Talk:Grandfather paradox

Parallel timeline, Ripple effect concept: What if, (refering to the grandfather paradox), you were succesfull in killing your grandfather. The Paradox theory states that it is not thoerically possible (my interpation) due to bloodline problems. My remany to this problem is the merging of Parallel timelines and ripple effect. To spare a long techinal disscussion, the concept works like this;

1)there are parallel timelines/universe (I believe these words can be interchangable saftey). These timelines can merge and spilt, being dyanimic in time-space. If muiltpile timelines are very close to each other (chacteristics based), then they merge. When actions that can affect the future are made, a slipt occurs.

For Example: The 9/11 attacks. What if it didn't happen. The US would probably not be in Iraq, so on and so forth. But what if, Instead the attack occured 10 years later. Would it create a mirrior image of the Current US status and thus rendering the current timeline and the parrallel timeline satuts quo?

2)Getting back to killing the grandfather thing. The Universe Probably has a protection feature to prevent this, but if there isn't, Could killing a person before the fact cause you in enter a time bubble in which only you exist until a remany. Possible ways to render you back into the regualr timeline:

A)You cease to exist via reaction (you kill grandfather, something kills you)

B)If you were able to go back that point in memory (my interepation of the past is the distance between memories), there is no problem going a tad bit futher past, to prevent yourself from commiting the crime. If a collsion occurrs (ie Both versions of you die) then this off spurt of time ceases to exist, meaning there is no known memory of it and life continues on as if nothing ever happen.

Hopefully I did not confuse or bore anybody with my 2 cents worth. KB1KOI 02:14, 4 October 2006 (UTC)

Concerning the paragraph:

In the 2001 film Donnie Darko, a rift in spacetime is created when a jet engine lands on the title character's house approximately 28 days before the plane carrying it flies over. This creates an unstable parallel (or tangent) universe which will cease to exist at the end of those 28 days if the engine is not returned to the primary universe. The laws of nature in the parallel universe are roughly the same, except characters and events close to the time portal are "manipulated" to return the engine to the primary universe before the parallel universe collapses on itself and becomes a blackhole of spacetime. If the portal were still open when this happened, it would destroy the primary universe and all of spacetime. How this works is never explained, but implies the idea of some universal defense mechanism.

This is not one of the many popular interpretations of the film. Even if it were, it should be labeled as an interpretation, not as the single possible narrative presented. I suggest it be removed completely unless the author wishes to dilute it with a whole lot of, "one interpretation," and, "it could be said..." --202.164.194.254 08:55, 22 June 2006 (UTC)

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Orson Scott Card dealt with this in his book Pastwatch: The Redemption of Christopher Columbus. I'm not sure if his explanation is worth repeating in the article since the book isn't widely-known, but I will explain it somewhat here.

The moment you travel to a previous point in time, all time past that point ceases to exist. You (and anyone traveling with you) continue to exist physically, but you are not "tied" to the future in any way.

After looking at what I've typed I realize it's close to the parallel universe theorem, but Card's method was logical and well-written. Goatasaur

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Nice summary and notes on fiction authors 'dealing' with it. Would be nice to note the origin of the term. Carl Sagan said it was science fiction, others seem to claim Einstein made it up. Tempshill 05:57, 1 Dec 2003 (UTC)

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The grandfather paradox is rather overused though. For those people rather bored with killing their grandfather, there is an alternative which we'll dub "The Oedipus paradox". The essential physics is the same, but the story is different. In the Oedipus paradox the time traveller returns in time and 'loves his mother' (to quote Tom Lehrer). The time traveller then has the potential of never himself being conceived (as his mother is already pregnant at the time of his conception). To avoid the getout of the time traveller being his own father, which would be possible genetically, though statistically unlikely, this would have to take place several months prior to his own conception.

One could argue though, that Novikov could prevent this paradox from occurring - as many time travellers would not be able to follow the lead of Oedipus.

We aren't supposed to dub it anything at all. If this scenario happened in some science fiction story or other, a reference to that story could be made, but this just looks like a contributor's own ideas. As an encyclopaedia we are only supposed to report ideas that have already been made known elsewhere. -- Oliver P. 08:02, 1 Dec 2003 (UTC)

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This particular resolution works well because some consider Parallel universes to be a neccesity in order to travel in time. Consider a line. How do you move backwards in the line? Someone - either yourself or others in line must move to the side before you can move backwards.

Therefore for time travel to exist there must be a "side" space-time for you to enter and travel in. This "side" space-time must have physical laws that allow life to exist in it. Therefore if time travel is possible there must be a place where an alternate universe could develop. If there is space for one alternate universe why not an infinite number of them? If an infinite number of universes exist than there would be an infinite number of parallel universes.

Who believes this? Certainly not scientists. If science fiction authors then which ones?

