Einstein, like Planck, was very fluent in thermodynamic theory. Before 1905, Einstein published several papers on thermodynamic topics. One of these dealt with the fundamentals of thermodynamic theory [Einstein, 1903]. In this work, he studied whether the thermodynamic laws could be derived from a minimum amount of elementary assumptions. In 1905[1] he published a study in which he explained the photoelectric phenomenon. In that explanation, he not only used the results of Planck’s discrete energy packets for the black body radiation description, but fully acknowledged Boltzmann’s work, calling the expression *S = *k ln*W* “the principle of Boltzmann.”

How highly Einstein regarded thermodynamics can be appreciated in the following quote:

*“A law is more impressive the greater the simplicity of its premises, the more different are the kinds of things it relates, and the more extended its range of applicability. (..) It is the only physical theory of universal content, which I am convinced, that within the framework of applicability of its basic concepts will never be overthrown.”*

Einstein is best known for his invention of relativistic theory where time is no longer invariable[2]. Less remembered is that he searched his whole life for a theory that could unify the electromagnetic theory of Faraday and Maxwell on one hand, and the mechanical theory of the material particles of Newton on the other. For instance, Newton unified the observations of falling objects on earth with the fact that the earth and planets orbited the sun. He did this by using a *single* concept – namely, gravity – to explain both phenomena. Maxwell showed that seemingly quite different magnetic and electric observations could be described by a single theory of electromagnetic waves.

Around 1900 several outstanding physicists were working to explain Planck’s black body radiation. Planck had to introduce quantum theory to explain the experimental observation of the relationship between energy and wavelength. Einstein did not like this explanation, since it introduced yet another theory rather then unifying existing theories. Einstein was convinced that the answers could be found in thermodynamics, since this theory was based on structure-independent assumptions. Indeed, the special theory of relativity can be considered as a theory of principles analogous to the theory of thermodynamics [Klein, 1967].

What brought Einstein to his Special Theory of Relativity was his idea (conceived when he was 16 years old!) that the velocity of light must be the same for all observers, regardless of their respective speeds. He derived this conclusion from Maxwell’s electromagnetic equations and so kept his mind puzzled for a long time. His familiarity with thermodynamic theory also gave him a lot of inspiration. We can appreciate the challenge he found from two questions (taken from the publication of Martin Klein: “Thermodynamics in Einstein’s Thought”; *Science*, Vol 157, 509 (1967). In essence what the classical thermodynamic accomplishment was, was to find mathematical expressions to the dilemma:

*“What must the laws of nature be like so that it is impossible to construct a perpetual motion machine from either the first or the second kind?”*

This question refers to the empirical fact that perpetual machines have never been observed that could violate the first principle that energy cannot be added or destroyed in an isolated system, or contradict the second principle that entropy always increases for spontaneous processes in, again an isolated system. Similarly, while developing the Special Theory of Relativity, Einstein wondered:

*“What must the laws of nature be like so that there are no privileged observers?”*

This question refers to the fact that the speed of light is the same for all observers, regardless of how fast their platform (a planet, a rocket, or an angel’s wings) is going. Therefore, one must derive expressions that will obey the principle of the constancy of light speed. In the same way that classical thermodynamics does not worry about *why* energy is conserved or why entropy increases, so Einstein didn’t try to puzzle out *why* the speed of light was constant, but merely accepted it as fact. Once accepted, the equations that describe this assumption are pretty straightforward!

Thus, the Special Theory of Relativity can be viewed as a theory of principles analogous to thermodynamics, and not as a constructive theory – as, for instance, gravity or the kinetic gas theory[3]. This means that no model is needed (like a model of an atom in the case of quantum mechanics) in either the Special Theory of Relativity or in thermodynamics, in order to arrive at the end results of both theories. The nice thing is that both theories can live on indefinitely with little risk of needing adjustment because of new insights. That is, in fact, what we’ve seen: both thermodynamics and the Special Theory of Relativity have not changed since their conception. [4]

Taken from:

“The Second Law of Life, Energy, Technology and the Future of Earth As We Know It”

[ http://www.elsevier.com/wps/find/bookdescription.cws_home/715243/description#description]

© Copyright 2009 John Schmitz

[1] 1905 was also the year Einstein published his Special Theory of Relativity, along with his articles on the photoelectric effect, the explanation of Brownian movement, and an article where he stated his famous equation,

*E=mc*^{2}. Because of Einstein’s overwhelming amount of important material in one year, 1905 is sometimes called

*Annus Mirabilis (the MiracleYear)* [Bushev, Michael, “A Note on Einstein’s Annus Mirabilis”,

*Annales de la Fondation Louis de Broglie*, Vol 25, no 3 (2000)].

[2] Einstein worked for several years at the Swiss patent office in Bern. During that period, because of the ongoing electrification and synchronization of clocks in the cities and across the countries, many patent applications came in that proposed all sort of ingenious ways to implement the synchronization. Because of that Einstein saw of course many proposals dealing with these kinds of problems and that may have very well triggered his interest in time, see also footnote 72, [Galison, Peter, *Einstein’s Clocks, Poincaré’s Maps, Empires of* *Time*; W.W. Norton & Company, Inc., New York (2004)].

[3] The kinetic gas theory starts with the existence of gas molecules, their continuous motion, and their finite dimensions. Then, by applying Newton’s mechanical kinetic theory it is possible to derive a relation among the macroscopic gas parameters: pressure, temperature, and volume. In this way a model can be built that has predictive and verifiable power.

[4] I feel that a few more words are needed here. Einstein himself pointed out in an article in 1919 in the *Times* of London that a theory of principle is based on empirical observations without the need for a particular model whereas a constructive model will first make assumptions about a fundamental structure then will built a mathematical description of that structure that hopefully will give relationships between the empirically observed parameters. In his own words: *“Thus the science of thermodynamics seeks by analytical means to deduce necessary conditions, which separate events have to satisfy, from the universally experienced fact that perpetual motion is impossible”*. Thus, classical thermodynamics can be regarded as a theory of principles, whereas statistical thermodynamics (i.e., Boltzmann approach) should be categorized as a constructive theory. In 1904 it was Poincaré who made a similar classification in scientific theories in his book *The Value of Science*.