What is a black body and why do black body radiations prove that classical physics is wrong?
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The black body is just iron. Yes, it’s wrong, but let me explain: German scientists/engineers back in the days wanted to study the temperature-spectrum relation of hot glowing metals. Because if you could know how exactly hot it is only by looking how bright it is, then it could be very useful for metallurgy.
To study such relation, one guy suggested a theoretical framework by introducing an object that absorbs 100% of any electromagnetic wave, so that we’re guaranteed any light coming out of it is emitted purely thermodynamically by itself – thus a theoretically ideal body to try out physical models for temperature-spectrum relation. This, we call the blackbody.
The black body radiation didn’t prove any classical theory wrong. But no classical theory could correctly explain the black body radiation. But quantum mechanical concept, retrospectively speaking, could. This is the very beginning of QM.
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