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Time Travel For Dummies
Back to the Future
Time travel is theoretically possible. Unlike many stunts that are depicted in movies, it is, in theory possible to move to a different point along the time line.
Putting a time machine in a DeLorean or giving the Libyans a bomb filled with pinball machine parts is entirely a different matter.
The Sidewalks of Time
Space is a fabric that can be warped by gravity or speed. If you have enough gravity or enough speed, time travel becomes possible.
Ordinarily space and time make a continuous path like a smooth sidewalk. You can ride your bicycle down that walk at breakneck speed and be none the worse for wear. But if a sudden pothole should show up on that sidewalk you would be in a world of hurt. If the hole were big enough, you might entirely disappear from the sidewalk universe and enter another universe.
Black holes and Warped Space
When enough matter gets together in in place, there comes a point when the underlying structure of space-time can no longer support the mass. All that stuff collapses into a black hole.
Look up into the night sky. You will see planets and stars. For anyone one of them, if you had enough energy you could escape their orbits. It is always possible to go fast enough to leave. For earth, that escape velocity is 7 miles per second.
Now suppose you had an object that was so massive that its escape velocity was 186,282 miles per hour. That is the speed of light. So not even light could reach the escape velocity for such an object. Since no light can escape it, we call it a black hole.
Not all black holes are created equal. Some spin a lot. Some spin a little. some have an electric charge and others don't. Some radiate at a fast rate and others at a slow rate. The fast radiators are evaporating to nothing.
In particular some black holes have funny shapes. And some black holes actually let you see some of what is going on inside them. So you can see the violations of the laws of the universe going on--or so some would say.
If you had a long cylindrical or cigar shaped, naked singularity--a black hole that is at least partially transparent--and you had a space ship that was built for speed, you could travel around the black hole in circles. And that physical travel through that immense gravitation field would allow you to travel through time. If you could survive it.