Does it make sense to translate a submanifold in a manifold?

95 Views Asked by At

Given some manifold $M$ which is also equipped with some metric, for example Riemannian metric, let $$S^r(x_0)=\{x\in M| d(x_0,x)=r\},$$ where $x_0\in M$ and $d$ is the distance. Now given another point $p\in M$,

Does it make sense to talk about the submanifold $S=S^r(x_0)+p$?

Can I say that $S$ is a translation of $S^r(x_0)$ by $p$?

1

There are 1 best solutions below

0
On BEST ANSWER

In general, no. For instance, consider what happens if you take the unit sphere (call it the earth), and translate the equator "by the north pole"? If you add a point on the equator to the north pole (in 3-space, where addition makes sense) you get a circle...floating in the tangent plane to the north pole, i.e., not even a subset of $S^2$.

There are some notions of translation in some manifolds, particularly ones with an ample supply of self-isometries (e.g., the torus), but ... they're not based strictly on "addition," which may not even be well-defined.