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I'm curious about a proposed solution presented by Douglas Adams which was phrased (IIRC) "It all works out in the wash". In that you can travel back and kill your grandfather, which might prevent you from going back and killing your grandfather, but the other changes would make the "second take" of the intervening period of time slightly different. After enough "takes" of that particular period of time (which might be a very large number), one would work out that was consistent and stable and time would continue on from there. My questions are 1) did that make sense, and 2) is there a name for this idea? Matt 19:03, 23 Dec 2004 (UTC)

If I understand it correctly, it sounds like a variation on the Novikov self-consistency principle, i.e. the universe prevents paradoxes by making sure that no paradoxical action can succeed, only in Adams's scenario the universe is self-correcting; reactive rather than preventive. In practice, however, the two may be indistinguishable.

Consider - you go back in time and kill your grandfather. According to the NSCP, you either won't be able to do that, or if you succeed, it will turn out that he really wasn't your grandfather. In a self-correcting universe, if you go back in time and kill your own grandfather, history will alter itself so that you will discover he is no longer, and never was, your grandfather. Either way, the result is the same. -khaosworks 19:15, 23 Dec 2004 (UTC)

question about this proposition: so then, what happens if you kill the entire human race?

Terence Mckenna's solution

I don't know if this is significant enough to warrent inclusion, but Terence Mckenna offered an interesting solution to the grandfather paradox. He postulated that the realization of time travel would be either the catalyst for or the result of a sort of temporal singularity that he called Timewave Zero (see the article on Novelty Theory) and that the grandfather paradox would be negated by the fact that all events in time would then exist simultaneously. Or something like that, I don't have the source material on hand. If someone can supply citations for this it may be worth including either here or perhaps in the article on Novelty Theory.

Pogo Paradox?

OK, I consider myself a Star Trek fan and I have never heard of this. Can someone explain this? --Feitclub 03:08, Apr 20, 2005 (UTC)

My only theory is that it was mentioned in the Voyager episode where Braxton is teaching Seven about the rules of time travel. Ether that or it was something that Gene Roddenberry just mentioned once. Can anyone confirm how this Pogo thing relates to Star Trek? Arctic.gnome 17:45, 23 Apr 2005 (UTC)

It was mentioned in the Voyager episode as per Arctic.gnome —UTSRelativity 18:13, 23 Apr 2005 (UTC)

Restricted action resolution

About the "Restricted action resolution" - I'm not sure I understand the "free will" part, so I would like to make sure I got it currectly: does it simply mean that, if time travel is possible and this solution is correct - then every action in the past is consistent with every time travel in the future (and everything which lead to it), and therefore everything is deterministic and the future is already "set"?

Yes, that's pretty much it. It's the whole of history that's also set, since even if you go back in time and tell the inhabitants of the past what the future holds, there is no way for them to avert it. --khaosworks 13:07, Jun 8, 2005 (UTC)

"One potential snag to this, however, is that if one were to travel far enough back in time, the time traveller's mere existence, however brief, would still cause changes that would branch out, which would inevitably change the future enough so that the time travel never occurred (see Butterfly Effect)."

How is that a snag? That's not any different than any other situation. - Omegatron July 6, 2005 21:11 (UTC)

I guess the person who wrote this thought that determinism was dependant on other people being around. My view in relation to this theory is that if you mere presence would create change, either these change were already done (the "I created life on earth by leaving my bacterias behind" theory) or you would find it impossible to travel to that point (your time machine broke down on the way there).--Marc pasquin 17:04, 13 August 2005 (UTC)

Paradox, how come?

How is it that this is listed as a paradox? It’s a self-solving case, nothing to do with a paradox?

If I go back and kill my dad (or grandfather, or grand-grand-father), I will not be born, right? Now if I’m not born, I cannot go back in time at a later date cause I don’t exist, right? And since I don’t exist I cannot go back and kill my dad - and thus I will be born! It’s a loop you can run infinity if you like, but the outcome is always the same, you can’t change it.

Trying to change the loop alters the very existent of the change you try to make, thus the changes no longer exist, and thus the loop is not changed!

What would actually happen I think, speculation of course, is that you simple find yourself infinity pulling the trigger. The second you pull the trigger; you erase the very event (pulling the trigger) you are doing right now and you are back to zero – pulling the trigger :D. You could do this infinite, not realizing that you have already done it infinity times, cause every time you pull the trigger, you erase all knowledge of any previous attempts. Infinite times will blast by in a split second. The loop will continue till one of the small greys says, at the 60.000 gazillion run of the loop “naaar I don’t want to kill my dad” – and bammmm you are out of the loop. You will never know that you just spend an infinite in a loop, cause no time has passed and to you it still seems like the first run.

This is not a paradox, but an easy self-solving loop. Twthmoses 14:55, 10 July 2005 (UTC)

What you are describing is essentially what happens in the Restricted action resolution of the paradox. The reason this is a paradox is because ultimately, it cannot take place - we know we cannot go back in time and kill our grandfather because then we won't exist to do it. The problem is that there is nothing logically preventing us from doing so, so we have to come up with theories as why this cannot happen. What you have laid out is simply one possible solution to the problem as formulated. --khaosworks 15:47, July 10, 2005 (UTC)

I’m not disagreeing with that there are many solutions to this case; I’m disagreeing to the very fact that this is perceived as a paradox. It is not a paradox.

