Talk:Time travel/Archive 2

Question/Something to Think About
If you go back in time to stop a disaster from happening, and you succeed, why is there any reason to go back in time to begin with? Which means you never go back in time to stop the disaster, which means it does happen. Just wondering if this would create some type of infinite time loop?


 * The questioner is making the assumption that going back in time to change a past action will lead to the SAME reality changed. You could now be in a new reality, which has split off from the original, with no way to get back to where you came from, because the path back there has been changed, unless you can go back and undo the change.


 * There is also the issue of whether the person who decides to go back, or not go back, has any personal memory of the trip, depending on the vehicle of travel back. User:AlMac|(talk) 16:54, 3 January 2006 (UTC)


 * Also, if time travel is ever created, we will have already known it because if someone came back at this exact moment, and they told us about the future, we will know if there is time travel in the future. Therefore, you can almost assume that the future has already happened.--Weatherman1126 22:23, 9 February 2006 (UTC)

Dreams Time Travel?
The definition of time travel given from this site sounds like dreams to me... Although it isn't very controlled, perhaps like our conscious body moves physically through space, our subconcious moves mentally through time and alternate universes. What do you think? &mdash;The preceding unsigned comment was added by Jebus96ae (talk &bull; contribs) on 07:31, 14 February 2006.
 * Many claim to have Déjà vu sourced in dreams that are of future events which they later experience, is this what you mean? A laymens theory to this (if taken outside the general psychology of it as only being an illusion) could align itself with quantum theories which claim particles travel through time regularly on the highly microscopic level, and that this somehow interacts with brain firing mechanisms such as neurons when the brain is in the receptive sleep mode. Which would require that there be some space-time loci in physical matter, such as that composing the brain, which anchors this energy transference to a single place (ones brain) through time; and is a form of movement of "information only" through time. Otherwise we're speaking of either A) exotic matter and the mind, i.e. an exotic matter composing the subconscious (and there is no reason to believe this), or B) a metaphysical belief that the subconscious mind is separate from any matter composing it, even that it posits matter itself rather than the other way around. A little off topic for the time travel discussion page I would think. 67.5.156.138 02:50, 28 April 2006 (UTC)

Impossibility of time travel
I argue that time travel is impossible. Lets say that "bob" hops in a space craft possible of light speed. The space craft is designed to orbit the solar system at the speed of light for one year, and then return to earth. Scientist on earth monitor the crafts every move till it returns. Einstein says that Bob would be in the future, but what would happen the space craft while the scientists were monitoring it? &mdash;The preceding unsigned comment was added by Usafcbrown (talk &bull; contribs) on 23:25, 28 February 2006.

No, Bob would not be in the future. He would be one year ahead of when he left. The spacecraft would have continued to be monitored by the scientists. Bob would not have aged as much as the other people on Earth. —The preceding unsigned comment was added by 67.142.130.13 (talk • contribs) on 00:28, 23 April 2006.

The Morphail Effect
The Morphail Effect is cited as an example of Time travel, yet no information is given! Can somebody shed light on this or should it be removed?

--James Bond-- The Morphail Effect is cited as an example because of the temporal distortion matrix regulation engines in place whenever it is implemented in a manufactured time paradox (which is purely theoretical of course). Duh.

I "fixed" the Morphail Effect stub, which was incomplete, but I'm basing the fix on rather fuzzy memories. If somebody else wants to give it a go, I'd be happy to have the additional input from those that have read the End of Time books recently. User:MattShepherd

past vs. future time travel
Moving at a faster rate of time into the future as an object moves faster relative to another has been experimentally confirmed, such time travel isn't under question and it creates no paradoxes etc. The article contradicts itself on this point, mostly due to a lack of clarifaction between moving forward and backward in time.
 * There's a novel by Steven King, I forget the title, in which some Nazi scientists invented time travel, and sent explorers into their future, our present, to steal future technology, to help them win WW II. They were ultimately defeated by sending someone to the British who would be believed about the importance of bombing the laboratories of the Nazi Time Travelers. In my opinion, this novel illustrates the notion that changes to history can cause paradoxes, even when the travel is into the future. AlMac|(talk) 04:54, 21 September 2005 (UTC)
 * No - the only way for that to change the past woud be if they were able to send the information they obtained back to the past, which would require backward-in-time-travel (for information, if not for mass). --Cheese Sandwich 18:42, 29 September 2005 (UTC)
 * The novel you're referring to is actually Lightning, by Dean Koontz, not Steven King. Doctortoc 18:50, 25 February 2006 (UTC)
 * Perhaps I oversimplified. The Nazi agents were in combat with a double agent who was trying to undermine their actions.  They were jumping backwards and forwards in modern times, seeing some event, going back and killing some people so the event would not take place.  It was not a one time dimensional novel. AlMac|(talk) 00:48, 30 September 2005 (UTC)

fact v.s. fiction
An article on Time travel and no mention of Dr Who or Isaac Asimov's The End of Eternity - "Shurley shome mishteak" as they say.

Time travel can be described as the ability to move through time in a non-linear manner (such as we do and space ships are assumed to do).


 * At one time there was an extensive section in this article on Time travel in fiction, Hollywood, Games, etc. and that got moved to a separate article on Time Travel in fiction (see links on the article) with Time Travel as scientific fact getting to adopt the main article. AlMac|(talk) 07:11, 26 October 2005 (UTC)

Should the "Film and Television" section of "Reference" be replaced with a pointer to Time travel in fiction? Gentaur 17:08, 5 December 2005 (UTC)
 * Editors arrive at articles and enthusiastically add material. From time to time chunks of info on the summary of fiction on the main Time travel (in science) article should be moved and merged into the Time travel in fiction article, with suitable explanation to avoid getting into an edit war with the new enthusiasts. User:AlMac|(talk) 16:58, 3 January 2006 (UTC)

Do you'all think it might be possible to copy / dupecheck the entire fiction list into Time travel in fiction, Category:Time travel television series, and List of television series that include time travel? Replace the entire fiction chapter here with an explanation and links to those three? The list here is just slowly growing into a dupe of those three articles. Weregerbil 15:24, 27 February 2006 (UTC)
 * Heh, KarlBunker beat me to it :-) Weregerbil 15:29, 27 February 2006 (UTC)

Timeline Theory
Delete this if this repeats other stuff. Or is plain wrong. :(

I have a simple theory that goes, time in all its complexity could be represented in a 2-D diagram similar to a tree.

Any action, decision, quantum fulctuation in the whole universe 'creates' another branch. It is easier to assume all probaboilities are represented in the tmeline tee theory.

