Talk:Time dilation

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 Time dilation is a current good article nominee. If you have not contributed significantly to this article, feel free to evaluate it according to the good article criteria and then pass or fail the article as outlined on the candidates page.

Nomination date: 8 December 2006

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Contents

[edit] Etiology

I re-worded some of the introduction to mention the transverse doppler effect.

I could not find any free illustration software, so I just drew the necessary diagrams on my whiteboard and took a picture of them. The result is, shall we say, less than professional. Someone more graphically atuned than I should probably re-draw them. There are also layout issues.

The proposed explanation is, however, about as simple as you can possibly get. It is likely accessible to the aforementioned "12th grader" (though I recall being taught Euclidean geometry well before then), despite the fact it does have some diagrams and some simple algebra. Frankly, graphs and math are going to form part of the description. This is physics.

I am well aware the explanation is hardly a proof, but I assert this is not the place to deal with what happens when the clock is moved along it's axis, spatial isotropy, realizing the implicit experiment (the problem of doppler) and the like. "Just the facts."

If this proposal more or less stands, I think the sections from "Temporal coordinate systems" to "Time dilation and space flight" can be removed -- in this, I completely agree with "Anon" in that they are unnecessarily complicated. mdf 13:59, 24 October 2005 (UTC)


mdf, Why use the word "appears"? We already all agreed that time dilation has a real component. I think we need to agree on terminology. No enclosed experiment can detect the differing rates of ticking (this is because people and things inside such a lab are also affected). However, using somewhat complicated math and knowledge of the theory, it is possible to continuously measure this using the NIST time-sync protocol for satellites by sending a signal to said satellite and comparing the time signal as received at the satellite with those at the ground stations. So the local measurement of time appeared fine in all respects, except that the dilation was exactly measured in the end. In other words, ignoring relativistic simultaenity for a moment, since we're only talking about satellite speeds here for now, you could write a program to calculate earth-time and satellite-time and continuously verify it with the NIST time-sync system and watch the 2 *computed* clocks fall slowly out of sync, gaining or losing time and also hope to one day bring the calculated clock back to the earth if some nae-sayers still wanted to argue with its reality as compared to the clock on earth. The problem with "appears" is the same as ems's associating my use of "laymen" as implying I am clergy, this is the wrong use of the word in the context. A layman is a non-pro in the context given(..and I'm a buff, not a pro). Similarly "appears" in your context is supposed to mean "is seen to", but a layman wandering by might read it as "only appears to be as the reality is different". Jok2000 15:20, 24 October 2005 (UTC)
He uses "appears" because velocity time dliation is symmetrical: Each clock is found to be running slow in the other frame of reference, but physically the clocks are running at the same rate. None-the-less your semantic point is well taken, which is why I used "is found to be" above in the place of "appears". Hopefully that would alleviate your concern. --EMS | Talk 16:44, 24 October 2005 (UTC)
How does EMS know that "physically the clocks are running at the same rate"? E4mmacro 06:51, 29 December 2005 (UTC)

This new section of yours has a lot of issues. The big problem is that it collides with Cleon's animated GIF, which for me is a better way of explaining the same thing. However, there are others as discussed below. So I will revert it out.

I asked you before to establish a sandbox version of this article. That means placing a copy in a location like User:mdf/sandbox/Time dilation, and playing with it there. Efforts like that should be commented on first before being placed before the world.

That is a nice experiment that you did with the new section and the illustration. However, I think that the contents should be placed in a seperate article called Mathematics of velocity time dilation. Also, Wikipedia has adequate facilities for formatting mathematics. There is no need to clutter up an illustration with it, especially since that math needs some supporting text to make is accessible to readers who are initially unfamiliar with this material. --EMS | Talk 16:05, 24 October 2005 (UTC)

It was clear to me that had I established a "sandbox version" you would have ignored it. Instead, I chose to be bold. Don't you remember telling me to do that as well? Or did you mean I was only allowed to be bold' in ways that you would ultimately approve? And as far as I know, no material in the wikipedia needs to be "commented on" prior to being "placed before the world". If I am incorrect in this assumption, then please cite relevant wikipedia policy on my talk page that supports your contention in this regard.
As I noted, it is basically impossible to not use a diagram, and some simple mathematics, to explain the cause of time dilation. The material you left basically proves this point: it is virtually an unreadable mass of confusion. Clock synchronization? Temporal coordinate systems? Totally beside the point, as my submission shows.
Your complaints that the graphics had the math are simply style vs. substance. I invited improvements. I guess that would have been hard, eh? Easier to just revert.
But on a deeper level, I find it perplexing that a few sentences and a simple diagram that more or less explain the phenomena in the simplest manner is somehow lacking compared to the stream-of-consciousness confusing babble that you left. What, exactly, was defective in my submission? Can you offer anything quantifiable, beyond your Royal Say-So? What "supporting text" was needed? Can you explain, clearly, why I or anyone else shouldn't just revert your reversion?
Fortunately for you, though, you don't need to answer any of these questions: as I said above, one revert and I'm gone. mdf 17:39, 24 October 2005 (UTC)
It is easier to destroy than to create, and that goes for the both of us. In any case, to be more specific:
  1. You hand drawing covers the same ground as the animated GIF in the section Time_dilation#The_Space-time_geometry_of_velocity_time_dilation. I would prefer that the explanation of that be modified.  ::#* You put your eitology before my text defining what in the most general terms time dilation is. So it is misordered IMO
  2. The math clutters up the second illustration, and the lack of supporting text means that t is not explicitly defined.
  3. I can't see how this stuff is any less a "stream of consciousness" than what is already there
  4. It is not integrated at all with what is already there. Instead if covers the same ground in a different fashion, potentially confusing readers.
I assure you that you are wrong about my not worrying about a sandbox page. Myself and a few others will, given an announcement of it, establish watches on it and actively give you feedback (and some added editting also). This approach has been used successfully by a number of editors, including myself.
You impress me as someone with potential, but you need a chance to play around with this medium and get used to it. Also, be advised that this page needs a good, solid, thoughtful rewrite. I don't want it to be clutterred up with your text and mine and Cleon's with each going off in a different direction. Instead I was something that can act as a coherent whole.
In any case, please don't be put off by my reverting your section. You edit to the intro caused me to remove some of my own text, and if you can moot the section on coordinate systems and/or Cleon's animated GIF, then I will let those go away too. However, your writing this time was not of that level. Just remember that if you don't try again you can't fall flat on your face again, but neither can you succeed in producing something good. --EMS | Talk 19:45, 24 October 2005 (UTC)


I think you guys are talking about 2 different things. mdf's diagram explains the real time dilation (bring 2 clocks back together and they are different), while the animated .gif explains a purely symmetric observational time dilation of 2 ships who do not wish to establish their intertial reference frame nor necessarily ever directly compare their clocks. As such, I propose that the page be broken down into "purely observed" and "real" time dilation halves.Jok2000 20:29, 24 October 2005 (UTC)
"purely observed" time dilation is the "real" time dilation! The same symmetry exists for the mdf's diagram even if he did not show it. --EMS | Talk 21:05, 24 October 2005 (UTC)


Nope, its not symmetric. You should read the twin paradox page closely. This isn't even controversial. It's on PBS or Discovery like twice a week. This page is grossly in error, and quite obviously so. When are you going to put in the "disputed" thing, by the way?Jok2000 01:54, 25 October 2005 (UTC)
I think the "cleanup" tag is mor effective IMO (although that is not my doing). As for the twin "paradox", that includes an acceleration on the part of one of the twins, making their referece frames non-equivalent. (That is a good point however, and should be covered in the article.) --EMS | Talk 05:54, 27 October 2005 (UTC)

[edit] Restoration of Eitology section

I think that I would like it better if it did not make this article look more like a used book store than a well organized article. I won't contest its restoration, but this article needs to have someone "take the bull by the horns" and really redo it a ways. (I regret that I am too busy for that at this time.) --EMS | Talk 06:00, 27 October 2005 (UTC)


Okay, cleanup can be be based on the expert opinion at http://scienceworld.wolfram.com/physics/TimeDilation.html for the non-symmetric part, and the symmetric space-ship fleet .gif then works best if it contains a third body like the Earth.Jok2000 12:23, 27 October 2005 (UTC)

I'm not a user of Wikipedia, however, I am very familiar with time dilation. You need to word the article better. I am familiar with time dilation, but I don't even want to read the article because the first few sentences are so complicated. You need to word it in more "user-friendly' terms so it is easier to read. http://www.geocities.com/superstringtheory42

---above by anon

Well, when you learn to read, come back and check the version history of this topic and suggest some changes that might survive the reversionists. My reference to a very easy to understand book on time was reverted a long time ago. The "symmetric" part is not really relevant to time dilation and can go, IMHO, unless it takes on the idea of propogation delay and doesn't pretend to describe time dilation. Here, I'll put it back in and see what happens.Jok2000 18:34, 1 December 2005 (UTC)


[edit] question

Is the idea that at the speed of light no time passes and time travelled = distance in light years? So if you travelled to the end of the universe (15 billion light years) at light speed it would seem instantaneous for you, but you would arrive in 15,000,002,005 AD ??? Astrokey44 11:29, 2 December 2005 (UTC)

Try Talk:Time_dilation/Archive_1#Recent_edits_by_ems57fcva Jok2000 14:19, 2 December 2005 (UTC)

They seem to only talk about speeds which approach light speed, what about travelling at light speed itself. looking through that led me to this table from an older version of the page, would this be any use in the current article? Astrokey44 14:41, 2 December 2005 (UTC)
v (%c) length due to length contraction time due to time dilation
0 1.000 1.000
10 0.995 1.005
50 0.867 1.155
90 0.436 2.294
99 0.141 7.089
99.9 0.045 22.366
99.999 0.00448 224.658

[edit] "proper time locally"

It says now: "Time dilation is the phenomenon of proper time passing at a different rate for a remote and/or moving object than it does locally. " That's certainly not yet optimal, for here "proper" and "local" mean effectively the same thing, similar to writing "local position is measured far away at a different location than locally".

That may be an improvement, but I'm sure we can do better than that. For example:

"Time dilation is the phenomenon of time passing at a different rate for a remote and/or moving clock than it does locally and/or in rest."

or, IMO again better:

"Time dilation refers to the phenomenon that the proper time rate of a remote and/or moving clock differs from that of a reference clock."

