SOLAR SYSTEM

Detailed explanation-1: -It might have enough energy density to stop its expansion and recollapse, it might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but, theoretically, the universe had to slow.

Detailed explanation-2: -The energy from the Big Bang drove the universe’s early expansion. Since then, gravity and dark energy have engaged in a cosmic tug of war. Gravity pulls galaxies closer together; dark energy pushes them apart. Whether the universe is expanding or contracting depends on which force dominates, gravity or dark energy.

Detailed explanation-3: -Hubble’s brilliant observation was that the red shift of galaxies was directly proportional to the distance of the galaxy from earth. That meant that things farther away from Earth were moving away faster. In other words, the universe must be expanding. He announced his finding in 1929.

Detailed explanation-4: -The first theory claims the Universe will end with a Big Rip, as the pull of the Universe’s expansion gets stronger than the gravity it contains. This would tear apart galaxies, followed by black holes, stars and even our own planet.

Detailed explanation-5: -Gravity as we understand it would work to hold the universe together, not let it race apart from itself into eventual oblivion. Enter the counterpart to dark matter, dark energy, which is what scientists call whatever is pulling the universe apart.