# I Inconsistencies in classical physics

1. Dec 13, 2017

### jackferry

A question I've had about the black body problem and classical physics in general has to do with the conservation of energy.

One of the first things you can derive in classical mechanics is that for a conservative force the total energy of the system doesn't change. However, one of the typical examples of the failure of classical mechanics is the prediction of infinite energy radiated by a black body radiator. My question is how the classical EM theory predicts the radiation of infinite energy when the EM force is conservative. Is there some assumption that allows for the breaking of the conservation of energy in this case?

2. Dec 13, 2017

### Staff: Mentor

The infinite power is more like an expectation than a derived value, and it wouldn't occur with a finite object made up out of a finite number of atoms.

On the other hand, atoms don't work in classical mechanics anyway - the electrons would fall into the nucleus.

3. Dec 13, 2017

### lekh2003

Classical theory is flawed. It does not work in microscopic situations or many situation for that matter. To avoid such a "breaking" of the conservation of energy, quantum physicists created the appropriate theories to tackle the problems. Quantum physics was their solution.

4. Dec 14, 2017

### Delta²

The flaw in the classical EM wave theory is that EM energy is absorbed (or emitted) in a continuous way. This flaw might be hidden when studying other problems regarding EM waves but it shows up in the case of the black body radiation as that emitted power goes to infinity as frequency goes to infinity (while we would expect by typical reasoning and for the main reason of conservation energy that as frequency tends to infinity the emitted power would go to zero).

To correct this flaw, scientists initially suggested that EM energy is absorbed or emitted in discrete packets (photons) but travels as classical EM wave. This leads to some other difficulties as well, in order to fix all the difficulties a new theory emerged , Quantum ElectroDynamics. QED has as "a low frequency limit " the classical EM wave theory because at relatively low frequencies f the energy of the discrete energy packet (photon) is low $E=hf$ where h is plank's constant which is pretty small number, so the energy is absorbed or emitted in very small packets $hf$ could say infinitesimal packets , so it is like it happens in a continuous way, like the classical EM wave theory suggest..