If you think about it, over the last four hundred years humanity’s growing science and technology has given us an enormous amount of control over many aspects of nature. The speed and distance we can travel has steadily increased, as has both the size and number of structures we can build. We grow more food than ever and whether we like it or not we are even changing the weather. Can you say climate change! We have discovered the very code of life itself and begun to understand how to alter and mold living things to suit our desires. We now have many ways of controlling space and material objects that would seem like magic to our ancestors of a thousand or more years ago.
But we still have virtually no control over time. Oh, we can measure it’s passing with an accuracy that, at the risk of repeating myself, is almost magical. We can’t stop time of however, and although Einstein’s two theories of Relativity do describe how the passage of time can be slowed that slowing requires either velocities approaching the speed of light or immense gravitational fields such as those around black holes.
And even theoretically we can’t go backward in time. In fact many scientists have steadfastly maintained that time travel to the past is logically impossible because of something known as the grandfather paradox.
What is the grandfather paradox? Well it works like this. What if you were to travel backward in time and murder your grandfather before he fathered your own father? In that case you would never have been born and if you were never born how could you go backward in time to kill someone?
This idea of the dire consequences to the present of doing anything in the past has been the central idea in many Science Fiction stories like Ray Bradbury’s ‘The Sound of Thunder’ as well as movies such as ‘Back to the Future’. Many scientists feel that the logic of the grandfather paradox is so tight that traveling into the past is simply a pipe dream better left to science fiction writers.
Still theoretical physicists and mathematicians looking for solutions to Einstein’s field equations occasionally came up with equations that, while physically hard to interpret seemed to include the possibility of going backward in time. Collectively these solutions are known as ‘Closed Timelike Curves’ or CTCs and where initially discovered back in 1937 by Jacob van Stockum and later extended by Kurt Gödel in 1949. Basically a CTC describes the movement of a material particle that loops endlessly through time and space in a circle. This would imply that the existence of a particle following a CTC would be extremely limited in both time and space.
Physically it is hard to understand how any particle following a CTC could interact with other more normal particles. Such a path in Space-Time would seem to imply the possibility of events happening without causes since to the normal particle the CTC particle can appear to pop into existence without reason. At the same time to an outside observer a particle inside a CTC might appear to experience an event before its cause!
Because of such paradoxes many physicists expect, or perhaps hope that an eventual unified theory of gravity with quantum mechanics might eliminate CTCs as even being mathematically possible. Other physicists however prefer to try to make sense of these weird solutions to the field equations.
One of those physicists is Germain Tobar, a student at the School of Mathematics and Physics at the University of Queensland in Australia. With the assistance of his colleague Dr. Fabio Costa, Tobar has analyzed CTCs in such a way that he maintains opens up the possibility of time travel into the past.
But what about the grandfather paradox? What about the problem of actions in the past changing the present? Well in Tobar’s analysis what happens if you were to try to change the past then the universe would react so as to avoid the paradox, to repair the damage you have caused in other words.
I won’t go into the math. (Actually I am going through the Math, trying to remember what I learned in my course in General Relativity but I won’t impose it on you.) However, it appears to me that in Tobar’s treatment if you were to go into the past and kill your grandfather then when you returned to your present you would find yourself with a different grandfather or something equivalent. Sounds to me kind of like what Marty and Doctor Brown did to repair things in ‘Back to the Future’ except that this repairing would occur naturally, automatically.
I have to admit I have real problems with that idea. Remember, the past starts just an instant ago! What if you were to step into a time machine and go back ten minutes and murder yourself just as you’re stepping into your time machine? I’m sorry but I can’t imagine how the Universe could repair that damage, how it could change things so much so quickly in order to somehow avoid the paradox!
Time Travel would be the ultimate power, the ability to undo all of our mistakes, to right all of the wrongs we’ve done. Perhaps for that very reason it is the one power that will always elude us.