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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 described the inflationary universe as the "ultimate free lunch": [108] [109] new universes, similar to our own, are continually produced in a vast inflating background. Gravitational interactions, in this case, circumvent (but do not violate) the first law of thermodynamics ( energy conservation ) and the second law of thermodynamics ...
These proposals have been criticized as inconsistent with the Borde–Guth–Vilenkin theorem, however their modifications with only one bounce (as opposed to cyclic series of bounces) circumvent this problem (particularly if the contracting phase is empty, i.e. compactified Milne, and (2+1)-dimensional, due to the inherent stabilizing rigidity ...
Guth coined the term "inflation," and was the first to discuss the theory with other scientists worldwide. Guth's original formulation was problematic, as there was no consistent way to bring an end to the inflationary epoch and end up with the hot, isotropic, homogeneous universe observed today. Although the false vacuum could decay into empty ...
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.