The main trunk, Origin, perhaps starts with the First Action that made all the other branches. Semi-valid theories can be fitted in to 'explain' Origin or to disbunk it.

Thus almost all paradoxes can be eliminated. Example:

Guy @ Branch A2.1 wants to kill Grampa before his birth (at Branch A1.1) to test stupid theory. Guy jumps back in time. Guy is now at Branch A1.2 and Grampa is now dead. Guy jumps back to his 'current time' and realises that there are two copies of him.

Notice that Branch A1.2 is NOT his own timeline. Thus he killed another Grampa. Multiple futures and permutations thus exist, so, he may also find that he's gone back to 'current time' but at Branch A2.2 and his alter-Guy does not exist. Notice also that it is extremely improbable that Guy returns to Branch A2.1 as his decisons, quantum fluctuations, etc. has made him go down many other Branches.

Thus in this multiverse, anything can happen, you may meet yourself time-travelling. Touching yourself may be unadvisable as the you(s) are at a somewhat similar and you may poke your hand through yourself like the theory that one day you may punch through the wall as the molesules are aligned such that your hand atoms pass through tha wall.

Reply
This is actually a theory proposed by Everett as mentioned in this very article. Did you read it all the way through?

''The Novikov self-consistency principle and recent calculations by Kip S. Thorne indicate that simple masses passing through time travel wormholes could never engender paradoxes—there are no initial conditions that lead to paradox once time travel is introduced. If his results can be generalised they would suggest, curiously, that none of the supposed paradoxes formulated in time travel stories can actually be formulated at a precise physical level: that is, that any situation you can set up in a time travel story turns out to permit many consistent solutions. The circumstances might, however, turn out to be almost unbelievably strange.''

''Parallel universes might provide a way out of paradoxes. Everett's many-worlds interpretation of quantum mechanics suggests that all possible quantum events can occur in mutually exclusive histories. These alternate, or parallel histories would form a branching tree symbolizing all possible outcomes of any interaction.''

An approach to clean things up
It would be nice if there was a seperate section that addresses What is Time. This would help when discussing Time travel from a scientific grounding and then how it relates to science fiction. Also its usefull if 'personal theories' are excluded as this goes against the wikipedia guideline and at the very least confuses things. 86.7.107.45 18:22, 6 November 2005 (UTC)
 * There is a separate article on Time theory. Perhaps better linking needed to make it more obvious what articles exist, so we can collectively work on improving them all. User:AlMac|(talk) 17:06, 3 January 2006 (UTC)

Most time travel ideas have the wrong frame of reference
Most authors see time travel as a change in the time coordinate of the entire universe except the time traveller. This vision is wrong. Any device allowing time travel may only change the time coordiante of the traveller while the universe goes about it's business. Thus time travel will happen in one of the following ways:
 * The traveller slows himself on the time coordinate and the universe will sped by him, which can be considered a travelling into the future;
 * The traveller accelerates on the time coordinate and will grow older much faster, with the posibility of super-human speed in relation to the rest of the universe;
 * The traveller reverses the flow of time for himself, which would make him younger, reverse cause and effect localy within the time-machine, will result in a younger version of the traveller in an older universe, an extreme form of traveling into the future.

If this is the correct frame of reference, then, theoretically, travelling to the past is impossible as the past does not exist. The universe is in the present and the whole universe would have to be reversed in time while the time traveller keeps his time coordinate, as this seems impossible without god-like powers it should be dismised as an option for a time machine.

I haven't seen this idea formally presented, so I'm putting it in here. If somebody has some comments and/or references please add them. Richard1984 12:10, 21 December 2005 (UTC)


 * This is only one of many possible interpretations of time travel. In particular, it overlooks the classes of travel where either a) the traveller's worldline is discontinuous (vanishes at the departure point, appears at the arrival point, always proceeds normally otherwise), or b) the traveller experiences time normally relative to the patch of space they're embedded in, but events inside and outside this patch of space seem to experience time flowing in opposite directions relative to each other. Both of these allow travel into the past (relative to some arbitrary inertial frame) without de-aging the traveller. See also closed timelike curve and the "time hole" implementation of a wormhole (which can result in a CTC). Both of these produce spacetime geometries where an object's worldline can intersect itself (allowing "future" and "past" versions to meet). --Christopher Thomas 15:47, 21 December 2005 (UTC)
 * In one of my favorite Time travel in fiction stories, there is a multiverse of multiple universes, or realities, where the traveler is able to move from one universe to another. The arrow of time is going in a different direction in different universes.  In the story, we can only travel in the time direction of the universe we are in at current time, but we can have two universes traveling in opposite time directions, at different time speeds.  So you go thru a "portal" to another universe, travel forwards in time a month there, to a different portal, and you end up 100 years in the past in the original universe, without traveling in time per se.  I think this kind of discussion should move to Time travel in fiction or to some other main article, from the dsicussion of what our current science believes is possible. User:AlMac|(talk) 10:06, 2 January 2006 (UTC)

Philosophy section required
This article needs a section on the philosophy of time travel, since it is as much an issue of metaphysics as of physics. (That is, whether time travel could be possible, not just whether it is possible.) For example, the word of Paul Horwich. Ben Finn 18:18, 30 December 2005 (UTC)
 * Check out the Wiki article Philosophy of space and time. Is this what you were looking for?  Perhaps the interlinking could stand improvement, so it is obvious what all related articles exist. User:AlMac|(talk) 17:10, 3 January 2006 (UTC)

