Black Holes or General Relativity in a Coffee Break
Black holes, one of the most mysterious constructs in space, were discovered almost by accident. When astronomers were looking through some high-powered telescopes, they noticed a strange phenomenon. Identical objects in the sky. The chance of having two masses in space emitting exactly the same light and taking exactly the same form is so low that this merited a second look. Using principles of gravity, they were able to figure out that light was bending around a massive object, and coming to earth from two different directions. In order to get a good idea of just how this phenomenon worked, they examined objects that were viewed as being 'close' to the sun, and found that depending on where the earth was in relation to the object (ie, on the object's side, or with the sun right beside the viewing angle), light from distant objects bent around the sun and came to earth from a different direction. The main problem was that when they used the same equations on these distant stellar objects, the mass of the body that was bending the light was so large that if it was of any reasonable density, we shouldn't have been able to see the object at all!
The natural reaction to this finding was that there had to be super-dense objects out there, so dense that if the entire earth was compacted in to one of these 'black holes', it would be the size of a small marble. The name 'black hole' came from the fact that at this density, the escape velocity (or the speed at which an object must travel to escape the gravitational field of the body) was faster than that of light. This explained why we couldn't see them. The first big theory concerning the nature of black holes was published in Einstein's theories of General Relativity, in which he conjectured that time passed slower near massive objects, and that the universe essentially had a fourth dimension, density. This four-dimension concept is important, verified by experimentation, and the subject of a few misconceptions. The idea that time is a fourth dimension is false. The universe is established as a vector space, and without going in to the math, the logic is that since time vectors can't have inverses, time can't actually be a dimension. Regardless, the fourth dimension concept makes the universe impossible to visualize, because the human brain can't make pictures in any number of dimensions greater than four, so the best way to interpret it is to hold one dimension 'constant' and to figure out things based on the three-dimensional result. In science and engineering, the density factor is usually held constant, which lets us build buildings, and plan the trajectories of rockets, etc. Now let's see what happens when we instead hold one of the directions constant, and imagine that our three-dimensional plane of existence is actually two-dimensional.
The third dimension, which we like to call density, makes the universe look like a sphere, with the normal 3d world as the surface of that sphere. Before we go any further, remember that this is just an abstraction, because the universe may act like a four-dimensional sphere, but that doesn't mean that you can actually 'see' density. Super-dense objects are viewed as creating indents in the sphere, and theoretically, infinite density would place an object at the center. This concept brewed the 'wormhole' misconception, which was that going close to a dense object would make the distance from point A to point B smaller. The problem is that this assumes that we can go inside the sphere, which we can't. Our 3-d world is just the surface area, and it's impossible to exit the surface area my any means. If that doesn't make sense, grab a piece of paper, draw a stickman, and then draw a line to another point in the paper. Even if you bend the paper so that the stickman is a millimetre from his destination, nothing he can do will let him take any other path than the line if he actually wants to get there. This may seem like a trivial fact, but it actually led scientists to test and prove some of their predictions.
In math, there are calculations for 2-d geometry on a sphere, and one of the biggest things to notice is that triangles don't have their angles add up to 180 degrees. A fun fact is that the angles in the triangle between the sun, the moon and the earth don't add up to 180 degrees, which was verified in order to prove the space curvature theory. An important result of this theory explains why time passes slower closer to massive objects than it does elsewhere. The actual reasons for this result are complex and related to more modern physics, but it's interesting to note that when we flew atomic clocks up in to the stratosphere and compared them to atomic clocks on the earth (after a few days of flight), we found that the ones on earth had actually recorded less time than those up in the sky.
So we've discussed dense objects, but what about black holes? Black holes hold all of the properties of dense objects, meaning that time passes a lot slower when in close proximity to one, that light that escapes from nearby objects get shifted to be more red (this happens because the wave frequencies get changed by the differing passage of time, much like how sound waves change when they go from a dense medium to a less dense one) and that light bends around them. It’s also interesting to note that any light that gets really close to a black hole has the chance of going in to orbits, or spinning around and possibly even coming back in the way that it was sent. This phenomenon has few recorded sightings, simply because most black holes are surrounded by a big cloud of dust.
Black holes also have a significant place in theories of how the universe may end. It was a common thought that it was possible for the entire universe to become one big black hole, since nothing can escape from them. This theory was dropped after Stephen Hawking showed how photons could escape the surface of a black hole in the form of infrared light, since escape velocities don’t account for the energy levels and some results of quantum theory that apply to them. This means that large black holes radiate energy, and slowly lose mass until they die, meaning that there’s almost a cyclical nature to them. While this does suggest that it may be possible for the universe to end in ‘heat death’, which happens when all matter and energy is equally distributed around the universe, a contending theory says that there is a push/pull between entropy and the collection of mass that may allow the universe to persist indefinitely.
Right now, scientists are examining black holes to try to gain a better understanding of matter when it is put under high pressure. It was initially believed that black holes were so dense that electrons were forced in to protons in order to create masses of neutrons, which would be compressed in to a lattice inside of a black hole, but newer readings are suggesting further breakdowns in the composition of matter at this state. Anyways, I hope you enjoyed reading up on black holes. If you enjoy these kinds of articles, check out these other ones, concerning Special Relativity and Quantum theory: