The Commutator of Vector Fields: Explained & Examples

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SUMMARY

The discussion focuses on the commutator of vector fields, specifically addressing its geometric interpretation and computational utility. An example provided illustrates two non-commutative vector fields, denoted as ##X## and ##Y##, where the difference in outcomes from following the flows of these fields in different orders is quantified by the expression ##[X,Y]=X \circ Y - Y \circ X##. The discussion references section 6.2 of a resource linked for further clarity on this concept.

PREREQUISITES
  • Understanding of vector fields in differential geometry
  • Familiarity with the concept of commutation in mathematical operations
  • Basic knowledge of flow dynamics in vector fields
  • Exposure to the text "General Relativity" by Robert M. Wald
NEXT STEPS
  • Study the geometric interpretation of the commutator in vector fields
  • Explore examples of non-commutative vector fields in differential geometry
  • Learn about the implications of commutation in physical systems
  • Read section 6.2 of Wald's "General Relativity" for deeper insights
USEFUL FOR

Students and researchers in mathematics and physics, particularly those studying differential geometry and general relativity, will benefit from this discussion on the commutator of vector fields.

Zhang Bei
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Hi,

I'm just starting to read Wald and I find the notion of the commutator hard to grasp. Is it a computation device or does it have an intuitive geometric meaning? Can anyone give me an example of two non-commutative vector fields?

Thanks!
 
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Zhang Bei said:
Hi,

I'm just starting to read Wald and I find the notion of the commutator hard to grasp. Is it a computation device or does it have an intuitive geometric meaning? Can anyone give me an example of two non-commutative vector fields?

Thanks!
Here is an easy example in section 6.2: https://www.physicsforums.com/insights/journey-manifold-su2-part-ii/

As a geometric intuition, you can imagine to start at a certain point ##p## and follow a flow along vector field ##X## for a small distance, from there along vector field ##Y## for a while and reach point ##s##. If you now start again at ##p## but follow first along ##Y## and then ##X##, you will usually end up at a different point ##t \neq s##. That difference is measured by ##[X,Y]=X \circ Y - Y \circ X##. If ##[X,Y]=0## then ##t=s##.
 
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