I've been fascinated with black holes ever since the Disney movie The Black Hole came out in 1979 (I was 7). I actually dragged my family back to the theater to see it a second time, because I was so intrigued by the idea and scope of it. While the irony of Anthony Perkins being killed by a blade-wielding robot was lost on me, the whole idea of black holes, a place where the logic of the universe as we know it ceases to exist, irreversibly lodged itself in my brain.
I think most people know what black holes are, but here's my attempt at a nutshell definition anyway: when a truly massive star collapses at the end of its life cycle, its own mass crushes it down into an infinitely small point, creating a spherical area around it where gravity is so strong that nothing, not even light, can escape. It essentially creates a hole in space, pulling in everything around it, never to be seen again. Since, like I said, light can't escape, there's no way to see it. It's totally black... hence the name.
Now, gravity by itself is a pretty weak force. Pick up any object, and you're singlehandedly trumping the fact that the entire Earth is trying to hold it down. But gravity has two things going for it: it's everywhere -- every particle in the Universe pulls on every other one -- and it never, ever rests. There are no known exceptions to gravity. Which makes black holes all that much more impressive.
I remember reading in the movie's tie-in magazine that black holes were theoretical. In 1979, no one had ever observed one (which is kind of a weird way to say it, because by definition you *can't* observe one... you have to look for its effect on things around it). By now, we've learned that not only are they real, they are responsible for the formation of galaxies, most of which (including our own Milky Way) have supermassive black holes in their centers.
In the movie, the surviving protagonists (35-year old spoiler alert!) actually manage to fly through the black hole and come out... well, somewhere else. Of course, no one knows whether black holes actually go anywhere. That was kind of a problem for physics, this bottomless pit that seems to defy the second law of thermodynamics -- it seemed like all the stuff that fell in had to end up somewhere. But then Stephen Hawking realized that everything *does* radiate back out, just one particle at a time, super-slowly. It makes me think of a far-future Universe where all the stars have burned out, and there's nothing but these black holes slowly spitting reconstituted matter back out into the otherwise empty, ever-expanding Universe for quadrillions of years...
But that's what I love about black holes. They take everything we think we understand about space, time, matter, and energy, and push it to extremes. And there are all kinds of cool thought-experiments you can do with them. One of these -- which you can hear Neil deGrasse Tyson giddily describe in many places -- is how your body would be stretched if you fell into a black hole. When you're that close to such a strong gravitational body, its pull on whatever part of your body is closest to it (I'm assuming that's your feet, because we tend to think of gravity's pull as "down") is much stronger than the pull on the farthest part. The closer you get, the bigger the difference in pull, so you'd eventually be stretched thin and broken apart into smaller pieces, which would then also be stretched and broken down.
I actually got to see Dr. Tyson speak at the home office of Borders (back when that was a thing). And his description of "spaghettification" -- the official term he's been campaigning for when talking about this phenomenon -- led me to start wondering not so much about what would happen to you if you fell into a black hole, but what you would *see*. Disregard the fact that your eyes would be just as spaghettified as the rest of you... what would falling into a black hole look like? Well, here's what I've come up with... Again, feel free to have any physicists you know tell me whether/where I've gone wrong.
The main thing has to do with what we call the "event horizon". It's essentially the spherical "edge" of the black hole's full effect, inside of which nothing can come back out. It looks black to you because no light inside its boundary can come out. But let's say *you* drifted across this boundary. The Universe wouldn't suddenly go dark, because light can still come in through the event horizon, exactly like you just did. You can turn around and see perfectly well where you came from, because the only light that can't get to you will be that which is now closer to the black hole than you already are.
And this, I think, would create a weird optical illusion. Rather than being aware that you've passed any kind of barrier, you would appear to be continually hovering on the edge of the event horizon, which would be getting smaller and smaller. Not only that, but the light around its edge would get more and more severely bent as the gravity ramps up (in fact, now that I think about it, some light would actually go whipping around the back side of the hole and come back at you, meaning you could conceivably see a super-distorted picture of yourself!).
The weirdest part -- assuming that I'm understanding the physics right -- would be that the same kind of distortion would happen with *time*. You see, Einstein's theory of special relativity says that you can cause time to move slower for yourself in several ways. You can either move through spacetime, or you can be in the presence of a strong gravitational force.
Both of these things have been measured here on Earth. People who spend a significant amount of time traveling at great speeds (say, those on the International Space Station) live at a slightly slower speed than we here on Earth do. That's been proven -- GPS satellites actually have to be programmed to compensate for time dilation when they're locating your phone as they whizz by overhead.
It works the same way with strong gravitational fields... the harder you're being pulled by something, the slower your personal time goes. Given that, it makes sense that moving in to a progressively stronger and stronger gravity well makes your personal time slower and slower...
But here's the catch with slowing your personal clock... time doesn't actually appear to pass differently from your point of view. Everything else around you just moves faster. That's general relativity at work... because physics-wise, there's no difference between you walking down the street at three miles an hour and the earth turning under your feet at three miles an hour.
So here's what I think would happen if you fell into a black hole... Like I said, you'd appear to be hovering on edge of an ever-shrinking event horizon, which would have a larger and more distorted halo of bent light around it. When you turned around to look back at where you were... you would get to see the Universe evolve in fast motion. Although time still ticks along normally to you, you're actually speeding faster and faster into the future. You'd see the galaxies start accelerating... centuries, millennia, and then thousands of millennia of the Universe's evolution passing right before your eyes.
And, if the theory really is correct that in the very center of a black hole, mass collapses into an infinitely small point and thus creates an infinitely strong gravitational field... you would see the entire future of the Universe before you reach that center. In fact, the Universe itself would end before you actually get there. It would be like the ultimate fireworks display.
Of course, this is all providing you can hold your body together long enough to witness it, which I guess is true even if you're not falling into a black hole.
(One caveat: because the speed of light is always constant from your perspective no matter how you're moving through spacetime, I think that the eons of light piling onto you would be of ever-higher wavelengths. So you'd soon be unable to actually "see" the ensuing x-rays and gamma rays that would start pelting you, but let's assume that you have some kind of tech that could translate it into visible light for you. Cool?)
No comments:
Post a Comment