Cheers, Harald88 18:28, 12 December 2005 (UTC)

Regretfully, I find the last proposal insufficient: in the phrase

"Time dilation is the phenomenon of proper time being observed to pass at a different rate for a remote and/or moving object than it does for the observer",

the words "observed" and "observer" may cause confusion. On top of that, "observer" is jargon that risks to be interpreted at face value, causing considerable misunderstandings. Thus I'll do an attempt to do better. Harald88 08:35, 13 December 2005 (UTC) PS I did not include "proper time" in the intro sentence, as it's not necessary and a burden for newbees. It should be mentioned somewhere later though. Harald88 08:58, 13 December 2005 (UTC)

I think that you have done a good job of capturing the essense of my sentence, so I will not quibble. You are however quite right that proper time needs to be mentioned here somehow. (At the least we have gotten beyond the weird edit whereby the into was talking about "accelerated clocks".) --EMS | Talk 19:15, 13 December 2005 (UTC)


[edit] Seems accurate on a glance

Why is the factual accuracy of this article disputed? I didn't read the whole thing, but what specifically has been called into question? --Monguin61 03:20, 15 December 2005 (UTC)

The green ships / red ships explanation does not agree entirely with the Twin paradox resolution. More precisely "both the green and the red fleet are entitled to consider themselves as "non-moving" in their own frame of reference." from this page and "The usual resolution of the paradox is that the twins are not symmetrical: the travelling twin has a "turnaround" and not all reference frames are equivalent." from the Twin paradox page are not in agreement. Jok2000 04:04, 15 December 2005 (UTC)

*Sigh*. The twin paradox page explicitly notes that in that "paradox" three interial frames are involved. In this write-up, only two inertial frames are involved. As for the statement "not all reference frames are equivalent": That is true. However, in SR, all inertial frames are equivalent. I will look at the twin paradox article and see if I can clarify the point being made there. However, that {{disputed-section}} tag is IMO inappropriate, and I will remove in within 24 hours unless you can make a better case for its being there. --EMS | Talk 05:03, 15 December 2005 (UTC)
Okay, sure, the ships came from somewhere, either 1 or 2 other inertial reference frames. How's that? ..however I'll caution you not waste much effort debating me, as I don't have much to say. I'm the kind of guy, to borrow a line from Dire Straits, who if I see two guys claiming to be Jesus, might say "1 of them must be wrong", not because I deny Jesus and can be excommunicated by the Pope, but rather, have employed logic that even the Pope cannot deny. Jok2000 13:04, 15 December 2005 (UTC)
This is irrelevant. While each observer remains in the same inertial frame, the reciprocity of this effect applies. For example, how do you know that these are not aliens on stars which are passing each other? In that case, they have been in those frames of reference throughtout their lives! What more do you want?
Kindly note that this is the reason why the twin paradox is such a perpetual nuisance! For example, if traveling twin has a time dilation factor of 0.5 (which means v = 0.866c) and his trip lasts 10 years in the view of the stay-at-home twin, the traveling twin must see the stay-at-home twin pass through 20 years if his coordinate time with the stay-at-home twin's clock ticking at half-time all the while. Because of how the traveling twin's perception of spacetime changes at turnaround, that is indeed the case. (This is something that the twin paradox page itself should cover. Maybe someday I will take care of that.)
I hope that this satisfies you. In any case, I kindly request that you remove that tag now. I principle, you "own" the tag. However, your failure to understand that section does not mean that it is wrong. The tag therefore is more a form of harrassment than a bona-bide warning of a conflict between groups of editors. --EMS | Talk 15:41, 15 December 2005 (UTC)
I think there's a term in psychiatry for imagined harrassment. However, like I said, I don't have much to say. You clearly think space is empty and the time dilation follows the object. I haven't been to the vatican recently to see if that's part of accepted canon, however the boys on the inertia page are busy debating even inertia ad nauseum, so its good you removed the disputed tag -- we barely exchange a harsh syllable any more. Actually, I was hoping you'd have changed it to "disputed section" shortly after I added it, but then I went off to more productive topics and the dispute kinda fizzled. Jok2000 20:30, 15 December 2005 (UTC)

[edit] The GIF-animation is sufficient

Time dilation in transversal motion.
Time dilation in transversal motion.

In the GIF-animation the fleet do compare their clocks!
The lightpulses that are being emitted at regular intervals provide the information that allows the ships of the respective fleets to maintain constant distance to each other, and for each fleet the regular lightpulses serve to maintain a single fleet-time.
Pulses traversing from one fleet to another are equally informative and meaningful.
Every second of red time a time-bearing pulse is sent to the green fleet, and the green fleet counts two seconds of green time between each pulse recieved from the reds.
Conversely: every second of green time a time-bearing pulse is sent to the red fleet, and the red fleet counts two seconds of red time between each pulse recieved from the greens. They do compare their respective rates of proper time, that is what the pulses traversing from one fleet to the other are all about.

The GIF-animation is designed in such a way that the time-bearing pulses of light are a true indicator of the way the rates of proper time of the reds and the greens relate to each other. It is in this GIF-animation a true indicator because it is designed in such a way that involvement of classical Doppler effect is avoided.

Recapitulating: the twin scenario entails that two space-ships depart from each other, and later make a rendez-vous, and if one spaceship has traveled more distance than the other, they will on rendez-vous be seen to not have had the same lapse of proper time.

I suppose that it is tempting to believe that to defer the comparison of lapse of proper time to when the rendez-vous point has been reached is a more solid comparison. Is it more physical to compare clocks that have been brought into co-moving status? There is no support for such a hypothesis. There is no support for thinking that the twin scenario singles out something that is somehow more physical than what is depicted in the GIF-animation.

Any of the ships of either of the fleets can make a U-turn at some stage, and have a rendez-vous with a ship that has been passed by earlier. The ship that has made a U-turn in order to get to the point of rendez-vous will then be seen to have had less lapse of proper time. If both a "red ship" and a "green ship" make a U-turn, then both will have less lapse of proper time than the ships they rendey-vous with.

I vote to not discuss the twin scenario in this article. There is a separate wikipedia article for the twin paradox. Of course, the two subjects are interrelated, but I think discussing the twin scenario in the time dilation article is unnecessary duplication.

The GIF-animation is designed to emphasize the symmetry that is at the heart of special relativity: the principle of relativity of inertial motion. --Cleon Teunissen | Talk 14:58, 15 December 2005 (UTC)

Yeah, the twins thing doesn't belong here. Let's delete the green & red ships nonsense completely. Jok2000 15:10, 15 December 2005 (UTC)


Also, quoting Cleon: involvement of classical Doppler effect is avoided. The issue is that Transverse Doppler effects are related to the time dilation. Its a terribly contrived example ignoring several major points. The best 2 sentence description for both time dilation and the twins thing is here: Wolfram We really need to delete misleading fluff out of this article. Jok2000 19:39, 15 December 2005 (UTC)

Then name the points that are being ignored. IMO, that GIF needs a much better description, but overall is quite accurate and useful. That rewrite has been on my to-do list for some time, and this may just force the issue. In the meantime, that {{disputed}} tag has been removed. You have not shown me that there is anything to dispute here. --EMS | Talk 20:04, 15 December 2005 (UTC)
I had a look at the Wolfram intro: "Time Dilation : The apparent shortening of time relative [...]" -> hardly possible to be more confusing than that, since length contraction means the apparent decrease of a rod's length unit, and time dilation the apparent increase of a clock's time period ... Harald88 22:07, 15 December 2005 (UTC)
In reply to Jok2000: The name 'transverse Doppler effect' is a misnomer. Time dilation in transversal motion is unrelated to classical Doppler effect. The two have only one thing in common: a shift of the frequency of signals; the causative mechanisms of the frequency shifts are unrelated. Trying to force a comparison with classical Doppler effect would only introduce confusion.
I checked out the Wolfram link. Sure, it's concise, it's also so incomplete that it is incorrect.
I also feel that the current time dilation article is overburdened, but by the looks of it I would delete quite different passages compared to what you would delete.--Cleon Teunissen | Talk 22:21, 15 December 2005 (UTC)
I fully agree with Cleon that "transverse Doppler effect" is a misnomer, despite it being rather standard jargon. It has nothing to do with Doppler's theory, it just happens to be part of the same measurement. For explaining such mix-up terms are counter productive.

BTW, which passages are proposed for deletion? Harald88 22:28, 15 December 2005 (UTC)

Okay, let's suppose we fix up the wording of the green & red ships part. I must take exception with Harald88's edit of 15:40 27 November 2005 that prompted me to finally put the disputed-tag in there. He changed "is" to "seems to". Time dilation is an experimentally verified phenomenum. The article shouldn't need wishy-washy language. The "considering yourself non-moving" bit in the green and red ships section is also superfluous to the discussion, or at least in the wrong place. What EMS said about aliens and what not is utterly irrelevant. There are no meteorites landing on earth with odd half-lives of radioactive elements or any such thing, well that's an exaggeration, the equivalence principle takes care of physical experiments on that scale. Most assuredly, if the green ships were launched from earth and the red ships were parked relative to the Earth, the GIF would be totally incorrect -- again, experimentally verified. Haefel-Keating trumps all this thought-experiment silliness. So I still propose that the green/red ships part be deleted, it only agrees with Haefel-Keating if the green ships are still relative to the Earth or sun or something not moving too quickly around these parts. :) Jok2000 02:24, 16 December 2005 (UTC)

SRT is about observations, whereby what is measured (seems to be so) from one point of view (inertial coordinate system) is measured differently (does not seem so) from another point of view. Now that is a fact about the theory. If you remove the "seems to" at inappropriate places, you end up with self contradiction (or a multi-universe, but that is not officially agreed on!). Such sloppyness is exactly the cause of much confusion and debate in literature and it is good to avoid that mess here. Harald88 08:01, 16 December 2005 (UTC)
Haefel-Keating is not relevant to this since it combines general relativity and special relativity. Like it or not, that GIF is correct for green ships launched from the Earth that then go out a ways, turn around, and zoom past the Earth and the red fleet before turning around again and coming back home. However, the GIF is only concerned with the part where the green fleet zooms by the red fleet, or in between (and not including) the turnarounds. By contrast, the twin paradox does include a turnaround, and Haefel-Keating is was done on a spatially closed path. All that you are demonstrating is a lack of understanding about what time dilation and the twin paradox are about.
BTW - We may not have meteorites with strange half-lives around, but muons created in the upper atmosphere regularly make it down to the surface of the Earth even though is takes many, many times the half-life of the muon to get down here even at nearly the speed of light. The trick is that they are time dilated as they come on down. How that occurs is very much described that GIF. --EMS | Talk 03:18, 16 December 2005 (UTC)

[edit] What provides the clearest window on time dilation

I copy and paste from above.

Most assuredly, if the green ships were launched from earth and the red ships were parked relative to the Earth, the GIF would be totally incorrect Jok2000 02:24, 16 December 2005 (UTC)

Again, your objection seems to stem from a conviction that time dilation occurs if and only if a traveller makes a turnaround and rejoins the people he has departed from.

The GIF depicts the situation of, say, the outbound leg of the journey of the travellers. Let a string of space stations be situated from the Earth to Sirius, each say, one lightweek apart. Let those be the "reds". Let a fleet of traveling "green" ships travel to Sirius. The GIF dipicts the situation during the journey from Earth to Sirius. The GIF depicts how the lapse of green proper time and the lapse of red proper time relate to each other.

