# Meaning of the torsion tensor

1. Mar 16, 2007

### tetraedro

Hi, I've been studying extensions of general relativity with the torsion tensor and I have been wondering about the following fact: what is the physical meaning of the three indices of this tensor? That is, do these three indices represent some directions in space? (For example, the translation axis and the plane of rotation). Can you please help me?
Thank you

2. Mar 17, 2007

### tetraedro

Thank you for the answer. I've read on the paper "General Relativity with torsion: Extending Wald's Chapter on Curvature", the following sentence:
"...If $T^{z} _{xy}>0$ (where $T^{z} _{xy}$ is the torsion tensor), parallel transport along the x direction will cause v (parallely transported vector) to rotate about the x-axis in a left-handed manner".
Is it correct? This is the reason why I thought that the indices meant spatial directions.

Last edited: Mar 17, 2007
3. Mar 17, 2007

### MeJennifer

This is a forum right?

Last edited: Mar 17, 2007
4. Mar 17, 2007

### fireball3004

some one must have removed the "answer" because I saw it here not to long ago.

5. Mar 18, 2007

### tetraedro

What's the matter with the "answer"? Anyway, does someone know anything more about the issue I have exposed?

6. Mar 18, 2007

### pervect

Staff Emeritus
If anybody does know more, they don't seem to be talking. I can add that I know very little about torsion (Wald's textbook is probably the most advanced I own, and as you've noticed it talks very little about the subject - MTW doesn't have much either IIRC) and I can also say in general that CH is very knowledgeable about GR.

7. Mar 18, 2007

### MeJennifer

This is very confusing folks, may I ask what is going on?
I seem to not be able to read certain postings that others apparently can see.

8. Mar 18, 2007

### robphy

Yes, there was a reply (that was #2) that was apparently deleted or withdrawn from the thread.

In any case,

here is the article mentioned above:
http://theory.uchicago.edu/~sjensen/teaching/tutorials/GRtorsion.pdf
.. on my list of things to read carefully.

FYI: Here are some recent discussions in PhysicsToday:

This may be useful (hopefully this obscure link to Nakahara's text works):

notes by Visser
http://www.mcs.vuw.ac.nz/courses/MATH464/2006T1/Lecture-Notes/notes.pdf

9. Mar 20, 2007

### tetraedro

torsion again

I have another question about torsion, maybe someone can help me.
I have been studying the Einstein-Cartan extension of general relativity and I have seen that apparently (as far as I know) no one reports the mathetical procedure one has to follow in order to derive the field equation satisfied by torsion. Since I know how this is done for the standard Einstein field equation, I wonder if some of you knows the corresponding procedure for the Einstein-Cartan field equation or can suggest me a book or a paper where I can find it. Thanks

10. Apr 28, 2007

### affinefield

Please read Richard Hammond's article "Torsion Gravity",Reports on Progress in Physics,from,I think,2002.It is an excelent article dealing with the evolution of what possible meaning the quantity "torsion" could have in physical theory,from Einstein-Cartan to the String Theory rumpus.Ideas of what torsion "means",geometrically,usually fall victim or prey to the person doing the imagining not distinguishing between a FINITE picture of torsion,e.g.,parallelograms failing to close,and the INFINITESIMAL DEFINITION of the torsion tensor itself,in terms of locally defined quantities in the tangent-plane to a point on a geodesic or curve.The fact that the mathematical form of the torsion tensor is similar to the form of the Maxwell field strength tensor tantalized Einstein for a good three years,1928-1931,in one of his schemes to connect gravitation and electricity geometrically.For that theory,visit Living Reviews In Relativity,Hubert Goenner's "On The History of Unified Fied Theories".Ciao.