Question

How the universe is expanding?

Answer 1

According to Einstein's general theory of relativity, the expansion of the universe is actually an expansion of space itself, and galaxies are moving away from each other because they are “being carried along by space.”

Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart. One explanation for dark energy is that it is a property of space.

The American astronomer Edwin Hubble made the observations in 1925 and was the first to prove that the universe is expanding. He proved that there is a direct relationship between the speeds of distant galaxies and their distances from Earth. This is now known as Hubble's Law.

The accelerating expansion of the universe is the observation that the universe appears to be expanding at an increasing rate, so that the velocity at which a distant galaxy is receding from the observer is continuously increasing with time.

For every million parsecs of distance from the observer, the rate of expansion increases by about 67 kilometers per second. There are dynamical forces acting on the particles in the universe which affect the expansion rate.