Quantum Mechanics

Quantum mechanics (QM) is the modern physical theory of very small (microscopic) systems, typically atomic-sized or smaller. Along with Einstein's theory of relativity, QM represented a major revolution in our understanding of physics, which was previously described by Newtonian (classical) mechanics. Problems with Classical Physics The enormous success of Newtonian mechanics led Lord Kelvin to state the following in 1894 [2]: " There is nothing new to be discovered in physics now. All that remains is more and more precise measurement. " How wrong he was! However, it seemed that way for many physicists at the end of the 19 th century. Nevertheless, there were several unexplained problems with classical physics at this time, most notably the blackbody radiation problem, the photoelectric effect, and the existence of spectral lines. The Blackbody Radiation Problem A blackbody is a theoretical substance that absorbs all radiation incident on it. Many physical systems are very good approximations to blackbodies, for instance, stars and boxes with a tiny hole. Gustav Kirchoff first discussed the blackbody radiation problem in 1859. The problem is that according to classical physics, a blackbody should radiate more and more energy at higher and higher frequencies (shorter and shorter wavelengths), and should thus radiate an infinite amount of energy. Since this obviously does not happen, an explanation was required. Max Planck solved the blackbody radiation problem by postulating that radiation was not continuous but discrete, coming in lumps known as quanta. The energy E of a quantum of radiation is given by the formula , E hf  where f is the frequency of the radiation and h is a fundamental constant, which became known as Planck's constant. Planck's formula leads to the correct prediction of the blackbody spectrum. The value of Planck's constant is tiny; it is approximately equal to 34 6.6 10   Joule-seconds. This is why quantum mechanics is not apparent in everyday life.