It has well defined parameters, it has a beginning and an end, and there is nothing illogical over it. It is a simple case. Why should this is any way be a paradox?

1) You are born. Without birth there is no case. This whole case rests on this very beginning.

2) You go back and try to erase your birth.

3) You succeed in doing this. However consequently in succeeding in this, you also erase the very action that made you succeed.

4) You are never born

5) You never travel back

6) You never kill yourself.

7) see 1)

What is illogical or paradoxical in this? It’s a loop that has no strange mechanism requirement to sustain itself, to start or even end. Of course you need to be able to time-travel. At any given moment can you choose to start it or end it anywhere in the sequence and it will leave no door open for exploits. I see nothing paradoxical in this?? Twthmoses 16:41, 10 July 2005 (UTC)

How are you able to choose to enter and exit if by this formulation you are not even aware of the loop in the first place? --khaosworks 16:48, July 10, 2005 (UTC)

That’s easy. Just choose too: D

What makes you decide on a warm summer day to go and get a coca-cola and not a Pepsi (or any other for that matter). Or better what makes you take this bottle and not the one right next to it? Its that little spark in the brain. How exactly it works, I can’t tell you, but it makes you make a decision about a specified subject at a specified movement, every second - all life long.

That little spark is (presumably) available in ever loop of the grandfather case, regardless if you have knowledge of the loop or not. And by sheer statistic in one of the loops, you will choose to not pull the trigger in last sec. For you it will simple seem like you just chose to abandon your original plan, and not pull the trigger – not a big deal.

In fact now that I think of it. Our very existents could be a series of loops all life long and we would not know anything about it, and the very decisions we make daily, makes or breaks these loops. Heheh.. ok, I got a little philosophically carried away there :D Twthmoses 17:20, 10 July 2005 (UTC)

The reason why it is presented as a paradox is that it is assume that having lived you would have made the same decision: you lived, you killed your grandfather. The paradox comes from the fact that no matter what you did, you encounter an impossibility: You killed your grandpa, you don't exist, you can't have killed your grandpa or you didn't killed your grandpa, you lived so you do go and killed your grandpa (which obviously can't have happened). Of course, this is based on the theory that there is but one timeline (the other theory described here wouldn't all find it to be impossible).

A loop on the other hand you be something self-fulfiling: you receive a time machine from some stranger, you spend your entire life trying to figure out how it work. moments before you die you figure out how to use it, go back in time and give it to yourself. Not going back would be the thing that would create a paradox.--Marc pasquin 17:04, 13 August 2005 (UTC)

^^Not to mention an ontological paradox. Where did the time machine come from to begin with?

"Thrice Upon a Time" in wrong subsection?

The page lists Thrice Upon a Time under "Parallel universes resolution", but I just reread the book a few months ago and it explicitly assumes a single timeline -- there's even a diagram. Whenever a message is sent into the past, the timeline gets "reset". Because of the arrival of the message in the past, subsequent events are altered, often to the point that nobody even sends the message into the past. The message, however, remains.

I suspect the confusion is caused by Hogan's decision to call moments in time "universes". In other words, right now is a universe, one second ago is another universe, and one second from now is yet another universe, and each of these universes is visualized as sliding along the timeline from the past to the future. In Hogan's usage, sending a message to a prior universe modifies that universe and triggers a cascade which alters all subsequent universes.

I believe that this book should be listed under the "Relative timelines resolution" subsection, but I thought I would seek input since I have never modified a Wikipedia page before.

TuklaRatte 04:17, 7 December 2005 (UTC)

Faulty logic

This whole chain of logic;

"

1) You are born. Without birth there is no case. This whole case rests on this very beginning.

2) You go back and try to erase your birth.

3) You succeed in doing this. However consequently in succeeding in this, you also erase the very action that made you succeed.

4) You are never born

5) You never travel back

6) You never kill yourself.

7) see 1)

"

is faulty due to the fact that in the timeline, 1 takes place after, and not before, you try to erase your own birth (2 & 3) Since you are in the past, before your own birth, you existed before your own birth, and thus it rightly cannot take place. (You cannot, to my knowledge atleast, exist twice at the same time, although that is besides the point.)

Yet it will not matter since you, by going to a time before you were born, existed prior to your own birth. As such you will never be born, but you still existed before both your time trip (2) and your birth (1).. So you would simply exist, birth or no birth.

Matter that is moved through the timeline would probably exist before it was made. Example: You owe a fork, its made in 1998. You take this fork back to 1960. Since your fork has not been created, and cannot be created either (since it already existed prior to its creation).. Would the fork simply vanish? Remember that in the timeline, the fork now already existed in 1960, and thus wasn't created in 1998. (But maybe it miracolusly was 'created', without someone actually creating it, in 1960, since that's the first time it appears in the timeline.)

