Hmm good post and seeing Im going away for a few days i'll get a post in early.

Well I see three ways you can look at it.

1) The most obvious first. If time is linear then you would negate your own existance. By killing your grandfather, your father and therefore you can never be born.

2) However if there are several time lines, you could create a parallel time line to your own, a time line where you were never born but you still survive in your own time.

3) A more philisophical way of looking at is that everyone is meant to and will exist at a certain period in time. Therefore by killing your grandfather you will only change your lineage, meaning that you will still be born, but just to different parents.

Of course im looking at it from a stand point that you can just flick a switch to go back in time.
I do remember seeing somewhere on Discovery (i think) about how it is possible to travel back in time but I can't remember the theory behind it....It was something about spinning around a circle incredibly fast that bent time or something along those lines. Anyone else see it?

i was studying a page on wormhole theory the other day.

ive forgotten the page, i was looking at, however i do remember this.

wormholes are unstable due to there nature and need to be stablised with 'exotic matter'

and, if you did try to enter a wormhole, its a one way trip, you wont make it out the other side.

however, they seem to thing they link to an alternate universe, and the only thing that can go both ways is light.

"What? Another girl! Tell me my boy. *whispers* what have you been doing?" - Tobias

First of all I commend you for for listening and actually do something about the situation

Now about the question at hand:

It´s a very difficult question to answer, because it raises many contradictions. What would one do ? Go back and stop your loved one from leaving in her/his car, because you are now aware of the fact that he/she is going to die from a car crash otherwise. Are you going back in time to tell yourself to quit smoking, because you´ll eventually end up with lung cancer ? Choose another major at college, because you know now that you didn´t make the right decision back then ? Very difficult indeed IMO. Many movies/books/magazines have covered this item before, but the conclusion is often that it´s best that it will never be possible. Some people believe in fate and that the things that happen, happen for a reason. Others do not believe in fate, simply because they don´t want to believe that someone or something is in control of their lives other than themselves. Either way, one shouldn´t interfere with history (which is the conclusion of many debates on this subject.) Why ? Because if you can do it, then everybody can do it ! You might believe that no harm is done if you stop your loved one from dying....The other site of the coin is that there are people who want to stop certain political figures from dying ! (like Hitler and such) Sure, most people would love to go back and perhaps change some minor things about their past or just to take a grand tour in history, but in most cases it would mean disaster. Besides, something else to think about...If everyone would have the possibility to change things in their history, then that means they are changing the history of the entire humankind and that would cause our present and future to be instable which will lead into the end of time...

plain and simple: you cant, by going back in time and altering ANYTHING that would stop you going back is impossible, you simply couldnt do it.

If you were to try and walk through the wall, you cant, theres no maybe about it, you cannot occupy the same space as something else. if you were then...well who knows what would happen? anyway, time travel in itself, the idea, means that the future is already written, you could go to the future as well and see how things work out. People have a hard time with this idea cause they dont beleive they are in control of their lives or whatever but its true.
you go back in time and meet yourself 10 years ago, for that instance of yourself you beleive that your living in the present, so this other version of you has come back from the future. therefore, if that present's future already exists, then our future NOW must also exist.

have i still gotcha?

good. so weve established the future already exists right? ok, so now lets go back to meet our grandparents (presumably not having given birth to one of your parents). now you have to be certain of one essential fact...YOU EXIST!
this means, up until the present (acording to you..i.e. that day when you went back in time) you exist. now if you were to kill your grandparents, you would cease to exist. Meaning: you were never born, never grow up, never go back in time, never kill your grandparents.

Now heres the tricky part: its impossible to self terminate in this way. if you prevent yourself from being created, how will you be able to go back and prevent yourself being created? you cant can you? NO so its physically impossible. you'd create a paradox, an impossiblilty. and as it goes, its impossible to create a pardox so you would not ever be able to kill them. (dont ask me HOW you wont be able to, its just that way it works)

Inrestingly, say you went back in time with your mate dave and you pissed him off so he went off and killed your grandparents. well guess what? he cant either...can you guess why? thast right, if dave erased you from history, there would be no one to piss him off an no motivation to remove you from time, paradox again.

