Lab Notes for a Scientific Revolution (Physics)

March 29, 2008

Stepping Back from Kaluza-Klein: Planned Revisions

Those who have followed my Weblog are aware that I have been putting in a lot of work on Kaluza-Klein theory.  This post is to step back from the canvas, lay out the overall picture of what I am pursuing, and summarize what I plan at present to change or correct in the coming days and weeks.  This is in keeping with the concept of this Weblog as “Lab Notes,” or as a public “scientific diary.”

There are really two main aspects to this Kaluza-Klein work:

First, generally, I have found that 5-D Kaluza-Klein theory is most simply approached by starting with (classical) Lorentz force motion, and requiring the Lorentz force motion to be along the geodesics of the five dimensional geometry.  I am far from the first person who recognizes that the Lorentz force can be represented as geodesic motion in a 5-D model.  But I have found, by starting with the Lorentz force, and by requiring the 5-D electromagnetic field strength tensor to be fully antisymmetric, that all of the many “special assumptions” which are often employed in Kaluza-Klein theory energy very naturally on a completely deductive basis, with no further assumptions required.  I also believe that this approach leads to what are perhaps some new results, especially insofar as the Maxwell tensor is concerned, and insofar as QED may be considered in a non-linear context.   The latest draft of this global work on Kaluza-Klein may be seen at Kaluza-Klein Theory and Lorentz Force Geodesics.

Second, specifically, within this broader context, is the hypothesis that the fifth-dimensional “curled” motion is the direct mainspring of intrinsic spin.  More than anything else, the resistance by many physicists to Kaluza-Klein and higher-dimensional theories, rests on the simple fact that this fifth dimension — and any other higher dimensions — are thought to not be directly observable.  In simplest form, “too small” is the usual reason given for this.  Thus, if it should become possible to sustain the hypothesis that intrinsic spin is a directly-observable and universally-pervasive outgrowth of the fifth dimension, this would revitalize Kaluza-Klein as a legitimate and not accidental union of gravitation and electrodynamics, and at the same time lend credence to the higher-dimensional efforts also being undertaken by many researchers.  The latest draft paper developing with this specific line of inquiry is at Intrinsic Spin and the Kaluza-Klein Fifth Dimension.

Now, the general paper at Kaluza-Klein Theory and Lorentz Force Geodesics is very much a work in progress and there are things in this that I know need to be fixed or changed.  If you should review this, please keep in mind the following caveats:  

First, sections 1-4 are superseded by the work at Intrinsic Spin and the Kaluza-Klein Fifth Dimension and have not been updated recently.   

Second, sections 5-7 are still largely OK, with some minor changes envisioned.  Especially, I intend to derive the “restriction” \Gamma^u_{55}=0 from F^{{\rm M} {\rm N} } =-F^{{\rm N} {\rm M} } rather than impose it as an ad hoc condition.   

Third, sections 8-11 needs some reworking, and specifically: a) I want to start with an integration over the five-dimensional volume with a gravitational constant G_{(5)}  suited thereto, and relate this to the four dimensional integrals that are there at present; and b) I have serious misgivings about using a non-symmetric (torsion) energy tensor and am inclined to redevelop this to impose symmetry on the energy tensor — or at least to explore torsion versus no torsion in a way that might lead to an experimental test.  If we impose symmetry on the energy tensor, then the Maxwell tensor will be the J^{\mu } =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.  

Fourth, I am content with section 12, and expect it will survive the next draft largely intact.  Especially important is the covariant derivatives of the electrodynamic potentials being related to the ordinary derivatives of the gravitational potentials, which means that the way in which people often relate electrodynamic potentials to gravitational potentials in Kaluza-Klein theory is valid only in the linear approximation.  Importantly, this gives us a lever in the opposite direction, into non-linear electrodynamics.  

Fifth, I expect the development of non-linear QED in section 13 to survive the next draft, but for the fact that the R=0 starting point will be removed as a consequence of my enforcing a symmetric energy tensor in sections 8-11.  Just take out all the “R=0” terms and leave the rest of the equation alone, and everything else is more or less intact.

Finally, the experiment in Section 15, if it stays, would be an experiment to test a symmetric, torsionless energy tensor against a non-symmetric energy tensor with torsion.  (Basically, metric theory versus Cartan theory.)  This is more of a “back of the envelope” section at present, but I do want to pursue specifying an experiment that will test the possible energy tensors which are available from variational principles via this Kaluza-Klein theory. 

The paper at Intrinsic Spin and the Kaluza-Klein Fifth Dimension dealing specifically with the intrinsic spin hypothesis is also a work in progress, and at this time, I envision the following:

First, I will in a forthcoming draft explore positrons as well as electrons.  In compactified Kaluza-Klein, these exhibit opposite motions through x^5 , and by developing the positron further, we can move from the Pauli spin matrices toward the Dirac \gamma^\mu and Dirac’s equation.

Second, I have been engaged in some good discussion with my friend Daryl M. on a thread at sci.physics.relativity.  Though he believes I am “barking up the wrong tree,” he has provided a number of helpful comments, and especially at the bottom of post #2 where he discusses quantization in the fifth dimension using a wavelength n \lambda = 2 \pi R .  (I actually think that for fermions, one has to consider orientation / entanglement issues, and so to secure the correct “version,” one should use n \lambda = 4 \pi R  which introduces a factor of 2 which then can be turned into a half-integer spin.)  I am presently playing with some calculations based on this approach, which you will recognize as a throwback to the old Bohr models of the atom.

Third, this work of course uses x^5 = R\phi to define the compact fifth dimension.  However, in obtaining dx^5, I have taken R to be a fixed, constant radius.  In light of considering a wavelength n \lambda = 4 \pi R per above, I believe it important to consider variations in R rather than fixed R , and so, to employ dx^5 = Rd\phi + \phi dR .

There will likely be other changes along the way, but these are the ones which are most apparent to me at present.  I hope this gives you some perspective on where this “work in flux” is at, and where it may be headed.

Thanks for tuning in!

Jay. 

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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