The universe is commonly defined as the totality of everything that exists, includingplanets, stars, galaxies, the contents of intergalactic space, and all matter andenergy. Definitions and usage vary and similar terms include the cosmos, the worldand nature. Scientific observation of earlier stages in the development of the universe, which can be seen at great distances, suggests that the universe has been governed by the same physical laws and constants throughout most of its extent and history.
There are various multiverse theories, in which physicists have suggested that our universe might be one among many universes that likewise exist. The furthest that humans eyes have seen is described as the observable universe. Observations have shown that the universe appears to be expanding at an accelerating rate.