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Black holes (and event horizons) are not caused by density. And yes they always start at the center, even if 100% of the mass and energy is located on a shell very far away from the center. The first thing to remember is that you don't feel an event horizon. In fact of aliens were heading to earth from all directions and they were hoarders (or just ...


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This is not a full answer because HDE's comments cover your main point (I think), it's just to deal with your first question: With less dense bodies, such as the earth and the sun, the center has less gravity/density (since there's an equal amount of mass surrounding the center, pulling out on it from all directions). An estimate of the densities 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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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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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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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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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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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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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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It is not the definition of an event horizon, and in fact you can choose coordinates that are regular near the event horizon. A common reason for coordinates that are irregular at the horizon is if the coordinate is primarily made to represent time far away. In that case, a timelike curve has a negative interval in your convention, so you can have time ...


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The area of an event horizon is an invariant, so it doesn't matter what coordinate system you use to calculate it. The area is of physical interest because it's proportional to the entropy of the black hole, and in a second law kind of way that means the area cannot decrease.


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Q: How reasonable it it to conclude that, from a remote observer’s frame, matter falling towards a black hole never crosses the event horizon, because ∆ t → 0 as v → c (according to the Lorentz transform)? This is not reasonable at all because the property of the equivalence principle indeed does say that the infalling object falls into the black hole. The ...



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