The initial singularity is a singularity predicted by some models of the

Big Bang theory The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...

to have existed before the Big Bang and thought to have contained all the energy and spacetime of the Universe. The instant immediately following the initial singularity is part of the

Planck epoch The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. Research published in 2015 estimates the earliest stages of the universe's existence as taking place 13.8 billion years ago, wit ...

, the earliest period of time in the history of our universe.

Traditional models of our Universe

The use of only general relativity to predict what happened in the beginnings of the Universe has been heavily criticized, as quantum mechanics 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 string theory-based model in which two

branes In string theory and related theories such as supergravity theories, a brane is a physical object that generalizes the notion of a point particle to higher dimensions. Branes are dynamical objects which can propagate through spacetime accord ...

, enormous membranes much larger than the Universe, collided, creating mass and energy. Although there is no direct evidence for a singularity of infinite density, the

cosmic microwave background In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space ...

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

loop quantum gravity Loop quantum gravity (LQG) is a theory of quantum gravity, which aims to merge quantum mechanics and general relativity, incorporating matter of the Standard Model into the framework established for the pure quantum gravity case. It is an attem ...

, aims to explain the beginnings of the Universe through a series of

Big Bounce The Big Bounce is a hypothesized cosmological model for the origin of the known universe. It was originally suggested as a phase of the ''cyclic model'' or ''oscillatory universe'' interpretation of the Big Bang, where the first cosmological even ...

s, in which quantum fluctuations cause the Universe to expand. This procreation also predicts a

cyclic model A cyclic model (or oscillating model) is any of several cosmological models in which the universe follows infinite, or indefinite, self-sustaining cycles. For example, the oscillating universe theory briefly considered by Albert Einstein in 1930 t ...

of universes, with a new universe being created after an old one is destroyed, each with different physical constants. Another procreation based on

M-theory M-theory is a theory in physics that unifies all consistent versions of superstring theory. Edward Witten first conjectured the existence of such a theory at a string theory conference at the University of Southern California in 1995. Witten's ...

and observations of the

(CMB), states that the Universe is but one of many in a

multiverse The multiverse is a hypothetical group of multiple universes. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them. The di ...

, and has budded off from another universe as a result of

quantum fluctuation In quantum physics, a quantum fluctuation (also known as a vacuum state fluctuation or vacuum fluctuation) is the temporary random change in the amount of energy in a point in space, as prescribed by Werner Heisenberg's uncertainty principle. ...

s, as opposed to our Universe being all that exists.

References

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