There two identical haircombs which can slide along each other. One is at rest and the other is sliding with velocity v.
The combs have teeth 1 tooth per 1 mm. The comb which is moving is relativistcally contracted by factor 1/ˆš(1-v²), right?
As a result teeth of the combs are un phase in some places and are out of phase in the other places. Where they are in phase the light can pass, and where they are out of phase there is shadow.
The periodic pattern of lights and shadows on the screen behind has wave vector k and frequency Ï‰.
“I don’t think the problem was meant to be so simple as to just give you k and omega. From the comb spacing and the speed, you can find those and then find the mass of your “particle”, which could certainly turn out to be imaginary, making it a “tachyon”.”
Thank you Bekki for pointing it out.