## Brief history of the development of quantum mechanics

**Karl Patrick S. Casas**

Any object of higher temperature than its surroundings radiates and loses heat. More radiation is produced if you raise the temperature even higher. Even objects at room temperature glow, but in the form of infrared radiation, which is not detectable by the eye. A black body absorbs all frequencies and emits larger quantities of some wavelength. In 1900, Max Planck invented a function that explained the spectrum at all frequencies. He later interpreted his law: the electromagnetic field can absorb and emit electromagnetic radiation only in integer multiples of a fundamental unit of energy equal to Planck’s constant multiplied by the frequency. This discovery marks the start of the old quantum theory. The ideas in classical mechanics were assumed to hold but with the additional assumption that only certain values of a physical quantity is allowed.

In 1905, Albert Einstein proposes that light, which has wave-like properties, also consists of discrete, quantized bundles of energy called photons. This theory explained the photoelectric mystery. Niels Bohr, in 1913, combined the postulates of Planck and Einstein to build characteristic discrete energy states that atoms should possess. These results accounted for the series of lines observed in the spectrum of light emitted by atomic hydrogen. Arnold Sommerfield added Bohr’s principal quantum number **n** with orbital quantum number** l** and angular quantum number **m**. As a consequence, the Bohr-Sommerfield theory could explain the stark effect and the normal Zeeman Effect but failed to explain outstanding problems such as the helium problem and the anomalous Zeeman Effect.

In around 1924, due to unexplained results and anomalies, it became clear that the old quantum physics was not the whole story. In 1925, Werner Heisenberg, together with Max Born and Pascual Jordan developed a complete theory of quantum mechanics called “Matrix Mechanics”. Each parameter of classical mechanics can be assigned a corresponding matrix in quantum mechanics. In that same year, Wolfgang Pauli formulates the exclusion principle of electrons in an atom.

Going back in 1923, Louis de Broglie proposed his “Wave Nature of Matter”. Particles of matter have dual nature and in some situations act like waves. This idea is developed into a new formulation of quantum mechanics by a German Edwin Schrodinger. He became famous of his Schrodinger equation that views orbiting electrons as matter waves. Schrodinger’s interpretation of the wavefunction [eq]\psi[/eq] as the density distribution was wrong and it was Max Born who figured out the statistical meaning of [eq]|\psi|^{2}[/eq] as the probability density. In Born’s interpretation, if something is observe it will be a whole electron unlike Schrodinger’s idea that a small fraction of an electron will be detected there.

These two competing versions of new quantum physics were on debate over which one was correct. It was soon shown that Schrodinger’s formulation and Heisenberg’s formulation are equivalent.

In 1925, Wolfgang Pauli had inferred from the laws in the Periodic System of the elements the well-known principle that a particular quantum state can at all times be occupied by only a single electron. Pauli’s exclusion, in 1926, gave birth to the discovery of the fourth quantum number, electron spin **s, by Samuel Goudsmit and George Uhlenbeck **which has only two quantized values. In that same year, Paul Dirac extended the theory to relativistic and field-theoretic situations. In 1927, Heisenberg formulates the uncertainty principle in which the more precisely one property is known, the less precisely the other can be measured.

The differences of Quantum Mechanics and Classical Physics became clear. Classical world is deterministic, that is, future can be predicted by using known laws of force and Newton’s laws of motion. In the quantum world, it is impossible to know position and velocity with certainty. Only probability of future state can be predicted using known laws of force and equations of quantum mechanics.

About the author. Karl Patrick S. Casas is a graduate student in Mindanao State University- Iligan Institute of Technology, Iligan City, Philippines. He hopes to finish his master’s degree as soon as possible.

June 13th, 2010 at 6:45 pm

Buenos días!. Excelente artículo, agregaré tu blog a mi lector de noticias. Nos vemos!

August 23rd, 2010 at 5:45 am

gracias por tu apreciación. Esperamos que usted lea el resto de los artículos aquí. o usted puede sugerir este sitio a tus amigos.

June 23rd, 2011 at 5:15 am

,,hehe,,internal bleeding lageh q aneh,,joke,,

..but, totally,,

the article was briefly and clearly stated.

July 15th, 2011 at 9:13 am

trabajo agradable señor. puedo ver que usted ha dado su mejor para hacer este artículo.. keep on, not only keep up, the good work…… best lucks…

November 9th, 2011 at 7:50 am

wow!!!! I will really congratulate myself if i can write as heavy as this!!

November 14th, 2011 at 1:49 am

Hola!El articulo es muy bien! La leccion es no mas deficil a comprender.(toinkzz..nakisali ba naman sa pag.español..tama ba naman kaya??) Bueno, I like it!

February 17th, 2012 at 5:07 am

nice ang article,,maauha sir ai

October 24th, 2015 at 11:25 am

nice sir. a good introduction for our subject this coming semester. (mayng gabie dra sir. hehe)