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The Borde–Guth–Vilenkin (BGV) theorem is a theorem in physical cosmology which deduces that any universe that has, on average, been expanding throughout its history cannot be infinite in the past but must have a past spacetime boundary. [1]
In publications, he would propose that the Borde–Guth–Vilenkin theorem is sufficient evidence for a beginning of the universe. [50] [51] [52] Craig has stated that, if anything existed before the past boundary described by the theorem, it would be a non-classical region described by an as-yet-undetermined theory of quantum gravity.
In 1982, Paul Steinhardt presented the first model of eternal inflation, Vilenkin showed that eternal inflation is generic. [9] Furthermore, working with Arvind Borde and Alan Guth, he developed the Borde–Guth–Vilenkin theorem, showing that a period of inflation must have a beginning and that a period of time must precede it. [10]
For scientific evidence of the finitude of the past, Craig refers to the Borde-Guth-Vilenkin theorem, which posits a past boundary to cosmic inflation, and the general consensus on the standard model of cosmology, which refers to the origin of the universe in the Big Bang. [44] [45]
Guth proposed inflation in January 1981 to explain the nonexistence of magnetic monopoles; [51] [52] it was Guth who coined the term "inflation". [53] At the same time, Starobinsky argued that quantum corrections to gravity would replace the supposed initial singularity of the Universe with an exponentially expanding de Sitter phase. [ 54 ]
2003 – Arvind Borde, Alan Guth, and Alexander Vilenkin prove the Borde–Guth–Vilenkin theorem. [233] [234] 2002 – First data collection of the Laser Interferometer Gravitational-Wave Observatory (LIGO). 2002 – James Williams, Slava Turyshev, and Dale Boggs conduct stringent lunar test of violations of the principle of equivalence. [235]
Physical cosmology is the study of the largest-scale structures and dynamics of the Universe and is concerned with fundamental questions about its origin, structure, evolution, and ultimate fate.
In physical cosmology, the graceful exit problem refers to an inherent flaw in the initial proposal of the inflationary universe theory proposed by Alan Guth in 1981. [1]In Guth’s model, the period of accelerated expansion (a.k.a. inflation) makes the universe homogeneous and flat but can never end.