-1
votes
1answer
35 views

How to calculate the gravity level at the boundaries of a black hole? [on hold]

Imagine that a body is attracted to a black hole and it has a mass $M$, if the body is moving with $v=.99c$, will its speed and mass affect the gravity relation between the body and the black hole? or ...
3
votes
0answers
60 views

Doesn't the Schwarzschild metric combined with Hawking radiation imply that nothing ever gets past the event horizon of a black hole?

According to the General Theory of Relativity, the coordinate time distance per spacetime distance traveled by a particle freely falling into a black hole gets closer and closer to $0$ as the particle ...
3
votes
0answers
91 views

The difference between an apparent horizon and event horizon?

I'm currently writing a project on minimal surfaces and general relativity - however I don't understand the difference between the apparent and event horizon? They ultimately both seemed to be defined ...
1
vote
1answer
119 views

How can a black hole have spin?

How is it possible, or even meaningful, to say that a black hole has spin? (Tangentially, if the singularity is assumed to be a point, it must have either zero or infinite angular momentum, in both ...
0
votes
2answers
157 views

If NASA could send a camera into a black hole, could we then see what's inside the black hole?

Inspired by Stephen Hawking I recently tripped upon an idea of what is really inside a black hole. I thought if NASA (or any other space agency) could send a super protected camera into a black hole, ...
5
votes
4answers
192 views

Is it possible to escape from within event horizon?

I always think that it is not possible to escape from within event horizon. However, some one recently told me with deep conviction that it is possible with sustained energy output. I countered with ...
3
votes
0answers
98 views

Further explanation of the Penrose Conjecture

I'm currently a third year maths undergrad, writing a dissertation on the application of minimal surfaces in space. I have recently come across the Penrose Conjecture that the mass of a spacetime is: ...
4
votes
1answer
118 views

Non-coinciding event horizon and apparent horizon

Proposition: the event horizon and the apparent horizon of a black hole always coincide. As a reminder: the event horizon is defined as the boundary of the closure of the causal past of future ...
1
vote
1answer
105 views

Why can't we see things swallowed by black holes?

Apologies in advance, I'm a layman with only a school-level education in physics. If an object approaching the event horizon of a black hole has its light cone progressively bent towards the black ...
3
votes
0answers
80 views

Trapped Surfaces. Any good articles?

I'm currently writing a dissertation on trapped surfaces as minimal surfaces. I have exhausted all of the resources I have, and the internet is pretty limited (in that it is fairly repetitive on just ...
5
votes
0answers
101 views

Why can apparent horizon be computed based on its local geometry?

Why can apparent horizon be computed based on its local geometry? In the paper titled Black Holes, Geometric Flows, and the Penrose Inequality in General Relativity by Hubert L. Bray, has been ...
2
votes
1answer
73 views

Physical meaning of the Rindler hyperbola vertex and the Rindler lines

Two questions regarding the Rindler diagram: 1) Does the vertex of a given hyperbola in the diagram have physical meaning? I know it is the inverse of the constant proper acceleration ($\alpha$) ...
2
votes
0answers
87 views

Gravitational waves as information carriers

Is it possible to utilize gravitational waves as a delivery system for information between two observers straddling the event horizon of a black hole? And why ?
2
votes
1answer
68 views

If charged particles always attach to black hole event horizons, how can ordinary matter fall in?

(A friend at work kindly loaned me loaned me his copy of Kip S Thorne's "Black Holes & Time Warps". This may have been ill-advised... :) BH&TW 1994 paperback p.410 Figure 11.5: ... all ...
0
votes
0answers
33 views

How much extra distance to a CERN event horizon? [duplicate]

How much extra distance would a scientist have to travel to get to the event horizon of a mini black hole if they ever make one?
1
vote
1answer
153 views

How much extra distance to an event horizon?

How much extra distance would I have to travel through space to get from Earth to a stellar mass event horizon? (compared to the same point in space without a black hole)
4
votes
0answers
83 views

Euclidean black hole extrinsic curvature

I have read that the extrinsic curvature at the horizon of a euclidean black hole is zero? Does anybody know how this can be shown?
5
votes
1answer
115 views

Could dark energy make a large black hole less black?

Theoretically, if a black hole grew to a huge scale such that the effect of dark energy was large, could the black hole become 'normal' space again (i.e. no horizon or singularity)? What I'm trying ...
11
votes
2answers
456 views

Can matter really fall through an event horizon?

This question is closely related to Event horizons without singularities from about a year ago (May 2012), which John Rennie answered nicely and persuasively. My variant of the question is this: ...
1
vote
2answers
177 views

Second law of thermodynamics implies a linear cosmology?

If one applies the second law of thermodynamics to the Universe[1] as a whole then one might expect that the entropy of the Universe always increases as time goes forward (or more accurately that the ...
3
votes
1answer
219 views

What does “all future lies within the event horizon” mean?

