# Parallel transport and the covariant derivative

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1. Feb 20, 2015

### "Don't panic!"

I have been reading section 3.1 of Wald's GR book in which he introduces the notion of a covariant derivative. As I understand, this is introduced as the (partial) derivative operators $\partial_{a}$ are dependent on the coordinate system one chooses and thus not naturally associated with the structure of the manifold, therefore we introduce a new derivative operator $\nabla_{a}$ which fulfils this criteria. Intuitively, the covariant derivative is constructed in such a way as to remove any artefacts arising from any particular coordinate system, such that the rate of change of a tensor field in a direction along the manifold is itself a tensor field. Is this correct?

He then goes on to say that a vector $\mathbf{v}^{a}$ given at each point along a curve $C$ (with tangent vector $\mathbf{t}^{a}$) is said to be parallely transported as one moves along the curve if the equation $$\mathbf{t}^{a}\nabla_{a}\mathbf{v}^{b}=0$$ is satisfied along the curve.
Intuitively, is this a statement that a vector $\mathbf{v}^{a}$ is parallely transported along the curve if it remains constant as it moves along the curve, this can be translated into the mathematical statement that its directional derivative along the curve vanishes, i.e. $\mathbf{t}^{a}\nabla_{a}\mathbf{v}^{b}=0$. Is this correct?

2. Feb 20, 2015

### PAllen

Both of these seem like reasonable verbalizations to me.