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Name: Alec
Status: student
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Question:
Does absolute zero have a microwave frequency? I have heard that the cosmic microwave radiation that is theorized to be a resonance of the big bang is at a frequency that corresponds to a temperature a little above absolute zero.



Replies:
No. The energy of electromagnetic radiation is proportional to its frequency. An object at absolute zero has no energy to spare, so it cannot emit any radiation. This fits nicely with the energy radiated decreasing as temperature decreases, so the frequency of radiation emittee decreases as the temperature of the emitter decreases.

The cosmic microwave background corresponds to an emitter a bit above absolute zero, close to 2.6 Kelvin. That is cold, but much lower temperatures are routinely attained in laboratories.

Richard Barrans
Department of Physics and Astronomy
University of Wyoming


All bodies naturally emit radiation. The radiation emitted depends on the temperature of the body. Thus, something ever so slightly above absolute zero would still emit radiation. It turns out that at these very low temperatures, the radiation is microwave frequency. At absolute zero no black body radiation occurs.

The reason this ties to the big bang is that there is a uniform, constant microwave background radiation in the Universe. As you said, it corresponds to roughly 3K, just above absolute zero.

If you want to read more (and TONS of info is on the web), Google 'black body radiation', 'black body radiation absolute zero', or similar terms.

Hope this helps,

Burr Zimmerman


Dear Alec,

A body at any temperture T emits electromagnetic radiation characteristic of that temperature. Except that a body at the absolute zero of temperature does not radiate at all. The radiation is caused by the movement of charges (actually, their accelerations) and a body at absolute zero is not moving at all.

The microwave background radiation is characteristic of a temperature of 2.7K, which is just 2.7 Celsius degrees above absolute zero. This what one would expect some 13 billion years after it was at an almost infinite temperature at the time of the "Big Bang".

Best, Dick Plano, Professor of Physics emeritus, Rutgers University


If one examines the standard equations relating radiation and temperature, the frequency corresponding to absolute zero would have zero frequency, or equivalently infinite wavelength. These arise from the Planck --Einstein treatment of "blackbody radiation".

However, "absolute zero" is not attainable in a real world experiment. It is an idealized limiting value that is never reached. Another example would be infinite density. When one begins to experiment in the range of these limiting values often our large scale models fail, and some assumptions or notions need to be rephrased.

Vince Calder



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