Cosmological Inquiry (like wow, man...)

[ParanoiA]

Ok, so last I heard most of science suspects multiple universes. My gee wiz questions for the day are, what would happen when two universes collide? How would we experience that? Is there such a thing as trajectory when analyzing the collision of universes, and thus a range of impact intensity or even more of a merge than a collision?

 

Oh, another one that's always bugged me, is it assumed the laws of physics would be the same within other universes? If not, I wonder how that would effect the outcome of an impact with each other...

[ajb]

There are brane cosmologies that people study. The ekpyrotic model suggests that our universe originated from the collision of two branes. It has been suggested as an alternative to the big bang model, but I think as the cosmology evolves the same as the FRW cosmologies it is better viewed as an explanation of the initial "explosion" of the big bang.

 

 

W. Perkins considered a model in which our world is a spherically symmetric bubble wall in 5-dimensional anti-de Sitter spacetime. (This is a particular brane world scenario.) He then suggests that our world will undergo many collisions with similar bubbles pre-existing in the anti-de Sitter bulk. He shows that the collision rate is independent of the age of our universe. If his model is accurate then we could be colliding all the time. Collisions with these other bubbles would be seen as a inflow of energy to our universe. Larger bubbles could be catastrophic!

 

(This inflow of energy could be used as a test of this model. In essence there would be a random injections of energy into our universe due to each collision.)

 

Perkins also shows that the late time evolution of the scale factor is governed by the Friedmann equations and so does look like a more standard cosmology theory.

 

Colliding Bubble Worlds W. Perkins arXiv:gr-qc/0010053v1

[ParanoiA]

There are brane cosmologies that people study. The ekpyrotic model suggests that our universe originated from the collision of two branes. It has been suggested as an alternative to the big bang model, but I think as the cosmology evolves the same as the FRW cosmologies it is better viewed as an explanation of the initial "explosion" of the big bang.

 

That's an interesting model. I followed that link and noticed toward the bottom of the article they talked about how colliding branes are still not understood by string theorists. That's the perfect hole for what I'm doing. I wonder then, if branes could simply merge, effecting time, space and mixing the laws of physics of the two branes.

 

Do you know if there are any theories or suspicions about the nature of the physics in these other branes? It would be interesting if their physics were different...like 5 fundamental forces...or maybe there are more types of particles...or less...or maybe matter is arranged differently...maybe the nuclear forces do not exist and matter and energy is just not built the same...

 

W. Perkins considered a model in which our world is a spherically symmetric bubble wall in 5-dimensional anti-de Sitter spacetime. (This is a particular brane world scenario.) He then suggests that our world will undergo many collisions with similar bubbles pre-existing in the anti-de Sitter bulk. He shows that the collision rate is independent of the age of our universe. If his model is accurate then we could be colliding all the time. Collisions with these other bubbles would be seen as a inflow of energy to our universe. Larger bubbles could be catastrophic!

 

(This inflow of energy could be used as a test of this model. In essence there would be a random injections of energy into our universe due to each collision.)

 

Perkins also shows that the late time evolution of the scale factor is governed by the Friedmann equations and so does look like a more standard cosmology theory.

 

Colliding Bubble Worlds W. Perkins arXiv:gr-qc/0010053v1

 

That's a pretty interesting theory too. I tried to follow the link, but I guess you have to pay to play? Fair enough. I tried to look up anti-de Sitter spacetime, and that's thick with concepts I'm not even remotely familiar with. The larger bubble catastrophe sounds like an interesting focal point to use in a fictional application. Very neat. I just wish I understood it.

Edited February 13, 2010 by ParanoiA

[ajb]

Gauge theories arise from branes when you consider coincident branes and string attached to them. Three branes can lead to supersymmetric version of QCD. So, I guess we can build worlds with gauge theories.

[Moontanman]

I like the idea of colliding branes as compared to sheets hanging on a clothes line, the sheets are branes in a 5 or more dimensional bulk. Gravity between the two branes attracts them to each other as they collide you get a universe wide big bang. The energy released causes them to spread apart, energy condenses back to matter the same way as what we think of as the big bang.

