Question

We say that the universe is constantly expanding. The area of the universe was certain in the past. In which area is the universe expanding

Answer 1

In the beginning of time, as stated by the Big Bang theory all the mass present in universe was centralised as a point size thus making it of infinite density. Because of the intermoleculer imbalance in the forces, the point exploded and started expanding. Every element started moving away from each other because of repelling force created. This started the expansion of universe in all directions. Stars, galaxies, planets etc all started moving away from each other. The gravitational force existing between heavenly bodies counter the repelling force of Big Bang and it(gravitational force) is increasing as the universe expands. The expansion of universe will be happening till gravitational force equals the repelling foce.