It a philosophical point, I suppose, as to what provides the clearest window on the properties of time dilation. An example: let there be two space-ships, one is moving inertially, the other is using rocket thrust to circle around the non-accelerating ship. That is an a-symmetrical situation and then the circling ship has consistently less lapse of proper time than the non-accelerating ship. Accumulation of time dilation is a function of difference in pathlength; the circling ship is clocking up more mileage, and in accordance with that the circling ship has less lapse of proper time. --Cleon Teunissen | Talk 10:18, 16 December 2005 (UTC)

Cleon - Good explanation. I will only add a couple points to it:
  1. See the proper time article for the math relating to Cleon's last example.
  2. Not only does the GIF work for the outbound leg of a round trip to Sirius, but aslo the inbound leg. That is the crux of the twin paradox. It fails in the view of the "green" fleet at turnaround because of how turnaround affects the green view of spacetime.
--EMS | Talk 11:34, 16 December 2005 (UTC)
My main conviction is that the GPS satellite system works. The red/green diagram requires the reader to make an assumption for it to be true, that is, it must be executed in a particular way to come out as stated. EMS loves to call it lack of understanding, but I did actually read the article the way you folks are arguing it the first time through, however I never operate with unwise assumptions, and went back through the argument leaving out the assumptions and discovered rather quickly that it is in error. Jok2000 13:51, 16 December 2005 (UTC)
The GPS is a gravitational time dilation phenomenon. That material used to be a part of this page, but was exported some months ago to the other page, although this page still references it. Gravitational time dilation involves accelerated frames of reference, while velocity time dilation in an effect of inertial frames of reference. There is a difference:
  1. In the velocity case, each observer sees the other clock as running slow.
  2. In the gravitational potential case, if one observer sees the other clock as running slow, then in the view of the other observer the first clock is running fast.
You are correct that there is an apparent contradiction in each clock ticking slow in the other's viewpoint. However, when you work through the math, you find the Lorentz contraction and the relativity of simultaneity combine to with time dilation to make special relativity self-consistent. So whether you like it or not, the GIF is correct. --EMS | Talk 18:39, 16 December 2005 (UTC)
I don't know if it's much of a reference, since I wrote it, but the math you deleted the first time I edited this page about 2 months ago, which I've seen in several reputable sources, states that the GPS system's time dilation is a combination of 3 factors, SR, GR and something I am wholely unfamilar with, the Sagnac effect. The GIF cannot be correct, because it suffers from the same issue as the Twin Paradox, when it is viewed as a paradox (as opposed to when it is resolved). It is easy to see from the GPS SR equation that the effect is continuous, not at turn-around. Suppose a budding GPS (or Gallileo) engineer came to this page? He'd be fired on the spot if he quoted it without laughing. You seem to want to describe propagation delay, although you do seem to know what time dilation is. Jok2000 20:34, 16 December 2005 (UTC)
Excellent! I now understand your gripe.
This is as I thought: You do not appreciate the symmetry of the SR time dilation effect. You are quite correct that the GPS effect is asymmetrical, while what is being displayed here is symmetrical. However, just look at your own writing:
the GPS system's time dilation is a combination of 3 factors, SR, GR and something I am wholely unfamilar with, the Sagnac effect.
So SR is not the whole story here. You also note that
It is easy to see from the GPS SR equation that the effect is continuous
which is true, but it is also true of the red-green ships model in either frame of reference. In general, the GPS time dilation factors are computed for an Earth-centered inertial frame of reference. In a GPS-based frame of reference, the same SR slowdown would be present for the Earth, but different GR values (and to a minor extent Sagnac effect values) would be present to compenstate for the SR effect being symmetrical.
A warning - You are not going to resolve this philosophically. SR is based on mathematics, and to show a problem you must show that the math is inconsistent. People have been trying that for over 100 years, and noone has succeeded. In fact, the success is Hermann Minkowski's 1908 proof that SR is really self-consistent. --EMS | Talk 21:55, 16 December 2005 (UTC)
My guess is that the depiction in the GIF seems incorrect to you, because somewhere along the line you make some inappropriate assumption. The GIF is not intended as paradoxical. The GIF depicts aspects of motion in Minkowski space-time. It is an axiom of special relativity that Minkowski space-time geometry is the proper geometry to use. The GIF depicts a theorem of Minkowski space-time geometry.--Cleon Teunissen | Talk 21:53, 16 December 2005 (UTC)

[edit] Rate versus amount of lapse of proper time

In my previous entry I used the expression 'accumulation of time dilation'. That needs some clearing up, I think.

In the case of time-dilation-in-transversal-motion (depicted in the GIF) there is not a one-on-one relation between red proper time and green proper time. The situation is symmetrical however; red is to green what green is to red. What is compared in the GIF is rate of lapse of proper time, and the determining factor is relative velocity.

In the a-symmetrical case of one space-ship in inertial motion, and another space-ship using rocket thrust to circle around it, there is a non-symmetrical time dilation and consequently a buildup of difference in amount of elapsed proper time. For difference in amount of elapsed proper time the determining factor is difference in pathlength.

Earlier I glossed over that by using the expressions 'less lapse of proper time' and 'more lapse of proper time', not specifying whether it referred to 'comparative rate of proper time' or 'amount of proper time'.

Presumably the symmetrical time dilation and the a-symmetrical time dilation are different aspects of the same thing, but I find it not straighforward to envision how they are related. The a-symmetrical time dilation is still somewhat intuitive, it's the symmetrical time dilation that boggles the mind.

I concentrated on the symmetrical case because (1) the muon example (2) generally, symmetry is the physicist's best friend. --Cleon Teunissen | Talk 12:39, 16 December 2005 (UTC)

There is in principle no difference between "symmetrical time dilation" and "a-symmetrical time dilation": they are both calculated with the same equations, relative to inertial frames. Harald88 12:50, 16 December 2005 (UTC)

[edit] Time dilation aspects of the GPS technology

I copy and paste from above:

I don't know if it's much of a reference, since I wrote it, but the math you deleted the first time I edited this page about 2 months ago, which I've seen in several reputable sources, states that the GPS system's time dilation is a combination of 3 factors, SR, GR and something I am wholely unfamilar with, the Sagnac effect. Jok2000 20:34, 16 December 2005 (UTC)

OK, lets review the GPS.
The Sagnac effect is a fundamental geometric effect. Let's put it this way: the Sagnac effect is a theorem of light propagation in newtonian absolute space and time, it's a theorem of Minkowski space-time geometry, and it's a theorem of the Riemannian geometry that is applied in GR. It's a theorem of any geometry that is suitable for modeling physics. The Sagnac effect is so fundamental that all theories predict it.

All terrestrial clocks that are located at sealevel have the same rate of proper time as compared to each other, and thus keep running in synchrony with very little adjustment. For a satellite in orbit there are two time dilation factors.
(1) Since it is orbiting, the satellite is clocking up more mileage than the terrestrial clocks, wich corresponds to less lapse of proper time than terrestrial clocks. This is non-symmetrical time dilation.
(2) Since the satellite is higher up in the Earth's gravitational well there is correspondingly more lapse of proper time. This is also non-symmetrical time dilation.
For GPS-satellites, in their orbits with a period of 12 hours, the gravitational time dilation is the strongest contribution, and for the clocks on the GPS satellites there is more lapse of proper time as compared to terrestrial clocks.

I have familiarized myself with the physics problems that the engineers of the GPS system have solved, and it is with that knowledge as background that I present my views on time dilation. --Cleon Teunissen | Talk 22:06, 16 December 2005 (UTC)

[edit] Possible new animated GIF

Cleon -

I have an idea for a new animated GIF that may help people like Jok2000 to see what is going on with velocity time dilation being symmetrical. What you need to show is the red fleet passing the green fleet. Notice my emphasis on the word "fleet". This would not be one ship, but each as a series of ships. The ships will have spaced thenselves out at intervals of 0.866 light-seconds, so that a red ship will move between successive green ships in one second in the green ship frame of reference and vice-versa. Note that this spacing out and a clock synchronization was done within each fleet, with the master clocks (in the lead read and green ships) set so that they would read zero as they passed each other.

Now look at this in the red frame of reference. At red time t=0 all red clocks read t=0. Alao, the lead green clock reads t=0. Furthermore, the red ships are at locations 0, 1, 2, 3, 4, ..., but the green ships are at locations 0, -1/2, -1, -3/2, -2, ... . This is of course due to the Lorentz contraction. Even more interesting are the clock settings in the green fleet at t=0: 0, 3/4, 3/2, 9/4, 3, ... . This is due to the relativity of simultaneity. Now here is a table noting the places of the green fleet in the red reference frame (in units of 0.866 light-seconds), and the clock times of the green fleet and 1/2 second intervals of red time:

Red time Green ship 1 Green ship 2 Green ship 3 Green ship 4 Green ship 5 Notes
  place clock place clock place clock place clock place clock  
0.0 0 0 -0.5 .75 -1.0 1.5 -1.5 2.25 -2.0 3.0 Green ship 1 at Red ship 1
0.5 0.5 0.25 0 1.0 -0.5 1.75 -1.0 2.5 -1.5 3.25  
1.0 1.0 0.5 0.5 1.25 0 2.0 -0.5 2.75 -1.0 3.5 Green ship 1 at Red ship 2
1.5 1.5 0.75 1.0 1.5 0.5 2.25 0 3.0 -0.5 3.75  
2.0 2.0 1.0 1.5 1.75 1.0 2.5 0.5 3.25 0 4.0 Green ship 1 at Red ship 3

Notice some things: When Red ship 1 is next to green ship 2, the green clock reads 1 second! Simlarly, when red ship 2 is next to green ship 1, the red clock also reads 1 second. So there is the symmetry, courtesy of the time offset of the relativity of simultaneity. This possibly could be animated for better effect. --EMS | Talk 04:01, 17 December 2005 (UTC)

Good idea! Indeed, that's much more clear. Harald88 05:09, 17 December 2005 (UTC)

Hi EMS,

the reason the GIF came out as it did is that I tried to steer away from explicit depiction of length contraction, as that would add complexity. Of course, time dilation, length contraction and relativity of simultaneity are interconnected; any animation that has one of them has (implicitly or explicitly) all three of them.

My view is that the article should in equal measure acknowledge the two aspects of velocity time dilation.
(1) Symmetrical velocity time dilation. Comparative rate of lapse of proper time. It is determined by relative velocity.
(2) Non-symmetrical velocity time dilation. Comparison of amount of proper time that has elapsed. It is determined by difference in pathlength. (Example: one spaceship moving inertially, a second space-ship circling the first. The second ship's worldline in space-time is longer then.)

What needs to be avoided in the article is a suggestion that acceleration is a determining factor in any form of time dilation. Acceleration breaks symmetry, but time dilation is not a function of acceleration.

As it is, the article is not consistent. The statement, "gravitational time dilation involves accelerated frames of reference" is untenable. Satellites in orbit are moving inertially, and for satellites orbiting at different altitudes a non-symmetrical time dilation is observed: different amounts of lapse of proper time as compared to each other.( see the entry about GPS-technology for more details) --Cleon Teunissen | Talk 09:54, 17 December 2005 (UTC)

