# Weak equivalence principle tests

on the wikipedia article about the equivalence principle there is a mention about testing the EP against parity-violating masses;

"The equivalence principle is untested against opposite geometric parity (chirality in all directions) mass distributions. A parity Eötvös experiment contrasting solid single crystal spheres of identical composition α-quartz in enantiomorphic space groups P3121 (right-handed screw axis) versus P3221 (left-handed screw axis) is appropriate. Equivalence principle parity violation validates a chiral vacuum background forbidden within general relativity but allowed within Einstein-Cartan theory; affine, teleparallel, and noncommutative gravitation theories."

I don't understand any of this, is this correct? why the crystal layout has anything to do with a parity-violating fields? (AFAIK electro-weak force is the only known force to be parity-violating, but this force is short range) so why the alignment of the by-comparison-macroscopic crystal atomic layout does matter? is this crackpot physics or i just don't understand it?

Dear lurscher, the quote is the kind of C-physics described by the C-word which is a favorite word of mine but is discouraged on this server, so I won't use it - but you have used it. You don't misunderstand anything - quite on the contrary, you're right on the money.

These comments about a non-existent test of parity in the equivalence principle are due to "Uncle Al" Schwartz, see e.g. the first comment under

http://www.iac.es/galeria/masc/Outreach_files/Dark-energy_particle_spotted_NatureNews290609.pdf

to see that even extremely microscopic details about the "idea" coincide with the paragraph you quoted. "Uncle Al" is known to most physics bloggers - as well as many other physics forums.

From a physics viewpoint, the claims are completely preposterous. First of all, one needs pretty special objects to get a parity-violating physics in 4 spacetime dimensions: either chiral (Weyl) spinors or self-dual 2-forms (and their interactions). None of those things is included in GR; Einstein-Cartan theory; conventional affine, teleparallel, and noncommutative gravitational theories - which is why all these gravitational theories automatically preserve parity. Moreover, self-dual 2-forms don't exist in 3+1 dimensions (although they do exist in 4+0 dimensions) because $*^2=-1$ in 3+1 dimensions.

As you correctly say, only the weak interactions as expressed by the electroweak theory violate parity which is because the gauge field interacts with chiral (Weyl) spinors. The gauge fields $A_\mu$, when coupled to spinors, get naturally multiplied by $\gamma^\mu$ which switches the chirality (because it anticommutes with $\gamma_5$); on the other hand, $g_{\mu\nu}$ with an even number of indices preserves the chirality, so the spinors interactions with the metric have to be parity-preserving.

Moreover, the existing tests of the equivalence principle de facto eliminate the possibility of substantially different interactions of left-handed and right-handed helixes, too. For example, Newton's apple contains vitamin C (L-ascorbic acid) which is parity-asymmetric, and it would accelerate differently if the laws of gravity cared about the mirror images. There's really no way compatible with an effective field theory how to make the two mirror objects accelerate differently.

For some semi-serious paper by authors from well-known places who talk about gravitational parity violation, see e.g.

http://arxiv.org/abs/arXiv:1005.3310

and the papers mentioned by it (by Stephon Alexander and others). It would still be impossible for me to say that any scenario in those papers is defensible but at least those papers don't sound as a self-evident nonsense of the kind that "Uncle Al" Schwartz has managed to incorporate into the Wikipedia page.

• thanks, it did sounded preposterous, but it being in wikipedia covered it with some resemblance of credibility - my bad – lurscher Mar 29 '11 at 20:43
• He did an extremely good job in squeezing it in - otherwise it wouldn't survive, indeed... It was very reasonable for you to consider the possibility that it's some serious stuff - but the fingerprints are way too obvious for those who have been pleased to receive similar creative comments by Uncle Al on their physics blogs. ;-) – Luboš Motl Mar 29 '11 at 20:47
• Good observations regarding "Uncle Al" and also +1 for mentioning work by Stephon ;) – user346 Mar 29 '11 at 20:57
• Deepak, Stephon is a fun guy. It's always been great to listen to him, and it's good for the physics establishment to have guys like that - I just think that it's bad if the bulk of the community is made out of people thinking as freely as Stephon which may be where the matters are converging. – Luboš Motl Mar 29 '11 at 22:27
• I now feel that I've been intellectually violated by Uncle Al. And here was me thinking all these years that Uncle Al was too intelligent to be a deluded crackpot and therefore a misunderstood genius. – Physiks lover Apr 22 '12 at 19:49