Monday, September 25, 2006

Why do physicists want to study particles?

A few "cosmic rays" pass through our body every second of every day, regardless of where we are.

They consist of particles created when high energy atomic nuclei (mainly protons) coming from outer space collide with the atoms at the top of the earth's atmosphere. Such particles are not just electrons, protons and neutrons, but also other kinds of particle.

Near the ground, the cosmic rays include muons, similar to the electrons but more than 200 times heavier. Unlike electrons, which live forever, a muon will live about 2.2 microseconds, and then convert into an electron and two neutrinos (electron-neutrino and muon-neutrino; these are like a very light neutral version of the electron and of the muon).

The muons themselves emerge mainly from the decays of other short-lived particles. Some of these particles, called pions, are made from up and down quarks. However, others (kaons) contain a third type of quark, called the strange quark.

Cosmic matter is then made up of more components than the atoms. In addition to the electron, electron-neutrino, up quark and down quark, we have the muon, the muon-neutrino and the strange quark.

Do Blackholes Radiate

The possibility that non-radiating "mini" black holes exist should be taken seriously; such holes could be part of the dark matter in the Universe. Attempts to place observational limits on the number of "mini" black holes (independent of the assumption that they radiate) would be most welcome.

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