Dark Matter

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Over the past years and decades, an enormous amount of evidence has been found for the existence of invisible, or dark matter. Galaxies and clusters of galaxies rotate at speeds that would cause them to fall apart if not for the presence of extra mass beyond ordinary known stars and gas. More recently, studies of the cosmic microwave background (CMB), distant supernovae, gravitational lensing and large scale have profoundly increased our understanding of dark matter. What makes up the dark matter of our universe is not yet known. The most compelling possibility for dark matter's identity is a class of objects known as weakly interacting massive particles, or WIMPs. WIMPs are quantum particles that interact with ordinary particles (such as protons, neutrons, electrons or light) only very slightly, through what particle physicists call the weak force. A WIMP can pass through your body, or even the entire Earth, without being noticed in the least. There are thought to be thousands of WIMPs in any cubic meter of space in the vicinity of our Solar System. Many of the particle physics theories which have been proposed predict the existance of stable, weakly interacting particles which would be a suitable candidate for dark matter. Among the most prominent examples of such candidates are neutralinos in supersymmetry theories and Kaluza-Klein states in models with extra dimensions of space. A wide range of experimental efforts are currently underway to detect such particles and hopefully deduce their identity. These programs include underground detectors designed to observe the impacts of individual dark matter particles, and gamma-ray, neutrino and anti-matter detectors designed to detect the radiation produced when pairs of dark matter particles annihilate one another. Furthermore, physicists using particle colliders, such as the Tevatron at Fermilab and the Large Hadron Collider at CERN, hope to produce dark matter particles in their experiments. In 2004, I co-authored a review article for the journal Physics Reports which summarizes the status of our understanding of particle dark matter. This article can be found here.