12:51 AM
1

When an electron approaches the speed of light, the emission pattern is sharply collimated forward, in the direction of motion. I can see how this is mathematically true from taking the relativistic limit of the angular distribution of the radiated energy (as is done on the Wikipedia page about s...

3 hours later…
3:48 AM
7

D-branes are best known as hypersurfaces in spacetime on which open strings with Dirichlet boundary conditions can end. Furthermore, they have several geometric properties associated with them, such as stacking, being able to wrap around cycles, etc. As explained in this answer however, a dual pi...

5 hours later…
8:50 AM
4

Suppose I have some colorful solid, which I cut into two halves (both are identical). Take the first and cut it into two parts, and then repeat this again and again. I know that a single atom doesn't have a color. So there will be a point at which the solid loses its property of being colorful. I...

2 hours later…
10:31 AM
3

https://en.wikipedia.org/wiki/Blast_wave#Characteristics_and_properties says: "A blast wave travels faster than the speed of sound and the passage of the shock wave usually lasts only a few milliseconds." I thought a blast wave was a sound wave, so I don't understand this.

10 hours later…
8:24 PM
5

Consider an arbitrary set of coordinates $x^\mu$ and another set of coordinates $y^{\mu}$, which is a (lorentzian) transformation from $x^\mu$ given by $y^\mu = f(x^\mu)$. So I want to know whether \$\frac{\partial}{\partial x^\alpha}\frac{\partial}{\partial y^\beta} = \frac{\partial}{\partial y^\...