Anti-Matter

Anti-Matter

Ordinary matter has negatively charged electrons circling a positively charged nuclei. Anti-matter has positively charged electrons - positrons - orbiting a nuclei with a negative charge - anti-protons. Only anti-protons and positrons are able to be produced at this time, but scientists in Switzerland have begun a series of experiments which they believe will lead to the creation of the first anti-matter element-Anti- Hydrogen.

Early scientists often made two mistakes about anti-matter. Some thought it had a negative mass, and would thus feel gravity as a push rather than a pull. If this were so, the antiproton's negative mass/energy would cancel the proton's when they met and nothing would remain; in reality, two extremely high-energy gamma photons are produced. Today's theories of the universe say that there is no such thing as a negative mass.

The second and more subtle mistake is the idea that anti-water would only annihilate with ordinary water, and could safety be kept in (say) an iron container. This is not so: it is the subatomic particles that react so destructively, and their arrangement makes no difference.

Scientists at CERN in Geneva are working on a device called the LEAR (low energy anti-proton ring) in an attempt to slow the velocity of the anti-protons to a billionth of their normal speeds. The slowing of the anti-protons and positrons, which normally travel at a velocity of that near the speed of light, is necessary

so that they have a chance of meeting and combining into anti-hydrogen.

The problems with research in the field of anti-matter is that when the anti-matter elements touch matter elements they annihilate each other. The total combined mass of both elements are released in a spectacular blast of energy. Electrons and positrons come together and vanish into high-energy gamma rays (plus a certain number of harmless neutrinos, which pass through whole planets without effect). Hitting ordinary matter, 1 kg of anti-matter explodes with the force of up to 43 million tons of TNT - as though several thousand Hiroshima bombs were detonated at once.

So how can anti-matter be stored? Space seems the only place, both for storage and for large-scale production. On Earth, gravity will sooner or later pull any anti-matter into disastrous contact with matter. Anti-matter has the opposite effect of gravity on it, the anti-matter is 'pushed away' by the gravitational force due to its opposite nature to that of matter. A way around the gravity problem appears at CERN, where fast moving anti-protons can be held in a 'storage ring' around which they constantly move - and kept away from the walls of the vacuum chamber - by magnetic fields. However, this only works for charged particles, it does not work for anti-neutrons, for example.

Though anti-matter can be manufactured, slowly, natural anti-matter has never been found. In theory, we should expect equal amounts of matter and anti-matter to be formed at the beginning of the universe - perhaps some far off galaxies are the made of anti-matter that somehow became separated from matter long ago. A problem with the theory is that cosmic rays that reach Earth from far-off parts are often made up of protons or even nuclei, never of anti-protons or antinuclei. There may be no natural anti-matter anywhere.

In that case, what happened to it? The most obvious answer is that, as predicted by theory, all the matter and anti-matter underwent mutual annihilation in the first seconds of creation; but why then do we still have matter? It seems unlikely that more matter than anti-matter should be formed. In this scenario, the matter would have to exceed the anti-matter by one part in 1000 million.

An alternative theory is produced by the physicist M. Goldhaber in 1956, is that the universe divided into two parts after its formation - the universe that we live in, and an alternate universe of anti-matter that cannot be observed by us.

Though they have no charge, anti-neutrons differ from neutrons in having opposite 'spin' and 'baryon number'. All heavy particles, like protons or neutrons, are called baryons. A firm rule is that the total baryon number cannot change, though this apparently fails inside black holes. A neutron (baryon number +1) can become a proton (baryon number +1) and an electron (baryon number 0 since an electron is not a baryon but a light particle). The total electric charge stays at zero