# Tag Info

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I'm pretty sure this question has been asked before, Here and Here and a non stack exchange explanation can be found Here and another, perhaps the easiest read of the bunch: Here Now, I've read (not word for word), but I've read a chunk of those answers and I still find it a little confusing without a clear and concise "yes" or "no" - which would be nice, ...

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Gravitationally time dilated muscles are weak, and gravitationally time dilated magnets are equally weak. If muscles and magnets were not equally weakened by gravitational time dilation, then a person falling while holding magnets would notice something changing. Now I choose to calculate how much gravitationally time dilated muscles are weakened: Let's ...

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Firstly particles can reach event horizon in finite time in the frame of an observer at infinitely far away (This is the frame of reference for describing black hole radiation). But the above phenomenon of particle reaching to the event horizon in finite time has nothing to do with black hole radiation. Hawking radiation is a quantum effect. The pair of ...

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You do see the universe speed up. You just don't see the whole future of the universe play out before you cross. If you cross there are some things you never see. You can take the of your crossing and look at it's past light cone and this will include a last moment that you see before you cross. It's actually the view you see in the sky the moment you ...

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There will be spoilers if you keep reading Firstly, he is shown surviving inside black holes. From where did he got oxygen? Perhaps from oxygen bottles. But, in an intense gravitational pull, how he survives? He would have got torn apart! am I right? The popular press says the word black hole and it is a bit vague what they mean because there are some ...

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General relativity is a theory that tells us the geometry of spacetime. However it predicts that in some situations the geometry of spacetime is undefined - this happens when we get a singularity. There is a singularity at the centre of a black hole, and the Big Bang was also a singularity. So we have the odd situation that the theory of general relativity ...

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The math in that article is based in Cartesian space. Note specifically figure 4, where a portion of a Cartesian plane is pinched in at one side to show the supposed warping due to gravity. Using the shown transformation, she concludes that space is compressed near a black hole rather than stretched. The diagrams after that along with the process ...

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It wouldn't be a static dipole field. It would have some dynamics associated with it, and there would be net radiation. The no-hair theorem only applies to late-time, evolved spacetimes. And is about the horizon itself, not about apparent observations made by distant observers. Less rambly, more bullet-pointy answer: Distant observers would see a ...

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If two black holes hit head on at 99% the speed of light, the result would be one black hole sitting stationary in the center of mass frame with roughly twice the mass and some fraction of the energy expended as gravitational radiation.

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Actually its perfectly possible within standard GR to do so! The question then becomes at what point does GR break down, and if it formed a mass at that point would it have time to decay via hawking radiation down to a Planck remnant? Many types of matter exhibit what is called type II critical collapse where if you carefully tune initial data, you can ...

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Since another answer claims that a massive magic device would form in finite time I have to disagree. You have to wait forever, but only because your device is magic. The simplest problems are the spherically symmetric ones. And if you can get things close to an event horizon and magically bring them away as long as they stay outside then it is possible to ...

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Rod Vance's answer explains why your proposed explanation seems unlikely to many. I'd like to explain what the observations you allude to really show. The correlation between black hole mass and stellar velocities is known as the M-sigma relation. First, note that it does not involve the outer stars in the galaxy. While it is true that the outer stars (and ...

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The mass which fills 'empty' space is beginning to be referred to as the 'dark mass' in order to distinguish it from the baggage associated with dark matter. 'Dark Energy/Dark Mass: The Slient Truth' https://tienzengong.wordpress.com/2015/04/22/dark-energydark-mass-the-silent-truth/ "That is, all that we are certain about [is] the dark mass, not dark ...

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In case your ball is infinitely lighter than the black hole, the answer is infinity. You can never be sure it is not coming back. But in reality your ball has a finite mass which can not be neglected. Its mass is to be added to the black hole's mass M, therefore increasing its size. An outside observer will see that his ball got sucked into the black hole ...

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An event horizon is not a magic place where magic things happen. For instance in universes without dark energy and that are denser than ours (denser than the critical density actually) there are no event horizons. Even for extremely massive stars because everything eventually gets crushed in a big crunch. An event horizon is an imaginary surface between a ...

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Black holes are black because everything that enters don't exists anymore. They are actually extremely red and you see things near them move slowly and the light from then looks very very very red. Like redder than red, like infrared then microwaves then even radio waves. And eventually it is too blurry to really make anything out and too faint (light ...

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Yes and no. A vacuum solution could be stationary, could be static, could be neither. For the orbiting black holes you end up with gravitational waves and gravitational radiation. You either have some going out, and the bodies in spiraling or you have some coming in and driving the system or both. And the point is that you have to specify the state of the ...

