Question

With Hubble's Law in mind, how can we assume that the velocity of receding galaxies has always been constant?

Answer 1

See explanation.

Explanation:

Hubble constant, `H_0=71` km/sec/parsec, `to` age of our

universe `> 13.77` billion years, is a parameter for the

expansion formula. After a long period from now, it might be slightly

different. Also, the precision of the measuring instruments that

approximate redshift matters.

At the time of measurement, within the limits of precision of

instruments that measures redshift of galaxies, due to Doppler

effect, `H_0` is regarded as a constant.

Reference:

http://www.physicsoftheuniverse.com/topics_bigbang_expanding.html