Questions tagged [singularities]
Use this tag for questions about singularities in physical quantities, i.e. cases where a quantity becomes or appears to become infinite or ill-defined. Consider the more specific tags [black-holes] and [wormholes] for certain kinds of singularities occurring in general relativity. For the procedure of "getting rid" of singularities, consider the [regularization] tag.
992
questions
2
votes
3
answers
197
views
Necessity of Singularity in General Relativity
The Schwarzschild solution is the standard example used to describe a black hole, its important points being the event horizon and the central singularity. But this solution is derived by assuming an ...
- 9,500
-1
votes
1
answer
72
views
Can you calculate the radius of a hypothetical singular surface inside a black hole from observing changes to its linear momentum?
Say there is a ball of unknown radius surrounded by a bubble. The ball represents a hypothetical singular surface inside a black hole and the bubble represents the event horizon.
If you threw marbles ...
0
votes
3
answers
187
views
Is the size of a black hole singularity smaller than a fundamental particle?
I am wondering about the size of a black hole singularity. We know that a classical black hole is infinitely dense. I am not asking about size of event horizon. I am asking about actual size of the ...
0
votes
0
answers
33
views
Hydrogen radial equation solution's boundary condition for $r \to 0$ [duplicate]
I am studying the hydrogen atom and I am analysing the radial equation: $$\left[\frac{-\hbar^2}{2m} \frac{\partial^2}{\partial r^2} + \frac{\hbar^2l(l+1)}{2m}+ V(r)\right]u=Eu$$ with $V(r)$ equal to ...
- 41
2
votes
1
answer
87
views
As per Friedmann Equations, is big-bang singularity necessary?
The Friedmann Equations do not directly require that the scale factor $a(t)$ was zero in the beginning. Since Einstein's static universe is still a valid solution, is it possible that before the Plank ...
- 1,161
2
votes
0
answers
60
views
Under what circumstances can a 4D singularity occur in General Relativity?
I've tried to find on the literature about 4D (single point) singularities, but most of the theorems about singularities pertain to either space-like or time-like singularities, which always have some ...
- 159
0
votes
0
answers
72
views
Where is the mass in a Black Hole without a "central" curvature singularity?
Not all black holes have a curvature singularity at their center (an example). But in principle, I thought that the curvature singularity was a direct result of the fact that the mass is concentrated ...
- 770
-4
votes
0
answers
46
views
Simple question about finite Universe [duplicate]
If, by Big Bang, Universe was created from initial singularity, with finite "speed" of expansion of matter, shouldnt it be finite as well?
0
votes
2
answers
105
views
Realistic black holes
If I understand the answers provided in this Link Why singularity in a black hole, and not just "very dense"?
Then the singularity at $r=0$ may just be a mathematical artifact, and may not ...
17
votes
1
answer
1k
views
Can a Kerr black hole become super-extremal?
Let's assume there is a large Kerr black hole, which is almost
extremal and would become extremal with the addition of a small
amount of mass $M$ with spin $J$ to make the final $J=M$.
What if this ...
- 751
3
votes
1
answer
52
views
Deriving OPE between vertex operator: Di Francesco Conformal Field Theory equation 6.65
How does one get Di Francesco Conformal Field Theory equation 6.65:
$$ V_\alpha(z,\bar{z})V_\beta(w,\bar{w}) \sim |z-w|^{\frac{2\alpha\beta}{4\pi g}} V_{\alpha+\beta}(w,\bar{w})+\ldots~?\tag{6.65}$$
...
- 327
0
votes
1
answer
81
views
Removing the cosmic horizon in the de Sitter metric
The metric for de Sitter spacetime in static coordinates is
$$ds^2 = \left(1-\frac{r^2}{\ell^2}\right)dt^2 - \frac {1}{1 - \frac{r^2}{\ell^2}}dr^2 - r^2\,d\Omega_2^2.$$
It is evident that there exists ...
- 785
32
votes
8
answers
5k
views
Explain to a non-physicist what goes wrong when trying to quantize gravity
I am not a physicist, but I'm trying to get a little bit of an understanding of why it is hard to extend the standard model with quantum gravity (i.e. why it's hard to combine QM and GR), cf. e.g. A ...
- 1,772
0
votes
0
answers
36
views
How to deal with the divergence in tree-level diagrams? where the propagator momentum is on-shell
Only consider the interaction term between electron Higgs and $Z$ boson
$$
\mathcal{L}_{h ff}=-\frac{Y_f v}{\sqrt{2}} \bar{\psi} \psi\left(1+\frac{h}{v}\right)
=-m_f \bar{\psi} \psi\left(1+\frac{h}{...
- 19
0
votes
0
answers
25
views
How to study regularity of a Green's function when solving field equations perturbatively?
Preliminaries
Consider a nonlinear differential operator $\mathcal{O}$ acting on a field $\phi$, with source $\rho$
$$\mathcal{O}(\phi)=\rho$$
Let's say the charge density is small, so we can define $\...
- 4,827