# Is it possible for photons to dissappear in vacuum.

1. Jan 27, 2010

### leoneri

Hi, I am reading Introduction to Statistical Physics by Kerson Huang. On chapter 10 about Bose Gas, a statement intrigued me. He explains Photons.

"Photons are the quanta of the Electromagnetic field. They are bosons whose number is not conserved, for they may be created and absorbed singly. The Lagrange multiplier corresponding to total number is absent, and the chemical potential $$\mu$$ is zero. This means that the particles can dissappear into the vacuum."

I can't help but wondering myself if this is really true. If it's gone then where does it go? Is it disappear because Photon is a quantization of energy and not a 'real' particle? What is the definition of vacuum in this context?

From my Physics course, what I understand about EM field is that an exponential decay ~$$e^{-x}$$ only occurs when there is material (and hence not vacuum) that absorbs the photons. While in vacuum, the field will oscillate harmonically ~$$~ e^{i x}$$ and will goes on forever ...

2. Jan 27, 2010

### ansgar

you can represent things in different contexts, for instance in high energy physics the photon is treated as a "real" particle just as everyone else.

Now in statistical mechanics, photons are excitations of the EM field as you said, and what "This means that the particles can dissappear into the vacuum" only means that we also can deexcite the EM-field to the ground state - i.e. no excitations in energy and hence no photons - and the vacuum is just a fancy word for the ground state.

3. Jan 27, 2010

### meopemuk

A photon cannot "disappear into vacuum". Each photon has a non-zero momentum and energy. Photon's disappearance would mean violation of both momentum and energy conservation laws.

Eugene.

4. Jan 27, 2010

### torquil

And angular momentum.

Torquil

5. Jan 27, 2010

### inempty

It can disapear but it just means that it's absorbed by another particle. If you have changed the Energy of a system, you must have a particle scattered by that.