So I think that it wouldn't vanish. Do you? If not, then why should this be different with a human?

Added 14/03/06

Chat

HELP!

Could someone please translate this into easier to understand terms? I don't get it one bit.

I've noticed that your question was never answered when this debate started, so I've rearranged the subtopics. I'll try and see if I can make the theories in the article itself easier to understand. -arctic gnome 21:58, 30 March 2006 (UTC)

it is all irrelevant

I am not surprised that you do not understand it- it is all irrelevant. Consider the following view of spacetime, which makes all of the paradoxes disappear (incidentally, I have a PhD in theoretical physics, so I am not just a crank)...

Suppose the present is the year 2006. You exist in the present. More precisely, you are composed of inumerable fundamental particles that exist in 2006. These particles existed in earlier times too- in 2005 most of them were part of you, but not all of them: some, for example, would have been in growing food that you subsequently ate. In the year 1806, say, all of the particles that currently form you must have been doing something else (since you did not exist then). Likewise, all of the particles which comprised your great great grandfather in 1806 are now in the present doing something else (possibly being part of other people, for example). So, imagine you find a way to travel back to 1806. You will find absolutely nothing whatsoever when you get there, because all of the particles that make-up the universe will be still in 2006 where you left them. Although the atoms that make up you might have gone back in time, none of the other atoms in the universe did, so you will be in 1806 all by yourself. Expressed in terms of a 4-dimensional spacetime, you, and the rest of the earth and the people who inhabit it, are currently occupying a region of spacetime corresponding to a time coordinate t. You 'go back' to a region of spacetime with a time coordinate of t' (say to 1806), but the rest of the earth is still in the region with time coordinate t where you left it.

So, the point is that the universe is here today and has left earlier times behind. Even if travel back through time were possible (which I doubt), it would mean travel back to a point in spacetime in which nothing existed, and certainly not the atoms which comprised you or your grandfather (which have moved on to the present). Therefore all of the so called paradoxes are eliminated. -unsigned

I don't think you're helping that user understand the theories by giving him a new theory to deal with. --arctic gnome 00:08, 26 March 2006 (UTC)

You are probably right- I apologise. It was late at night when I wrote it in rather an exasperated frame of mind having read some of the other comments. -unsigned

Though you make a good point. If you're right, you could only go back in time and see stuff there (like in the movies) if there are universes full of matter "following" us at every moment through time. If that's the case, then the grandfather paradox would be solved by the relative timelines resolution. You kill your grandfather in the "60 years ago" universe, and you are not affected, but that universe's history will unfold from then on without you. So then, if you waited another 60 years, you could go back to today and see the what the "60 years ago" universe looks like without you in it. -arctic gnome 07:48, 26 March 2006 (UTC)

That is a good 'if'. Suppose it were possible to go back to any time t, then there would have to be an infinite number of universes full of matter following us, such as the '60 years ago' universe, and the 'sixty years plus 4.7 nanoseconds ago' universe, and the 'three second ago' universe and so on (leaving aside the possibility of a corresponding infinite set of future universes). Even then, the argument breaks down. Suppose, for example, I go back to the 'sixty years ago universe' and instantly kill my grandfather, and the history of that universe then starts to unfold with my grandfather dead. My sister wants to go back in time by sixty year less one second to hug my grandfather- does she find him alive or dead? Does this mean that there has to be not just an infinite number of universes, each separated fom the next by an infinitessimal fraction of time, but also every one of them has to be available in any number f possible states? Does anybody really believe anything like this? There is no justification whatsoever in physics for supposing that there are an infinite number of earlier universes, and I think it is patently wrong to suppose it.

Consider, therefore, the two possible resolutions of the grandfather paradox- one, which is supported by the mainstream concepts of spacetime, is that if you travelled back in time you would find nothing there, and hence no oportunity to influence the future- the other, which has no theorectical basis whatsoever, is that there are infinitely many universes, each separated from the next by an infinitesimal change in time, each capable of evolving in different ways if visited by someone from one of the other infinte universes. Which seems the more likely? -unsigned

I’m not so much trying to find a theory that makes the most sense, but find one that is at least theoretically possible so that science fiction stories can work. The other theory I can think of that might allow for the classic sci-fi time travel is if particles actually have a length in the t dimension. What if atoms are 100 years long in the t dimension and we are experiencing the front of them? Then you could go back 99 years and see the world around you. It doesn’t matter that the particles have moved in 3-dimentions since then; in the t dimension they are all still moving at a constant speed with each other. In this case, you could create a time travel paradox by moving (in 3-dimentions) particles in 1905 that are in your body or will effect your body in 2006. The big problem with this one is how the particles in your body exist in 1905 twice. Maybe they “bend” back, or maybe when you go back 99 years, your whole mass dose, so in 1805 there is empty space with nothing but the scattered particles that will one day make up your body. -arctic gnome 18:30, 26 March 2006 (UTC)

