In the previous post I covered black holes in general, the origin of the idea and a brief explanation of what they are. Now let’s take a look at some of the unusual rules that operate inside the event horizon.
So we have crossed the event horizon and now neither we nor any light can escape back to the outside, the singularity that lies at the center of the black hole is now in our future and there is no way to avoid crashing into it. As you can see the horizon has some very unusual geometrical properties. If you were an observer sitting far away from the black hole, the event horizon would seem to be a very nice, static and unmoving spherical surface (originally called “frozen stars” for this property, since no light escapes). As you got closer and closer you would find that it has a very high velocity. Actually you would see that it’s moving outward at the speed of light! This is why it would be so easy to fall into a black hole, but impossible to ever get back out. Since the event horizon is moving outward at the speed of light, you would have to be able to travel faster than the speed of light to escape, which is a violation of Einstein’s relativity.
On the one hand, the horizon is sitting still, while on the other it’s actually moving outward at the speed of light. Sounds contradictory, but its true, let’s look at the unusual rules that apply inside an event horizon. Once on the inside, space-time is distorted to such a high degree that the coordinates describing radial distance and time switch roles. What that means is the coordinate that normally describes how far you are from the center (“r” radial distance) now becomes a time coordinate, and the coordinate that normally describes time (“t” time) becomes a space-like coordinate. One result of this is you cannot stop yourself from moving to smaller and smaller values of “r”, just as in normal life you cannot avoid moving toward the future. Eventually you will hit the singularity where “r” = 0. Trying to avoid the singularity is like trying to avoid tomorrow. Just how strong is the gravitational pull inside a black hole? The further in you go, the stronger the pull is. It’s so strong that if your feet were closer to the center than your head, the difference in pull between your head and your feet (tidal forces) would literally pull you apart in a horrendous fashion known as spaghettification.
Now lets see how all of this looks to an outside observer who is watching someone else enter a black hole. There are two space travelers, one is stationed very far away from the black hole, and the other is you poised just outside of the event horizon. As you start to move toward the event horizon, the other astronaut sees you move more and more slowly. No matter how long the observer waits he or she will never see you reach the event horizon and it would appear to him/her that it takes an infinite amount of time for you to enter the black hole. The reason for this is simple, the closer you get to the event horizon, the longer it takes for the light you are emitting to climb back out and escape. Actually, the light you emit just as you cross the event horizon will hover right there at the horizon forever and ever never reaching the observer. From the observers point of view you will have frozen in space.
Keeping with the fact that massive objects distort the space-time around them, time near the event horizon really does move more slowly. If you were able to get very close to the event horizon, but managed to keep from being pulled in, you would find when you returned to talk to the observing space traveler that he or she has aged much more than you have. Time has passed more slowly for you than it did for the rest of the universe.
So we have crossed the event horizon and now neither we nor any light can escape back to the outside, the singularity that lies at the center of the black hole is now in our future and there is no way to avoid crashing into it. As you can see the horizon has some very unusual geometrical properties. If you were an observer sitting far away from the black hole, the event horizon would seem to be a very nice, static and unmoving spherical surface (originally called “frozen stars” for this property, since no light escapes). As you got closer and closer you would find that it has a very high velocity. Actually you would see that it’s moving outward at the speed of light! This is why it would be so easy to fall into a black hole, but impossible to ever get back out. Since the event horizon is moving outward at the speed of light, you would have to be able to travel faster than the speed of light to escape, which is a violation of Einstein’s relativity.
On the one hand, the horizon is sitting still, while on the other it’s actually moving outward at the speed of light. Sounds contradictory, but its true, let’s look at the unusual rules that apply inside an event horizon. Once on the inside, space-time is distorted to such a high degree that the coordinates describing radial distance and time switch roles. What that means is the coordinate that normally describes how far you are from the center (“r” radial distance) now becomes a time coordinate, and the coordinate that normally describes time (“t” time) becomes a space-like coordinate. One result of this is you cannot stop yourself from moving to smaller and smaller values of “r”, just as in normal life you cannot avoid moving toward the future. Eventually you will hit the singularity where “r” = 0. Trying to avoid the singularity is like trying to avoid tomorrow. Just how strong is the gravitational pull inside a black hole? The further in you go, the stronger the pull is. It’s so strong that if your feet were closer to the center than your head, the difference in pull between your head and your feet (tidal forces) would literally pull you apart in a horrendous fashion known as spaghettification.
Now lets see how all of this looks to an outside observer who is watching someone else enter a black hole. There are two space travelers, one is stationed very far away from the black hole, and the other is you poised just outside of the event horizon. As you start to move toward the event horizon, the other astronaut sees you move more and more slowly. No matter how long the observer waits he or she will never see you reach the event horizon and it would appear to him/her that it takes an infinite amount of time for you to enter the black hole. The reason for this is simple, the closer you get to the event horizon, the longer it takes for the light you are emitting to climb back out and escape. Actually, the light you emit just as you cross the event horizon will hover right there at the horizon forever and ever never reaching the observer. From the observers point of view you will have frozen in space.
Keeping with the fact that massive objects distort the space-time around them, time near the event horizon really does move more slowly. If you were able to get very close to the event horizon, but managed to keep from being pulled in, you would find when you returned to talk to the observing space traveler that he or she has aged much more than you have. Time has passed more slowly for you than it did for the rest of the universe.
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