Talk:Time travel/Archive 4

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Clocks work faster/slower on planes than on the ground

I forget if they work faster or slower, but they are different on planes. People use this as a fact to state that this is a form of time travel.

BUT

Wouldn't the gears in the clocks be working with more/less friction because of the gravity? And so impact the clocks performance? Same with electronics. So this concept is useless, no?

-G —Preceding unsigned comment added by 134.117.158.83 (talk) 05:16, 8 November 2007 (UTC)

Electronics, such as modern atomic clocks (which are required to measure the relativistic time dilation from e.g. flying an airplane around the world or getting good positions from the GPS network), have no moving parts larger than electrons and photons, which are not affected by gravity except from gravitational time dilation. Michaelbusch 05:23, 8 November 2007 (UTC)

Vandalism

Another experiment was one of Dwane Allen. His favorite song was "Push it to the Limit". He was a true time traveller. He had only done it once before. He put out an ad asking for someone to go back in time with him again. One must bring his own weapons, he would be paid upon return and most importantly, 'safety was not guaranteed'.

This keeps popping up in different forms. It's a YTMND reference, if you weren't aware, and maybe also a reference to something else of which I'm not aware. Can't we just ban whomever is responsible? I'm too lazy to investigate who that is right now. --Sethomas 04:38, 22 March 2007 (UTC)

Problem is is that it's a meme. There are hundreds of people responsible for adding this content to the page. We can't just ban one person. Just keep an eye out for these kinds of edits and revert them. McKay 15:17, 22 March 2007 (UTC)

Time travel

Is the time machine we ever expect has already built in the future on this Earth? Well, I think the location must be at the Bermuda islands, because all mysterious disappearing of ships and aeroplanes happened there, the were brought to the past by the flows of the current of TIMES. UFO must be the ship of the peolple travel from the future to study their history. Think about it. —The preceding unsigned comment was added by 210.186.206.195 (talk) 12:14, 28 December 2006 (UTC).

If you think of looking at a clock on the wall. It reads 12 o clock exactly. If you move away from the clock at the speed of light you are moving into the future relative to the present where the clock is situated as the light from the clock reading 12:00:01 will never reach you. This explains that you age less as you move closer to the speed of time. But if you move back towards the clock which you moved away from at the speed of light, should you not start instantly ageing at the speed of light as you now 'catch up' with the light reading the time 12:00:02 etc up to the present time??? i believe that if you go back to your origin at the speed of light you will return to the age that you would be if you never time travelled at all. WC213.202.187.52 17:05, 11 January 2007 (UTC)

What complete and utter codswallop. Why did you post this here? Rosenkreuz 20:07, 11 January 2007 (UTC)

I think it's a valid question, this is a fairly common misunderstanding of time dilation in relativity. In fact, the reason moving clocks appear to slow down is not just a function of you moving away from the light signals as you have suggested--that's a separate factor known as the Doppler effect. But time dilation is something separate from the Doppler effect, which remains even if you factor out the delays in your seeing the light signals from successive clock ticks due to moving away from the source. Also, note that if a clock is moving towards you, you'll actually see it ticking faster than your clock due to the Doppler effect, not slower--but again, when you factor out the light-signal delays, you'll conclude it was "really" ticking slower. For example, suppose at t=10 seconds according to my clock I see the light from a ship at a distance of 10 light-seconds from me (a light-second being the distance light travels in 1 second), with its clock reading "5 seconds", and then at t=14 seconds I see the same ship at a distance of 4 light-seconds, with its clock reading "13 seconds". If I then factor out the signal delays in each case, I'll conclude the ship was "really" 10 light seconds away at t=10-10=0 seconds in my frame, and that it was "really" 4 light-seconds away at t=14-4=10 seconds in my frame (meaning it travelled 6 light-seconds in 10 seconds, moving at 0.6c). Because the real time between those events is judged to have been 10 seconds, yet its clock only advanced by 13-5=8 seconds, I conclude the clock was actually slowed by a factor of 0.8, even though I saw it ticking fast. Hypnosifl 21:42, 11 January 2007 (UTC)

Here's something to ponder. People say there can be no time travel because we have no visitors from the future. But one has to reason, if these people are smart enough to go back in time, do you really think they're stupid enough to get caught? —The preceding unsigned comment was added by 68.79.26.142 (talk • contribs).

mabye there are laws about getting caught or where you can go or how long your aloued in the past mabye the time pireod is pre-set so you cant mess time upsailor cuteness-ready for love 16:35, 24 January 2007 (UTC)

I like the argument that if you are smart enough to travel through time would you really spend time on things as stupid as us? Maybe the diffrence in intelligence between them and us is simmilar to us and ants? Do we waist time trying to explane complex concepts to ants or just step on a few? John Doe or Jane Doe 14:10, 8 March 2007 (UTC)

Who says ants aren't intelligent? I personally think ants are suited to take over the world - there are so many and they are so small they could likely survive anything us humans do to kill ourselves and 88% of life on this earth. 81.79.255.76 20:17, 8 August 2007 (UTC)

we can timetravel and redo it but wait, uz an inmate stading a the purly gates

Time Travel

We are of course considering returning to the past: all of us, like it or not, are impelled into the future at a rate which is quite out of our control.

The past, it seems to me, is a definite thing: a definite sequence of events ordered in a definite way in space and time. If this definition of the past is accepted, then if one returns to the past, one must do so in a way that leaves intact every facet of historical fact. This stipulation includes the exact sequence of mental states of all persons alive at the time, including any who might be intruders from the future.

For such intruders, there can be no memory of their future unless such “memories” had been experienced as premonitions. Furthermore, the time traveler is constrained to do precisely what he had done: he cannot choose, or even think, to do otherwise. If these constraints were to be violated, the traveler would not be in the past, but in some ersatz pseudo-past.

The traveler thus has no free will, but he cannot be aware of this absolute constraint on every aspect of his behavior. Of course, it is manifestly obvious that he can only return to times and places in which he actually lived.

A little reflection shows that within this definition of the past, any and all of us may be time travelers from the future: there is no way to tell. Within this definition of the past, the whole concept of travel to the past becomes vacuous, absurd.

It is clear that when Kip Thorne and other experts in relativity talk about returning to the past in time machines, they are really talking about visiting an ersatz-past: a “parallel universe,” the history of which is as much like the real past as possible, but just enough different so as to accommodate the intruder from the future. It is not clear to me whether such experts imagine that these parallel universes are created on the spot to accommodate the junketing time traveler, or whether they have an (almost) independent existence.

