Covariant Derivative Equivalence: Exploring an Intriguing Result

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Discussion Overview

The discussion revolves around the mathematical interpretation of covariant derivatives and the implications of using perturbed basis vectors represented by partial derivatives. Participants explore the relationships between different expressions involving derivatives and the role of the Christoffel symbols in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes that the expression ##\frac{\partial}{\partial x^\nu + \Delta x^\nu} = \frac{\partial}{\partial x^\nu} + \Gamma^\sigma{}_{\mu \nu} \Delta x^\mu \frac{\partial}{\partial x^\sigma}## holds to first order in ##\Delta x##.
  • This same participant suggests an alternative representation involving ##\frac{\partial x^\kappa}{\partial x^\nu + \Delta x^\nu}##, questioning the validity of the equality and noting that if ##\Delta x## are not functions of ##x##, the ##\Gamma## terms vanish.
  • Another participant expresses confusion regarding the mathematical meaning of the derivative with ##\Delta##, indicating a lack of understanding.
  • Some participants attempt to clarify the notation by comparing it to other derivative expressions, but express that they have not encountered such notation before.
  • Concerns are raised about the non-standard nature of the notation used, leading to further questions about its clarity and validity.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the validity or meaning of the expressions involving the covariant derivative and the notation used. Multiple viewpoints and uncertainties remain regarding the interpretation of the mathematical relationships presented.

Contextual Notes

There are unresolved questions about the assumptions underlying the expressions and the definitions of the symbols used, particularly the notation involving ##\Delta x## and its implications for the covariant derivative.

kent davidge
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If we are representing the basis vectors as partial derivatives, then ##\frac{\partial}{\partial x^\nu + \Delta x^\nu} = \frac{\partial}{\partial x^\nu} + \Gamma^\sigma{}_{\mu \nu} \Delta x^\mu \frac{\partial}{\partial x^\sigma}## to first order in ##\Delta x##, correct? But in the same manner we could write ##\frac{\partial}{\partial x^\nu + \Delta x^\nu} = \frac{\partial x^\kappa}{\partial x^\nu + \Delta x^\nu} \frac{\partial}{\partial x^\kappa} \approx \frac{\partial}{\partial x^\nu}(x^\kappa - \Delta x^\kappa) \frac{\partial}{\partial x^\kappa}##.

But these two equalities seem to lead to a weird result, namely that if ##\Delta x## are not function of ##x## then the ##\Gamma## vanish. But I'm even not sure about the validity of the equality. Could someone shed some light on this?

(If someone is curious about why I'm asking this, it's just something that I was thinking about, out of curiosity.)
 
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What does that derivative with that Delta mean mathematically? Personally, I have no idea to be honest, so I can't help you.
 
haushofer said:
What does that derivative with that Delta mean mathematically? Personally, I have no idea to be honest, so I can't help you.
Well in the same way that ##\frac{d}{d g(x) + f(x)}##. Think of the ##\Delta x## just as a different symbol.
 
Where are you getting this notation from? It seems non-standard and it is unclear what you mean.
 
kent davidge said:
Well in the same way that ##\frac{d}{d g(x) + f(x)}##. Think of the ##\Delta x## just as a different symbol.
I've never seen such a notation.
 

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