Talk:Time travel/Archive 7

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 :) DumZiBoT (talk) 06:20, 8 August 2008 (UTC)
 * "Gott" :
 * p.33-130
 * p.76-140
 * "Thorne1" :
 * p. 499
 * p. 499
 * p. 499

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)

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)


 * No 1.2 is not an subset of 1.1 because a key point of the Novikov self-consistency principle is that the traveled objects experience the same physical laws as non traveled objects. In 1.2 universe this is not the case.  However I should add that the example given under "Immutable timelines" is a poor one as such events can occur "History is change resistant in direct relationship to the importance of the event" realities as well.--BruceGrubb (talk) 22:40, 13 February 2010 (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)


 * I believe Prof. Hawking maybe missing something a little more obvious here. That time travel into the past is impossible because no time machines exist, thus there is no mechanism in place to allow such a portal to exist. This does not make backwards time travel impossible however, but it does set a specific date and time limit on how far back one can go; the date and time that a time machine was created and activated. At that point, any future person(s) should be able to travel back in time to any date back to, but not past, the first activation. IE: Bookmarks in time. Let us consider manipulating wormholes at the speed of light, locking that specific date and time into the wormhole stream which would cause travelers to exit at the date and time that the light speed manipulation began, regardless of what date and time they entered it. While that is not the same thing as a time travel machine, the underlying laws of the universe and quantum mechanics are basically the same.


 * I would ponder that if that is the case, the grandfather effect might be a moot issue. Since the future is determined by what happens in the present, just as our present was determined by the past, the act of creating and activating a time machine would automatically alter the future, because the present would have already been altered by agents of the future the instant the machine was turned on. Since it would inherently be impossible to travel back in time to a point where the timeline had not already been altered (pre time machine activation), one could not actually alter the time line. Because of this limitation on how far back one could go, the only changes in the timeline would have to be post time machine activation, and thus would not have an impact on the future since those timeline events already took place. --98.211.145.167 (talk) 08:42, 29 April 2010 (UTC)


 * The idea that we don't see time tourists because they can't travel back to a time earlier than when the time machine was created is already mentioned in the "Tourism in time" section, that's what this sentence is talking about:"Hawking notes elsewhere that time travel might only be possible in a region of spacetime that is warped in the right way, and that if we cannot create such a region until the future, then time travelers would not be able to travel back before that date, so 'This picture would explain why we haven't been over run by tourists from the future.'"I don't understand why you think this alone would solve the grandfather paradox though. Suppose the first time machine is built in the year 3000, and in 3010 Sam conceives a daughter Maria, and in 3035 Maria conceives a son Sam II...if Sam II then uses the time machine to go back to 3005 and tries to kill his grandfather Sam ten years before his mother was conceived, you still have the potential for paradox unless you invoke something like the Novikov self-consistency principle or branching timelines. Hypnosifl (talk) 19:25, 29 April 2010 (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)

how do we know that a time travel machine hasn't been made? Or the guy might have been crazy... —Preceding unsigned comment added by Fangtheorc (talk • contribs) 20:19, 12 May 2010 (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.
 * Actually, that's incorrect. If your trip to 1960 is already a part of history, then your time travel is predestined as surely as if it were part of a causality loop.  The paradox (such as it is) lies in the predestination aspect, not the causality loop.  The wiki definition of predestination paradox is flawed and misleading.76.166.24.51 (talk) 16:58, 14 February 2010 (UTC)
 * I think you're taking the name of the term too literally--"predestination paradox" does not refer to any predestined event! If it did, then even situations that didn't involve any time travel at all, like my having lunch at a certain restaurant tomorrow, would involve a "predestination paradox" in a deterministic universe. I believe that the wikipedia article is correct that "predestination paradox" is normally used to refer specifically to causality loops--if you think the definition is "flawed and misleading", can you point to any sources that use it in the more general way you're proposing? Hypnosifl (talk) 17:47, 15 February 2010 (UTC)
 * Not every predestined event, every predestined event of time travel. The paradox (such as it is) lies in the fact that your time travel is already a part of history before you've actually performed that act.  Most people are confused because they commit what's called the "second time around fallacy." I see your point about predestination existing in linear time, too, but so do causal loops -- see, e.g., feedback loops.  There's nothing remotely counter-intuitive about A causing B causing A.  As for another source, that's tough because most sites simply copy the wiki definition word for word.  However, I note that at least one person already tried unsuccessfully to edit this wiki to reflect the point I'm making (i.e., predestination paradox occurs any time effects precede causes through time travel).  76.166.24.51 (talk) 19:20, 15 February 2010 (UTC)
 * How is that a "paradox"? In a deterministic universe, especially one where we assume the truth of eternalism where future events are just as real as past ones, it is also true that whatever you do tomorrow is "already a part of history before you've actually performed that act" (the only difference is that it's part of future history from your present perspective). And no, a feedback loop is not a causal loop--if event 1 in system A causes event 2 in system B which causes event 3 in system A (which is similar to event 1 in that it's an amplified version of it, but it's different from event 1 in the sense of happening at a different point in spacetime) which causes event 4 in system B (again similar to event 2, but amplified and at a different point in spacetime) and so forth, then this is a feedback loop between A and B, but the individual events in the loop still only cause things in their future. Again, I wonder if you actually have any sources that support your notions, or if you're just inventing what seems like the most logical definition to you based on your own personal interpretation of the word "predestination paradox" (remember wikipedia's policy on original research). Searching on google books, the sources I found seemed to support the notion that the standard usage involves a causality loop, as with this entry from the Star Trek encyclopedia (it actually looks to me like the term was probably coined by Star Trek, although the idea of such loops had been around for a while in time travel stories). Hypnosifl (talk) 02:34, 16 February 2010 (UTC)
 * As others have noted, predestination is not a "paradox" in the sense of being logically contradictory. Predestination via time travel is no more or less "paradoxical" than predestination in linear time.  Unfortunately, as I mentioned, I can't cite any sources because it appears most assume incorrectly that predestination paradox requires a causality loop, even though there's no reason why that should be so.  However, I can provide you with sources that say "predestination" is neither "paradoxical" nor "logically contradictory" even where time travel is involved.  []  Also, on the Predestination Paradox talk page,[] I posted an example of what I think most people would call a predestination paradox, but that doesn't involve a causality loop.  I'd love to get your thoughts on that, as well.  I'm also going to poll some physicist friends on this question, though I'm not sure how to cite their responses since they will be personal correspondence.  Any suggestions?76.166.24.51 (talk) 19:12, 14 March 2010 (UTC)


 * 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)