Talk:Time travel

Bot report : Found duplicate references !

In the last revision I edited, I found duplicate named references, i.e. references sharing the same name, but not having the same content. Please check them, as I am not able to fix them automatically :)

• "Gott" :
  • {{cite journal | first = J. Richard | last = Gott | title = Time Travel in Einstein's Universe | year = 2002}} p.33-130
  • {{cite journal | first = J. Richard | last = Gott | title = Time Travel in Einstein's Universe | year = 2002}} p.76-140
• "Thorne1" :
  • {{cite book | last = Thorne | first = Kip S. | authorlink = Kip Thorne | title = [[Black Holes and Time Warps]] | publisher = W. W. Norton | date= 1994 | pages = p. 499 | id = ISBN 0-393-31276-3}}
  • {{cite journal | first = Thorne| last = Kip S. | title = [[Black Holes and Time Warps]] | year = }} p. 499
  • {{cite journal | first = Thorne| last = Kip S. | title = [[Black Holes and Time Warps]] | year = }} p. 499

DumZiBoT (talk) 06:20, 8 August 2008 (UTC)

blogging

Can we please (push it to the) limit this page to discussions of how to improve the article? This is not a blog about time travel. Tvoz/talk 07:56, 1 November 2008 (UTC)

Safety

It is important to remember that when traveling through time, safety is never guaranteed. Especially when you've never done it before, or only once before. —Preceding unsigned comment added by 211.60.45.185 (talk) 07:41, 30 November 2009 (UTC)

you can travel time!

Just look at your clock/watch and in five minutes look at it again! lol!

you can also review the past by acting it out by yourself or looking at ablums, and old movies, reading up on history books. Punkymonkey987 (talk) 17:23, 2 December 2008 (UTC)

Missing One's Coach

the detile about the story "missing one coach " supposedly the first time travek to the past from 1838 is suspect. checking in the 2 relevant volumes of Dublin literary magazine from 1838 which are in google here

http://books.google.com/books?id=jfPAwAnj9JUC&printsec=frontcover&dq=editions:LCCN03010566&lr= and here

http://books.google.com/books?id=d7wp_FpOWaQC&printsec=frontcover&dq=editions:LCCN03010566&lr=#PPA1,M1 failed to find it . either the antologist derlet which ,mentioned this story in his 1951 anthology was mistaken in the story date of placement . or it was invented by him. at the moment it is uncear where and when the story had actually apperred befor his 1951 publication if at all. please correct. —Preceding unsigned comment added by 87.68.199.140 (talk) 04:30, 8 December 2008 (UTC)

The two google volumes you link to are dated "January 1838" and "July 1838", suggesting a monthly publication--perhaps google just hasn't scanned the other ten months. Hypnosifl (talk) 15:35, 31 December 2008 (UTC)

It was in the June 1838 edition, p. 701: http://books.google.com/books?id=jfPAwAnj9JUC&pg=RA1-PA701 66.191.102.29 (talk) 03:07, 30 August 2009 (UTC)

Proposed major revision to "Philosophic understandings of time travel"

Hello, all-

I would like to propose a major revision to the "Philosophic understandings of time travel" section of the Time Travel entry. I am currently enrolled in a "Philosophy of Time" course at Southern Connecticut State University. One of our final projects in the course is writing and integrating improvements to articles on Wikipedia relevant to our course and the material we've covered so far. Myself and two classmates have chosen to improve the "Philosophic..." section.

I would like to propose a substantive revision (and possibly moving the section to its own article (but this is unlikely due to time constraints)). We would cover some of the theories and arguments proposed by David Lewis, Ted Sider, and Lawrence Sklar. Are there any thoughts or major objections to this?

MikeAltieri (talk) 20:08, 8 December 2008 (UTC)

Type 1.2 is an subset of type 1.1

Isn't 1.2 just an subset of 1.1 where consistency-preserving improbable event is the time travel? Novikov self-consistency principle also applies in 1.2 just as it applies in 1.1. --193.198.17.211 (talk) 08:21, 2 December 2008 (UTC)

Any thoughts, anybody? --193.198.17.211 (talk) 10:21, 12 December 2008 (UTC)

Tourism in time

This heading seems extremely misleading 18:05, 26 April 2009 (UTC)~~ —Preceding unsigned comment added by 84.189.222.85 (talk)

How so? It describes Hawking's observation that time travel from the future must not exist because we have seen no "time tourists". Were you expecting a travel agent's pitch? 12.233.146.130 (talk) 22:28, 22 June 2009 (UTC)

Probably worth removing the profanity? —Preceding unsigned comment added by 91.109.38.194 (talk) 02:49, 14 November 2009 (UTC)

Origins date list

Surely this list would be better elsewhere - "list of time travel in fiction" or something. It seems strange to start off the bulk of the article with a big list. -mattbuck (Talk) 22:27, 13 October 2009 (UTC)

Claims of Time Travel

I'm wracking my brains trying to remember a true historical account of a man in 18th century France (or Spain, can't remember which) who claimed to be a stranded time-traveller from the future. His story could be a useful link here (or in the Time Tourism section!). As memory serves me, he was found wandering confused in a small town in the south of either France or Spain; his only posession being an unidentified spherical object. When questioned by authorities, he claimed he was an experimental time-traveller from three hundred years in the future, but the spherical object, which was supposed to transport him back to his own time, had failed or become broken. He was considered a lunatic by many, but some rich fellow took pity on him and provided him with lodgings and a laboratory, where he lived for the next few years struggling to mend his 'time machine', but eventually died before succeeding.

