MathNugget
Junior Member
- Joined
- Feb 1, 2024
- Messages
- 195
If g and g' are 2 metrics on the smooth manifold M, [imath]\nabla[/imath] is the Levi-Civita connection of g, [imath]\nabla'[/imath] is the Levi-Civita connection of g'.
Is [imath]\nabla+\nabla'[/imath] the Levi Civita connection of g+g'?
If it was so, then the following 2 properties should work:
a) [imath](\nabla+\nabla')(g+g')=0[/imath]
b) [imath](\nabla+\nabla')_XY-(\nabla+\nabla')_YX=[X, Y][/imath]
I suspect this isn't true, but then I'd have to find a counterexample. I can't find how these things work, besides some really abstract articles, like the wikipedia one. I'll go out on a limb:
[imath](\nabla+\nabla')(g+g')=\nabla g + \nabla g' +\nabla' g +\nabla' g' = \nabla' g + \nabla g'[/imath].
Side question: what even is [imath]\nabla g[/imath]? I read that the connection applies to vector fields, and the metric applied to vector fields gives a scalar. What is the connection doing to the metric? All I can find is intuitive concepts, like "the Levi Civita connection preserves the metric", and "an affine connection connects tangent spaces". In other words...what would [imath]\nabla g[/imath] even be, if it were not 0? Would it be a number, some constant expression, a vector, a tensor...
Is [imath]\nabla+\nabla'[/imath] the Levi Civita connection of g+g'?
If it was so, then the following 2 properties should work:
a) [imath](\nabla+\nabla')(g+g')=0[/imath]
b) [imath](\nabla+\nabla')_XY-(\nabla+\nabla')_YX=[X, Y][/imath]
I suspect this isn't true, but then I'd have to find a counterexample. I can't find how these things work, besides some really abstract articles, like the wikipedia one. I'll go out on a limb:
[imath](\nabla+\nabla')(g+g')=\nabla g + \nabla g' +\nabla' g +\nabla' g' = \nabla' g + \nabla g'[/imath].
Side question: what even is [imath]\nabla g[/imath]? I read that the connection applies to vector fields, and the metric applied to vector fields gives a scalar. What is the connection doing to the metric? All I can find is intuitive concepts, like "the Levi Civita connection preserves the metric", and "an affine connection connects tangent spaces". In other words...what would [imath]\nabla g[/imath] even be, if it were not 0? Would it be a number, some constant expression, a vector, a tensor...