Jeheighway 05:59, 30 December 2006 (UTC)= jeheighway

No, Kip Thorne and most GR experts are not talking about visiting a parallel-universe version of the past, they are assuming a single self-consistent history--read Thorne's book Black Holes and Time Warps for more (especially the section on wormholes and billiard ball 'paradoxes'), or check out the Novikov self-consistency principle article. You say "if one returns to the past, one must do so in a way that leaves intact every facet of historical fact. This stipulation includes the exact sequence of mental states of all persons alive at the time, including any who might be intruders from the future." and conclude from this that "there can be no memory of the future"--but how do you justify that conclusion? How can you be sure that it is not a "historical fact" that the single unique past did contain some individuals with memories of having arrived there from the future? There's no notion of there having been an "original" version of the past free of time travelers here and then a "changed" version affected by the presence of the time travelers, the idea is that the past has contained these time travelers all along. Personally I doubt the ultimate laws of physics will end up allowing for time travel (see chronology protection conjecture), but I see nothing logically inconsistent about the idea of a single self-consistent timeline where the past contains time travelers with memories of the future. Hypnosifl 16:43, 2 January 2007 (UTC)

Seems likely that if somebody can travel through time they could also conceal their identity such that nobody would know they were a time traveler. I wonder if Stephen Hawking considers that there are tourists from the future here but they have some advanced technology such that we are unable to detect them, which incidentally would also largely satisfy Novikov. 12.41.40.20 20:56, 3 January 2007 (UTC)

---

Has anyone considered how matter (the stuff we are all made from) actually interact with time and time travel? If I were to travel back in time, would I be 'frozen' and isolated in spacetime, whilst everything else around me travel backwards in time, or will I also physically and biologically travel back in time, that is I get younger and younger, and then disappear because I was not yet created, thus defeating the Grandfather Paradox? Although if it were possible for signals (or information) to travel backwards and forwards in time, does this possibility automatically extend to matter as we know it (ie particles giving rise to electrons, protons and neutrons, and ultimately biological beings such as ourselves)? 81.155.103.36 02:30, 30 July 2007 (UTC)

Also, as faster-than-light travel is postulated, what about if there exist some sort of exotic matter where mass is negative; would the equations of physics then allow a reverse in the time dimension, ie travelling backwards in time? 81.157.100.44 21:58, 4 September 2007 (UTC)

How about if there are more than one time dimension? For example if there are 3 time dimensions like there are the 3 geometric dimensions that we experience; and that they follow the same mathematical rules of vector multiplication, and that we only live in one of the time dimensions. Then could we move back and forth in time in one of the other time dimensions if there is a meaning to a vector multiplication of the other 2 time dimensions? 81.157.100.44 11:53, 17 September 2007 (UTC)

Does a negative sign in front of a time quantity in physics necessarily mean a reverse in time at all? After all, even when the solution (wave function) to the Schroedinger equation is complex, there is still a physical interpretation that meets our reality. 81.157.100.44 11:57, 17 September 2007 (UTC)

Also what if There are people from the future that can travel back... but they are simply on another planet. Imagine that our planet is simply dead from Global warming and there is no human life but on some other colonized planet, terrestrial object or so on we have discovered ways of traveling back so if they traveled backwards they would not be on our planet. - Calvin Scott, 14, guitaristcal@hotmail.com

Non-article related discussions

Is there any recomendations about what to do with talk pages being inundated with comments that have to do with the topic, rather than those about the article (like the two sections above this one). I'd like to delete them out right (because they are right out), but them I'm removing someone elses content. Could we create two major headings? What about moving all of their content to another page? a subpage? McKay 18:30, 2 January 2007 (UTC)

The Talk Page Guidelines say, "... Irrelevant discussions are subject to removal." Perhaps it would be reasonable to remove them while encouraging the editors (via their personal talk pages?) to find an appropriate forum for their content-related discussions. Petershank 20:32, 20 February 2007 (UTC)

Theory and practice

In the section about time travel as theory:

"Additionally, Stephen Hawking once suggested that the absence of tourists from the future constitutes an argument against the existence of time travel..."

This makes no claim about the theoretical possibility of time travel, only that it is never developed in practice. For example, perhaps in the future people are more interested in distributing food to the billions who don't have enough, instead of researching time travel. At any rate its a quite unscientific statement that clearly only gets a mention because its attributed to a scientist. 12.41.40.20 20:44, 3 January 2007 (UTC)

Or there might be some consistency principle that prevents you travelling back before the creation of your time machine.1Z 00:13, 18 January 2007 (UTC)

Yes, but if we knew it was never going to be developed in practice, that would be one argument for thinking it less likely that it's possible at all. Not a definitive argument, but still something to take into account, in the same way that the Fermi paradox should be taken into account when judging the likelihood of alien civilizations in our galaxy. Of course, most theoretical arguments suggest that even if time travel were possible you couldn't go back further than the date the "time machine" (wormhole, alcubierre drive, whatever) was created, so this would weaken the argument, and Hawking mentions this idea as well. Hypnosifl 20:16, 5 January 2007 (UTC)

Couldn't "agents" travel back in time to fix what ever the "tourists" messed up, and thus, we current folk would NEVER know about it?

-G —Preceding unsigned comment added by 134.117.158.83 (talk) 05:12, 8 November 2007 (UTC)

Time dilation section

I was reading the time dilation section, and it is both wrong and misleading. The whole bloody point of relativity is that there is no `Absolute Clock' against which observed time can be measured, and hence speaking of historical astronauts `travelling into the future' is a physically meaningless statement: what actually happens is that their measurement of passing time differs from the measurement of passing time on the earth, and there is no physical reason to insist that the earth people's measurement is correct (democracy of hyperplanes and all that, eh? We may just as well say that flinging astronauts into space for a while pushes the earth a few milliseconds into the past on their return: it's just as accurate). These statements should all probably be rephrased to tell the truth, i.e. that the astronaut will measure less time passing than the `distant observer' or `earth person'. That is what relativity predicts, not that they will travel `into the future' (because even `future' is only defined relative to some observer).

I am not `boldly' editing the article, because I can imagine that there is an equilibrium on these sorts of physics articles just as delicate as on 9/11 conspiracy theories and creationism and all the other crank attractors, which equilibrium I would fain not disturb too much. But could an established editor here please try to restore a bit of sanity to the article? I daren't look at the rest of it, lest I suffer an irreversible increase in my blood pressure. Rosenkreuz 09:15, 9 January 2007 (UTC)

I tried to clarify the limited meaning of "travel into the future" in these sections, let me know what you think. Hypnosifl 15:36, 9 January 2007 (UTC)

Those changes you made to the section's introduction certainly do help clear up ambiguity in that regard. However, I removed the paragraph about astronauts time-travelling to the future, since as I explained above this is not what is happening. I am going to leave this article alone now. Rosenkreuz 08:56, 11 January 2007 (UTC)

I disagree, the astronaut "travels into the future" in the same sense that the time traveler in H.G. Wells' "The Time Machine" traveled into the future--by having the world around him age faster than he ages. If the astronaut were simply moving in a straight line then there could be disagreement about whether he or the earth was aging slower depending on which reference frame you used, but since he's orbiting in a circle, all frames will agree that the astronaut ages more slowly.