I cannot remember enough details to find further information about him in order to post a reference - does anyone know any more? Even a name would be useful.Butcherscross (talk) 15:44, 7 November 2009 (UTC)

Sure this wasn't a scifi story, or some made-up legend on the internet? Sounds pretty unlikely, since the "time travel in fiction" section indicates that no one had even thought up the concept of backwards time travel using a time machine until the 19th century. Hypnosifl (talk) 05:35, 17 November 2009 (UTC)

No, this was a factual article, describing an historical personage, but it's about 10 years since I read it and cannot remember the chap's name or exact details, or even which magazine it was in. The fact that it is such an early claim of 'backwards time travel' made me think it would be worth adding to this Wiki slot,if I could find out more about him, but no amount of 'googling' on the few details I remember have shed any light on it! Butcherscross (talk) 16:31, 18 December 2009 (UTC)

Better breakdown that is at best questionable

I was looking at the 'Types of time travel' (in fiction) section and found it severely lacking compared to what was done in GURPS Time Travel and its replacement GURPS Infinite Worlds. My problem is that since these are role-playing supplements and therefore not exactly reliable in of themselves (though the references at the end of the book are quite useful) is what to do. The section as it currently stands feels like it has OR issues anyhow but I am not sure these would improve the article. The Cliff notes of the relevent section is as follows in case anyone is interested:

• Paradoxes (Assumes Fixed Time with one past, one present, one future.)
  • The Grandfather Paradox
  • The Free Lunch Paradox (The example given has the time traveler give Shakespeare a book detailing his plays which Shakespeare copies. The result is no one actually writes the plays!)

• Plastic Time (past can be changed but there are dangers to doing so)
  • Traveler at Risk (Example: Back to the Future movies)
  • World at Risk (Example: short story "Sound of Thunder")
  • Past or Traveler at Risk (Example: New Twilight Zone Episode "Portrait in Silver")
  • Returned Blocked

• Chaotic Time (extreme version of Plastic Time where small changes can result in big alterations. Example: short story "Sound of Thunder")

• Plastic Time with High Resistance (It is very hard to change history and the larger the event the more difficult it is to change. Examples: Twilight Zone episode "Back There", The Time Machine (2002 film)

• Paradox-Proof Time (Extreme version of Fixed Time where the past cannot be changed and any attempt to do so snaps you back to your present.)

• New Timelines

• Parallel Worlds.

What do you think? It is better than what we have or worse?--BruceGrubb (talk) 23:04, 28 November 2009 (UTC)

It is unfortunately worse, because it uses neologisms and introduces unnecessary complexity.

Basic distinction should be whether timeline is immutable or mutable, as it was. Furthermore, if timeline is immutable there can be single timeline which is self-consistent (which isn't really an imposed restriction, but logical necessity), or there can be many timelines in which everything is allowed to happen.

So it should be simply:

• 1. Timeline cannot be changed
  • 1.1. One selfconsistent timeline
  • 1.2. Multiple timelines (which can interact)
• 2. Timeline can be changed

Additional categories are unnecessary, because everything is covered by this categories: timeline either can or cannot be changed, so by law of excluded middle there can not be third basic type, and there can be either one or many timelines.

And there is no need to use neologism and bad capitalization (such as "Multiple Timelines" instead of "Multiple timelines"). --antiXt (talk) 16:49, 29 November 2009 (UTC)

Saying that a timeline being changed or not being changed is an Fallacy of the excluded middle because a timeline is nothing more than a sequence of events and some sequences don't go anywhere or our understanding of them changes. This is why the subcatatories are needed under Plastic Time (BTW GURPS Infinite Worlds is using the same terms GURPS Time Travel did over a decade ago (1995) and quick search of "Fixed Time theory" you will get a load of hits so the terms I used are hardly "neologisms") as Plastic Time has a LOT of different variants (see GURPS Time Travel/Infinite Worlds, Crichton's Timeline, Multiverse (DC Comics), and Multiverse (Marvel Comics) for examples).

I should also point out what I replaced had a LOT of fluf that didn't really need to be there. While not exactly reliable GURPS Infinite Worlds is notable as an Origin Awards winner and to my knowledge is the only place where every (and I mean every) time travel theory imaginable is either addressed or you can put together form what is there.--BruceGrubb (talk) 11:37, 30 November 2009 (UTC)

I don't see how saying the timeline either changes or doesn't change is a fallacy of the excluded middle. I don't understand what you mean by "some sequences don't go anywhere" (what does it mean for a sequence of events to 'go' anywhere?), and "our understanding of them changes" doesn't imply there has been any objective change in the events that took place (unless you want to deny that there is an objective truth about what events actually happened at any point in the past, even without time travel being involved--if you do want to argue that this should be mentioned as a possibility, you should find a fictional example that used this premise). And if you think the article had a lot of unnecessary fluff, then please point out what you consider to be fluff so others can weigh in before you go ahead and delete it. Hypnosifl (talk) 13:05, 1 December 2009 (UTC)

Remember that in this part we are talking about how Time Travel is presented in fiction. (contrast that with Lewis, David "The Paradoxes of Time Travel" American Philosophical Quarterly, Vol. 13, No. 2 (Apr., 1976), pp. 145-152 that deals with the Philosophical aspects of time travel--and gives any layman who reads it a headache) A RPG compliment in of it self is a work of fiction and therefore relevant to the topic of Time Travel in fiction especially if it meets the notable requirement which GURPS Infinite Worlds does.

Plastic Time with high resistance universe would be for the most part nearly identical with a Fixed Time one (Fixed Time I might add can easily be found so it is not a term unique to GURPS) . As stated in [Twilight Zone episode "Back There"] "Mr. Peter Corrigan, lately returned from a place "back there", a journey into time with highly questionable results, proving on one hand that the threads of history are woven tightly and the skein of events cannot be undone, but on the other hand, there are small fragments of tapestry that can be altered."

