In practice, the problem can be stated as follows: if a time traveller departs from his present, visits his past and returns to what should be his present, it can turn out to be the wrong present. Thus, in "Delenda Est," Manse Everard and Piet van Sarawak return from the Pleistocene to what should be 1960 A.D. but the year is not called that and no one speaks English because the two puzzled time travellers find that they are in a history where Carthage won the Second Punic War. Measures must be taken to protect time travellers from suffering such mishaps and the answer to this problem is the Time Patrol.
Theoretically, how can the problem be accounted for? Some propositions would obviously make no sense, e.g.,: A time criminal departs from 1960 A.D. to 218 B.C. In that year, he ensures that the Scipios die at the Battle of Ticinus. Then, in 1960 A.D., immediately after the time traveller's departure, the world changes to whatever state it would have been in if the Scipios had died at Ticinus! I trust that everyone can see that this makes no sense. And yet I have spoken to someone whose initial response was that the time traveller's intervention in 218 B.C. would cause the world to change in 1960.
I have accounted for the problem by assuming that, just as there are three spatial dimensions, there are two temporal dimensions. Thus, in the first temporal dimension, state A of the three dimensional universe is succeeded by states B, C, D etc of that same universe. In the second temporal dimension, an entire four-dimensional continuum in which Rome won the Second Punic War is succeeded by a 4D continuum in which Carthage won that war.
There are at least two problems with my account. First, it does not fit with the way Time Patrol agents discuss the issue. Secondly, although my account seems clear to me, it does seem clear to everyone else and we wind up not understanding each other.
There is something about the concept of time travel that gets us confused. People who are trying to imagine that an effect, a time traveller's arrival, can precede its cause, the time traveller's departure, continue to assume that effects succeed causes and thus, for example, that the effects of the time traveller's intervention in 218 B.C. happen not immediately after that intervention but after his departure from 1960.
Addendum: At least some of what the Time Patrollers say must surely be incoherent but I have argued this before.
9 comments:
It's only incoherent if you're reasoning from assumptions that don't include time travel.
And 1960 doesn't change, the whole stretch after the POD changes.
I think that, if someone says (I am paraphrasing but accurately), "It might turn out to be the case that I who exist and am saying this here and now do do not in fact exist and am not in fact speaking here and now," then that proposition has to be considered incoherent.
One too many "do"s.
Paul: not in the slightest, given that (exempli gratia) that it's perfectly possible for a particle to be in two different positions at the same time.
That's what gives Everard the willies as time (or 'time in terms of his world-line') goes on in the Time Patrol series: that existence is -conditional-. Never settled, never secure.
"All that is solid melts into air", as the Bard put it.
Not only can an individual cease to exist at any moment -- that's always been realized -- but the entire world, and universe, can -cease to have ever been-.
That turns out to be the role of the Time Patrol: to prevent that type of ever-branching chaos.
Superimposition? So the "I exist" and "I do not exist" scenarios would both exist? But the Patrol thinks that it has to be one or the other.
If a time traveller departs from now to prevent my parents from meeting each other seventy five plus years ago, then I do not cease to exist now.
Possible Timelines:
(i) My parents meet. I am born and live into adulthood.
(ii) Someone prevents my parents from meeting. I am not born and do not live into adulthood.
An Impossible Timeline:
(iii) Someone prevents my parents from meeting. I am not born but nevertheless live into adulthood and then cease to exist.
The "someone" need not be a time traveller.
Paul: if someone prevents your parents from meeting, you never existed... until some other quantum fluctuation (of the type in the later Time Patrol stories) ensured that they meet... and then they don't, 'again'... and then the universe never expanded... and then...
Scary, eh?
Incidentally, the Patrol can rectify a random -historical- variation, but not one in the really remote past... say, two hominids never meet...
The successive "again"s are successive moments in a second temporal dimension.
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