What are tensors and why use tensors in Quantum Physics and Relativity ?

This video is the 15th one in the series, and introduces the concepts of tensors (which are not always clearly defined/explained in the litterature or internet), and explains why they are so useful to "simplify" the equations describing our Physical World, in particular in General Relativity theory.

In this series of videos we will "resolve" some of the supposed "mysteries" in Quantum Physics and Relativity (Wave/particle duality, Schrödinger's cat, Constant Speed of Light, Paradoxes in Relativity, etc.).

The first 7 videos are with (almost) no maths. The rest are videos which get into the details by explaining why certain math tools are used for these topics, and explain more thoroughly why they can help solve some of the "mysteries" in Q.P. and R.
I recommend that you view all the videos in the right order, as we will introduce some concepts that we will use later in the series.
Finally I apologize if you find the videos too provocative, in particular to physicists... Please take my comments with a grain of salt...

Here is the full playlist link:
   • Resolving (some of) the "mysteries" i...  

With (almost) no maths:

1.abc: Preliminaries (a good model to explain physics, and in particular Q.P. and Relativity "mysteries"; the Thrifty Universe Principle; States and Simultaneity)
2. (Re-)defining Space
3. (Re-)defining Time)
4. Explaining (some of) the Q.P. mysteries)
5. Explaining (some of) the Relativity mysteries)

Understanding Math Tools in Q.P. and Relativity:

6. Why use complex numbers (complex numbers-part1)?
7. Why use Hilbert Spaces vectors in Q.P.?
8. Why Hermitian Operators in Q.P.?
9. Examples of complex numbers usage in Q.P and Relativity theories (complex numbers-part2)
10. TUP (definition and applications)
11. Explaining particle/wave duality and using TUP to explain stochastic character of Q.P. (complex numbers-part3)
12. Covariance and contravariance
13. Why use tensors ?
14. Why use metric tensors ?
15. TUP: how to derive Einstein Fields Equations from TUP ?
16. Why a constant speed of light (postulate vs derivation) ?