Thought Exercise,how do you think timetravel changes history

[MKSheppard]

And why would hypothetical future time travelling cultures give a fuck about Hitler? Do we give a fuck about Atilla the Hun?

I chose Hitler because he's one of the first things that springs to mind. Other people who spring to mind on some thought would be Abraham Lincoln -- counterattempts to prevent the assassination, and counter counter attempts to cause his assassination earlier.

And while the Time Travelling Morlocks from 802,701 AD don't care about Hitler in the same way we don't care about Genghis Khan; once time travel occurs, the chances of secondhand users of time travel go up -- e.g. the Morlocks make a visit to 2080 AD and forget to lock the machine -- leading to it being hyjacked by a group of bored college students who want to see what happens if Kennedy was never shot -- that kind of stuff.

[Stark]

Except that's impossible, because any culture with time travel can effortlessly retrieve any 'lost' time machine, even if they're dumb enough not to have a remote control.

[MKSheppard]

Except that's impossible, because any culture with time travel can effortlessly retrieve any 'lost' time machine, even if they're dumb enough not to have a remote control.

Once time travel's invented; it can't be uninvented -- and the main limitation on time travel is how long the culture lasts after invention of the time machine -- does it last for another thousand years, or does an asteroid hit the planet six months later?

The first fifty or so time-travellers will be like you posited; smart and making sure that they can recover the machine easily, either by adding in lockouts or the aforementioned remote.

But eventually, the technology of time travel -- or at least the access to it will spread to the lowest common denominator -- like Grad Students -- and civilization will weep.

[Havok]

Wow. Do you have any kind of evidence to back up the multiple claims you are stating as fact? 'Cause I hear that potential world/galaxy/universe changing/destroying technology always finds it's way into the hands of grad students.

ITT Shep is a fucking idiot and likens time travel technology to cell phone technology.

[CarsonPalmer]

But eventually, the technology of time travel -- or at least the access to it will spread to the lowest common denominator -- like Grad Students -- and civilization will weep.

Except for the part where the smart folks go back in time to prevent the grad students from ever getting their hands on the time machine, since they can use time travel to undo time travel. Or just make the interference of the grad students undetectable.

[Werrf]

But eventually, the technology of time travel -- or at least the access to it will spread to the lowest common denominator -- like Grad Students -- and civilization will weep.

Except for the part where the smart folks go back in time to prevent the grad students from ever getting their hands on the time machine, since they can use time travel to undo time travel. Or just make the interference of the grad students undetectable.

But then we're getting into TimeCop territory, and I don't think I could cope if Van Damme turned up on the thread.

Although, on a serious note, if time travel ever were to become established, most likely nobody will ever know what happens if you alter the past, because as soon as the past has been altered, all your memories, all your references, every bit of history will be based on that alteration. For that reason, if nothing else, I can see any society that possesses time travel having some kind of time police and/or extremely rigid control over all use of time travel*, because prevention will be the only way of making sure nobody is mucking around with the past for their own profit.

*Gallifrey may be an exception.

[Stark]

Except that's impossible, because any culture with time travel can effortlessly retrieve any 'lost' time machine, even if they're dumb enough not to have a remote control.

Once time travel's invented; it can't be uninvented

Irrelevant?

-- and the main limitation on time travel is how long the culture lasts after invention of the time machine

Wrong.

-- does it last for another thousand years, or does an asteroid hit the planet six months later?

So.. what?

The first fifty or so time-travellers will be like you posited; smart and making sure that they can recover the machine easily, either by adding in lockouts or the aforementioned remote.

You mean those guys that will control all of history by virtue of being time travellers and able to interfere in any other attempt to use the technology?

But eventually, the technology of time travel -- or at least the access to it will spread to the lowest common denominator -- like Grad Students -- and civilization will weep.

Unless anyone has time travel... oops!

Like Simon said last page, if it's possible to change history, the history we have is the final result of all changes, and everyone who's going to try to change it already has (or never will).

[Flagg]

Except to us, those events haven't happened yet.

And why would hypothetical future time travelling cultures give a fuck about Hitler? Do we give a fuck about Atilla the Hun?

Oh wait, you think time travellers are all YOU! Your hilarious misunderstanding of paralell timelines is really mindblowing.

