Question

How did scientists determine the Big Bang occurred 13.7 billion years ago?

Answer 1

Hubble constant `H_0` is estimated as 71 km/s/megaparsec ( `[H_0]=T^(-1)` ). The reciprocal 1/71, expressed in billion years, is 13.77 that is an estimate of life of our universe, since Big Bang.

Explanation:

The speed of a galaxy receding from another was estimated by the

Doppler Effect ( the light emitted by a source is shifted in wave

length by thee motion of the light source ). Edward Powell Hubble (

1889-1953) had discovered in 1929 a linear correlation between the

speed and the distance.

Hubble constant `H_0` is estimated as 71 km/s/megaparsec (

`[H_0]=T^(-1)`= 1/Time ). The reciprocal 1/71 expressed in billion

years is 13.77. This is just a problem in unit conversions.

In my opinion, this is perhaps a lower bound for time that had

elapsed, since Big Bang. There are further research developments

that take this up, to a much higher upper bound.