Do you have an alternate notion of what it would "really" mean to travel into the future, beyond just seeing the earth and galaxy aging faster than you? If not, I think that a trip away from and back to the earth at relativistic speeds is a valid form of "traveling into the future". Hypnosifl 21:32, 11 January 2007 (UTC)

einstein rosenberg bridge

Some mention of the einstein rosenberg bridge would be nice. -- Sy / ^(talk) 02:23, 29 January 2007 (UTC)

It's actually called an "Einstein-Rosen bridge", and it's a type of wormhole (a non-traversable type because it collapses instantaneously, meaning it wouldn't be useful for time travel)--there's already a discussion of wormholes in the article, and the Wormhole article has a subsection on Einstein-Rosen bridges. Hypnosifl 21:23, 30 January 2007 (UTC)

Experiment carried out

I created a new heading on experiments carried out within the framework of retrograde effects. To the moment, one does not observe yet a violation of causality according to the scientific community. BBSM 00:50, Febuary 1, 2007 (UTC)

124.168.172.126 00:20, 2 February 2007 (UTC) This section uses ambiguous terms and unclear use of English, it requires complete revision to re-express its contents using clear statements and unambiguous terms.

It is difficult tom to express myself in English. BBSM 11:5, Febuary 2, 2007 (UTC)

Categorization of Time Traveler Convention and related events?

Hi, I am responsible for the MIT Time Traveler Convention and was perplexed to see it in "Fiction and Humor." This probably indicates a misunderstanding of the purpose--I have described it, along with the existence of prior art, in a separate section in experiments. —The preceding unsigned comment was added by 156.109.18.18 (talk) 19:58, 16 February 2007 (UTC).

multiple universes

I firmly believe that there are multiple universes.I have thougt about it over and over again.Suppose you make a time machine and go to the past.You kill your father who was small at that time.so if your father is already killed,how were you born?This cannot take place without the existence of multiple universes. —The preceding unsigned comment was added by 121.247.22.45 (talk) 13:35, 24 February 2007 (UTC).

 i have a nother example if u go to kill some one in the futer then when u go back to right befor u left u would never go cuse he is dead so then u would be stuck in a loop hole can some one explane this better

new page?

How about a Time travel fringe theories page, where all that stuff can go. This page would be dedicated to more scientific treatments, and generally accepted fact? We could really use a split. the page is getting too largeMcKay 20:20, 1 March 2007 (UTC)

I think it would probably be justifiable to just delete the "Fringe theories" section based on wikipedia's reliable sources policy, which says: "A questionable source is one with no editorial oversight or fact-checking process, or with a poor reputation for fact-checking. Such sources include websites and publications that express views that are widely acknowledged as fringe or extremist, are promotional in nature, or rely heavily on rumors and personal opinions. Questionable sources may only be used in articles about themselves." Also see the "sources of dubious reliability" section in Wikipedia:Verifiability Hypnosifl 18:56, 4 March 2007 (UTC)

Can premonitory dreams be explained via the possibility that "future" already exists?

Little is known of our brain capacities. If some people had a or some premonitory dreams in their life, can it be explained by the fact that they "feel" the future because it already exists?

Let say I dream during the night that in 10 days my plane I am scheduled to take will crash. Of course, even if it is a "dream" my subconscious will be very reluctant for me to take that plane. So I do not and the plane crashes. They are 2 ways of explaning this, either that it is a mere coincidence or that the future in which the plane crashes already existed when I had the dream and for unknown reasons, my brain could "feel" it.

If that is the case, it must means we, presently, are at the same time the future and the past (and this applies to every moment up to the smallest division of time which had happened or will happen). And if we are the past for those who are in the future, it would imply that going backwards into the past may be feasible.

May we say that if there is no such thing as "the present" that time does not "flow" but that every moment, which happened or are to come, exist at the same time? (We rather flow through time)

I think there is no way of explaining that seeing the future unconsciously imply that this very same future already exist if they are not mere coincidences.

Of course, premonitory dreams have been subject of personal experiences rather than scientifical research but every scientist must consider every theory plausible unless he proves otherwise.

24.200.217.233 18:26, 9 March 2007 (UTC)

While scientists need to consider this as a possibility (and I think they have? If not, you could probably make some decent money selling a book on the topic), This page is for the mainstream theories of Time Travel, so if there should be an article about it (WP:NOTABLE), then it probably belongs elsewhere, and merely a link will exist from here to there. McKay 21:48, 9 March 2007 (UTC)

Of course, there's also the fact that, in reality, you don't see the future. Many claim to be able to see the future, but the reality is they cannot, because they've provided absolutely no evidence that they do so. What you're talking about is what is commonly known as pseudoscience. I've heard this before, but its not real. Whether or not the future exists (which according to some models of time, it does, though I highly doubt those models are correct) we don't see it with our minds. Our minds are the same as everything else in the universe. A lot of people are eager to believe they can see the future, but they can't beyond the predictions of normal people. A lot of people claim to have dreams about 9/11 occuring, but beyond the fact that they all said so only after 9/11 occured, there's the minor issue that people dream of burning towers on a fairly regular basis. That is to say, any given week, there are proably a dozen or more people who dream of something that could be interpreted as 9/11 or whatever. The problem is, this isn't seeing the future; this is sheer probability. No one remembers when they dreamed of burning towers and no towers burned. Titanium Dragon 00:00, 14 March 2007 (UTC)

---

I'll bet that because with every action there is an equal and opposite reaction, if you had an action withOUT a reaction, the reaction would appear in another period in time! Such as matter disppearing without a trace or a reaction. It would have another reaction in another time period in compensation!!!!

Curving space-time for time travel

If space can be curved, time must also be capable of cuvring for space and time are binded together. Let us say you draw a line on a sheet of paper starting from A and going to B. How can you go back to A when you're at B (vice versa) is indeed to fold the sheet and bring A and B together. If we could "fold" time, we will be able to warp from period A to period B (vice versa).

A good example are black holes. Space-time is so curved that the time itself either stops or slowy progress. We should look for a mean to curve space-time to a further level unsing singularities.

Let's take the logic further again. We could make use of dark energy which seems to have a "repulsive gravity" behaviour to curve, strech, to rip space-time.

Of course, all of this is highly hypotetical.

24.200.217.233 15:36, 19 March 2007 (UTC)

Yes, hypothetical, but we've already got this kind of stuff in the article. McKay 16:58, 19 March 2007 (UTC)

Lack of visitors from the future doesn't prove anything

If someone uses the statement that since we never had visitors from the future to claim that time travel (at least backwards) is impossible, he or she must take in consideration some explanations before claiming that statement as valid.

1- When you go back in time, your sole presence affects the spacetime continuum and therefore you travel back in the time of a parallel dimension created by your own travel. But we can argue that we could see people from the future from another dimension.

2- We did indeed have visitors from the future but they hide themselves. Could they be those UFOs?

3- Time travel is indeed possible but going backwards in time would cause so much distortion into their present that such travels are forbidden.

