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Chalnoth
#17
May23-11, 03:51 AM
Sci Advisor
P: 4,782
Quote Quote by mrspeedybob View Post
So far what I know about dark matter...
Dark matter interacts very weakly, if at all, with electromagnetism.
Dark matter interacts very weakly, if at all, with itself or with normal matter.
Dark matter is approximately 25% of the observed mass/energy content of the universe, dark energy - 70%, normal matter - 5%
Dark matter is observed by gravitational lensing of light and by its effects on galactic rotation.
Dark matter halos surround galaxies.
The dark matter in the universe usually exists in roughly, but not exactly the same places that luminous matter exists.

What properties of dark matter do I not know about about? What properties of dark matter are incompatible with normal matter spread over multiple parallel universes?

If the objection is more to the idea of many parallel universes then that is a different (though related) discussion.

I'm sorry if it seems like I am, but I'm not stuck on this idea. I just want to understand if/why it is incompatible with previous observations before I go wasting a bunch of time on it. If it is incompatible with previous observations then please use it to shine a light on the gap in my understanding so I can fill that gap in.
The most important observation for dark matter, really, is the cosmic microwave background. Basically, before the CMB was emitted, the universe was a plasma. Normal matter in a plasma interacts very strongly with light, and when it falls into a gravitational potential well, this interaction causes the normal matter to feel pressure and bounce. Dark matter, on the other hand, doesn't interact with light, and so experiences no such bounce.

Observing the relationship between how much matter falls into a gravitational potential well and how much bounces gives us a very accurate measurement of the ratio between normal matter and dark matter.

Your "normal matter in an alternate universe" would bounce just like normal matter here does, so it would show a dramatically different signature in the CMB.