Time-travel question...

[Scarey Nerd]

OK, I take over the world, stuggling for nigh on 20 years to do so, and finally overthrow the world's ruler. I then go back in time by 100 years, and take over the world before I'm born, establish enough defences against insurgency that I won't be overthrow for at least 100 years, then go back to my present time. Have I now had a reign of 100 years, or overthrown myself?

[MikelaC1]

OK, I take over the world, stuggling for nigh on 20 years to do so, and finally overthrow the world's ruler. I then go back in time by 100 years, and take over the world before I'm born, establish enough defences against insurgency that I won't be overthrow for at least 100 years, then go back to my present time. Have I now had a reign of 100 years, or overthrown myself?

You do both.

[paddyfool]

then go back to my present time

If you went back to the present time, how could you have been ruling the world for the past 100 years? (I'm guessing you didn't go there the long way...)

[Weezer]

Well it all matters how causality is dealt with in the universe. If the Many Worlds theory is correct you have just split off yet another world that is slightly different than all the others in which you conquered the world before you were born. In this case it can't be known if you will overthrow yourself or fail because the situation has changed so much its impossible to tell how much of an effect your time traveling has had on the original timeline.

If on the other hand there is only one causality then you had already gone back in time and conquered the world before you were born when you were born. Lets try to make it more clear. Lets call the "you" that goes back in time A and the other one B. A grows up, conquers the world and goes back in time conquering it again. But then B is born (who is the same person as A) grows up, conquers the world, goes back in time, conquers it again just in time for C to be born and repeat the cycle all over again. The problem with this view is to figure out who really started the cycle, and that is where real headaches come from.

DISCLAIMER: This is just the musings of someone who has read far too many sci-fi stories about time travel and has probably thought about it too much. There is no actual scientific fact behind any of these ideas.

[Joran]

Depends on which version of time travel you want.

If you subscribe to the alternate universe theory, where every time you time travel, you split off an alternate universe, then there are two universes. One where you overthrew the ruler, the other where you're the ruler for 100 years.

BTW, how are you living for 100+ years?

P.S. One issue you have is that according to current thinking, you can't time travel back in time to before the creation of your time machine.


DISCLAIMER: This is just the musings of someone who has read far too many sci-fi stories about time travel and has probably thought about it too much. There is no actual scientific fact behind any of these ideas.

Alright, here we go: Here's a physicist about what time travel would look like if it's possible with our current understanding of physics.

http://www.slate.com/id/2225223

1. No parallel universes, this is the only universe we have.
2. Can't go back past the creation date of the time travel machine.
3. No grandfather paradox, which leads to an odd thing about free will...

Basically, Kip Thorne, the theoretical physicist who came up with wormholes, came up with a seemingly solution to the grandfather paradox.

There's a thought experiment very similar to the grandfather paradox called the impossible cue shot. Imagine you have a time machine aperture at the end of a pool table and place the time machine exit at another place on the table. Set it up so that when you fire the cueball at the entrance, it'll exit at just the right time and speed to intercept the cueball and knock it away from the entrance so that it nevers enters the entrance. What happens when you fire the cueball at the entrance?

The compromise is that as the cueball goes towards the entrance, another cueball comes out of the exit at a different angle than you intended and redirects the cueball at a different angle into the entrance, which exits at the angle of the observed cueball.

How this would work with humans and free will, that's for the writers to decide up until we can do it.

[ApeofLight]

You either create a paradox and make the universe implode

Or

You created another universe when you traveled back into time.

[Sliver]

When you try to do it, a bearded guy slaps you with a fish.

[Thajocoth]

You changed the past. Everything that previously happened up to that point ceases to have happened. You were never actually born... You spontaneously existed 80 years before your birth, with memories of events that will never occur. No alternate dimensions or alternate timelines... The future simply never happened.

[2xMachina]

And thus you don't exist to change the past? Thus you exist again? And thus you change the past again, and doesn't exist?

Schrodinger Coup? The Coup that might be happening.