OR 4, and I think that's the most plausible one to explain the lack of visitors from the futre if going backward in time is feasible, is that humanity has vanished before we created such a device. We mustn't think that we will last forever on this planet. And if indeed humanity has vanished in the future (and so that is why we don't have any visitor) then everything we do is already planned out. Sort of eerie isn't it?

24.200.217.233 21:24, 21 March 2007 (UTC)

If a time travel or traveling in the past DID or could happen. What period or how much further could humans go? Could we past 600 years or just few minutes? If it succeeds traveling back to the past, could we possibly physically have hold or touch what is the past. Not sure how to put it. Phu2734 15:35, 11 April 2007 (UTC)

And if we DO NOT vanish in the future, then everything we do is NOT already planned out? That being the logical opposite of what you said. I do not think the conclusion follows from the premise, in either case. — SWWright^Talk 23:29, 13 April 2007 (UTC)

Proof?

Ok, I am not a physicist but some of the uses of the word "proof" in the physics-y section of the article seem rather specious. I thought a proof was something very hard to pull of in physics. WookMuff 22:10, 13 April 2007 (UTC)

It is possible to prove that if a certain theory of physics (such as general relativity) is exactly correct, then certain consequences must necessarily follow. But it's never possible to prove that the theory itself is indeed exactly correct, even if the experimental evidence so far seems to match its predictions, since it might turn out to be just an approximation to a new theory which makes the same predictions about those experiments. Hypnosifl 16:35, 14 April 2007 (UTC)

So how can Stephen Hawking "prove" the impossibility of a time machine? I really don't get it. WookMuff 19:03, 14 April 2007 (UTC)

What quote are you talking about? In "Other approaches based on general relativity", there's this:

"A more fundamental objection to time travel schemes based on rotating cylinders or cosmic strings has been put forward up by Stephen Hawking, who proved a theorem showing that according to general relativity it is impossible to build a time machine in any finite region that satisfies the weak energy condition"

but the bolded part doesn't say it's impossible to build a time machine, it says that according to general relativity it is impossible in a finite region where the weak energy condition is satisfied. This doesn't rule out the possibility that the weak energy condition could be violated (that's the assumption behind wormhole time machines, which rely on negative energy), or that the theory of general relativity itself could be wrong. In either case, time travel might still be a possibility. Hypnosifl 19:33, 14 April 2007 (UTC)

No, it was the next two uses of prove that had me confused, but when taken in conjunction with the text you bolded, i suppose it makes sense that he is just continuing the "according to general relativity" thread. WookMuff 22:21, 14 April 2007 (UTC)

OK, I added some text to the end of that paragraph so hopefully it'll be a little clearer. Hypnosifl 23:02, 14 April 2007 (UTC)

Needs philosophy

Unfortunately this article is rather long and says rather too much about physics (and sci-fi!) with hardly a mention of philosophy. There is a short section on paradoxes of time travel, but paradoxes are logical problems and hence part of philosophy rather than physics. Perhaps a philosopher with more time and patience than me could patch it up? For example, the article should say something about Paul Horwich, David Lewis, etc. Ben Finn 16:03, 16 April 2007 (UTC)

I think I disagree, Not to say that there couldn't be a Philosophy of Time Travel article or even a small section here, but I think that it's pretty well covered. They talk about paradoxes in the relevant sections. Most views of time travel don't even allow paradoxes (mutable timeline, kerr-newman wormholes with center points out of each other's light cones, time dilation, diverging universes), so I don't think it deserves much of a mentioning, though it could be mentioned a little more than it is. McKay 19:24, 16 April 2007 (UTC)

Science-fiction ideas like the "mutable timeline" are confused enough that I would say they do open up the possibility of paradoxes (what does it mean to 'change' the timeline, when change itself seems to require time?); but physicists only consider ideas that avoid paradox in a clear way, like the fixed timeline view, the diverging universes view, or the backwards-time-travel-forbidden view. I think it might be reasonable to have a section on why these are the only views that philosophers consider to adequately avoid paradoxes (see the discussion here for example), but I don't know enough about philosophical writings on time travel to do it myself. Hypnosifl 22:16, 16 April 2007 (UTC)

190.6.195.46 04:30, 22 April 2007 (UTC)Paz== About Time Travel ==

Well, there are some things to consider about time travel. First of all, there are some things that are theoretically possible, while others not. For example, the fact that we might travel around Earth (by the Equator)in the opposite direction it rotates, with the purpose of getting back to any day. That is impossible in the practice; we must consider the concept of time as the space between two events. In fact, we might spend the rest of our lives trying to move the opposite way Earth is rotating, at a time smaller than the 24-hrs time, and still don´t return to historical events such as World War II or our first birthday. My second consideration is the ¨pinpoint to the faster-than-light¨ idea. For traveling at a speed grater than light´s, we must build a vehicle that might accelerate to a speed greater than light. That acceleration would need for a great amount of fuel, to the point of having an near-infinite amount; the thing is that we must have a container that might store this fuel. And due to the not exact idea of the number infinite (I mean, like Phi equal to 3.14), we can´t build this ship. My third consideration is based on the Law of Conservation of Mass-Energy (the total amount of mass and energy in the universe is constant). We might agree that E=mc², in such a way that matter might become energy and viceversa, without altering the equation. Now, if we travel to the past, we are adding an extra amount of mass and energy to the constant amount, changing the amounts and violating that Law...unless we try to consider that constant amounts as the ones of a more-complex system(universe at past, universe at present, universe at future). This idea of a vast universe-time system would be dificult to prove, because the amount of chances of having an infinite amount of futures is infinite. What I can only say is that we can only travel, if possible, to the past, but not to the future. —The preceding unsigned comment was added by 190.6.195.46 (talk) 04:28, 22 April 2007 (UTC).

Special relativity, new section addition

I reverted the addition of a new section, which had been added by the same user several times before, since I have concerns it may be original research and generally unclear. At the very least, I think a citation to a source is needed, but also a better exposition would be a good idea. Thoughts? --TeaDrinker 02:11, 4 May 2007 (UTC)

days of future past

this is probably my favorite article of all time. no pun intended. well maybe not =) if anyone knows of anything better be sure to let me know. TomSkillingJr.

?

