# How do branes emerge in cyclic universe?

how do branes emerge in cyclic universe??

ok so in the cyclic model of the universe...two branes are colliding and this is causing big bangs every few trillion years. this solves nicely the initial singularity and explains many things

but i have two questions

1) how do these branes emerge? from what?

2) how is it possible for this collisions to be going on forever...i do not believe there is such thing as infinity becouse its not logical. all this had to have a begining before it starts colliding, right?

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There are several models of the "ekpyrotic universe" models.

It is simplest to think of them as 5d models, and ignore the compact Calabi-Yau dimensions from string theory.

In one of them, the fifth dimension collapses and reinflates itself periodically. On each 4-boundary is a brane, one of which is our observed universe. The collapsed state corresponds to the big bang in our observed universe. As the traditional big bang model, this is also a severe geometrical singularity, so it would not be correct to say that it "solves" this. In that model, the branes always existed, and the model doesn't have an origin of time.

Then there is the "bulk brane" version, which has no such spacetime collapse singularity. Also in this case, two boundary branes always existed, but a spontaneous generation of a third "bulk brane" happens at on boundary. This bulk brane moves in the fifth dimension (in a potential generated by the interaction between it and the boundary branes), eventually colliding with the other boundary brane (our universe). This collision corresponds to the big bang as seen in our 4-d universe.

Since the second scenario doesn't contain a spacetime collapse singularity, I find it more attractive. If you want, you can take a look at some work I did on that model:

http://arxiv.org/abs/hep-th/0502136