Hewitt explains that the time machine must return to the present, a moment after departing, before going to any other time. As a consequence, time used in the present day is lost forever.
Every time they move in time, they have to come back to just slightly later than they left, and if anything delays them in the “current” time, that time is lost, which creates the dramatic urgency to get things done “in time”.
Of course, at the end of the novel, they find a way to work around this limit “at the last minute”. It involves a self-existing diagram, just for fun.
Hendrickson is all set to walk into Greenspan’s office empty-handed, when he is stopped by a surprise visitor—a future version of himself, carrying a finished copy of Viking Columbus … This Hendrickson reassures him that all he has to do is return to the past and complete Viking Columbus, and that everything will work out in the end. Hendrickson #2 then walks into Greenspan’s office with the completed film.
Hendrickson #1 realises how the film can be completed in time: once they return to the present they can take as long as necessary in post-production, then jump back to before the deadline with the finished product. Filled with confidence, he returns to Vinland to complete filming.
Which would explain the Mandela Effect. I go back to the past and convince the Monopoly illustrator to not have a monocle on Mr. Pennybags. That change ripples through the temporal universe but for some reason in a few people that change does not 100% take place.
Speaking of Mandela effects, when I saw I had replies in a thread called Time Travel in Fiction, I was like, “Did I post to a thread called that?” before seeing that a mod has taken the tangent and made a new thread.
Silly me; I just remembered that I have written a time travel story myself which requires events in two different time periods to happen ‘simultaneously’.
If you use a wormhole to connect two different locations in space time, you will experience time at the same rate at both ends of the wormhole - so if you go back in time through the wormhole, then wait ten minutes and go back through the same wormhole, you will find that ten minutes have passed at the other end of the wormhole too.
Of course it is more complicated than that, if you start buzzing back and forth through the wormholes willy-nilly; but in the simplest case, time passes at the same rate at both ends of the portal.
Another trope I have seen mentioned a lot, but never actually seen firsthand in fiction, is the notion that if you travel in to the future or past, you find yourself floating in space because the Earth/the galaxy/the universe has moved while you stayed in the same place.
It always kind of yanks me out of the suspension of disbelief, this one, because it requires a privileged or absolute frame of reference for there to even be any such thing as ‘staying still while the universe moves’
There was also a thing I saw somewhere (maybe in fiction) that time travel can’t exist because in any timeline where it is invented, it ends up being used in a way so as to create a butterfly effect that results in time travel not being invented
I’ve seen this in Strontium Dogs, the comic strip in 2000AD. Mildly amusing, of course, that when this strip was written, 2000 AD was way in the future; now it is ancient history.
If
the laws of the universe permit time travel
and
the past can be changed
then
A time machine will never be invented in that universe.
His reasoning: after you invent a time machine, too many people have too many good reasons to change the past. Sooner or later, someone is certain to meddle. The only timeline that never gets changed is the one where time travel is never invented.
Darn it, ninja’d multiple times while I was typing one post!
It also just assumes that whoever invented time travel couldn’t just… account for it? Gravity and time are connected anyway, so it’s really, really easy to throw in some handwavium about tachyon particles following gravitic gradients that keep the traveler anchored to the same geographic location, or similar hokum.
My favoured method of time travel, which is chronologically-displaced wormholes, automatically accounts for it; you can only travel to the location where the other mouth of the wormhole is located, and if that is on the surface of Earth, problem solved.
Hawking’s Chronology Protection Conjecture is different from the Niven Effect. In the Niven Effect, time travel is physically possible, but just never gets invented. In Hawking’s conjecture, there’s some absolute law of physics that we just don’t know yet that makes it impossible.
One place this is used is in the third-party quel* to Portal, called Portal Reloaded. In it, the Portal Gun can now create a third portal, connecting to a point exactly 50 years in the future. So in addition to all of the standard Portal weirdness, now you have to travel back and forth between the “present”, when Aperture Labs are all new and clean, and the “future”, where they’re ruined (things like some panels missing, so you can’t put portals in the same places, but also some walls crumbled, so you can go through them). The goal, of course, is to find clues in the future as to just why it’s all ruined.
*Because of the time travel, it’s unclear whether to call it pre- or se-.
I agree that is a very good pick, but I think the end of 2001: A Space Odyssey is even better, because nobody understands it; it makes no sense. Which seems fittingly unsatisfactory to me.
Another thing that worries me is that nobody in this thread has mentioned Stanislaw Lem’s Ijon Tychy, in particular The Seventh Voyage. Is Lem that little known in the USA? That would be a pity. I think I should page the guy who is pretty good at SF Story Identification: @Andy_L, what is your take on Lem?
I’m surprised no one has mentioned the movie ‘Primer’ yet. I have to admit when I first saw it I did not quite understand it, and I only dimly remember the plot, but I believe it’s considered one of the more plausible time travel movies.
That one interesting aspect is that the only way to travel back in time is to go back to a time machine device that already existed in the past. So no DeLoreans going back to 1955, and the real scientist who wanted to see his dad in the past is out of luck; you have to build a machine today, then tomorrow you then can then go back to the today which is now yesterday.
That might seem like it would make for a more much more boring time travel movie, but in Primer this results in a crazy mess of twisty timelines:
Quantum Leap was like this. While Sam is dealing with events in the past, time is also progressing in the future for Al, who can only ever interact with Sam linearly.
In one episode in particular, the Quantum Leap project’s funding is under threat, and Al tries to get Sam to change something in the past to show future senators that the project is viable. At the end of the episode, when it looks like Senator Stodgy Old White Guy is about to pull the plug, Sam is in the past helping a woman study for her bar exam. He corrects her on a major point she had wrong, which would have caused her to fail the bar… and in the present, just before Senator Stodgy Old White Guy votes to cut the project, he’s suddenly replaced by Senator Thoughtful Lady, who is now a senator because she didn’t blow her bar exam, and she extends the funding.
I’ve always thought that’s nothing more than a cop-out to create a false sense of urgency, unless the writers come up with a plausible explanation (like in Quantum Leap).
I liked how the final season of Agents of SHIELD subverted this one. “Meh, we’ve got an infinite amount of time to solve this problem. Let’s take a few years off and have a kid.”
