MadSci Network: Physics

Re: Does a photon have a temperature ?

Date: Tue Jan 15 12:33:12 2002
Posted By: Dietmar Hildebrand, Post-doc/Fellow, Radiation Biophysics, Scientific Services
Area of science: Physics
ID: 1010817762.Ph

A temperature is a macro property of matter. A photon is a single energy 
quantum, an electromagnetic wave, thus a disturbance in the geometric 
properties of space, which gives it a mass. Modern physics is too much 
tied up in mind models centered around the "particle" extreme, which 
causes thoughts like yours.
No, photons are not dancing particles in almost empty space with a speed 
distribution of gas particles at 5K they all move nicely at exactly "c" 
speed. It is the other way around: from looking at the electromagnetic 
spectrum of all areas of the Universe, which are almost "dark" and fitting 
Plank's distribution into it, we conclude that the radiation of the dark 
space of our Universe matches the one from a piece of matter at a few 
You could abuse the Boltzmann constant, which couples energy and 
temperature (E=kT) to assign a "temperature" to a photon as T= hf/k.
Some times we rape words and concepts in physics, it would be better to 
simply say: the concept of "temperature" does not apply to a single energy 

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