# Black Holes & String Theory

Particles can’t move faster then light, infact if they have mass they can’t even reach the speed of light. This means that degeneracy preassure can’t grow infinetly high in a star, since it depends of the speed of the particles. So when a star more massive then 3 solar masses collapse, degeneracy pressure can’t no longer hold up the massive gravitational pressure produced by the stars mass. The star implodes on itself to zero size and forms a singularity. A singularity is a place with zero volume and an infinetly high density. At the singularity space time is infinitely warped and therefore gravity is infinitely strong. In fact, at the singularity spacetime is so severely warped thatit cease to exist which is a very serious thing since then, time ends and space ends. The singularity is like the edge of the universe.

But string theory makes away with singularities and instead of creating a singularity it should stop contract at the Planck length(10-33cm). I will still use the term ‘singularity’ since string theory isn’t proven right.

And when the star collapse and forms the black hole, all information about the star and all the irregularities(i.e mountains e.t.c) gets destroyed and it’s impossible to from the black hole deduce what the star which created it looked like. It’s said that a black hole has “no hair”.
To get away from the gravitational pull of earth, e.g when a space ship is going out into space, you need to accelerate yourself up to some velovity. This is called the escape velocity(actually, since gravity is a force which acts over an infinte distance you can never really get out of an objects gravitational pull. But you can get as far away so that the pull become insignificant, so better stated is that escape velocity is the velocity you need to get so far away so that you don’t notice a planets gravity). But the singularity creates such a immense gravity around it so that not even light can escape from it, it has a escape velocity higher then that of light. And since light has a constant velocity and nothing can move faster then light, then if light can’t escape from the black hole then neither can anything else. The distance from which light cannot escape doesn’t lay exactly at the singularity itself. It lays some distance away from it, and how far away or how big the black hole is, is determined by how strong its gravitational pull is, and so on how massive the star which collapsed and formed the black hole was. The border from which not even light can escape is called the ‘event horizon’.

The singularity disserves a more in-depth look. What happens when you fall into a black hole and its event horizon?
Lets say you throw youself toward the hole and its horizon. And you buddy(who is happy to get rid of you) stays at a constant position somewere outside the event horizon.

In Einsteins theory of relativivty, gravity causes time to slow down but in the same theory time isn’t anything constant, time is measured differently by different people or ‘observers’ it’s said that they are in different reference frames(a reference frame depends on how big gravitational field the observer is in). As you plunge towards the hole you have a little radio with you, and every second it sends out a little ‘peep’ to your friend. Your friend will notice that the closer you get to the event horizon the interval between the peeps will get longer and longer, it will take longer time then one second between them. And when you are right at the event horizon your buddy will no longer hear any peeps. From his reference frame you will fall untill you hit the event horizon. But then you will freeze at the event horizon, to him it will look like time has stoped(because of the gravitational field you’re into).

But to you, time continues as normal. you pass the event horizon. Then you would first get stretched more and more until you reached the singularity and gets crushed into zero size.

But a black hole doesn’t have to bee the final end station for everything which falls into it. If the black hole is rotating(if the star which formed the black hole rotated the black hole will also rotate) there is a chance that you can ‘miss’ the singularity and fall out of a white hole(see below). There’s also a couple of proposals in which the implosion might change into an explosion. But not an explosion into our universe, but into another. In fact a black hole might create a new universe. When it collapse from our universe it would start to inflate spacetime into another universe. This new universe would be connected to ours only by the black hole. So our universe might be a black hole in another universe.

There seems to be a problem with black holes and thermodynamics. Thermodynamics is a part of science where you study how large groups of particles works. Thermodynamics has a set of laws. The second law of thermodynamics state that entropy in a closed system always must rise.
Entropy is a measurement of distortion or chaos. To see why it should always increase, we could take a normal example of your untidy room(I know you got one). An untidy room is a room in chaos, things lay around everywhere. Lets say hypothetically that you do decide to tidy it(an action forbidden by the laws of physics). Then it might seems like the entropy is gone, and everything is neat and ordered. But in the process of cleaning you developed heat by the effort and also started to breath faster. All those things cause the molecules in the air to move around in a chaotic fashion and in fact the total entropy has increased. (CONCLUSION: Never tidy your room. You’re wasting entropy).

But a black hole could get rid of entropy. Since everything inside the event horizon is cut off from our universe, you could throw the entropy down into the hole. Then the total entropy in our universe would have decreased and the second law of thermodynamics would be violated.
A thought would be that the black holes horizon was a measurement of its entropy, the larger horizon the more entropy. This would make sense, since the more you throw into a black hole the more it grows. There’s just one problem, entropy also means heat. Think of one litre petrol, in it the molecules lay orderly, it has low entropy. But the if you burn it, the molecules starts to fly around in a chaotic pattern, it now has high entropy. So motion equals entropy, and motion equals heat. So the black hole should radiate.
So if a black hole has entropy should radiate heat. Which seems ridicules since a black hole only sucks things into it, right?