Talk:Time travel

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[edit] WikiProject Time assessment rating comment

Needs a lot of cleanup, but basically a B.

[edit] Can someone Incorporate the LHC at Cern

Cern is the largest Physics project in history and employs the guys who have Ph.D's from MIT and the like. Like 2000 of the smartest guys in the world are employed over there and work full time using the fastest computers, strongest magnets, and brightest intellectual capital in our galaxy. http://en.wikipedia.org/wiki/Large_Hadron_Collider This is going to be finished within 6 months and has spent billions of dollars and over 13 years of construction. They plan to create new novelties, including technology that is related to time travel, such as manageable black holes. I do not know how to bring this section into the article, as this topic might be adminned by people who aren't famaliar with high level physics and think its vandalism, but if someone can begin to incorporate a paragraph about the LHC, I will smoothe it out and make the links work. Sentriclecub (talk) 08:21, 8 March 2008 (UTC) Can someone who is in charge of this page or moderates it, please reply below.

Begin here, thanks!


Want to help write or improve articles about Time? Join WikiProject Time or visit the Time Portal for a list of articles that need improving. -- Yamara 15:56, 10 January 2008 (UTC)

if time travel were true i would have met myself by now —Preceding unsigned comment added by 172.163.75.184 (talk) 03:34, 25 February 2008 (UTC)

[edit] Time Machine

I personally believe that any form of Time Machine cannot currently exist due to the lack of visitors from the future or past. I believe that if a time machine ever did exist it's location would not be on this Earth but in outer space, because all theories and principles of the Speed-of-Light are developed from the properties of light in a vacuum. I do however believe that it is possible for a time machine to be built on earth and implemented on earth using a Casimir Vacuum and a man made Black Hole formed in a Gigantic Particle accelerator(Gigantic so that a self sustaining Black Hole could be formed, or at least one that would not collapse in less than one second). I also believe that time travel is possible through the use of a space craft and an Alcubierre Warp Drive(although there is no method for creating one, Yet!)--Mjeden2006 20:07, 9 January 2007 (UTC)

  • there is work currently being done useing an aray of lasers to accelerate a particle and send it back in time... John Doe or Jane Doe 14:06, 8 March 2007 (UTC)
Unfortunately, if it's ever built, it will only be able to send information back to the point in time this device is built, not before... —Preceding unsign ed comment added by 72.67.35.112 (talk) 05:10, 29 January 2008 (UTC)
Unless of course we are wrong about those laws of physics. 86.151.228.86 (talk) 22:15, 4 March 2008 (UTC)

vinamra mattoo--

well I think that there is an another method of making a time machine . we know that the speed of electrons is much higher than light .if we increase the kinetic energy of the atom to such an extend that its electronic shell becomes large then there can be an opening of a portal .the more the kinetic energy .more back we go.and if we change the charge of the electron {by converting it into positron }then we can go to the future


Guys, I'm sorry to enter this discussion with nothing to add, but I just have to put my two cents in on the above statement.

"we know that the speed of electrons is much higher than light"

It is impossible for electrons to travel faster than light.

"if we increase the kinetic energy of the atom to such an extend that its electronic shell becomes large then there can be an opening of a portal"

  1. The kinetic energy of an atom has nothing to do with electron energy. Kinetic energy is simply a measurement of how fast an atom is moving. You would measure this with a thermometer ; ).
  2. Increasing the energy of electrons would not increase the size of the "shell". It would simply move it into a higher quantum energy state.

Also, I don't think it's possible to convert an electron into a positron. However, antimatter is not my area of (relative) expertise.

Good thinking, but sadly time travel seems to be only a thing of science fiction. Perhaps you should look at some of the articles on positrons or quantum energy states for more information. Nice theory though! -- X Wild Irishman x (talk) 02:49, 14 May 2008 (UTC)

[edit] Safety

Are there any theories on the safety of time travel? --NEMT (talk) 20:30, 20 November 2007 (UTC)

Yes, its well known that when time travelling your safety is not guaranteed, especially when you push it to the limit. —Preceding unsigned comment added by 88.106.16.89 (talk) 01:21, 27 February 2008 (UTC)


[edit] make money on time travel

immagine this, you find a wormhole connecting a point in the past with the future. near the worm hole is a dollar. you pick up the dollar and throw it into the future end. now when you find the worm hole it has two dollars in front of it. you pick both up and repeat the process.soon you'll be very rich.what concerns me is that this can be done with anything. by this means you can in a sense create mass or produce exponentional amounts of energy. if this is done with energy would there eventually be a really big explosion from the infinite loop? —Preceding unsigned comment added by 70.111.221.127 (talk) 03:03, 14 February 2008 (UTC)