Distance in time travel
The second paragraph in the "distance in time travel" subsection was removed by User:Dudegalea and restored by User:Capitalist. I've left it in, for now, but have heavily edited that section both for narrative viewpoint (should be third-person) and for accuracy. My concerns with it are as follows: In summary, as far as I can tell, while the comparison between distance and time can be made, conclusions about the ease or difficulty of time travel can't be meaningfully drawn from the comparison, and the paragraph in its original form actually presented misleading claims. --Christopher Thomas 04:26, 2 January 2006 (UTC)
 * The difficulty of travel through space can be whatever you want it to be. If I wave a laser pointer at the heavens, photons from it will eventually travel at least hundreds of millions of light-years, and potentially forever (depends on assumptions about change in the rate of expansion of the universe, among other things). If I'm willing to wait an extremely long time for it to reach its destination, I can put an ion drive craft built with off-the-shelf parts on a similar trajectory. The perception that travelling large distances through space is "difficult" lies with the fact that there are a number of other assumptions being made (we want the probe to still be working when it arrives, and to arrive within much less than one human lifetime). The level of difficulty is also strongly tied to assumptions about who's doing the travelling. We can send objects into space (or across continents, for that matter) far more easily than the ancient Romans could, for example.
 * Assuming that the difficulty of travel through time is comparable to the difficulty of travel through space is extremely questionable. In practice, the difficulty of either type of travel depends on the mechanism by which the travel is accomplished. In the case of time travel, it also depends on where you're intending to go. Travel to somewhere in your forward light-cone can be done by waiting around and possibly hitching a ride on a sub-lightspeed rocket. Travel outside your forward light-cone looks like FTL or even travel into the backwards light-cone of an observer moving quickly relative to you, and is considerably harder (if it's possible at all).
 * Energy requirements, which were mentioned in the paragraph before I revised it, actually involve two separate topics. The act of travelling itself may require energy exchange, but this is intimately tied to the mechanism used. Traversing a wormhole set up to act as a "time hole" doesn't take energy from the traveller, but towing one end of the wormhole at near-C to a distant location and back to set up the time delay does. Furthermore, any time travel mechanism involving closed timelike curves may require a large or even infinite amount of energy to set up (to the best of my knowledge, this question hasn't been settled yet; see wormhole).


 * Your second and third points appear valid on their face, but the first point seems specious to me. I think the original writer of the paragraph was simply making a "ceteris paribus" comparison, and you have obscured that by adding several additional variables that were meant by the writer to be held constant over the domain of "time travel vs. space travel"; You added variables like:
 * the thing traveling (photons vs. a person)
 * the time you're willing to wait (which is confusing because it's dependent on velocity and distance T=D/V which is what the original writer's point was)
 * the condition of the object when it arrives
 * and so forth
 * The fact that there are a bunch of different variables like this does not detract from their point. They were saying that GIVEN some situation (for instance, a 170 pound male and his dog are doing the traveling, and we would like to get them there in approximately the same condition as when they left, etc.) then it seems reasonable that comparable amounts of energy would be needed to move either one second in time, or one light-second (186,232 miles) in space.


 * That being said however, I can point out at least one simple flaw in the original argument, which is that an object moving at a constant velocity needs NO energy to keep going (Newton's first law), so I agree with your conclusion that the idea is flawed. I just didn't think your first bullet point did any justice to that position though.  capitalist 03:49, 3 January 2006 (UTC)


 * I consider the first point to be one of the more important ones, actually. The original poster used travel across space as a yardstick for difficulty of travel, and drew conclusions based on that, while apparently oblivious to the fact that as a yardstick the difficulty of travel through space is extremely poorly defined. --Christopher Thomas 05:51, 3 January 2006 (UTC)


 * The ceteris paribus assumption would require that all variables with the exception of distance are given and constant across both situations (time travel vs. space travel). In that case, wouldn't the relationship between distance and energy requirement be extremely well defined?  For example, if my goal is to move a mass of 4Kg (given) from a state of rest on the earth's surface (given) over a certain distance "D", back to a state of rest on the earth's surface (given) in exactly 11.3 minutes (given), then wouldn't the energy required to do that vary as a precise function of D? capitalist 07:38, 4 January 2006 (UTC)


 * My point is that there isn't any specific value of the "given" variables that is intrinsically more meaningful than others. Your stipulation of 11.3 minutes, for example, means that any distance of more than 5.65 light-minutes is flat-out impossible to traverse - but rather than reflecting any fundamental truth about the ease of traversing distance, it only reflects the arbitrary constraint you've applied to the problem (the round-trip travel time). Similarly, if I wanted to be pedantic, I'd point out that it's a lot easier to send 4 kg of photons on a round-trip journey that long than 4 kg of matter that needs to be boosted to a hair short of light speed. While you can indeed nail down a relation for energy given enough constraints on the problem, my point is that the comparison isn't terribly meaningful precisely _because_ it requires a large number of arbitrarily defined constraints in order to be performed. --Christopher Thomas 17:51, 4 January 2006 (UTC)


 * Science is essentially the study of how one variable is related to another variable. In order to study such a relationship, the scientific method requires that you isolate the variables under study.  You do that by holding all other possible variables (whatever long convoluted list anyone can come up with) CONSTANT.  It doesn't matter what value you choose for those constants.  If you don't add such "constraints on the problem", you can't do any meaningful science.


 * The original writer of the "energy requirement paragraph" may have anticipated an incorrect conclusion, but their METHOD was right. They focused on the relation between energy requirment (E) as the dependent variable, and distance (D) as the independent variable, holding all other possible variables constant (ceteris paribus). By throwing in all kinds of extraneous variables and asking "what about these?" like you are trying to do in your first bullet point, you are violating a basic precept of the scientific method.


 * An example would be an experiment to study the relationship between an object's mass (M) and it's free fall acceleration (A). The only quantity you would vary would be the masses...you might want to test 10 different masses from 1kg up to 100kg or whatever.  You would then design your experiments so that all other factors remain constant; you would choose objects of the same size and shape to make the effects of air resistance constant (or use a vacuum chamber to eliminate that factor), you would drop them from the exact same height every time, you would use the same stopwatch every time, you would do it under the same weather conditions and in the same place on the earth's surface every time, you would do it at the same time of year, WHATEVER.  Once you do that, lo and behold you find that all masses fall at the same rate.


 * Then what would you think of someone who comes along and says, "well that's not valid because you have all kinds of constraints on your experiment"? "There is nothing intrinsically more meaningful about dropping things off the Tower of Pisa than from anywhere else", etc. etc. You would think they don't understand science.  And you'd be right.


 * As for getting 4kg of photons, I think that would be quite a bit harder since it involves a division by zero to determine how many photons you would need. Unless there's been quite a revolution in Physics (which of course is possible) photons don't have mass (which is why they can travel at c under relativistic equations). capitalist 03:54, 5 January 2006 (UTC)


 * I am quite familiar with the scientific method. Measuring the acceleration of several test masses in Earth's gravity provides useful results because you get the same answer each time. The resulting model - that for masses substantially smaller than Earth, dropped near Earth's surface, you get a constant acceleration - is much simpler than hashing through Newtonian gravity and motion DEs, so it's useful to apply in practice. Attempting to pin a "difficulty" on travel through space in general, as opposed to for specific, constrained applications, doesn't give useful results. The resulting relation isn't useful for the discussion in its original context, as rather than given _a_ yardstick value for difficulty, it gives a wildly varying range of possible difficulties depending on parameters that are arbitrary with respect to the problem as-described (leaving aside the application difficulties noted in my other points). The resulting relation isn't terribly useful for other applications involving traversal of space because using the overly-complex model that results isn't appreciably simpler than solving the problem from scratch with the constraints added by the application you're interested in (be it lifting a load on a crane or sending a probe to the next star with well-defined mission constraints). Does this illustrate to you why I consider a result that varies wildly depending on the values of free parameters a bad thing?