I think you have made an incredibly huge initial assertion which may in fact be flawed. The assumption that a particle can only exist in the present, or that a partical has "length in the t dimension". This is due to a fundamental misunderstanding of the concept of time. I believe the reason for your misunderstanding comes from juxtaposing a movement of a particular in realspace over a given time. As a particle which has moved from point A to point B over time T no longer exists at point A, you suppose that going back to point A means it is no longer there. At that point in time it was there, and the particle did indeed exist there. Thus returning to that exact point in time should mean that everything is exactly how it was back then (if it was any different... then it obviously wouldn't be that point in time would it?). If you look at the fractured timeline below, you can see that no such time paradox exists as killing yourself in the passed would not effect your present as the moment of change would mean a different future occurred. Yourself being out of time (ie not when you are supposed to me) means you are not effected. Whats more, nobody would ever know that the timeline had changed because everyone else who is living through that period in time would consider it to be the normal flow of events. Enigmatical 04:08, 11 May 2006 (UTC)

So the past hasn't existed?

"So, imagine you find a way to travel back to 1806. You will find absolutely nothing whatsoever when you get there, because all of the particles that make-up the universe will be still in 2006" -unsigned

Where is your logic, 'unsigned'..??

Where then, were these particles back in 1806? Did they never exist? Did 1806 never exist? :D You're not going to some other 1806, you're going to the one that has already existed..

You're practically saying these particles will be thrown into the future (2006 that is, which surely would qualify as 'future' back in 1806) the instant you traveled to the past.

In 1806, these particles were located, well.. Wherever they were located back in 1806.

See, 1806 didn't happen after 2006, but before. So if what you're saying is true then the past wouldn't have existed.

Just WHY exactly would the particles that were in place back in 1806, all of a sudden only be in the future, 2006 instead?

If that's the case then the particles didn't exist at all in 1806 then, and thus couldn't exist in 2006 either (or would be miracously created out of nothing, like thats going to happen!).

Thus there would be no past, and through that; No future or present. In short; there wouldn't be a universe at all. So what you're saying doesn't make any logical sense... At all.

I also think you're confused about the (highly fictional) concept of time travel.. The only thing unaffected by the time travel would be the thing/s being displaced in the timeline, everything else would be 'rewinded' to the way it was in 1806..

Hope this was easier to understand for you than my last writing. I don't want to confuse you, cause that doesn't seem necessary. Cause forgive me for saying so, but you're pretty confused as it already is.

Added 27/03/06

I'm not saying that Unsigned is right, but he does at least make sense. His theory is that there is only a universe at one point of time. For his theory to work you have to see time as a dimension just like the three normal dimensions. Just as an object can move through the x, y, or z dimensions, the universe moves through the time (t) dimension at a rate of 1 second per second. Right now the universe is at the coordinates t=2006, there is no universe at coordinates t=1806 or at t=2206. Two hundred years ago the universe was at coordinates t=1806 and there was no universe at t=2006, it had not gotten here yet. If you went to coordinates t=1806 right now, there would be nothing there because all of the particle that once made up the 1806 world had left there 200 years ago and were now in coordinates t=2006 (they also would all have different coordinates in the x, y, and z planes). -arctic gnome 01:08, 27 March 2006 (UTC)

Notice what you have said... "Just as an object can move through the x, y or z dimensions". The only thing which makes "movement" possible is the passage of time. Thus an object does not necessarily move through realspace, it simply has a different "existence" at a given point of time. Where your theory breaks down is in the assumption that time is not an infinite vector. Consider this. Just as "Length" is a vector (mathematically and scientifically), which simply has a direction... no beginning and no ending, so is "Time" a reflection of a chronological equivalent. In order for "Length" to be finite a "width" must be applied, and a "depth". Only when all 3 dimensions are applied does it gain a finite quantification (and thus a position within space). "Time" is then used to "activate" this finite quantitfication, allowing it to alter its location within space. Why then is time any different? Why then can we not extrapolate further... we have the "length of time" already, why then would the next dimension not be the "width" of time? And the the "depth" of time? Ultimately upon reaching an existence in 6 dimensions would we be able to move around time just as an object within 3 dimensions is able to move around space. I believe this is just a simple philosophy built upon the Super string theory which I belive postulated that there are 2, 10 or 28 dimensions (Myself believing there are 10, 3 sets of 3 + 1 more). Just as we are able to take an object and return it to its original realspace location because we exist in 1 dimension "higher" (ie 4th dimension, time allows us to change the 3-dimensional location), so too would a being of the 7th dimension be able to move an object in time. Of course those of us living in the 4th dimension would never see it, because to us what we saw is what has always existed. As 4th dimensional beings we cannot fathom the concepts of 4+ dimensional travel... just as a 2-dimensional being could not fathom the concept of "depth". Enigmatical 04:19, 11 May 2006 (UTC)

You do understand that for time travel to be possible even in fiction, you have to accept the idea of moving the universe backwards through your 'time dimension'.. Right? If you cannot even imagine that, then the whole argument is pointless. As I said, you're obviously confused about the concept of time travel.

