Question

now the universe is expanding.Is there any possibility for the universe to start contract one day?

Answer 1

Yes some scientist belief that it may start to contract one day and will again start expanding with the second big bang

Answer 2

It will continue to expand, in fact we live in aRunaway Universe with an acceleratingexpansion. This is the result of gravity!

But with the opposite sign, sort of an anti-gravity. You see, matter, energy, and pressure all contribute to gravity.

Our universe is about 2/3 dark energy and the rest is matter (ordinary and dark) as measured by energy and mass content. Recall E=m⋅c2E=m⋅c2is the rest mass energy.

The pressure associated with the dark energy is negative. And in the equations of general relativity it enters with 3 times the weight of the dark energy’s term, which is positive.

The matter weighs in at 1/3 approximately, and the dark energy at 2/3 and they are both attractive, the kind of gravity you are used to. But the dark energy pressure weighs in at -2, and the sum of everything is around -1 in units of the critical mass energy density. A negative result here means that on the largest scales, above that of clusters of galaxies the universe will continue to expand, in a runaway fashion.