We hear about “Black Holes” all of the time in our daily lives. The term refers to a situation where a question is asked or a request made, and nothing ever comes back. This is, of course, a popularization of the phenomena from Physics.
Black holes are essentially dark regions scattered through the universe. They are areas in space made up of matter that is incredibly dense. Due to the gravitational pull, virtually everything is pulled into this area, and virtually nothing can escape. The idea of such a concentration of extreme mass has been around since the 1700’s, but the theory that they actually might exist only became more accepted after Einstein came up with his general theory of relatively in the 1930’s.
It is impossible to see a black hole because no light can escape from them. The edge of a black hole is called the event horizon. Once the event horizon is passed, no object (light) can be seen. Theoretically, if the event horizon could expand rapidly enough, everything in the universe could be swallowed up. However, due to the massive amounts of mass and gravitational pull in other parts of the universe, the event horizon reaches a point of stasis or equilibrium.
There is what is called a point of singularity in the center of a black hole, which is where the force of gravity is theoretically infinite. It compresses all of the matter within the confines of the event horizon, event light. To give an example, if 10 of our suns were compressed into a black hole, the radius of the black hole would only be about 30 kilometers.
According to the theories, black holes are formed from supernovas, which is the explosion of energy when a supergiant star is blown apart. During the explosion, most of the energy is used up through a fusion reaction so the gravity of the star gets denser and denser. There is not enough energy left to repel the mass of the star so as the matter gets closer and closer together, the amount of gravity increases as well.
Inside a black hole, the gravity is so intense that it is theorized to distort space and time. Even light cannot escape because the speed at which light travels is lower than the escape velocity required for escaping. To give you an idea, Einstein’s theory proposes that the speed of light is 186,000 miles per second and that no object can surpass this (Sorry Star Trek fans). The escape velocity of a black hole within the event horizon would thus be greater than 186,000 miles per second. As a contrast, the escape velocity for Earth is about 7 miles per second (forgetting air friction).
The mathematics behind these theories is very very complicated. It involves a set of theoretical constants and theoretical “knowns” like the mass of the black hole, which are themselves products of other advanced theoretical “knowns” and constants. Suffice it to say that formulae are derived to explain theories and when the last figure fits, the theory is said to be explained. It is this way with black holes. Mathematically we know they are there, and we also know they are there because of what we don’t see – light in certain regions of the universe.
We also know that supernovas occur about once every 300 years or so in our galaxy and go on to form neutron stars, which are the objects that eventually collapse in on themselves when they get too large, and form black holes. We have identified several neutron stars using radio telescopes and, in neighboring galaxies, about 500 neutron stars exist. Physicists are thus pretty confident that there should be some black holes.
So, other than providing lifetime employment for physicists, what are black holes really good for? They have figured strongly in various science fiction stories over the years. In these, they are seen as potential gateways to alternative realities, gateways also for time travel since time moves differently in and close to black holes. In order to escape from a black hole, you would have to travel faster than the speed of light; hence all t\of the “warp drives” on starships.
Given that nothing, once inside of the event horizon, can escape, some people have more or less jokingly proposed that black holes could be the ultimate garbage dump. Others have thought that if they could “control” a black hole and its’ event horizon, it would represent the ultimate super weapon. Of course, that is like riding a wild tiger – what do you do when you get off?
Now, we come to the big conundrum. The laws of Quantum Physics tell us that matter can be neither created nor destroyed. Black hole theory basically has said that matter entering a black hole is effectively destroyed, or in Stephen Hawking’s terms, sent to some parallel universe. Theoretically speaking, eventually all matter would be consumed and destroyed (eventually is really too small a word to use here).
Hawkings theories and mathematics are truly the stuff of genius. His thinking has been so profound and elegant that most have simply accepted his constructs and moved forward. His black hole theory became popular in the late 1970’s and 1980’s. However, he began at that time to rethink, and his rethinking related to the paradox mentioned above with respect to quantum physics.
He reported to the 17th International Conference on General Relatively and Gravitation that he had solved the black hole information paradox and wanted to talk about it in front of the conference. He was granted the audience, which took place July 21, 2004 in Dublin. Hawking, who is Professor of Mathematics at Cambridge, has been wheelchair bound since his 20’s due to suffering from amyotrophic lateral sclerosis, know commonly as Lou Gerhig’s Disease, and communicates via computer and speech synthesizer.
Essentially Hawking now feels that black holes do not destroy everything they consume, but rather hold their contents and eventually fire it back out into the universe when they desintigrate and eventually die. The process takes eons. Given that the basic information is preserved, there is no possibility according to Hawking that one could use black holes to travel to another universe. The mass energy eventually returns out to the universe albeit in a mangled and more or less unrecognizable form.
While Hawking was only able to present for an hour, and simply sketch out his theory, he was pleased to be able to come up with a solution to the paradox that had troubled him and others for more than 30 years. He will present the detailed mathematics behind his findings at some point in the near future, where his colleagues (and critics) will go through the constructs and equations in high detail. So at the end of the day, what are black holes? Not unlike us…complex entities whose identities grow more complex as they evolve. And that is the job of physics. It is about evolution and discovery.