressing against it on both sides, will the dark energy in A and C exert any force against the dark energy in B? Will this slow B's inflation at all?

7. Oct 23, 2012

### phinds

No, clearly you DON'T get it. Reread post #3

8. Oct 23, 2012

### mustang19

Well, going by that post, I'm left with the impression that the universes would more or less merge, with negligible compression between them. I appreciate the answers to my rather crude questions.

Last edited: Oct 23, 2012
9. Oct 23, 2012

### phinds

First, "universe" === "all there is" and it is unlikely that there is more than one.

There ARE "multiverse" theories that postulate more than one "all there is", but first, they have ZERO evidence and are highly speculative, and second, even they do not say there is any connection of any kind among the different ones.

You should read the forum rules that prohibit personal theories (that is, ones that have no apparent basis in fact). This is a forum for mainstream science and you are just making up speculative concepts.

There are lots of forums on the internet where you can let your imagination run wild, but this is not one of them.

10. Oct 23, 2012

### mustang19

You seem like you're speaking from experience. Well, again, thanks for the response. I'll try to stick to solid evidence from now on while I'm here.

11. Oct 23, 2012

### phinds

I should add that multiverse theories are not banned at all on this forum. Despite evidence, they are a valid topic for mainstream (well, sort of) science. My point on your speculation was about your concept that "universes" somehow occupy the same space-time continuum without being part of the same universe. Actually, that isn't really speculative so much as just nonsensical.

It IS good to let your imagination run, and to "think outside the box". BUT ... on this forum, you are required to first know what's in the box, or to ask questions about what's in the box, not speculate about what's outside the box without any basis in actual physics.

It's a great forum, really.

12. Oct 23, 2012

### mustang19

By "universes" I meant something along the lines of "identical Hubble volumes within the same universe", but I guess the answer is the same.

Apologies if there are stacks of threads on this, but one thing I never understood is what dark energy was. I assume it's something like light, which transfers energy through space. Light is made up of photons, so I'm not sure if dark energy has a similar hypothetical particle which transmits and mediates it, or if it is even supposed to have a particle nature.

It's just a question. If this isn't a place for asking questions about Physics 101 (or would it be 103?), I understand completely.

13. Oct 23, 2012

### Staff: Mentor

Do not use "universes" then, please, if you refer to parts of our universe.
The Hubble volume is a mathematical result of some calculation about our (here: earth) current state in the universe. They "merge" or do not merge in the same way as "a sphere around earth with radius 100km/s*t" and "a sphere around sun with radius 100km" would "merge". Just a mathematical thing.

14. Oct 23, 2012

### phinds

There are, so do a forum search. Doing that is something you should get in the habbit of doing before asking basic quesions.

15. Oct 23, 2012

### mustang19

Thanks for the clarification.

Got it.

16. Oct 23, 2012

### phinds

Also, FIY, you would likely find it VERY informative to read the FAQ in the cosmology section

17. Oct 23, 2012

### mustang19

Good stuff. Thanks again, phinds.