LHC Black Holes

But that sound energy escaping from your mouth comes from a different source. ;-)

Here is why it can't cross the event horizon other than toward the black hole. The event horizon is where the escape velocity from the force of gravity equals the speed of light. It is not possible to accelerate any matter or energy beyond that speed. In the case of matter, there is no way to accelerate it *to* the speed of light. Therefore there is no amount of energy that can move an object from the inside of the black hole to the outside or even from the event horizon to the outside. Even light can not exit from within the black hole clearly. I would say that light can not leave from the event horizon either. If it were aimed perpendicular to the black hole surface, it would be infinitely red shifted to zero energy which means it would disappear.

It's not different, but you aren't thinking in relativistic terms. With the gravitational field anything moving away from the black hole inside the Schwarzschild radius would be accelerated beyond the speed of light which is not possible. Nowhere inside the Schwarzschild radius can anything move away from the center.

Don't confuse the black hole with the matter around the black hole. That outside matter is not significant to this discussion.

This does not make any sense. Of course the potential energy of the brick is extracted when you release it.

but it can, if the thing has a means of propulstion, it's only free particles that are trapped.

yoager 1 was never traveling 11km/s, it has never exceeded 2km/s and yet it escaped earth. thust makes a difference.

such light rays either intersect the swatschild radius (curve back in) or are redshifted to 0 energy by gravity.

FAIK they aren't very black.

there is, but it's one of terminology.

it can't _all_ escape. but it can sacrifice some mass (rocket fuel) to climb above the swartzchild radius.

You seem to not understand relativity. It is not possible to accelerate any matter to the speed of light. Therefore it is not possible to move against a gravitational field that has an escape velocity greater than the speed of light. You seem to think escaping the earth's gravitational field is like escaping a black hole. Do the math can calculate the amount of energy required to cause an electron too exit a black hole. I think then you will understand this problem.

That is not how escape velocity works. You are assuming that the object trying to escape must be accelerated up to the escape velocity, and then released. Instead, you need only apply a force of the same order as the force you are escaping from so that you don't decelerate too much. Thus when a rocket is sent from earth to outer space, it is not fired from the surface at 11,000 km/s and left to "free fall" out. Instead, the engines are powered all the way and it never gets anywhere close to that speed.

The same applies when a spaceship is leaving the black hole. It never needs to get to the speed of light, because it is not trying to "free fall" out of the black hole (as a photon or complete object would). A key point to note is that not all of the mass of the spaceship can leave

- to be able to provide force going out, mass needs to be pushed back towards the gravitational centre of the black hole.

So as I say, there may be time complications or other relativity limitations on getting out of a black hole, but the escape velocity is /not/ a fundamental problem.

You seem to not understand escape velocity.

yeah.

That does not follow. and furthermore, is contrary to relativity.

See my other post - you are assuming that the escaping object must be accelerated to escape velocity (which in this case would be impossible, since it is greater than the speed of light). This is not necessary if there is a force acting upon the object as it leaves (such as firing thrusters).

You seen to be incorrect here, according to The Internet. As I said in my vague post before, "all the light cones point inwards"

Because general relativity.

Not quite. The spaceship fades out becoming ever more redshifted and the photons ever more widely spaced in time.

Also true for a sufficiently large BH so that there is plenty of time to see the world from inside the BH before spagettification occurs.

This is completely wrong. Once the spaceship is inside the BH it will fall to the centre in a finite clock time by its metric. Life getting ever more unpleasant as the gravitational gradient becomes ever more severe as the hapless visitor reaches the singularity.

There are no stable orbits inside a BH. And the last stable circular orbit depends only on the mass and spin of the black hole (and the direction you chose to orbit in).

You can do one for a distant observer with a good telescope watching from a safe distance and one for a traveller on the spaceship itself. They are the two most interesting viewpoints. Only the first of these observers will be able to publish his observations afterwards.

A more comprehensive list of such simulations with the first ones done back in the mid 1990s is at :

They concentrate on getting the background light paths right through ray tracing in the gravitational metric. They aren't quite as flashy as the Hollywood versions but they are pretty good.

There is a subtle difference in relativity between what you see which includes the light travel time from distant objects and what you observe which is only defined for objects at your spacetime coordinates.

No, it is not /completely/ wrong - and not for the reasons you say below. But after reading a bit more, I can see I'm /mostly/ wrong here.

My first point - that the passage of time is completely different for the two observers - is, I think correct.

But the spaceship cannot escape from the black hole even by thrusting its way out. This is not because of the escape velocity, as Rick keeps saying - my reasoning there was sound from a Newtonian viewpoint (and by keeping a low speed, I had hoped to remain Newtonian). But when you look at the /energy/ involved, there is no escape - you'd have to have infinite energy to get out. Relativity is unavoidable here.

Not a problem, either from the Newtonian or relativity viewpoints - you just have to turn round within that finite time.

That's a practical problem, but not for the theory.

That is true, but not directly related to the problem.

Thanks for that link. I'm going to enjoy that when I get the time.

Thanks for that link. It gave me the point I was missing - "Forget about speed. Think in terms of energy". My speed argument was reasonable enough, but I had thought to avoid relativity effects by keeping a low speed. However, when you think of the energy involved in escaping, it turns out to be infinite - no matter how good your thrusters are.

Yes, but that does not preclude what I said.

The singularity is an assumption. It will form in some amount of time, but it may not be present when the space ship enters the black hole. As you say, given a sufficiently large black hole... But his statement was about the difference in perspective.

When the gravity of the black hole warps time, it also warps space. I believe the distance to the center of the black hole becomes infinite. I'm not sure how the distance to the Schwartzschild radius of a space ship falling into it is warped.

Well, duh! There is no amount of energy that will allow you to return from inside the black hole. How does it matter if you call it relativistic or "escape velocity"? The point is your earth escape velocity analogy is not appropriate to a black hole which is what I said. Just two ways of explaining the same thing.

Turn around? There is no amount of energy that will even keep you from falling once inside the black hole.

It is exactly the problem.

The escape velocity is an expression of the energy required to exit orbit. It matters not how you apply the energy. To exit a black hole requires more than an infinite amount of energy.

Speed is irrelevant. Energy is the problem. Escape velocity is just a way of expressing that energy.

When you encounter relativity in trying to attain the escape velocity it is. It matters not if your speed is just 1 MPH, you are fighting gravity that is the same as acceleration which puts you in the relativistic domain whether you like it or not. Trying to get out of a black hole is relativistic no matter what.

No, it has nothing to do with actual speed, it has to do with acceleration and energy. See my other post.

??? How is it "contrary" to relativity?

I see David Brown has finally figured it out. What's holding you back?

All this is analogous to the argument that the energy of an electron should be infinite, because that's what you get if you integrate the field all the way to zero radius. We know that it's finite: 511 keV.

The energy in a black hole is huge, to be sure, but still finite.

Jeroen Belleman