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Q & A: higher dimensions and dark matter and energy

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Most recent answer: 12/24/2009
Q:
Here is a question that has been bothering me for at least half my life time. It has to deal with dark matter. First I must state the standard fact that there is no center of the universe. This is the reason for the big bang noise coming in from all directions. This indicates that our universe system has more dimensions than the time-space co-ordinate set we can observe. So my question is, how come everyone's dark matter calculation assume that there is no forces acting on our universe outside of the time-space set? Let's say our time-space experice is 3d ballon shell in a 4d space. Could there not be forces in the time-4d space effecting the expansion or contraction of our time-space uniserve we obserb? Would they not effect the dark matter calculations?
- Robert J Dunn (age 59)
Montreal, Quebec, Canada
A:
I'm not sure if your question is about dark matter or dark energy. I'll answer first about dark energy, since it's fairly likely that dark matter is something like familiar matter, but consisting of particles which don't interact much with us except via gravity.

It's not clear how you go from the universe's lack of a center to the conclusion that other dimensions exist. Nonetheless, there are other chains of thought, mostly connected with integrating General Relativity and quantum mechanics, which suggest that there are likely to be some other dimensions.

There are now a number of efforts to do exactly what you propose: consider the effect of the contents of these other dimensions on the expansion of our space. Some concern tiny folded-up dimensions, and their contribution the energy density of space. Others, more recent, are more like what you're suggesting- parallel spaces separated by a small distance in another dimension, interacting with ours.

Getting back to dark matter, some of those ideas do suggest that dark matter also may be the effect of a nearby space. Fortunately these ideas are testable, and we should be hearing soon which fit better with detailed observations.

Mike W.

(published on 12/24/2009)

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