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

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Discussion Overview

The discussion revolves around Paul Steinhardt's cyclic model of the universe, specifically addressing the concept of time dimensions in relation to multiple universes or branes. Participants explore the implications of relative speed between these entities and the nature of time in higher-dimensional spacetime.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the existence of a time dimension outside our universe in the context of Steinhardt's cyclic model, questioning if there is an additional time dimension or a shared one among multiple universes.
  • Another participant clarifies that the entities in question are branes, which are 4-dimensional objects in a higher-dimensional spacetime, suggesting that there is a common time dimension in that higher-dimensional context, though its relationship to perceived time within a brane may not be straightforward.
  • A participant inquires whether particles, such as gravitons, can be exchanged between different 4-branes and speculates that what is termed "dark matter" might be classical matter from other branes exerting gravitational effects on our brane.
  • Another participant acknowledges the inquiry about particle exchange between branes but notes uncertainty regarding the specifics of Steinhardt's model and its implications for such interactions.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of time dimensions or the interactions between branes, with multiple competing views and uncertainties remaining in the discussion.

Contextual Notes

The discussion reflects limitations in understanding the specifics of Steinhardt's model, particularly regarding the nature of time and the interactions between different branes, which remain unresolved.

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 ?
 
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lolofromfrance said:
According to Paul Steinhardt, 2 universes get closer.

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

lolofromfrance said:
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.
 
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) ?
 
lolofromfrance said:
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.
 
Ok thank you for your answer Peter [emoji6]
 

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