We have a damned good understanding of macroscopic gravity at this point. When we simulate the creation of a galaxy, there's a huge missing link. The math shows that there has to be non-luminescent matter comprising 80% of the universe. This elusive Dark Matter provides the mass that makes our models click into place nice and neat.
One theory is that Dark Matter is the undiscovered particle called the WIMP (weakly interacting massive particle), and is all around us. The "weak" this is referring to is the weak nuclear force, a fundamental force in physics mediated by the W and Z bosons. Basically, weak force can turn a quark into a different type of quark. Since different combonations of quarks translate into different composite particles, weak nuclear interaction can turn a neutron into a proton (with a couple extra particles as byproducts).
So far, we haven't detected WIMP's because they don't interact with the electromagnetic force OR the strong force. They only react to gravity and weak force. Weak force occurs in the nucleus of an atom, which gives us a means to dectect these WIMP's. Here's where the dark matter detector comes in.
If the theory is right, WIMP's are zipping right through the earth (and us) every second, and if a WIMP happens to run smack dab into an atomic nucleus in one of our dark gravity detectors, we should be able to detect it.
The Xenon100 detector is deep underground in a shielded lab in Italy. It's a cylinder with an electric field along its vertical axis, filled with almost perfectly pure liquid xenon. One of the reasons they use xenon is that it shields itself, meaning that a detection closer to the center of the container is less likely to be a false positive. For this reason, detections not in the center are tossed aside just to be safe.
When a WIMP collides with a xenon nucleus, it creates a primary light source, and then a secondary light source due to the electroluminescent quality of xenon. In this way, we're translating a weak force interaction into an easily observable electromagnetic interaction. From these light sources we can pinpoint where the WIMP hit and also evaluate the light to make sure it WAS a WIMP.
So far we haven't observed any, but hopes are high that we'll find this particle, so crucial in the model we have for understanding the universe.
Also, WIMP's can't throw footballs very far, and chicks don't seem to like them.
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