Light in a box (split from Cosmological redshift, thought experiment)

[Danijel Gorupec]

Sorry, if I am a bit off topic, but just a side question out of curiosity - can bouncing light in a fixed box have any wavelength, or only some discrete values?

[swansont]

1 hour ago, Danijel Gorupec said:

Sorry, if I am a bit off topic, but just a side question out of curiosity - can bouncing light in a fixed box have any wavelength, or only some discrete values?

In 1D, it should be easy to see that there are discrete wavelengths, since you will get destructive interference if the path length is not a multiple of the half-wavelength. So other wavelengths will not persist.

If you consider 3D, there are more paths available and you have more options that avoid destructive interference, but you will still have wavelengths that are excluded from possibility.