Time Travel

Michael Coughlin and Time Travel

This intriguing idea is from Michael Coughlin!

* * * 

I’ve been working on an article for Lisa and Mused for years.  It is not going well. The subject is complicated and has a vast literature.  I want to summarize everything ever thought of in a few  paragraphs. So I must take a bold step to at least get started even  tho I can’t write logically flowing steps the way I’d like. I reserve the right to make radical changes, especially if you send me suggestions.

I still can’t find an easy way to get 64 characters per line. 


Michael Coughlin

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Years ago my mother told me she did not enjoy science fiction stories about time travel. The idea was too impossible. How could I have a mother with such a limited imagination? I decided to think of a way to build a time machine and expand her horizons. After a while I realized all you would have to do is place every atom and subatomic particle in the universe back exactly where it used to be and travelling in the same direction at the same speed. Oh, wait a minute, that is impossible. It is even more impossible than anything I’d ever read of why a time machine is impossible. My mother was right! 

Making up a story about time machines creates many paradoxical ideas. The past has never gone away and the future has a short cut to visit it. Where does our imagination stop and reality start?  The past does not exist, except in our minds. The future has yet to happen. What we see is what we have.  And not only can’t we put everything back the way it was at some distant time, we can’t know exactly where everything was there in the first place. 

Travelling forward in time presents a different set of impossibilities then going backwards. Actually it is possible to travel forward in time a little bit as shown by Einstein’s theory of the relativity of simultaneity. Global positioning satellites need to take this into account. Suppose you wanted to make a big trip into the future? Then Einstein’s paradox of the twins comes into play. Build a space ship that can accelerate constantly forever. This is, of course, not possible. But I think this idea is more interesting than the usual fictional space ship magic of disappearing from one part of the universe and instantly showing up in another. As this space ship travels thru the galaxy constantly accelerating at 32 feet per second per second, all the people on-board will comfortably experience the same force they do on earth from gravity. Makes filming the story very easy. The space ship will travel faster and faster till after only a few months it will be travelling close to the speed of light. The passage of time and the view of space will be radically changed. After a few years the ship can be anywhere in the galaxy or even beyond. Half way thru the trip turn the ship around and decelerate at 1 G. Then travelers can explore their chosen stars and planets at their leisure. Reverse the procedure and come back to Earth. Surprise. Time on Earth has gone forward much more than time on the travelling space ship. 

The idea of a 1 G space ship was written about years ago and it didn’t catch on. Too bad since it might have been an educational lesson for the theory of relativity. What was not known at the time is that the universe is not as empty as it looks. The night sky looks really dark and black but we now know there is a faint glow of light at various wavelengths. When the space ship accelerates to interesting speeds this light becomes blue shifted and strong enough to destroy things. Also the universe is filled with unknown “dark matter” that could also collide with and destroy speeding space ships. Then there is interstellar ordinary matter of various sizes. Colliding with a grain of sand while travelling near the speed of light is a very bad thing. Never mind colliding with a rock or comet. 

Time machines have nothing to do with “science” fiction. They are fantasy. Mark Twain had the right idea when he wrote “A Connecticut Yankee in King Arthur’s Court”. No machine needed, just a strong blow to the head to go back and then the right spell cast by Merlin the Magician to return. Time travel is an exercise for our memory and imagination. You can’t put things back the way they were. But you can look back and decide how things could be different so you might know what you should do when similar events show up. 

The laws of Physics are the same for time going forwards and backwards. Maybe time does go backwards, sometimes, for a little bit. Time might not apply to subatomic particles colliding. Maybe time does not exist and can be replaced by rules of how parts of atoms bump into each other. Physicists want to compute the state of the universe forward and backward without limit. And also account for things that happen in the smallest possible spaces in the shortest amount of time, as well as the largest things we can see and beyond what we can see. 

This is not a subject only for Physicists. Impossible time machine stories are a refection of how we perceive reality as well as the passage of time. In many stories, the hero goes backwards and creates a disaster that prevents him from returning to the time from where he started. Perhaps other events occur to cancel his actions, or he needs to do something amazing to happily return home. The author has decided that the passage of time actually cannot depend much on what we do. Our lives are fixed by fate and  we must follow a path that we have little ability to change.  At certain places and at certain times people have thought that way.  Now that I have invented an imaginary impossible time machine, I can look at things in a different way. It is not possible to go back in time since all the atoms can’t be put back where they used to be. At least in the past the atoms were in a certain place at a certain time. Travelling into the future is a whole different situation. The atoms of the universe have never been where they are going to be. Our impossible backward going time machine can’t just shift into reverse to go forward in time. It must be able to calculate where everything is going to be to put it there. An impossibility piled on top of another impossibility. 

We can do much more than cavemen could, not because we are more intelligent, but because we know more about the world and how things work and don’t work. Learning about what is impossible is as important as learning what is possible. Right now the science of Physics has not neatly connected the radical new ideas from the 1920s of quantum mechanics combined with general relativity. Thinking about time machines is another way to try to learn what time really is and how to keep track of it.