Black Holes 101

What is a black hole? It is a certain distance from a singularity. That certain distance is the point where the escape velocity of the singularity is the speed of light.

The escape velocity is that speed at which an unpowered projectile (a photon, a bullet, a ball) must travel to continue moving indefinitely away from an object (usually the object is a planet, moon, star, etc.). It is important to note that the limitation of escape velocity applies only to unpowered projectiles. Once the photon is moving at its speed or the gun has fired the bullet or the ball has been thrown, the projectile in question can receive no more power.

A powered projectile, such as a rocket, does not need to reach escape velocity in order to pull away from the Earth. It just uses more power to dig its way out.

Therefore, in simplest terms, no unpowered projectiles can leave the inside of a black hole due to gravity because the surface of a black hole is where the escape velocity is the speed of light. And no thing can travel faster than the speed of light (according to our best knowledge today).

A singularity, which creates the black hole, is a collection of mass that has (for whatever reason) generated so much gravity that the force of its gravity is greater than any of the other forces that exist and so no force stops it from contracting to the smallest possible size.

It is at this point that there is a difference of opinion. Some scientists feel that the collection of mass shrinks to zero size while others feel that there is a lower limit to the size. I am of the latter persuasion and will continue on that vein.

As a side note: it is often said that the gravity of a black hole is infinite; this is wrong. It is properly considered to be the highest source of gravitational power and it is AS THOUGH its power were infinite because the fastest thing in the universe, light, cannot escape from it.

So the proper picture of a black hole is that there is a singularity in existence that exerts great gravitational force. There is a distance from the singularity at which the escape velocity is the speed of light, which is also called the event horizon, which is the "surface" of the black hole.

There are also distances from the singularity at which the escape velocity is substantially less than the speed of light and distances at which the escape velocity is a leisurely stroll.

The reason that there is so much hoopla about a black hole which is only a singularity and a certain amount of space surrounding it are the events which occur at the event horizon and those that occur closer to the singularity (where, for simplicity's sake, the escape velocity is some given figure above the speed of light, also ignoring that nothing of which we know can go faster than the speed of light.)

For the sake of simplicity, we will ignore the fact that the gravity at the surface of a black hole is so great that anything would be instantly flattened/destroyed/and so forth. We will simply assume that a person can stand on the surface of a black hole for our experiment and let it go at that.

I have been leading up to what is so fantastic about black holes (and the following is just the tip of the iceberg) and here it is.

Einstein put forth the idea that time does not pass at a constant rate everywhere in the universe. All our normal lives, we have accepted the notion that time passes at the same rate everywhere because that is what we experience.

A pair of twins is used in this experiment. They are (essentially) the same age; that is, they are both a certain number of years old. One stays at home and the other takes a trip around the world. When the traveling twin gets back home, will she be a different age than her twin brother?

Of course not. That is a ridiculous question.

What if she flies in a plane for a hundred years going around the world non-stop all that time? Then would she be a different age than her twin brother when she gets back?

Of course not. Are you taking the drugs or something? This is all common sense, you know.

And so, it was all common sense for thousands of years until Einstein thought about traveling at the speed of light in his thought experiments. Suffice it to say that he eventually came to understand that if one were to travel at very close to the speed of light, time for the traveler would pass at a different rate for the traveler than for the brother at home.

It is now accepted by science that if this twin girl were to travel at near the speed of light, when she returned she would be much younger than her stay-at-home brother. Simply, time passed more slowly for her.

But what does this have to do with the fantastic gravity machine that we call a black hole?

It turns out that the same thing that happens with time at the speed of light ALSO happens in gravitational fields. Simply put, the more gravity an object experiences, the slower time passes for that object.

So if you were standing on the surface of a black hole, an outside observer looking at you would see that you stand perfectly still for all time. AND you would see all of time pass in the very shortest time. Your stay-at-home brother would age billions of years (given that he stayed alive) while you do not age but one tiny bit.

As I said, this is only the tip of the iceberg when it comes to the fantastic things that occur in relation to a black hole.

The next step is to take this thought experiment one step further. If time slows to the slowest possible speed at the event horizon of a black hole, what happens when you move into a stronger gravitational field to increase the effect of time dilation?

The answer is: we don't know yet. Everything up to this point has been worked out mathematically. However, to calculate what happens further into a black hole requires math that doesn't exist... yet. The math would have to allow you to divide by zero and by non-imaginary, non-negative, non-fractional numbers less than zero.

So would you be so kind as to take this challenge and invent such a math? Someone has to do it eventually and it surely won't be me; I am too tired.