 * I think what may be confusing is the original writers use of the term "difficulty" or "hard" or whatever they said, because I notice you put it in quotes as if it's some kind of vague undefined concept. I believe that the writer was referring specifically to energy requirements with those terms.  In that case, it IS a useful general statement.  I'll try to express it in yet another way:


 * "If I want to accomplish movement task "T" over some distance "D", then I can determine the energy "E" that is required to do that (right down to the tenth of an erg or whatever). If I keep all the specifics of task "T" the same, but I increase "D", then "E" will increase as well.  If I decrease "D" then "E" will decrease".


 * "What makes it a general statement is that it doesn't matter what "T" is. "T" could be getting an elephant to the moon by next Tuesday, or it could be moving my Mountain Dew can from here to the other side of the room in 15 seconds.  WHATEVER the task is, energy requirements "E" FOR THAT TASK will increase as distance "D" increases and vice versa.  By bringing up all these extraneous factors, you seem to be trying to say that this GENERAL relationship between "D" and "E" might be true for the Mountain Dew can, but it might not be true for getting the elephant to the moon.


 * I'm giving a lot of straightforward examples to illustrate what I'm saying, but your objection seems very vague. Maybe you should give an example that illustrates what you're trying to express. capitalist 05:27, 7 January 2006 (UTC)


 * You appear to continue to be missing the _point_ of the objection. You're specifying travel time as part of the problem constraint. Even if you neglect all of the other variables, and assume that the "difficulty" of travel is proportionate only to the theoretical minimum energy expenditure required, the energy expenditure varies wildly for different choices of trip time. The choice of trip time is arbitrary, making "energy required to traverse distance X" useless as a yardstick, because its value can be whatever you want it to be, depending on your assumptions about trip time. Do you understand what I'm getting at, here? Saying "time travel over time delta-t is as hard, or as energy-expensive, as distance travel over distance C delta-t", as the original poster did, is a meaningless statement as a result of this ambiguity. There is no way do derive an answer to "how much energy does it take to travel duration X in time" without additional constraints being specified, even if the relation between travel in time and travel in space is taken at face value. The comparison is useful solely as a rhetorical device, to get the reader thinking that durations they perceive as trivially small might not be as trivial as they appear. That's the only reason I left it _in_. --Christopher Thomas 23:19, 8 January 2006 (UTC)


 * I think the crux of the disagreement is this: You think the original writer was trying to discuss the relation "energy required to traverse distance D".  I think they were trying to discuss the relation "energy required to accomplish travel-task K".  Travel Task "K" in this case involves getting some definite object from one particular place to another in a certain amount of time, and it could also include a lot of other specifications such as condition of the object upon arrival, etc.  But Travel Task "K" always involves at least the three variables D, T, and M.  For any given travel task "K" you can calculate a minimum energy requirement.  So let's compare two different travel tasks "K1" and "K2".  Imagine if you will that the two tasks are the same in every respect except for one:  D2 > D1, ie. the second task involves a greater distance.  All other variables (including T = trip time) remain the same between the two tasks.  Now, which task has a higher minimum energy requirement?  Task "K2" does. This is because the "difficulty" (minimum energy requirement) of each task is a function of the distance traveled, WHEN ALL OTHER FACTORS INCLUDING TRIP TIME ARE HELD TO BE EQUAL (ceteris paribus).


 * I think the original writer's vision was this:


 * Task #1: If you want to send a ton of rock to the sun in a period of 3 weeks, it takes a minimum of 46 kazillion joules (or whatever) to do that.  If you want to send a ton of rock back through time 8.3 minutes, and you would like the journey to take 3 weeks (from the rock's point of view) then you will also need around 46 kazillion joules.


 * Task #2: If you want to send the same ton of rock to the moon in 3 weeks, then you only need 1.3 kazillion joules. Similarly, if you want to send the rock back in time by 1.2 seconds, and you would like it to take 3 weeks from the rock's perspective, then you will need about the same 1.3 kazillion joules.


 * Now this idea is probably incorrect for other reasons that you've cited, but not because of any kind of "arbitrariness" or "vagueness" in the concept of difficulty. Difficulty is related to the ENTIRE TASK, and I think the original writer was thinking in terms of "tasks" as well (that's what time travel is all about after all; "cool stuff you could do", ie: tasks).  It's true that you can't assign a "difficulty value" (minimum energy requirement) to just a distance by itself, but no one is claiming that it's possible to do that.  You're just setting up a straw man and knocking it down, which was my original objection.  Your ultimate conclusion is totally correct as far as I can see, but this particular argument in favor of that conclusion is just rhetorical. capitalist 04:57, 9 January 2006 (UTC)


 * As for the mass of photons, you may wish to check your physics texts. Photons have zero _rest_ mass, but they have relativistic mass equal to E/C2. Among other things, this is why light sails work (if photons were massless, they'd have no momentum to transfer to the sail). --Christopher Thomas 05:07, 5 January 2006 (UTC)


 * Photons have momentum, but not mass. If you want the math, it's posted by an astrophysicist imagine.gsfc.nasa.gov/docs/ask_astro/answers/960731.html here. capitalist 05:27, 7 January 2006 (UTC)


 * You may wish to read your citation more carefully. $$m$$ in the equation $$E^2 = m^2C^4 + p^2C^2$$ is rest mass. Let's denote rest mass $$m_0$$, and relativistic mass $$m_r$$, to avoid confusion. Consider movement of STL particles first (I'll justify it a few paragraphs down). For this case, it's easy to show that $$E = m_r C^2$$ and $$p = m_r v$$. This is in fact one way of deriving the Lorentz factor. The reverse of this derivation is as follows:


 * $$m_r = m_0 \gamma$$ (where $$\gamma$$ is the Lorentz factor) (Given as true.)


 * $$m_r^2 = m_0^2 \left ( \frac{1}{1 - \frac{v^2}{C^2}} \right )$$


 * $$m_r^2 \left ( 1 - \frac{v^2}{C^2} \right ) = m_0^2$$


 * $$m_r^2 - \frac{m_r^2 v^2}{C^2} = m_0^2$$


 * $$m_r^2 C^4 - m_r^2 v^2 C^2 = m_0^2 C^4$$


 * $$(m_r C^2)^2 = m_0^2 C^4 + (m_r v)^2 C^2$$ (True if you accept the definition of the Lorentz factor as true.)


