Posted by Steve Simon on January 24, 2014, 5:53 pm, in reply to "Bosons"
Good question. We will discuss this more when we get to phonons later in the course. One has to remember that in quantum mechanics particles and waves are the same thing. If we pick a particular k-mode in the box, and we think of this as a harmonic oscilator, we can excite that oscillator up to the n^th level. This is equivalent to saying that we put n boson particles in this k-state.
There is a difference, however, between bosons, like Helium atoms or pions, and bosons like photons or vibrational excitations of a harmonic oscillator. In the former case ("real" particles) the number of bosons is fixed --- helium atoms don't just disappear spontaniously. You have to fix the chemical potential in order to get the right number of bosons in your system. However, with photons the number of photons, or number of vibrational quanta (phonons) is not fixed. If you add energy (temperature) to the system, you will get more photons.
Does that help?
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