Question

The elongation of light waves occurs not because galaxies are moving away from each other, but because light waves are stretching along with the fabric of expanding space (cosmological redshift). Although the Milky Way is held together by gravity, space expansion occurs everywhere, including within the Milky Way. Since space expansion occurs in the Milky Way and light stretches due to space expansion, why don't we observe cosmological redshift within the Milky Way?

Answer 1

Cosmological redshift within the Milky Way is not observed due to the galaxy's gravitational forces overcoming the minor effects of universal expansion at the galaxy's scale, thus light within it does not stretch enough to notice a redshift.

Step-by-step explanation:

The reason we do not observe cosmological redshift within the Milky Way, despite space expansion occurring everywhere, is because the gravitational forces within our galaxy bind it together, effectively counteracting the minute effects of universal expansion at such small scales.

The cosmological redshift is a phenomenon observed in distant galaxies, where light waves stretch along with the expanding fabric of space, resulting in a redshift as the light travels through the stretching space over great distances. Since light from objects within the Milky Way does not travel through enough expanding space to accumulate a noticeable redshift, we do not observe this effect in our own galaxy.

The reason we don't observe cosmological redshift within the Milky Way is because the expansion of space occurs everywhere, including within our own galaxy.

However, the effect of cosmological redshift is only noticeable for distant galaxies that are farther away than 50 million light-years. Since the Milky Way is within this distance range, the redshift is not significant enough to be observed.