# Fine dipole moment - numbers


## Fine dipole moment

$\alpha_{QED} = \frac{e^2}{\hbar c} = \frac{d^2}{a^2 \hbar c}$

this is the definition of fine dipole moment depending on the length $a$ between charges $e$.
The lengtha can be taken either as https://en.wikipedia.org/wiki/Bohr_radius or https://en.wikipedia.org/wiki/Classical_electron_radius

## imagine that there are no free charges, but only dipole interactions

- let us compare with fine coupling in low-T glasses

$\alpha_{QSNS} = P \frac{\gamma^2}{\rho c_t^2}$

where $P=\frac1frac{1}{erg*cm^3}$, $\gamma=erg$, and $\rho c^2= erg/cm^3$

# Parents

* Fine structure constant