 * Compare this to:


 * $$E^2 = m_0^2 C^4 + p^2 C^2$$ (Given as true.)


 * It is obvious from the last two equations that declaring $$E = m_r C^2$$ and $$p = m_r v$$ is consistent with both, and causes no problems. In practice, you can take these relations as axioms and derive the Lorentz factor from the equation you cite, but the derivation works fine for demonstrating the validity of the relations if you accept the Lorentz factor as an axiom.


 * Now, for the case of a photon, $$v = C$$. This gives:


 * $$m_r^2 C^4 = m_0^2 C^4 + m_r^2 C^4$$


 * $$0 = m_0$$


 * Zero rest mass, finite nonzero relativistic mass, from the equation you yourself cite. The Lorentz factor blows up at C, but it's not taken as fundamental (the equation you cite is, instead, and the Lorentz factor derived from it by the reverse of the method above). I hope this clears up how I've been using the terms "rest mass" and "relativistic mass". I think you'll find that these definitions and derivations are accepted by most physicists, but by all means grab a few and get them to look at the talk page to confirm it. The link you cite answers the question "do photons have rest mass", and I agree that the rest mass is zero. --Christopher Thomas 23:06, 8 January 2006 (UTC)


 * I think this KB is running out of colons! Great explanation; One of the most common questions asked about the link that I cited is "if $$ p=mv $$ then how can a particle with zero mass have positive momentum? If one looks closely at your derivations, the answer is in the substitution you made from  $$ (m_r v)^2$$ to $$p^2$$; relativistic mass is not zero, so neither is momentum.  Got it.  I'm completely with you on the distinction between relativistic mass and rest mass.  However, we WERE discussing rest mass.


 * Remember that your original contention was that it would be "easier to send 4kg of photons" somewhere than 4kg of something else, and I said it would be a lot harder. It would be harder because I assume you would somehow have to pile the 4kg of photons onto a scale (to make sure it's not 3.7kg or whatever).  In order to do THAT wouldn't the photons have to be standing still?  But then, according to quantum theory, since the precision with which you can determine a particle's position is inversely related (through Plank's constant I believe) to the precision with which you can know its momentum, and a bunch of photons at rest on a triple beam balance scale obviously have zero momentum, then I actually DON'T know that they're sitting on the triple beam balance scale...they might be over in my Mountain Dew can!  So now I'm totally confused about how to actually measure out 4.000kg of photons.


 * This supports my original position on the question that it would be a LOT more difficult; not easier. QED!  :-)  capitalist 05:35, 9 January 2006 (UTC)


 * I removed the paragraph because it was propagating a grossly naive (but common) understanding of the relationship between energy requirement and distance, and also because it was naively comparing space with time travel. Your edit does a good job of purging the over-simplification, while preserving the information for those who want to know why it is a naive argument. Nice. Wish I'd written it myself. :-) --DudeGalea 08:59, 2 January 2006 (UTC)


 * Now that there is an explanation of why it was removed, I'm satisfied to leave it out. capitalist 03:49, 3 January 2006 (UTC)
 * The only thing about the rewritten version that would concern me now is the violation of the "passive voice" guideline in Avoid weasel words, however that happens all over Wikipedia and I'm not involved enough with this article to mess with it (my own weasel words for being too lazy lol). capitalist 03:59, 3 January 2006 (UTC)

wont change it
my opinion is no one can change the past no matter how they try. assume that you go back to the past to change something, but no matter how you try it you wont be able to change it. its like on minority report, tom cruise found out that he is going to shoot a guy, then he did everthing he can to prevent it, but in the end he still shoot the guy

202.170.56.242 06:42, 6 January 2006 (UTC) dying loser


 * If you could go back in time is it even possible NOT to change the past? Just by being there, you have changed the past slightly - you've breathed the air, your body has refected light in a slightly different way than it would have been reflected if you had not been there. It's true, these are tiny changes, but changes nonetheless. If you walked into a store, and bought the last doughnut, that's a change. Small changes can build up to larger events.--RLent 18:30, 16 February 2006 (UTC)

Time travel & intelligent design
The article Intelligent designer includes a reference to time travel in Prof. Michael Behe's book Darwin's Black Box, which challenges the theory of evolution. The author suggests that a time-traveling cell biologist could have been the originator of human life. Any thoughts about if (and where) a reference to this item from science/pseudoscience/religion might be included in the time travel entry?? JXM 09:47, 15 January 2006 (UTC)

Paradoxes
There is so much potential and interesting material (both scientific and fictional) on paradoxes with time travel that a new Time travel paradox article would be a good idea to pull it all together (imo). There is a lot of work in quantum theory which looks to a layman like me to suggest that actually we're not actually certain what is happening or not happening in the present and you can set up experimental conditions in such a way that particles will both do something and not do it.

It could be that paradoxes are just another weird quantum effect which when you look at something on a macroscopic scale just cancel each other out (for all intents and purposes). So in theory there are an infinite number of possible pasts for any present but in practice we all observe basically the same past. If we used some quantum device to travel back our actions would cause the possible pasts to collapse into the one past which would match the one observed from the present. We obviously cannot conceptualise of being in this state as we interact so profoundly with the universe all the time but we are nevertheless a product of quantum mechanics like everything else and yet it still seems completely alien to our everyday observations of the universe.

Btljs 22:02, 16 January 2006 (UTC)]]

Prophecy and Theology
In addition to biblical references showing that messengers bring information from the future to those in the past for what is called "prophecy", I've included references from outside the theological North-American mainstream, from the Book of Abraham (I quoted 3:6-9).

If I had included such text from an ancient Asian or African source, I believe that we would welcome that and my addition would not have been removed. The Book of Abraham includes some interesting insights about how some feel about God's relationship to time.

Another Wikipedia writer and observer stated that this is not a page to promote your favorite religion, but it is just an article on time travel. I do not wish to promote anyone's religion, I just wish to point out an interesting insight that fits well into this section, perhaps one of the best theological references on time. Why is this not welcomed? Is the bias with the writer or the observer?

I believe that this is very interesting insight into the views of some on time if a section on Prophecy and Theology is truly relevant to the Time Travel article. If we are to assume that this is a promotion of the Book of Abraham from anything outside of a scholarly point of view, then we may assume that the reference to the Bible is offensive to many English speaking users as well. I believe that any source of text is acceptable as long as it is insightful.

