Understanding Tangent Vectors in GR Notation

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Homework Help Overview

The discussion revolves around understanding tangent vectors in the context of General Relativity (GR) notation, specifically using a curve defined in Euclidean 3-space. The original poster is attempting to calculate the components of tangent vectors at a specific point on the curve and is seeking clarification on the notation used for the basis vectors.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate tangent vector components using the derivative with respect to a parameter, but questions the meaning of the basis vectors denoted as \{\partial_x, \partial_y, \partial_z\}. Some participants provide insights into the definition of vectors as directional derivatives in differential geometry.

Discussion Status

The discussion is exploring the interpretation of the basis vectors and their application in the context of the problem. Some participants suggest that the problem may not be complex, comparing it to concepts from earlier calculus courses, but there is no explicit consensus on the level of difficulty or clarity of the problem.

Contextual Notes

The original poster expresses uncertainty about the new notation and its implications for calculating tangent vectors, indicating a potential gap in foundational understanding that may need to be addressed.

Irid
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I'm trying to learn some GR from Carrol's textbook, but I'm a little lost there. For example, this simple problem:

In Euclidean 3-space, let p be the point with coordinates (x,y,z) = (1,0,-1). Consider the curve passing through p:

[tex]x^i(\lambda) = (\lambda, (\lambda-1)^2, -\lambda)[/tex]

Calculate the components of tangent vectors to these curves at p in the coordinate basis [tex]\{\partial_x, \partial_y, \partial_z\}[/tex].

The attempt at a solution

The components of tangent vectors are given by

[tex]V^i = \frac{dx^i}{d\lambda}[/tex]

It is of course in the basis of x,y,z. But I don't understand what does the basis [tex]\{\partial_x, \partial_y, \partial_z\}[/tex] mean. The notation is new to me, but I think that

[tex]\partial_x \equiv \frac{\partial}{\partial x}[/tex]

so how can this be used as a basis? If you just take these derivatives at each component of the curve, you always get (1,1,1), right?
 
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In GR, and differential geometry in general, you often define a vector as a directional derivative. So the vector ai+bj+ck (where i,j,k are the usual unit vectors) is written as a*d/dx+b*d/dy+c*d/dz. Since the derivative along the direction i is d/dx etc.
 
Alright, so this is a trivial problem then, right?
 
Irid said:
Alright, so this is a trivial problem then, right?

Sure. Just like what you did in Calc I but written in GR type notation.
 

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