Despite a wealth of sophisticated experiments and contributions from some of the greatest intellects of our time, the search for dark matter continues. It might account for a quarter of the energy density in the universe, but to date, all attempts at direct detection have proved fruitless.
The enigmatic matter does not absorb or emit light. It also doesn’t interact with the three of the four fundamental forces of nature. These elusive properties make it almost impossible to pin down.
Researchers across the globe are itching to uncover the mysteries of dark matter—from the search for WIMPs at the Large Hadron Collider (LHC) to the University of Washington’s cutting-edge axion detector. While some theories predict the answer will be found in an extra hidden dimension, others prefer black holes and neutron stars.
Despite the lack of direct evidence, the vast majority of astrophysicists still believe that dark matter is out there. Cosmic phenomena like the rotation of galaxies cannot be explained through traditional physics unless a hidden form of matter is present.
1 Weakly Interactive Massive Particle (WIMP)
For decades, the most popular candidate for dark matter has been the weakly interacting massive particle (WIMP). The hypothetical particle was first dreamed up in the 1970s as an expansion of the traditional Standard Model of particle physics. The theory is that the cosmos is swarming with invisible, neutrally charged particles that came into being shortly after the big bang.
The idea of invisible particles is nothing particularly new. Scientists are already aware of the neutrino—the difficult-to-detect subatomic particle that races across galaxies with a mass fractionally above zero. In comparison, WIMPs are believed to be much heavier and more sluggish, trudging across the sky in dense clumps and intricate structures. That is, if they even exist at all.
Despite a large array of experiments, none of the attempts to find WIMPs have been successful. It was originally thought that the LHC in Geneva would be able to shed light on their existence. But almost a decade after it opened, no evidence has been found. Similarly, the highly sensitive tanks of liquid xenon buried deep under South Dakota discovered nothing in their search, either.
With scientists continually failing to detect these particles directly, hypotheses surrounding WIMPs are now cast in serious doubt. One astrophysicist writing for Forbes Magazinecompared the persistent search to a “drunk looking for his lost keys beneath the lamppost.”
It would be an oversight to rule out WIMPs altogether. But it looks like scientists have to return to the drawing board and consider alternative theories of dark matter as well.