In the article it says

Physicists take for granted that if one were to move away from the Earth at relativistic velocities and return, more time would have passed on Earth than for the traveler, so in this sense it is accepted that relativity allows "travel into the future"

Strictly speaking, this isn't travel into the future. The most we can say in this case is that, if you put two plants down in identical conditions and accelerate one to very high speeds relative to the other, then the former plant will be older than the latter. When the plants meet again, they will meet in the same instant of time. This also occurs to me: there is nothing to prevent the slow plant from accelerating or decelerating the fast plant. Evidently they exist in the same time all along. For a mathematician none of this is surprising, but in any case I don't agree that special relativity can be identified with time travel. --VKokielov 21:50, 9 June 2007 (UTC)

Well, what if I were able to travel 10 years in the future? Presuming you were still alive and I knew where you lived, I could knock on your door, and we will have met at the same instant. Let's say I traveled through the future via a wormhole. A topologist could map the space-time continum (in several dimensions) showing time linearly, and they would have to map certain places along the wormhole with different points in time. From this relative perspective, traveling through a wormhole is merely accelerating the speed at which one travels through time. If one could make a machine that could accelerate an object to the speed of light, and decelerate it, it would be no different from the time machine in The Time Machine (2002 film) except it could only travel forward in time. Time Dilation is no different from forward time travel. McKay 23:10, 9 June 2007 (UTC)

The question is subjective. How much older would you be if you traveled to the future, according to the popular conception? --VKokielov 03:47, 10 June 2007 (UTC)

If I were to traverse a wormhole with a constant delta T of 10 years, and you were born on the same day as me. I would be 10 years younger than you. Similarly, if I were to travel at 1/sqrt(2) times the speed of light for 34.15 years. and we met up again, I would be 10 years younger than you. Is that what you're asking? McKay 22:46, 10 June 2007 (UTC)

Well, what I mean is, isn't time travel supposed to be instantaneous? Of course we travel through time when we accelerate; we travel through time, then, if we don't accelerate at all -- at the same rate as everybody else. I don't think that time contraction deserves to be identified with time travel. --VKokielov 04:41, 11 June 2007 (UTC)

Ahh, I understand what you're saying, and no, I think (but am nowhere near certain that) it would violate the theory of relativity if time travel were instantaneous. If you're familiar with Star Trek: Deep Space 9, you'd picture their wormhole that travels between quadrants, it takes at least some time to travel through space. If it were instead a time-hole, they would still have to spend time to go through time. In Bill and Ted's, the phone booth has to navigate the circuits of time. But even still, even if time travel was instantaneous or very close to it, it is merely a degenerate case (one mathematicians would be very familiar with) of the delta t naught reducing to 0. I still see nothing mathematically or even scientifically different between full-fledged time travel, as described in science or science fiction, with time contraction or time dilation, except that time dilation is limited to one direction. McKay 16:35, 11 June 2007 (UTC)

Understood. Merci. --VKokielov 01:36, 13 June 2007 (UTC)

In an encyclopedia article we must keep our notions apart. `Einstein's laws say that the speed of light is a singularity, and physicists accept that only photons can travel at the speed of light. If you accept the unified theory of quantum mechanics, then it's a given that anything with finite inertial mass may not be accelerated to the speed of light. And, even if you don't, a little bit of reasoning will convince you that the force you have to apply grows without bound as you approach the speed of light, which means that an infinite amount of energy must be expended to do it. --VKokielov 03:50, 10 June 2007 (UTC)

I'm sorry, we seem to have drawn from your original problem with the article. I don't quite see where you're going with your recent statement.

Aliens and Time Travel

I'm not sure which page fits more with this topic, aliens or time travel. ever thought about something like this? So time travel is traveling to the future or past. The universe is a tremendous place, what if there are lots and lots(infinite) planets, galaxies, etc. Current theory, life is all developed from simple DNA structure, then basically the domino effect. What if there is a planet exactly like the Earth in another place in the huge universe. That planet might be formed perfectly exactly the same way as Earth, the same kinds of comets crashing in same places as Earth, thus the domino effect would begin which can only be changed if something from the outside changes it. However, the only thing different about this planet is that it lags behind Earth by like 500 years?

This would make everything happen the same, George Washington, Roman empire, geography, etc except they're 500 years behind us. Here's something important, if a person from earth watches the planet, that person might not be smart enough to know, can't travel there, or he would be an outside factor and alter the whole domino effect.

This is sort've creepy and crazy if you get what I mean and just said. 

I want ur feedback on this plz.

Something to note: Snowflakes, every single one is different. There is nothing to prove the same snowflake can't form again, snowflake makers don't remember what they made before, sooner or later, the combinations would run out, we haven't recorded enough snowflakes, just unlucky.

Removed material.

I put this in the talk page of the user who removed it. I think it does warrant some mention, but maybe it requires it's own subsection (as it is related to time travel and presentism regardless):

Hello, you removed:

"Within fiction the possibility of time travel has been conceived without violating the view of presentism. For example, an instance of time travel occurred inside a "presentist" framework in the 1999 film Galaxy Quest, wherein a device called the "Omega 13", which was thought to be an explosive weapon having enough power to annihilate the universe, in fact only rearranged every molecule in the universe to their position thirteen seconds prior (except seemingly for the individual activating it). Thus keeping future and past both within the arrangement of the condition of the present, and so never actually transversing "through" time."

You say "this section is for real philosophy" Two points on that, anything posited is "real philosophy, is it not? Real philosophy can be science fiction, it is anywhere to the level of 'real science' anywhere in this article, second point; then why does the article mention things like "Doctor Who"? You also say "--I doubt there are any philosophers (or scientists) who would say that rearranging the universe even qualifies as "time travel"" isn't doubting what scientists would or wouldn't think the definition of non-NPOV article editing? Putting everything the way it was previously is "altering time". The case is, the fiction work presented considered it time-travel, and it would fall within the scheme of presentist view-points about the limitations of the universe and space time. Thanks.

It might bring up a larger more pertinent question of the difference between "altering time" and time travel, but I don't see those two semantics requiring a separate page, maybe a section here. 67.5.156.130 18:44, 30 June 2007 (UTC)

Another point. If under "presentism" time is simply "the constant movement of things" and equated in that respect to space. Then the definition of time, to mean anything in the scheme of presentism, is the arrangement of the delineation of happenings. The re-arrangement of space, equated with a delineation of occurrence, therefore, I must argue, makes this fictional account an example of time travel possible and compatible with presentism. I honestly think as an idea it should be, as it is attested and notable, included in the article. Does anyone else agree? 67.5.156.130 18:52, 30 June 2007 (UTC)

This was my response, which I also posted on your (and my) talk page:

By "real philosophy" I meant philosophical ideas discussed by professional academic scholars, and by "this section" I meant only the section on presentism, I wouldn't have a problem if you added something about Galaxy Quest to sections after 6.2, which discuss time travel in fiction as well as physics/philosophy (I'll change the section heading to make that more clear). Doubting whether any published academic sources on time travel (whether in philosophy or physics) would consider rearranging all the matter in the universe to be a valid form of time travel isn't a violation of NPOV, because the burden of proof is on the editor who adds some information to verify that there are reliable sources for the edit (of course I am not challenging your description of what happened in the movie, I'm just saying that in order to fit in that section, there should be some evidence that professional philosophers or physicists would consider this a form of time travel). I disagree that rearranging all the matter in the universe is "altering time", it's just moving matter around in a way that does not violate causality in the physics sense, nor does it match the ideas of presentists who consider the possibility of time travel. Hypnosifl 22:36, 1 July 2007 (UTC)

Disputing SR

Recently the user 76.22.207.34 added this to the section "time travel, or space-time travel?"

In simpler terms, according to this particular argument, time travel as presented in the popular film trilogy Back to the Future would require the Earth to be stationary in space (See Geocentricism).

