Randy Goldberg asked:
I was listening to the "Ask the Naked Scientist" podcast this morning, and two of your answers prompted other questions.
Regarding parallel universes, is it possible that so-called "dark matter" isn't actually physically present in our universe? Could it be a manifestation of gravity crossing over from parallel universes?
Randy Goldberg MD
Dominic - Thatís an interesting and rather topical question actually. We donít have a good idea at all what dark matter is. We can only see its gravitational influence on other objects in the universe.
If you look at galaxies and you measure how fast those galaxies are rotating and estimate how much mass is in those galaxies, you'll realise that they should really spin apart because of a centrifugal force. There must be some gravitational glue in there, sticking that galaxy together and that mass isnít producing any light, so we call it dark matter. But we have very little idea what that mass is.
Weíve had some theories and one of the leading theories, up until a few weeks ago was particles that particle physicists call supersymmetric particles. But you may have seen in the news in the last few weeks, the latest news from the Large Hadron Collider is that those supersymmetric particles probably donít exist. So I think weíre back to the drawing board actually in trying to work out what dark matter actually is.
Chris - Itís a tough one, isnít it because we know itís there. We can see its effects, but we have no idea how to actually start trying to measure it.
Dominic - Thatís right. I think the evidence will come from experiments like the Large Hadron Collider. This is almost certainly some new kind of particle that we donít actually know yet about, but which I'm sure we would discover at some point.