Time Travel
The concept of time travel has always fascinated me, from both a scientific and science fiction perspective. From a science fiction perspective, some of my favorite science fiction plots involve time travel, and, put me in front of a show that has time travel in it, and I'll be glued to the set, regardless of how campy or inane the plot and acting are.
But from a scientific perspective, I've always rejected the notion of time travel -- or, at least, backward time travel. (Forward "time travel" is easily described by Relativity Theory: a person goes into a space ship which travels near the speed of light; time slows down for that person; and they return to their starting point "in the future," since more time would have passed in their absence than they experienced on the space ship.)
But backward time travel is problematic. For one, despite the campy science fiction plots that I love so much, a person going back in time would create a second copy of that person at a given point in time. Even if one conjectures that the two copies would be prevented from meeting each other, this would still reject the basic law that matter in the universe can neither be created nor destroyed, but only converted to and from energy.
Of course, one could argue that if time is actually a fourth dimension of space-time, that the second instance of the person is not "created," but is, instead, "borrowed" from another point in the space-time continuum. And, while that might be logically sound, it would create its own problems. For example, if time is to be included in the equation of the "total sum of mass in the universe," and if time stretches infinitely into the future, then the total sum of mass in the universe is infinite. Or, if time is finite and perhaps circular, then we are just beings existing on a pre-determined grid of space-time. And so on.
The point here is that, to me, is seems that backward time-travel is an absurdity -- a fun concept for science fiction, but nothing that really has any place in serious scientific consideration. (What would happen, for example, if a person enters a time machine and goes one minute into the past; meets himself about to enter the time machine, which he does, and, again, goes one minute into the past, creating a third copy of himself; and so on?)
However, I was perusing Wikipedia tonight (thank goodness for Wikipedia! :-) ) and came across a series of articles related to time travel and the mathematics of it all, and I realized that many great men, with brains capable of conceiving things far beyond the reaches of my feeble mind, have given this, not just serious, but rigorous consideration.
And so I find myself in the position of being similar to those who scoffed at Pasteur when he proposed germ theory, or being one of those people that Einstein was referring to when he said, "Great spirits have always encountered violent opposition from mediocre minds." My mind is, perhaps, just too mediocre to appreciate the possibilities of backward time travel.
And so I explored it a bit, and came across this cool article on "The Grandfather Paradox" (http://en.wikipedia.org/wiki/Time_paradox).
The Grandfather Paradox basically says that if someone travels back in time and kills their grandfather, then they would never have been born, and, thus, could never have traveled back in time to kill their grandfather. (A similar one is that the person goes back in time and kills himself as an infant.)
Some proposed resolutions for this paradox are that the person would travel back in time to a parallel universe, and, thus, not affect the timeline in which he traveled back in time at all; or that he would be prevented by the laws of nature from creating the paradox, and, thus, would not be able to kill his grandfather.
Still another theory (which actually seems more true-to-life in terms of the way the universe actually works) is that creating a self-sustaining paradox such as this (he kills his grandfather, which prevents him from being born, which prevents him from going back in time, which allows his grandfather to live, which allows him to be born, which allows him to go back in time and kill his grandfather, which pevents him from being born, which prevents him from going back in time, etc.) would actually destroy the universe -- or at least that part of the universe affected by this paradox. The universe would just go round and round trying to resolve the paradox until at least a portion of it, apparently, just "implodes."
This is all fascinating. I had no idea that so much time and effort had been placed into resolving these theoretical contradictions.
One of the more fascinating considerations I read about was whether the person traveling back in time, rather than affecting the timeline, was actually causing the timeline that he knew:
I find this just fascinating, that the person may have actually caused the events he was experiencing by going back in time to try and prevent those same events! I find that just fascinating -- a sort of universal game of "gotcha."
The best resolution to the Grandfather Paradox may have come from the animated TV show "Futurama," as noted at the end of the article. In one of the episodes of the show, Fry travels back in time and inadvertently kills his grandfather. Rather than creating a self-perpetuating paradox that destroys part of the universe, it instead leads the discovery that Fry was actually his own grandfather, having conceived one of his parents during that trip to the past!
This resolves the Grandfather Paradox in a logically sound way. But it creates all sorts of problems of its own.
For example, what if someone went back in time, met his mother and conceived himself, and then returned to the future; but then, when that child grew up and came to the point in time where he needed to go back in time to conceive himself, he, for some reason, didn't go (not knowing that he was his own father)? What would happen to him? Since he didn't go back in time to conceive himself, would he just disappear? Would the record of him having existed up until that point just disappear, as though it never happened? The mind reels with possibilities.
There's so much fun that one could have with all of these time-travel scenarios! And none of this even touches upon the Butterfly Effect, or the fact that the time traveler could never return to the future because the future would have been altered, ever so slightly (or significantly) by his having interacted with the past, causing the future from which he came, in which he went back to the past, to no longer exist.
I mean, it boggles the mind to consider all the scenarios that one could find oneself in with time travel. Who needs video games, really? :-)
But from a scientific perspective, I've always rejected the notion of time travel -- or, at least, backward time travel. (Forward "time travel" is easily described by Relativity Theory: a person goes into a space ship which travels near the speed of light; time slows down for that person; and they return to their starting point "in the future," since more time would have passed in their absence than they experienced on the space ship.)