I'm glad I could start a bit of discussion. Good for the brain! Ricardo630 21:37, 24 January 2006 (UTC)Ricardo630


 * Re. quoting the passages from the book of Abraham: I submit that this is inappropriate because they are only likely to be of interest to people with a strong interest in the Mormon bible, plus an interest in the nature of time, plus an interest in the relation between those two things. As such, the passages aren't likely to be of enough interest to enough readers to warrant their inclusion. There are no doubt a lot of religions that have include some writings about the nature of time, but we can't include those writings from all of them.
 * As for the section on Prophecy and Theology in general, I submit that, at least as it now stands, it adds nothing to the article.
 * It begins by stating that "any religion which postulates the existence of fulfilled prophecy requires, [...] an agent which can move information from the future into the past. In the first place, this is of questionable interest in an article about time travel, since a minority of people accept the literal truth of religious prophecies. Secondly, this statement doesn't stand up logically. Prophecy could be effected through some preternatural ability to extrapolate the past and present into the future. In the case of prophecies that come from an omniscient god in particular, assuming that god is omniscient about the past and present, it stands to reason that s/he could make "omniscient extrapolations" about the future.
 * The section goes on to tell us that some scholars consider "existing outside of time" to be a part of omnipotence and/or omniscience, and that these people further believe that God is omnipotent and omniscient, and that these people therefor believe that God exists outside of time. Um, yeah.
 * Finally the section tells us that the Yoga Sutras of Patanjali say something about the nature of time, and that a physicist/author wrote a book about whatever it was that those Sutras say.
 * KarlBunker 11:56, 25 January 2006 (UTC)

major trim-down
I've done a lot of edits to this article recently, and reduced its size a lot in the process. I think it's a much better article now; a coherent piece that someone could conceivably read from start to finish and feel that they got something out of it.

My thoughts on why so much of the article deserved "throwing away":

In general, Wikipedia articles tend to collect cruft over time. People do a quick read and think "Oh! I'll add my thoughts about xxx!" Without necessarily thinking carefully about whether their addition adds new information. I think an article about time travel is especially prone to this, because it's a fun subject to think about, but a difficult subject to write clearly and meaningfully about. It's easy to think that one's own thoughts (or the thoughts from some movie or book) along the lines of "hmm, maybe time is like this" are new and meaningful and a worthwhile speculation. Also, the very length of the article was probably encouraging people to make unnecessary additions to it. It was a chore to read all the way through, and some people undoubtedly went ahead and added stuff without reading all of what was already there. KarlBunker 18:26, 27 January 2006 (UTC)

The Bible on time travel
The Bible on time travel The Bible states that time travel is not possible for beings that are in the stream of time.

Responding to a question by one of his disciples on the end of time (Mat 24:3), Jesus replied “"No one knows when that day or hour will come-not the angels in heaven, nor the Son, but only the Father”. - Mat 24:36 (ISV)

This indicates that neither angels nor demons have the ability to travel in time. It is something that only God, who is not in the stream of time, can do. He is therefore the originator of true prophecy. -Roelf 5 April 2006

YTMND WARNING
Expect regular changes which revolve around the safety of time travel. Note to whomever is doing the reverts here: you missed two "safety not guaranteed" refrences, and I suggest you simply lock it. Penis Gourd 08:16, 8 February 2006 (UTC)

It appears that only the Admin bots have done it later. And still, yet another person modified it afterwards. I do agree that this also needs to be locked. I like YTMND and all, but this is just plain annoying. Lightning Jim 14:25, 8 February 2006 (UTC)

I think there should be at least one reference to the internet meme --Stilanas 17:47, 8 February 2006 (UTC)
 * I was browsing ytmnd (yes I'm a ytmnd'er, but I don't vandalize wikipedia), and I saw this on the top 15 atm:

timetravelingsafety.ytmnd.com/ Expect more vandelism all day to-day. (Bjorn Tipling 18:36, 8 February 2006 (UTC))

I undid some more YTMND vadalism I think --Stilanas 18:37, 8 February 2006 (UTC)

How does one request protection? --Stilanas 18:39, 8 February 2006 (UTC)

YTMND has pushed it to the limit, this is true lunacy! Someone lock this page.

Made this: safetywikivandal.ytmnd.com/ --Stilanas 19:59, 8 February 2006 (UTC)

Requested protection from the ceaseless vandalism. -- Gun Metal  21:00, 8 February 2006 (UTC)
 * And semiprotection was received. Thanks to howcheng we can rest from constant rvv's for a while. -- Gun Metal  21:58, 8 February 2006 (UTC)


 * i would try and be careful dealing with ytmnd. there is a good chance that this could spread to other topics within wikipedia on new topics and fads. maybe we can include some sort of reference to the SNG ytmnd so everyone is happy. otherwise i just think things like this will get worse. 1 <3

I created timetravelingsafety.ytmnd.com/. It was not my explicit intention to “vandalize” Wikipedia. The edit was done in such a way that it did not alter the existing content of the article, and in a language consistent with said article. I felt it was humorous, in good taste, and informative. Perhaps I went to far. One might even say that I pushed it to the limit. However, I knew the safety of the edit was not guaranteed and someone might go back in time to remove the addendum to the article. Truth is, I have only done this once before. -- Ralph The Magician

Maturity not guaranteed apparently - HighPriest15

For reference, here is the background picture from the joke:
 * Image deleted

If any references to YTMND is not included then all other fictional references should be erased. - GWatson

The fad should be referenced once, and only once, in the list of references. Fair compromise. Crazyswordsman 17:07, 16 February 2006 (UTC)


 * Why should it be referenced here? Aren't things like this fad already covered in the mental retardation article? KarlBunker 17:43, 16 February 2006 (UTC)

Vandalism?
Why would anyone vandalism on this page?

