Can torsion avoid the big bang singularity

[Naty1]

Interesting theory for consideration:

Cosmology with torsion: An alternative to cosmic inflation

http://arxiv.org/abs/1007.0587Nikodem 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.

... 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...

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...

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.

 

[Mordred]

Interesting article it seems to imply there is a universe inside every black hole. I've seen various articles posted on the web to that effect. Nice to see the supporting mathematics.

Can't help you with spin my understanding of spin is limitted.

edit: Besides me helping answer your questions after reading many of your posts would be like a Kindergarden student trying to teach a math professor how to add 2+2

 

[skydivephil]

I wonder if this paper was inspired by Smolins idea of Cosmic Natural Selection. I get that its slightly different but the main idea seems the same.
http://arxiv.org/abs/gr-qc/0205119

 

[Naty1]

Here are some related discussions on torsion.

Turns out, it seems to me, torsion and curvature are more closely related than I realized.

Mentioned in one of these is a description by Roger Penrose and I read that section in his Road to Reality...Apparently the amount of torsion affects the closing of a parallelogram of geodesic edges about a point. He says going in two opposite directions around the parallelogram yields two different points of closure resulting from the presence of torsion.

..My description has been very brief and I refer the uninitiated interested readers to the literature concerning this remarkable and ubiquitous topic.

Spin Density and Non-symmetric Stress-Energy Tensor
https://www.physicsforums.com/showthread.php?t=615574&highlight=torsion

[Interestingly, Stevendaryl answers one of my uncertainties. It turns out the paper I posted here seems to offer one perspective regarding his question. ]

Stevendaryl:

In General Relativity, the assumption is made that the stress-energy tensor Tαβis symmetric. However, if there are particles with intrinsic spin, then this assumption is false, as described here: http://en.wikipedia.org/wiki/Spin_tensor

Ben Niehoff: [On Wikipedia Einstein-Cartan theory]

The article does contain other inaccuracies, such as suggesting that geodesics "twist around each other" in the presence of torsion. No such thing happens; the torsion does not enter the geodesic equation. (Torsion does cause parallel-transported vectors to "twist around", but this is not the same thing).

Does torsion make parallel transport direction dependent?
https://www.physicsforums.com/showthread.php?t=652327&highlight=torsion

Is frame dragging the same as torsion?
https://www.physicsforums.com/showthread.php?t=644506&highlight=torsion

Tom.Stoer:

I strongly believe that Einstein-Cartan theory - which is equivalent to GR experimentally, except for the tiny torsion effects - is a much more natural mathematical setup for dynamical spacetime, especially when coupled to fermions.

 

[Naty1]

Marcus makes the following point in this thread, which seems to address one of my questions...

https://www.physicsforums.com/showthread.php?p=4230463#post4230463

...Spin networks are used extensively in loop quantum gravity, where they represent states of quantum geometry...LQC recovers classical FRW cosmology, and cosmology is almost sure to be the main testing ground for theories of quantum geometry+matter.

 

[Mordred]

The main problem I have with the multiverse black hole models.
Is that black holes are more violent when they are feeding. That change in feeding rates would reflect in variations. Stronger during feeding times slower when the BH is not feeding. I'd have to look at what can get by the event horizon to name those variations. The electromagnetic readings would certainly reflect the BH feeding rates. Hence I cannot see us being in an event horizon.

The work on spin association is however useful so still a good paper.

 

[Naty1]

Mordred,
I was more interested in the inflation rather than the black hole aspect of the paper. I did not read details in the paper about a collapsing black hole spawning new universes; however, that seems to happen in general when our side of the horizon is cold,black and empty...at least in the vicinity of the BH.

[I was hoping someone would offer comments about the robustness of the math underlying the gravitational torsion repulsion at high density eliminating the big bang singularity.]

But I have seen simulations regarding black holes combining or absorbing matter.

One is here, http://en.wikipedia.org/wiki/Black_hole

but there is another around in which black holes are shown to oscillate when combining...and the oscillations dampen after combination.

 

[Mordred]

A massive star, that is causally connected, collapses gravitationally to a black
hole and an event horizon forms. Inside the horizon, spacetime is nonstationary and matter contracts to an extremely
dense, but because of torsion, finite-density state. In the frame locally moving with matter, this contraction looks
like the contraction of a closed universe [22, 35]. Such a universe is initially causally connected and anisotropic.
Extremely large tidal forces cause an intense pair production which generates the observed amount of mass and
increases the energy density, resulting in isotropization of this universe [32–34]. Additional terms in the Lagrangian
density containing torsion could also generate massive vectors [36].

The article is full of references to the multiverse BH model. As I stated prior there would be fluctuations in Radiation/energy levels derived from the feeding rates of the BH. As its feeding there would be higher levels compared to when its matter/energy source is further away form its gravity well.
There was an article written several years ago that described a BH forming a spacetime bubble that as it expanded formed a long tunnel sperating the BH from the bulge. This tunnel eventually squeezed of seperating the created spacetime with the BH. That scenario could create a universe with constant inherent spin/torsion from a BH.

I can't help you on the mathematical side, I do enjoy the article as it shows how one can apply spin to general relativity, it is definitely useful in those terms. For those reasons its definitely worth examining. I too had hoped more ppl were interested in comenting on the paper.