You would still only have one dollar. --RLent (talk) 20:24, 17 April 2008 (UTC)

That is probably impossible, given that wormholes are designed to travel space-time, not copy items. —Preceding unsigned comment added by 68.48.94.53 (talk) 11:45, 23 May 2008 (UTC)

Designed? BreathingMeat (talk) 01:07, 27 May 2008 (UTC)
Anything that can be used for time travel should also be usable for having at least the appearance of multiple "copies" of the same item--think of how if you went back in time and met with your younger self, it would appear as if there were two "copies" of you in the same place. But if something like the Novikov self-consistency principle is true, you could only actually spend the dollar that had been through the time machine the most times and was thus the "oldest"--if you tried to spend any of the "younger" versions of the dollar, you wouldn't be able to send it through the time machine again and this would be inconsistent with the fact that you can see "older" versions lying around. Hypnosifl (talk) 19:39, 27 May 2008 (UTC)

[edit] Time travel is not only possible; it is actionable.

Time travel will certainly become a reality; all things the human mind can comprehend can be accomplished. The claim that only photons can travel at the speed of light will be ridiculous to a first year student in the year 3008. Ask almost anyone on the planet 108 years about travelling from New York to San Francisco in 8 hours and they would have said its impossible. Ask someone 508 years ago about travelling 70 miles in one hour and they would have said thats impossible. Any problem is solvable given enough time and resources. The atom did not even exist in the year 1744, at least not to scientists of the day, yet in 1945 we smashed a few together over Japan with spectacular results. One new discovery leads to discovering something else which will lead to travel faster than the speed of light. If the human brain can think it, then it can be done. —Preceding unsigned comment added by 131.44.1.69 (talk) 11:03, 27 February 2008 (UTC)

I can think of jumping to the moon, but I can't do it. There is a difference between that which is difficult and that which is impossible. Just because difficult things have been done does not mean that there are no impossible tasks.--RLent (talk) 20:27, 17 April 2008 (UTC)
I think that jumping to the moon is much more likely then travelling in time, but i believe both scenarios are accomplishable. - Thymo —Preceding unsigned comment added by 62.63.25.18 (talk) 12:11, 19 May 2008 (UTC)

[edit] Time travel

We can theorize only about time travel in the past, because travelling in the future cannot be possible due to the future timeplace (spacetime) still not exists, so there isn't no place where to travel (Presentism). If we assume that future timeplace exists, then we also must assume that we are living in the past, what would sound incredible.
But speaking about travelling in the past, the problem is where the past spacetime information is stored. Because to see something in the past, there must exist adequate timeplace. But it's completely unimaginable how and where the all past states of all events and all materia can be stored, inclusive those not only on the Earth, but also in the Space.
We also must not mix up travelling in time and travelling through Wormholes (one over Bermuda Triangle), what isn't travelling in time, but travelling between different Universes. Roberts7 13:28, 29 February 2008 (UTC)

You might want to look into the relativity of simultaneity, which makes a pretty good argument against presentism. And note that the alternative to presentism, eternalism, does not say we are "living in the past", it says there is no absolute truth about whether a given time is "past" or "present" or "future", these terms are understood as purely relative to the speaker like "here" and "there" or "left" and "right". See also A-series and B-series. Hypnosifl (talk) 17:57, 8 March 2008 (UTC)
In a very real sense, we are living in someone's past, and living in someone's future. When I was a kid, the year 2000 was "the future", now it's the past. It used to be the present.--RLent (talk) 20:34, 17 April 2008 (UTC)

[edit] High gravity as a substitute for high speed relatistic time dilation effect

From the article:

Using time dilation under the Theory of General Relativity, for instance: Residing inside of a hollow, high-mass object;

Are you sure this is accurate? I was under the impression that according to the shell theorem, the net gravity inside a hollow, symmetrical sphere was zero. If the hollow object isn't symmetrical, there could be some gravity inside, but in that case it would be no different from (and probably less efficient than) standing on the outside of a high-mass object. —Preceding unsigned comment added by 67.117.209.190 (talk) 09:16, 10 March 2008 (UTC)

