Celestial objects’ speed through space is measured relative to other things. Often that speed is based on the reference of the cosmic microwave background radiation. Cosmic microwave background radiation is photons, that are remaining from the first light that was able to travel freely through the universe. Light is traveling at C (and experiences no time). Eli5 How is that light/photon cloud a standard for a motionless frame of reference when its photons are moving at the speed of light?
In: 4
The reference frame is measured using blueshift and redshift of the light from doppler effects. As you move towards or away from a source of light, it will squish the waves or stretch them out. Since all of the photons came from the same source and because the CMB is more or less equal in all directions, and since light is going the same speed in all directions, we would expect to see all of the light with the same average wavelength.
But we can observe that the CMB is slightly redshifted in one direction and slightly blueshfited in the opposite direction. That shows that we’re moving relative to the CMB.
Latest Answers