I have a question about the really meaning of the fine structure constant. Actually, my doubt is why the physicist look to a meaning for this constant. I understand the difference between this constant and the ordinary constant, that is, it carry no units with it. But is not this just like pi or ...

Griffiths says The energy of a point charge is infinite$W=\frac{\epsilon_{0}}{2\left(4 \pi \epsilon_{0}\right)^{2}} \int\left(\frac{q^{2}}{r^{4}}\right)\left(r^{2} \sin \theta d r d \theta d \phi\right)=\frac{q^{2}}{8 \pi \epsilon_{0}} \int_{0}^{\infty} \frac{1}{r^{2}} d r=\infty$ And then he s...

It is my understanding that Hawking radiation is observed by esternal observers and at the same time a necessary condition for having Hawking radiation is the formation of an event horizon during a gravitational collapse. Since the emergence of an event horizion takes infinite time for an observe...

I learned that a tensor is a linear map from some number of vectors to the real numbers. For example, $t(\vec{u},\vec{v})=\vec{u}\cdot\vec{v}$ is a rank-2 tensor as it takes 2 vectors as arguments and combines them into a real number. I then read that a rank-1 tensor is a vector. How is that poss...

It is often said that special relativity doesn't handle acceleration since you general relativity for that. If I understand correctly this is incorrect just with some caveats. Rindler coordinates are coordinates as experienced by a constantly accelerating observer such that the observer is at res...