Also, time as a dimension with the universe moving through it, positioned in it using simple x, y and z..??? No, I don't buy that idea. Time is not the same as room/space. Should be obvious.

Added 27/03/06

Where are you getting information on what I can and cannot imagine? Even if Unsigned's theory is wrong, it does have some logic to it. Your conclusion that his theory "doesn't make any logical sense... At all" is groundless; you only backed up your argument with the fact that in his theory there is no past or future, which is the entire point of his theory. To reject the idea of time as a dimension with the universe moving through it, you have to give a better reason that the fact that "you don't buy it", because there are countless professional physicists writing papers on the topic.

The one big problem with Unsigned's theory is that it does not allow any fictional time travel stories to take place. That is why above I offered two ways that traditional sci-fi time travel could work with his theory; not so much to back him up, but to back up fiction. -arctic gnome 07:42, 27 March 2006 (UTC)

Actually the reason why unsigned' theory makes no sense is that the basis of his theory revolves around a universe that can traverse only forward through time as if it is an entity seperate to time itself. Einstein didn't call it space/time for nothing. The very fabric of space itself is intrinsically tied into time and in fact can be considered one in the same for most theorists. Unsigned disjointed this, seperating space and time into seperate entities. If time is a seperate entity, and "space" is moving forward through it, then what exists in front of us and behind us? It cannot be "nothing", or vacuum because the concept of being able to move through it automatically gaurantees that there is something to move through. Enigmatical 04:24, 11 May 2006 (UTC)

Impossible.

Allright.. A few reasons then, these should be really easy to understand.

1. Time is not the same as room.

2. Even if it would be so, where is this space located?

"the universe moves through the time (t) dimension at a rate of 1 second per second" -arctic gnome

What ACCELERATION would the universe be moving at? A second is not a distance, its a human term for a certain amount of time.

3. How could I come to a place where there would be 'nothing' if the universe is, as it is held to be, infinitly large?

This is actually quite easy to explain using Einsteins theories. The universe itself being the largest mass in existance causes its own gravity (as all mass causes gravity). Due to its incredibly size, the "bend" in time/space is so sufficient that it bends back on itself. Imagine a sphere in 3 dimensions, now imagine yourself as a 2-dimensional creature. You could walk in any direction (length or width) on the surface of the sphere and will always end up where you started. Now extrapolate that example to the universe being essentially a 4 dimensional sphere (ie one that has folded in on itself just like a 2-dimensional universe folding in on itself to form a sphere in 3 dimensions). Now you are able to travel in any direction you choose (length, width and depth) and will always end up at your starting point. Thus the universe is both finite (ie has a limited mass/size), and infinite (you will never find an "edge" and there is nothing "beyond") at the same time. Enigmatical 04:27, 11 May 2006 (UTC)

If the whole universe moves through a dimension, then that dimension would need to be larger in size than the universe. This dimension would need to be of infinite x infinite size. This would suggest that either the universe is much smaller than expected, or your time dimension theory is rubbish.

Also, time travel would be EASIER with your theory, since you would only need to match the acceleration of the universe yet travel in the 'opposite direction' (so to speak), and voila! You would be frozen in time. But then would arise the question; wouldn't you and whatever vechile you are using, still age/decay? They probably would, which they couldn't do if your theory is correct, since it would indicate a 'personal' timeline for every object. But time is held to be the same everywhere.

4. My last objection to you might be that every t position must be able to hold an infinitly large universe, and there must be an unlimited amount of said t positions (one for atleast every nanosecond, an unlimited amount of nanoseconds.) I don't think I need to explain just why such a thing, and through that your whole theory, would be impossible.

And yes, if we leave fiction, then yeah, time travel is impossible. But that is because time is really nothing, we perceive time because things change. And we then think of it in terms of days, years, minutes and seconds because we live on a planet that revolves around a star, where one rotation around the star takes a 'year', one rotation around the planets own axle takes a 'day', and then we simply split that into 24parts, which we call 'hours' and then split them in turn into 60parts we call 'minutes', and so on and so on..

But the universe hardly follows human notions of time or human labels for certain amounts of it.

Added 27/03/06

"Time is not the same as room." Clearly. I'm not an expert on theoretical physics, but I think that a lot of really complicated problems that people with doctorates do start making sense when you start treating time as a dimension. One might be able to argue that time only seems different because of how we perceive it, but you'd be right in thinking that there does seem to be something fundamentally different about it. You'd have to talk to someone who knows more about the theory than I do about this one.

"Even if it would be so, where is this space located?" It's in the fourth dimension. Think of it this way, if you lived in a 2-dimentional world where everything only had an x and y coordinates, your 2D universe could be moving through the z axis and you wouldn't be able to perceive what direction that movement was in. Even if time wasn’t the fourth dimension, there still could be a few more "directions" that we couldn’t know about.

