I understand that every body of some temperature above the absolute zero radiates EM waves. When we heat it up enough it enters the visible spectrum and than proceeds to go upwards to higher and higher energies.
But why would matter radiate EM waves in the first place ? What is the underlying mechanism for such a phenomenon?
Addendum:
I am also interested when this radiation stops. I know that I am now radiating infrared radiation. A block of $1$ by $1$ m solid material would also radiate EM proportional to its temperature. If we slice it in half, also. But what if we take a really small chunk of it (one or a couple of atoms)? Would it still radiate EM waves? Since temperature is only defined for a system of a large number of particles how would it radiate proportional to its temperature since temperature is ill defined on such small scales?
