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Cosmology with torsion: An alternative to cosmic inflation

http://arxiv.org/abs/1007.0587

Nikodem J. Poplawski

(Submitted on 4 Jul 2010 (v1), last revised 2 Nov 2010 (this version, v2))

We propose a simple scenario which explains why our Universe appears spatially flat, homogeneous and isotropic. We use the Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity which naturally extends general relativity to include the spin of matter. The torsion of spacetime generates gravitational repulsion in the early Universe filled with quarks and leptons, preventing the cosmological singularity: the Universe expands from a state of minimum but finite radius. We show that the dynamics of the closed Universe immediately after this state naturally solves the flatness and horizon problems in cosmology because of an extremely small and negative torsion density parameter.... Thus the ECKS gravity provides a compelling alternative to speculative mechanisms of standard cosmic inflation. This scenario also suggests that the contraction of our Universe preceding the bounce at the minimum radius may correspond to the dynamics of matter inside a collapsing black hole existing in another universe, which could explain the origin of the Big Bang.

In this work, we considered the ECKS theory of gravity which is the closest theory with torsion to general relativity. We used the spin density of matter as the source of torsion, which has a natural physical interpretation in the context of the Poincar´e group and does not introduce additional ﬁelds or coupling constants.... .... we show that extending Einstein’s general relativity to include the intrinsic angular momentum (spin) of matter, which leads to the Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity, naturally explains why the Universe is spatially ﬂat, homogeneous and isotropic, without invoking inﬂation. We also propose that the torsion of spacetime, which is produced by the spin of quarks and leptons ﬁlling the Universe and prevents the formation of singularities (points of spacetime with inﬁnite curvature and matter density), provides a physical mechanism for a scenario in which each collapsing black hole gives birth to a new universe inside it.Gravitational repulsion induced by torsion, which becomes signiﬁcant at extremely high densities, prevents the cosmological singularity.....

Wikipedia:

[the Einstein–Cartan theory, also known as the Einstein–Cartan–Sciama–Kibble theory or the Cartan–Sciama–Kibble theory is a classical theory of gravitation similar togeneral relativity but relaxing the assumption that the metric be torsion-free. Introducing torsion allows greater freedom to couple classical spin angular momentum to the metric.]

Avoidance of singularities

http://en.wikipedia.org/wiki/Einstein-Cartan_theory#Avoidance_of_singularities

In 2011, Nikodem Poplawski showed that the Einstein-Cartan theory eliminates the general-relativistic problem of the unphysical singularity at the Big Bang.[7] The minimal coupling between torsion and Dirac spinors generates a spin-spin interaction which is significant in fermionic matter at extremely high densities. Such an interaction replaces the singular Big Bang with a cusp-like Big Bounce at a minimum but finite scale factor, before which the observable universe was contracting. This scenario also explains why the present Universe at largest scales appears spatially flat, homogeneous and isotropic, providing a physical alternative to cosmic inflation.[6]

Torsion also requires fermions to be spatially extended.[10] Such particles cannot be point-like, which avoids the formation of singularities in black holes and removes the ultraviolet divergence in quantum field theory. According to general relativity, the gravitational collapse of a sufficiently compact mass forms a singular black hole. In the Einstein–Cartan theory, however, it forms a regular Einstein-Rosen bridge (wormhole) with a new, growing universe on the other side of the event horizon.

Does string theory offer any additional insights as to how particle spin and space-time geometry interact?

edit: somewhere I read that including torsion makes the stress energy momentum tensor non symmetric.....Including torsion is what appears to be the source of the high density repulsion.

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# Can torsion avoid the big bang singularity

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