"What ACCELERATION would the universe be moving at?" Zero, it's not accelerating; it's going at a constant velocity. Or if it is accelerating, we can't tell because our brains are changing speed at the same rate.

"This dimension would need to be of infinite x infinite size." Yes, just like with the 3 existing dimensions. A 1D universe would be infinitely long; a 2D universe would be infinite x infinite in size; and the 3D universe that we're use to is infinite x infinite x infinite in size; it is infinitely large in three different directions. Adding a fourth dimension to be infinite in doesn’t seem to be a problem.

"wouldn't you and whatever vechile you are using, still age/decay?" That's a very good question; I'm not sure how a physicist would answer that. A 'personal' timeline in time travel might work the same way as they do for objects moving at near the speed of light or close to a strong force of gravity, though it's not quite the same situation.

"there must be an unlimited amount of said t positions" That's not a problem. There are also an infinite number of positions in the x-axis, one for at least every nanometre, and an infinite number of nanometres.

"time is really nothing" I see you're saying, but there is more to it than that. Physics that it based off of Einstein and Hawking's work deals with time in such a way that assumes that it can be effected by stuff. -arctic gnome 18:17, 27 March 2006 (UTC)

Dear actic gnome- I am the unsigned who sparked-off the last round of debate. Can I say that I was very impressed with the way you picked-up my views and defended tyhem- you have clearly understood the concept very well.

As for the person debating with you, I suggest he/she reads a few of the more scientific articles about the nature of time. The idea of a 4 dimensional space is quite hard to grasp if you take it too literally. In physics, however, there can be many other types of dimension. I can give you another example. Consider the combination of your weight and your position in a flat space- these comprise a 3d 'space' with coordinates w,x,y where w is your weight and x and y your geographic coordinates. Imagine walking through a flat desert and losing weight as you go- you would be able to depict your 'trajectory' as a line through the three d weight space. In physics a dimension just means an independent variable quantity. It is when you try to envisage them as if they were physically comparable to 3d space that it gets confusing.

Best regards

best regards

So would this be a true statement? I am from your future and my past.

INTERESTING THOUGHTS

THink about this: What if u go back in time to kill your friend but from the time u came from your friend was the one that gave u that gun. (so if u killed your friend your friend would have never given u the gun which is the one u used to kill him with.)

What if u went back in time to create a technology research center (so when u went back to your own time it would be more developed and have higher technology) but in order to create this place you had to tear down an abandoned clock shop which an homeless guy lived in and that place inspired him to create a time machine, but before he could get inspired you had torn down the place. (so time machines wouldn't have existed so u would have never went back so....)

what if you had went back in time to tell your self something. You could never say anything diffrent than what u remember because your memory would be of what u just said. Futurechromex3x 05:47, 6 May 2006 (UTC)

Fractured Timelines

I noticed that none of the scenerios provided seemed to suggest the possibility of a fractured timeline. This theory was the driving force behind Back to the Future 2 yet it isn't clearly mentioned in the article.

The theory that was mentioned was that a change to the timeline would cause it to split into 2 parallel time lines. The original one would of course continue (thus allowing you to go back into the passed in the first place), while the new one would be created based on what would have happened given the changed conditions (and in this new timeline you were never born because you killed your grandfather). This principle has the most plausibility as it eliminates the grandfather paradox completely.

The difficult then comes in how you would move through such a universe. It might be possible to travel back in time further in an attempt to "correct" problems you have already corrected before (ie Butterfly effect), but any attempt to travel forward would take you only down the current timeline. One school of thought may indicate that the very fact you have travelled back would in itself cause a split, making it impossible to ever get back to your original timeline, while another school of thought would indicate that unless there were major changes, a timeline would not split.

This principle was also used (in my opinion) for the Terminator movies, in which the destruction of the original terminator may have prevented the original timeline from occurring, the new timeline actually "used" the terminator's parts to create a new cyberdyne. This could be seen as a time paradox but in reality it isn't, because it is a persisting of one concept from an alternative timeline in the current one though they would not have been the same. The eventual destruction of cyberdyne itself in the second movie would again have caused the original timeline to split. In the book it showed Sarah Conner growing old and watching judgement day come and go. This would have been the new timeline. If however either of the other two timelines sent a terminator back prior to the original jumps, then it would have gone back to the original timeline and caused a further split allowing for more posibilities.

Original timeline

------------------------------------------------------------------------------------- Original

Timeline after 1 jump

                             |<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|
-----------------------------+-----------------------------+------------------------- Original
                             |
                             +------------------------------------------------------- Altered

Timeline after a 2nd further jump

             |<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|
             |               |<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|     |
-------------+---------------+-----------------------------+-----+------------------- Original
             |               |
             |               +------------------------------------------------------- Altered
             |
             +----------------------------------------------------------------------- New Altered

Its not a "school of thought", its fiction. Thus not mentioned. 12.41.40.20 21:55, 3 January 2007 (UTC)

Unlinked reference

I've removed the following reference from the page, as I don't know what part of the page it belongs with. If anyone knows, please can they add it back to the appropriate section?

