>California State University at Fresno

http://www.csufresno.edu/

Saturday, April 9, 2005

Don’t miss this talk!

## Invited Speaker: Michael Nauenberg, UC Santa Cruz

#### Einstein’s quantum theory of radiation revisited

In 1916 Einstein published a remarkable paper entitled “On the Quantum Theory of Radiation” [1]-[3] where he derived Planck’s formula for black-body radiation by a new statistical hypothesis for the emmision and absorption of electromagneic radiation based on discrete bundles of energy and momentum which we now call photons. Einstein radiation theory replaced Maxwell’s classical theory by a stochastic process, and in this talk I will show that it also gives the well known quantum statistics of massless particles with even spin [2]. These statistics however, were not discovered by Einstein but communicated to him by Bose in 1924. Like Boltzmann’s classical counterpart, Einstein’s statistical theory leads to an irreversible approach to thermal equilibrium, but because this violates time reversal, Einstein theory can not be regarded as a fundamental theory of physical processs [2]. Apparently Einstein and his contemporaries were unaware of this problem, and even today this problem is ignored in contemporary discussions of Einstein’s treatment of the black-body spectrum.

#### References:

[1] A. Einstein “On the Quantum theory of Radiation”*Phys. Zeitschrift*

**18**(1917) 121. First printed in

*Mitteilungender Physikalischen Gesellschaft Zurich*. No

**18**, 1916. Translated into English in Van der Waerden

*Sources of Quantum Mechanics*(North Holland 1967) pp. 63-77. [2] M. Nauenberg, ” The evolution of radiation towards thermal equilibrium: A soluble model which illustrates the foundations of statistical mechanics”

*American Journal of Physics*

**72**(2004) 313 [3] D. Kleppner, “Rereading Einstein on Radiation”

*Physics Today*, February 2005 , p. 30

Last modified 15 March 2005.