Question

How can astronomers infer approximately how long the universe has been expanding?

Answer 1

Not only astronomers, but all scientists use the technique of rock dating to determine the age of the universe. From the Big Bang Theory, all the celestial bodies were made at the same time. So, the age of the Earth is just the same with the age of the universe. So, they gather rocks deep down in the crust of the Earth and let it undergo radioactive decay. By determining the amount of radioactive material left and half-life, they could compute the age of the Earth.

Answer 2

Answer:

Explanation:

As we know that universe is not constant, it is expanding from a very long time.

Scientist and astronomers have been working for a very long time to know the age of universe and for how long it has been expanding. This can be determined by  calculating the age of rocks and objects found in universe.

The decay rate and the emission of radioactive elements also give us information about the expansion of universe.

The expansion rate can also be determined by a number called as hubble constant. Astronomers determine the regulation of dark energy.

A low density matter in universe is older, hence all these factors tells us about the expansion of universe and its age.