Paradoxes don't matter

[Darth Ruinus]

A man jumps back in time to kill his grandfather. In time travel settings I've seen/read, this would either: cause an alternate timeline where the man succeeds in killing his grandfather and he is never born, or all attempts to kill the grandfather fail.

However, are there settings in which a man can go back in time and succeed in killing his grandfather, with no alternate timeline being created? Or similarly, where a computer can appear in 2010 with data on technology created in 2100 and give rise to that technology 90 years earlier? Settings in which the universe doesn't care about paradoxes, and people can cry "That doesn't make sense!" all they want, but it still happens?

I think the Xeelee setting is like this, but I'm interested in knowing if there are more.

[Sarevok]

Uh Star Trek ? They cry all about Paradox but mere presence on 20th century Earth for a few seconds is enough to change everything through butterfly effect.

Then there is Futurama. Fry became his own grandfather and the universe did not care.

[Darth Ruinus]

Uh Star Trek ? They cry all about Paradox but mere presence on 20th century Earth for a few seconds is enough to change everything through butterfly effect.

Then there is Futurama. Fry became his own grandfather and the universe did not care.

Really? I thought Star Trek followed the "alternate timeline is created" route? And yes, now that you mention it I remember that Futurama episode.

[LionElJonson]

I think the Homestuck universe might count. Maybe.

[dworkin]

A common idea is that of 'the future, which now does not happen'. Going back in time and doing things differently results in a different future despite some evidence to the contrary like the time traveler's memories, or a history book they convieniently have.

A good example is the Bellisarius saga by Eric Flint and David Drake. Both sides send an agent back to 5th century Earth. Both have complete records of history and then seek to alter that. In the story the standard history now doesn't happen, even though it did before.

[NecronLord]

Doctor Who is like this. Sometimes. There are technologies to allow paradoxes to happen without consequence.

[Lord of the Abyss]

In Thrice Upon a Time by James P Hogan time travel - or rather, time communication - causes history to rewrite itself from the moment the message is received. No alternate universes, no paradoxes. They did it once to stop a plague, and another time to warn the past that their new fusion plant was going to create hundreds of stable micro black holes (a consequence of the same physics that allows time travel).

Einstein's Bridge by James Cramer time travel is essentially the process of "unraveling history" until the desired time is reached. No alternate universes, but your home time is destroyed.

In Simon Hawke's Time Wars books, small changes to the timeline without producing an alternate universe are perfectly possible*. The Principle of Temporal Inertia allows for such changes by slowly pushing events after the change into approximating the original timeline, which prevents any small changes you make from becoming large long term ones. Which is why they can have large numbers of people running around in the past and the future still stays the same. So yes, you can go back in time and successfully kill your grandfather; but grandma will still probably marry someone much like him, produce a father much like your original one and so on.

In Ben Franklin's Laser the ability to genuinely change the past was the whole point of the exercise; they wanted to kickstart human progress.



* As it happens, creating an alternate universe in this series is a very bad thing since they aren't stable thanks to that Principle of Temporal Inertia; eventually they remerge with the main timeline with unknown but apparently very bad consequences.

[Stargazer]

I don't think it is possible to erase your own existence through time travel without creating a paradox. However, going back and changing something without erasing yourself could be workable. One must simply make a message that tells your future self to be sure to go back in time to do something.

[Simon_Jester]

But what would be the consequences of a paradox? It seems incredible that the whole universe would somehow unravel if a paradox was created. What would happen?

The fear of paradoxes is strong enough that I, for one, was greatly amused to see this Shlock Mercenary strip that pretty much subverts the whole concept.

[Dragon Angel]

The Zipang anime is like this (imagine The Final Countdown's story, but featuring a Japanese battleship instead of an American one), when one of the main characters discovers that his father was accidentally killed by a car carrying someone his crew had earlier rescued. Technically, he no longer exists at that point, but he is still shown solid and mostly healthy, and is implied to be continuing to survive.

[Lurks-no-More]

People worry about paradoxes because they are breaches of causality, and the fact that causality can't be broken - that effects follow causes and have causes - is pretty much the cornerstone of not only science and technology, but of every human worldview.

I'm not sure if a single paradox would cause the universe to unravel, but I'm pretty sure that they are unhealthy if at all possible.

