I read an interesting article today on new experimental data from the XENON dark matter search. But first I should give a little background...

For the last few decades there has been growing evidence that the majority of matter in the Universe is in some unknown exotic form. All we know about it is that it has a mass, and that it doesn't interact very much if at all with light. There are literally thousands of proposed models for dark matter, and it seems at times that there are just as many experiments searching for it.

About five years ago, a large experiment called DAMA found that there was a signal of dark matter colliding with the Earth as it orbits the sun. 

Another experiment called CDMS went looking, and they found that the dark matter signal does not exist. Theorists immediately point out that this could happen if dark matter is about as heavy as a hydrogen atom.

Last year CDMS-II, the next generation detector, discovered a signal of dark matter. But this week another experiment, called XENON, released their data that shows both DAMA and CDMS-II are wrong and there was no signal.

Except that XENON itself could have missed the signal if the dark matter particle weighs more than 80 times the mass of a hydrogen atom. But if that is true then the original DAMA-CDMS conflict may re-arise.

Assuming that all three experiments are accurate (which is never certain in this business) that means that dark matter must be even more exotic than we thought.

What a great time to be a physicist!