My objection to this is that, as explained later in the paragraph, this is based on a premise that is contradicted by special relativity, namely the idea that there is a single frame-invariant notion of what it means to talk about the "same point in space at different times". The user justified this by saying there are physicists who disagree about the validity of SR, citing two sources: "Simple (but Big) Problems With Special Relativity: Is Unification Of The Forces Even Possible? by Bruce Barron" and "Correct Derivation Of Lorentz Transforms Eliminates Contradictions Of Einstein's Relativity By Harry H. Ricker III". But both of these are fringe sources, not published by mainstream physicists in peer-reviewed academic journals--Bruce Bannon is a Canadian doctor and his ideas are published in his own self-published book rather than any peer-reviewed publication (see a review from the Yale Scientific Magazine here, whose opening line is 'Have you ever wondered what would happen if your crazy uncle wrote a book on physics?'), and Harry H. Ricker III's paper is published here on a website called 'The General Science Journal' which is non-academic, non peer-reviewed, and a decidedly fringe site devoted especially to relativity denial (see their purpose of site page). These would both definitely fall under wikipedia's definition of fringe theories, which states:

Since Wikipedia self-identifies primarily with mainstream opinion, and because other mainstream sources often view our project as a contender for mainstream status, it is important that Wikipedia itself not become the notability-validating source for these non-mainstream theories. If another, adequately reputable source discusses the theory first, Wikipedia is no longer the primary witness to notability. Furthermore, one may not be able to write about a subject in an NPOV manner if the subject completely lacks mainstream discussion. If all available sources aren't neutral but instead put forward a point of view, doing so risks violating the No original research policy.

"Mainstream" here refers to ideas which are accepted or at least somewhat discussed as being plausible within major publications (large-circulation newspapers or magazines) or respected and peer-reviewed academic publications.

So I think it's clear that the sources you point to would not qualify as reliable sources meeting wikipedia's verifiability criterion (see especially the section on self-published works, which notes that 'Anyone can create a website [like 'The General Science Journal'] or pay to have a book published [like Bruce Barron's book]').

Finally, even if you could find an example of a mainstream physicist putting forth an alternative to SR in an academic peer-reviewed source, I still think the sentence about Back to the Future would be out of place because it's giving a simple layman's explanation of an idea which most mainstream physics theories would judge to be completely false, without even pointing this out to the reader. If you do find such a mainstream source, I would suggest adding a sentence which points it out with a footnote to the journal where it was published, and then you could point out that in the context of such an alternative theory, if time travel took a person to the same position in a preferred reference frame, they would probably not remain on Earth unless the Earth just happened to be at rest in the preferred frame. But without making the non-mainstream context very clear, the sentence is highly misleading (and unless you can actually find such a reliable source for an alternative to SR which posits a preferred frame, the sentence doesn't belong regardless of what context is given). Hypnosifl 16:51, 5 July 2007 (UTC)

Re:

What I wrote was not an endorsement of any non-SP P.O.V. It was merely a clarification in layman's terms of a P.O.V. immediately thereafter countered by mainstream science. I find your assertion that it somehow promotes any idea to be ludicrous and inferential of paranoia. And I think that the record will clearly illustrate that.

On a personal note, because the Earth is constantly revolving around the Sun, and because the Sun is constantly moving throughout the galaxy, and because our galaxy is constantly moving throughout the Universe, the Earth is never in the same place twice. Special Relativity, something that I myself subscribe to (I found it quite annoying that you had me look up any evidence against it to begin with) does not resolve this matter. The resolution given on the Wikipedia page, which itself is completely unsourced and should therefore be removed, is a cop-out. On that note, I would call for the paragraph to be removed unless and until propper citation is given.

Thank you.

Actually, I'm willing to concede your point that the sentence is just meant to clarify the previous (incorrect) argument (but please do not accuse me of "paranoia", both because it's not very nice, and also because it goes against wikipedia's assume good faith policy). Your original edit, which I first deleted, read:

To put it another way, time travel as the Back to the Future movie trilogy portrays it would necessarily require a geocentric universe.

I hadn't noticed, but your later edit was modified to read:

In simpler terms, according to this particular argument, time travel as presented in the popular film trilogy Back to the Future would require the Earth to be stationary in space (See Geocentricism).

Because of the part in bold, it's more clear that the sentence is just clarifying the argument without endorsing it. I still think the sentence is unecessary, since the previous sentence "The idea that a traveller can go into a machine that sends him or her to 1865 and step out into the exact same spot on Earth might be said to ignore the issue that Earth is moving through space around the Sun, which is moving in the galaxy, and so on" is already a perfectly good explanation in layman's terms. Still, I wouldn't object on the grounds of it promoting fringe theories any more.

Aside from this, if you really think the argument about reappearing in space is consistent with special relativity, I think you're failing to appreciate some important points about SR. In SR it makes no sense to say that one "should" reappear in space because the Earth has "moved", since there is no such thing as absolute motion in SR, the motion of one object can only be defined relative to other objects, and different frames disagree about how far an object has moved between any two points in its history. There can be no objective frame-independent notion of "the same position in space at two different times" in SR--do you disagree? I can certainly provide sources for this claim if you do. And if you don't disagree, then presumably you agree that there's one frame where the Earth's position today is a billion miles from its position in 1865, another frame where its position is only a million miles from where it was in 1865, and another where its current position is exactly the same as its position in 1865, and that none of these frames represents reality any better or worse than any other according to SR. So how does it make sense to say you "should" reappear in space? Hypnosifl 23:38, 5 July 2007 (UTC)

Using may instead of might

Please see the 1993 edition of the Columbia Guide to Standard American English for proof that using may instead of might is not standard English, but rather an increasingly prevalent mistake. For further proof, do a simple Google search for the phrase "may instead of might". You will find that the mistake is the bane of many who prefer good grammar. But if you insist on keeping the page grammatically flawed, I will not interfere. It is enough for me that this note will show that I did try to help you.

Your own reference says that "may" or "might" are both acceptable for the present or near future tense: For events in the present or immediate future, use either may or might. Most sites seem to agree that "may" is generally used for present events with reasonable probablity, "might" is used for either past tense or events with low probability--see here, here, here here, and here, for example. Hypnosifl 05:49, 9 July 2007 (UTC)

It is impossible to accurately predict the future.

