Physical mechanism for radiative cooling

[k9b4]

http://en.wikipedia.org/wiki/Radiative_cooling

Why does an object lose heat by emitting EM radiation? Could someone please help me understand? I tried asking this on physicsforums.com but I got banned because one of the admins is a fucking idiot.

I understand how EM radiation can heat up objects:

Oscillating EM field pushes around the charges in an object, making them oscillate faster, thus giving them more 'heat'.

But I do not understand why the emission of EM radiation causes the charges emitting it to oscillate more slowly.

 

[redbaron]

There's more than one type of EM radiation, so I'll assume you mean thermal radiation, which is the primary source of heat transfer in the infrared and visible light spectrums. In the most basic terms, in any object above absolute zero (-273.1 Celsius) the atoms oscillate and therefore radiate on the IR spectrum.*

Radiation in simple terms is energy. As objects radiate they lose energy through that process of radiation. Therefore atoms oscillate slower and the object radiates less heat (cools down).

Maybe the easiest way to understand it is this: "All objects possessing a temperature above absolute zero produce thermal radiation to a degree relative to that object's temperature."

*This also explains why (generally) objects don't cool past absolute zero. Once atoms stop oscillating there's no more thermal radiation. You can't have less than no thermal radiation.

 

[k9b4]

As they emit radiation they lose energy.

As they lose energy they oscillate more slowly.

What the fuck is energy? Energy is only a concept. There is no magical energy stuff which is being transferred from the oscillating charge to the EM wave.

I am sorry, but everyone gives me this answer, which is not the answer I am looking for. I want the physical mechanism.

A physical mechanism explanation for why EM waves heat things up is:

EM waves cause objects to heat up by pushing around the charges, which causes other charges in the object to be pushed around, which results in an increase of total 'kinetic energy' of the object.

 

[ProxyAmenRa]

The energy is conveyed by photons. The positron or electron spontaneously releases photons and in turn momentum is lost causing vibration to decrease. If you want the specific underlying mechanics of this you will have to study a university level quantum thermodynamics course. My engineering degree never covered quantum thermodynamics or quantum statistical mechanics. Ask a physicist...

Wikipedia:

Thermal radiation is the emission of electromagnetic waves from all matter that has a temperature greater than absolute zero.[3] It represents a conversion of thermal energy into electromagnetic energy. Thermal energy results in kinetic energy in the random movements of atoms and molecules in matter. All matter with a temperature by definition is composed of particles which have kinetic energy, and which interact with each other. These atoms and molecules are composed of charged particles, i.e., protons and electrons, and kinetic interactions among matter particles result in charge-acceleration and dipole-oscillation. This results in the electrodynamic generation of coupled electric and magnetic fields, resulting in the emission of photons, radiating energy away from the body through its surface boundary.

 

[k9b4]

The positron or electron spontaneously releases photons and in turn momentum is lost causing vibration to decrease.http://en.wikipedia.org/wiki/Thermal_radiation

Why is momentum lost when releasing photons?

 

[ProxyAmenRa]

A photon is a "packet" of energy. The energy being released as a photon needs to come from somewhere as energy can't be created out of nothing. The energy is taken from the atom's kinetic energy.

Edit: I wish I could give you a more in depth answer. Even though I had to study a number of subjects on thermodynamics, I never studied what occurs on a quantum level.

 

[redbaron]

There is no magical energy stuff which is being transferred from the oscillating charge to the EM wave.

Without an internal power source (such as nuclear fusion) one object cannot heat another without losing heat itself.

Simple example is putting ice cubes in water. The water is a higher temperature and produces more thermal radiation, therefore transferring energy to the ice cubes in the form of heat - increasing the rate of thermal radiation within the ice cubes.

Simultaneously the ice cubes slow the rate of thermal radiation in the water. Eventually the two objects will reach equilibrium at some point between where they both began.

So the final, cumulative amount of thermal radiation being produced at this equilibrium after the ice and water were mixed, is exactly the same as when the ice and water were separated.

 

[Ex-User (9086)]

What the fuck is energy? Energy is only a concept. There is no magical energy stuff which is being transferred from the oscillating charge to the EM wave.

Classical:
http://en.wikipedia.org/wiki/Conservation_of_energy
Quantum:
http://en.wikipedia.org/wiki/Noether%27s_theorem

 

[Thurlor]

From what I remember from my university course it has to do with electrons dropping to a lower energy state resulting in the production/emission of a photon, but that was a long time ago and I may be wrong.

 

[Cognisant]

So do you need to cool something?

 

[Reluctantly]

The somewhat technical answer, as has been already stated, is that photon emission means the atoms drop to a lower energy state. The somewhat more intuitive less technical answer that I use is that all objects are interacting with each other and when they radiate, they are transferring kinetic energy, thus losing some energy. So EM radiation could be thought of as a reflection of the kinetic energy an object is emitting to its surroundings.