The CORRECT statement is that time travel is impossible because otherwise history would be full of time travellers... but even that falls down because arguably a) it hasn't happened yet or b) those guys were later repaired by other time travellers. It's pretty childishly simple to see that the current history is either immutable or is the end-state of all time travel ever; after the Time War clearly the 'keep Hitler alive' guys beat the 'kill Hitler' guys.

Or UFO's are time travelers.

[Stark]

Those UFOs that don't do anything and only appear to fat white people?

[Flagg]

Those UFOs that don't do anything and only appear to fat white people?

Hehe. Seriousely though, I could see future humans sending unmanned observer drones back that occasionally malfunction and get spotted by aforementioned rednecks.

[Oskuro]

On why Time Travel is impossible, I've been toying with a wacky idea. The thing is that, to travel through time, you would require a certain amount of energy to reach an specific destination, the problem being that timeline alterations would increase the energy requirement since you would need to travel back through the "new" timeline before you can reach your original destination. Since alterations to the past are bound to create paradoxes (loops), this energy requirement quickly shoots up to infinity, making time travel impossible.

And, lo and behold, reaching the speed of light requires infinite energy!

[Havok]

Stephen Hawking has a new show that addressed time travel (in terms I could understand ) in one of the premier episodes that talked about the energy needed for time travel to the past. IIRC he compared it to 'feedback' and saying that the amount of it you would get would destroy any mechanism that (even if it had a magical energy source) opened any type of gateway to the past. I may be misremembering, so take that with a grain of salt.

[Simon_Jester]

But eventually, the technology of time travel -- or at least the access to it will spread to the lowest common denominator -- like Grad Students -- and civilization will weep.

Except for the part where the smart folks go back in time to prevent the grad students from ever getting their hands on the time machine, since they can use time travel to undo time travel. Or just make the interference of the grad students undetectable.

How will they know they need to? The past has been changed. The history books record that some random fool stumbled out of nowhere during the assassination of Julius Caesar, prevented Caesar from dying, and that the entire history of Rome is [blah blah blah].

How would you know that:
-The random fool in question is actually a time traveler
-That you "need" to stop this fool in order to restore a "true" history which is NOT YOUR OWN history
-What will happen if you do?

[RedImperator]

There are physicists who think seriously about time travel and time machines. One possible answer to the question "Where are all the time tourists?" is that a real time machine wouldn't travel with you, like a car. It would be fixed, like a tunnel--you built it in, say, 2010, and then you can get inside and travel as far into the future as the time machine exists (so if it's shut down in the year 2020, that's as far as you can go). People from the future can also travel to the past, but only back to the year 2010.

In which case, the minute you switch on the time machine, a crowd of time tourists might come pouring out, but it's not possible to go back in time and kill Hitler because there were no active time machines before the year 2010.

Cue sci-fi thriller plot about Heisenberg's secret Nazi time machine.

[Surlethe]

There are physicists who think seriously about time travel and time machines.

Out of curiosity, who? All I've heard of is crazy GR solutions that require negative energy and traveling faster than c, which are for all intents and purposes curiosities and nothing more.

[Edi]

An interesting piece of fiction that deals with the consequences of far reaching, widespread time travel going out of control, see C.J. Cherryh's Morgaine Saga. It starts out looking like standard fantasy, but it goes off in a very interesting direction very soon.

[RedImperator]

There are physicists who think seriously about time travel and time machines.

Out of curiosity, who? All I've heard of is crazy GR solutions that require negative energy and traveling faster than c, which are for all intents and purposes curiosities and nothing more.

I can't recall. It's possible my bullshit detector was on the fritz and I took some crank on TV at face value.

[Rye]

I'm pretty sure Red's right. I distinctly remember something involving spinning black holes, and being told that you could only go back to the time it started spinning. I don't recall any specific names though, this was years ago.

[Havok]

As far as I know, the reason black holes have anything to do with time travel is because time literally is slower around them and their event horizons. I guess if you could orbit them long enough without getting sucked in, you would basically age differently than the rest of the universe around you. If you were to break free of the pull and return to Earth it would have aged proportionately at X (the multiplier depends on how close you got and how big the BH was) times the time you spent orbiting the black hole while you would have just aged the actual time you spent orbiting, in effect, you would have gone forward in time, but you couldn't use this means to go back in time, only forward.

