6.7 KiB
Time travel system
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Author: u/Chaigidel *
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Score: 12
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Created: 2015-10-10T19:59:57
Post:
Comments:
u/SpeakKindly [+7] (7 hours later)
On Earth-sized scales, light cones are basically flat. If we go back in time to kill Hitler when he was sixteen, the universe has 100 years to interpolate between the two fixed points. Statistically, most of the "weird things" should not happen in the last second of those 100 years: a Brownian bridge has value close to 0 when t is close to 1. So a second before you time-travel, everything within a light-second of you is basically unchanged.
But most of the interesting bits about history are happening within a light-second of you. So the fixed point of your departure screens off any real effect you might experience. There's only a couple of kinds of things that wouldn't get affected:
- Imagine if aliens 50 light-years away from us listen to our radio broadcasts, and start just in time to catch the end of World War II and send a reply. Then after the time travel, confused humans that remember World War II as we know it get a message from aliens referring to a history without Hitler.
- Maybe with no World War II, there's been a much more successful space program. Things it launched into space sufficiently far might survive, though they'd have to be going at a good fraction of the speed of light to stand a reasonable chance. Say a single, atomic twiddle at any point in time is enough to adjust for the space program. If the alternate-history spaceship made it 1 light-day out, roughly comparable to Voyager 1's distance, then it has a (1 day)/(100 years) chance of "surviving" the time travel: the probability that the twiddle occurs in the last day of those 100 years.
Most things we care about don't look like this. So most things we care about wouldn't be any different. Any future cosmic noise we observe might be different to the extent that our actions influence it to begin with, but to a first approximation, future cosmic noise is just random, anyway.
u/Aabcehmu112358 [+1] Utter Fallacy (7 hours later)
This seems like it'd be handled by the fact that the time travel machines appear to also be teleporters. Assuming a time traveler brings a time machine with them when they time travel, then the horizon of human expansion is suddenly extremely large, and the probability of something escaping rises significantly.
u/SpeakKindly [+2] (20 hours later)
That's true. Don't time travel to kill Hitler; time travel to bring back an army of Hitler clones!
u/want_to_want [+4] (an hour later)
Here, the universe starts to rearrange things so that the blue point is unchanged. Causality isn’t exactly going backwards, but it is being funnelled in a particular direction. People who descended from others who “should have died” in WW2 start suddenly dying off. Memories shift; records change. By the time you’re very close to the blue point, the world is essentially identical to what it would have been had there been no time travelling.
Why can't the universe just create a delusional time traveler who thinks WW2 happened?
u/None [+1] (2 hours later)
It's less interesting from a Time War point of view (in my opinion). This way, people get a chance to actively fight over whether their history exists.
u/want_to_want [+1] (3 hours later)
No, I mean, if the universe is editing history for consistency between two particular points in spacetime, why doesn't it do it in the most economical way?
u/None [+7] (4 hours later)
Economical to who? Maintaining a delusion is tricky business requiring continuous contrivance and monitoring. Random heart attacks can be caused by a few molecules in the wrong place, just the once.
u/Uncaffeinated [+4] (6 hours later)
If you want a Time War, Achron has the best mechanics for one that I've ever seen.
Of course, it does fail your fourth criteria, since it relies heavily on the concept of meta-time.
u/TimTravel [+3] (7 hours later)
This makes little sense to me. It guarantees that all circumstances of the departing time traveler remain consistent, instead of just the ones that are important. It also requires "first cause", which is inconvenient.
https://www.reddit.com/r/HPMOR/comments/2xie39/time_travel_and_why_everyone_gets_it_wrong/
u/Aabcehmu112358 [+2] Utter Fallacy (6 hours later)
This time travel machine is also a teleporter. If you add in self-replication, then a low-priority time traveler can just print out a copy of the time machine, take the copy with them, and then as soon as they start getting to close to their exit-point, enter their copy-machine, and teleport out of the danger zone.
Another problem is that, as I understand it, the timespace volumes of every jump is relative. That means that, potentially, time travelers will appear to have different priority to different observers, which in turn implies that those observer's will have different histories.
u/Chronophilia [+2] sci-fi ≠ futurology (18 hours later)
Well, a second jump is a time jump that would not happen if the first jump hadn’t. So for each arrival in a time jump, you can trace it back to the original jump-point. Then your priority score is the (negative) of the volume of the time-space cone determined by the arrival and original jump-point.
What if the original jump-point is not in the future of your arrival? E.g. make a first jump back, wait in normal time until you've left the past light-cone of your departure point (travelling through space if necessary to avoid being erased by your departure point), and then make a small jump back? You might end up with negative or even imaginary priority, if I'm reading the description right.
I'm fairly sure there's some way in this system to create arbitrarily many duplicates of an object or person, which seems OP, but I can't quite work out the details so maybe it's not possible.
u/ArgentStonecutter [+1] Emergency Mustelid Hologram (50 minutes later)
This looks like it'll end up much like Fritz Leiber's "Time Wars" series, with "the law of conservation of history" replacing your blue and red light cones.
u/NasalJack [+1] (6 hours later)
It seems like there's too big a risk to ever interact with another time traveler. The instant you know you've met another time traveler it is in your interests to jump elsewhere to avoid potential erasure, since whichever one of you had the higher priority could have easily jumped in the near future, erasing both of you from time.