I tried to calculate the casimir force. I need to know if the way I doing it is correct. So I note some steps: 1. I calculate the energy in the space without the plates 2. I calculate the energy between the two plates And then I speculated. I thougt of taking the difference of one and two and set the energy in F=-dE/dx --> correct? And second: Someone told me that we can derive the casimir force by working with the cavity radiation. I think that can't actualy be true, is it? (If yes: what has cavity radiation to do with the Casimir effect?) Thirdly: Why does cavity radiation/black body radiation happen? My thoughts: The electromagnetic waves can only have certain wave lengths in the body and the probability of finding these em waves ("phonons") is not zero right out of the body because it can not be zero everywhere. Is that the reason of cavity radiation?