It’s the age-old problem–“But if I go back in time and accidentally kill my grandpa, then how could I have time traveled in the first place?”
Or, well, it’s an age-old problem for fans of time travel fiction. Lucky for us, computers can fix everything. Well, the answer to the infamous Grandfather Paradox at least.
Computer scientist Doron Friedman programmed a computer with his own automation software to tackle the issue of a man going back in time and killing his own dad. According to Cosmos Magazine, this is how the process unfolded:
When Friedman ran this plotline through his program, it noticed the paradox by reporting a contradiction – namely that if the son travels back in time and kills his father, then how could the son have been conceived?
And when Friedman requested a resolution to the contradiction, the algorithm worked through thousands of possible scenarios to find those that were logically consistent – in other words, where the murderous son’s actions don’t rub him out of existence.
Once the program had worked through the scenarios, Friedman described two of the many possibilities that the computer had worked out. The first is notable for being one that Futurama viewers will likely recognize–it was employed in their Emmy Award-winning episode “Roswell That Ends Well.” This work-around involves that guy becoming his own grandfather; after going back in time and killing pops, the man then goes back and sires a kid who will become his father. (Of course, this requires the unpleasant possibility of getting involved with one’s own grandmother.)
The second possibility is exceptionally cool. It involves the guy’s dad having his own time machine (with George and Marty McFly used as the stand-ins, of course):
In 1954 Marty’s father George travels forward in time one year to 1955, when he impregnates Marty’s mother Lorraine before immediately returning back to 1954 – just as his future son, Marty, arrives and kills him.
Because George’s quick foray into the future allowed him to already conceive his son, the paradox disappears.
Yeah okay, it’s a bit silly because why would you decide to travel one year into the future to sleep with your significant other? But surely some savvy author could come up with a plausible reason for it, and prevent the Grandfather Paradox from ever causing a problem in their sweeping time travel epic.
Just make sure to thank our computer overlords in the acknowledgements, as there’s no telling what they might compute next if you don’t….
I don’t know if it’s the Asperger’s, but I’ve never worried about the grandfather paradox. I think that were time travel something humans could do, and a Traveler went back in time and did something stupid, the Traveler would not cease to exist. Rather, the Universe would resolve this inconsistency by “forking” to a new reality where the past events happened as experiences/caused by the Traveler, but in which the Travel still exists (albeit from a non-trunk reality now).
The Two Machine plot reminds me of a part from The Time Traveler’s Wife, notably, the origin of their daughter.
Well, if you are not allowed to have sex before marriage, time traveling to the future when you already are solves that problem.
A more plausible alternative: The grandmother is the one with the time machine. After her husband’s paradox-inducing death, she travels back in time to conceive with him.
It’s logical, the characters have enough knowledge to make it work, and there’s some real pathos in the narrative of someone getting one last chance to see their beloved partner, but only to set in motion the events that cause their death.
It’s nice to know that even if computers can beat us at Chess, we can still outthink them when it comes to giving female characters agency.
I like @3’s idea. Because I don’t know if the computer solution is all that logically consistent. If he goes back in time after conceiving with the future version of his partner, and is killed, then in another year when the time remnant shows up the person is all like “HOLY CRAP! YOU DIED! GET AWAY FROM ME!!!” and the conception still doesn’t happen.
It depends on your view of how alternate timelines are created, and whether they are separate from the original timelines rather than rewrites, in which case the grandfather paradox is moot anyway.
They missed the super obvious one: the person he thinks is his grandfather really isn’t. That is, the grandmother had an affair (in the original timeline, anyway. In the “grandfather’s dead” timeline, maybe she remarries the guy who is the actual grandfather).
Or, if we’re restricting it solely based on genetics and we know for sure that man is his grandfather, then maybe he had a twin.
A fun thought experiment, however I don’t believe backwards time travel to be possible. The only thing that makes any real sense would be the many universe theory, where you only *think* you’ve traveled back in time, but in actuality have simply shifted to another universe where things are nearly identical to ours. In which case, you’re free to muck about as you wish.
Forward time travel is entirely possible with FTL or near-to light speed travel. But forward time travel doesn’t make for good paradoxes.
Still, I do love a good stable time loop in fiction when it’s done well, as unlikely as such a thing is.
I built me a machine
To take me back when I was green
And paradox was strictly not allowed
But when I finally came to earth in the place that gave me birth
I found my grandpa standing tall and proud
And I’m my own grandpa, I’m my own grandpa
It’s a situation strange, but one I can not change
‘Cause I’m my own grandpa.
@naupathia: I disagree on your thought experiment. Assuming the many-universe hypothesis (by which I assume you mean that every possible outcome creates a new universe in which that outcome occurred), I think backward time travel should be fine and future time travel should be the broken one.
If you think of the many-verse as a tree of branching universes, then if you built a machine to go back in time, there is only one possible past to travel to. Your universe has only one past but infinite futures. I think you have the tree backward, so maybe we’re just picturing time differently.
I see the problem as going forward — if there are infinitely many universes created at every moment in time, how does one choose?
In fact, as soon as you arrived in your one correct past, you have by definition changed it and are therefore are immediately on a different branch of the tree. So unless you have some kind of marker to follow back to a different univers, you can never go home again. Best case, maybe you can go to a place that’s pretty much like home for all intents and purposes.
Of course, now Marty is 12 years older, meaning he’s had completely different life circumstances and probably wouldn’t have been hanging around with Doc Brown in 1985, nor could he have passed himself off as a teenager in 1955. So he ends up annihilating himself from existence anyway, because now he’s a different person entirely. Also I guess his brother and sister are toast.
Scenario #1: “after going back in time and killing pops, the man then goes back and sires a kid who will become his father”.
Because of how sexual reproduction works, the man would have only 50% of his father’s genes (randomly selected). Therefore, any child the man sired would have only 25% of his father’s genes, when he needs 100% for the loop to work.
Hint: Try cloning instead of sex.