Lab Notes for a Scientific Revolution (Physics)

March 28, 2008

Further Considerations on the Energy Tensor: Metric versus Torsion

After reviewing some very helpful discussion on sci.physics.foundations and sci.physics.relativity in the threads I initiated regarding non-symmetric energy tensors and a suggested Kaluza-Klein experiment, and going back to Misner, Thorne and Wheeler’s “Gravitation,” I am starting to shift my viewpoint to be in opposition to the idea of using a non-symmetric (Cartan / Torsion) energy tensor because of the adverse impact this has on formulating a metric theory of gravitation.

There is a non-symmetric energy tensor in equations (15.11) to (15.13) of:

Kaluza-Klein Theory and Lorentz Force Geodesics Rev. 6.0

which is based upon the *non-symmetric* energy tensor of trace matter derived in (11.6).  What I have been turning over, is whether I ought to be comfortable with this result, and my sense runs against it.

However, at the point of original derivation in sections 8-11, there is actually a choice: one can construct the variation of the Lagrangian density of matter with respect to g_{\mu \nu}  such that a symmetric tensor will result, or one can choose not to, by creating a symmetric term or not.  This is actually a form of gravitational “symmetry breaking” that occurs in the process of taking the variation of the matter Lagrangian density with respect to the metric tensor.  I think both paths need to be developed, because they lead to on the one hand to a symmetric energy tensor, and on the other to a non-symmetric energy tensor.  In either case, the key term distinguishing this energy tensor from the Maxwell tensor is J^\mu A^\nu .

If we impose symmetry on the energy tensor, then the Maxwell tensor will be the J^u=0  special case of a broader tensor which includes a J^\mu A^\nu + J^\nu A^\mu term and which applies, e.g., to energy flux densities (Poynting components) T^{0k} , k=1,2,3 for “waves” of large numbers of electrons.

Then, the experiment becomes — not a test of the torsion tensor — but a test as between an energy tensor with and without torsion.  That is, the experiment as reformulated, becomes a test of metric-style versus Cartan-style theories of gravitation.

Dealing with the currents J^\mu  is clear.  Regarding how to deal with the potential A^\mu  in doing the experiment, think about a beam of electrons. They of course will all repel, so the beam will emerge conically from the electron gun if nothing is done to force them onto a parallel path. Now, take a circular cross section of electrons from the beam striking an energy flux detector.  One can think of the cross-sectional surface where the electron stream meets the detector as a “disk,” not unlike a charged, flat, frisbee, which is also productively thought about as a dielectric.  I would submit that one can assign a “zero” potential to the center of the cross section, and a varying non-zero potential to the periphery.  That is, if one were to take a circular dielectric disk and fill it with electric charge, then float some positive charge nearby, the positive charge — I believe — would be attracted toward and seat itself at the center of the disk, and so that would be a natural place to define the zero of potential.

This would also mean that regional detections of flux toward the fringes of the detector will be different than toward the center, assuming uniformity of charge distribution, because the energy created by the potentials among the electrons are different in different regions.  So, there is a way to assign potentials even without applying an external voltage, though someone conducting this experiment may want to also apply an external voltage simply to vary the range of experiments.

Now, to the main point: one should do the experiment with random, unpolarized electrons, and then again with spins aligned with and against the direction of propagation, merely to test the symmetric versus non-symmetric energy tensors one to the other.   One will win, the other not.  Metric versus torsion.

I am planning a restructuring of the paper at the above link.  In the near future, I will outline the proposed restruturing — what I would plan to keep and what I plan to change.

Jay.

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