Apparently the observer inside would not feel any gravitational force (the spacetime inside the shell would be flat), but the time dilation (measured relative to an observer far away from the shell) would be the same on the inside as it is right on the outside of the spherical shell--see the post by pervect at the end of this thread, or this paper on arxiv.org. Hypnosifl (talk) 18:13, 11 March 2008 (UTC)

[edit] My Thoughts

It would be so cool if time travel was possible because if you embarassed yourself you could go back and change it.

so cool —Preceding unsigned comment added by 91.105.158.7 (talk) 14:08, 26 March 2008 (UTC)

  • A little reminder of Talk page guidelines: The purpose of a Wikipedia talk page is to provide space for editors to discuss changes to its associated article or project page. Article talk pages should not be used by editors as platforms for their personal views. Thanks for reading. :) --Bisqwit (talk) 15:04, 27 March 2008 (UTC)

[edit] Not Possible

There are some physicists that think (sorry, no citations) time travel is not possible because time has no dimension. Since there is no there to go back to, or to go forward to, any talk of time travel is silly.

To be complete, this article should add a contravening section with this point of view. Shawncorey (talk) 00:17, 31 March 2008 (UTC)

You really need citations for a claim like this; it sounds more like the philosophical notion of "presentism" discussed in the article, I've never seen any physicist use this argument, and it doesn't sound like a genuinely physical argument either, so I would suspect you're just misremembering. Hypnosifl (talk) 03:41, 1 April 2008 (UTC)
what you ARE is a collection of energies that is no longer where you WERE, but has migrated to a new location, there is no travelling back to where they WERE and expecting to find them there. For some reason this absurdly simple thought has escaped some modern science due to a mis-reading of a space-time charting of changes as a map of some real places that still exist. The past is chartable but not there any more, and the future only exists as thoughts in the imagination of men, it has no REAL location and it should be absurdly obvious why no one has yet travelled back from there, because there is no one there yet.

Consider, if all moments in existance are said to be like a strip of 4-D film, then pray tell me who made the film strip and WHEN? secondly tell me how any of those moments can be considered by anyone as THE present moment? thirdly tell me what is moving? all those moments would appear static to a godlike being, yet we are fully aware of motion and that would not happen unless we were somehow more than 4 dimensional and moving through all these moments... and if that were so, it would mean that we were not human, but some sort of omni-dimensional soul moving through all those souless bodies statically awaiting our presence. And while that may be possible, it does not seem very likely!Jiohdi (talk) 21:49, 8 April 2008 (UTC)

[edit] Time travel, or space-time travel?

The first paragraph of this section is wrong. It is based on the assumption that the Earth does not undergo any acceleration. Its argument of relative velocity is overshadowed by the accelerations. The first acceleration is angular acceleration; the Earth is spinning. If I were to go back 12 hours in time (and ignore the other accelerations), I would end up on the opposite side; same latitude but 180 degrees difference in longitude. Not only that, the relative velocity of the place where I "started" would be 180 degrees from when I started. If I were to go back 6 months, the Earth would be on the opposite of the Sun and its velocity would be 180 degrees different. To come up with a successful argument, you would have to use general relativity, not special relativity.--Shawncorey (talk) 17:32, 16 May 2008 (UTC)

It's not correct that you need general relativity to deal with acceleration--special relativity can certainly deal with acceleration in flat spacetime where gravity is negligible, see the way SR deals with the twin paradox on this page for example. If you were standing on a spinning sphere of negligible mass, then if you take your position on the sphere when your clock reads 3:00 and your position on the sphere when your clock reads 4:00, you can certainly find an inertial reference frame in SR where both of these are the same point in space--just imagine a projectile fired from your position at 3:00 which moves at constant velocity and has just the right speed and direction so that it arrives at your position at 4:00. In the rest frame of this projectile, this means you have returned to the same position at 4:00 that you occupied at 3:00.
Of course, in the case of the Earth we do need general relativity, not because of accelerations but because of the fact that the Earth's gravity curves spacetime. However, in general relativity you are free to use arbitrary smooth coordinate systems, and the laws of physics obey the same tensor equations in all the coordinate systems, thanks to what's known as "diffeomorphism invariance" (also known as general covariance)--see this page for a discussion. So again, it would certainly be possible to find a coordinate system where your position at 4:00 is the same as your position at 3:00, even if you are standing on a spinning orbiting planet, and this coordinate system is physically no better or worse than any other in GR. Hypnosifl (talk) 22:44, 18 May 2008 (UTC)

OK, gone--Mr. Shawn H. Corey (talk) 00:54, 17 May 2008 (UTC)

Or, you could rewrite the section so that it makes better sense... instead of blanking a paragraph about a frequently-discussed issue in time travel SF, while leaving the paragraph full of cruft intact, baffling any new readers. --Yamara ✉ 02:25, 17 May 2008 (UTC)

No, I cannot.

