Can anyone provide me with a complete mathematical proof about why an observer frame cannot surpass the vacuum speed of light? I have looked for answers in Quora and FB groups but no one is really convincing. In fact the majority assume that the constancy of vacuum speed of light in all referent...

Here's a question that has been nagging at me: Suppose I've got a sum of two stationary states from the particle in the box: $\Psi(x,t)=c_1\psi_1(x)e^{-iE_1t/\hbar}+c_2\psi_2(x)e^{-iE_2t/\hbar}$ The probability density is $\Psi^*(x,t)\Psi(x,t)$ Which works out to $\lvert{c_1}\rvert\psi_1^*(x)\psi...

I wonder if the problem in the image can be solved with the Wigner-Eckart (W-E) theorem. These elements have to vanish. I tried introducing the identity operator in between $r$ and $p$ to then use the W-E theorem for the new matrix elements. I was hoping that the selection rules for each of the C...

How could light from a TV screen refract when viewed through a helmet's transparent visor?

The low-energy effective description of a given QFT is an expansion of the form $$ \mathcal L_\mathrm{IR}\sim\sum_{n,m} \lambda_{n,m}\phi^n\partial^ m\phi $$ where we include all terms that are compatible with the symmetries of the original UV theory. The usual narrative is that $\mathcal L_\math...