Internet Meme on YTMND --Stilanas 20:19, 8 February 2006 (UTC)


 * In our current reality universe, in any sub-group of humans, we have people of good will, people who have nothing better to do with their time than cause trouble such as vandalism, and people who are interested in neither, they just want to make money or satisfy their needs. Fortunately we have enough of the first group of people at Wikipedia, to overcome the damage from the second. User:AlMac|(talk) 06:32, 9 February 2006 (UTC)
 * YTMND isn't trying to 'cause trouble.' It's just a joke, you should stop taking yourself so seriously. (Bjorn Tipling 07:22, 9 February 2006 (UTC))

This comment is NOT vandalism. I just want to point out to all these Wikipedia "meter maids" who want to accuse "vandals" of having nothing better to do than cause trouble, how about if you take a look in the mirror. You're fuckin' policing vandalism on fucking Wikipedia and having a hissy fit over a few guys trying to through the day with a few yuks at your expense. Instead of questioning the maturity or social aptitude of these "vandals", why don't you take a look at your own pathetic lives, realizing that you're getting off on a very tiny power trip of being able to police vandalism and ban people from editing Wiki-FUCKING-pedia! How about as a resolution, we all just admit that every last one of us, from the "vandals" to the "meter maids", are all fucking dorks for having anything to do with the editing of content on this site. &mdash;The preceding unsigned comment was added by Monosylab1k (talk &bull; contribs) on 19:58, 9 February 2006.


 * Please see Vandalism for a definition of what is considered vandalism on Wikipedia. Inserting nonsense into articles is one of the items listed. Just like scribbling in library books, you are making a resource less useful and are making work for the people who have to fix it. The joke on YTMND is quite funny; but cutting and pasting it _here_ isn't. --Christopher Thomas 21:20, 9 February 2006 (UTC)

Problems with the "Types of time travel" part of the "in fiction" section
Firstly, Back to the Future Part II's time travel does not truly fall under the alternate-timeline-creating time travel type (labeled here as 1.3) and thus should not be used as an example of one. All of the time travel throughout the Back to the Future trilogy alters the timeline in a ripple effect which moves progressively forward from the point of the change (suggesting some form of time beyond normal time in the process). This is best seen in the first movie when after Marty accidentally breaks the series of events that would lead to his own birth, he is not immediately removed from the timeline. Instead the changes slowly progress forward, visible via the family photo Marty has in which first his older brother fades and disappears, then his older sister (younger than the older brother) follows, and finally Marty himself (both in the picture and his actual body) begins to fade from existence.

The time travel in question in Part II, when Biff from 2015 travels back in time and gives his 1955 counterpart the Sports Almanac is also of this type. Though technically non-canon, due to its being cut from the theatric and home releases of the film, Biff was originally to be seen fading from existence just after returning to 2015 and stumbling out of the DeLorean. This was removed because it would probably confuse the audience (no direct in-film explanation is given), but can be seen on the deleted scenes on the DVD release. The commentary explains that the reasoning was that in the altered timeline Biff dies long before 2015 (possibly killed by Loretta).

The only question then is why Doc, Marty, and Jennifer are unaffected by the ripple. One could propose that they are unaffected because they travel back in time past the ripple, but if the ripple had already reached a point where Biff had died before they began their trip back they should have already been affected... Unless the ripple's ability to effect things outside of their own time frame when it reaches their correct time frame only works on things that are in the past, where the ripple has already been.

The other problem I need to point out is another type of time travel not mentioned in the article at all: the so-called "predestined" time travel. This is the kind where anything the traveler does in the past had already occurred according to history before they even travel back in time. This results in an apparent lack of free will, which is a large reason why this type is disliked by many fans. Interestingly, this type of time travel could be considered both paradoxical in nature, since activities of a time traveler in the past can lead to events which caused them to make the trip back in time in the first place (and thus the trip caused itself to occur), and it can also be considered paradox-free because the timeline is never altered in any way. Typically this means that an author/writer would need to put a lot of forethought into the storyline for this to work well. One example of a series that pulled this off fantastically is Babylon 5.

JDavis1186 01:27, 9 February 2006 (UTC)


 * The second point was covered under "immutable timelines" the last time I checked, but I haven't done a detailed review of the article in quite a while. --Christopher Thomas 07:41, 9 February 2006 (UTC)


 * I seem to have accidentally skipped over the given example of predestined time travel (From Harry Potter and the Prisoner of Azkaban) on my initial reading of the article. This brings up a different issue, though, as predestined time travel is quite different from time travel where events mysteriously conspire to prevent paradox (the other example under 1.2), and should not be labled as the same type. Perhaps 1.2 should be split into 1.2.1 and 1.2.2. JDavis 20:36, 9 February 2006 (UTC)


 * The whole article could actually use a rewrite (at least, as of my last review of it), but I'm not in a position to be able to devote that amount of time to it now. If you see a way of improving it, by all means go ahead (though it's best to propose _major_ changes here to see if there are objections rather than implementing them without discussion). --Christopher Thomas 21:18, 9 February 2006 (UTC)


 * Well, as I have only just registered, the lock is preventing me from making any edits at the moment. JDavis 07:07, 10 February 2006 (UTC)

Ytmnd is going to swallow the internet unfortuanately. I'm afraid there is nothing we can do but sit down and take it. (Unsigned by ParkerPathWalker)

Only if we let it. We won't let it. --Coyoty 15:37, 10 February 2006 (UTC)

Help Me Clean these Sentences
I feel like I'm taking crazy pills. These sentences fight all flow and it really takes me out of trying to understand the article.

''"The theory holds that, relative to a stationary observer, time appears to pass more slowly for faster-moving bodies: for example, a moving clock will appear to run slow; as a clock approaches the speed of light its hands will appear to nearly stop moving. The effects of this sort of time dilation are discussed in the popular "twin paradox" which asks the question, "If two twins are moving relative to each other, they will each appear to the other to have aged more slowly. But when they reunite, how can each twin be younger than the other?"

A second, similar type of time travel is permitted by general relativity, where a distant observer sees time passing more slowly for a clock at the bottom of a deep gravity well, and a clock of an object lowered into a deep gravity well and pulled back up will indicate that less time has passed than the distant observer's clock."''

I purpose changing the text to the following:

"The theory holds that, relative to a stationary observer, time appears to pass more slowly for faster-moving bodies. For example, a moving clock will appear to run slow as a clock approaches the speed of light; meaning the hands on the clock face will appear to nearly stop moving.* *This last sentence is repetitive, but is it so for elaboration?* The Twin paradox elaborates further on this phenomenon."

"A second, similar type of time travel is permitted by general relativity*, where a distant observer watches a clock at the bottom of a deep gravity well, and then lowers another clock into the deep gravity well, but then pulls it back up showing that less time has passed than the clock at the bottom of the well." *Isn't the first example of general relativity as well?

