Physics Questions People Ask Fermilab

Absolute Zero

You Wrote:
If absolute zero is the temperature when atoms are almost stopped and temperature is the speed of vibration of the atoms and the speed of light is the absolute speed then absolute temperature must occur when the atoms are vibrating at the speed of light. Is this true, and if it is , what temperature is this , Kelvin.

Marty Foy

Dear Marty,

Indeed, absolute zero is the temperature at which the atoms composing the substance we are considering have no kinetic energy. (This is easiest to think of for gasses, where the molecules of gas can be flying about and bumping into each other at high temperatures. They also are vibrating internally and rotating and generally exercising any degree of freedom they have.) I believe what you are thinking of are the translational degrees of freedom, in which the molecules can move about in three dimensions rather randomly. As we reduce the temperature of the gas, the average speed with which these molecules move is reduced. At absolute zero, we would not expect them to move at all. Any of them. We can get pretty close to absolute zero, zero kelvin, within a tiny fraction of a kelvin, but that's it.

The other end of the energy scale, going toward infinite temperature, is the end where the average speed of the particles increases substantially. It never gets to the speed of light, however. Even colliding galaxies and collapsing black holes can't do that: Particles with mass are forbidden by the law of relativity to go to the speed of light. In that sense there is an absolute speed limit, but the absolute limits of zero temperature and the speed of light are the limits at opposite ends of nature.

I hope this answers your question.

Peter Mazur

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