# Two-photon physics/quantum electrodynamics

1. Jan 30, 2014

### Antigone

In a Wikipedia article about two-photon physics it is stated: "From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but half wavelength is a positive charge and the next half wavelength is a negative charge."

This is the article:

http://en.wikipedia.org/wiki/Two-photon_physics

Does the statement "half wavelength is a positive charge and the next half wavelength is a negative charge" mean that photon actually consists of negative and positive charges at once? That one half of the wavelength is positive and the other one is negative? Is that a true statement?

2. Jan 31, 2014

### Simon Bridge

No.
No.
The one in wikipedia? It's a descriptive statement.

Note: you have to be careful about thinking of anything as "actually" happening in quantum mechanics.
QED does not tell us what is "actually" going on, it just tells us how to do some math that helps with predicting the outcome of experiments.

In this case the picture being painted helps visualize how photon-photon EM interactions can happen - when it is a neutral particle and EM works with charged particles.