[LionElJonson]

Or, of course, the universe could be a giant paradox-generating machine, and sometimes you just have to toss your corpse out the window.

[Stofsk]

Uh Star Trek ? They cry all about Paradox but mere presence on 20th century Earth for a few seconds is enough to change everything through butterfly effect.

Then there is Futurama. Fry became his own grandfather and the universe did not care.

Really? I thought Star Trek followed the "alternate timeline is created" route? And yes, now that you mention it I remember that Futurama episode.

Trek is hardly consistent with this, but TOS was fairly consistent in that going back in time would change the time traveller's future (it could create an alternate timeline for all we know, but the point was that the time traveller would not be able to go to any of those timelines, he was stuck with the one he was on that he'd changed).

The many timelines theory was brought in by Brannon Braga in 'Parallels'. I am not a fan.

[Archaic`]

Or similarly, where a computer can appear in 2010 with data on technology created in 2100 and give rise to that technology 90 years earlier? Settings in which the universe doesn't care about paradoxes, and people can cry "That doesn't make sense!" all they want, but it still happens?

Apparently, this might be how time travel actually would work in our universe, if this recently published theory about "post-selection" is correct.

As for fiction...pretty sure Stargate did this. Messages sent back in time totally rewriting history, but those who went back in time remained as they were.

[thegreatpl]

ok, here is something. Apart from one example i think, any of these could have alternate timelines and universes created as a result of the time travel. That future is carrying one like nothing happened, but a new one has been created.

How would we even know that a new universe had been created? Or had not been? Especially if once a new universe is created you couldn't travel to the hold one.

Or, as i remember one book i read having, Paradoxes simply dont get created because the universe makes sure they dont happen. This book i remember had 2 experiments done to try and witness the people leaving messages for the future selves before they had left them. Or rather, to watch the messages appear.

The first attempt the aircar (or plane) carrying the watches in the future crashed before they got there, and the 2nd time, when they were in place before the time traveling group left, the message was never left because the time traveling group got attacked.

[Simon_Jester]

People worry about paradoxes because they are breaches of causality, and the fact that causality can't be broken - that effects follow causes and have causes - is pretty much the cornerstone of not only science and technology, but of every human worldview.

Why does that mean the world would end (or even that crises would occur) if something that confuses us happens? The universe is not obliged to refrain from confusing us.

[bilateralrope]

Then there is Futurama. Fry became his own grandfather and the universe did not care.

That wasn't a paradox because Fry has always been his own grandfather. Instead it's a stable time loop.

As for the universe not caring, it did cause Fry to have some unusual brainwave patterns.

[lordofchange13]

in some of the newer doctor who storys he discribes time travellers becomeing part of that time. so for instance a amn kills his own grandfather but the man is still there is becuase he is part of the time as a completly new person with no ties to who he was before he time traveled.
somewhat similer to the multiverse thing. on a secound note if there world ended you wouldn't notice becuase you'd be dead.

[RowanE]

How about Schlock Mercenary? there was a big storyline with a galaxy-ending disaster, and one character went back in time, saved the galaxy, and continues to exist in the same universe as his past self, without worrying about a paradox.
(should that be spoilerised?)

[Patrick Degan]

In Simon Hawke's Time Wars books, small changes to the timeline without producing an alternate universe are perfectly possible*. The Principle of Temporal Inertia allows for such changes by slowly pushing events after the change into approximating the original timeline, which prevents any small changes you make from becoming large long term ones. Which is why they can have large numbers of people running around in the past and the future still stays the same. So yes, you can go back in time and successfully kill your grandfather; but grandma will still probably marry someone much like him, produce a father much like your original one and so on.

Farscape had a second season episode which employed a similar principle —Chricton, Aeryn, Stark and D'Argo wound up accidentally projected back in time to a critical juncture point in one world's history in which, originally, a Peacekeeper officer averted a massacre at a temple, which ushered in an era of peace and mutual cooperation between the planet's two main ethnic groups. Their actions changed history three or four times until one result ended up witih a massacre occurring, which was then covered up by Peacekeeper propaganda and an enforced truce in the succeeding centuries. But none of the time changes which occurred on the planet ended up affecting the larger universe —though the crew left aboard Moya observed multiple alterations of the planet they were orbiting, including its temporary disappearance at one point.

