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The definition of Blackbody states that they absorb all incident thermal radiation. Why does this imply that its radiation spectrum is independent of its composition? Is there some thermodynamical argument I'm missing there?

Thanks.

Andrew V
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  • There is an argument that otherwise you could make a black body to heat up to a temperature higher than its surroundings. –  Apr 05 '18 at 14:15

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Why does this imply that its radiation spectrum is independent of its composition?

A good definition of a blackbody is a "theoretically ideal radiator". It is independent of its composition because it is not a real object and we simply said it would be.

Real objects do have spectrums that are dependant on their composition, which is why you have to be clever when you make something that approximates a blackbody.

Maury Markowitz
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