Let's say I have a uniformly charged wire with some constant linear charge density. Along a line parallel to the $z$-axis and passing through $(0,y,0)$ and asked to find an electric field at a point $(p,q,r)$. Then the vector should be $p \textbf{i} +(q-y)\textbf{j}+r\textbf{k}$. My books say the...

From Maxwell's equation, we can find out that there exists certain waves. However, it's unclear to me why 19th-century people thought that wave is what they had called light. As far as I know, 19th-century people weren't able to make visible light with electronic and magnetic devices in that era....

Assume a Euclidean space with signature $(+,+,+,+...)$ If we know $R_{ab}R^{ab} = 0 $ does this imply $R_{ab}=0$ ? And if so, will this test fail in Minkowski space with mixed signature? We know $\sum_{ab} R_{ab}R_{ab}=0$ defines ricc-flatness since it is just the sum of the squares of the compon...

In topology, there is a concept of compactification which is defined as follows. A space $Z$ is a compactification of $X$ if $Z$ is compact Hausdorff and there exists an embedding $j:X \rightarrow Z $ such that $\overline{j(X)} = Z$. I would like to know if the compactification in String theory i...

If fusing of nuclei in stars requires pressure, heat, and gravity, why not use a centrifuge to increase the gravity? We currently have the technology to make diamonds, and generate immense temperatures. Thus surely if you increase the effective gravity, that would reduce the required temperatures...

In case of static point mass we have the following stress energy tensor $T_{00}=m\delta(\vec{r})$ And other components are zero What are the components of this tensor in case of moving point mass with angular momentum?

Based on general relativity mass and energy distribution curves spacetime. Thus, if an object with 1kg rest mass moves with constant speed and has a speed very close to speed of light, then it has an enormous kinetic energy which should curve spacetime much more than a 1kg body at rest would. On ...