TITLE: Extension of Vector field along a curve always exists?
QUESTION [8 upvotes]: Let $c:I\to M$ be a $C^{\infty}$ curve on smooth manifold $M$ of dimension $n$ and $X:I\to TM$ be a vector field along $c$, 
$$\forall t\in I\qquad X(t)\in T_{c(t)}M.$$
does there exist a vector field $\bar{X}:M \to TM$ such that $X=\bar{X}\circ c$?

REPLY [9 votes]: As @Bebop showed, globally it is not always possible to find the extension of a vector field along $c$, but (as you might guess) $\textit{locally}$ we can. We can do this by the help of Constant Rank Theorem provided that the curve is regular ($c'(t) \neq 0$ so that the curve $c$ is an immersion). By this theorem, we can find an adapted coordinates for the curve. And using this coordinate chart we can build the local extension for $X$.
Construction :
By constant rank theorem,  $\forall t_0 \in I$ we can always find a small interval $J$ contain $t_0$ and a chart $(U,\varphi)$ contain $c(t_0)$ s.t the curve $c : I \rightarrow M$ has the following representation
$$ c(t) = (t,0,\dots,0) \qquad \forall t \in J$$
The vector field along $c$, $X : I \rightarrow TM$ has representation on $J\subset I$
$$ X(t) = X^j(t) \frac{\partial}{\partial x^j} \Bigg|_{(t,0,\dots,0)}$$
where $c(J)\subset U$. Because $c(J)$ is a closed subset contained in $U$ then by
Extension Lemma for Smooth Function (also in Lee's Smooth Manifold) we can define the component functions $\tilde{X}^j : U \rightarrow \mathbb{R}$ of a local vector field $\tilde{X} : U \rightarrow TM$
$$ \tilde{X} (x^1,\dots,x^m) = \tilde{X}^j (x^1,\dots,x^m) \frac{\partial}{\partial x^j} \Bigg|_{(x^1,\dots,x^m)} $$
such that the restriction to $c(J)$ in the chart $(U,\varphi)$ is
$$ \tilde{X}^j |_{c(J)} (x^1,\dots,x^m) = \tilde{X}^j (t,0,\dots,0) := X^j(t)$$
equal to the component functions of the vector field along curve $X^j(t)$.
Therefore by construction $\tilde{X} \circ c = X$ on $J\subset I$.