There is a gravitational (or acceleration) field between ourselves and the satellites. So the vicinity of the Earth is an accelerated frame of reference. It also is a curved spacetime. I personally would like to leave GR out of this mix, although some reference is needed. In the end, you have really hit the nail on the head by noting the path length is what is important. However, you have goofed in one respect: The "length" of a world line is the proper time elapsed while traveling along it: When the second ship is circling the first (and the first ship is moving inertially), it is the first ship that has the "longer" world line.
As for the proposed GIF: This may not be the right place for it, but I think that it may be useful. --EMS | Talk 16:21, 17 December 2005 (UTC)
The problem, if I understand it correctly, is that EMS defends Einstein's original GRT interpretation while Cleon defends the current mainstream interpretation. If I'm right about this, then also Cleon was right with his objection: if the statement "gravitational time dilation involves accelerated frames of reference" is disputed, it can not be presented as fact. Harald88 17:42, 17 December 2005 (UTC)
You gentlemen have discussed and expanded on my original quibble admirably, and why it did not qualify as a dispute and a resolution is a bit of a puzzle, however I'll assume its just semantics. I'm off on a trip for a couple of weeks, so I'll leave you with a thought while I'm gone: symmetry is easily achieved with only 2 frames of reference, however with 3 one is forced to re-evaluate the situation. As much as the sci-fi fans might like 2 fleets of spaceships, aliens and distant outposts in the galaxy, we have an active system (GPS) we can study closer to earth and if this were my article, I would give priority to the material and the here and now. So as a minimum, the spaceships .gif would require a 3rd reference frame, the one they originated from, preferably the earth, and then proper calculations could be made. As for philosophical points, I have read Einstein's "Ideas and Opinions" and it speaks volumes for the general scientific philosophy of the 1950s. Jok2000 16:47, 18 December 2005 (UTC)
EMS is of course correct in pointing out that in Minkowski space-time geometry the natural definition of length-of-a-worldline is the proper time along that worldline. In the example of one space ship moving inertially and a second spaceship circling the first then as measured in the inertial frame (co-moving with the first ship), the spatial length of the two paths is different, the circling path being longer spatially.
It is my understanding that the amount of gravitational time dilation is a function of how deep a clock is down a gravitational well, but that it is not directly a function of whether the clock is resting on the surface of a gravitating body, or in orbit around the gravitating body. (For the clock in orbit there will be an asymmetrical velocity time dilation, in accordance to the orbital motion.)
The expression 'being-in-an-accelerated-frame of reference', is not quite synonymous to 'being in curved space-time'. The expression 'being-in-an-accelerated-frame of reference' also emcompasses 'being in an uniform gravitational field'. Gravitational time dilation correlates with 'being-in-curved-space-time. So when an object is being accelerated while moving in Minkowski space-time, I categorize the asymmetrical time dilation associated with that as an aspect of velocity time dilation.
I agree with EMS that it is best to discuss first velocity time dilation, and treat gravitational time dilation separately. I'm currently working on another animation, which I hope will be useful. I will keep my big mouth shut until that is finished. By the way, my signature is changed, I have been granted a change of user name from Cleon Teunissen to Cleonis. --Cleonis | Talk 21:45, 20 December 2005 (UTC)
Harald88 wrote "The problem, if I understand it correctly, is that EMS defends Einstein's original GRT interpretation while Cleon defends the current mainstream interpretation."
It does seem a matter of interpretation. See also the following article by Peter M. Brown, about GR interpretation (PDF 67 KB). I am committed to the interpretation where the concept of gravitational field is exclusively associated with curvature of space-time. Einstein disagreed with that, as a matter of principle, and he did have a point, it's worthwile to appreciate the depth of Einstein's considerations. --Cleonis | Talk 21:45, 20 December 2005 (UTC)
*Sigh*. As a practial matter, gravitational time dilation is associated with gravitational potential, and there are no "asymmetrical" time dilation effects that do not fall into that category. In the rotating disk example, the central observer is not in an accelerated frame of reference, but because of his rotation his view of spacetime is accelerated. Because inertially moving objects are accelerated in this frame of reference, I say that a gravitational field exists in this view of spacetime. It is as simple as that. Curved spacetime makes it so that all observers will perceive inertially moving objects accelerating with respect to themselves in at least some regions of the spacetime. Yet to me a gravitational field is defined by the result and not the cause. --EMS | Talk 05:15, 21 December 2005 (UTC)
That will soon (hopefully) be handled in the Twin paradox, as originally it was about Einstein's relativity concept. Harald88 07:59, 21 December 2005 (UTC)

[edit] Origins of time dilation

I apologize if I am supposed to write this in a different section. Please forgive my ignorance.

The introduction states that Time Dilation originated out of Einstein's Special Theory of Relativity. This is incorrect. Time Dilation was one of two parts of the Fitzgerald-Lorentz Contraction introduced in 1904, whereas Einstein's theory, introduced in 1905, was merely expounding on that —The preceding unsigned comment was added by 24.10.164.230 (talk • contribs).

Sectioning added; welcome aboard! You may wish to create a user account, to avoid confusion with other users of your IP address (I count three vandalism warnings given to it). --Christopher Thomas 06:13, 20 December 2005 (UTC)
On re-read, only two warnings. I've also added the "welcome aboard" template spiel, which contains links to useful tutorials about editing. --Christopher Thomas 06:18, 20 December 2005 (UTC)
There are a number of errors in this anon's statements:
  1. The Lorentz-Fitzgerald contraction dates from 1889, not 1904 [1].
  2. Time dilation is not a part of it at all.
  3. Time dilation is a prediction of the Lorentz transformations, first derived in 1887 and rediscovered by Lorentz in 1899 - E4mmacro 21:44, 21 December 2005 (UTC) What is the reference for 1887? see Joseph Larmor for a 1897 reference? Is 1887 a misprint? E4mmacro 21:44, 21 December 2005 (UTC) - I see that 1887 is probably a reference to W. Voigt's paper. Voigt's transformation involves a time dilation of γ2, rather than γ. All the experiments seem to confirm the Lorentz transformations, not the Voigt transformation (which also gives a universal speed of light. See Woldemar Voigt page E4mmacro 06:37, 29 December 2005 (UTC)

Both time dilation and the Lorentz-Fitzgerald contraction arise from the effects of the Lorentz Transformations. In 1904, Lorentz published a famous article on how the Lorentz Transformations of an electromagnetic field correctly account for their observed properties, but even at that time failed to grasp the significance of the time transformation for time itself. (The view at the time was that the time transformation was a mathematical artifact.)

From the number of times the words, "seems", "appears", and variants are used, I get the distinction impression that many contributors still consider the time transformation as a mathematical artifact. E4mmacro 10:40, 30 December 2005 (UTC)
  1. Einstein was not merely expounding on the known. Instead he introduced a truly radical way of looking at and dealing with the Lorentz transformations. Before Einstein, everyone assummed that Newtonian physics underlaid everything, and that even the Lorentz Transformations had a classical cause. Einstein instead said that they are the real unerlying rules of physics, and that their descriptions of space and time were real.
So it was Einstein who took the admitedly known Lorentz transformations and its admitedly known time transformation into his theory, but used them to predict the previously unknown phenomenon that someone traveling in a fast enough spaceship will return having aged less than those who stayed at the home planet. --EMS | Talk 15:48, 20 December 2005 (UTC)
That is all more or less correct (undisputed), I think, until the last paragraph: time dilation is more general than the twin effect, it's foremostly the apparent slowing down of a clock that is moving relative to one's own clock. And that has, as anonymous correctly claimed, already been proposed by Lorentz (and next apparently forgotten by him!) as well as by ... (now I have a blank, sorry); only they didn't realise the reciprocity of those effects, but that was published by Poincare before Einstein finished writing his paper about it. In any case, it originated out of electromagnetic theory, and is used in special relativity, which BTW isn't exclusively of Einstein: metaphysical time and space are not official part of the principle theory that is called SRT. But that doesn't make, IMO, the intro really wrong; why can't one say that it's (also) a consequence of SRT and GRT? It's just slightly inaccurate. Harald88 17:25, 20 December 2005 (UTC)
I can't see any inaccuracy in the intro as written, unless you want to argue that time dilation is not a part of the theories of relativity. Also, even if others were aware of the time effect of the Lorentz transformations, they certainly did not give it the physical significance that Einstein did. Poincare was headed in the direction of SR, but did not quite get there, or at least not as I understand it. The view that I have encountered is that Einstein, although he was not the first to work with the Lorentz transformations, was the first to interpret them correctly as the underlying rules of the universe. --EMS | Talk 17:40, 20 December 2005 (UTC)
That definitely was Poincare, despite the nonsense that is told about him; nevertheless, we agree that that that doesn't make the intro wrong; and it's certainly counterproductive to start the article with talk about a dispute. However, the way it is stated now (I had not noticed it had changed) looks even better to me.Harald88 15:06, 24 December 2005 (UTC)
I think it is better if this article does not express opinions about who "really understood" time dilation, i.e. Einstein was smarter than his pre-decessors. So what? The article now states the facts, that Voigt, Larmor and Lorentz thought that moving clocks ran slow. The place to argue (if you must) about who was smarter is in the page on special relativuty? E4mmacro 09:16, 30 December 2005 (UTC)
If someone thinks that it is a fact that according to Voigt (what year?) moving clocks run slow, please cite him on that. I think that he didn't think so, at least not before the others came with that. It is a feact however that accoring to Einstein (1905), moving clocks run slow. Harald88 12:54, 12 February 2006 (UTC)

[edit] Operational definition of gravitational time dilation

I copy and paste from above:

[...] to me a gravitational field is defined by the result and not the cause. --EMS | Talk 05:15, 21 December 2005 (UTC)

It is also my opinion that the concept of gravitational field should be defined in terms of unambiguous result, that is: an operational definition.

First an example of no gravitational field present (Minkowski space-time): Let there be an empty (no air inside), rotating space-station, situated in Minkowski space-time. The space-station is just an emtpy hull. If you are inside that space-station, and you are not in contact with the hull, then as long as your center of mass does not move relative to the space-station's center of mass you will float indefinitely. As long as you float there will be no time dilation between you and a reference clock outside the station (A reference clock that does not move relative to the station's center of mass.)

Second example: gravitational field present (curved space-time): If you are orbiting a planet then you are following an inertial path in space-time; you are floating, and if your orbit is circular, then your distance to the planet remains constant. The operational definition of gravitational time dilation is that it occurs even in the absence of any mechanical force. There is gravitational time dilation, both in the case of resting on the surface of a planet, and in the case of orbiting a planet.

I agree with EMS that definitions should be stated in terms of observable results. Certainly a definition should never invoke some or other hypothesized cause. --Cleonis | Talk 02:39, 23 December 2005 (UTC)

Very right. But that's what the article does, isn't it? Harald88 15:00, 24 December 2005 (UTC)

[edit] Clarification sought

quote: "Time dilation occurs with respect to temporal coordinate systems set up in this manner."

A non-physicist reader might be forgiven for thinking this means time dilation does not occur unless the clock synchronisation procedure is used. He could then ask, "So clocks never ran at different rates until sometime in the late 19th century? It is just an illusuon?". I guess the time dilation always occured, but it is always difficult to write about this without making it sound like a mere "appearance" on the one hand and a "reality" on the other.

E4mmacro 22:51, 21 December 2005 (UTC)

It's not just "mere appearance", but it's difficult to explain. Maybe something like "it's a real effect, but the measured quantity depends on the measurement"... Harald88 15:14, 24 December 2005 (UTC)

[edit] request on editing

Hi please try not to save endless times small incremental edits; it makes for a horrible mess on the article spaces -- see for example: http://en.wikipedia.org/w/index.php?title=Time_dilation&action=history If you have internet problems or computer problems, you can use a text editor for the purpose of saveguarding your edits. Thanks, Harald88 15:22, 2 January 2006 (UTC)

[edit] www.wbabin.net?

There are more and more links to articles on wbabin.net and it has some interesting articles; but apparently those are in no way peer reviewed nor handed in with peer recommandation -- perhaps the editor decides if he likes the looks of it? Thus I think that that site is not a good source, so that any link to an article it should only be included in the exceptional case that there is consensus about that link being helpful. Any other ideas? Harald88 22:06, 16 January 2006 (UTC)

[edit] Animation of nonsymmetric velocity time dilation

Asymmetric velocity time dilation
Asymmetric velocity time dilation

I have created an animation showing asymmetric velocity time dilation. This applies for example in the case of particles following a circular trajectory in a particle accelerator. Historially, the asymmetrical case is interesting, because it served to suggest the equivalence principle. Any object that is being accelerated by a force is pulling G's.

The acceleration with respect to the inertial frame has a symmetry breaking effect. The operative factor for the amount of difference in lapse of proper time is the difference in spatial distance travelled.

