Unanswered Questions
1,969 questions with no upvoted or accepted answers
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Angle sum of triangle in Schwarzschild solution
Curvature of space is often intuitively explained as angles of a triangle not adding up to 180 degrees. My questions concerns that.
Suppose you have a perfectly spherical star of uniform density - so ...
CommunityBot
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Situation after Saini & Stojkovic's paper on unitarity in gravitational collapse and non-formation of black holes?
In their paper, Anshul Saini and Dejan Stojkovic [1] claimed that by calculations it is possible to demonstrate that in a gravitational collapse of a disk, an event horizon is never made for a far ...
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Can some components of metric be Finslerian while the others be Riemannian?
A Finsler metric reduces to a Riemann metric in case it loses its dependence on velocities. Now, my question is this: Can we have a Finsler metric in which some components of the metric have velocity ...
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Level quantization of 7d $SO(N)$ Chern-Simons action
In 3d, one can write down the $SO(N)$ Chern-Simons action to be $$S(A)=\frac{k}{192\pi}\int_{M}\text{Tr}(A d A +\frac{2}{3}A^3),$$ where $A$ is an $SO(N)$ connection. The level quantization can be ...
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Hayden-Preskill informational mirrors and decryption
I do have a question about an assumption made in the very interesting Hayden-Preskill paper of black holes as informational mirrors. Alice throws her top secret quantum diary which is $k$ qubits long ...
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Pseudo-Riemannian 2D manifold (visualize time curvature)
My goal is to visualize somehow the curvature of time, as opposed to the curvature of space. I know that we generally talk about spacetime curvature altogether; however, the fact that spacetime has ...
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Could harm due to spaghettification be mitigated by entering a black hole at almost the speed of light?
Say that we wanted to send a probe into a black hole, perhaps hoping to see if it's actually a wormhole that might transport the probe elsewhere.
Upon approaching a black hole, the probe would undergo ...
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Black Holes and QED
So, in quantum electrodynamics (at least to my rudimentary knowledge), the electromagnetic force is mediated by photons.
On the other hand, in classical general relativity, the Kerr Black Hole ...
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Is the Schwarzschild singularity a limit of the Kerr singularity?
In a Schwarzschild black hole, the singularity is spacelike. In a Kerr black hole, it is timelike.
Is there any continuous transformation between those solutions? Can the Schwarzschild solution be ...
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Entanglement island distance = quantum width of BH horizon?
In this recent paper, Bousso and Penington (B&P) finds that the protrusion distance outside the horizon of an entanglement island from a 4D Schwarzschild black hole is $\sqrt {l_P r_{hor}}$, where ...
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Is it possible to create a Nil geometry in real spacetime according to general relativity? (What metrics are possible in the real world?)
Background
I've heard that it is possible to construct a Penrose triangle in the 3D geometry Nil. And I wondered: Can we build a Penrose triangle in the real world if spacetime is appropriately ...
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Sum of geodesic deviation around a triangle in curved spacetime?
So I was pondering about geodesic deviations and I'm confused about the following. Let's say I have $3$ geodesics $\gamma_1(t)$ , $\gamma_2(t)$ and $\gamma_3(t)$. I introduce a parameter $s$ such that ...
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Can two points always be joined by timelike curve?
I have asked this question on MSE but now I think it is better suited for the Physics Stack Exchange. Suppose $p$ and $q$ are connected by a causal (i.e. its tangent vectors have non-positive norm) ...
- 207k
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What is the physical motivation behind the mathematical definition of an inertial system?
In this German Classical Mechanics lecture by Frederic Schuller, it is given that a Newtonian spacetime with an absolute inertial frame is one in which
$$ \nabla_{v} G=0$$
Where $\nabla_v$ is the ...
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Complex, Holomorphic connection, and Symplectic — a not-so-Kähler manifold?
While studying mathematical physics, I wondered whether if there is a mathematical theory for a manifold that
has a complex structure [almost complex structure $J^\mu{}_\nu$ with vanishing Nijenhuis ...
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