[Thajocoth]

And thus you don't exist to change the past? Thus you exist again? And thus you change the past again, and doesn't exist?

Schrodinger Coup? The Coup that might be happening.

Nope. You spontaneously exist, with memories of that which never happened. You exist, you were just never born.

[Lillith]

Unless you manage to set up events in a way that your parents will still meet, breed and create you. But I think unless you can set up their lives exactly as it went, this chance might be pretty slim.

[The Deej]

According to the self-consistency principle, your time traveling will cause your entire past to play out as it did, therefore your younger self will be the one to usurp older you (or older you's successor, since you would likely die after 100 years). Younger you would still somehow have to not realize that older you is simply an older version of himself. If older you is killed in the coup against him, then you effectively cease to exist once younger you travels back in time.

[Emperor Ing]

You overthrew yourself, obviously, or rather your successor because you probably won't survive 100 years.

[Thajocoth]

According to the self-consistency principle, your time traveling will cause your entire past to play out as it did, therefore your younger self will be the one to usurp older you (or older you's successor, since you would likely die after 100 years). Younger you would still somehow have to not realize that older you is simply an older version of himself. If older you is killed in the coup against him, then you effectively cease to exist once younger you travels back in time.

Why would the universe care about consistency?

[Suzuro]

I FREAKING HATE TIME TRAVEL!

There, now that that is out of the way and you all know how I feel about it, I still subscribe to the multiple universe model of theoretical physics: Namely both happen.


-Suzuro

[Nate the Snake]

Time travel questions answered here (http://www.mjyoung.net/time/).

But on to your question. For reference, the timeline in question starts when you arrive in the past and ends when you travel back to the past after taking over the world.

Timeline AB, original timeline
You take over the world, stuggling for nigh on 20 years to do so, and finally overthrow the world's ruler (whose identity is irrelevant). You then decide to go back in time by 100 years, and take over the world before I'm born, establish enough defences against insurgency that I won't be overthrow for at least 100 years. You make the trip at point B, and this timeline ends.

Timeline CD, first changed timeline
You arrive in the timeline at point C, which corresponds to point A. You take over the world, struggling for nigh on 20 years to do so, but you do it 80 years sooner. You establish enough defenses against insurgency that you won't be overthrown for at least 100 years. You then travel to the time you consider to be your present, but in doing so you leave the timeline.

In the meantime, time moves on without you, since you disappeared in a time machine. Either someone fills your position as world ruler, or your empire collapses. In any case, history plays out differently, so the younger version of yourself who takes over the world in the present is a different you. When CD-you goes back in time, the timeline ends at point D (which corresponds to point B in the original history). Either AB-you doesn't arrive in the present at all, or AB-you arrives shortly before the timeline ends; in any case, AB-you ceases to exist.

Timeline EF, second changed timeline
This timeline is fairly similar to the previous, except it's CD-you doing things instead of AB-you. You arrive at point E, you take over the world, you disappear, and EF-history is more or less the same as CD-history.

Fast forward. EF-you takes over the world the same way CD-you did, then goes back in time. However, EF-you is virtually identical to CD-you, so time can continue past point F. CD-you arrives sometime around point F, and finds his EF-self's newly established world empire waiting for him. CD-you quietly takes the place of EF-you and lives happily ever after. EF-you ceases to exist, effectively replaced by CD-you.

---------

TLDR: Your reign isn't any longer as a result of your meddling with time, and the you that returns from making changes isn't the same you as the one who originally left to make them.

[golentan]

First: Nobody knows. This is a purely masturbatory philosophy exercise.

Second: I'm pretty sure you fail (categorically) to alter the past. When you travel back in time, if you know that Officer Davis betrayed the ruler and helped you overthrow you in the future, you take steps to keep him from doing so (maybe sending a hitman after him, or something). This in turn leads to irritating him sufficiently that he betrays you, directly causing your overthrow at your own hands and yada yada yada.

[SinisterPenguin]

My feelings on the matter can be neatly summed up by this (http://www.mspaintadventures.com/?s=6&p=003151).

