Initial singularity

The initial singularity was a of seemingly infinite density thought to have contained all the mass and  of the  before s caused it to rapidly expand in the  and subsequent, creating the present-day Universe. The instant immediately following the initial singularity is part of the, the earliest period of time in the history of the universe.

Traditional models of the Universe
is used to predict that at the beginning of the Universe, a body containing all mass, energy, and spacetime in the Universe would be compressed to an infinitely dense point somewhere between the size of a human head and a skyscraper-filled city block, according to today's best models on inflation. The use of only general relativity to predict what happened in the beginnings of the Universe has been heavily criticized, as becomes a significant factor in the high-energy environment of the earliest Universe, and general relativity on its own fails to make accurate predictions. In response to the inaccuracy of considering only general relativity, as in the traditional model of the Big Bang, alternative theoretical formulations for the beginning of the Universe have been proposed, including a -based model in which two, enormous membranes much larger than the Universe, collided, creating mass and energy.

It is impossible to see the singularity or the actual Big Bang itself, as time and space did not exist inside the singularity and, therefore, there would be no way to transmit any radiation from before the Big Bang to the present day. Although there is no direct evidence for a singularity of infinite density, the is evidence that the universe expanded from a very hot, dense state.

Alternatives to the singularity
Various new models of what preceded and caused the Big Bang have been proposed as a result of the problems created by quantum mechanics. One model, using, aims to explain the beginnings of the Universe through a series of s, in which quantum fluctuations cause the Universe to expand. This procreation also predicts a of universes, with a new universe being created after an old one is destroyed, each with different s. Another procreation based on and observations of the  (CMB), states that the Universe is but one of many in a, and has budded off from another universe as a result of s, as opposed to our Universe being all that exists.