Also the section I am replacing has many problems--Paradoxes can occur in a Fixed Timeline.--BruceGrubb (talk) 20:47, 1 December 2009 (UTC)

I'm not saying the RPG scheme is too non-notable to be mentioned at all, but I don't think it deserves to be the basis for the organization of the entire section. And "plastic time with high resistance" is nevertheless a version of fictional time travel where history can be changed, just not by very much...the possibility that the timeline might be mutable but highly resistant to change is already mentioned in the original version of the article. Finally, true logical paradoxes, like simultaneously concluding a time traveler will and won't kill his grandfather, can't happen in a fixed timeline, although of course there can be "paradoxes" in the more general sense of "things which are highly counterintuitive or contradict common sense", like the predestination paradox. Perhaps the section you mention should be edited to mention that there are two different senses of the word "paradox" and that only the first type is prevented by a fixed timeline. Hypnosifl (talk) 22:45, 1 December 2009 (UTC)

(remove indent)The Free lunch paradox is a paradox due to it violating the second law of thermodynamics and it just as much a headache as a time travel going loopy and going back in time to kill his grandfather. I have revised the section again using more neutral terms and noting that few authors can even agree where the Many-worlds interpretation idea goes.--BruceGrubb (talk) 14:04, 6 December 2009 (UTC)

Let me repeat the simple classification:

• 1. Timeline cannot be changed
  • 1.1. One selfconsistent timeline
  • 1.2. Multiple timelines (which can interact)
• 2. Timeline can be changed

Many-worlds interpretation obviously belongs to 1.2. --antiXt (talk) 20:50, 6 December 2009 (UTC)

Not everyone uses "timeline". Many writers talk about history and there in as they say is the rub. Some writers hold that history cannot be changed in a meaningful way ie the Twilight Zone episode "Back There".

Also why history is changeable is not always explained such as in the case of L. Sprague de Camp's Lest Darkness Fall. Is de Camp's a one timeline universe or a Many-worlds interpretation one? Neither the traveler or the reader knows. Furthermore the issue of traveling to the future and then returning is a problem. Take the The Time Machine (2002 film) for example. Here we are presented that while history will not allow paradoxes (saving his fiancee would result in him never building the time machine) it is implies that he can change "the future" but there is something this handwaving in such stories is the future can be change "because it hasn't happened yet" or some such nonsense.--BruceGrubb (talk) 05:32, 7 December 2009 (UTC)

So what? History and timeline are synonyms in this context. --antiXt (talk) 09:01, 7 December 2009 (UTC)

Not really. "timeline: a sequence of related events arranged in chronological order and displayed along a line" (WordNet Search). With system theory you can have many "timelines" within the same history as demonstrated by James Burke's Connections.--BruceGrubb (talk) 15:10, 7 December 2009 (UTC)

Time Travel Question

Lets say to have a machine that can move you backwards and forwards(past and future) in time. You start out on the main time stream and go back in time. Once you go back in time, it starts a new time stream that branches off the original one. So technically, when you go back in time, you can never get back to your original spot, right? —Preceding unsigned comment added by Savre123 (talk • contribs) 00:07, 3 December 2009 (UTC)

Well technically Savre123, if you start out on the main time stream and go back in time, you enter a reality where nothing is moving or existing. If attained at high enough speeds, (hundreds of lightyears/hour) one can literally stop aging. SO therefore by entering the main time stream, you would stop aging and defy time and space indefinitely. Forbes6969 (talk) 23:27, 3 December 2009 (UTC)

Interesting concepts, but I have something for you two to contemplate. Consider the fact that time travel has been a staple of science fiction. With the advent of general relativity it has been entertained by serious physicists. But, especially in the philosophy literature, there have been arguments that time travel is inherently paradoxical. The most famous paradox is the grandfather paradox: you travel back in time and kill your grandfather, thereby preventing your own existence. To avoid inconsistency some circumstance will have to occur which makes you fail in this attempt to kill your grandfather. Doesn't this require some implausible constraint on otherwise unrelated circumstances? We ponder this in attempt to explain time's paradox, but we will ever be able to attain the speeds required to test's Forbes6969 theory? Probably not. InterestTopicHunter (talk) 23:38, 3 December 2009 (UTC)

Yes, I have heard of that paradox. But If you were successful in killing your grandfather what would happen? Would you disappear? or would you actually end up somehow never having a grandfather? And if you went back to the present would anyone know that you exist? or would you even be able to go back? —Preceding unsigned comment added by Savre123 (talk • contribs) 23:42, 3 December 2009 (UTC)

Guys, this talk page should only be used to discuss revisions to the article, take note of the line in the box at the top which says "This is not a forum for general discussion of the article's subject." If you want to discuss how time travel might work in physics there are a number of science-related forums you could go to, like physicsforums.com...here is a post I wrote a long time ago on a thread there that discusses the issue InterestTopicHunter brought up about "implausible constraints", for instance. Hypnosifl (talk) 05:04, 4 December 2009 (UTC)

On a side note Carl Sagan brought up this very issue in the "Journeys in Space and Time" episode of his Cosmos: A Personal Voyage: "Perhaps time has many potential dimensions even though we are condemned to experience only one of those dimensions." Black Holes and Warped Spacetime by William J. Kaufmann states that in a rotating black hole the freedoms you have in space are switched with those in time on pages 86 and 108 per the Penrose diagram. But that would mean time would have to have at least three dimensions (forward-back, left-right, up-down) complicating all theories that have black holes as time machines.--BruceGrubb (talk) 12:24, 8 December 2009 (UTC)

