I hope some of you must have heard about the story that how Einstein introduced, cosmological constant in general theory of relativity (GR) to discard the expanding model of universe.

Einstein used cosmological constant in his theory to balance the contraction of universe in his equation’s were indicating, he said spacetime exhibits self tendency to stretch on its own and this stretching of space gets balanced by gravity between matters.

Mathematical framework for expansion theory

But in 1922 a Russian scientist Alexander Friedmann published a article – “About the curvature of space” giving mathematical framework about Expansion of universe Based on two simple assumption.

1) universe look identical whichever direction we look

2) second is above assumption would also be true if we were observing the universe from anywhere else

This two points abstract is that the mass distribution in universe is same even if you calculate it far away from different place in space it doesn’t implies that it is identical its just saying mass density is same throughout universe .

He successfully proofed that equations of Einsteins represents non static universe But Friedmann’s finding didn’t got much appreciation because that time everyone was in strong delusion of static universe.

Redshift of distant galaxy proofed expansion

some other theoretical physicist also confronted GR and obtained more or less same result but it was Hubble who presented hard empirical evidence that, indeed celestial bodies are moving further away from each other this conclusion was based on red shift.

Edwin Hubble (1889-1953)

Red shift of light is increase in wavelength of light when source of light is receding from observer, color of light tends toward red spectrum , inverse of red shift is known as violet shift.

When the expansion of universe proofed by empirical data then static universe supporters including Einstein accepted the fact that universe is expanding.

Questions about expansion

Now the question arises what’s the rate of expansion, is it eternal or there is a dark matter manufacturing factory in center of universe which keep producing dark matter which is pushing matter on shores outward as it appears to be expanding, so far we have been able to answer some of this question’s.

Rate of expansion of universe

The rate at which universe is expanding is known as Hubble constant and this constant isn’t so constant according to Hubble law –

All objects are moving away from each other and the relative velocity is proportional to distance between them .

That’s mean more further away the object more receding relative velocity between them means more value of Hubble constant must be there .

the velocity of expansion rate of universe 74km/s per mega parsec is which is huge and it is contradictory to special theory of relativity it could be possible that in near future we have to do some new edition to the special theory of relativity.

a very good analogy of expanding universe given by Stephen hawking in his book “A brief history of time ” every person who is interested in cosmology should read it –

The situation is rather like a balloon with a number of spots painted on it being steadily blown up, as the balloon expands, the distance between any two spots increases, but there is no spot that can be said to be the center of the expansion. moreover, the further apart the spots are, the faster they will be moving apart .

Dark matter

there is another theory which explains expanding universe theory of, dark matter and dark energy according to this theory dark matter makes about 27% of the universe,dark energy makes 68% and rest is normal matter and this dark matter is reason of expanding of universe.

physicists suggests that this dark matter have properties like anti gravity which produces repulsive forces but this theory are still on the paper there has been no evidence to be found about anti gravity phenomenon.

As we know for now that universe shouldn’t be expanding because it has enough matter (normal matter) density to contract it but its not contracting that’s mean there are more part of puzzle which are still to be solved .