I was trying to find an answer as to why light does not escape black holes and I stumbled upon this Phys.SE question. In the answer it said that: "Since all future lies within the event horizon, ...
3
votes
2answers
732 views

What is the shape of a black hole?

I was thinking; what shape does a black hole have?. By 'Shape', I mean its form (e.g, circle , cylinder, sphere, torus, etc..). We usually think of black holes as if they're plugholes (e.g, a flat ...
5
votes
3answers
465 views

What is the “Event Horizon” of a black hole [duplicate]

Can someone please explain what the event horizon of a black hole is? I mean is it the actual surface of the black hole or is it the point of no return where light can no longer escape?
1
vote
1answer
62 views

Can we build a synthetic event horizon?

If we imagine ourselves to be a civilization capable of manipulating very heavy masses in arbitrary spatial and momentum configurations (because we have access to large amounts of motive force, for ...
11
votes
1answer
218 views

General definition of an event horizon?

Horizons are in general observer-dependent. For example, in Minkowski space, an observer who experiences constant proper acceleration has a horizon. Black hole horizons are usually defined as ...
2
votes
3answers
179 views

Why are black holes special?

A black hole is where it's mass is great enough that light can't escape at a radius above the surface of the mass? I've been told that strange things happen inside the event horizon such as ...
0
votes
1answer
115 views

Can you enter a timelike hypersurface?

As I understand it, a timelike hypersurface is one that has only spacelike normal vectors. But does this not imply that a the geodesic of a particle crossing it must be spacelike at that point? But ...
4
votes
2answers
269 views

How does the evaporation of a black hole look for a distant observer?

Let's assume an observer looking at a distant black hole that is created by collapsing star. In observer frame of reference time near black hole horizon asymptotically slows down and he never see ...
2
votes
1answer
178 views

Would dense matter around a black hole event horizon eventually form a secondary black hole? [duplicate]

Possible Duplicate: Black hole formation as seen by a distant observer Given that matter can never cross the event horizon of a black hole (from an external observer point of view), if a ...
0
votes
0answers
41 views

Can a black hole actually grow, from the point of view of a distant observer? [duplicate]

Possible Duplicate: Black hole formation as seen by a distant observer I've read in several places that from the PoV of a distant observer it will take an infinite amount of time for new ...
4
votes
2answers
270 views

Black hole formation as seen by a distant observer [duplicate]

Possible Duplicate: How can anything ever fall into a black hole as seen from an outside observer? Is black hole formation observable for a distant observer in finite amount of time? ...
6
votes
2answers
609 views

Can we have a black hole without a singularity?

Assuming we have a sufficiently small and massive object such that it's escape velocity is greater than the speed of light, isn't this a black hole? It has an event horizon that light cannot escape, ...
-2
votes
1answer
155 views

Way to escape from a black hole

I’ve had a question on WHY a traveler couldn’t “escape” from a black hole under specific conditions (I have an image I'd like to send to clarify, but the website won't let me)> The key is for the ...
3
votes
2answers
393 views

What do you feel when crossing the event horizon?

I have heard the claim over and over that you won't feel anything when crossing the event horizon as the curvature is not very large. But the fundamental fact remains that information cannot pass ...
3
votes
1answer
149 views

How does nature prevent transient toroidal event horizons?

How does nature prevent transient toroidal event horizons?.. and does it really need to? Steps to construct a (transient) toroidal event horizon in a asymptotically flat Minkowski spacetime: take a ...
2
votes
2answers
184 views

event horizons are untraversable by observers far from the collapse?

Consider this a followup question of this one In the classical schwarszchild solution with an eternal black hole, the user falls through the event horizon in finite local time, but this event does ...
5
votes
1answer
303 views

Falling into a black hole

I've heard it mentioned many times that "nothing special" happens for an infalling observer who crosses the event horizon of a black hole, but I've never been completely satisfied with that statement. ...
1
vote
0answers
194 views

How can things at the event horizon slow down and appear to stop to a remote observer?

So they say the remote observer will never see anything fallen to the black hole, because any object will slow down as it gets closer to the event horizon and eventually stop to stay there forever. Am ...
24
votes
12answers
3k views

How can anything ever fall into a black hole as seen from an outside observer?

The event horizon of a black hole is where gravity is such that not even light can escape. This is also the point I understand that according to Einstein time dilation will be infinite for a ...
3
votes
1answer
235 views

Could a ship equipped with Alcubierre drive theoretically escape from a black hole?

Also could it reach parts of the universe that are receding faster than the speed of light from us?
9
votes
4answers
317 views

Solid objects inside the event horizon - can they remain “solid”?

So, once something is inside a black hole's event horizon, it can only move towards the center. This is fine for a point-object. But 3D solid objects rely on molecular forces to stay in one piece. ...
2
votes
2answers
208 views

Do all event horizons emit radiation?

So, the event horizon around a black hole emits radiation, and Rindler space is full of thermal energy. I guess I have two questions- does the Unruh effect have anything to do with radiation from the ...