[CMOTDibbler]

When you try to do it, a bearded guy slaps you with a fish.

I completely agree with this answer. It obviously makes the most sense out of all the others. :smalltongue:

[Devils_Advocate]

You changed the past.
Change is things being different at one time than they were at a previous time. The idea that the past exists in the present seems incoherent. The relevant idea would seem to be that e.g. at 5 o'clock today, yesterday morning could be different than it was at 4 o'clock today. That's like a scenario in which, in Buffalo, it's raining in New York, but in Pittsburgh, it's not raining in New York.

Either it's raining in New York or it's not. "It's raining in New York in Buffalo" either means the same thing as just "It's raining in New York", or it means "It's raining in New York and New York is in Buffalo". The truth value of "It's raining" depends on location, but "It's raining in New York" is either true everywhere, or only true in New York.

Similarly, it cannot be the case that at 4 PM today I had pancakes for breakfast yesterday, but at 5 PM today I did not have pancakes for breakfast yesterday. Either one statement is false or both are false, depending on how one interprets them. Regardless, either I had pancakes for breakfast yesterday or I did not. Whichever is the case, it is true at all times or only during my breakfast yesterday, again depending on how one interprets such statements.

Or so it seems to me.

[Thajocoth]

Change is things being different at one time than they were at a previous time. The idea that the past exists in the present seems incoherent. The relevant idea would seem to be that e.g. at 5 o'clock today, yesterday morning could be different than it was at 4 o'clock today. That's like a scenario in which, in Buffalo, it's raining in New York, but in Pittsburgh, it's not raining in New York.

Either it's raining in New York or it's not. "It's raining in New York in Buffalo" either means the same thing as just "It's raining in New York", or it means "It's raining in New York and New York is in Buffalo". The truth value of "It's raining" depends on location, but "It's raining in New York" is either true everywhere, or only true in New York.

Similarly, it cannot be the case that at 4 PM today I had pancakes for breakfast yesterday, but at 5 PM today I did not have pancakes for breakfast yesterday. Either one statement is false or both are false, depending on how one interprets them. Regardless, either I had pancakes for breakfast yesterday or I did not. Whichever is the case, it is true at all times or only during my breakfast yesterday, again depending on how one interprets such statements.

Or so it seems to me.

Exactly! Therefore, you spontaneously appeared with erroneous memories, thinking you traveled through time, and did something that will prevent your erroneous memories from ever being of events that occur.

[Moff Chumley]

As long as it obeys Chumley's three rules for surviving Greek Mythology, Live Sound, and Time Travel:
1) No, it's not incest.
2) Just roll with it.
3) Don't eat the damn sun cows, it's just a bad idea.

Then we're cool.

[Lev]

http://www.smbc-comics.com/index.php?db=comics&id=1887#comic

[Threeshades]

If you just go back to the present after you established your world domination in the past, you would have only overthrown yourself, because you werent there to rule the world in the last 100 years. If you stayed though you would be overthrowing the 100 years of global dominion, you will yet have to be have established. Basically you will overthrow yourself and then have 100 years of world leadership before you overthrow yourself again.

How did the time travel related tenses go in the Hitchhiker's Guide again?

Good thing time can not be travelled except maybe in one direction (that would be the future, and only by removing yourself from existence long enough)

[RandomNPC]

why all the IFs and whatnot? we're already using time travel. I'd like sto speed it up a bit, but right now I'm traveling at 1 second per second, or 1s/s.


as the goblin thingie said in bards tale:
Gob: "This boat also takes you into the future!"
Bard: how far into the future?
Gob: Well, that depends on how long it takes to cross the river.

[Crimmy]

I'd say you simply cannot go back to YOUR time.
Don't get me wrong, I mean you cannot go back to the timeline from which you came.

It's like this:

You take X time to conquer the world.
You travel backwards in time, and give yourself power over the world.

The past changes, and as such, the future from which you came does not exist anymore.

So, in a way, you will have sent yourself to the Tesseract.