Neutrinos

Neutrinos are energetic particles in the Universe, and abundant (for each proton in the Universe, there is one billion neutrinos; 300 per cubic centimeter); they are invisible, have almost no mass, and pass through almost anything (one billion neutrinos pass through our body each second; they pass through strong magnetic fields, interstellar gas and dust clouds, and even the core of stars). They are remnants of the Big Bang. They are thought to come from the most energetic events at the far reaches of the Universe: quasars, gamma rays bursts, supernovae, black holes). Another species of neutrinos, less energetic, is produced when cosmic rays hit the Earth's atmosphere

Existence of neutrinos was predicted in the beginning of the 30s by the physicist Wolfgang Pauli, in the purpose of solving a trouble in one equation -Pauli was saying: "I have done a terrible thing. I have postulated a particle that cannot be detected". Fermi, in 1933, called it neutrino (literally "little neutral one") and pushed the calculations further. But it was not until 1956 that the particle was detected for the first time (Frederick Reines et Clyde Cowan detected evidence of neutrino interactions in a liquid's mixture near a nuclear reactor)

Neutrinos are interesting as they may be used to yield informations, at the same time, about objects which emit them, and, too -as they may pass through media that other radiations do not cross- about unprecedented media or objects, about which one never thought. The principle to detect neutrinos (for example, AMANDA, South Pole) is to have the radiations other than neutrinos blocked by the whole mass of the Earth (from the South Pole, one really looks to neutrinos coming through the North Pole) and to count neutrinos by the bias of the muon (charged particle) they emit: when neutrinos cross the Earth and bump into a proton, they emit a muon; the muon emits a blue light (which is known as the Cherenkov radiation -which some have called the optical equivalent of a sonic boom); the event is rare: less than a neutrino in one million bumps into a proton when crossing the Earth

A trouble with neutrinos is that the theory predicting the number of neutinos coming from the Sun, one should observe the said number. But, in fact, one doesn't. This question pending, a study in April 2002 would in fact lead to a questioning of the Standard Model (the theory by which all the fundamental elements are explained): the team seems to have understood that observed neutrinos have the same number than the emitted neutrinos but, however, a great part of Sun neutrinos change identity as they pass from the Sun's core to its upper layers; indeed, such a change is only possible if neutrinos have a mass; but the Standard Model states that neutrinos do not have a mass and this, so, would be an important trouble. Another study, Japan, December 2002, which worked about neutrinos (in fact, antineutrinos) emitted by Japanese nuclear plants, found however that the number of observed neutrinos (as they worked about nuclear plants, this number was precisely known) is less than the number emitted, and that, so, there is indeed neutrinos vanishing along the way. The general trend of the question is maybe that there really is a difference between the number observed and the number emitted but this difference would be based on the fact that neutrinos change identity