I Why is Planck radiation the most radiation a body can emit?

[Julia Coggins]

Why is Planck radiation the greatest amount of radiation that anybody at thermal equilibrium can emit from its surface, whatever its chemical composition or surface structure?

 

[Simon Bridge]

The clue is in the definition... what would it mean if the body could emit more?
What would happen?

 

[Julia Coggins]

The clue is in the definition... what would it mean if the body could emit more?
What would happen?

So that's an inherent fact? Planck radiation depends on the temperature of the body, so for example at room temperature a body emits infared radiation and cannot be seen. Whereas at the surface of the sun, it emits visible light as well. I guess Planck radiation is inherently the limit, but referring to it when in fact in radiates another light by means of Plack confuses me.

 

[Simon Bridge]

The definition of plank radiation is not "the inherent limit of radiation"... it's a bit more complicated than that and it arises as a consequence of other things. However: if a body radiated beyond the plank limit, then that would be a contradiction in terms ... so say the body is emitting radiation that can be found by the plank-limit equation ... we can ask, how is it that this is the limit? What mechanism says "no more"?

Your question amounts to asking about the physical mechanism governing the "inherent" limit.
I asked a guiding question designed to help you to think about it.

I'll try again:
The amount of radiation a body emits depends on it's temperature - the amount of radiation it receives depends on the temperature of it's environment.
If the body emits more than it receives, the environment heats up until what happens?

Plank radiation is for a blackbody: what is the definition of a blackbody?