Upon Reflection

Black holes are often seen as a prediction of Einstein's theory of general relativity, but black holes also appear as a consequence of Newton's law of gravity. If the universe obeyed Newtonian gravity exactly we would still have black holes, albeit of a slightly different form. To show this, all we need is ask the question "how much energy does it take to escape from a planet?"

The basic model of a black hole can be summed up as follows: gravity wins. The root cause of all black holes—be they tiny primordial black holes, solar mass black holes, or supermassive galactic black holes—is gravity. Squeeze enough mass into a small enough volume and gravity does the rest. The problem (at least according to general relativity) is that gravity does its job too well. Once matter enters a black hole, it simply cannot resist the pull of gravity. As a result all the matter within a black hole is squeezed down to a point of zero volume and infinite density, known as a singularity.

Science is about being specific. Scientific terms such as energy, speciation and fusion have very specific meanings within a specific context. These terms often have common meanings as well. If we say that reggae music is a fusion of calypso and jazz, we don't mean it was created from calypso and jazz nuclei in the core of a star. But while words can have poetic and even multiple meanings, their scientific meanings are precise. This difference between scientific and general word usage can be difficult to distinguish without practice. When these two uses get mixed up, all sorts of problems occur.

One of the challenges of astrophysics is interpreting what we observe. Here on Earth we can set up experiments to test phenomena, but when it comes to the cosmos all we can do is sit back and watch. We've sent probes to the furthest regions of our solar system, but even that is just a tiny corner of the heavens. So how can we possibly know that there are galaxies light years away, or that the universe is billions of years old? The answer is that we take what we know about physics here and apply it to what we observe there. This process can often be complicated, but sometimes even a little physics can tell us a great deal.

For example, consider pulsars.