Since it is necessary for a body to be above 0K in order to irradiate, I was wondering if a theorical body at 0K would be visible at all.

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    $\begingroup$ A body at $0$ K will not emit anymore radiation. That's how absolute zero is defined. It's like asking if you can extract any more energy from a quantum system once it reaches the ground state. But note that it is impossible to reduce the temperature of an object to absolute zero in a finite number of steps. $\endgroup$ – Andrei Geanta Nov 5 '17 at 14:46

Even if it doesn't radiate, it can still reflect light. Thus, it would be visible.

However, its albedo wouldn't be exactly 1, thus the light hitting its surface would be only partially reflected. The absorbed light would heat it.


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