Nor, you little worm, can you blame me for the lack of physics that agree with your imagination.

The paragraph is wrong...and it is gone.--Mr. Shawn H. Corey (talk) 04:51, 17 May 2008 (UTC)

The section is not wrong. There is no such thing as absolute space in relativity, and hence no absolute notion of which point in space at a later time is at the "same position" as a point in space at an earlier time. One can choose different coordinate systems which give different answers as to whether a given object is at rest or not (spatial coordinate not changing with time), and none is more "true" than any other in relativity. The paragraph already contains a reference for this in the form of a book by physicist Robert Geroch, if you doubt what I'm saying I suggest you read it. Hypnosifl (talk) 22:59, 17 May 2008 (UTC)

after seeing mention of this on Wikipedia:Editor_assistance/Requests i decided to take a look, while im not an expert on relativity As the inclusion of something is based in the requirements of Verifiability and Notability, Relativity is defiantly notable and therefore comes down to is it verifiable. At first look the source appears to be reliable, but as I don`t have access to it I cant really tell, but can accept on good faith

I can't see any specific reason for its removal unless can be demonstrated that the cited source is not reliable or does not say what is stated in the article.

also the argument itself is not just dependent on relativity (general or special) but also the "method of time travel" involved and how that effects the start and end points, as ending up elsewhere makes the assumption that the time travel process does not take any such effects into account.

You might want to ask at WikiProject Relativity for someone more knowledgeable.

but as a general point stated in Verifiability wikipedia relies on is verifiability, not truth.

The threshold for inclusion in Wikipedia is verifiability, not truth—meaning, in this context, whether readers are able to check that material added to Wikipedia has already been published by a reliable source, not whether we think it is true

--Firebladed (talk) 13:51, 19 May 2008 (UTC)

[edit] Vote on paragraph

An editor has been removing the following cited paragraph, or parts thereof, over the past couple days:

Time travel, or space-time travel?
An objection that is sometimes raised against the concept of time machines in science fiction is that they ignore the motion of the Earth between the date the time machine departs and the date it returns. The idea that a traveler 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, so that advocates of this argument imagine that "realistically" the time machine should actually reappear in space far away from the Earth's position at that date. However, according to the theory of special relativity, this argument is based on a false premise. Special relativity rejects the idea of absolute time and space; there can be no universal truth about the spatial distance between events which occurred at different times (such as an event on Earth today and an event on Earth in 1865), and thus no objective truth about which point in space at one time is at the "same position" that the Earth was at another time, because the distance depends on the observer's frame of reference.
[ref]Geroch, Robert (1978). General Relativity From A to B. The University of Chicago Press, 124. 

I see no reason for it to be summarily removed, especially the cited section. Some arguments for or against are cited above, which may be helpful in making a consensus on whether it should remain. -Yamara ✉ 00:50, 19 May 2008 (UTC)

  • Strong Keep - It's a common criticism of time travel in fiction, beginning with H.G. Wells' The Time Machine, and a discussion is clearly merited in the article. Special relativity's challenge is plainly part of this criticism. -Yamara ✉ 00:50, 19 May 2008 (UTC)

Again, you don't read what I have written.

I said the first acceleration is angular acceleration.

Until you can read, nothing else is important. —Preceding unsigned comment added by Shawncorey (talk • contribs) 23:53, 27 May 2008 (UTC)

As pointed out here, special relativity can handle acceleration just fine as long as gravity isn't involved. And in any case, the current version of the text covers both special and general relativity. Do you disagree that both theories reject the notion of absolute space, and hence they reject the notion that there is any unique definition of the "same place" at different times? Hypnosifl (talk) 01:42, 28 May 2008 (UTC)

OK, you are Absolutely Right.

Nothing I can say will change your minds.  I was foolish to think so.  —Preceding unsigned comment added by Shawncorey (talk • contribs) 01:54, 28 May 2008 (UTC)

"The only sense in which special relativity is an approximation when there are accelerating bodies is that gravitational effects such as generation of gravitational waves are being ignored. But of course there are larger gravitational effects being neglected even when massive bodies are not accelerating and they are small for many applications so this is not strictly relevant. Special relativity gives a completely self-consistent description of the mechanics of accelerating bodies neglecting gravitation, just as Newtonian mechanics did."