Bruce, you've again made rather sweeping changes to the section on time travel in fiction without really discussing or seeing whether others agree with you. I think nearly all of your changes are unwarranted, for example:

• You change types of time travel to the more clumsy-sounding "Rules" of time travel with the justification "Type is the wrong word here as it more commonly refers to the *method or means* of time travel itself not the law by which time travel operates", but I disagree that "type" more commonly refers to "method or means", people use it all the time to refer to any sort of division into categories, like "types of animals" or "types of cars".
• You change "alternate histories" into "many-worlds interpretation", but this is simply incorrect: the many-worlds interpretation is a technical physics term which refers to a particular way of interpreting what's going on with quantum mechanics, it's not correct to use it as a generic term for any idea about branching parallel histories which might have nothing to do with quantum mechanics (for example, many time travel stories imagine that history only branches as a consequence of time travel, not that it's naturally branching all the time; also, logically it is quite possible that the many-worlds interpretation of QM could be true and yet time travelers would remain in the same history they started in, with each branch obeying the Novikov self-consistency principle, rather than traveling to a new branch). You also say in your edit notes that "sentence for many world consent contradicts itself" but don't explain how. And your edits here and in other sections go into an unnecessary level of detail about a pretty obscure book called "The Proteus Operation", having it just be listed as one example of the branching parallel universe idea was fine.
• You erase a lot of stuff from the section on type 1 time travel with no justification, like the point that logical paradoxes are ruled out in this type of time travel (the predestination paradox and ontological paradox are not logical paradoxes as you suggest--what contradictory conclusions can be drawn from them?), and some of the examples of how paradoxes are avoided in a self-consistent type 1 universe.
• You say that the predestination paradox is simply a case of an effect preceding a cause, but this is incorrect. For example, if a time traveler in 2009 is hungry and decides to travel to their favorite pizza place in the 1960s to get lunch, here the effect (the time traveler eating a 1960s pizza) precedes the cause (the time traveler being hungry in 2009) but this is not an example of the predestination paradox. The predestination paradox is all about a causal loop where two events at different times are both causes and effects of one another.
• The entropy paradox you refer to is not a genuine contradiction with any fundamental laws of physics--the second law is understood to be only statistical in nature, spontaneous decreases in entropy are improbable but not impossible (see for example the fluctuation theorem), and under the Novikov principle otherwise unlikely-seeming events can conspire to prevent inconsistencies (like someone's gun coincidentally jamming when they try to kill their grandfather). Also your notion of the watch aging more and more in "each cycle" makes no sense in the context of a discussion of a type 1 universe, since in this type of universe there must be a fixed unchangeable fact about the watch's condition at any given point in space and time, if the watch was in a certain condition on Sep. 18 1952, then there can't be another "cycle" where it was in an older condition on Sep. 18 1952.
• As with your unnecessary detail on the obscure book "The Proteus Operation", you also go into unnecessary explanation and editorializing about time travel in the DC and Marvel universes in the alternate history section. Again, examples should be just used to illustrate, we don't need to have digressions which recommend or condemn particular authors.

If you disagree with some of my points above that's fine, we can debate them here, but please don't make further sweeping edits until some kind of consensus has been reached in the talk section that these kinds of changes are good ones which add to the article. Hypnosifl (talk) 19:52, 15 December 2009 (UTC)

Type is still the wrong term with time travel because it is a form of travel. When you talk about travel you talk about car, train, boat, plane, bike, whatever you are talking about methods of travel and since time travel is at the end of the day is a form of travel type is clearly the wrong word. A type of time travel would be machine, physic power, magic, black hole or whatever other method you used.

What I had used actual referenced by Carl Sagan and Kelley L. Ross a PHd in Philosophy a relevant field while the stuff you reverted to had none of that. If you want to edit my changes hitting the undo option is NOT the way to it less you want be considered a vandal or too lazy to actual read the material referenced.--BruceGrubb (talk) 18:20, 16 December 2009 (UTC)

The majority of the changes I discussed above had no references attached to them, and the Carl Sagan reference had nothing to do with the predestination paradox, if you look at the context on p. 215 here you can see he was talking about the possibility that the arrow of time would reverse in a contracting universe, nothing to do with time travel at all. I agree that a link to the Kelley L. Ross page is fine, in fact I was the one who originally added that link to that section, but his opinions are not the be-all-and-end-all, you can check the fluctuation theorem page or any textbook on statistical mechanics to see that spontaneous entropy decreases are improbable but not impossible according to accepted laws of physics (and Ross did not specifically say he was talking about a logical paradox as opposed to just a situation which was paradoxical in that it defied common sense). Finally, I didn't simply undo everything you did with no justification, my explanation of disagreements above covered pretty much all the changes you made and why I thought they weren't appropriate, as I said if you think my judgments are wrong then I invite you to discuss them in more detail here.

