I've been following the derivation from Ch. II-31 of Feynman's Lectures, and there is a bit that I don't understand. We start from the relation between the strain $T_{ij}$ and the stress $S_{ij}$, $$T_{ij}=\sum_{k,l}\gamma_{ijkl}S_{kl}.$$ Feynman's argument is as follows: How can the components ...

Covariant derivatives take into account for both component and basis changes, thereby applicable for curved spaces - where partial derivatives only take component changes into account - is this statement correct? In a polar coordinate system basis changes, even though the space is flat. Will that...

Imagine spreading double-sticky tape all over the surface of a car or a plane. Would there more significantly more aerodynamic drag as a result of the adhesive 'sticking' to air molecules and slowing down? This would certainly cause more resistance in solid mediums but would this cause more resis...

In the case of a pure inductor ac circuit the source emf is equal to the induced emf hence the current is blocked. In a pure inductance circuit V = V°sin(wt) In the very next step we assume that, -L(di/dt) = V°sin(wt) Here is where the induced emf equals the source emf. By integrating and re arra...

I’m studying QFT and I learnt that we didn’t change the Schrödinger equation into relativistic one but Klein-Gordon and Dirac equation are now the equation of motion of our fields operator. But our states (or wave function) are evolving with Schrödinger equation yet, I cannot understand how can ...

Consider a free massive relativistic scalar field in $d+1$ dimensions. Its Hilbert space can be taken to be the bosonic Fock space on $\mathfrak h = L^2(\mathbb R^d)$: $$\mathcal F = \bigoplus_{n=0}^{+\infty} S^n\mathfrak h.$$ On this space we have creation-anihilation operators corresponding to ...