The weak and strong forces are effective only over a very short range and dominate only at the level of subatomic particles. The electromagnetic force also has infinite range but it is many times stronger than gravity. Gravity is the weakest but it has an infinite range. They work over different ranges and have different strengths. There are four fundamental forces at work in the universe: the strong force, the weak force, the electromagnetic force, and the gravitational force. The electron, the muon and the tau all have an electric charge and a sizeable mass, whereas the neutrinos are electrically neutral and have very little mass. The six leptons are similarly arranged in three generations – the “electron” and the “electron neutrino”, the “muon” and the “muon neutrino”, and the “tau” and the “tau neutrino”. Quarks also come in three different “colours” and only mix in such ways as to form colourless objects. The six quarks are paired in three generations – the “up quark” and the “down quark” form the first generation, followed by the “charm quark” and “strange quark”, then the “top quark” and “bottom (or beauty) quark”.

All stable matter in the universe is made from particles that belong to the first generation any heavier particles quickly decay to more stable ones. The lightest and most stable particles make up the first generation, whereas the heavier and less-stable particles belong to the second and third generations. Each group consists of six particles, which are related in pairs, or “generations”. These particles occur in two basic types called quarks and leptons. All matter around us is made of elementary particles, the building blocks of matter.

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