[Omeganian]

There is The End of Eternity, where no paradoxes exist because the organization which creates timeline changes exists outside of time. At one point, the characters even discuss the Grandfather Paradox in ancient (our) science fiction. It is stated that just about every Reality Change will after a few thousand years smooth out if not to zero, then below detectability threshold.

[Kythnos]

There is The End of Eternity, where no paradoxes exist because the organization which creates timeline changes exists outside of time. At one point, the characters even discuss the Grandfather Paradox in ancient (our) science fiction. It is stated that just about every Reality Change will after a few thousand years smooth out if not to zero, then below detectability threshold.

You must be talking about the "individual" changes to the past? (or I don't remember the book very well) I remember that Eternity's changes to the past pushed back human technological development by more than ten thousand years. Yes they were protected by being "outside the stream of time" but the world still suffered because of their changes.

[thegreatpl]

How about Schlock Mercenary? there was a big storyline with a galaxy-ending disaster, and one character went back in time, saved the galaxy, and continues to exist in the same universe as his past self, without worrying about a paradox.
(should that be spoilerised?)

If i remember correctly, that could only happen in the first place because the galaxy was being destroyed. Time Travel is impossible otherwise in that universe, as had been strongly emphasized. Seems the universe has a galactic reset button if you throw part of it off the timeline.

Schlock and Kevyn both could exist because they came from an alternate universe or something. I'm pretty sure there was mention of the galaxy being thrown off the regular galaxies FTL interface or something, which was why they couldn't just flee the galaxy in any teraport ship.

Although they did worry about paradox to begin with. Then proved it did not apply.

[Rossum]

The way I see it, the only way for time travel to be profitable is for one to create a stable time loop and work to avoid paradoxes.

If you send someone back in time to stop an accident (such as stop Hitler from causing WWII) then you are asking them to alter events that have already happened. At best they will fail and you will find the destroyed remains of their time machine in the past or something. Either that or they go on to create some alternate timeline without WWII and you never get to see your time machine again. Worst case scenario, they go back in time and erase history causing you to either cease to exist or have all your memories erased and overwritten with a history where WWII never happened.

However, if you were to go out of your way to orchestrate a whole bunch of stable time loops where you rescue all the people who would have died in WWII and replace them with realistic corpses while covering all your tracks so that nobody would ever know that time travel was involved in WWII then you could rescue everyone from WWII. It results in a stable time loop where you rescued everyone and everyone had always been rescued.


In short, paradoxes might not actively destroy the universe or anything but I can't imagine a situation where society as a whole could benefit from a paradox or really control what happens.

Sure, you could use time travel to dispose of radioactive waste by causing a paradox that shoves it into an alternate timeline or something (Just locate a point in time where you know there is no time machine full of toxic waste and then have your time machine of toxic waste travel there). But then you've just set an uncomfortable precedent where people are dumping toxic waste into alternate timelines. How do you know that some future versions of yourself aren't loading radioactive isotopes into Time Dumpsters and sending them to your world?

Keep in mind that if someone actually wanted to use time travel to get rid of garbage they could probably put it into a time machine that doesn't compensate for Earths rotation and effectively send it into space. If thats the case then there should be no paradox involved... a Time Barge full of trash appears in outer space where nobody cares about it and it always had appeared in a place where nobody cares about it. No paradox involved. Heck, if in the future scientists develop a way to use radioactive waste as a fuel source and it becomes valuable then they could just travel to our time and buy it with future dollars (or not, they just offer to cart it away). As long as they are smart enough to have always asked to cart away our radioactive waste then no paradox should be necessary... or they could wait until we bury our radioactive garbage in a place where nobody is looking and 'steal' it in such a way that nobody cares if it goes missing.


The point is that paradoxes are confusing and confusing things are not always profitable. If your method and strategy for time travel involves things randomly appearing from futures you will never have or sending time travelers and their expensive equipment to alternate timelines you will never meet again then you are either going to lose alot of money or wind up with future crap you will have no control over.

Though... I'll admit that if you are facing an End of the World scenario and your mission is to send a message or people back to your past selves to ensure that they don't run into the same problem that you ran into then paradoxes can be desirable.

[LionElJonson]

The way I see it, the only way for time travel to be profitable is for one to create a stable time loop and work to avoid paradoxes.

Not if the demon you're trying to kill can only be killed after ensnaring him in a giant mesh to time paradoxes.