But backward time travel is problematic. For one, despite the campy science fiction plots that I love so much, a person going back in time would create a second copy of that person at a given point in time. Even if one conjectures that the two copies would be prevented from meeting each other, this would still reject the basic law that matter in the universe can neither be created nor destroyed, but only converted to and from energy.
Of course, one could argue that if time is actually a fourth dimension of space-time, that the second instance of the person is not "created," but is, instead, "borrowed" from another point in the space-time continuum. And, while that might be logically sound, it would create its own problems. For example, if time is to be included in the equation of the "total sum of mass in the universe," and if time stretches infinitely into the future, then the total sum of mass in the universe is infinite. Or, if time is finite and perhaps circular, then we are just beings existing on a pre-determined grid of space-time. And so on.
The point here is that, to me, is seems that backward time-travel is an absurdity -- a fun concept for science fiction, but nothing that really has any place in serious scientific consideration. (What would happen, for example, if a person enters a time machine and goes one minute into the past; meets himself about to enter the time machine, which he does, and, again, goes one minute into the past, creating a third copy of himself; and so on?)
However, I was perusing Wikipedia tonight (thank goodness for Wikipedia! :-) ) and came across a series of articles related to time travel and the mathematics of it all, and I realized that many great men, with brains capable of conceiving things far beyond the reaches of my feeble mind, have given this, not just serious, but rigorous consideration.
And so I find myself in the position of being similar to those who scoffed at Pasteur when he proposed germ theory, or being one of those people that Einstein was referring to when he said, "Great spirits have always encountered violent opposition from mediocre minds." My mind is, perhaps, just too mediocre to appreciate the possibilities of backward time travel.
And so I explored it a bit, and came across this cool article on "The Grandfather Paradox" (http://en.wikipedia.org/wiki/Time_paradox).
The Grandfather Paradox basically says that if someone travels back in time and kills their grandfather, then they would never have been born, and, thus, could never have traveled back in time to kill their grandfather. (A similar one is that the person goes back in time and kills himself as an infant.)
Some proposed resolutions for this paradox are that the person would travel back in time to a parallel universe, and, thus, not affect the timeline in which he traveled back in time at all; or that he would be prevented by the laws of nature from creating the paradox, and, thus, would not be able to kill his grandfather.
Still another theory (which actually seems more true-to-life in terms of the way the universe actually works) is that creating a self-sustaining paradox such as this (he kills his grandfather, which prevents him from being born, which prevents him from going back in time, which allows his grandfather to live, which allows him to be born, which allows him to go back in time and kill his grandfather, which pevents him from being born, which prevents him from going back in time, etc.) would actually destroy the universe -- or at least that part of the universe affected by this paradox. The universe would just go round and round trying to resolve the paradox until at least a portion of it, apparently, just "implodes."
This is all fascinating. I had no idea that so much time and effort had been placed into resolving these theoretical contradictions.
One of the more fascinating considerations I read about was whether the person traveling back in time, rather than affecting the timeline, was actually causing the timeline that he knew:
"It also may not be clear whether the time traveler altered the past or precipitated the future he remembers, such as a time traveler who goes back in time to persuade an artist—whose single surviving work is famous—to hide the rest of the works to protect them. If, on returning to his time, he finds that these works are now well-known, he knows he has changed the past. On the other hand, he may return to a future exactly as he remembers, except that a week after his return, the works are found. Were they actually destroyed, as he believed when he traveled in time, and has he preserved them? Or was their disappearance occasioned by the artist's hiding them at his urging, and the skill with which they were hidden, and so the long time to find them, stemmed from his urgency?"
I find this just fascinating, that the person may have actually caused the events he was experiencing by going back in time to try and prevent those same events! I find that just fascinating -- a sort of universal game of "gotcha."
The best resolution to the Grandfather Paradox may have come from the animated TV show "Futurama," as noted at the end of the article. In one of the episodes of the show, Fry travels back in time and inadvertently kills his grandfather. Rather than creating a self-perpetuating paradox that destroys part of the universe, it instead leads the discovery that Fry was actually his own grandfather, having conceived one of his parents during that trip to the past!
This resolves the Grandfather Paradox in a logically sound way. But it creates all sorts of problems of its own.
For example, what if someone went back in time, met his mother and conceived himself, and then returned to the future; but then, when that child grew up and came to the point in time where he needed to go back in time to conceive himself, he, for some reason, didn't go (not knowing that he was his own father)? What would happen to him? Since he didn't go back in time to conceive himself, would he just disappear? Would the record of him having existed up until that point just disappear, as though it never happened? The mind reels with possibilities.
There's so much fun that one could have with all of these time-travel scenarios! And none of this even touches upon the Butterfly Effect, or the fact that the time traveler could never return to the future because the future would have been altered, ever so slightly (or significantly) by his having interacted with the past, causing the future from which he came, in which he went back to the past, to no longer exist.
I mean, it boggles the mind to consider all the scenarios that one could find oneself in with time travel. Who needs video games, really? :-)
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