raattgift

12 ms·

61.
by raattgift 1y ago
Ok, what I take from your comment is that you're identifying General Relativity with certain solutions of GR's Einstein Field Equations. That's like deciding that algebra is just a handful of popular equations. (Aside, I hav
62.
by raattgift 1y ago
The key parameter is mass. The no-hair conjecture says that a Kerr-Newman black hole (KN BH: stationary, eternal) has only position, linear momentum, angular momentum, and electromagnetic charge. 3 components of linear momentum and three of
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by raattgift 1y ago
The mean density of the interior is much much much lower than you think, because the Schwarzschild interior volume is enormously larger than that of a closed Euclidean 3-ball of the Schwarzschild radius. Some details: Christodoulou & Ro
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by raattgift 1y ago
I agree with you so much that I can't resist a nitpick. I'll also amplify your points in the last two paragraphs and justify "the popular scientists". > the event horizon moves outwards to meet it The event horizon
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by raattgift 1y ago
First off, let's assume General Relativity (4d time-orientable manifold) is true. That means among other things that when I write "black hole" I mean an approximate solution which is a small perturbation of an exact solution
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An Extreme Cousin for Pluto? Possible Dwarf Planet at Solar System Edge(ias.edu)
23 points by raattgift 1y ago|11 comments
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by raattgift 1y ago
What do you do if some incident halts full trains (possibly depowering them but for things like emergency lighting) near the midpoints of longer sections of 40 degC deep tunnels?
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by raattgift 1y ago
Sure but using a physical pendulum as a frequency standard is unreliable; an unreliable frequency standard is a bad basis for any sort of time-of-travel definition of length. Many difficulties of using pendulum clocks (and in transporting a
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by raattgift 1y ago
Neither Jupiter nor Saturn is close to thermal equilibrium, whereas the sun is. Bounded self-gravitating gas spheres in thermodynamic equilibrium can show negative specific heats [The classic LBLB, Lynden-Bell & Lynden-Bell, 1977 <
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by raattgift 1y ago
Latitude, mass concentrations, and climate also messed with the half-period/metre ("seconds pendulum") definition; with increasing frequency precision, one would need an almanac, an accelerometer, and probably other tools. A
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The Trinity Clock monitoring project(clock.trin.cam.ac.uk)
1 points by raattgift 1y ago|0 comments
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by raattgift 1y ago
Why quarks? There are untold bazillions of those inside each proton, and there's no quark conservation law (rather than conservation of (for example) isospin and strangeness, but only under electromagnetism not under weak interactions
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by raattgift 1y ago
Hawking 1974, "Black hole explosions?" (Nature paywall) < https://www.nature.com/articles/248030a0 > (sci-hub antipaywall) < https://sci-hub.se/https://www.nature.com/arti
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by raattgift 1y ago
> accelerating observer Note that this is proper acceleration which is measurable locally with e.g. a weighted spring, contact with a piezoelectric scale, or any other sort of accelerometer apparatus. > a black hole reuires an accel
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by raattgift 1y ago
> See https://www.youtube.com/watch?v=XRr1kaXKBsU for the video where he does it. I'd be grateful if you take me to the time stamp, because in a casual watch of the video there was nothing like your: Gravity pul
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by raattgift 1y ago
How do you propose to measure the ultralocal Riemann curvature? I agree with you that it can be there in an exact solution, but I don't really agree that it's necessarily physical (there are many many exact solutions which aren&#
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by raattgift 1y ago
> You need to be near huge, dense masses, or on/in them to see LIV violations A sufficient LLI violation in a compact object is likely to lead to a difference in pressure/contact line broadening, thanks to a modified dispersion
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by raattgift 1y ago
> I don't know enough about physics I'll try to keep this understandable, but can expand or ELI5 bits of it if that would help you. Physically, local flatness is a statement about the local validity of Special Relativity. Prac
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by raattgift 1y ago
> Gravity pulls things in by causing space-time to accelerate in a particular direction. Ok, how does this sketch work for a low-ellipticity eccentric orbit? > "The space-time that is in our frame of reference" Isn't th
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by raattgift 1y ago
tl;dr: drop the use of tensors in the wording and the slogan works better. This sort of "classic" line only applies to a 3+1 slicing or 1+3 threading of the fully-solved Einstein Field Equations, and only in a certain limit. A com
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Duel of the Dual: The Mystery of a Quasar Pair(astrobites.org)
2 points by raattgift 2y ago|0 comments
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by raattgift 2y ago
Sundials are really really cool, and the shadow sweeps in the clockwise direction at mid-latitudes in the northern hemisphere, but https://en.wikipedia.org/wiki/Sundial#In_the_Southern_Hemisp... So "clockwise&quot
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by raattgift 2y ago
When two black holes collide, gravitational radiation shoots out into space. The origin of the radiation is in the dynamical spacetime outside each black hole's horizon, however. This is what the gravitational wave detectors operat
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by raattgift 2y ago
In most mathematical circles, Bolyai-Lobachevsky geometry is strictly a (family of non-Euclidian) hyperbolic geometry. János Bolyai, not Bolshai. And certainly in the 1820s-1830s he investigated the Euclidean parallel postulate, arriving a
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The Canadian roots of Elon Musk's conspiracist grandpa(cbc.ca)
12 points by raattgift 2y ago|0 comments
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General Relativity and Geodesy(arxiv.org)
2 points by raattgift 2y ago|0 comments
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The Dirac equation in General Relativity and the 3+1 formalism(arxiv.org)
1 points by raattgift 2y ago|0 comments
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Is It Time to Redefine Time?(scientificamerican.com)
2 points by raattgift 2y ago|0 comments
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Discovering a Stunted Giant: Intermediate Mass Black Hole Hiding in Milky Way(astrobites.org)
4 points by raattgift 2y ago|0 comments
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by raattgift 2y ago
You probably found a video discussing Olbers's paradox < https://en.wikipedia.org/wiki/Olbers%27s_paradox >.

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