A possible disadvantage of this animation is its size: 114 KB. I think that is very large. --Cleonis | Talk 15:17, 28 January 2006 (UTC)


I like the animation, it's very simple. But it definitely needs a simple explanation...what kind of a caption would you put to go along with it?Pkeck 05:02, 31 January 2006 (UTC)

If you click on the image you get the description page. What is written there is pretty much what I would add as accompanying text if the animation is included in the article. --Cleonis | Talk 05:22, 31 January 2006 (UTC)

[edit] Time Dilation Equation

Shouldn't the equation at the top of the page be: T_1 = T_0 \sqrt{1 - v^2/c^2}

Not: T_1 = {T_0 \over \sqrt{1 - v^2/c^2}} [unsigned by 86.0.228.241]

No it's correct, but the way it is presented is confusing, and even not sufficiently defined. I'll try to rephrase it. Harald88 12:57, 12 February 2006 (UTC)


Oh, I see, got the T's mixed up. But I would think the equation should be in terms of T0, since that would probably be the given (just like relativistic mass is in terms of m0, and length contraction is in terms of L0). Plus, it's interesting to note that \begin{matrix}\frac{L_1}{T_1}\end{matrix} = \begin{matrix}\frac{L_0}{T_0}\end{matrix}. Well, I suppose it doesn't matter. Thanks for the response. --24.236.173.129 18:02, 12 February 2006 (UTC)

Actually, this thing L1/T1 = L0/T0 is not interesting at all. See http://en.wikipedia.org/wiki/Special_relativity_for_beginners under 'Caveats and Warnings' - DVdm 6-May-2006


You are right that that can be confusing. Note that T has memory. We can replace T_0 by a more standard notation with primed for co-moving, and unprimed for rest frame; but I think that your suggestion is the clearest. OK I change that. Harald88 22:53, 12 February 2006 (UTC)

Wow, now the equation is really confusing, especially with that explanation of the variables "where T is the time period as measured by a stationary observer of the time T0 between two ticks on a moving clock, traveling at velocity v relative to the stationary frame." I see what you're saying, but why be so confusing. Ok, how about this:

T_1=T_0\sqrt{1 - v^2/c^2}

Where T0 is the time experienced by a stationary observer, T1 is the time experienced by an observer moving at velocity v, and c is the speed of light in a vacuum. --Magnus VII 22:14, 13 February 2006 (UTC)

I have no clue what could be confusing about it. Perhaps you want to first explain in one sentence that the time between two ticks is (by definition) the time period? If you like, go ahead! But by all means avoid to use without definition the ambiguous word "time", and define about time on which clock you are talking! Usually time means coordinate time, but not here. And no, the indice "0" is commonly used for "proper", but the indice "1" is not commonly used for the frame of observation/stationary frame. Often used alternative is one version back (T and T'). People who simplify it to such an extreme level of ambiguity usually completely misunderstand time dilation... Harald88 22:01, 14 February 2006 (UTC)

[edit] Voigt and SR

Just so that you know where the Voigt business came from: [2]. BTW - I did not put that reference into this article. --EMS | Talk 19:24, 12 February 2006 (UTC)

It looks correct about Voigt: "Voigt who was writing on the Doppler shift when he wrote down the transformations." The Doppler shift is not about time dilation. Harald88 22:00, 12 February 2006 (UTC)
To my knowledge the transformations that Voigt wrote didn't play a part in the exchange of ideas surrounding relativity.
What I think is interesting is that Voigt's transformations are generally applicable in the context of wavemechanical equations; the paper by Voigt was "Über das Doppler'sche princip".
I just found this webpage that discusses connections between doppler shift and Lorentz transformations, suggesting a connection between the Lorentz transformations and wave mechanics. --Cleonis | Talk 20:20, 12 February 2006 (UTC)
Oops, the site above is an anti-relativity site. I should have read it more carefully first. --Cleonis | Talk 20:27, 12 February 2006 (UTC)
A quick look at the first page yields: "We also know that Relativity is true and that it involves the Lorentz transformation" Thus that site may be anything, but hardly an anti-relativity site. Harald88 22:00, 12 February 2006 (UTC)
Gabriel LaFreniere opposes relativity in the sense that he assumes that every object has a particular velocity with respect to the ether. It is one thing to accept the Lorentz transformations, and another thing to accept the axiom of special relativity that there is full blown symmetry of all inertial frames of reference. Unfortunately, many people who accept the Lorentz transformations, but reject the full blown symmetry, claim to be supportive of special relativity, since they feel that the full blown symmetry shouldn't have been incorporated in the first place. It is very awkward that this mis-appropriation of the expression 'special relativity' occurs, it leads to a lot of babylonian confusion.
Apart from that, I think Gabriel LaFreniere's site is very interesting, I hope to gain more understanding of the connection between Doppler shift and the Lorentz transformations through his animations. --Cleonis | Talk 10:55, 13 February 2006 (UTC)
Cleonis, on the symmetry question and those who believe in an absolute rest frame. If, as Lorentz appeared to think and Ives too, one might say that there is an aether, or absolute rest frame; the speed of light is isotropic in this rest frame, and the length and time rates change for moving objects (as a function of velocity relatibve to this rest frame). One can accept the clock synchronisation procedure in moving frames leading to Lorentz's local time as shown by clocks in moving frames when so synchronised. A new measured-velocity addition law follows. Then measured-cordinates in all other reference frames are related to the mesured-coordinates in the rest frame by the Lorentz transformations. It then follows that the rest frame is identical to any inertial frame of special relativity. The symmtery properties of the measured-coordinates follow from the equations. Thus, I think for Lorentz the symmetry is a symmetry of the coordinates defined by a certain convention. It is not a symmetry of real contractions, which Lorentz woudl say was illogical. He can still believe that for the real lengths and real times (i.e. defined relative to the rest frame) there is no symmtery; objects moving faster are contracted more. That is, he says "one of these rest frames (I don't claim to know which one) is the rest frame", the length contrations and time dilation predicted by special relativity in frames moving wrt this rest frame are real, the symmetry lies only in the way the coordinates are defined, a symmetry between measured-lengths and indicated-times". He hasn't said anything wrong, and can't be contradicted. He can just be criticised for the style of expression (i.e. you could say it is not necessary to assume a rest frame, it adds nothing important). Or am I missing something? E4mmacro 22:40, 11 April 2006 (UTC)

[edit] Senselessness

I know, it makes no sense, anyway! If universe is a closed system, conservation of momentum takes place. So, at, before, during, after the big bang, momentum should be the same, what ever happend. Therefore there exists a point of view (and so a lot of frames TypeX), where momentum is zero. But, universe contents energy, therefore objects are moving relative. But, an object with zero momentum in a frame TypeX "has speed zero" and therefore the highest rate of time. In this sense, there is an absolute frame. But, all macroscopic objects in the universe are very close to rest and all object with relativistic speed, we observe, are moving relativ to TypeX and, therefore are timedeleated. Still the laws of physics are the same for all inertial systems and there is no contradiction between a fixes frame and RT. ErNa 09:30, 12 April 2006 (UTC)

[edit] Gravitational redshift/time dilation is now crappy

It is an often heard misconception that photon's "fall" so that light speed increases and the frequency increases. Instead, light speed decreases but in steady state that's irrelevant: the only thing that matters is the difference in local clock rate. I have papers about that somewhere (starting with Einstein 1911) but I won't have much time to bother about this in the coming weeks. Anyway it's well explained elsewhere on this page as well as in the redshift article, if it hasn't been messed up of course.Harald88 22:13, 12 February 2006 (UTC)

I'm pretty sure that "light speed" stays constant. Thats one of the postulates of relativity. What are you trying to say about light speed decreasing? User:fresheneesz 128.111.95.147 21:51, 10 April 2006 (UTC)
This actually depends on how you define your coordinate system. The problem is especially noticeable when trying to build a coordinate system to describe a black hole. While my personal preference is for coordinate systems where the speed of light is treated as constant, you can certainly construct ones where it isn't that end up being mathematically equivalent. --Christopher Thomas 03:52, 11 April 2006 (UTC)
It's not a postulate of GRT. Einstein's basic calculations of bending of light (1911, improved in 1915/1916) rely on Huygens bending - which, as every physicist knows, depends on local differences in the speed of light. In fact he explains it very clearly in his 1916 paper which is linked to from the general relativity page. Light speed is lower near the earth, quite the opposite of what "falling" suggests! Harald88 06:27, 21 April 2006 (UTC)
One might add that if the speed of light were not lower near the earth we wouldn't even existed since there wouldn't be any gravitation to hold things together.
It's really funny how little people (physicists including) know about basic physics. Most of them don't even know that the reason for gravitation is this variable speed of light. They "assume" that speed of light is "constant". It happens 90 years after Einstein's discovery of the mechanism of gravitation.
But if one tries to explain in Wikipedia the mechanism that Einstein proposed then your page gets deleted by someone who never understood Einstein's idea and so he is against it. As Einstein said: "There are two infinite things ...". Jim 06:23, 3 May 2006 (UTC)
I think you misunderstood that. According to GR light travels at constant speed in a straight line - it's space itself that's curved. Catch up on your reading, folks. Shinobu 17:39, 13 June 2006 (UTC)

[edit] Revert by Harald88

I was wondering why you reverted the explanation of "lower potential in a gravitational field". First of all, that is a long drawn out way of saying "stronger gravitational field" as i put in parens. My version (i think) is easier to understand, and shorter at that. Secondly, accellerating reference frames are postulated to be the same as reference frames in a gravitational field, so why did you remove the addition of accelleration to the "gravitational time dialation" part? User:fresheneesz 128.111.95.147 21:51, 10 April 2006 (UTC)

It's not the field strength but the potential that matters - just as in electricity it's not correct to replace potential by strength. And what is regarded to be an accelerated frame in SRT can be regarded as an inertial frame with gravitation in GRT - which isn't at all what you made of it! When we assume an accelerating frame (without gravitation) at low speed, then we have no time dilation but only a Doppler effect instead. Harald88 12:55, 12 April 2006 (UTC)
Hmm. But doesn't field strength increase directly proportional to gravitational potential? I don't see the difference here. In electronics it would be just as correct to replace potential with Efield strength, but.. it would be mathematically much harder. Also, when you say "what is regarded to be an accelerated frame in SRT can be regarded as an inertial frame with gravitation", that is true - but accelleration is not gravity - especially when talking to people who may not be well versed in general relativity. Gravity does not mean accelleration, but they have equivalent effects, which is why I added both into the explanation. Also, at low speeds you have low time dialation - not none. Fresheneesz 10:29, 20 April 2006 (UTC)
It's mathematically just as erroneous to confuse gravitational field strength with potential as in its electrical equivalent: one can make a zero field strength zone at high potential. Apart of that, acceleration is indeed not gravity; most important difference is that acceleration does *not* directly relate to time dilation, while gravitation and speed do (just look at the equations, or read the article on Twin paradox). Harald88 06:37, 21 April 2006 (UTC)
? I was under the impression that accelleration *does* directly relate to time dilation, and I would have cited the twin paradox myself. In the twin paradox, one twin is older than the other *because of his accelleration* - not because of his speed.
As for potential, you're saying that if one person was directly between two large point masses (ie he had no net force on him), then he'd be in a different frame than someone infintely far away from those masses (also with no net force on him)? Fresheneesz 09:04, 21 April 2006 (UTC)
That's wrong: time dilation is a function of speed v, not of acceleration dv/dt - as also explained in Twin paradox. It's a similar error as mixing potential with field.
And I'm saying that GRT's time dilation is a function of gravitational potential, and not of gravitational field strength (an easily verifyable fact). That implies a redshift even of light that is emitted from gas between two stars (double star). Harald88 13:25, 21 April 2006 (UTC)
Isn't potential a function of the strength?
I'm pretty sure that ones time dilation *does* depend on their acceleration. How else do you explain the twin paradox? I thought that one twin accelerates away, then deccelerates and accellerates back - finnally deccelerating again and stoping at earth. Both had the same speed relative to eachother, but the one that underwent acceleration had a bit of time dilation that *does not* depend on one's inertial reference frame. Am I wrong here? Fresheneesz 22:46, 22 April 2006 (UTC)
Acceleration only indirectly affects time dilation, as explained in twin paraodox. But twins can have had equal accelerations during equal times and still end up with a time difference, because time dilation is a direct function of speed and not of its derivative. If that article isn't clear (indeed it's an often misunderstood subject), please use the corresponding Talk page. Harald88 11:55, 23 April 2006 (UTC)

Let me see if I can straighten this discussion out a bit, but I would start off by saying the this is about gravitational time dilation, which is a different topic. Fresheneesz wrote:

As for potential, you're saying that if one person was directly between two large point masses (ie he had no net force on him), then he'd be in a different frame than someone infintely far away from those masses (also with no net force on him)?

