If you have wondered where I have been, then you have no reasonable activities in your life. But let’s put that aside. I am writing here again.
What do you know about black holes?
I assume that anyone with an Internet connection has heard of black holes. That doesn’t mean those same folks really know anything other than junk science from movies and TV and fantasy stories. Kinda like political news, only worse. A bit of not too technical pieces of information to start us off.
Black holes are a whole lot of stuff crunched down to a size that is so tiny we can’t really imagine it. As physicists would say, it’s a whole lot of matter. Really they would say it is a region of spacetime that has is so warped that electromagnetic radiation attracted into it cannot escape; since light is electromagnetic radiation, the term black hole is used to say that no light can be seen from outside the black hole.
I doubt if this helps you understand even a bit about black holes. Let’s try some lame analogies that should help. Take a heavy (to us) object like a bowling ball and place it in the center of s bed sheet tied at its four corners. The weight of the bowling will cause the sheet to sag in the middle. If you were to drop a ping pong ball onto the sheet, you realize it would roll to the center and land next to the bowling ball.
Roughly, that is spacetime curvature. A massive object with its gravitational field curves spacetime. If you vaguely remember science, you may recall being told that light will curve as it passes near a massive object. It isn’t really curving, like a car on a road or a curve ball, but rather following the curve in spacetime the large body has caused. When Einstein proposed the Special Theory of Relativity, one of the predictions is that during a total eclipse of the stars that were actually behind the sun at that time would be seen on the side, displaced from their real location. In 1919, these predictions were found to be true.
Curvature of spacetime has implications for time as well as space; what a surprise. If space is curved near a massive body, it means that light or anything else traveling near it follows that curvature, and the path it travels is longer. Relativity predicts, then, that to a stationery observer farther away, time slows down. What? I got you to understand the bowling ball thing but not that your watch is affected? Relatively says it depends on your point of view, and it does.
Suppose you are wearing a special watch that flashes a beam of light once every second. And suppose you are on a space ship traveling near a massive body which curves spacetime. To you, your watch keeps flashing once every second. To an observer quite a distance away, not in the significant curvature of spacetime, your watch is slow because, even though it flashes once every second to you, the curvature of spacetime gives light a longer path to travel to reach the observer. hence your watch needs adjusting.
Apply this to black holes
So much matter is in a black hole that spacetime is curved so much that light can’t travel out of it. In other words, spacetime has curved so much that the path light must travel is far longer than the 186,000 miles per second speed that light is limited to zooming around. It is not, then, some form of cosmic Velcro that grabs hold of light and won’t let it go. It is that space has gotten so big that there is nothing fast enough to travel across it.
What is the implication for time, then? Think about your watch with the flashing light. If you and it fall into a black hole (we’ll mention the effects on you and it later) what would you see from the outside? As the watch got close to the edge of the black hole, curvature would be so great that light would take a very long time to travel to you. Hence, you as an outside observer, would think the watch had slowed way down. Then it falls into the black hole, no light comes out, so you would think it has stopped completely; you would never see a subsequent flash of light. That doesn’t mean that inside the black hole, wearing the watch, you would see it still running at one flash per second. (It wouldn’t actually work that way but let’s ignore that for now).
Orbiting a black hole
Suffice it to say that at the right distance from a black hole inside your space ship traveling at the right speed, you could orbit a black hole. This ignores angular momentum, relativity and some other stuff that we can briefly – and permanently for this blog posting – ignore. So you go round and round. Just close enough to the black hole but not too close. You want to stay away from the event horizon. The what?
Imagine you are in a canoe on a river upstream from a big water fall. As the river nears the waterfall, the current increases and your canoe goes along with it. If you aren’t too close, you can paddle hard and turn around back upstream. But get too close to the waterfall and you can’t paddle fast enough to keep from falling over it. There is some point where you could just stay in place if you paddled hard enough, but past that you are going over the edge. Near a black hole, that is the event horizon. Just past it, light can’t travel fast enough to cover spacetime curvature to get away from the black hole. In other words, we can’t “see” over the event horizon; things that happen past it are out of our line of sight.
But to that orbit. Your space ship would probably have to be going very fast to stay in orbit, and that would call relativity into all sorts of considerations. But the one I want you to think about is time. Let’s suppose your spaceship has a big watch with a flashing light attached to its outside hull. Every second its light flashes. You see it keeping perfect time, and another traveler in orbit near you would agree that the time is correct. But back here on earth, the time between flashes would be way slower than once a second. Not because we are a long way off – it’s not how long the first flash takes to get here but how long BETWEEN flashes – but because the curvature of spacetime near the black hole means a much longer path for the light to travel.
Said another way, your twin brother here on earth observing your orbit will experience time a lot faster than you will in orbit. For grins, every time your one second flash appears to him on earth, his own watch may have flashed several times or more, depending on fast you are traveling in orbit and how close you are to the BH. So when he is a year older, having no life at all other than watching you out there, you may be only a few months or so older, if that.
How about a BH in our neighborhood?
It might be like the immigrant family who moved in from the Middle East or Asia or Eastern Europe a few months back. Yes, they look a bit different, have different customs and practices, maybe a different religion, but they seem nice enough. Their English may not be perfect but if we got to know them better we could definitely learn something from each others’ backgrounds and experiences.
A black hole might be a little more disruptive than that, however. You would have to hang onto your stuff, not that your new neighbor might take it, but things will definitely curve in its direction. But that’s not why a BH as a close neighbor would not be a great thing.
In late October of this year, we could have sent a whole bunch of people who did not vote in the election along with the “protest voters” who voted neither for Clinton nor Trump. Now, we could get them to come back and it will still be November 7th. They all could vote. Better or at all.
You might be thinking this country has fallen into a black hole. Unlikely. It takes a bit of science and thought experiments – which require thought, right? – to “get” black holes. There is certainly no sign of either past 11/8/16.