I do take your point on "types of time travel" suggesting modes of transportation through time rather than types of universes in which time travel is possible. I think having quotes around "Rules" makes it sound a little awkward though, so if you don't mind I'll just change it to "Rules of time travel". Hypnosifl (talk) 18:48, 16 December 2009 (UTC)

There are problems with point "3. The timeline can branch into multiple coexisting alternate histories" because that is NOT how time travel as outlined in Michael Crichton's novel Timeline, Echos in the Homeline setting of GURPS Infinite Worlds, or James P. Hogan's The Proteus Operation works as no branching of the timeline occurs! Sure Timeline has some really bizarre M-theory like connections between the various parallel worlds allowing changes in one to effect the others but there is still no branching and it is using multiverse theory. Functionally Crichton's multiverse functions as a type 2.x reality even though there isn't one timeline.--BruceGrubb (talk) 00:21, 17 December 2009 (UTC)

Proof of Future Time Dilation

Could you please explain why you removed my addition to Time Dilation ie: "This form of Time Dilation has been proven experimentally," when other articles in Wikipedia claim that it has been proven ? —Preceding unsigned comment added by 66.244.196.62 (talk) 08:58, 4 December 2009 (UTC)

I don't know why your comment was deleted, but maybe it was felt that the specific scheme mentioned--"Traveling at almost the speed of light to a distant star, then slowing down, turning around, and traveling at almost the speed of light back to Earth"--had not been tested so it could be misleading to say it had been proven. Anyway, I added a paragraph on experimental evidence at the end of the "Time Dilation" section, let me know if that's not satisfactory. Hypnosifl (talk) 14:47, 4 December 2009 (UTC)

Thanks Hypnosifl, I think perhaps the editor was not familiar with the subject matter, and too quick on the trigger finger to delete.

Where I had a slight problem was with the statement " This form of "travel into the future" is theoretically allowed using the following methods". This statement was no longer true after 1971, even though the time involved was only a few nanoseconds. The effect has been verified experimentally using precise measurements of atomic clocks flown in airplanes, by the The Hafele–Keating experiment in October of 1971, where four caesium-beam atomic clocks were taken aboard commercial airliners and flown twice around the world, and then compared against those of the United States Naval Observatory.

Because the experiment was reproduced by increasingly accurate methods, there has been a consensus among physicists that the relativistic predictions of gravitational and kinematic effects on time have been conclusively verified, there is no longer any theory involved, the experiment was sound, and proved it was possible. In fact, even president Nixon got in on the situation after this by welcoming astronautics to the future (of I believe a few nanoseconds) when some astronautics returned to earth in their space capsule after their high speed (although pretty slow compared to light) travel.

I have restored the edit I made, and hopefully the editor will be more careful in the future.

(ps: I am the same person just different computer)

75.159.102.237 (talk) 18:40, 4 December 2009 (UTC)

I added a link to a page on the Hafele-Keating experiment in my edit. But I think your edit confuses matters, because adding "this form of time dilation has been proven experimentally" to the part about velocity-based time dilation but not to the part about gravitational time dilation makes it sound like one has been "proven" while the other hasn't, whereas in truth both are on firm experimental ground. I also think the word "proven" is a bad choice of words in science, you can only accumulate evidence that strongly supports a given theory, but you can't prove things absolutely as you can in mathematics. And the specific idea of traveling at near-light-speed to another star and back is indeed "theoretical" in the sense that no one has done that specifically yet (even though there is essentially no room for doubt that it would work), just like the idea of sitting in the middle of a massive hollow sphere, so I think the original statement is fine as is. Hypnosifl (talk) 21:51, 4 December 2009 (UTC)

I see where your coming from, but I was trying to be as brief as possible (perhaps too much) because I really liked the tone of the article, and I wanted to change as little as possible. Good point about "proven", perhaps that is just too strong given the fact that the Russian Cosmonaut has only traveled presumably 20 milliseconds into the future, so yea it can be done, but on a practical standpoint, not really. But I still have a problem with the statement "This form of "travel into the future" is theoretically allowed" it doesn't matter how you cut it, that statement is flat out false. Also being on firm theoretical grounds, and having actually done something are not the same. Do you have any ideas how to keep it short, but correct it, because as it sits right now I just don't believe that its correct. 75.159.102.237 (talk) —Preceding undated comment added 02:24, 5 December 2009 (UTC).

Well, I guess I don't think that saying something is "theoretically allowed" is mutually exclusive with there being strong experimental evidence for it, "theoretically allowed" just means it's a prediction of the theory that it would work, regardless of what the evidence says. For instance, you could say it'd be theoretically allowed to destroy Mt. Everest with sufficient dynamite, even though there is really no doubt that this would be possible since we know how dynamite works and have used it to blow up smaller hills and so forth. The time dilation example is similar, there's no reason to doubt it'd work since we've created smaller differences in aging on atomic clocks, though no one has actually sent an astronaut to a nearby star at a high fraction of light speed. Hypnosifl (talk) 04:02, 5 December 2009 (UTC)

I believe you are right in saying that “theoretically” is not mutually exclusive, but the problem I have is that “theoretically”, means concerned primarily with theories or hypotheses rather than practical considerations, but to only use “theoretically”, I think is misleading, because in this case there are practical considerations (the experiments themselves).

Your Everest example is a good one, and captures my concerns exactly, so what do you think about adding the following within the brackets in the ‘see the Twins Paradox’ text.

“This form of time travel has been demonstrated experimentally on a very small time scale”

75.159.102.237 (talk) —Preceding undated comment added 05:49, 5 December 2009 (UTC).

Is there anyone else out there that would like to comment on the proposed above addition ? —Preceding unsigned comment added by 66.244.196.62 (talk) 00:05, 10 December 2009 (UTC)

Sorry, forgot to get back to this...I'd be OK with the above addition (although I don't think this is really necessary since the experimental confirmation is discussed soon after), although only if some similar note about gravitational time dilation being demonstrated on a small scale was added to the subsequent paragraph, in order to avoid giving the impression that velocity-based time dilation has been demonstrated but gravitational time dilation has not. Hypnosifl (talk) 01:56, 12 December 2009 (UTC)

I was not aware that gravitational based time dilation was on such a solid footing (I am still trying to wrap my head around the special theory). Clearly my above suggestion would not be correct, it would have to be balanced as you suggest. I think that the experimental evidence (at only three paragraphs down) is fine where its at, but in the same breath, to wait three paragraphs before at least presenting the existence of significant experimental evidence still doesn't feel right. What do you think about adding the following to just below 'Residing just outside of the event horizon':

