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5:04 AM
Q: Resolving an apparent contradiction between Schwarzschild and ingoing Eddington-Finkelstein coordinates

GleesonI believe this is basic differential geometry issue. This may be obvious to many, but I was quite confused about it, and it took me quite a while to find the resolution. I'm going to ask and answer this myself, since I believe this kind of thing is encouraged. I'm going to neglect the angular coo...

Q: Help with strange notation involving fractions of tensors

ГенивалдоI'm currently reading the paper Open strings in background gauge fields by Callan et.al. It is frequently used a notation that is not explained anywhere. If $F_{\mu\nu}$ is the electromagnetic field strength tensor, the author write two expressions: $$\tag1 \left(\frac{1 - F}{1+F} \right)_{\mu \...

5:50 AM
Q: Exponential operator approximation

XhorxhoOne cannot solve the transition amplitude $\langle{x}\vert e^{-iHt}\vert{y}\rangle{}$ with $H=H_0+V$ by just applying the operators one after another on the bra/ket, because the free hamiltonian $H_0$ doesn’t commute with $V$ in general. This gets clear when you expand the exponential operator $e...

4 hours later…
10:04 AM
Q: Why isn't the "Dark Matter" in the Bullet Cluster supermassive black holes?

The ShepardI've seen several videos that claim that the Bullet Cluster is evidence for Dark Matter. The general idea is that the gas is trapped on one side of the collision and the light-bending "Dark Matter" appears to have passed through the collision without slowing down and forming a lense. What I don't...


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