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.

I might be missing something, but what does relativity have to do with this? You could do the same thing with two combs at home with slightly different spacing of the comb rakes.

You’re not measuring particles but the images created by the light pattern. Nothing prevents these patterns of light and dark from exceeding the speed of light. No tachyons required.

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Thx M. Bekki. Learn something new everyday.

A tachyon is a theoretical particle, one has never been detected in our universe.

“A second class of tachyonic particles has real rest mass and imaginary energy; they do not interact with matter, nor is there the effect by gravitation of attraction since that requires relativistic reference frames FTL and STL and these tachyons are, of course, FTL as well as the gravitons. Gravitation is therefore a force of repulsion to them and they would be curved away from gravitational sources. Since the space-time continuum is so curved in the presence of mass, an obvious conclusion is that they compose the “fabric of space”. By vibrating FTL, as an observer’s speed increases, an increasing… Read more »

I don’t think you need to know any of the stuff about the hairbrush dimensions or the speeds. If they give you the frequency and the wave number, that is sufficient to calculate mass. The algebra is simpler in natural units, so I’ll supress the h-bars and c’s. Put em back in at the end if you need to. So if we assume that that periodic pattern is a “particle”, we apply the deBroglie hypotheses to it: E = omega p = k So the relativistic energy/momentum mass relationship: E^2 = p^2 + m^2 will become: omega^2 = k^2 +… Read more »