[Math] On Learning Tensor Calculus

calculusgeneral-relativitylinear algebratensors

I am highly intrigued in knowing what tensors are, but I don't really know where to start with respect to initiative and looking for an appropriate textbook.

I have taken differential equations, multivariable calculus, linear algebra, and plan to take topology next semester. Since Summer break is right at the corner, I was wondering if anyone would tell me if my mathematical background is able to handle tensor calculus, or if I need to know other subjects in order to be ready to learn about tensor. Any and all help would be appreciated.

Best Answer

What is a tensor? In short, a tensor is a generalization of a vector which is needed to express physical quantities which have more data than we can fit into a single vector field. However, it's more than that. We also need tensors of different transformation type. Ultimately, in physics, we wish to write equations which are independent of the choice of coordinates. Yet, we use coordinates. So, this brings you to the focus on components which transform inversely. With objects whose transformation properties are mirrored we are able to create scalars which are invariant. In math, a tensor product of vector spaces is a way of multiplying spaces. Or, for specific matrices, the tensor product is the Kronecker product which is pretty easy to understand calculationally; for $A \otimes B$ we just make a new matrix with blocks formed by $AB_{ij}$. A tensor is simply a multilinear mapping on a vector space and its dual. The tensor products of the basis and dual basis of the vector space are used to build a natural basis for the tensors over the given vector space. Of course, then from a manifold perspective, this is all just "at a point", we then wish to consider tensor fields... of course there is much to learn. I think Lawden is a good book, I used it in a General Relativity course, it was readable and I got a good amount out of it. As a beginning physics student, I used the big black book Gravitation by Misner Thorne and Wheeler. There's about 100-200 pages of plain old tensors and forms which are helpful, lots of exercises. From a physics perspective it was good. From a math perspective, it's not optimal. I thought the math in Sean Carrol's General Relativity text was also quite good, and a bit more modern than MTW.

All of this said, I suspect the book that you would enjoy is: Manifolds, Tensors, and Forms: An Introduction for Mathematicians and Physicists by Paul Rentein.

It's not just about tensors, and, I think that's a good thing. Tensors are part of a larger story and this book is written for someone with your general leaning.

Related Question