The simple answer to that is "yes". At the least, the clock of the observer between the masses would tick slower that that of an observer distant from the masses.

Gravitational time dilation appears in accelerated frames of reference. In this case, the people being accelerated are constantly shifting from one intertial frame of reference to the next. When you work througth he math, you find that the magnitude of the effect is proportional to the sqaure of the change in velocity for a freefalling object as it goes between the positions, which is itself given the gravitational potential, or Φ = gh. I hope this settles the issue. --EMS | Talk 00:42, 23 April 2006 (UTC)

Ok, thanks EMS. The issue isn't quite solved tho, since I would like to make it clear that acceleration causes "gravitational time dilation" - not just difference in potentials. Fresheneesz 11:18, 23 April 2006 (UTC)
Precision: Gravitational time dilation appears when one uses an accelerated frames of reference and pretends that it's an inertial frame of reference. It disappears when one takes into account that it's an accelerated frame, as it's fully covered by the Doppler effect. In fact, that's how Einstein, using the equivalence principle, predicted gravitational time dilation in the first place! He assumed no time dilation effect from acceleration. In agreement with that, acceleration in ultra centrifuges has been found to have no measurable time dilation effect on radioactive particles - only their speed matters. That's why I revert such erroneous statements. Harald88 11:55, 23 April 2006 (UTC)
Hmm, thats very interesting. However, I wouldn't say its "fully" covered by teh Doppler effect - just as much as inertial time dilation isn't "fully" covered by the invariance of c. We can derive the dilation from the invariance of c and the doppler effect, but that doesn't mean that we shouldn't say that accelleration causes time dilation.
I'm quite interested in the effects of gravity and acceleration in relativity, but I can't find anything on it here on wikipedia. I'm simply trying to give the accelerative effects of relativity their fair spot. Fresheneesz 21:11, 23 April 2006 (UTC)
Theory as well as experiment can't be denied in Wikipedia by editors who are "saying something else". In relativity, acceleration has no other effect on time dilation than by means of speed change - that's all there is to it.
About acceleration, see twin paradox (I already told you, couldn't you find it?); and about gravitation, see general relativity. See also redshift (soon to be a featured article candidate). Harald88 22:48, 23 April 2006 (UTC)
I've read over some of the twin paradox a couple times now. Its still very unclear what you mean. You say "acceleration has no other effect on time dilation than by means of speed change" this is obviously true because acceleration is only a speed change. However, from what I've gleaned from all this, acceleration *does* have an effect on time dilation, but only if you choose an accelerating reference frame. Obviously, one twin must choose an accelerating reference frame. Its also unclear why " physicists have increasingly treated general relativity as a theory of gravitation, rejecting its aspirations to be a theory about relative motion including acceleration" (quote at end of twin paradox). Obviously there are effects of accelleration that aren't explained by inertial time dilation - despite the fact that they come from the same principles. Fresheneesz 03:21, 26 April 2006 (UTC)
What I meant is relevant for your last sentence: there is no known (measured or predicted) "time dilation" effect of acceleration that is not already accounted for by what you here call inertial time dilation. Cheers, Harald88 21:20, 28 April 2006 (UTC)
Hi Fresheneesz, don't worry. Physics is a very vast field and no physicist can be an expert in all areas. So they fight against those, that say, RT is principally wrong. But, they do not spend efforts to find out, what RT really means. RT is old fashioned! They main point is: laws of physic to not depend on the related inertial frame. That is clear. But, this does not say: there is no inertial frame of absolute rest! What is true: When to particles are in relative rest, gaining speed is equal to acceleration. Therefore it is clear, which ones time will be dilated. Particles know about there history. The twin paradox -in the sense of symmetrical timedilation- arises from the fact, that each twin "forget" his history. And most people say, there is no experiment, that can proof, which one was accelerated. But, this experiment is very simple, but not well known. ErNa 07:19, 28 April 2006 (UTC)

The problem here is mixing math with physics. The "velocity" has no physical existence (one can't even meassure "velocity" because it is always relative to a ref frame which means that it is only a mathematical idea connected with masurement. The "acceleration" on the other hand has physical (absolute) existence (measured absolutely by an accelerometer). Time dilation, to have physical meaning, must therefore depend on acceleration. And it does, since it is the time integral of acceleration times the distance at which the observation is made. Since at the distance zero, regardless of acceleration, this time integral is zero our "time dilation" is zero as well. But at a non zero distance the "time dilation" is non zero and so integrating acceleration at this distance we accumulate dilated time. And that's why the time dilation looks like depending on velocity because the velocity is also the time integral of acceleration.

I hope that now you understand why one is right saying that "time dilation" does not depend on acceleration (when at zero distance) and why one is right saying that it depends on acceleration (as in the twin paradox when there is non zero distance to the point where twin's acceleration is relevant and why accelerations at start and end points don't matter). Jim 07:42, 3 May 2006 (UTC)

If speed has physical existence has been the subject of endless debate, and it has never been solved officially (that is, different authors reached opposite conclusions in peer reviewed publications). However, that acceleration has no direct effect on time dilation is well known and also explained in the article twin paradox. If it's not clear, please comment there and explain what is wromg or not made sufficiently clear according to you so that the article may be improved. Note also that the distance to an ultracentrifuge doesn't affect the amount of time dilation - thus it's at best misleading to present time dilation as due to acceleration at a distance. Harald88 10:15, 3 May 2006 (UTC)

[edit] Time periode

ΔT is the time period as measured by a stationary observer,
ΔT0 is the time period of the moving object as seen by the stationary observer,

I miss the definition of "time periode" ErNa 15:24, 13 April 2006 (UTC)

Perhaps clock cycle is clearer. But, on second thought, "time interval" is probably more standard. Harald88 10:31, 6 May 2006 (UTC)

[edit] Urashima effect

Dear Harald88, perhaps you were not familiar with this term. For clarification, the term "Urashima effect" is not used to suggest that there is really anything magical, or fairy-tale like going on.

What is meant is the relativistic time dilatation, and it's often called Urashima effect due to the parallels of the physical effect of diverging eigentimes, and the old fairy tale. Shinobu 20:20, 23 May 2006 (UTC)

Dear Gerbrant, perhaps it's sometimes called so in Japan?
For sure, I've never seen it called like that in the English scientific literature; it certainly isn't common enough for the intro. And for possible inclusion in the article, please provide references.
Harald88 21:07, 23 May 2006 (UTC)

In my experience scientific literature tends not to contain any kind of colourful wording whatsoever. At my university we are even trained not to use any kind of language that is not dry as sand, and from the books and papers I've read I'd say this practice must be commonplace - the horror... but I digress.

Doing a websearch for terms like "Urashima-effect", "ウラシマ効果" and "浦島効果" yield plenty of hits. A lot of those from Japan (most certainly those with the Japanese characters), which stands to reason as this metaphor is based on a Japanese fairy tale, but not all.

These searches even revealed that this article has a sister-article in the Japanese language version, to which I'll add an interwiki link straight away.

As for the location of the addition, I chose it because "Urashima effect" should redirect here, and hence the term should be boldfaced, and I don't like it when boldfaced definitions are somewhere at the bottom of the article. But maybe that's just me.

As for wording, language and detail, that can, perhaps, be improved upon - a much more sensible reaction than blindly reverting in any case. Have a bit of good faith in your fellow editors - we're all in it together. Shinobu 22:47, 23 May 2006 (UTC)

I don't think this it merits enough significance to be mentioned in the introduction, if indeed it should be mentioned at all. This is the first I've ever come across it. Perhaps the claim could be included somewhere, properly sourced, but I would favor its removal. — Knowledge Seeker দ 23:10, 23 May 2006 (UTC)

First off, I'm surprised you don't know the term - but then again, people have different backgrounds. I've researched this matter some more, and it seems that this is the term for "time dilatation" in Japanese, as in the most commonly used. I'm not Japanese, so it has at least some penetration outside of Japan as well. Maybe I'm too much of an SF fan? Maybe.

But I still think it's notable enough to warrant inclusion, although possibly not in the lead paragraph. I also think it's a good metaphor, providing the reader with an interesting bit of general knowledge. Shinobu 00:09, 24 May 2006 (UTC)

I have moved it down to "Time dilation in popular culture", which, although not a perfect match, seemed the most fitting for now. Shinobu 00:13, 24 May 2006 (UTC)

[edit] Suggested Subdivision of Article for Clarity

It strikes me that this article has three audiences: (1) the inquiring layman who's just looking for a very general overview in everyday language (ie, "The results of a great number of experiments have been interpreted as confirming Einstein's theory: that time runs more slowly for objects moving at speeds approaching that of light."); (2) nonexperts with some significant scientific background who find themselves "unclear on the concept" and would like a discussion of apparent inconsistencies, objections, and misconceptions; (3) persons looking for the math. Couldn't the article be restructured accordingly, in three labelled sections? -S. Dickerson

Anyone can edit Wikipedia. So I advise getting to work. As a practial matter, it is best to create an account, draft the revised article in one's user space, and when it is ready tell people about it here and get their opinions. --EMS | Talk 05:30, 10 June 2006 (UTC)

[edit] Errors in this subject.

Ok lets start off with the statement: Time dilation is not a function of speed, or at least only possibility a perceived effect and not a real one as in a kind of illusion.

Reasoning:

Ship a moving a some percent the speed of light traveling from point a to point b 17 light years apart:

Here is a table of the different effects of time dilation for different speeds:

A B C D E
66.00% 197863022.28 25.75757576 34.28557863 49.58%
67.00% 200860946.86 25.37313433 34.17896546 49.74%
68.00% 203858871.44 25 34.09654535 49.86%
69.00% 206856796.02 24.63768116 34.03890897 49.94%
70.00% 209854720.60 24.28571429 34.00680204 49.99%
71.00% 212852645.18 23.94366197 34.00114314 50.00%
72.00% 215850569.76 23.61111111 34.02304549 49.97%
73.00% 218848494.34 23.28767123 34.07384375 49.89%
74.00% 221846418.92 22.97297297 34.15512692 49.77%
75.00% 224844343.50 22.66666667 34.26877889 49.61%
76.00% 227842268.08 22.36842105 34.41702873 49.39%

The first number is the speed the ship is moving according to a person on the ship.
The second column is the actual speed.
The third column is the time in years to make the trip.
The fourth column is the time that will pass on point a or b before the ship will complete the trip.
Formula =C*(1/SQRT(1-((B*B)/(299792458*299792458))))
The last column is the speed a person at point a or b will calculate that the ship was moving.
formula = (speed of light)/D


So you can see by this that as the ship passes 71% the speed of light it appears to take long for a person at point a for the ship to make the trip and thus seams to be going slower.