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It just means the Schwarzschild coordinate system is faulty at the horizon because it assigns the same coordinates $(t,r,\theta, \phi)$=$(\infty,2m,\theta,\phi)$ to multiple events that are actually distinct events. If you look at the Kruskal-Szekeres coordinate system you can pick an event on the horizon and then draw the past light cone and those are ...

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How can black holes be observed to grow? Like a hailstone. See Kevin Brown's formation and growth of black holes. He says things like this: "Incidentally, we should perhaps qualify our dismissal of the "frozen star" interpretation, because it does (arguably) give a servicable account of phenomena outside the event horizon, at least for an eternal ...

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There is no requirement for a central black hole in a dynamical sense. Many galaxies are not known to have one, or if they do, its mass is relatively small. The gravitational influence of the SMBH can be quite negligible at distances that are only a tiny fraction of the size of a Galaxy. What I mean by this is that say the BH at the centre of the Milky Way ...

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I don't think I can explain all the technical stuff, but first things first. Primordial means "at the creation", so if it was created today it wouldn't be primordial. Now "Primordial size" black hole, is probably what you mean and even that is a bit vague as estimates vary on the possible sizes of Primordial black holes, (and there's some uncertainty as ...

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Like most proposals, it is possible of course; in physics we must ultimately test proposals experimentally. In the meantime (i.e. in this case whilst waiting for experimental observation and study of dark matter here on Earth), one must resort to assessing plausibility in the light of what we already know. There are two ways your proposal, if true, could ...

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The stars in the galaxy don't really orbit the black hole in the center of the galaxy. They all orbit a common center of gravity. Obviously, a lot of the mass is in the black hole, and the center of gravity could very likely lie inside the black hole's event horizon, but it's not required. Look here for a cool animation of Pluto and Charon orbiting a center ...

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If people brought all the trash in the galaxy to a single place and dumped it, a black hole could eventually form from the ever-increasing density without ever forming a star. Hypothetically, a bunch of heavier elements (incapable of starting a fusion/fission process to hold the gravitational collapse at bay) could happen to end up in the same region of ...

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The equivalence principle only holds for extremely small regions of spacetime. Which means they hold for short time intervals as well as small spatial regions. Consider an event near the event horizon. If the event is outside the horizon there might be a frame moving away from it that cover a very small region that is also completely outside the horizon and ...

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An object inside a black hole horizon cannot send signals outside of the horizon, but something falling into the black hole can fall through the signal. Take the example of the camera attached to the astronaut's foot. When the astronaut is halfway through the horizon, the camera is about a meter inside the horizon and the transmitter is about a meter ...

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In general relativity, (unlike in special relativity where time-space can be made universal) there is no concept of universal time-space, thus general observers have observations those are highly dependent at the space-time locations of the observers. Two observers who are standing apart in space-time may observe the same phenomena with astonishingly ...

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We have never seen a singularity before so we aren't sure what happens. We can't therefore even be sure they actually form, maybe he theories we use to predict their formation start to break down before they form. But if they did form we have no idea what they do the instant after they form because the theory that predicted them actually breaks when they ...

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Due to gravitational time dilation, for an observer of the planet, the frequency of electromagnetic radiation would be slower. Visible light emitted from the planet would appear as infrared or micro-waves. The amplitude of the radiation would not change. Since frequency decreases while amplitude remains constant, the radiometer would receive less ...

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Hawking radiation is indeed usually calculated as a semiclassical effect (classical gravitational field and quantum matter), which is invalid at high energy ($\langle T_{\mu\nu}\rangle >> 1$) and high fluctuations ($\langle T_{\mu\nu} T^{\mu\nu} \rangle - \langle T_{\mu\nu} \rangle \langle T^{\mu\nu}\rangle >>1$). Still, it is a result that is ...

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While photons can in principle form a black hole, the black hole will not be massless. The mass of the black hole will be related to the energy of the photons that went into it by Einstein's famous equation $E = mc^2$. The black hole will be a regular black hole, and classically it has an infinite lifetime. Once you include Hawking radiation the black hole ...

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To someone outside it looks the same as a regular, massive black hole. Classically the lifetime is the lifetime of the universe. It might merge with another black hole. It might last forever. It might meet a singularity in a big crunch if the whole universe contracts to a singularity. If you are worried that it can't decay by Hawking radiation because an ...

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The mathematics of general relativity is clear and unambiguous. The trouble comes when you try and describe what is going on it non-mathematical terms, because there is no precise way to do it. Kip Thorne is attempting to talk about black holes in non-mathematical terms, and he is adopting a different perspective from (probably) most of us. That doesn't mean ...

