To my knowledge, 3 or more indices may not appear in a given term, as I've found in a video produced by "Faculty of Khan": However, on page 30, Sean Carroll writes: As obvious, the indices 0 and 1 are repeated 3 times in the RHS of the underlined equation. I am aware that Carroll keeps an e...

I understand tension force, but my question is, why do we define it only in strings and ropes and rods and such? Shouldn't every object experience tension force? Like when you pull a paper from opposite sides, it gets taut, and experiences what seems like a state of tension.. If every object does...

Consider the equality \begin{equation}\exp(-\frac{i}{\hbar}\boldsymbol{\phi J})\left|x\right>=\left|R(\phi)x\right>\end{equation} Where $\left|x\right>$ denotes a position eigenstate, $J$ the total angular momentum operator on the ket space and $R(\boldsymbol{\phi})$ the $\mathbb{R}^3$ rotation m...

A friend of mine told me that if you were to stand beside plate of metal that is millions of degrees hot, inside a 100% vacuum, you would not feel its heat. Is this true? I understand the reasoning that there is no air, thus no convection, and unless you're touching it, there's no conduction eith...