If anyone can tell me where I am wrong I would be grateful as I'm assuming I must be doing something wrong as this is so widely excepted but from everyone I have talked to they all seam to agree with my statements.

The first number is the speed the ship is moving according to a person on the ship.
That speed would be about zero, since there is not much relative motion between the ship and the person on the ship.
It appears to me that column A is rather v/c, where v is the relative motion of ship and points a and b and c is the speed of light.
From a person at a or b 's point of view, column C would be the time experienced from departure until arrival of the ship.
The person on the ship actually sees the same velocity as the stationary observer; however, the distance is shortened (see length contraction) and therefore the time is shorter; multiply the stationary time by a factor of sqrt(1 - v^2/c^2), so column D should maybe be the travel time as experienced on the ship, which would be (in years) 19.35078, 18.83603 etc..
And there is also the relativity of simultaneity: An observer at a and an observer on the ship will not agree on what happened at b at the time of the ship's departure (I assume that e. g. there was an explosion at b at the time of the ship's departure, as seen in the reference frame of a; the observer on the ship will argue that the event was actually before the ship's departure).
For the full mathematical picture, see Lorentz transformations.
Icek 10:00, 2 June 2006 (UTC)


Another error, more serious I think since the time dilation contradicts in general the basic concept of special relativity. According to this article: "In special relativity, clocks that are moving with respect to an inertial system of observation (the putatively stationary observer) are found to be running slower. This effect is described precisely by the Lorentz transformations." Let us reverse the inertial systems and move the observer to moving object. Now from his point of view his inertial system is stationary while the other one is moving in another direction. Then the clocks in that system which is now moving should be running slower. But they aren't. According to Lorentz transformation they are running faster, because the Lorentz factor is now in denominator.

Let's go back to the article: "Time dilation would make it possible for passengers in a fast moving vehicle to travel into the further future while aging very little, in that their great speed retards the rate of passage of onboard time. That is, the ship's clock (and according to relativity, any human travelling with it) shows less elapsed time than stationary clocks. For sufficiently high speeds the effect is dramatic. For example, one year of travel might correspond to ten years at home. Indeed, a constant 1G acceleration would permit humans to circumnavigate the known universe (with a radius of some 13.7 billion light years) in one human lifetime. The space-travellers could return to earth billions of years in the future (provided the Universe hadn't collapsed and our solar system was still around, of course). A scenario based on this idea was presented in the novel Planet of the Apes by Pierre Boulle."

1G acceleration causes only 0.000075% time dilation which means that influence of general relativity is nonessential. So we may safely assume that the system of space shuttle is inertial. If the concept of special relativity is universal from standpoint of its passengers the shuttle is stationary, while the Earth is fast moving, then on Earth few years should elapse while the ship's clock should register billions of them. Can someone explain that?

There's nothing wrong with this article. I think there is something wrog with Lorentz transormation and it needs major rewriting. You can only have one clock running slower, on Earth or on fast moving object. You can't have them both. If we don't rewrite Lorentz transformation we can't use it on fast flying space ship. Greg park avenue 17:23, 28 August 2006 (UTC)

Look again at the Lorentz transformation. For a clock moving in the x direction at v with t = t' =0 at x = x' =0, you have x=vt for the moving clock. So the t Lonrentz transformation becomes
t' = (t-vx/c^2)/\sqrt{1 - v^2/c^2} = t(1-v^2/c^2)/\sqrt{1 - v^2/c^2} = \sqrt{1 - v^2/c^2}. So the moving clock runs slower. This math also is reciporical in that to the "moving" observer the "stationary" observer's clock runs slower.
On the matter of acceleration: 1G is 9.8 m/s², not 9.8 m/s. Over time, a constant acceleration builds up one's speed more and more. Now in relativity, coordinate and proper accelerations are different (since otherwise a constant acceleration could cause you to go faster than c), but even so the example given is valid. --EMS | Talk 18:58, 28 August 2006 (UTC)


Agreed with Lorentz transformation. Yet, only one clock can run slower than the other, not both simultaneously. This paradox known as twin paradox Einstein predicted in 1905 will be removed by general relativity. Unfortunately his prediction proved untrue for small and continous values of acceleration and deceleration like 1G. 1G is here the thrust of the space ship engines, not the actual acceleration, and is an equivalent to the gravity of Earth on its surface. Assuming that gravitational radius of Earth is 0.9cm (rg), time dilation due to this thrust is given by
t' = t\sqrt{g_{00}} = t\sqrt{1 - r_{g}/r} = \left(1 - 0.00000075\right)t
and is too small to recompense for much bigger time difference shown by clocks running on high speed space shuttle and on Earth, which should be down to zero after ship's return to Earth. All those theories based on assumption that clocks on returning vehicle run differently than on departing one are subject to the same paradox and Minkowski space diagrams simply don't apply here.
I would like to introduce new concept which perhaps would restore symmetry of Lorentz transformation without much headache. Let's replace four dimensional time space by six dimensions - three for space and three for time. Proper time (time on space shuttle) will be then projection of the time vector in three dimensional time frame on one of its axis. Transformation from a stationary integral system to moving one would be then nothing else than rotating the time vector about an angle which cosinus is Lorentz factor. Reverse transformation (from moving vehicle to stationary) will be also projection of this very same vector under the same angle, just like in regular coordinate system transformation by rotation. Lorentz transformation becomes then Gallilean only in six dimensional time space. Simple, easy and full symmetry is restored.Greg park avenue 16:50, 29 August 2006 (UTC)
Ah, you are proposing a novel theory of physics. By all means you should start a website of your own and advocate your theory. If your ideas are fertile, then soon the scientific community will flock to you. Wikipedia policy (like any encyclopedia's policy) is to represent exclusively those theories that have gone through the entire process of gaining wide support. This is called the no original research policy. --Cleonis | Talk 11:38, 30 August 2006 (UTC)
.Greg park avenue wrote:
... only one clock can run slower than the other, not both simultaneously.
The key word there is "simultaneously". Simultaneity is relative in relativity. Events which are considered to occur "at the same time" in one frame of reference are found to occur at different times in other frames of reference. Because of how time is offset as a function of distance between frames of reference in relativity, both observers can find the other's clock running slow with respect to the temporal coordinates in their own frame of reference. So Greg's complaint is actually a common mistake that relativity novices make. --EMS | Talk 15:30, 30 August 2006 (UTC)


Thank you for friendly advise, but why bother with page when this is only new form of expressing Lorentz transformation and very simple indeed? Perhaps as an expert on rotation would you take a little time to review this proposal below I would like to place in wikipedia as an extra chapter? It's kind of unique but that's what wikipedia is about and I don't think we break any rules. However, I wait for any suggestions.
To show symmetry in Lorentz transformation regarding time dilation and twin paradox, one can write it as an rotation of time coordinates in six dimensional time space x, y, z, t1, t2, t3. System of two coordinates t1, t2 has been rotated around axis t3 about an angle u and has become t'1, t'2, t'3 while sinu = v / c. Then cosu is the reciprocal of Lorentz factor, and the rotation has the very well known form:
t'1 = t1cosu − t2sinu
t'2 = t1sinu + t2cosu
where t1 = t and v = x / t1. You can show this system of equations in another form:
t'_{1} = \frac{t_{1} - t'_{2}sinu}{cosu}
t_{2} = \frac{t'_{2} - t_{1}sinu}{cosu}
Now, when you substitute second pair of time coordinates for space coordinates x and x' along which the system moves as follows
t'_{2} = \frac{x}{c}
t_{2} = \frac{x'}{c}
then you get nothing else than Lorentz transformation
t' = \frac{t - vx/c^2}{\sqrt{1 - v^2/c^2}}
x' = \frac{x - vt}{\sqrt{1 - v^2/c^2}}
Note that the function transforming coordinates t2 is inverse to function transforming coordinates x. I think it needs a bit explanation, there is also some problem of idiom but this is only a rough sample and any help would be appreciated. What do you guys think about it? Greg park avenue 19:47, 30 August 2006 (UTC)
You are proposing a novel theory of physics. By all means you should start a website of your own and advocate your theory. If your ideas are fertile, then soon the scientific community will flock to you. Wikipedia policy (like any encyclopedia's policy) is to represent exclusively those theories that have gone through the entire process of gaining wide support. This is called the no original research policy. --Cleonis | Talk 21:11, 30 August 2006 (UTC)
I must agree with Cleonis. This page is to talk about time dilation as it is known and in relation to this article, not as you think it should be. Wikipedia is not a soapbox. --EMS | Talk 22:47, 30 August 2006 (UTC)
Maybe you reconsider, EMS. I didn't propose major changes and full blown on Richter scale theory, just the simple explanation how the time dilation could be represented by equivalent of rotation of time vector. When you want full Lorentz transformation in 6 dimension metric then you got:
t'_{1} = \frac{t_{1} - t'_{2}sinu}{cosu}
t_{2} = \frac{t'_{2} - t_{1}sinu}{cosu}
t' = \frac{t - vx/c^2}{\sqrt{1 - v^2/c^2}}
x' = \frac{x - vt}{\sqrt{1 - v^2/c^2}}
Both pairs of transformation are reversing each other, something I have pointed before that it needed an explanation, that's why you won't get any time dilation when space ship returns to Earth. And full symmetry will be this way conserved which no theory explained that far. But we don't go that far in wikipedia, are we? By the way, it's only a discussion, so don't get upset too much. I was only asking. Greg park avenue 00:00, 31 August 2006 (UTC)
*Sigh* You don't need six dimensions. The LT are a "rotation" of space and time which physically is a change of velocity. The standard spatial rotations are also technically Lorentz transformations (as together with the x-t transformations they form a group known as the Poincaré group). This does in four dimension what you want to do in six. Besides, your proposal is original research, and Wikipedia has a very proper ban on that. --EMS | Talk 00:33, 31 August 2006 (UTC)
You definitely need six dimensions to compensate for time dilation which is only an illusion, especially, when experimental data agrees with that. Look, when you bring in the resultants
T = \sqrt{t_{1}^2 + t_{2}^2}
T' = \sqrt{t_{1}'^2 + t_{2}'^2}
and the first pair of the above system of equations express by them, then this part of transformation becomes Gallilean again T' = T and x' = x - vT, while the second part stays unchanged. T is the real time we are experiencing, while t = t1 is only its component. And that's it.
When you still claim that this is an original research, why don't you send it to Physical Review? It's only one page or two and your scientific language skills to argue with types from Brookhaven are sufficient to do that. Mine are not. Otherwise, it will stay on this back burner to the Judgement Day. Besides, time dilation is your baby, not mine. Just to be on fair side and not to take full credit, call it somehow in my memory. Greg_park_avenue transformation is OK with me. Greg park avenue 14:04, 1 September 2006 (UTC)

Dear Greg, Wikipedia is not a place for original research. That said, the two theories of relativity conform very well with the physical reality we can measure, and is does not, as you try to assert, contain contradictions. This discussion ends here. If you want to persue this quest outside of Wikipedia, feel free to do so, but I suggest you follow a course in General Relativity first. Shinobu 16:06, 4 September 2006 (UTC)