So what have we learned?
1) You cant go back in time and alter ANYTHING that may directly or marginally change your reasons for going back in time in the first place
(The 'Kill Hitler' scenario, if you were to go back and assassinate hitler in 1938, the world wouldnt have heard of him, the 2nd world war would never have happened and in 2003, you would never have wanted to go back in time and kill a man called Adolf Hitler, a small time Socialist Politician from Germany)
2) You cannot erase yourself from time
3) You cannot effect someone to erase you from time
4) You CAN accidentally kill someone as long as it doesnt contrevene rules 1&2

-arcon
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In the classic example of killing your grandfather, you get a paradox, yadda yadda yadda. But my theory is that because you exist to try to kill your grandfather, you won't succeed. You could still go back in time and try to kill him, but you won't.
1) You might just suck and fail at it.
2) You might kill someone, but he isn't your grandfather
3) You might be at the point where you were going to kill him, but you get cold feet.
4) You might be at the point where you were going to kill him, but an even more future self pops out of the future and stops you.

End result: You never did kill your grandfather, because you exist as proof.

But there's nothing to prevent you from going back in time a couple hours many times to overlap yourself. You could create your own baseball team this way . Of course, if you lose , then you'll get really ticked off, because you lose 9 times in a row every game you play. .

In my opinion, that aside from relativistic effects that time travel is impossible. Like Arcon said, theres simply too many opportunities for paradoxes to occur.

Well well well... the old minds are flexing now.
My ideas...
It's NOW (2003), you're alive, you go back 50 years, kill Grandpa. Your Dad ain't born, you aren't born, you don't go back therefore Grandpa doesn't die, Dad is born, you're born, you go back etc etc... Paradox, plain and simple.
OK, you go back, you kill grandad, you go back to the future, you end up in alternate reality where you were never born... this is what we called the Back to the Future theory (Biff went back made himself rich thus creating the alternate 1985 where biff owned everyting)
However, that very same film lead me to develope my own idea. That scene (Or 4) is a paradox in itself. Old Biff goes back, makes himself rich. How did he get back to the ORIGINAL time line? Doc Brown himself said it in his own workshop that they could only go back to the future created by the reality of making Biff rich... So how did he get there? He couldn't... At least not panning to anyway, and what did would have made it impossible to get back in a mere time machine, and here's why I think that...
Imagine two points in space. Imagine a spaghetti. At one of the points all the spaghetti is tied together in a point. Not an atom sized point, not a quark sized point. A POINT. Lets label this point the past (Not the beginning, the past). Now, imagine all the spaghetti sort of flows and mingles freely, just like in a collinder after you've cooked some to go with nice bolognase you just made. Get a spagetti comb (Effectivly a comb, but with really big teeth for each strand of Spaghetti.) and drag it from the PAST to the other point, lets call it the FUTURE. (Not the end) That comb is called the PRESENT. So, we have the present moving from the past to the future via the ever moving present. On that comb (the comb will have to be 2D, no surface along the past>future axis) is a little ant. That's us. (Our universe) Now this ant is can only look backwards, but walks forwards. It knows where it's been, but not where it's going. Every choice it makes further defines which Spaghetti strand it's on (Cos it doesn't know). At half way along the ant could be on any one of say (For the sake of argument) 50 strands of spaghetti. Ant invents time machine. (Clever ant eh? ) OK, so if it want to go into the past it knows where to go. Going into the future is a bit of a pain, cos it doesn't know where it's going. The future only exists in potentia so to speak. Even if it arrived at the past it couldn't get back to his own spaghetti strand, as his mere arrival would disrupt the flow of the odd atom or some. Ever so slightly different strand. So, long story short, I think going back into the past would be quite easy (Shhhyeah) however going forward wouldn't be possible without you ending up at some unknown destination. Your arrival in the past could trigger unknown events that you cannot monitor. (See Quantum Weather Butterfly, Terry Pratchett) Even if you sent back one atom, you'd be playing on the unknown.

Hope that made sense! Please hsare you;'re thoughts, weather or not you agree with what I just said.

/wanders off to read other peoples posts in this thread.

OK:
@Mustang: The Spinning circle theory is a good one. The film Contact used it too.
I also read somewhere thaton the absolute defining edge of black holes time travel does occur when an X-ray hits it. It splits in two or something. One part gets hurtled into it, the gets hurtled out, but cos it escapes the black hole and yet cnnot go faster than light it sort of slips through to escape. Dunno where that is now though, it was years ago when I read it, and it was only a theory.
@ Freighter Fighter: I'm sorry, but you said that yo uwas looking at wormhole theory but that theory stated that wormhoels are made up of'exotic matter'. How did the theorist know, he's never seen one. (Or if they have they ain't telling) Worm holes could be perfectlt stable, and you could make the trip both whys which is more than I can say for my local bus service.
@Eraser: Thank you. Thought I'd make an effort. Yes it does raise many contradictions. That's why it's so much fun. It's like the "Prove it" argument. (Prove anything, totally and utterly. Very difficult, and I'm not sure it's been done. Many people say the sun will rise tomorrow. Will it?) The Hitler thing is a good one, ever play C&C Red Alert? Entirely possible.
@Arcon. You haven't proved the future exists, merely that something exists. If you, tonight, met yourself from the future, then killled yourself, you just made yourself not exist. Paradox. Oh, and paradoxs aren’t an impossibility. Paradoxs exist everywhere there is a circle. Roll a coin across a table. Take a point on that coin. That point will start at the top move down in an arc until the arc gets closer and closer to vertical. At some point it will start to go up again, the arc going the other way. Mathematically the arc must have stopped to change direction. If it stopped, that means the marked spot did. If the spot did, why is the coin rolling across your table?




