k9b4 said:
I know that EM radiation can heat things up, and I understand the mechanism for this, but my question is why does an object emitting EM radiation cool down?
It's the same process, but in reverse. If you understand one you should understand the other.
One of the problems we have with answering is that we don't know exactly you level of understanding.
Anyway, let me try and take it from the bottom. (all links to wikipedia)
Any object made of atoms that is not at absolute zero (which means
every object) emits
thermal radiation.
The emission can be understood as follows:
Atoms are made of charged protons and electrons. Since temperature has the meaning of average kinetic energy, all atoms are constantly moving and/or oscilating. Even the hardest, coldest steel has got its atoms vigorously vibrating in its crystal lattice. It is important to note here that while from far away atoms are often electrically neutral, in the lowest of scales they can be no longer treated as such, as the distribution of charges between the nucleus and the orbitals becomes significant. Same thing with molecules, only on a bit larger scale.
Any acceleration of a charge means that the electric field surrounding it is not static - it changes with time. This creates a coupled magnetic field which in turn affects the electric field. The two oscillate in a characteristic fashion and the oscillations propagate through the electromagnetic field as
electromagnetic radiation - light.
As anyone who has ever tried to spin an elecric generator (e.g. a bicycle dynamo) can tell, charges resist motion in magnetic field. It takes energy to make electrons move through the wires of the generator as a current.
Similarly, moving in the magnetic field created by their own motion as charged particles slows down atoms.
This slowing down translates to lowering of temperature.
So, to summarize:
-temperature means motion of particles (fas=hot)
-particles are charged (protons and electrons)
-moving charges create disturbances in the EM field (radiation)
-this slows down their motion (->cold)Note, that there can be other processes that emit EM radiation. Fusion in stars is one of them.
Additionally, to explain why you got the "it's energy!" answers.
At some point trying to visualise how things work, especially in the micro-scale, by using macro-scale analogies stops making sense. When you get down to it, everything you see in the world of quantum interactions and elementary particles is just a set of properties that you've ascertained the system to have.
For example, you say electron "exists" in a more definite way than energy. But the electron is just a set of properties, like its charge, mass, typical behaviour in various circumstances, etc. This includes the property called energy. It's no less real nor more of an abstract concept than mass is.
One can try and visualise particles bouncing off each other like tiny billiards balls, or light waves being akin to waves in water, but the real understanding comes not from how you imagine things to behave using crude analogies from our everyday lives, but from knowing the properties and interaction (this is especially a big issue when learning quantum mechanics).
So saying that it takes energy to emit radiation and it has to come from somewhere is describing the situation in more precise and useful terms than painting a vivid picture.