There are those that claim you can't go back in your own timeline and change anything without introducing a paradox of some kind, correct?
Incorrect.
First of all there is the case of the Ignorant Time Traveller. If someone who had never heard of the Titanic were to go back in time and inadvertantly convince it to go off-course (and therefore avoid the iceberg), there is no paradox, since there is no reason why the Ignorant Time Traveller wouldn't do it again.
The Ignorant Time Traveller could travel to places and times with which he or she was unfamiliar, and even if the changes were deliberate rather than accidental, they would still not necessarily introduce paradoxes.
It is naturally possible that the Ignorant Time Traveller could accidentally kill a key ancestor, or somehow affect something that prevents his or her ultimate ability to travel in time, but it's not guaranteed - it is possible that the Ignorant Time Traveller would not, and that's the point.
There is also a scenario where time travel is possible even with those who aren't ignorant. Though the Knowledgeable Time Traveller could not prevent the Titanic disaster, he or she could arrange for a rescue ship to save everyone and take them somewhere (or some time) where they couldn't (or wouldn't) tell anyone who they were. Perhaps even to a point in the future, beyond the point from which the Knowledgeable Time Traveller originally went back.
Of course, this would require a great deal of precise knowledge about the Titanic disaster so the right evidence could be left behind. Perhaps he or she would have to bring and leave behind certain realistic-looking corpses, know exactly when and where to show up, and with what, in order to leave no evidence of the rescue mission behind. In essence, he or she would have to be a Very Knowledgeable Time Traveller to leave no evidence of the incursion.
Though paradoxes are still possible, the absence of paradoxes is also possible.
Therefore, time travel within one's own timeline without paradox is possible at opposite ends of the spectrum: the Ignorant Time Traveller and the Very Knowledgeable Time Traveller, but not necessarily at any point in between.
1 comment:
"Perhaps he or she would have to bring and leave behind certain realistic-looking corpses, know exactly when and where to show up, and with what, in order to leave no evidence of the rescue mission behind. In essence, he or she would have to be a Very Knowledgeable Time Traveller to leave no evidence of the incursion."
Heya. You've rediscovered key elements of the plot of the 1983 novel "Millenium" by John Varley. I read it around 1986 or 1987.
From http://en.wikipedia.org/wiki/Millennium_(novel):
Millennium features a civilization that has dubbed itself "The Last Age". Due to millennia of warfare of every type (nineteen nuclear wars alone), the Earth has been heavily polluted and humanity's gene pool irreparably damaged. They have thus embarked on a desperate plan; time travel into the past, collect healthy humans, and send them to an uncontaminated planet to rebuild civilization.
The time travelers can only take people that will have no further effect on the timeline: those who have vanished without a trace, or died without being observed; otherwise they would be changing the past, which risks a temporal paradox and perhaps even a catastrophic breakdown of the fabric of time. Though they collect everyone they can, they exert a great deal of effort on those destined to die in various disasters such as sinking ships and crashing airplanes (and once a century of Roman soldiers lost and dying in the North African desert). As such incidents leave no survivors to report interference and change the timeline, they can freely remove the living but soon-to-die victims, and replace them with convincing corpses they have manufactured in the future.
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