raattgift

9 ms·

31.
Jet and black hole formation from a binary neutron star merger [video](youtube.com)
2 points by raattgift 1y ago|0 comments
32.
Neutron star merger visualized (2021) [video](youtube.com)
2 points by raattgift 1y ago|0 comments
33.
by raattgift 1y ago
The "river model" you mean isn't very general, as one eventually becomes interested gravitating systems where there isn't a suitable congruence, e.g. in close binary compact objects. In such systems, one has to add term
34.
Inertial forces (indirect terms) in problems with a central body(astro.theoj.org)
11 points by raattgift 1y ago|0 comments
35.
New evidence that some supernovae may be a "double detonation"(arstechnica.com)
8 points by raattgift 1y ago|0 comments
36.
by raattgift 1y ago
See also the more technical https://astrobites.org/2025/07/02/unburnt-helium-sne-ia/
37.
Unburnt Clues: Spectral Signs of a Double Detonation(astrobites.org)
8 points by raattgift 1y ago|0 comments
38.
Astronomers get picture of aftermath of a star's double detonation(reuters.com)
3 points by raattgift 1y ago|1 comments
39.
Could Mysterious Black Hole Burps Rewrite Physics?(scientificamerican.com)
4 points by raattgift 1y ago|0 comments
40.
Multiple telescopes produce new view of Andromeda Galaxy(skyatnightmagazine.com)
4 points by raattgift 1y ago|0 comments
41.
Is Mathematics Mostly Chaos or Mostly Order?(quantamagazine.org)
2 points by raattgift 1y ago|2 comments
42.
by raattgift 1y ago
If everything must be constrained to the lattice points, yes. However, empty space has high Boltzmann entropy: you can cut a patch of empty space from here and swap it for the same volume of empty space from there, and the two coarse gra
43.
by raattgift 1y ago
The (Newtonian) Shell Theorem is fairly sensitive to spherical symmetry. In General Relativity one can write down a metric wherein inside any boundary surface there is flat spacetime. It's easiest to do this for a spherical boundary,
44.
by raattgift 1y ago
The local theory part of the Carney et al paper (preprint < https://arxiv.org/abs/2502.17575 >) is interesting in that it isn't obviously related to string theory / holographic entropic gravity. Instea
45.
by raattgift 1y ago
The bit of math is the Shell Theorem < https://en.wikipedia.org/wiki/Shell_theorem >.
46.
by raattgift 1y ago
No, here "entropic" is as in the entropic force that returns a stretched rubber band to its unstretched condition, which (as it tends to be scrunched a bit) is at a higher entropy. https://en.wikipedia.org/wiki&#x2
47.
by raattgift 1y ago
> Any infalling object at Kruskal diagram crosses the line clearly labeled as t=infinity Do check out Lemaître and Gullstrand-Painlevé coordinates for the Schwarzschild black hole.
48.
by raattgift 1y ago
Sorry, I don't want to get into metaphysics. Black hole mergers are studied using post-Newtonian methods and numerical methods because there is no general analytical approach known. SXS, Simulating eXtreme Spacetimes, and the black ho
49.
by raattgift 1y ago
tl;dr The farrrr-from-the-horizon part of Schwarzschild spacetime is just not like our spacetime. Only near and outside the horizon (or better, in the absence of a horizon) does Schwarzschild become a decent physical approximation for anyt
50.
by raattgift 1y ago
In 1+1 dimensions one can analyse the gravitational behaviour of an infinite line of ...-wire-resistor-wire-resistor-... with an adaptation of Bell's spaceship. Throwing away two dimensions eliminates shear and rotation (and all sorts
51.
by raattgift 1y ago
Not sure what you mean; you can't have any mass in a flat spacetime and obey the Einstein Field Equations for a Lorentzian spacetime (because T_{\mu\nu} doesn't vanish everywhere). There are a variety of types of variable speed of
52.
by raattgift 1y ago
The problem is probably connecting an image of a tilted causal cone at p near but outside a regularized r_s in Schwarzschild spacetime with the idea that from p there is a limited number of null geodesics escaping to the asymptotically flat
53.
by raattgift 1y ago
I think given time at a blackboard we could walk through Newton's cannon in the context of Poisson gravity, and for extra credit with the cannonball inducing a perturbation of the Poisson vector field. Even without the cannonball&#x27
54.
by raattgift 1y ago
Physicists (and in particular the subset doing physical cosmology) don't usually explore parametrizations of c because they're not clearly physical (and sometimes even clearly unphysical), or alternatively don't help solve
55.
by raattgift 1y ago
No, there's no change in dimensionality. The swapping of timelike and radial dimensions are a "game" frequently played with families of coordinates, including Schwarzschild coordinates. One can apply any system of coordinate
56.
by raattgift 1y ago
The practical sense is the binary-merger waveforms detected at LIGO, Virgo, and Kagra, which were emitted in the detectors' (and humanity's) past lightcones. We don't even have to consider "the ... future history of hum
57.
Volcanic eruptions and the global subsea telecommunications network(link.springer.com)
4 points by raattgift 1y ago|0 comments
58.
by raattgift 1y ago
The National Film Board of Canada's documentary on black flies is an ear-worm: https://www.nfb.ca/film/blackfly/
59.
by raattgift 1y ago
> everywhere in the universe No, that's not correct. It only has to happen at one place in the spacetime, namely at the horizon itself. General Relativity is a theory of point-coincidences, after all. Additionally there are ordina
60.
by raattgift 1y ago
Solutions of the Einstein Field Equation give rise to the geodesic equation for each such solution. In an exact, analytical solution like Schwarzschild or Kerr, every geodesic is solved for the whole spacetime. The spacetime is a block

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