              "It is worth noting that these forms of time travel have been demonstrated experimentally on very small time scales"

or more bluntly,

                   “These forms of time travel have been demonstrated experimentally on very small time scales”

or something of the like... 75.159.102.237 (talk) 10:31, 12 December 2009 (UTC)

Yeah, in the subsequent section I included links to some info on evidence for gravitational time dilation, and you could also take a look at this fairly simple demonstration some guy did with an atomic clock taken into the mountains on a hiking trip: leapsecond.com Would you be OK with saying "these forms of time dilation" rather than "these forms of time travel"? Or maybe something like "It is worth noting that both velocity-based time dilation and gravitational time dilation have been demonstrated experimentally, though on much smaller scales than the proposals above." Hypnosifl (talk) 15:35, 12 December 2009 (UTC)

I should mention that some fiction writers have used the idea of a Big Bang followed by a Big Crunch to say that you can reach the past by traveling into the future because time itself is so warped as to close in on itself like a loop. DC comics used something like this for its Zero Hour event by having time one gigantic loop that Paralax-Hal caused to grow smaller and smaller until no time between the beginning and end of time remained.--BruceGrubb (talk) 05:26, 17 December 2009 (UTC)

Streamlining the Immutable timelines and Mutable timelines sections

The Immutable timelines and Mutable timelines sections were somewhat a mess. Let's keep the examples short and to the point. We do not need examples out of the latest Harry Potter book when much shorter examples are readily available. Please note that Sukys' book is printed by Ardsley House Publishers a publisher of college textbooks making it of higher rank than much of the material in this section.--BruceGrubb (talk) 07:16, 20 December 2009 (UTC)

On the topic of Sukys' book, you cited that book for the statement "The paradox in such situations is that it effectively requires the information to essentially exist before it existed"--this sentence seems confusing to me, would you mind quoting the paragraph(s) from the book that you based it on? Hypnosifl (talk) 15:42, 29 December 2009 (UTC)

Also, you quote Ross' argument that Reeve should get younger along with the watch as a counter to Novikov's argument about the external universe expending energy to repair the watch, but Ross is actually not addressing Novikov's argument here, instead Ross is addressing a hypothetical response to the paradox which he invented himself, one which differs significantly from Novikov's response. Specifically, Ross is imagining that someone might respond to the paradox by invoking a new physical law which uniformly says *all* physical objects should be restored to earlier states when traveling back in time--that's why Ross introduces the notion that "forms of matter would be restored to that state they would have been at the earlier period", and then responds that "this will not do, since Reeve himself would then be restored to the state his matter was in in the 19th century". But Novikov wasn't proposing any new physical laws (see Novikov_self-consistency_principle#Assumptions_of_the_Novikov_self-consistency_principle which notes the Novikov principle explicitly denies any new laws apply to time travel), instead he was just saying that the watch would necessarily have to be repaired *if* this was necessary to preserve self-consistency, in much the same way that my attempt to kill my grandfather in the past would be guaranteed to fail if this failure was necessary to preserve self-consistency. Just as the necessary failure of an attempt to kill my grandfather before he conceived children does not imply any general law of the form "all attempts to assassinate people in the past will fail", in the watch example the necessary fact that all wear/entropy the watch acquires must be repaired sometime before it completes the loop does not imply any general law of the form "all objects going back in time will have their entropy reversed", so nothing in Novikov's response requires that it would apply to Reeve as it would in Ross' hypothetical response (also note that Novikov's argument in no way assumes the repair to the watch happened at the moment it traveled back in time, as Ross imagines; it could be that 15 years before it went back in time it was repaired to a condition even *better* than its condition at the moment it was handed to Jane Seymour, and then that 15 years later the wear it had acquired during that timespan had returned it to exactly the condition it was 'supposed' to be when it was given to Seymour).

If you want to include a new paragraph in which you introduce the idea of responding to the paradox by imagining a new law which says "forms of matter would be restored to the state they would have been at the earlier period" and then point out Ross' argument against this, that would be something to discuss (I think the idea is a little too obscure to merit inclusion in the article, unless anyone has seriously advocated this as a valid response to the ontological paradox--Ross only brought up the idea briefly in order to shoot it down, not to advocate it himself), but I deleted the paragraph you wrote because you made it sound like Ross' argument somehow addressed Novikov's argument, when in fact Ross' hypothetical law is completely different from what Novikov was proposing (and Ross never *claimed* he was addressing an idea that had been advocated by any real person like Novikov). Hypnosifl (talk) 04:19, 30 December 2009 (UTC)

Sukys uses about two full page of examples such as "The process of putting the ideas and words together to create the novel cannot be generated by the novel itself.", a paragraph he quote from someone else and, things like "This would require the novel to exist before it has been written." "Boolean logic requires either that Hamlet was written before it was shown to Shakespeare, or that it was not." In simpler terms these some two pages worth of material are saying the paradox is that for a work to be copied it must exist before the copy is made ie it must exist before it existed. That is about as simple as I can make the some two full pages worth of material Sukys has.

As far as the the Novikov self-consistency principle is concerned Sukys points out that it requires the future to be set in stone as well (pg 270-271). Also I never said that Sukys addressed the Novikov self-consistency principle but rather the inconsistency regarding Reeve and the watch.--BruceGrubb (talk) 13:33, 30 December 2009 (UTC)

It sounds like Sukys is just restating the idea that the novel would have no origin--that the person who "first" wrote it was actually just copying a novel from the future that from their point of view "already" existed. So I don't think it's really necessary to have both the statement The "free lunch" is that no one really writes the plays! and the statement The paradox in such situations is that it effectively requires the information to essentially exist before it existed, as they're basically expressing the same idea but the second one is more confusingly worded.

