Virtual Photon

1. Nov 24, 2009

matt_crouch

In my lecture this morning i was told that charged particles interact by the exchange of virtual photons and that they serve as carriers of momentum and force. But it says that a photon is a boson with spin number 1, massless and zero charge.

The question is basically how can a massless particle carry momentum ?

2. Nov 24, 2009

dextercioby

I would ask you: on what mathematical grounds does a massive particle carry momentum ?

3. Nov 24, 2009

Dmitry67

It is irrelevant if it is virtual or not. Real photons are also masless, but they carry momentum. Massless = no rest mass, you are probably thinking about the 'relativistic' mass.

4. Nov 24, 2009

George Jones

Staff Emeritus
Elaborating a bit on what Dmitry67 wrote, according to special relativity, the energy, momentum, and rest mass of a particle are related by

$$E^2 - \left( cp \right)^2 = \left(m c^2 \right)^2.$$

For a photon, $m=0$ and $E = cp$.

Even classical electromagnetic fields carry momentum.

5. Nov 24, 2009

Staff: Mentor

And with the same relationship, if you considerf E and p as the energy and momentum densities of the fields.