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  Molecules are the building blocks of life. Most of the substance that we meet in everyday life are composed of molecules: our bodies, all plastics, all foods. Molecules are composed of atoms, which are bound together by exchanging or sharing electrons (see below).

Atoms are smaller than molecules, and are composed of a tiny nucleus surrounded by a cloud of orbiting electrons. The negative charge possessed by the electrons is balanced by the nucleus, which has an equal and opposite charge.

The nucleus contains protons, which carry the positive charge, and neutrons, which, as their name implies, are neutral and carry no charge. The nucleus is bound together by the strong force, whereas the electrons are bound in the atom by the electromagnetic force.

The electron and the positron are identical in every way apart from the fact that electrons have negative charge and positrons have positive charge. They are 2,000 times lighter than protons and neutrons. Electric current is simply the flow of electrons down wires. The positron is the antiparticle to the electron, which means that if the two meet they will annihilate each other.

Protons and neutrons are each made of three quarks, bound together by gluons (see below)—particle physicists were running out of names by this time. There are thought to be six types of quark: the up, down, strange, charmed, bottom and top quark. The top quark has yet to be produced, but its existence is predicted. Each quark comes in one of three colours, red, green and blue. These bear no relation to what we know as colours they are just labels for differences between the quarks.

These particles are the constituents of matter. There is another class of particle, called carriers, which are the medium by which forces operate.

Gluons are the field carriers for the colour force, which binds quarks together. The Z~ and W~bosons do the same job for the weak force. The as yet undetected graviton is believed to be the field carrier for the force of gravity. The photon, while being the particle that light is made of, is also the electromagnetic field carrier.

These field carriers come in very different sizes. The Z-and W-bosons weigh as much as a large atom, while a photon has no mass at all, but is pure energy. It is difficult to place a value on the mass of a gluon, due to the nature of the colour force, but they may weigh as much as a quark. The tiny graviton has little or no mass.

It is believed that at very high energies, all field carriers will look the same, as all fundamental forces are thought to coalesce into the same force at these energies. JJ



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