Among the " scientific " pursuits that qualify as hare-brained, Time Travel belongs at the head of the list. It's impossible, yet presumably intelligent people view it as a possibility and are working to make it happen. The simple fact is this:
TIME TRAVEL IS IMPOSSIBLE!
That might be putting it a bit strongly but it's true; the reason time travel is impossible is simple. Time is not a naturally occurring pheomenon. That's right; it's an invention devised by man, initially to regulate agricullture: when to plant, when to harvest - that sort of thing. After all, when was the last time you saw a clock hanging from a tree in the woods naturally? Ever seen a racoon wearing a wristwatch? Ever had a pigeon stop you on a downtown street and ask you for the correct tiime? Didn't think so.
Time is an immutable scalar that is used to measure change, therefore time travel would necessarily involve un-changing all the changes that have taken place between the present and the target period. That isn't going to happen anytime soon. Beside that you could only go back so far; what happens after you have changed all the way back to a fertilized egg? Which path would you follow? As you can see, it gets pretty complicated.
While an interesting subject for science-fiction buffs, time travel has no place in serious scientific endeavor. But time travel is not the only illusion that those who should know better still take seriously. Another is Time Dilation.
The idea here is: An atronaut travelling on a spaceship speeding away from the Earth will experience a slowing in time such that the faster he goes the more slowly time passes for him. He's gone for twenty years and when he returns five-hundred years have passed on the Earth. Think of it! Amazing, isn't it?
Well, no, not exactly. This is another bit of nonsense that belongs squarely in the realm of science-fiction. It's another version of A Note on Danger B.
In the 1930's the goal of aeronautics was to break the Sound Barrier. Scientists and writers both wondered what would happen when this challenge was mastered. One writer cooked up A Note on Danger B, a short story hat appeared in Reader's Digest at the time. The story was about a pilot who broke the Sound Barrier and - started getting younger! The faster he went, the younger he got, and the problem he faced was to slow the plane down before he regressed to infancy, where he could no longer reach the controls. In 1969 Chuck Yeager finally broke the Sound Barrier without getting a nanosecond younger.
The " theory " of Time Dilation is founded in Einstein's Special Theory of Relativity, published in 1905. The theory is based on the understanding that the speed of light, C, is finite: that is, it takes time even for a beam of light ( or a radio wave ) to travel a given distance. It takes a full eight minutes for the light from the Sun to reach Earth, about 93,000,000 miles. For this explanation we'll borrow Kepler's Astronomical Unit, AU, one Earth-distance from the Sun as our base.
The cosmonauts are happily speeding away from the Earth and have reached the first AU of distance. The Earth station has been sending time signals every hour, and this time it takes eight minutes to arrive at the vehicle. Assuming the Earth time to be the standard, the guys on the spaceship would have to turn their clocks back eight minutes to comply. At the second AU they would be sixteen minutes ahead, at 3AU, 24 minutes, and so on. But time would only be appearing to slow down; in actual fact time would pass normally in both environments. If the cosmonauts turned back and approached the Earth, the exact reverse would happen and they would be turning their clocks ahead to match the time signal from Earth: when safely back home both clocks would read exactly the same!
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