BLACK HOLES

BLACK HOLES

A black hole is a region of space-time exhibiting such strong gravitational effects that nothing—including particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.
The boundary of the region from which no escape is possible is called the event horizon.In short these are objects whose gravitational field is too strong for light to escape.



Simulated view of a black hole in front of 
the Large Magellanic Cloud. Note the 
gravitational lensing effect, which produces
 two enlarged but highly distorted views of 
the Cloud. Across the top, the Milky Way disk
 appears distorted into an arc.

   What happens in spacetime according to General Relativity.A star will curve and distort the spacetime near it, more and more, the more massive and more compact the star is. If a massive star that has burnt up its nuclear fuel, cools and shrinks below a critical size, it will quite literally make a bottomless hole in spacetime, that light can't get out of. Such objects were given the name, black holes, by the American physicist, John Wheeler, who was one of the first to recognize their importance, and the problems they pose. The name caught on quickly.It suggested something dark and mysterious.Although you wouldn't notice anything particular as you fell into a black hole.Instead, you would appear to slow down, and hover just outside. You would get dimmer and dimmer, and redder and redder, until you were effectively lost from sight. As far as the outside world is concerned, you would be lost for ever. Because black holes have no hair, in Wheeler's phrase, one can't tell from the outside what is inside a black hole, apart from its mass and rotation. This means that a black hole contains a lot of information that is hidden from the outside world.But there's a limit to the amount of information, one can pack into a region of space. Information requires energy, and energy has mass, by Einstein's famous equation,  E = m c squared. So if there's too much information in a region of space, it will collapse into a black hole, and the size of the black hole will reflect the amount of information. It is like piling more and more books into a library. Eventually,  the shelves will give way, and  the library will collapse into  a black hole.

IMPORTANT!!!!

As everyone knew, nothing could get out of a black hole. Or so it was thought, but Stephen haukinks discovered that particles can leak out of a black hole. The reason is, that on a very small scale, things are a bit fuzzy. This is summed up in the uncertainty relation, discovered by Werner Heisenberg in 1923, which says that the more precisely you know the position of a particle, the less precisely you can know its speed, and vice versa. This means that if a particle is in a small black hole, you know its position fairly accurately. Its speed therefore will be rather uncertain, and can be more than the speed of light, which would allow the particle to escape from the black hole. The larger the black hole, the less accurately the position of a particle in it is defined, so the more precisely the speed is defined, and the less chance there is that it will be more than the speed of light.
What does this tell us about whether it is possible to fall in a black hole, and come out in another universe. The existence of alternative histories with black holes, suggests this might be possible. The hole would need to be large, and if it was rotating, it might have a passage to another universe.But you couldn't come back to our universe. So, although I'm keen on space flight, I'm not going to try that.