From an outside observer you appear to never enter the black hole at the event horizon, appearing “frozen”, however, they wont be able to even sense you for more than a second or so if after you enter, as there are only a limited number of photons that can emerge from you so after they are statistically gone you will be effectively invisible.
On the other hand, if you hover stationary just outside the event horizon, you will see the outside world passing extremely quickly indeed. But in order to do so you will need acceleration equivalent to accelerating yourself to extreme relativistic speeds. All in all probably safer that you expend the same amount of energy just jaunting around the universe and experiencing time lag that way. Plus the stuff that’s falling in to the BH will be extremely blueshifted toward you because of all your constant acceleration relative to the black hole’s gravity.*
*which would also occur in an intergalactic jaunt but i’d assume that a Bh would attract more incoming matter?
A while back I started a thread asking what happens to the “infinite time to reach the event horizon” when taking into account Hawking evaporation. The consensus was that a remote observer would see someone reach the horizon just as the hole evaporated away*
*if they do completely, which is another question altogether.
The spacetime inside the black hole’s event horizon is curved in such a manner that there is no out. It doesn’t matter which way you head, how fast, or under how much acceleration. The exit is closed.
Light has no mass, therefore, is completely unaffected by the newtonian gravity aspects of the black hole’s mass. If it wasn’t for relativity, light could easily escape a black hole. However, gravity curves space and light has to follow the curve of space.
BTW, because of the severe curve of spacetime, as you approach a black hole, time slows down compared to being farther away from the black hole.
Imagine a person falling into a black hole while holding an alarm clock with a second hand. That person’s shipmate would notice the wayward astronaut falling slower and slower into the black hole and see the second hand of the alarm clock moving slower and slower until it appears to stop right at the edge of the black hole. If the ship sticks around for a few ten thousand years, they may notice that astronaut slowly disappears. (Actually, the astronaut would be pulled apart into separate atoms due to tidal gravitational forces. The poor fellow would be stretched like taffy since there is a great difference between the strength of gravity even a few centimeters farther out from the black hole. But, we’ll ignore this effect in order to concentrate on the time aspect of a black hole event horizon.)
Meanwhile, the unfortunate astronaut would observe no time disparity. To that astronaut, the second hand is still moving at its regular pace. However, the ship and surrounding area will look like it is moving at superfast speed.
So, once you enter the event horizon, relatively speaking, there is no way out. However, quantum effects do allow you (or at least your former particles) to escape due to random quantum fluctuations. A particle could randomly suddenly find itself outside the event horizon and thus escape. This means that black holes actually evaporate over time. This is known as Hawking Radiation after Stephen Hawking.
Actually, it’d only take seconds, not thousands of years, for the infalling astronaut to fade out completely. And he won’t be spaghettified if he falls into a sufficiently large black hole: One could quite comfortably pass through the horizon of the hole in the center of our Galaxy, for instance.
It does take only a few seconds to fall into a black hole, but time slows down as you approach a black hole. Thus, if you observe something falling into a black hole, it will take a long time simply because that object’s time is slowing down.
There’s a children’s book called Icarius at the Edge of Time that illustrates this point. In this story, Icarius flies too close to a black hole and when he returns to his ship suddenly realizes that 100,000 years had passed.
I can’t say whether the tidal gravitation forces of a sufficiently large black hole are weak enough not to tear you apart. I’ll have to give it a try.
So if an outside observer can never witness anything falling past the event horizon (because time seems to stand still for anything just about to fall in) an outside observer can never see the black hole swallow anything, right? So the black hole, from any point of observation, can never actually gain mass, right?
So…erm…what am I missing here? Black holes CAN get bigger, can’t they?
I didn’t phrase that too well. What you were meant to take away from this is more along the line that it’s not a sharp distinction between ‘points in space’ and ‘points in time’, since, for instance, things you see happen simultaneously might to some other observer, moving at some speed relative too you, appear to happen in some sequence, so there’s no absoluteness to the concepts (that’s why it’s called a theory of relativity, after all). (However, I should hasten to add, that this is only the case if the events are space-like separated; with two time-like separated events, where one could causally influence the other, it is fortunately the case that their sequence is fixed in all frames of reference, so you don’t have any possibility of causality violation this way.)
It’s perhaps better to talk about events, rather than points (and I haven’t really held up this distinction clearly in my previous post). Remember, events are points in four dimensions, x, y, z, and t. A point ‘in your future’ is then a point in your future lightcone – a point you can get to travelling slower than c. For instance, the sun, three minutes from now, is not a point in your future, since you couldn’t reach the sun in three minutes. However, the sun, nine minutes from now, is – since light takes a rough eight and a half minutes to get there, in theory, you could do it in nine (though this may never be practically feasible).
The singularity is in that sense a point in your future; one you couldn’t avoid if you tried.
I said “fade out”, not “cross over”. It’s true that, from the perspective of the distant observer, there never comes a time when the infalling object has crossed the horizon. But the infalling object will only emit a finite number of photons, so eventually there comes a point when the last photon is emitted (and that last one will be extremely redshifted). So from a the perspective of the outside observer, the object will still disappear, by virtue of fading completely from sight.
When we say that the time never comes when the infalling object has crossed the horizon, we’re speaking from a mathematical framework where the mass of the black hole is treated as constant. This is a good approximation if we’re discussing a human falling into a million-solar-mass black hole, but obviously not a good approximation if we’re talking about another star falling into a stellar-mass black hole.