Quantum mechanics
The branch of physics that deals with how energy behaves at the atomic and subatomic levels. It derives from the word “quantum” (Latin for “how much”) and “quanta” the discrete subatomic energy packets that are the building blocks of light waves. Accepted theories of quantum mechanics were established during the first half of the twentieth century by Max Planck, Werner Heisenberg, Niels Bohr, Erwin Schrodinger and others who wanted to explain the behaviors and characteristics of quantum energy (light at the atomic and subatomic levels) which behaves in ways that cannot be explained by classic Newtonian physics, classic theories of electromagnetism or Einstein’s general theory of relativity. Quantum mechanics led to a number of accepted and important theories. Planck’s quantum hypothesis explained how the energy radiated by an atomic system is proportional to the radiant energy generated by each discrete energy element in the system. Heisenberg’s uncertainty principle resolved what had been a major quandry regarding the inability to precisely locate electrons in an atomic unit. Einstein built upon Planck’s work to show that an electromagnetic wave such as light also consists of tiny energy particles called photons. This led to the theory of wave-particle duality in which particles and waves were neither one nor the other, but had certain properties of both. While quantum mechanics describes the world of the very small, it also helps explain how certain “macroscopic” quantum systems behave, such as superconductors. Quantum mechanics is regarded widely by professional physicists as the most fundamental framework we have for understanding and describing nature.