Edited by - Lutz on 17-07-2003 20:00:44

@ Arcon

The "kill hitler" scenario is possible only you got it half right
the 2nd world war was meant to happen just like the first world war. only it would happen on other terms.

the things that happened in our lives and others is a relevant matter
it consists of time , decision and opportunity (@bargib you should get an underline function for the forum) the opportunity is bound by time.
for instance: on september the 1st of 1939 hitler attacked Poland as we all know.
he made that decision based on the opportunity made by the fact that stalins armies attacked the border a day earlier on the eastern front so he could practice the blitzkrieg tactic. if that pact never existed hitler would have attacked but not poland but another country or perhaps he did attack poland but not with the blitz tactic.

on the other matters at and:

1) the wormhole, there is a possibility that a wormhole is a pathway to another dimensional plane. where "space"-time doesn't exist and therefore time is not known and you exist "out of time"

2) the "if you kill you're grandfather, will you still exist"-matter, the answer: yes.
you will still exist. because 1) you were meant to do so. and 2) if you were to endulge yourself into timetravel, you would enter another parallel plain of the same dimensional realm (RE. the multiverse theory)

note that these are all theories, not real-life fact! if you will use these theories in conversation or otherwise, be prepared to receive a lot of critical replie and comment. if you want to research these theories. then by all means do

__________________________________________________________
Oh, dear, How sad, Never mind!!-Battery Sergeant Major Williams





Edited by - Locutus on 17-07-2003 20:21:16

ok,
the future is written.
using your ant theory, say your an ant walking along spagheti (well call him antA), he goes back to 10 minutes ago and meet the himself (ant. now that ant (ant thinks its in the present and for all intents and purposes, it IS in the present, but antA has just come back in time and met him. So now antB knows that at least the next 10 minutes are gonna involve him walking and going back in time...see? if AntB's future is written...then EVERYONES future is written.

---
the 'Kill Hitler' thing, i think your missing the point.
lets say i, Arcon, go back to 1938 and go to assassinate hitler..ok?
so i'm there in berlin or wherever, and i kill him. WHABAM! instantly the 2nd World War Didnt happen (bear with me a sec). So now, fast forward this NEW timeline along 65 years and heres me with my time machine, i get in....i DONT go to 1938...why? cause hitler wasnt the cause of a great 5 year war, instead, there was peace and prosperity and Arcon never hears about Hitler and doesnt want to kill him in 1938. so now theres no one to go back and kill hitler so WHABAM! the 2nd world war DOES happen (this continues in a loop...hence paradox)

its simple cause and effect, but the underlining factor here: effect CANNOT alter the cause.

---
Time travel is a bit of a headf**k and i'll tell you why: going back in time and NOT creating a paradox is REALLY easy, thing is, everything you change doesnt make the slightest bit of difference, the way we are living RIGHT NOW is how its gonna stay forever. the timeline isnt set in stone, but if anything was to change, like maybe a world war, we'd just accept it and not know any different, we wouldnt remember life before the change, it would instantly be all we ever knew, so theres nothing to say that hitler wasnt a time traveler who, in a history lesson learned about how post WW1 germany was in a state of decay and didnt decide to go back in time and benefit from this by creating a nazi empire? think about it, ww2 may not have been in the original timeline, and the only reason it IS in the timeline is that in however many years till adolf gets time travel abilities, his ww2 disruption is cleared out and he is able to go back again.

heres something cool, make a promise to yourself that if time travel was to be invented, you'd go back and say hi to yourself around this time in your life just to prove a point in this argument. I will, and if tommorow, you see yourself from the future, i'll be right

-arcon
------

OK Arcon...

Erm...