As for Reeve and the watch, that comment wasn't about the Sukys book at all, rather it was about the Ross article--the immutable timelines section had ended with this sentence: In addition, the second law of thermodynamics only states that entropy should increase in systems which are isolated from interactions with the external world, so Igor Novikov (creator of the Novikov self-consistency principle) has argued that in the case of macroscopic objects like the watch whose worldlines form closed loops, the outside world can expend energy to repair wear/entropy that the object acquires over the course of its history, so that it will be back in its original condition when it closes the loop.

Then you had added the following paragraph: However Ross points out the logistic flaw in such an argument: "But this will not do, since Reeve himself would then be restored to the state his matter was in in the 19th century, which, whatever it was, would not be in the form of Christopher Reeve." In other words for the reversal of entropy idea to work it would have to effect everything that traveled in the past equally.

My objection was that this made it sound like Ross was pointing out a flaw in the argument by Novikov given in the previous paragraph, when in fact Novikov's argument in no way implies that Reeve should be an earlier state as well, and Ross was not really addressing Novikov's proposal. Again, what Ross was actually doing was attacking a hypothetical proposal (different from Novikov's) that there might be a general rule that said "forms of matter would be restored to the state they would have been at the earlier period". Hypnosifl (talk) 16:20, 30 December 2009 (UTC)

OK, you changed the summary of Sukys to read "The paradox in such situations is two fold; first the process by which such a work would be created cannot be created from the work itself and that the work must exist before it was "created" to be copied.[68]" But does Sukys actually say that the paradox is "twofold", or that a work "cannot" be created from the work itself (as opposed to just saying it seems strange or implausible that a work could be created in this way)? And again, I don't see how "the work must exist before it was created to be copied" is stating a different idea than the notion that the work has no origin because it was first written down by being copied from a future print of the same work, all of which was already covered in a less confusing way by the previous sentences you had written: GURPS Infinite Worlds gives the example (from The Eyre Affair) of a time traveler going to Shakespeare's time with a book of all his works. Shakespeare pressed for time simply copies the information in the book from the future. The "free lunch" is that no one really writes the plays! Hypnosifl (talk) 01:22, 31 December 2009 (UTC)

Sukys says both in the some two pages worth of material and since the section is readable through google books look at it yourself rather than continuing doing this waltzing mouse stuff. Ross even states "The vocabulary as a certain list of items arranged in a certain way was thus complied by no one whatsoever. The knowledge exists in a closed temporal loop and is in an important sense uncaused or uncreated."

As for Novikov the inconstancy here is that some sort of special rule applies to the watch and only the watch but not to Reeve, not to his clothes, or to the modern penny he leaves in his pocket. Remember that Friedman, John; Michael Morris, Igor Novikov, Fernando Echeverria, Gunnar Klinkhammer, Kip Thorne, Ulvi Yurtsever (1990). "Cauchy problem in spacetimes with closed timelike curves". Physical Review D 42: 1915 stated "We shall embody this viewpoint in a principle of self-consistency, which states that the only solutions to the laws of physics that can occur locally in the real Universe are those which are globally self-consistent." But to fix the watch problem Novikov is himself ignoring that statement as laws of physics that are being applied to Reeve and the watch are globally inconsistent. Something here doesn't look right.--BruceGrubb (talk) 01:46, 31 December 2009 (UTC)

The reason I ask about Sukys is that the page you cited was p. 237, and pages 236-237 are not available on google books. If Sukys says something to the effect that the ontological paradox situation where the work has no origin cannot happen, or that "the work must exist before it was created", then please provide the relevant quotes here so I can check whether I agree that your words are an accurate paraphrase of his argument.

As for Novikov, you misunderstand the whole principle if you think a special law applies to the watch, as I pointed out earlier it's a basic requirement that the local laws of physics are exactly the same for time traveling objects as they are for situations that don't involve time travel (again, see here). Even for an ordinary watch which does not travel back in time, if it is not isolated from its environment it's quite possible that the environment will expend energy to repair a watch which has acquired wear/entropy (and it's also possible, though highly improbable, that an isolated system will spontaneously reduce in entropy). These things don't involve any new laws of physics, any more than a failure of a would-be-assassin to kill his target requires new laws of physics. The point is just that in situations involving time travel where perfectly ordinary physical events like this *must* occur in order for the timeline to remain consistent, they *will* occur according to the Novikov self-consistency principle, which says that only self-consistent histories are allowed. Nothing about the self-consistency requirement implies that *all* attempted assassination attempts by time travelers should fail, or that all objects going to the past should have their entropy reduced before/during the trip, since in many cases these events would not be required for the purposes of self consistency. This has no relation to Ross' proposal that there could be a general rule saying that "forms of matter would be restored to the state they would have been at the earlier period"; as far as I know no one has actually seriously proposed such a general rule, and since Ross only brings it up to shoot it down (and on a self-published webpage rather than a journal article or book), I don't think it's worth including in the article. Hypnosifl (talk) 03:11, 31 December 2009 (UTC)

You have sidestepped the issue Ross expressly stated. In the example given Reeves and the watch go back in time but for some reason the watch experiences different physical laws from Reeve and everything else that also goes back in time. That is the problem and Gott doesn't really address it in the example of Somewhere in time he gives. Worse the Richmond Review of the book states "Gott denies the Jinn principle." but later on states "However Gott's own solution to the creation of the universe involves such a Jinn principle." This is akin to being on the Island of Knights and Knaves and having one of the locals walk up to you and say "I am a Knave." The logical impossibility of such a situation is self evident.--BruceGrubb (talk) 04:50, 31 December 2009 (UTC)

