Question

how does redshift demonstrate that the universe is expanding?

Explanation:

Redshift occurs when light - emitting objects move away from an observer. In astronomy, the light from distant galaxies shows a redshift. According to the Doppler effect, this indicates that these galaxies are moving away from us. Since most galaxies show redshift, it implies that the universe as a whole is expanding.

Answer:

Redshift of light from distant galaxies, due to the Doppler effect, shows they are moving away, indicating universal expansion.