So, AntB is in the present and AntA comes to see him, from ten minutes in the future. This does NOT mean that AntB will travel back in time 10 minutes later to see himself (Again) the reason being that when AntA arrived bank in time AntB was no longer on the same spaghetti strand as AntA as AntB past didn't contain the meeting and yet AntA's did. The arrival of AntB in the past has already changed the future of AntA. The ants could have a discussion that could lead to AntA telling AntB not to go back cos it's painful or something. Therefore AntB now has a different future ahead of him, one without painful timetravel. AntA on the other hand will go forward 10 minutes and will now have a choice. To timetravel back 10 minutes or not. He's already done it once, does he neeed to do it again? He;s stopped his past self from timetravelling, but he himself is now at a loose end. Therefore AntB's future isn't written, AntA just changed it, and AntA is free to do what he wants, except go back to his own time where "he" (Not AntB ) feels the effects of never time travelling.
---------------------
Hitler theory:
You go back, kill Hitler, come forward into new alternate reality where ther was no Hitler. The second world war didn't happen, and believe it or not, there's no paradox. (IMO) The paradox that you're suggesting is that cos WW2 didn't happen, you didn't hear about hitler, therefore you didn't go back, there fore he exist therefore WW2.
If you went back, killed him, went forward, you're now in an alternate 2003, AND YOU KNOW HITLER EXISTED AT SOME POINT IN TIME. The timeline however does not. What you're suggesting would only be true if all your memories and knowledge were altered into the appropriate timelines history when you jumped.
If I'm on strand A, (Our universe) and I kill Hitler making strand B I will end up on strand B in 2003 with the memories of strand A.
The other reason you don't get a paradox is that even if you jump to strand B another you from strand A will just go and kill Hitler again.
-------------------------
I won't go into your last point, cos I've mentioned it above. Unless all memories of all time travellers were altered at the change of a key event we would know about it. For all you know something like what happened in 12 Monkeys was the fate of us back in say 1999, but timetravellers fixed. we wouldn't know, we didn't time travel, but they'd know, cos they did. They'd have the knowledge of their past, and then they'd relive the new "past", at least new in their opinion.
And your promise, I will go back and say hi to myself, even better I listen to myself best and I'll tell me NOT to go back to say hi. Lets see where that'd get us.

Edited by - Lutz on 18-07-2003 09:09:34

Here's a thought...

You go back 10 mins and have a chat with yourself. You stay there for 10 mins.
Now there are 2 of you, so what would happen??????
Do you fade away, perhaps merge with yourself (Not that I'd want to, I know where I've been )

good thread by the way

Skymouse

Hi Skymouse. Yeah, nice thread! I always enjoy these ones. No true right or wrong, just opinions and theories.
Erm, in your scenario I'd say that you'd both exist. There would be the YOU you, and also the you where you had a converstaion with yourself.
You both have the same history, up until the point where YOU arrived back in the past 10 minutes ago. From that point one that other you that YOU are talking to is no longer YOU as such, just a slight variation. So after 10minutes the YOU would back to the point where you time travelled (This doesn’t mean you have to time travel again, as you're now in a different timeline, a timeline that involves a converstaion with yourself) and the other slightly varried you carries on like nothing has changed. At the point just before you arrived he didn't know what his future may bring, so he wouldn't know any different.

Hmmm……

Makes sense to me anyhow.

lutz, you seem to be under the impression that by going back in time you have created a new instance of yourself, a copy.

touching abck on the ant thing again:
antA meets antB, remembering that both ants are the SAME ANT, just that antA is 10 minutes older than antB. Now assume that antA talks with antB about stuff and tries to pursuade him NOT to go back..he cant, youve got a paradox again, cause if antB decides NOT to go back (thus becoming antA) then who would do the pursuading. youve got to think of it as a continuous line:


as for hitler, when you change something in time, your memories and your knowledge WILL change too because there is only ONE timeline..observe:

if the timeline no longer exists, WHO goes back in time? ok, you MAY still exist, but if you do, your motivation is gone..PARADOX BABY!

-arcon
------

Ahh… hear is where we disagree Arcon. AntA and AntB are NOT the same Ant IMO. The ants have diferent histories and are therefor different, albiet VERY SIMILAR ants. If AntA and B were the same, then yes, you're right we have paradoxial situations. However as the ants are ever so slightly different (Physically too, their brains won't match) then no pradox arises.
Also I don't think time is a continuous line, except into the past. Hence my spaghetti theory.

I like your pics too, and yes they're correct assuming that that all instances of you in all universes are the SAME you (and that paradoxes cannot exist. Maybe they do, but we don't know about them). If all instances of you are not the same then your theory falls down (Just like if they are, my theory falls down.)