• David Lewis, "The Paradoxes of Time Travel," American Philosophical Quarterly 13 (1976), 145-152

Thanks. Mike Peel 13:07, 25 May 2006 (UTC)

Similar paradoxes

I believe that there are many similar paradoxes.

• The mother paradox- the mother is killed before the woman marries the father, and so the child doesn't exist.
• The father paradox— the father is killed before the man marries the mother, and so the child doesn't exist.

--User:Angie Y.

Just being there would change everything. Seems more logical that a model using parallel universes is needed. Either that or you can only time travel to extremes of spacetime, like to the first second after the Big Bang or into a black hole. (Both of which would be rather briefly unpleasant.) 12.41.40.20 16:40, 4 January 2007 (UTC)

Just curious...

...As to whether the following would be considered relevant, in light of the video game 'Metal Gear Solid 3' being included.

Another game to have a narrative featuring the grandfather paradox is the game 'Prince of Persia: Warrior Within'. The storyline follows the path of the hero as he is mercilessly chased through time by a demon - The Dahaka, guardian of the timeline which he altered in the previous game, the result of which killed everyone he knew. He hatches a plot to go back in time, planning to prevent the Sands of Time being created, so subsequently, he cannot open them as they do not exist, and in theory, the Dahaka will have no quarrel with him. 144.132.120.128 04:45, 7 June 2006 (UTC)

placement of futurama solution

The solution in Futurama:

"The Futurama episode, Roswell That Ends Well, episode 3ACV19, in which a main protagonist, Philip Fry, travels back in time and humorously solves the paradox by (accidentally) becoming his own grandfather."

is listed under "Other examples", I belive this should be placed under "Restricted action resolution":

Quote from "Restricted action resolution" section :

"It can also occur that the time traveller does not merely fail to prevent the actions he seeks to prevent; he accidentally precipitates them"

Theories in science fiction, Parallel universes resolution

I think that the parallel universes resolution should not be put under the science fiction catagory. There are current physics theories that suggest, at least at a mathematical level, the possibility of parallel universes. One such theory is Stringtheory. http://en.wikipedia.org/wiki/String_theory

More accuretly it is M-theory. "M-theory A multiverse of a somewhat different kind has been envisaged within the 11-dimensional extension of string theory known as M-theory. In M-theory our universe and others are created by collisions between membranes in an 11-dimensional space. Unlike the universes in the "quantum multiverse", these universes can have completely different laws of physics—anything may be possible." http://en.wikipedia.org/wiki/Multiverse_%28science%29#M-theory

This is also talked about in a PBS Nova special entitled: The Elegant Universe. http://www.pbs.org/wgbh/nova/elegant/ And those videos are full of scientists and professors from various established scientific communities.

Butterfly effect

Anyone got a reference for the claim that "self-healing" would be impossible? Especially since this is the fiction section, and there are certainly stories that treat the time-line as self-healing. Goldfritha 23:23, 19 October 2006 (UTC)

Removed. Goldfritha 18:16, 29 October 2006 (UTC)

Already occured

Discussing the restricted actions, we get this statement:

In effect, the traveller will be unable to change history, because for him it has already occurred

and the cause is not often present. Characters for whom it has not occurred -- people who were actually in the past -- are also prevented from taking such actions that will change the future (to them). Goldfritha 18:19, 29 October 2006 (UTC)

Paradox

What if your grandfather also invented the time machine? I suppose it would be really, really, really hard to kill him. 12.41.40.20 21:46, 3 January 2007 (UTC)

More information

What about viewing the past or the future (as in A Christmas Carol)? Nothing about the grandfather paradox prevents passive viewing. Is there information about it on wikipedia?

Also bringing stuff here from other times somehow seems more plausible than sending stuff, but I doubt there's a theoretical difference. 12.41.40.20 16:49, 4 January 2007 (UTC)

Comment(personal theory)

Couldn't the universe be utterly ruined or destroyed, the very fabric ripped? I mean, if it loops constantly so you were never born yet you were born because you couldn't have killed your grandfather if you weren't born but then now you aren't born, and it looped forever, couldn't the whole time stream be entirely twisted/ripped?

--Heero Kirashami 06:02, 13 January 2007 (UTC)

Link to I'm My Own Grandpa (Song) article

Can I suggest this link be removed? It is of no relevance to the main article. It is a quirk of terminology used to describe family relationships but it is not a paradox and does not have anything to do with time travel. There is no reason to think that anyone interested in the main article would be interested in this link, therefore it has no place in this article. Thoughts? --58.165.64.100 20:21, 28 March 2007 (UTC)

A questions about this paradox

What if the act of time travel shunts one clear of the effects of time? That is what if while travelling through time the method you use isolates you from "normal" time, basically making you exist independently of the "timestream", would not that allow someone to actually kill their grandfather, since during the time they are travelling they are independent of the timestream so even if they cease to have a past they would continue to exist due to the fact of being independent of the timestream?