I Is There an Extra Time Dimension in Paul Steinhardt's Cyclic Model?

[lolofromfrance]

Hello. I think I don't understand very well the Paul Steinhardt's cyclic model of Universe(s). According to Paul Steinhardt, 2 universes get closer. Then, there's the big bounce, which products effects like a big bang. If 2 universes get closer, they have a (relative) speed (
speed is the derivative of the position with respect to time). So, for having a speed (for example in meters per second), we need a time dimension. However, we have a time dimension, but INSIDE our universe (a space-time universe). So, have we got ANOTHER time dimension OUTSIDE our universe ? Or have we a time dimension which is shared by several universes ?

 

[PeterDonis]

According to Paul Steinhardt, 2 universes get closer.

They aren't "universes", they're branes--4-d objects in a higher dimensional spacetime.

If 2 universes get closer, they have a (relative) speed

Note that this is way oversimplified for a brane model. However, since the brane model assumes, as I said above, a higher dimensional spacetime in which our universe is embedded (as well as the other brane with which it periodically collides), there is a common time dimension, the time dimension of that higher dimensional spacetime. But there might not be a simple relationship between that time dimension and what we, inside our particular brane, perceive as time.

 

[lolofromfrance]

Thank you very much Peter. So, if there are two 4-branes in the same universe, can we send or receive particles from the other 4-branes, gravitons for example ? More, that we call "black matter", could be it classical matter from the other 4-branes, which would have gravitationnal effects on OUR-4 branes (so this "black matter" would be not in our 4-branes but in the other 4-branes) ?

 

[PeterDonis]

if there are two 4-branes in the same universe, can we send or receive particles from the other 4-branes, gravitons for example ? More, that we call "black matter", could be it classical matter from the other 4-branes, which would have gravitationnal effects on OUR-4 branes (so this "black matter" would be not in our 4-branes but in the other 4-branes) ?

All of this would depend on the model. I'm not familiar enough with Steinhardt's model to know what it says about this.

 

[lolofromfrance]

Ok thank you for your answer Peter [emoji6]