I just thought of this proof that states that it is impossible to accurately predict the future:

Let's assume that it is possible to look (or travel) into the future. Then, one could build a machine like this: The machine would be connected to a light bulb, and would look one second into the future. If it sees that the light bulb is off in the future, it would turn it on, and vice versa. This would mean that the prediction is wrong as the light bulb will be in the opposite state than the one that was predicted, meaning that the prediction is inaccurate. Cyb3rdemon 17:51, 22 July 2007 (UTC)

A, this doesn't relate to the article, B, what you describe sounds very similar to as SR Latch with S and R equal to 1. Not a paradox, just a strange state. McKay 15:56, 26 July 2007 (UTC)

I think you misunderstand, Cyb3rdemon seems to be talking about a situation where information about the future state of the light bulb is sent back in time to influence our decision about whether to turn it on or not, it doesn't resemble an ordinary electronics latch with two different inputs. One resolution to this sort of problem is the Novikov self-consistency principle--perhaps if you tried to set up an experiment like this, you'd always fail for one reason or another (if you see the bulb is on in the future, and you try to turn it off, your hand slips and you accidentally leave it on, or you change your mind, or the switch breaks, etc.) Hypnosifl 15:18, 30 July 2007 (UTC)

Well I more or less agree with the argument, and I think it's one of the stronger arguments against time travel. The circumstances that are usually given, whereby the Novikov principle is hypothesized to avoid paradoxes, are almost invariably complicated tasks, which are easy to not accomplish. Killing one's grandfather is not a very simple task, I imagine, so leaves open many speculative alternate endings. _Instead_, suppose you have a time machine, even one that is capable of sending only information, and is only effective back to the date it was created. Now, if information can be sent backwards, what's to keep you from videotaping yourself and sending it back, so that a previous you gets to watch and study the mpeg. Now, not only do you need to actually MAKE the video, after you've been viewing it for a year straight, but you must fulfill every action timed just perfectly in order to remain consistent. All the while you're thinking "if I don't do precisely such and such right now I will have fulfilled a paradox." Seems very very unlikely such information time travel is possible, let alone physical matter, let alone people. 24.59.111.68 (talk) 01:54, 20 November 2007 (UTC)

Impeccable Prophecies

I beg to disagree with the above-theory of impossibility of future prophecy. I myself had accurately predicted the events and dire prophecies here in the Philippines about several deaths of Supreme Court Justices and the 3 mystic fires which happened this year. Light - violet and white - are the highest and in fact, these are the very essence of the universe. I added this BBC news DREAM of Time Travel, about a dr. and physicist's request for funding.

--Florentino floro 06:16, 8 August 2007 (UTC)

Splitting the page

I think the page should be split into three sections, the Physics of Time Travel, the Philosophy of Time Travel and Time Travel in Fiction. Possible a section in Fringe Theories, as suggested elsewhere on the talk page.

The Physics section could contain all the recent work on suggested possibilities for time travel, the philosophy section could contain all the stuff on the proposed solutions to the grandfather paradox, and the time travel in fiction section would be self explanatory. Certainly as it stands, this page doesn't really do justice to either the physics or the philosophy of time travel, and by mixing it in with the fiction degrades a serious topic (not like I'm suggesting it's the worlds most serious topic, but serious physicists and philosophers research it, they wouldn't be overly pleased to find their serious work mixed in with speculations based upon fiction!). Nikk50 19:43, 12 August 2007 (UTC)

Theory of Duality

Time travel has been controversial for years, almost the same way many scientists believe there is no God. What can be seen and understood, can obviously be explained. Up until this point (despite the actual facts proved through physics), people have only been able to theorize and portray ideas and equations to how time travel works. Perhaps then it is time to explain what I will call "Duality". There are two forces, one is physical (one we can see), and the latter is spiritual (one we cannot...but one we assume exists). Anything beyond logical explanation is NOT physical, but that doesn't mean it isn't there. It can still be possible. The same applies to Time Travel; a field brimming with endless possibilities... but with seemingly limited knowledge. If Duality were to be applied as a principle for research, then the un-seen and literally impossible may not be too far behind. The next focus should be to put our minds together, and to further research expanding our young human race.

--Sir Tyler Cole 07:53, 24 August 2007 (UTC)

Arrested Scientist?

I used to work with a guy named Roy Lee Rogers III who said he heard about a scientist who blew off the back of his house with what was intended to be a time machine, got arrested for disturbing the peace, and then got held after it was discovered his device was made with stolen parts. Either he is a good storyteller (and his vanity stories like his screenplay about beating up Jean-Claude Van Damme and having sex with Kristy Swanson suggest that he is not) or this is a really wild true story. Anyone heard of it? Maybe it was in Weekly World News or something.--Scottandrewhutchins 19:18, 20 September 2007 (UTC)

Possibility of Time Travel

As explained by Hawking's Paradox and other physical theories, time travel is impossible, due to the fact that the only energy source large enough to defy laws of spacetime, a black hole, disintegrates information. While it might be true that a black hole does not destroy information, as many believe, it would not matter either way, because any matter, including a physical time machine, or any physical time traveler, would be disintegrated by the sheer force of the black hole. If you suggest a wormhole as being a method of time travel, wormholes have not been proven, or even satisfactorily explained by the scientific, or the science fiction community. While the subject of time travel is an interesting topic, it should be referred to as a fictional subject matter, and not a scientific conjecture. Please take it off of 'Physics' discussion, as time travel does not merely 'bend' the laws of physics, but completely defies them. Masterfeatherpen 15:47, 24 September 2007 (UTC)

Angels, Prophecy, and Time Travel

Just recently reading this article, I read through the section on the origin of the concept. It mentioned an array of early works on the subject. Some of them involved either something like Rip Van Winkle or dreaming, but in a few of the stories time travel phenomenon gets instigated by either angels or demons. Reading about this reminded me somewhat of much earlier religious type works involving prophecies like in Revelation or some of the works in the Old Testament, or some of the ancient oracles. In those works, angelic beings sometimes predict the future, based upon the idea that a future timeline has been at least partially laid down in the present, and that these beings or entities are capable of sending some of this future information back to the present. A lot of these would severely pre-date the 1700s and give a much earlier origin of the concept. The question does arise, however, as to wheather categorically that would be the same thing. Do many of you think that something like that should be mentioned in the 'Origins' section of article? 66.248.121.138 15:23, 3 October 2007 (UTC)

I do not think so. If it were, we'd have to devote a lot of space to discussing why it is not the same as true time-travel, and would also have to go into the legend of Merlin. Michaelbusch 16:41, 3 October 2007 (UTC)

Your statement that it is not the same as true time travel might have some validity. At the same time, it might also potentially warrant the deletion of references to 'Memoirs of the Twentieth Century', 'A Christmas Carol', and 'Paris before Men'. Many of the legends of Merlin also seem to predate the 1700s. Could you explain your reasoning on the talk page? 66.248.126.133 23:25, 6 October 2007 (UTC)

Read Below and get Confused on my Logic!!!

Many Scientists talk about Time Travel but one thing I cant fugure out: They say we could travel to another Universe is how we alter time but If we did that then Nothing we do would effect this Universe just that one.

Or even if we Did here is a major way to cause a Paradox!!!

Lets say you are born in 1970 ok just as an example: If you went back to 1970 and shot yourself as a baby, then you would die, but that means you wouldn't have been able to go back in time to shoot yourself...Which of course means you couldn't have shot yourself if you died as a Baby..But then if you didn't shoot yourself you are still alive therefore you live and grow up to invent your time machine and shoot yourself again...and the Story Repeats..If I kept going it might give you a headache.

