# Why don't we “see” the classical Dirac field?

The electromagnetic field describes photons. If there are many photons then things become classical and we can use classical electromagnetism to describe the EM field. We can also measure the EM field placing an antenna and watching the voltage in its terminals.

If the Dirac field describes electrons in a similar manner the EM field describes photons, why don't we see electronic waves or other classical field phenomena? What would have to be done to observe this phenomena?

• Which specific "classical field phenomena" are you referring to? What specifically do you mean by "electronic waves"? If by "waves" you mean "traveling excitations of the field," then we already see those, as electrons are exactly those excitations. – probably_someone Oct 10 '18 at 13:15
• Tentatively the rather distinct phenomenology in the semi-classical limit for large number of photons vs large number of electrons may have something to do with the former being bosons and the latter fermions? Also maybe the fact that photons are massless, making them easy to emit/absorb even at low energy? – Luzanne Oct 10 '18 at 13:42

It is possible, however to collectively describe and observe classical effects for systems of many fermions. Mathematically, this is done performing a so-called multiscale semiclassical analysis: the idea is to consider a system with at the same time many fermions, and energy scales that are much bigger than Planck's scales. In other words, one considers simultaneously the limits $$N\to \infty$$, and $$\hslash\to 0$$ ($$N$$ being the number of fermions), in a suitable way (if I recall correctly, $$\hslash\sim N^{-\frac{1}{3}}$$ in three space dimensions).