What causes cosmological redshift of photons that reach us from distant galaxies?
A) The photons have moved from high gravitational field regions toward lower fields,thereby becoming reddened.
B) The photons were emitted from the galaxies much earlier in time when the overall temperature of matter was much lower.Hence,the observed photons are redder,the farther away from Earth that they were produced.
C) The photons have traveled across space that has been expanding and their wavelengths have expanded with it,becoming redder.
D) The photons were emitted by objects that were moving rapidly away from us,and thereby have been reddened by the Doppler effect.

Question

Quizplus · Accepted Answer

The most widely accepted explanation for the cosmological redshift is that the photons have been traveling across space that has been expanding, and their wavelengths have expanded with it, becoming redder. This is known as the cosmological redshift and is different from the Doppler shift, which is caused by motion relative to the observer. Option A is not a correct option as there is no direct relation between gravitational field and the redshift of photons. Similarly, option B is not a correct option as the temperature alone does not affect the wavelength of photons. Option D is also not a correct option since the Doppler effect causes shift only in the wavelength of objects relative to the observer.

What Causes Cosmological Redshift of Photons That Reach Us from Distant