"By His Bootsraps" by Heinlein plays with the self-perpetuating loop memorably and A Lamp for Medusa by William Tenn is {IMHO} probably the most brilliantly written example of that plot device in a longer format.
"By His Bootsraps" by Heinlein plays with the self-perpetuating loop memorably and A Lamp for Medusa by William Tenn is {IMHO} probably the most brilliantly written example of that plot device in a longer format.
I consider all time travel stories "hokey"... BUT, in order to participate...
James Hogan's The Proteus Operation described a system in which the characters found a way to travel back in time, in an attempt to improve their present, but in fact they could only travel to a parallel dimension, never their own. This allowed them to influence the timestream of the parallel world they stepped into because they were an immutable part of it. But their own dimension would never change. In effect, the best they could do was to escape to a dimension that better suited them.
Though this seems to me to be the only way time travel could actually work, I categorically do not believe in the infinite- and infinitely-multiplying parallel worlds required for this theory (it blows the notion of conservation of energy right out the window). Which is why I'm convinced time travel cannot work.
In addition to the alterantive universes or branching time lines theory, we also have:
*system where the time stream is analogized to a river, and if you go back and make a change, a wave propogates forward, changing the future, either right away, or after some period of "time". Can lead to hokey results -- for example, can lead to multiple copies of the same person proceeding forward in the new timeline.
*system where the timeline has some sort of overarching order and can "heal" or the like to maintain its overall direction. Arguably the least "plaussible" system, but still allows for a coherent/internally consistent story.
All three systems allow for good stories. The previously mentioned self-perpetuating loop stories, are not a separate system, but rather a member of the larger class of stories that make it up as they go along and/or just dont let a system get in the way of a story. They can be great stories, but they do not withstand logical analysis.
99.999% agreement.Originally Posted by Steven L Jordan
I avoided the Proteus Operation for years because it was a time travel story and involved WWII. But I finally broke down and read it because I usually like James P. Hogan stories and was tired of buying stuff I didn't like because it got lots of good reviews.
It was a really enjoyable story and quite scientific beyond the time travel crap. So stories can be entertaining and thought provoking even when they have a significant hokey factor.
psik
How about Asimov's short story The Message?
I'm also wondering if it is possible to go to the past at all. If you can't change the past how could you ever go to the past. You're very presence would change the past. You don't have to kill you're own grandfather. You only have to be there.
Asimov in "The Red Queen's Race" postulated that if you went into the past {or sent objects into the past} in order to change it, such "changes" are already part of the present; you haven't really changed anything--thus, if time is an immutable stream, then it includes everything--including attempts to divert its course.
I know you can't kill your grandfather because you had to exist to go. You'd have a contradiction. What I don't know if about other things not so important. Could you leave a footprint, for example? That changes the dirt doesn't it?
Here is a quantum solution:
There is neither objectively existing past, nor future, only present.
There is present which observer observe and there are probabilities of pasts which lead to this present. Different pasts exist in quantum entanglement state. As observer observe different event in present uncertainty of pasts change bunt never collapse to single past. As the observer observe departure of time traveler probabilities of the past change. Probabilities of the past there traveler appeared and did something increase, but his probable actions are constrained by what observer see in the present. Nevertheless probabilities of future with consequences of the traveler action are increasing.
Thus in this model traveler actions in the past propagate slowly and probabilistically in future from the moment of his departure, but in the manner consistent with observed world in the moment of his departure.
With several time travelers departing in different time, some of them affect future more, some less. Future will be mix of their actions, but without instantaneous switching, with waves of changes starting in the moments of departure.
Not only that Psik, but I enjoyed the characters in that story. I was sad to read that Mr. Hogan passed away this year.
That may be as good a definition of sci-fi as I've ever read!
The quantum solution would suggest that the present being observed by the observer automatically causes the past, in its quantum state, to become disentangled and set, the equivalent of opening the box on Schrodinger's cat. That would imply that the past, once the present is observed, becomes immutable and therefore cannot be changed after the moment of observation... which also happens to be the practical definition of past and present.
I'd suggest that the quantum solution only applies to present and future: It is the future that is in a quantum state, which doesn't collapse into one state until the future is reached (becomes the present), and thereafter it stays fixed as it becomes the past. The present does not change because the past does not change.
This suggests that time travel into the past is impossible, because once the present is reached, its quantum state is immutable from then on.
Sorry... I'm being a wet blanket here. I should probably move on.
I think everyone has covered the ways it can happen. I believe they all boil down to one of three things:
Fixed timeline: Everything has already happened, so it is forced to be self consistent. If a guy goes back to kill his grandfather, he will miss when he takes the shot, because we already know that his grandfather lives.
Changeable timeline: The timeline adjusts itself like in Back to the Future. A guy can kill his grandfather, and everyone's memories will change and people will fade in and out, including the time traveller who will disappear if he kills his grandfather.
Parallel universes: Discussed a lot already, they split off every time you time travel, and infinity never gets crowded, so you just have lots and lots of these.
Gravity propagates through time.
Interesting. What does this mean?
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