Monday, August 21, 2006

Dark matter press conference

Just a link to pages linking to the
that started at 1 p.m. Eastern daylight-saving time. Also, the following page with photographs was unlocked before 1 p.m.
The pink and blue clouds on the first picture represent the ordinary and dark matter, respectively. The blue dark matter has been deduced from a gravitational lensing analysis of those colliding clusters while the visible pink matter was determined optically. Because the two colorful clouds don't overlap, you might view it as a direct observation of dark matter. Unless there is a subtlety, MOND is ruled out as the full explanation of the facts that are normally explained by dark matter, much like all known theories that don't involve additional dark matter. At least, the MOND theories whose modified gravity depends exclusively and additively on the mass distribution are probably ruled out.

I don't think that it has really falsified some holographic versions of MOND that I've always found to be the best motivated kind of MOND - because such pictures could produce interference contributing to the gravitational lensing - but a more detailed analysis must be made. There is quite a clear prediction of the more general theories in which dark matter is not needed: whenever you see the same distribution of the visible matter, the distribution of the would-be dark matter that you get from the gravitational effects must also be the same in all cases.

If the people see several examples of the same pairs of clusters and the distribution of the visible and dark matter will be similar in all cases, that would be suspicious. On the other hand, if they see another example in which the visible matter is almost identical to the present case but the dark matter is completely different, that will probably eliminate all theories without dark matter, including the sophisticated holographic or at least velocity-dependent theories mentioned above.

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