[Stark]

Practical time travel (ie go to 1955 etc) is pretty impossible, but effective time travel (ie, go through a wormhole to a place in the universe that is in your 'past') might be possible, I believe.

[Surlethe]

Okay, I did a little bit of digging, and Wikipedia's citations say that some serious work* has been done on time travel, so I stand corrected. But I still stand by my characterization of the work as geometrical curiosities --- it's not going to be really physically relevant anytime soon.

* This is probably not the only piece done on it.

[Patrick Degan]

There are physicists who think seriously about time travel and time machines. One possible answer to the question "Where are all the time tourists?" is that a real time machine wouldn't travel with you, like a car. It would be fixed, like a tunnel--you built it in, say, 2010, and then you can get inside and travel as far into the future as the time machine exists (so if it's shut down in the year 2020, that's as far as you can go). People from the future can also travel to the past, but only back to the year 2010.

In which case, the minute you switch on the time machine, a crowd of time tourists might come pouring out, but it's not possible to go back in time and kill Hitler because there were no active time machines before the year 2010.

That's somewhat akin to a wrinkle I've toyed with regarding time machines: they can take you to the future as far as you'd like. They can bring you back to the present moment you left. But they could not be able to travel past that present moment and certainly could not go to any time period before the machine actually existed, whole and active.

[adam_grif]

A guide to SF Chronophysics.

Anyone trying to alter history decisively by (as my standard example) shooting Hitler in 1920. Any successful case of Führericide has four possible consequences; to wit...

* Divergent history: Nazism evaporates, Stalin invades Roumania, and there is a Russo-British nuclear war in 1952. Or whatever.
* Parallel history: You can eliminate "our" WW2, but there is still some kind of global conflict leading to a US/Soviet Cold War, etc.
* Convergent history: Imagine Heinrich Himler stepping in as Führer and doing exactly the things Adolf would have... ideally this would lead to a "replacement" 1997 precisely identical to the "original".
* Reverting history: As above, but with the corrections taking place over metatime. Saboteurs find life strangely confusing - perhaps they all paradox one another into oblivion...

I don't think there's much argument to be had here, but in order to affect changes on a timeline, you must be in some sort of parallel timeline where the original that sent you to where you are remains unaffected. Otherwise there would be paradoxes. If you can access your own past (in the same timeline, not some duplicate), then you can't change, or paradoxes would occur.

The other thing you have to be worried about with your time machine is that it has to also be a space-machine, otherwise you'll succesfully jump to the 15th century, but the Earth is in a completely different point in space, so you land in hard vacuum instead.

[AniThyng]

But eventually, the technology of time travel -- or at least the access to it will spread to the lowest common denominator -- like Grad Students -- and civilization will weep.

Except for the part where the smart folks go back in time to prevent the grad students from ever getting their hands on the time machine, since they can use time travel to undo time travel. Or just make the interference of the grad students undetectable.

How will they know they need to? The past has been changed. The history books record that some random fool stumbled out of nowhere during the assassination of Julius Caesar, prevented Caesar from dying, and that the entire history of Rome is [blah blah blah].

How would you know that:
-The random fool in question is actually a time traveler
-That you "need" to stop this fool in order to restore a "true" history which is NOT YOUR OWN history
-What will happen if you do?

The 2nd point you made hammers home the fact that in some model's of time travel, you effectively become a "mass murderer" by preventing the existence of billions of people who would never be born after your time altering stunt. Sure, you killed Hitler and prevented WW2, but then now the entire generation of Isreali's born of the consequences of WW2 will never exist. Ever.

(In the Axis of Time trilogy, the part that stands out to me is when Kolhammer reflects that rather than his son dying in a war, his son will now simply never be (his wife of course, had not yet been born, and with the changed timeline and the vagarities of conception, she may never be) and it's somehow more sad that way.)

[adam_grif]

The 2nd point you made hammers home the fact that in some model's of time travel, you effectively become a "mass murderer" by preventing the existence of billions of people who would never be born after your time altering stunt. Sure, you killed Hitler and prevented WW2, but then now the entire generation of Isreali's born of the consequences of WW2 will never exist. Ever.

Just like how every time you use contraceptives, you're murdering a child? Do the people caused by the alternate timeline have less of a right to live than the ones from the original?

Every time you make a choice, you prevent the alternatives from happening. It's just that in this case, we know, exactly, what would have been the outcome of the alternative.