posted
General relativity says that as gravity increases, time slows down. So the closer you get to a gravity creating object (like the Earth, or Sun) the slower your time goes in relation to the rest of the universe. This effect happens at a ratio such that when gravity is strong enough to keep light from escaping, time moves infinitely slow.
In other words when you reach a point in space where gravity is so strong that light can not move away from it, everything at that point is experiencing no time at all as the rest of the universe keeps moving.
A black hole is something that has such great gravity it has collapsed all matter into a single point (infinite density, zero size). The event horizon of a black hole is the point at which light can not escape the black hole, the same point mentioned above. However, black holes do emit radiation (Hawking radiation) and disperse there mass that way.
So imagine a ship falling into a black hole. It gets closer and closer, the ship thinking its moving at perfectly normal time. As you watch from some other vantage point however, the ship keeps moving slower and slower as it approaches the black hole, it’s time slowing down in relation to yours. It will reach the event horizon at a point infinitely far into the future, since that’s how long time will take to move at all. So from the universe’s vantage point the ship never falls into the black hole.
However, the black hole is continually releasing radiation (turning mass into radiation) until at some discrete point in the future it has expelled all of its mass in the form of hawking radiation and is dispersed. So the ship, which like all of the mass in the black hole, fell into it is released in such a way despite the fact that it never actually reached it. Interesting huh?
Of course, blackholes emit Hawking radiation so slowly, that this would not occur for many many trillions of years and that the ship most likely wouldn't be emitted as a ship but as either energy in the form of photons or other baryonic matter.
Posts: 154 | Registered: Nov 2000
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posted
Neat! Now, 'splain to me how we can actually watch whole galaxies being swallowed by a black whole. Are we actually seeing it, or are we seeing something for which time has stopped (at least from our frame of reference)?
Or, as I like to say whenever black holes are being discussed: "Get a grip!"
posted
Hobbes, are you monitoring my thoughts again? I bought Hawking's Theory of Everything on tape for my ride home and was just being fascinated by Hawking radiation, which I had never heard of before. Eerie! But kissably eerie.
I still think that string theory is by far the coolest weird physics. Unfortunately, I don't think there are even many physicists who truly understand it, so my trying to explain anything would be like my 4-year-old brother talking to you about how my computer works. Posts: 8504 | Registered: Aug 1999
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posted
Bob, it's a matter of distance. The majority of the galaxy is still so far away from its black hole that the lengthening effect is still very small. And, of course, up close to even a huge black hole is still a small area compared to the size of the entire galaxy, so there is not that much to watch in that region.
Um...am I right, Hobbes? I'm not a physics major, I just play one on tv.
posted
I haven't read the Gateway series in years! ::adds it to his ever lengthening list of things to read::
Posts: 16059 | Registered: Aug 2000
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posted
You have to start with Gateway Actually, but Beyond the Blue Event Horizon is a pretty good read, too.
But here's an interesting one for you: If time dilation approaches infinity as an object nears the event horizon of a black hole, how can the surface of the star itself, while collapsing, pass the event horizon in the lifetime of the Universe?
[edit]Have I mentioned this before here? getting senile in my old age...
[ December 24, 2003, 09:49 AM: Message edited by: T. Analog Kid ]
Posts: 2112 | Registered: Sep 1999
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posted
It can't, that was my point. Well kind of my point, the full point was that it is then ejected from the black hole in the form of radiation without ever entering the black hole. Freaky.
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