Now why do I object to that because it involves gravity, and not angular acceleration?

That's because I'm not stupid!

I'm tried of blaming me for your lack of imagination.

Grow up!

Mr. Shawn H. Corey (talk) 02:58, 28 May 2008 (UTC)

I'm not sure I get your meaning here--when you say "because it involves gravity, and not angular acceleration", what is the "it" that you're referring to ? Do you mean the paragraph is talking about gravity? Yes, the paragraph is saying that you only need to use general relativity if gravity is involved, and that as long as you ignore the gravitational waves produced by acceleration, which in most ordinary circumstances would be extremely tiny, then special relativity is perfectly capable of dealing with acceleration. Just look at the opening paragraph of that same page:
"It is a common misconception that Special Relativity cannot handle accelerating objects or accelerating reference frames. It is claimed that general relativity is required because special relativity only applies to inertial frames. This is not true. Special relativity treats accelerating frames differently from inertial frames but can still deal with them. Accelerating objects can be dealt with without even calling upon accelerating frames."
So clearly they are saying that special relativity can handle accelerations, including angular acceleration--do you disagree that this is what they're saying? Hypnosifl (talk) 03:14, 28 May 2008 (UTC)
Accelerating objects can be dealt with by special relativity but only if the frame of reference is NOT tied to them. The frame of reference MUST be linear. Otherwise there are pseudo-forces to reckon with.
But, if you care to read the original page, the frame of reference is tied to the surface of the earth. Therefore it an accelerated frame. Therefore specially relativity does not apply. EVER.
Gravity is not "insignificant". If you "time travel" back for 6 months, the earth is on the other side of the sun; over 200 million kilometres away. This is the last time I expect to read that a displacement of over 16 light-minutes is insignificant!

--Mr. Shawn H. Corey (talk) 02:27, 5 June 2008 (UTC)

You're still missing the point. There was never any assumption in that paragraph of the wikipedia article that we were using the Earth's rest frame (I should know, because I wrote the section on relativity); the point is just that if you take two events which happen on the Earth at different moments, it is possible to find a coordinate system where they both happen at the same position, and another coordinate system where they happen at different positions. This is true regardless of whether we're using inertial frames in a flat SR spacetime or arbitrary coordinate systems in a curved GR spacetime.
When I talked about treating gravity as "insignificant", I was only talking about treating the curvature of spacetime caused by mass as insignificant (as you may know, GR allows spacetime to be curved by mass and energy, while SR assumes a 'flat' spacetime with Minkowski geometry). If we replace the Earth with a hollow sphere of negligible mass which is still rotating about its axis and still moving in an elliptical orbit around some central point (perhaps because we're swinging it around this point on a tether rather than because of the spacetime curvature created by the Sun), then we have a situation where the movement of the sphere is similar to the movement of the Earth but where the spacetime curvature caused by gravity is negligible so spacetime is close to "flat" and we can treat the situation using SR alone. In this case it may be true that if you take an event A on the sphere 6 months ago and an event B on the sphere today, events A and B would be 200 million kilometers apart in the inertial rest frame of the central point the sphere is orbiting around (the position of the 'Sun'). The point is, you can easily find a different inertial frame where events A and B happen at the same spatial coordinates! This new inertial frame would not be the rest frame of the sphere, since the sphere is not moving inertially. Rather, it would be the rest frame of an inertial projectile which was fired at the position and time of event A, and which moved in a straight line at just the right speed and direction to intersect the sphere's orbit again at exactly the position and time of event B.
Do you disagree that if we have an object moving on a non-inertial path in flat spacetime, and we have two events A and B on the object, it will always be possible to fire an inertial projectile at the right speed and direction so that it is right next to both A and B as they happen? Do you disagree that this means that in the inertial rest frame of the projectile, A and B both had the same space-coordinates? Do you disagree that in SR all inertial frames are equally valid, so if different inertial coordinate systems disagree about whether A and B happened at the "same position" or "different positions" (for instance, perhaps in one inertial frame the two events happened 0 km apart while in another inertial frame they happened 200 million km apart), there is no basis for saying one frame's answer has more physical validity than the other's? Hypnosifl (talk) 16:39, 5 June 2008 (UTC)