The Darkest Corners of the Universe

Okay, black holes might not be corners, and sometimes they can be ironically bright, but we still recognize them as some of the darkest things around. The idea of black holes has been around for a long time. Since Einstein's theory of general relativity, physicists have solved the equations for a variety of different situations in which the equations could be useful. Eventually, the object is squeezed into a such a small volume that the density of the object approaches infinity. As the density approaches infinity, the change in curvature of space-time is so strong that nothing, not even light can escape its gravitational force. This is the basic explanation of a black hole.

Since black holes were theorized, they have been a huge part of the physics pop culture, everyone hears about black holes and wants to know more of what they are, and for good reason. They are some of the most exotic objects in the universe, and they can do some pretty crazy stuff, and we really don't know much about them.

As I said, they are basically an infinite source of density. This is referred to by physicist and mathematicians as a singularity, because it is impossible to actually deal with numbers at infinity. Instead they look at how things react when they approach infinity. 

Since the centre of matter is so condensed, this is not actually what you "see" if you were to observe a black hole. You would really see the event horizon, or a point of no return for the black hole. If something were to pass a black hole's event horizon, it would be gone forever. At this point the gravitational force is so strong that nothing could pull the object out. As you passed the event horizon, nothing would change from your perspective. You would pass through without nothing changing at all to you. As you approach the singularity at the centre, gravity would get so strong and would change so drastically as you go further that you would get spaghettified. Your feet would be pulled stronger than your head and you would literally be stretched out like a piece of spaghetti. Eventually, you would reach the centre of the black hole but your body would have gone through so much force that you would not recognize yourself. You would be a lifeless clump of matter.


This creates another interesting problem; what does an observer on the outside see when something falls in? According to general relativity, the object would be redshifted. What this means is as the object approaches the event horizon, the observer on the outside would look like they are constantly moving further and further away, so the wavelengths of light get longer and longer until they essentially disappear before ever crossing the event horizon.

Another answer to this question, from the point of view from string theory, is something called a firewall. As the object passes the event horizon, nothing on the inside of this area can ever get out, not even light so it would be impossible to see the object past this point. Obviously we don't see the object just disappear, instead we see something called matter annihilation. This is just as extreme as it sounds. Basically the object entering the event horizon appears to be completely converted into energy. This gives a pretty good ending to the object on the outside, but really it falls forever to infinity at the centre. When dealing with singularities and infinity, these counterintuitive paradoxical situations are essentially a necessity. Infinity does strange things to the world.

Now that you have the basic idea of what a black hole is and where the problems come from, we will be able to go even deeper into these conundrums of the cosmos in the next posts.