No, you're still misunderstanding, the watch doesn't experience any different physical laws in Novikov's proposal, though it does in Ross' proposal (which is why Ross' discussion doesn't even address Novikov's proposal). In Novikov's proposal, it just happens to be true that the the watch was repaired according to exactly the same physical laws that would allow a non time-traveling watch to be repaired (in much the same way that if a time traveler tries to assassinate his grandfather and it so happens that his gun fails to fire at the crucial moment, then no new physical laws would be involved here either, since the guns of non time travelers fail sometimes too). Do you understand that no special new physical laws are required in order for a watch to be repaired by the external environment (for example, it might have been taken to a repair shop), and that Novikov's proposal does not require that the watch be repaired at the actual moment it goes back in time? (I already made this point earlier when I said in an earlier comment "also note that Novikov's argument in no way assumes the repair to the watch happened at the moment it traveled back in time, as Ross imagines; it could be that 15 years before it went back in time it was repaired to a condition even *better* than its condition at the moment it was handed to Jane Seymour, and then that 15 years later the wear it had acquired during that timespan had returned it to exactly the condition it was 'supposed' to be when it was given to Seymour")

Also, I don't see where Gott "denies the Jinn principle", do you have a page number for that? In any case I only used Gott as a source for Novikov's argument, and AFAIK Novikov never denies the possibility of "Jinns" so there is no contradiction in his argument. Finally, please keep in mind my request about providing quotes from Sukys. Hypnosifl (talk) 13:32, 31 December 2009 (UTC)

I am quoting a review regarding Gott's book and few reviews give page numbers but it is an independent review of Gott's work and suggests something wonky about his position. Furthermore, the referenced piece from Physical Review states "self-consistency principle proposes that the local laws of physics in a region of spacetime containing time travelers cannot be any different from the local laws of physics in any other region of spacetime". In other words to salvage the watch Gott is ignoring something that was referenced from a peer-reviewed journal article.

Finally, Stephen W. Hawking, in A briefer history of time‎ Page 112 and Zukav in The Dancing Wu Li Master page 218 say two related things "But when the object is traveling back in time (from B to A), it appears as an antiparticle traveling forward in time." (Hawking) and "Feynman demonstrated in 1949 that this convention is more than an artistic device. He discovered that a positron field propagating forward in time is mathematically the same as an electron propagating backward in time! In other words, according to quantum field theory, an anti-particle is particle moving backward in time." (Zukav)

But take a real look at what both Hawking and Feynman are saying here. From our prospective the watch would get younger during the journey but from the watch's it is getting older. The entire premise that "the local laws of physics in a region of spacetime containing time travelers cannot be any different from the local laws of physics in any other region of spacetime"." falls apart as the watch experiences different physcial laws from Reeve and every other object on his person the exact point Ross points out.

I am restoring the fuller quote as there was no justification for removing it in the first place as Ross' premise is supported by two scientists nearly 50 years apart. Unless Gott explains how one piece of time traveling matter gets younger while other pieces of time traveling matter don't fits the premise referenced in Physical Review Ross' point.--BruceGrubb (talk) 11:27, 1 January 2010 (UTC)

traveling faster than light to travel back in time

This is complete rubbish. anything travelling FASTER than light by definition is still moving forwards in time. the fact that some may see things as if they were moving backwards in time does not mean they are actually moving backwards in time. This is only a consequence of the fact that the data stream can only arrive at light speed no matter how fast the object is moving... the frames of data will be arriving in reverse order but never before that data was actually produced. you will never see a signal prior to its actual transmission... the actual moment of transmission can still be calculated via Lorentz transformations and adjusted for all frames of reference. 2ndly the notion of faster than light leading to reversed time is primarily based on a mis-reading of the very same Lorentz transformation. It appears to have a negative time factor after light speed, but this is not quite the case. what it actually has is a squareroot of a negative number which is not the same as a negative number. its called an imaginary number and in electronics represents a phase shift. in hyper dimensional space it would represent a negative number which is 90 degrees out of phase with the 3 d space, or the 4th spacial dimension, hyperspace. that means that any object moving faster than light would be in hyperspace behind the expanding 3 d space and would move backwards away from the 3 d spacial bubble... not backwards in time, but backwards down a wormhole that still exists in current time... that wormhole does not link to any existant past, because the past does not exist, its only memories of where the current arrangement of things came from... the worm hole could link to other hyperspacial objects or if large enough to some other part of the current 3 d space. —Preceding unsigned comment added by Jiohdi (talk • contribs) 14:17, 22 December 2009 (UTC)

If you can find a good, and verifiable, reference to all of that above then it would make for a good section in the article. HumphreyW (talk) 14:27, 22 December 2009 (UTC)

Gott, J. Richard (2002). Time Travel in Einstein's Universe. pp82-83 is sited in the Faster-than-light article as to why FTL results in backwards time travel. Also one of the ideas about tachyons is that their FTL nature means they either have imaginary mass or travel backwards in time. So the idea that FTL and backwards time travel is not rubbish as shown by cited sources in the relevant articles.--BruceGrubb (talk) 13:43, 23 December 2009 (UTC)

You all must listen to me! I am from the year 2012, and I have come back to warn you all. The legend that the world will end as you now know it will indeed end. My means of returning to the past must be kept secret, but I promise that if I could tell you i would. All I can tell you is that all the governments of the world worked together to do it. I and the rest of the future world can only hope that my being here has altered the future from the catastrophe. You must all heed this warning, because it is the absolute truth, this is no prank or hoax.