Specifically why do they have $V = \frac{c}{β}$ as stated in this paper written by De Broglie: http://aflb.ensmp.fr/LDB-oeuvres/De_Broglie_Kracklauer.pdf ?
I follow the proof of “phase harmony” between the reference frames, but i’m getting confused between them and i don’t see why $V = \frac{c}{β}$
P.S i know matter waves are kind of an archaic concept, this is purely a historical exercise.
