Everybody loves black holes (part III)
I’m reasonably certain that the thing the majority of people out there find most interesting about black holes is their power to totally annihilate any matter unfortunate enough to get too close. It is pretty cool. Granted, if you were to step onto a neutron star, you’d be flattened into a thin, greasy film immediately, but it’s still not as exotic as what happens as you pass an event horizon. Of course, in that situation, perspective matters.
Let’s get one or two things out of the way though. First, despite what many movies would suggest, you can’t fly into a black hole and come out the “other side”, having traveled back in time to rescue your great-great grandfather from pirates or into an alternate reality where it rains donuts. Remember the neutron star example in the previous paragraph? Those are the things not quite dense enough to become black holes and you’d have about as much luck trying to fly through one of those. Second, to understand what happens “inside” a black hole, you have to open your mind to ideas that don’t play well with common sense experiences. If you’ve ever used a GPS (or even believe that they are real) you have been shown that Einstein’s theory of Relativity is an essentially perfect way to understand the relationship of space-time and gravity. Some of the concepts that allow us to understand this relationship seem counter-intuitive. but after 100 years, even with this recent neutrino fiasco, his theories hold up and are going nowhere. We know it works.
So, let’s get to it. You and your space faring buddies are exploring the old remnant of a supernova and all of a sudden, you realize you’ve flown right into the gravity well of a black hole! Oops. Don’t worry though, it’ll all be over soon.
As you approach the event horizon (also called the Schwarzschild radius), some unexpected things would happen. From your perspective, the event horizon would appear to recede as you approach. Your buddies, observing you from a safe distance, might see you pass through the point of no return, into the blackness, but for you, this is just the beginning of the end. Light is being bent around you and the event horizon you see is now not quite the same thing you were looking at before. How long you have left at this point now has everything to do with how massive the black hole is. Keep in mind, the singularity doesn’t have any size, but the apparent size of the event horizon is dependent on the mass, so the more massive the singularity, the larger the Schwarzschild radius/event horizon. Since this is a “stellar mass” black hole, your trip is a tiny fraction of a second. Blink and you miss your own demise.
Gravity’s pull follows an inverse square law, so if your pals are ten times further away from the singularity, the force on them is 1/100th what it is on you. This only ramps up, fast, as you fall in. Thanks to the way gravity works, when you’re standing up, walking around on earth, the watch on your wrist is actually being pulled towards earth’s center of gravity less (and ticking a bit faster) than the one on your ankle. Everyone wears two watches like that, right? Anyway, for we earthlings, this difference in force is SO small it requires a finely tuned gravimeter to detect it and it takes an atomic clock to measure the time dilation. But for the unlucky you on your way to singularityville, this becomes, um… more “pronounced”.
By the time this is going on, your watches don’t work anyway. You’ve been instantly pulled apart, starting from whatever unlucky part of you was closest to the singularity, let’s say your feet. The light by what’s left of your head has been shifted into the red, your feet into the blue. It’s all over. Your body has been torn to atoms, your atoms have been stretched out into their subatomic components and those have fallen into that infinitely small and dense point that has been your final destination. The black hole has gained a minute bit of mass and absolutely nothing is left of you. When you crossed the event horizon, you had become separated from space and time and all the information that was you, was gone at that moment.
Here’s a video associated with this article that illustrates this journey.