In my explanation of Dark Matter (click here) I talked about how we can’t see it, so you may be wondering why we have detectors trying to find someting that we can’t see. Dark matter detectors are designed to detect the tiny, rare signals produced when a dark matter particle interacts with ordinary matter. In noble-gas detectors, scientists look for these interactions by detecting the light and electrons produced when a gas atom is disturbed. But because the surface of the earth has a lot of existing background radiation from the sun and space (don’t worry, this stuff is perfectly safe and natural to us), it’s hard to see those tiny, rare signals. So we need to build these detectors in places where there is less of that background radiation (we call it “noise”) and that is why we typically go underground where the rock can shield us from a lot of it. We have yet to detect dark matter, but the experiments are getting larger and more fine tuned as we learn more and more about it.

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Imagine a huge museum containing thousands of extremely delicate objects. The museum of course has a security system with cameras pointed everywhere, and it recently got a new upgrade: whenever one of the objects is moved, it will light up. This will let the security team know if someone is trying to take anything. It’s a pretty popular museum, thousands of people visit it daily. Then the security team starts to notice something – objects are being bumped into and lighting up!

For the most part, they can see when it happens on their cameras. They see an elderly lady turn with her walker and accidentally shuffle into one item, and a young child running and stumbling into another. But then they notice that one of the items that lit up didn’t seem to have anything at all knock into it. They frown at the video, shake their heads, and figure they must have just missed it. But then it happens again. So they begin to get a bit paranoid.

So now they restrict security a bit more. They control the number of people that are allowed in at a time. Fewer objects light up, but still there seems to be an instance where one does with no one around to knock into it. So they restrict access even further, but it happens again!

Finally they decide to close the whole musuem down and watch the cameras. It’s completely silent inside. And then… there! A light! They race to the object in question, but the culprit is already gone. It turns out to be a famous elusive cat burglar who wears a special suit that hides him from the cameras and makes him invisible. But the word is out… the Dark Matter Bandit strikes again.