I hesitate instituting the changes myself as I am not an expert at these thought experience of have rudimentary knowledge of the subject. I wouldn't want to alter any of the elements of the experiment inadvertently to satisfy my need for better grammar. So I’m sandboxing it and hoping someone can either verify or suggest how to go about altering these sentences for greater flow. Thanks. Bear77


 * With regard to the first paragraph, I agree that the twin paradox description is probably too compressed to be understandable on its own. The simple link sentence you show would be better. Other than that I think the 1st paragraph as it stands is better. The 2nd paragraph could be improved by removing "of an object" from "a clock of an object". Otherwise, I think it's about as clear as it can be. Now you know why physicists who think about this stuff for a living always have funny-looking hair. I'll make those changes now. :-) KarlBunker 18:46, 10 February 2006 (UTC)

Paradoxes DO NOT exist
Paradoxes are impossible! If someone were to go back in time and change something, it would not create a paradox because what he or she had changed would have already occured, whether we realize it or not. If someone were to stop JFK's death, he or she could NOT do it because it would have already occured and whatever he or she would have done would have occured already and what should have happened, would have happened. It's kind of creepy to think about it like this, but time is already set in stone. If someone in the future comes back to our present (which is already made), it would be his past, and he would have already done everything to affect his future and our present in our future and his past.

Also "If you go back in time to stop a disaster from happening, and you succeed, why is there any reason to go back in time to begin with? Which means you never go back in time to stop the disaster, which means it does happen.  Just wondering if this would create some type of infinite time loop?", no, it wouldn't, because you would have already done it. You can't stop yourself from doing something. Even if you go into the future and kill yourself before you take the trip, you will still do it, because you  have to be there  in that space/time, no matter if you do everything in your worldly power to stop it because you know you just took a trip to kill yourself and you come back into the past armed with this knowledge, it would be "your past" even if it was in the future, because you would already know you were there, you would already have to kill yourself and you could do nothing to avoid it. No matter how much you try, when you kill yourself in the future, you will be there in that space/time when you killed your future self. And even if you had armed yourself with this knowledge, knowing the exact time when you would die and where, and done everything to prevent yourself from going to this place, you would have to be there, because your past already knows you were there and your future will not change, because it would have already occured.

Now lets take the opposite of this. You, in the future come to kill yourself in the past. Well, since you exist in the future, you must have survive your killing in the past. Otherwise, you could not exist in the future, and therefore could not come to kill yourself in the past. But since you know you exist in the future, it is impossible for you not to exist and therefore, you do exist in the future because you know it has already occured (wow, that is creepy, knowing that the future will occur).

Let's take you for a second. You just read my opinion. You know it happened. Is there anything you can do to stop me from writing this article? No, it exists now, which means it existed then and it will continue to exist unless I am moderated or Wikipedia dies (XD).

In theory, time could be represented as one dot. Each person has their own individual dot. The dot is made from experiences, all which occur at the same "time", from a perspective of someone observing the dot. From the human perspective, the events occur in sequence, knowing the past events, acting out the present events and not knowing of the future events. Every action we do is predetermined. Everything about that dot has already occured, whether the person that the dot represents realizes it or not. From the viewing perspective, every single thing in the universe would all occur at once, which may be beyond the human mind. There would be an infinite amount of dots, all being created at the same time. An infinite process occuring in a infinite amount of "time" with the time being represented as 0.000000000000000000000000000000000000... with no one in sight, forever. Complicated, isn't it?

I think it's all time we give up on these childish games of parallel universes where Martin Luther King Jr. isn't assasinated, the U.S. loses the Revolution, or life never occurs on the Earth at all because someone killed some microscopic creature while time traveling. No matter what point in time you are, it's somebody's past. And they already know what should happen, what will happen and what does happen.

CherryT 06:01, 12 February 2006 (UTC)


 * That is one interpretation. There are others, many of which are also self-consistent. These are all described in the article. The point of the article is to describe all of these interpretations, vs. assuming that any specific one is correct, as they all occur in literature.--Christopher Thomas 07:34, 12 February 2006 (UTC)

Whether they exist or not, they make good stories. --Coyoty 00:38, 13 February 2006 (UTC)

Indeed! ^^

Well, if they will or exist (or already do, in accordance with my dot theory), I am just stating that we are already living in a paradox, because we have changed the past already, and there is nothing you can do that hasn't already happened in the realm of time travel and of the past. Kind of sad, hmm? Just think, what would happen if Hitler was killed at birth? If we sent space travel technology into the past?

CherryT 06:41, 19 February 2006 (UTC)

Time travel as impossible by definition
The following text was added by User:Ncurses; I've moved it here:

"It has been argued that by the definition of motion, time travel is impossible, as it would be represented mathematically as dt/dt, which is simply 1, a dimensionless number, and therefore it is nonsensical to claim that anything moves through time. Often it is claimed that motion through time is at a rate of 'one second per second', but this is equally nonsensical as this expression also reduces to 1."

I'd like to see citations for where this "has been argued", please, as it seems to be playing semantics games with the term "time travel" as opposed to making a coherent argument against it. I haven't seen it formally proposed anywhere. It's certainly easy to make coherent formal definitions of what is meant by the colloquial term "time travel" to which this paragraph's argument doesn't apply, and this is how the term seems to be used in the vast majority of cases. --Christopher Thomas 08:02, 12 February 2006 (UTC)

At one time, human flight was considered impossible by definition. After that, human-powered flight. Space travel was once considered impossible. Organ transplants. Many athletic records. UPN and the WB merging into one network. Definitions change over time and time travel. --Coyoty 00:48, 13 February 2006 (UTC)


 * I'd like to share the following thoughts:
 * 1. Time is a convenient illusion. It's never yesterday, nor is it ever tomorrow. It's always now.
 * 2. The illusion is the result of the motion of physical objects in space. Some of these motions are regular, like the rotation of the earth, the vibration of atomic particles, or the weighted movements in a timepiece.
 * 3. The illusion is convenient because it has a utilitarian value, both for commerce and for the physical sciences. It is inconvenient because it is misleading.
 * 4. Much fun as it would be, it is impossible to travel in something that doesn't actually exist.
 * 5. If time travel were possible, there would have to be a physical universe for the people who "stayed behind" as well as a separate physical universe for the time traveller. Thus there would have to be an infinite number of physical universes, each of which would have to "exist" for all the sentient creatures inhabiting it, including some time travellers. As if. Although the parallel universes people might want to latch this.
 * --Twang 10:59, 19 February 2006 (UTC)


 * All very well and good, but what does this have to do with the article? Are you suggesting that some form of this information be added somewhere? If this is something you've come up with yourself then we can't include any of it on account of No original research. Otherwise, please be more specific about its source and about what you think should be done with it. Bryan 01:16, 20 February 2006 (UTC)