Having all these competing projects is ultimately necessary, if any result is to be believed.
"Most people in the field agree you're going to need to see evidence of this in more than one experiment and more than one type before everyone's convinced," Bauer said.
And WIMPs aren't the only candidate particles for dark matter. Another potential solution to the problem is called the axion. This is a theorized particle that is also neutral and weakly interacting, but might lighter than WIMPs. Therefore, if axions are dark matter, there would have to be a lot more of them around.
An experiment called the Axion Dark Matter Experiment (ADMX) at the University of Washington uses a large superconducting magnet to search for these particles. So far, that search has turned up empty as well.
And an even weirder explanation for dark matter comes from the idea that there are tiny hidden dimensions wrapped up inside the known four dimensions of space-time in our universe. If that's the case, there could be accompanying particles called Kaluza–Klein particles that account for dark matter. However, these would be even harder to detect.
And it's too soon to rule out even more the unlikely sounding explanations.
"The things we thought were higher probability haven't shown up yet, so we should keep an open mind," said theoretical physicist Lance Dixon of the SLAC National Accelerator Laboratory in California.
Keep the dark matter hope alive
Despite the difficulty of finding dark matter, whatever it is, physicists say they're not discouraged.
"I'm pretty confident that dark matter is real, and it seems attractive for it to be carried by an elementary particle, although I could think it might not be exactly that way," Dixon said. "We might not be lucky that the elementary particle that is one that is within the realm of detection."
Bauer said he's been working on CDMS for a long time, and admitted to thinking, at first, that he would have found something by now.
"I guess it’s the natural optimism of physicists to think this is something we might actually be able to find," he said. But even if his experiment never detects dark matter, that in itself tells scientists something interesting.
"It would be more exciting if we saw it than if we didn’t, but it's an important result either way," Bauer said.
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