Discovery of Parity 

Amit Roy is at the Nuclear Science Centre, New Delhi, building a superconducting linac booster for the pelletron accelerator. He spent over two decades at the Tata Institute of Fundamental Research, Mumbai investigating nuclei using accelerators and probing symmetries in physics. His hobbies are books and music.

Symmetry principles are very dear to physicists in their quest for the understanding of nature. These reflect the regularities that are present in nature and help in understanding the laws governing them. A good definition of symmetry in a physical system was given by Herman Weyl as: “A thing is symmetrical if there is something we can do to it so that after we have done it, it looks the same as it did before.” In other words the system is invariant under the operation we performed. A few examples of such operations for a physical system are: translation in space or time, rotation through a fixed angle, uniform velocity in a straight line, reversal of time, reflection in space, interchange of identical particles and change of matter to antimatter. They arise from our basic perceptions about the nature of space and time and usually lead to conservation laws. The invariance under translations in space and time lead to conservation of linear momentum and energy, respectively. Invariance under rotation leads to the law of conservation of angular momentum and invariance under mirror reflection, i.e. symmetry between left and right, leads to conservation of parity.

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Address for Correspondence
Amit Roy 
Nuclear Science Centre 
Aruna Asaf Ali Marg 
P.O. Box 10502 
New Delhi 110 067, India. 
Email: roy@nsc.ernet.in