The moral of this calculation, at least as it was presented to me in the early 2000s, was that dark matter—whatever it is—is likely to be made up of particles that interact predominantly through the weak force. We called this class of dark matter candidates weakly interacting massive particles, or WIMPs. Although many kinds of WIMPs had been proposed over the years, none had been directly detected in any experiment. The closest things to a WIMP that we had ever observed were the neutrinos, but these particles are far too light and fast moving to constitute much of our universe’s dark matter.
