It is unfortunate that the concept of time travel generates illogical thinking. I have been asked, "If I travel into the past and prevent my parents from meeting, will I cease to exist?" Why should you? It is logically possible that anyone cease to exist at any time but it is not logically necessary that anyone cease to exist in any particular circumstances. There can be a timeline in which my parents met and I exist and another timeline in which the man and woman who would have been my parents did not meet and I do not exist but, in the latter case, I simply do not exist. I do not somehow live into adulthood, then cease to exist.
I do not arrive home one evening to be greeted by a young woman who then ceases to exist because she is my daughter whose birth was prevented twenty or any other arbitrary number of years ago. If a time traveller arrives either from another timeline or from a prevented future, then he exists and there is no reason why he should not continue to exist. A time traveller arriving from a prevented and therefore nonexistent future is not illogical although he is certainly counterintuitive and so far counterfactual.
Does that answer the questions? (Probably not.)
12 comments:
It's not illogical if you factor time travel into the nature of existence. Then, as the crowd of new recruits get told, events can exist without causes because someone removed the cause. You travel back in time, you prevent your parents from meeting, and you're still there... but you were never born, except in your memories.
But, in that case, you haven't travelled back in time, just arrived from nowhen.
No, you've traveled back in time. The -events- have changed, the -duration- is still there. Time goes forward; what it goes forward into is a different matter.
Kaor, to Both!
And that is so weird, preventing one's parents from meeting, but you still "exist" despite not having been born.
Ad astra! Sean
Sean,
That a future can be prevented and non-existent is just one scenario.
I prefer a single consistent timeline as in THERE WILL BE TIME and THE TIME TRAVELLER'S WIFE.
But, if time travellers are to be allowed to "change the past," then I think that the second temporal dimension scenario is the best option.
Paul.
Kaor, Paul!
Meaning split off timelines? I agree.
Ad astra! Sean
Split or succession.
Sean,
In our experience, three-dimensional states of the universe succeed each other along a fourth dimension which is our only experienced temporal dimension. This universe from its Big Bang to its heat death is a single four-dimensional space-time continuum. Several such continua could succeed each other along a fifth dimension that would be a second temporal dimension. This would be a natural process in five dimensions as it is in four. There would be no need for any splits in either of the two temporal dimensions. (It is purely a terminological question whether we refer to successive continua or to successive states of a single continuum.)
Paul.
Paul: but time is not uniform, it's a function of velocity. If you speed up, time slows down, for example. It doesn't -appear- to slow down, for you it actually -does- slow down.
Time dilation. OK. Got that.
Kaor, to Both!
I sure as heck don't claim to understand this despite reading some popular science books discussing quantum mechanics/alternate or parallel universes.
Ad astra! Sean
Sean,
But I think that I have spelled it out as clearly as possible. I am a philosopher, not a physicist or a mathematician. I can cope only with relationships of consistency between verbal propositions.
Paul.
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