4 ms·

No, the origin of the cosmological redshift is not proposed to be due to differences in velocity, but metric expansion.

• platz 8y ago
  ... which causes a change in relative velocities
  • gcthomas 8y ago
    That makes it sound like cosmological redshift is a form of Doppler shift. In reality, the target object emits light towards us with little Doppler shift as it will have experienced little acceleration in its reference frame. The light becomes redshifted as it moves through the universe while the universe is expanding, effectively stretching out the wavelength of the light. The change in wavelength is exactly proportional to the increase in size of the universe during the time of flight, and it is not directly related to speed of recession except in common and inaccurate discussion. The link to relative velocity (if that concept makes sense for objects in widely separated and unrelated reference frames) is model dependent, while the metric expansion measurement is directly measured.
    • platz 8y ago
      Ok. I was under the impression that expansion had no effect on local phenomena because local phenomena always counteract expansion. But if you view light more as a wave instead of a particle then could see the argument that the light is locally stretched if there is no force keeping it from being stretched e.g. gravity or energy.