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The holographic nature of a theory is imprinted by hand as soon as the theory is quantised. That was the point David Bohm made. Quantum mechanics is inherently holographic. String theory is a quantum mechanical theory and is therefore also holographic. Possibly more related to your point is the string theory landscape that could potentially allow many ...

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A brief intuitive answer. Black holes are enormously difficult to work with, the warped space and tidal forces are enormous, but I think you want to ignore the difficulties. A black hole with 100 solar masses would have a radius of about 300 KM, if you put it next to the Earth, it would be a bit smaller than Texas. Lets say your friend's ship orbits at ...

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(as usual, we assume the static black hole solution for simplicity). If hovering outside the horizon, the gravitational time dilation goes to infinity as the distance from the horizon goes to zero. The elapsed proper time of the twin hovering outside the event horizon is given by \Delta \tau = \Delta t \sqrt{1 - \frac{r_s}{r}} = 10^9 \sqrt{1 - ...

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It does seem odd that a star that isn't a black hole can explode, and therefore presumbly lose mass, and still form a black hole. The explanation is that to form a black hole requires a high density not just a high mass. Even a small object such as, well, you or I could form a black hole if compressed enough, though obviously in practice that level of ...

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This can be understood by showing in general where curvature come from. Spacetime can curve naturally all on its own even in empty space. Matter can connect together regions that have two different types of curvature. One possible type of curvature is the funnel shaped curvature outside a star or outside a black hole. As the star collapses inwards to for ...

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Do black holes have a puff pastry point? No. If a person falls into a certain sized black hole they accelerate very fast, which increases the g forces on them. They don't feel any g forces at all, because there aren't any. These g forces flatten the person out into a pancake. There aren't any, a falling person doesn't flatten into a ...

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The quick answer to your question is no, cause nothing can spin that fast. It's an interesting question, though I think you need to take a step back and ask about formation. A spinning object will have less gravity around the equator than on the poles, but if an object spins so fast that it has zero gravity, most likely it would fly apart though there ...

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There are solutions to Einstein's Field equation (General Relativity) where the ratio of angular momentum to mass is so large that the singularity is visible to the outside instead of being shielded by an event horizon. But no known astrophysical black hole has a ratio that high. And it looks like when you try to give more angular momentum to an existing ...

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The first part of the argumentation is basically right: external objects influence the gravitational field so that the event horizon of the black hole in the middle will no longer be "exactly spherical and isotropic" when additional objects' gravity distorts the field. Well, the reality is that even the spacetime refuses to be spherically symmetric in the ...

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As a distant observer we can watch the shadow of the black holes forming in front of the background stars. According to a nice little paper by Daisuke Nitta, Takeshi Chiba, and Naoshi Sugiyama ("Shadows of Colliding Black Holes, 2011") the answer is yes. To a distant observer in a finite span of time two black holes form a shadow that is indistinguishable ...

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Like in most physically complicated cases, one would normally solve the dynamic system numerically. In the case of general relativity, the "3+1 decomposition" method or equivalent is used. There are some open source tools for aiding in numerical research.

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Your premise is that quantum gravity has effects near the singularity and that the event horizons is a barrier to getting information our from within the horizon. So a simple theoretical investigation is to look at a very very small black hole, one where the outside of the event horizon is still near the singularity and thus the quantum gravity effects are ...

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There are a number of attempts at constructing theories of quantum gravity, of which string theory and loop quantum gravity are the most developed. However none of these theories have been developed to a point where they can make uncontroversial predictions about what happens near a black hole singularity. The only even passably convincing attempt is using ...

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When gravity is strong enough, it bends light towards the source of the gravity. Roughly true So if you were on a small planet and gravity were to gradually increase, would the horizon rise as well, allowing you to see further? Yes! If so, at some point, could you look up at some angle and have the light go all the way around the planet ...

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Disclaimer for those who know more: I only talk about spherical black holes for simplicity; rotating black holes are more complicated. Indeed, a planet's gravity bends light and allows you to see a little bit farther; this is an observed effect (though not on planets), and is called gravitational lensing. If you've seen the movie Interstellar, you might ...

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A short answer is that frames themselves are moving towards the black hole and light moves relative to a frame and hence it can be stuck. Nothing passes through a black hole. Things can enter a black hole, they can't can't exit without going faster than light. Where do things go then? The important part of that question is the word "where" you ...

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In 1974 Stephen Hawking published a paper that provides a theoretical basis for the thesis that black holes eventually may radiate away all the mass, light, and other energy they accumulate. Evaporation of black holes has been called Hawking radiation. It takes place so slowly (at least until the black hole shrinks to a small size) that none has been ...

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