Postscript: Myriad Multiverses
A postscript related to a recent column.
My theory is this: time travel stories propose that there is no privileged frame of reference: any point in time the time traveler enters becomes his present, all before that point is past, and all after is future. But please note that any events affecting the time traveler himself, including his memories, retain their normal arrangement of past, present, future.
In other words, time travel stories always make the unspoken assumption that the time traveler is immune from the effects of time travel, partly or wholly. If he travels backward to yesterday, for example, he does not have 24 hours of memory erased from his mind, nor does he turn into a baby if he travels back to his birth. He is outside his own effect.
Paratime stories assume no privileged frame of reference for any probable event. What is actual in this continuum is in unrealized probability in another, and in that continuum what is unreal here, there is actual.
Likewise, paratime stories assume that every decision branches the time into both decisions, except for the decisions of the paratime traveler. Like the time traveler, the paratime traveler is immune from his own effect.
If the paratime traveler enters the continuum where Germany won WWII, you do not, at the same time decide not to do that, and create a new continuum where you did not enter, because you decided to go to the continuum where the South won the Civil War instead; but that continuum also splits because you decided not to enter; and to go to where the Brits won the war of 1812; but also not; and you also at the same time went to the continuum where the American revolution failed; and not; and so on and so forth.
Meanwhile, the parallel version of you who wants to enter the colonial timeline also splits, and one split decides not to enter that timeline, but instead to visit the German-victory line, and crashes into your ship. Along with an infinite number of other versions of you, the bald version, the girl version. All the ships crash, and the only survivors are the Negro Nazi version of you who is fighting the Jewish Nazi version of you over the corpse of the Golden Robot version of you from the timeline where Giraffes rule mankind.
That is just listing timelines where wars are won or lost. Imagine now that every decision splits a new timeline, or every quantum vibration of every subatomic particle.
So, most science fiction stories just assume that the paratime traveler is immune from paratime. (The one exception is “All the Myriad Ways” by Larry Niven) .
But both types of stories simply assume a counterfactual which humans cannot imagine, and which, if true, would make life impossible. Perhaps an adroit science fiction writer like Ted Chiang can portray what it would be like to live simultaneously, aware of all the events of your life from childhood to death all at once, or to portray the forking paths of all possible decisions made and not made at once; but for the rest of us, the concept cannot even be expressed in words.