Quantum

In physics, a quantum (plural: quanta) is the minimum unit of any physical entity involved in an interaction. Behind this, one finds the fundamental notion that a physical property may be "quantized," referred to as "the hypothesis of quantization"^[1]. This means that the magnitude can take on only certain discrete numerical values, rather than any value, at least within a range. There is a related term of quantum number. An example of an entity that is quantized is the energy transfer of elementary particles of matter (called fermions) and of photons and other bosons.

A photon, for example, is a single quantum of light, and may thus be referred to as a "light quantum". The energy of an electron bound to an atom (at rest) is said to be quantized, which results in the stability of atoms, and of matter in general.

As incorporated into the theory of quantum mechanics, this is regarded by physicists as part of the fundamental framework for understanding and describing nature at the infinitesimal level.

Normally quanta are considered to be a discrete packets with energy stored in them. Planck considered these quanta to be particles that can change their form (meaning that they can be absorbed and released). This phenomenon can be observed in the case of black body radiation, when it is being heated and cooled.

History and discovery

The word "quantum" comes from the Latin "quantus," for "how much". "Quanta" meaning short for "quanta of electricity" was used in a 1902 article on the photoelectric effect by Philipp Lenard, who credited Helmholtz for using the word in the area of electricity. However, the word quantum in general was well known] before 1900.^[2] Max Planck used "quanta" to mean "quanta of matter and electricity" (electrons) ^[3], gas, and heat.^[4] In 1905, in response to Planck's work and the experimental work of Lenard, who explained his results by using the term "quanta of electricity", Albert Einstein suggested that radiation existed in spatially localized packets which he called "quanta of light" ("Lichtquanta").^[5]

The concept of quantization of radiation was discovered in 1900 by Max Planck, who had been trying to understand the emission of radiation from heated objects, known as black body radiation. By assuming that energy can only be absorbed or released in tiny, differential, discrete packets he called "bundles" or "energy elements",^[6], Planck accounted for the fact that certain objects change colour when heated.^[7] On December 14, 1900, Planck reported his revolutionary findings to the German Physical Society and introduced the idea of quantization for the first time as a part of his research on black body radiation.^[8] As a result of his experiments, Planck deduced the numerical value of h, known as the Planck constant, and could also report a more precise value for the Avogadro-Loschmidt number, the number of real molecules in a mole, and the unit of electrical charge, to the German Physical Society. After his theory was validated, Planck was awarded the Nobel Prize in Physics in 1918 for his discovery.

Beyond electromagnetic radiation

While quantization was first discovered in electromagnetic radiation, it describes a fundamental aspect of energy not just restricted to photons.^[9]

See also

References

Further reading

• B. Hoffmann, The Strange Story of the Quantum, Pelican 1963.
• Lucretius, "On the Nature of the Universe", transl. from the Latin by R.E. Latham, Penguin Books Ltd., Harmondsworth 1951. There are, of course, many translations, and the translation's title varies. Some put emphasis on how things work, others on what things are found in nature.
• J. Mehra and H. Rechenberg, The Historical Development of Quantum Theory, Vol.1, Part 1, Springer-Verlag New York Inc., New York 1982.
• M. Planck, A Survey of Physical Theory, transl. by R. Jones and D.H. Williams, Methuen & Co., Ltd., London 1925 (Dover editions 1960 and 1993) including the Nobel lecture.