Both infrared radiation and microwaves warms up objects it meets, so therefore I wonder, is all long wave electromagnetic radiation hot?

And if it is, why?

  • $\begingroup$ What do you want to mean by saying that the radiation is "hot"? It heats up most successful of bodies as bodies and even the earth'and atmosphere is heated by long wave radiations. They are more absorbed than reflected. $\endgroup$ – Wrichik Basu May 14 '17 at 21:37

Objects are warmed up by electromagnetic radiation if their molecules have absorption bands at the radiation's wavelength and can thus be absorbed and turned into heat vibrations. A lot of materials have good-ish absorption in the IR- and Microwave-regime, thus these radiation regimes can often be used for heating - but this has nothing to do with the "temperature" of the radiation.

The other thing you should ask yourself is whether it makes sense to attribute a temperature to electromagnetic radiation.

  • $\begingroup$ How about the cosmic background radiation at 3K ? $\endgroup$ – Ronan Tarik Drevon May 14 '17 at 23:41
  • $\begingroup$ @RonanTarikDrevon Do you mean an electromagnetic emission spectrum which is the same as the one of a black body at 3K? My background in astrophysics is basically non-existent, so you'll need to elaborate $\endgroup$ – Sanya May 15 '17 at 21:10
  • $\begingroup$ Yes I am talking about the cosmic radiation background which is always said to be at T=3K. I have always thought that this temperature corresponds to the temperature of the gas of photons that we still receive from the big bang . $\endgroup$ – Ronan Tarik Drevon May 17 '17 at 9:05
  • $\begingroup$ @RonanTarikDrevon I needed to search around a bit here - but there are two excellent questions here and here. My understanding is that it is just a "theoretical", associated temperature according to black body radiation and no "real" temperature. $\endgroup$ – Sanya May 18 '17 at 17:31

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