Conservation Laws

In addition to the conservation laws already described, there are conservation laws that describe reactions between subatomic particles. Several hundred sub-atomic particles have been discovered since the discovery of the proton, electron, and the neutron. By observing which processes and reactions occur between these particles, physicists can determine new conservation laws governing these processes. For example, there exists a subatomic particle called the positron which is very much like the electron except that it carries a positive electric charge. The law of conservation of charge would allow a process whereby a proton could change into a positron. However, the fact that this process does not occur leads physicists to define a new conservation law restricting the allowable transformations between different types of subatomic particles.

Occasionally, a conservation law can be used to predict the existence of new particles. In the 1920s, it was discovered that a neutron could change into a proton and an electron. However, the energy and mass before the reaction was not equal to the energy and mass after the reaction. Although seemingly a violation of energy and mass conservation, it was instead proposed that the missing energy was carried by a new particle, unheard of at the time. In 1956, this new particle named the neutrino was discovered. As new subatomic particles are discovered and more processes are studied, the conservation laws will be an important asset to our understanding of the Universe.

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