 

Wrinkles in the branes might cause pin point "big bangs" all through our space/time but the result of the collision would still be the same and gravity eventually draws the branes back together for a repeat performance.

 

From our point of view the universe is expanding from each collision but most of the colliding branes are forever out side our experience because of the infinite size of the branes in our view of space time but from the stand point of the bulk they would still be finite.

[ParanoiA]

Gauge theories arise from branes when you consider coincident branes and string attached to them. Three branes can lead to supersymmetric version of QCD. So, I guess we can build worlds with gauge theories.

 

I really like the potential for this gauge theory, as you describe it here. So, I looked it up on Wiki to read more about it:

 

In physics, a gauge theory is a type of field theory in which the Lagrangian is invariant under a continuous group of local transformations.

 

The transformations (called gauge transformations) must form a Lie group which is referred to as the symmetry group or the gauge group of the theory. Associated with any Lie group is the Lie algebra of group generators. For each group generator there necessarily arises a corresponding vector field called the gauge field. Gauge fields are included in the Lagrangian to ensure its invariance under the local group transformations (called gauge invariance). When such a theory is quantized, the quanta of the gauge fields are called gauge bosons. If the symmetry group is non-commutative, the gauge theory is referred to as non-abelian, the most usual example of which being the Yang–Mills theory.

 

Gauge theories are important as the successful field theories explaining the dynamics of elementary particles. Quantum electrodynamics is an abelian gauge theory with the symmetry group U(1) and has one gauge field, the electromagnetic field, with the photon being the gauge boson. The Standard Model is a non-abelian gauge theory with the symmetry group U(1)×SU(2)×SU(3) and has a total of twelve gauge bosons: the photon, three weak bosons and eight gluons.

 

But man..I can't begin to get my head around any of that, at least not with that level of nomenclature. You physics folks really impress me. Must take a lot of time and effort to learn and absorb this science.

 

I like the idea of colliding branes as compared to sheets hanging on a clothes line, the sheets are branes in a 5 or more dimensional bulk. Gravity between the two branes attracts them to each other as they collide you get a universe wide big bang. The energy released causes them to spread apart, energy condenses back to matter the same way as what we think of as the big bang.

 

Wrinkles in the branes might cause pin point "big bangs" all through our space/time but the result of the collision would still be the same and gravity eventually draws the branes back together for a repeat performance.

 

From our point of view the universe is expanding from each collision but most of the colliding branes are forever out side our experience because of the infinite size of the branes in our view of space time but from the stand point of the bulk they would still be finite.

 

Sounds like that works with the cyclic model - the big bang/crunch cycle.

 

I like it too, because it's easier for me to visualize, even though I can't help but to wonder how much I'm missing by treating higher order (?) dimensions as extended lower order ones by thinking of 5th dimensional bulk as space between the sheets or containment for bubbles.

 

This reminds me..I thought I asked this before on a previous thread, but I don't think I ever got a good response: Is there any reason to believe the laws of physics as we know them in our universe would remain the same or change at some point throughout the process of a big crunch?

 

Being a layman, I would expect to see a more compact universe.

[Moontanman]

This reminds me..I thought I asked this before on a previous thread, but I don't think I ever got a good response: Is there any reason to believe the laws of physics as we know them in our universe would remain the same or change at some point throughout the process of a big crunch?

 

Being a layman, I would expect to see a more compact universe.

 

That is a good question, my understanding is that in the colliding brane scenario both branes are the same laws each time but that doesn't explain why they are the way they are. I guess it's possible each collision rests the laws at random but this seems counter intuitive to me at least.

 

Depending on how far up the dimensional ladder the bulk goes our whole universe would indeed seem to be very compact in comparison, at least that how I see higher dimensions in my mind.

 

Another way to look at it is the Bulk can easily contain an infinite number of branes of any and all configurations, some branes might not be anything we would recognize as universes at all.