Black Holes - Part 2

The Great Escape

This is the second post on the subject of Black Holes. In the first post I went on a little about General Relativity and how it describes the universe. The post then went on to discuss the idea of escape velocity and how it could be possible to have an escape velocity that was actually greater than the speed of light. In other words nothing, including light would be able to escape from such an object.

The secrets to most of this are held in the Einstein Field Equations, which as mentioned are rather difficult to understand. But that has not stopped some of the braver souls out there.

In 1915, Karl Schwarzschild managed to get a solution to the Einstein Field Equations for the gravitational field outside a non-rotating sphere. The solution had a rather bizarre property in that it contained a radius which became known as the Schwarzschild radius. It seemed that if all the mass of the an object was compressed within this sphere then it would be possible to create a situation where the escape velocity was greater than the speed of light.

Further, the gravity resulting from having so much mass compressed into this sphere would be the creation of a singularity.  The physical significance of this singularity was debated on and off during the decades taht followed.

In 1931 Subrahmanyan Chandrasekhar showed that if a star was above a certain mass then it could actually collapse under its own gravity (when its fuel ran out) and shrink to a size smaller than the Schwarzschild radius thus become what has been described as a singularity. The star would shrink and get so small that the entire star would end up smaller than an atom while having pretty much the same mass. The singularity is so small that is has no physical size!

(I'll be straight with you, I have a serious problem with the idea of a singularity because it is so small that it doesn't actually exist! and yet we are told that it does exist! Personally I can't help thinking that when this catastrophic collapse happens we get ourselves a type of Bose Einstein condensate, more on this in another post.)

For now we will continue with conventional wisdom. The big star collapses to give a singularity with a massive gravity. As the distance from the singularity increases the gravity will start to shrink and so will the escape velocity. At some distance from the singularity the gravity would have diminished enough that the escape velocity is the speed of light. Any further and light can happily escape the clutches of the singularity. This distance when the escape velocity equals the speed of light is known as the event horizon which is the Schwarzschild radius.

It is interesting to note that general acceptance of the possibility of a black hole did not occur until the second half of the 20th century. It was only around about  the1950s, just prior to the death of Einstein, that General Relativity entered mainstream theoretical physics. The next 30 years can be described as a golden age of General Relativity and Black hole theories.

This was helped by the discovery of pulsars by a hero of mine,  Jocelyn Bell Burnel, this will be covered in a later post, which were shown to be neutron stars. If neutron stars could exist why not black holes?


During the 60s and 70s contributions from Roger Penrose and Stephen Hawking, James Bardeen and Jacob Bekenstein helped solidify the ideas of black holes by developing a number of theories describing the properties and behavior. It was during this time the term Black hole was first introduced to describe a singularity and is usually attributed to John Wheeler.


But  here is the thing. Although all these really clever guys have spent years pondering and coming up with theories and ideas, the question remains do they actually exist?

Well the answer is we still don’t know. What we do know is that Einstein’s theory of general relativity made a number of other predictions that are backed up by experiment. So if we work on the bases that if these positive results show that the theory may be correct then it makes sense to assume that some other predictions, such as black holes, may also be true. That is why we THINK there are black holes, but we don’t know for sure.

Another theory may come along which explains the things that Einstein got right and have been tested and then goes on to show why black holes can't exist!

Personally I don't think black holes do exist. It just doesn't seem right to me. I accept neutron stars and I can believe that gravity can get so great that even the Pauli exclusion principle (the theory explaining why neutron stars don't collapse to black holes) may be over come, but that is where it ends for me. See I think at this point the following may happen.

The star collapses so that it is smaller than the event horizon. Neutrons (fermions) pair up and become bosons, the star then collapses into a Bose Einstein condensate.  Rather than continuing the collapse into a singularity, quantum effects take over and become apparent on a macroscopic scale. We then get something akin to Quantum tunneling where a particle tunnels through a barrier that it classically could not surmount. In this case the particles actually tunnel through the event horizon. Due to the increased gravity, particles get squeezed out much like toothpaste and appear, due to the rapid rotation of the "black hole" as a disk.

You can cross the event horizon and escape again. 

In this solution we get an event horizon, but what we don't get is a singularity.

So I suppose I do think there may be black holes, but I don't believe that there are singularities at the center.