The zero-energy universe hypothesis proposes that the total amount of energy in the universe is exactly zero: its amount of positive energy in the form of matter is exactly canceled out by its negative energy in the form of gravity. Some physicists, such as Lawrence Krauss or Alexander Vilenkin, call this state "a universe from nothingness" but, the zero-energy universe model requires both a matter field with positive energy and a gravitational field with negative energy to exist.
History
During WWII, Pascual Jordan first suggested that since the positive energy of a star's mass and the negative energy of its gravitational field together may have zerototal energy, conservation of energy would not prevent a star being created by a quantum transition of the vacuum. George Gamow recounted putting this idea to Albert Einstein: "Einstein stopped in his tracks and, since we were crossing a street, several cars had to stop to avoid running us down". Elaboration of the concept was slow, with the first notable calculation being performed by Richard Feynman in 1962. The first known publication on the topic was in 1973, when Edward Tryon proposed in the journal Nature that the universe emerged from a large-scale quantum fluctuation of vacuum energy, resulting in its positive mass-energy being exactly balanced by its negative gravitational potential energy. In the subsequent decades, development of the concept was constantly plagued by the dependence of the calculated masses on the selection of the coordinate systems. In particular, a problem arises due to energy associated with coordinate systems co-rotating with the entire universe. A first constraint was derived in 1987 when Alan Guth published a proof of gravitational energy being negative to matter associated mass-energy. The question of the mechanism permitting generation of both positive and negative energy from null initial solution was not understood, and an ad hoc solution with cyclic time was proposed by Stephen Hawking in 1988. In 1994, development of the theory resumed following the publication of a work by Nathan Rosen, in which Rosen described a special case of closed universe. In 1995, J.V. Johri demonstrated that the total energy of Rosen`s universe is zero in any universe compliant with a Friedmann–Lemaître–Robertson–Walker metric, and proposed a mechanism of inflation-driven generation of matter in a young universe. The zero energy solution for Minkowski space representing an observable universe, was provided in 2009. In 2010, it was proposed that zero-energy universes are born in pairs - with opposite rotation, thus ensuring the total energy and impulse of multiverse is still zero.
Experimental constraints
Experimental proof for observable universe being "zero-energy universe" is currently inconclusive. Gravitational energy from visible matter accounts to 26–37% of the observed total mass-energy density, therefore to fit the concept of "zero-energy universe" to observed universe, other negative energy reservoirs besides gravity from baryonic matter are necessary. These reservoirs are frequently assumed to be a dark matter.
Relation to quantum fluctuation
Although the hypothesis that a zero-energy universe was born out of a quantum fluctuation is not consistent with modern physics as of 2015, this hypothesis is still widely cited in popular sources.
