Consider two person one is travelling in a space ship and one is on the moon, now in the space ship there is a device where a light beam or photon is bouncing between two mirrors now when the space ship moves shouldnt the light beam or photon stay where it is relative to the observer on the moon meaning that space should should go ahead a the photon would not move along with the space ship


1 Answer 1


should'nt the light beam or photon stay where it is

Light, electromagnetic wave, is a classical manifestation of the superposition of zillions of photons. Photons are elementary particles. Both move with velocity c , and cannot "stay" anyplace. c is an enormous velocity with respect to motions of moons and spaceships.

At relativistic speeds the geometry of the reflecting devise will change relative to the observer on the moon due to length contraction.

  • $\begingroup$ So what would effect the light that it also starts moving horizontally along with the space ship when it is a bouncing vertically between mirrors $\endgroup$ Jul 28, 2020 at 6:20
  • $\begingroup$ it is always new photons (classical energy light too) as it moves with velocity c always.The vertical geometry should not be affected $\endgroup$
    – anna v
    Jul 28, 2020 at 8:18
  • $\begingroup$ youtube.com/… in this video at 1.42 the light ray can be seen travelling vertically and horizontally i cant understand how the light is travelling horizontally there is no medium to take the light with it but as the space ship moves so does the ray $\endgroup$ Jul 28, 2020 at 8:25
  • $\begingroup$ Light does not need a medium. see the mchelson morley experiment en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment $\endgroup$
    – anna v
    Jul 28, 2020 at 11:01

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