- #1
ianhoolihan
- 145
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Hello all,
I have been trying to figure out a clear rule for parallel propagating vectors on spheres, such as in the wiki http://en.wikipedia.org/wiki/File:Parallel_transport.png. There seem to be lots of rules that are proposed in this forum and online, but they often don't work well to explain, for example, precession of a vector when parallel propagated around a line of constant latitude.
Now, for some contenders:
If someone could clarify which is correct, that would be great. I have a feeling all may be correct, but it'd be nice to link them all together. If one is up for a challenge, giving a geometrical explanation of Bill K's solution (in terms of projection onto rotating tangent planes) would have me most satisfied!
Cheers
I have been trying to figure out a clear rule for parallel propagating vectors on spheres, such as in the wiki http://en.wikipedia.org/wiki/File:Parallel_transport.png. There seem to be lots of rules that are proposed in this forum and online, but they often don't work well to explain, for example, precession of a vector when parallel propagated around a line of constant latitude.
Now, for some contenders:
- Bill K's solution: https://www.physicsforums.com/showpost.php?p=3402912&postcount=21 is nice, but it doesn't explain it intuitively.
- Matterwave's solution:
You can take parallel transport on the 2-sphere to be "move the vector like you would in flat 3-D Euclidean space, and then project the resulting vector onto the tangent space of the sphere". That description matches with the Levi-Civita connection. That is, in fact, what the picture shows, and you can clearly see that the resulting vector is different than the initial vector. - Wikipedia solution:
A more appropriate parallel transportation system exploits the symmetry of the sphere under rotation. Given a vector at the north pole, one can transport this vector along a curve by rotating the sphere in such a way that the north pole moves along the curve without axial rolling. This latter means of parallel transport is the Levi-Civita connection on the sphere. - My professor's solution:
Something along the lines of projecting the vector onto the xy, xz, yz, planes, and transporting them along the projection of the curve there, and then projecting them back onto the tangent plane of the sphere. I suspect this is similar to Matterwaves (and it also has to be infinitesimal), in that the cause of the precession is the rotation of the tangent plane.
If someone could clarify which is correct, that would be great. I have a feeling all may be correct, but it'd be nice to link them all together. If one is up for a challenge, giving a geometrical explanation of Bill K's solution (in terms of projection onto rotating tangent planes) would have me most satisfied!
Cheers