The master of time travel fiction explains the fundamental problem with stories based on the concept:
The problem afflicting all time travel stories, which makes cause and effect paradoxical, is that time travel makes moral law is paradoxical.
In a universe without time travel, the things done by a man in the past are done.
What is in our past cannot be changed, and the future cannot be known. But introduce time travel, and, suddenly, anyone whose future actions you know (because he is from your past) can be treated as a creature without free will, that is, an entity with no moral self determination. He is an NPC.
This includes the past self of the time traveler himself: from the point of view of the Wednesday Dr Who, Tuesday Dr Who is a like a robot, or a historical character, someone who cannot change his actions because they are set in stone. An NPC.
With time travel, an immoral act like killing an innocent baby, whom the Time Traveler knows will grow up to be a tyrant, seems moral, and a moral act, like saving that same innocent baby, seems immoral.
To make matters worse, if the time traveler on Thursday wants to undo an act he did on Tuesday, such as killing a child fated to be a tyrant, and he leaps backward in time to shoot his Monday self in order to preempt the Tuesday attack on the child fated to be a tyrant, he is killing a man who is, at that moment on Monday, not yet guilty of any crime. Is this moral or immoral? Is this suicide or self defense?
So if yet another version of himself from his own future leaps out of Friday afternoon to land in front of Wednesday, pistols ready, to prevent his Thursday self before the fated this Monday crime of killing his Tuesday self preemptively, can the Wednesday time traveler rightfully defend himself?
Because if it is wrong for Thursday on Monday to kill his innocent younger self in order to prevent the killing of the child on Tuesday, logically, by the same token, it must also be wrong Friday to kill Thursday on Wednesday to prevent Thursday from killing Tuesday on Monday to prevent the prevention.
And yet, also equally logically, on Wednesday, the Time Traveler is guilty of killing a child, and so can be killed in retaliation, or, better yet, killed before he commits the crime, because, unlike human justice, time traveler justice actually can unmake the crime and restore the dead.
Therefore, logically, the fact that killing the innocent is immoral makes it moral for a time traveler to kill the innocent.
I won’t even mention the moral problems arising from the possibility that the tyrant the child is fated to become turns out, in a plot twist, to be the Time Traveler himself, and the one event that warped and embittered his young mind to set him on the path of tyranny was seeing all these murders taking place in the nursery when he was young.
That is the problem with time travel stories.
Mr. Wright is no doubt correct. That being said, his City Beyond Time is without question the greatest collection of time travel stories ever assembled.
Second beginning. This one brighter than the others:
I recall my first view of the city.
I thought it was a job interview. I had no other work, no future, and the best woman I had ever laid eyes on walked out on me the night before. I wasn’t in a great mood, but, at that point, I was willing to listen to anything.
Almost anything.
“Time travelers?” I said, trying to look chipper. I was trying to think of a polite way to say goodbye and get lost.
He didn’t look crazy. (The real crazies never do). Mr. Iapetus was a foreign-looking fellow in a long red coat of a fabric I didn’t recognize. He had dark, magnetic eyes, high cheekbones, and wore a narrow goatee.
His office was appointed with severe and restrained elegance. To one side, a row of dark bookshelves loomed; in the center was a wide mahogany desk, polished surface gleaming; to the other side, heavy drapes blocked a hidden length of window. I did not think it odd at the time to see bright sunlight shining from the carpet at the lower hem of the window drapes. But it had been raining outside when I entered the lobby just behind me.
Mr. Iapetus was standing by the window. He took up a fold of drapes in his hand. “I believe in what you might call the shock therapy method of indoctrination. It helps make the tedious period of disbelief more brief.”
A wide yank of his arm threw the drapes aside. A spill of blinding sunlight washed around me.
Blinking, I saw I was high up, overlooking a shining city. I had been on the ground floor when I came in. Now, I was miles up in the air. And glory was underfoot.
