I have watched BTTF approximately a million times and I have genuinely never noticed that. Right…another rewatch required methinks!
While not on Earth the Star Trek:TNG episode “Yesterday’s Enterprise” did this. An anomaly opens up in front of the Enterprise and they note a ship seems to be coming through. Then the bridge shimmers a bit and all of a sudden everything is a bit different. Of course, the crew are unaware of this at all. The previous Enterprise (C) limps out of the wormhole badly damaged. Things happen and Guinan (Whoopie Goldberg) has a “sense” that things are wrong and prevails on Picard to send Enterprise-C back despite that it will almost certainly be destroyed in the battle it had recently escaped because the wormhole will plop them back to the place and time they left. Ent-C goes back…bridge shimmers and they say it loooked like a ship but it’s gone now. Shrug…ah well. (but there is a twist which appears in a much later episode)
I wouldn’t say that there was a plausible explanation in Quantum Leap. Rather, the characters are all nearly as clueless about how it all works as the audience is. There are some rules that they (and we) learn, but the rules don’t make sense, and might in fact be due to direct divine intervention.
Which is a perfectly valid way to make an interesting story.
Exactly. It’s like Harrison Ford once said to someone asking similar questions about some other famous movie. “Hey kid, it ain’t that kind of movie”.
ETA: At least mostly. I think they messed up with Part 2 by trying to make it that kind of movie, and it was noticeably worse than Parts 1 and 3 for having made the attempt.
A few versions of time travel in fiction I can recall:
Time travel works, but “unravels” the universe back to the point the traveler or transmitted information arrives. So only a lunatic uses it unless there’s an existential threat.
Time travel works, but time is a whole; the universe is a “standing wave” and inconsistency can’t happen.
You can travel into the past and change things, but the effects are local and revert as soon as the time travelers leave. As a result history is full of rampaging gangs of rapists, torturers and murderers who wander through time committing atrocities, beyond all punishment because the universe erases all evidence of their crimes when they leave.
Time travel is possible; but information can only go forward, not back preserving the timeline. The protagonist in that short story liked scamming time travelers, buying all their antique goods and clothing in return for futuristic gifts that as soon as the traveler returned to their own time would just drop to the ground. The traveler didn’t even get to keep the memory he’d been scammed.
Time travel works, but there’s a sort of inertia that causes history to follow its original course and erases evidence that the travel ever occurred in the first place. Whether or not this inertia can be overcome and what happens if you do differs from setting to setting.
Time travel is possible, but cause and effect normally work only at the standard one second per second rate, so no changes you make in the past can propagate to your own time. And for the same reason each moment in time is essentially its own universe, where history has happened differently; you can’t go back in time to 1930 and shoot Hitler because the existing 1930 isn’t the moment that Hitler existed in, but a different world entirely.
I know there was a series of novels in a setting like that, although the name escapes me. The one part I recall was some characters meeting with President Lincoln in the 1860s about the ongoing crisis, and it being mentioned that the Civil War was really short when time travelers showed up and promptly stomped the Confederacy into the dust.
More importantly, IMHO, is they do something that’s seemingly rare in time travel fiction. They pull people from the past to the present and show how they react to all the differences between the present and their original time. The scenes with Napoleon at the ice cream shop and Genghis Khan, Beethoven, Sigmund Freud, Joan of Arc, and Abraham Lincoln at the San Dimas mall were hilarious. It’s a shame that this scenario (people from the past reacting to the present day) is such a rare scenario in time travel movies.
As I (barely) understand it, as the universe expands the total amount of energy/matter expands. Does this mean that, temporarily, the size of the universe has grown ever so slightly when both widgets exist at the same time, and shrunk ever so slightly in the future when the widget is sent back in time?
Well…there is your potential paradox. They find the keys behind the sign but they can only be there if, in the future, they follow through and arrange everything the way they wanted it. But, what if later, they decide it all worked out so don’t bother to do all the tasks needed to arrange their now past?
They knew the difference between manipulating time, and outright fucking with it.
I have read some Lem, but probably not as much as I should have. He’s certainly well-known in my mind
Mass is conserved, but only if you consider the fourth (temporal) dimension. Do too much time travel, and you could reverse the expansion of the universe by changing its instantaneous mass. Not recommended.
I’ve seen that used in fiction, I think - deliberately using time travel to make sure the universe eventually collapses
Nice to know. For all those who like SF and time travel (see title of this thread) and don’t know Stanislaw Lem, I can recommend him warmly. You will need a translation, as he wrote in Polish, but it is worth it. He is intelligent, funny and subversive in his short stories, and Solaris and the Futurological Congress are classics in my timeline.
Towards the end of the webcomic Narbonic, we learn that, in the future, one of the main cast will become president, but of a polluted, dying Earth that soon won’t be able to support life. She sends a message back in time with an instruction (“Open the pool cover.”) that she hopes will lead to a better future, but also explains that time travel, even just to send information, requires an amount of power roughly equal to the total amount of energy in the universe, so sending the message also means destroying the entire (future) universe. Which hopefully won’t matter, if they remember to open the damn pool cover.
Then the keys wouldn’t have been there.
Or maybe someone else could have done it. Maybe, 10,000 years in the future, some grad student was writing a thesis about Bill and Ted and found out that they never hid the keys, so he went back and did it himself. Who knows? That’s the thing about time travel - there’s always enough time for anything to happen.
In Starplex it was done to precisely balance the mass of the universe between expansion and collapse, to maximize its lifespan. Apparently multiple times, starting with entire galaxies and later fine-tuning things by sending back single stars.
That’s the one I was thinking of (though clearly I had the details wrong)
That’s a story Mark Hamill tells, and he does a spot-on Harrison ford impersonation (starts at the 1 minute mark):
Or, free will is an illusion. See, e.g. Wilson, Robert. An Investigation Into Certain Mathematical Aspects of a Rigor of Metaphysics (revised), unpublished Ph.D. thesis manuscript, as referenced in Heinlein, Robert A. By His Bootstraps.
That’s the way time travel works in Connie Willis’s stories (including the Hugo-winning Doomsday Book). Time travel is possible, but it doesn’t change the past because everything the time traveler does has always happened and the time-traveler’s actions have always shaped events.