The Next Thing I say is if Time Travel was invented do you think anyone would be able to go back in time without altering time. Just going back and kicking a rock a few inches forward could alter Time extremely!

Example:

Lets start with the Regular Time line ok:

Some guy at age 18 walks down a road and trips on a rock causing him to fall into the Road and Get killed by a Car hitting him

Now if you go back and are just strolling down the Street and you harmlessly kick that rock, then that guy wouldn't have tripped on it, meaning He will LIVE! Now no matter what happens this will alter time Substantually!!

If he grows up and becomes A Dictator that takes over the World and Kills billions!! Then you just killed Billions of people with a Rock!!!

On the Other Hand if he becomes a Genius Scientist and Invented the Cure for Cancer, then you just saved Many Millions, But what if normally 25 years down the line Some other Guy invents the Cure for cancer and he becomes a millionaire and donates a bunch of money to a Homeless guy, who eventually uses the money to buy weapons and start a Rebellion on the Government and Take over!! So you may have cured Cancer Indirectly but you also Overthrew the Government Indirectly. I can use even more examples, now there is a chance that what you do will not harm the timeline, But any little thing will cause Drastic results a few hundred years down the line.

These are just a Few Idea's I came up with. —Preceding unsigned comment added by Blackdeath610 (talk • contribs) 03:38, 28 September 2007 (UTC)

What you are talking about is the "grandfather paradox". Quite a known thing. Witnin general relativity it can be solved [see http://arxiv.org/abs/gr-qc/0109029]. I'll try to add a corresponding passage to the article (in a few days).--Seador 12:24, 28 September 2007 (UTC)

Back to the Future/Mutable timelines

The article says that "The Back to the Future trilogy films also seem to feature a single mutable timeline." However, Back to the Future part 2 features a second timeline in which Biff obtains the sports almanac and returns to the fifties to create a new reality. Doc Brown explains this and even gives a diagram describing the effect of multiple timelines. TWCarlson 17:15, 3 October 2007 (UTC)

Doc's blackboard diagram was just showing how the timeline was changed, it wasn't meant to imply that 1985-A coexisted in parallel with the original 1985...the original 1985 had just been "erased". For evidence that it's a mutable timeline as opposed to different parallel timelines, see the Back to the Future FAQ written by writer/producer Bob Gale and writer/director Robert Zemeckis--in answer to a question about why old Biff didn't return to an alternate "2015-A" after giving the sports almanac to his younger self, they explain that their intention was that he did--the original 2015 was erased and replaced with a new 2015-A around Marty and Doc. If they were going on the parallel universe theory, Marty and Doc would have remained in the first version of 2015 where Biff did not take over the town, while old Biff would have returned to a separate 2015-A that was the future of 1985-A. Here the quote from the FAQ:

Q: When Doc and Marty are in 1955-A, Doc says they can't return to the future to stop Biff from stealing the DeLorean, because it would be the wrong future. But if that's true, how did Old Biff manage to get back to the same future that he left? Shouldn't he have come back to a different future?

A: As should be clear from the answer to the previous question, we believe Old Biff DID indeed return to a different future -- a "2015-A," which would have transformed around Marty, Doc, Jennifer and Einstein (just as Doc explains how 1985-A would change into 1985 and instantly transform around Jennifer and Einstein). This would happen AFTER Old Biff returned with the DeLorean. For this reason, we made sure that Doc had caught Jennifer and exited the McFly Townhouse before Old Biff returned. Thus, by the time Marty and Doc are carrying Jennifer back to the DeLorean, there COULD be other residents in that townhouse -- or perhaps the McFlys still live there. It is just as believable that the physicality of the neighborhood did NOT change as it is to believe that it did -- so we didn't change it. We decided not to make anything of this idea because this is one of those difficult time travel concepts that general audiences have a real hard time understanding. (Try explaining this stuff to your mother and you'll see what we mean.) A detailed explanation of it would have slowed down the story, and most of the audience doesn't ever think about it. That's why we made certain things ambiguous and left various things open for interpretation in hopes that the possibility of at least one or two explanations would be better than a "definitive" explanation that you could find holes in. Let's face it, time travel is fantasy, so there's no way to "prove" anything. As filmmakers, we try to create a set of rule for our stories and stick by them, and stay consistent within the little "universe" that we've created.

Hypnosifl 20:12, 16 October 2007 (UTC)

Time and space theories

I am sixteen and completely fascinated with time travel and quantum physics.Please dont disregard me becuase of my age. I have read a few books and numerous article on time and space. all of these say time and space are connected and most refer to time as the fourth dimension of space. my question is, has anyone ever proposed a theory that time is not connected to space at all, that time is not the fourth dimension of space, rather that time has its own set of dimensions? or perhaps space is actually a dimension of time? My second question is, if one takes away all ways to measure time, does time then cease to exist at all? If anyone has any information on these topics, i.e. books articles or whatever, i would greatly appreciate where to find them.

children are all knowing, we do not learn anything, only as we age do we remember what weve always known.
contact me at <hllzbaseball@yahoo.com> —Preceding unsigned comment added by Hllzbaseball (talk • contribs) 20:48, 13 October 2007 (UTC)

All experimental evidence is that space-time has a Minkowski geometry - time is a fourth dimension, but does not act like the others because you cannot exceed the speed of light in any frame of reference. In consequence, you can't go backwards in time. Re. 'if one takes away all ways to measure time, does time then cease to exist' - within the context of modern physics, that is a rather meaningless question. You can measure time with three sub-atomic particles (perhaps less - but two doesn't seem enough to me), so time has meaning as long as there are at least that many particles in the universe - which had better be the case or your computer doesn't exist. Removing time from the universe isn't possible - it's equivalent to asking if space disappears when nobody's looking. I suppose that gets into such meta-physics as the observer effect in quantum mechanics and what counts as an observer. Your interest in physics should be cultivated, and I recommend Hawking's A Brief History of Time if you haven't read it already, but if you have questions not directly related to an article, please place them at the Wikipedia:Reference desk. Michaelbusch 05:32, 8 November 2007 (UTC)

Biblical time travel

I reverted to remove a section which had just been added on "biblical time travel." First and foremost, I think this might be original research. Even if not, however, I have doubts as to the notability of the work in relation to this article. Thoughts? --TeaDrinker 22:37, 15 October 2007 (UTC)

Biblical time travel (response)

I added that section Actually it says it was a vision NOT time travel, so it shouldn't of been there. if it was, tho it reeally wouldve belogned there. even now it MAY have inspired some time travel storys bringing it into play but that is just "Original Research" 4.239.117.90 17:46, 16 October 2007 (UTC)Spideyfan

Split-apart

I think this article is very long. I have postd a split-apart template; maybe you guys could split up this one in things like Theory of time travel and Origins of time travel, just like the Presentist view-piece. If you don't want to do it, talk on my User:Wnauta page, and i'll do.