In chemistry and human chemistry, thermalization is the process in which particles, atoms, molecules, or human molecules reach thermal equilibrium, i.e. that state in which no energy flows; through mutual interaction. [1] In physics, thermalization is the reduction of the kinetic energy of neutrons in a thermal nuclear reactor by means of a moderator (a substance that slows down free particles); the process of producing thermal neutrons. [2]

In 1885, author G.D. Liveing, defined what he called "equalization" in relation to changes of potential between bodies: [3]

“The fundamental notion connected with equality of potential being that when two forms of energy are at the same potential in the same substance there is no tendency for either to be increased at the expense of the other; but that if they are at unequal potentials there is a tendency to an equalization; also that when two bodies have their energies at equal potentials there is no tendency for the energy of one to increase at the expense of the other, while if they are at unequal potentials there is a tendency to equalization by the passage of energy from one body to the other.”

Into the 1950s, a “thermalization theory” had developed based on an energy mode concept and was being applied in particle physics, particularly in regards to a theory of “neutron thermalization”. [4]

In 1862, English scientist Herbert Spencer used term of "equilibration", of four different types, to explain evolution. [5]

1. (a) Thims, Libb. (2007). Human Chemistry (Volume One). Morrisville, NC: LuLu.
(b) Dressler, Rainer A. (2001). Chemical Dynamics in Extreme Environments. World Scientific.
(c) Mattis, Daniel C. (1993). The Many-body Problem: an Encyclopedia of Exactly Solved Models in One Dimension, (pg. 846). World Scientific. 2. Daintith, John. (2005). Oxford Dictionary of Physics. New York: Oxford University Press.
3. Liveing, G.D. (1886). “On the Measurement of Kinetic Energy on an Absolute Scale,” (pg. 318), Proceedings of the Cambridge Philosophical Society, University Press.
4. Author. (1954). Journal of Nuclear Energy, (pg. 251), Pergamon Press.
5. Bailey, Kenneth D. (1990). Social Entropy Theory (pg. 55-56). New York: State University of New York Press.

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