I would recommend taking course in simple relativity first. If you went to general first you might be suprised to find out that the shift of the Mercury perihelion in Schwartzschild metric was three times bigger than the same shift calculated on the basis of Kerr metric while the colapsar moment M → 0. That's a contradiction inside general relativity, but it's too big for wikipedia. What I suggested was a simple logic which even a high school student would comprehend but let me put it in more simple words yet. If we assume that the 4 dimensional time space may be curved, we must go up at least one dimension higher or two. Just like two dimensional sphere may be curved but only in three dimensional Euclidean space. This, as simple logic as that, ought to be inserted in every school book and science manual wikipedia nothwithstanding. And that's what I was trying to do. Why serve the kids with outdated theories like Minkowski space diagrams with its ict-axis? If time coordinate was an abstract number, than in case of g0i # 0 (Coriolis interactions), ds would contain an abstract number too, and then the energy and momentum which, as having been a differential mdxi/ds, would not even be real. What about the Hamilton Jacobi equation? And you call this simple logic an original research? You don't wait for the blessing of some smooth talking professor from MIT or anothor Ivy League joint. Them pompous asses killed even cold fusion without bothering to send a representative to the great state of Utah to check Fleischmanns - Pons findings and see how it was done and get to know how to properly repeat the experiment in their lab. They, the policy makers, have just said it cannot be done and that was the end of the latest major breaktrough in the history of mankind. And now you are one of them? If you can do nothing about this policy, at least don't confuse the kids. The last chapters of this article should be rewritten or removed because they contain major generic errors. If they remain like that I vote this article for not being neutral.Greg park avenue 19:55, 6 September 2006 (UTC)

Shinobu, I don't agree. Having read Greg's statement "Just like two dimensional sphere may be curved but only in three dimensional Euclidean space", I think that a course in General Relativity would be a waste of time. Having seen him call Minkowski space diagrams with ict-axis "theories", I think that just about every kind of physics course would be a waste of time. DVdm 10:27, 7 September 2006 (UTC)

I see that you've been to private schools and speak the perfect French, and most probably took one of the courses in sarcasm - Sarc1, Sarc2 or Sarc3. I can only say I Am Charlotte Simmons after Tom Wolfe or Don't Bother after Shakira for that. But no matter what language you speak or how good you speak it, you can't explain the unexplainable. When math says "no" you can't say "yes" in physics. Physics cannot be neither biased nor corrupted. I think you are in wrong part of wikipedia, politics department would be more preferable. Greg park avenue 15:27, 7 September 2006 (UTC)

Shinobu, just like I expected, he also entirely missed the point I was making, but I will not bother explaining. So I fully agree with your ending the discussion. DVdm 18:23, 7 September 2006 (UTC)

Shinobu, don't take this bait - hook, line and sinker from this hardly to be trusted friend of yours of unknown heritage. This selfish person is not worth to be Hooking Up with or even hanging around. You can do better than that. Just say I am who I am and be proud of it. Greg park avenue 14:29, 8 September 2006 (UTC)

This discussion is OT as well as being OR. I call on everyone not to respond further and let it end here and now. --EMS | Talk 20:26, 8 September 2006 (UTC)
This is not a political convention nor a fraternity formal to call on everybody. If someone had questions about the math above like how the Hamilton Jacobi equation shall look in six dimensional time space or what differences if any were there between its expression in four and six dimensions, the Einstein equations, the metric, the conservation laws, thr trajectory equations, the action e.t.c., I will still be here and take time to explain it to him or her as best as I can, and evereone even you is welcome to do that. If you're not interested, speak only for yourself, not for the entire international scientific community, because that makes you ridiculous. I will repeat that line one more time. This is only a discussion and I have never inserted any original research into wikipedia except into its Talk page. My comments about insufficiency of Lorentz Transformations were not the original research. This problem has been known since over one hundred years as the twin paradox and hasn't been satisfyingly resolved until this day, capisce? Many scientists will second that opinion and they did. Greg park avenue 19:21, 9 September 2006 (UTC)

[edit] Explanation requested

I am a nonexpert "with some significant scientific background". Is it meaningful to ask what actually causes time dilation? To my understanding, the article doesn't do that. Is it something that just IS, or is there some underlying cause? I think I understand length contraction (optical illusion) and mass increase (all that kinetic energy), but time dilation gives me a headache. Clarityfiend 09:27, 9 June 2006 (UTC)

It has been a never-ending but largely suffocated debate, depending on different beliefs. For example, not long ago a paper appeared in the AJP that emphasizes that length contraction is physical, while you seem to have read other opinions. The opinion of Lorentz was that such effects are physical in principle, but partially an optical illusion due to our own (unknown) velocity relative to space ("the ether"). Einstein's thoughts were difficult to follow (at one time he seemed to believe in a kind of relative reality and "relative motion" as cause) - I would be interested if someone could cite him on this point. Nowadays popular is the idea that the cause is one's trajectory through "space-time".
As such ideas are not directly verifiable, it is wise not to expand on such in an article about physics. A special article about the philosophy/philosophies of "relativity" over the ages may be appropriate for that. Harald88 12:05, 9 June 2006 (UTC)
Clarityfiend - Time dilation is physically real, and experimentally verified. It does have an underlying cause, which is described in the section Simple inference of time dilation. I advise studying that and the animated GIF in the following section. BTW - I have at time considered rewriting this article to reconsolidate and clarify it, but have yet to do so in part because I have not yet figured out what the rewritten article should look like. Perhaps you may have some ideas, given what you are trying to get out of this article. --EMS | Talk 15:34, 9 June 2006 (UTC)
I wasn't suggesting that time dilation wasn't real. I was just hoping that there was some relatively intuitive explanation of why it occurs. I already knew about the derivation (I remember it from 2nd year physics). So, I guess the best that can be said is that it is a consequence of the speed of light being the same in all frames of reference.
Has anybody proposed an experiment to determine if length contraction is actual and not illusory? I thought it was because light from the front and back of an object reached the observer "out of sync" (so to speak). I need more aspirin. Clarityfiend 01:11, 11 June 2006 (UTC)
You can look at the finding of muons generated high in the atmosphere as proof of length contraction. Since the muons have a half-life which is to short for them to reach the surface of the Earth in the time it takes for them to do so, their experiencing time dilation explains this. But what about the same as viewed by the muons? In that frame of reference the muon's clock is OK. Only if the distance to the Earth is reduced is there time in that frame of reference for the muons to get down here before decaying. --EMS | Talk 05:23, 11 June 2006 (UTC)
Thanks. Now I need to order aspirin by the case...
As for how the article should be rewritten, my first suggestion is to provide a introductory description aimed at the layman. The first sentence already starts to use jargon that would discourage the average reader. How about: "Time dilation is one of the non-intuitive phenomena associated with Einstein's theories of relativity. An observer watching, for example, a spaceship moving at a high enough velocity, would be able to detect time passing at a slower rate for those aboard, at least from the observer's point of view. A person on the ship, however, would not notice any difference. The dilation is negligible in everyday situations, only becoming noticeable at high speeds. This effect has been verified by numerous experiments." Then throw in a table showing how much time appears to slow down as speed goes up. Next, you could describe the experimental results: the muons, GPS, etc. (and find some way to put Ives at the end to minimize the impact of equations on the great unwashed). This could then segue into the space flight (what, no mention of Heinlein's Time for the Stars?) and popular culture sections (which should be merged together). That would satisfy the general public. After that, you could go into the grisly details, starting with the simple derivation.
Minor quibble: It seems kind of arbitrary to say that the effect only becomes "important" at 0.1 c. Clarityfiend 17:13, 11 June 2006 (UTC)
The problem with trying to pick a threshold like this is that the definition of "important" will depend on what you're doing. It might be better to pick an obviously-arbitrary value (such as, "length, mass, and rate of time flow change by 10% at about 0.xx C"). Heck, you could even do a table with an order-of-magnitude scale (10%, 1%, 0.1%), if it weren't for the fact that this information likely wouldn't be useful enough to justify the space taken by the table. --Christopher Thomas 20:08, 11 June 2006 (UTC)
Clarityfiend - I don't think the your proposals quite work. For example, a time dilation table was present at one point, and man was it ugly! Yet this article does need to be rewritten. My advice is that one of us set up a sandbox version, and we will work together to revise it a ways. --EMS | Talk 00:34, 12 June 2006 (UTC)

[edit] Time dialation and experienced time to circle the universe

In the section entitled 'Time dialation and space flight' the sentence, 'Indeed, a constant 1g acceleration would permit humans to circumnavigate the known universe (with a radius of some 15 billion light years) in one human lifetime. ', is interesting. Plugging 82 billion light years into the t* equation gives an experienced time of a little more than 25 years. But if you replace g with a slightly lower value, say 1.5 m/s2 then you get an experienced time of a little more than 150 years. It seems a strange coincidence that the universe fits us so well; If we lived on a planet with less gravity and were therefore incapable of sustained exposure to anything like 1 g, or if our life spans were similar to that of a dog, or if the universe were only a few times bigger then we could never hope to circumnavigate it. Yet our life spans, the size of the universe and the gravitation of Earth are all unrelated variables.

Are these equations accurate? I had heard than even with a high constant acceleration and time dialation it was impossible to reach the centre of the galaxy in a lifetime.

198.103.34.97 17:58, 9 June 2006 (UTC)Eric Saumur

I will take your calculations on faith, as I know that a constant acceleration really does get up to near light speed (with respect to the starting frame of reference) within a few years. At that point, your clock is all but stopped. For the galaxy: Going to the center within a human lifetime now does seem viable (and back too). However, where are you going to get the energy from for the accelerations and decelerations necessary for pulling off that trick? As for circumnavigating the universe, there is a problem: the Hubble expansion. As a practical matter, you will never get even halfway around it. --EMS | Talk 05:26, 10 June 2006 (UTC)
The phrasing of the question was careful about avoiding the expansion problem, if I remember it correctly (specified a sphere with the diameter of the presently-observable universe, as opposed to our universe, or even a spherical volume within our expanding universe). Regarding the equations, I was considerig doublechecking it yesterday, but so far have been too lazy. I'll do this within the next couple of days here on the talk page, showing my work. There are at least three ways of setting up the problem, though: Applying a thrust of constant magnitude from a stationary observer's reference frame, applying a thrust of magnitude scaling with the relativistic mass of the ship from the stationary observer's reference frame, and considering the ship to apply constant thrust in its own reference frame. These will give wildly different answers for travel time (in fact, the second option might make you approach C in a finite time, with thrust approaching infinity, now that I think about it). --Christopher Thomas 17:34, 10 June 2006 (UTC)

[edit] End of the universe (as they knew it)

I just realized there's something missing. The effect helped demolish once and for all the old deterministic view of the universe, yet this isn't mentioned at all. Maybe it belongs in a higher level article on relativity, but a cursory examination doesn't show it discussed anywhere except the determinism article. Clarityfiend 04:32, 13 June 2006 (UTC)

 ???. I assure you that relativity is a deterministic theory. Observers may not agree on the ordering of events which are not causally related, but for causally related events they will. See Minkowski space#Causal_structure. --EMS | Talk 04:59, 13 June 2006 (UTC)
The word "relativity" isn't in the Determinism article. The most I can find is mentions of chaos and quantum mechanics. Scientific determinism doesn't contain it either. As EMS described, as long as you're not looking through a Cauchy horizon, observers will agree on what spacetime looks like, though they may disagree on how to draw coordinate axes on it. --Christopher Thomas 05:39, 13 June 2006 (UTC)
Okay, I must be using the wrong term. Before Einstein, it was assumed that all parts of the universe were in sync, that time moved in lockstep everywhere. What's the word I'm looking for? Whatever it is, it should be mentioned somewhere. Clarityfiend 03:31, 14 June 2006 (UTC)
This would be simultaneity. The effects of SR on simultaneity are described at relativity of simultaneity.--Christopher Thomas 03:45, 14 June 2006 (UTC)
Naah. That's too narrow a definition for what I'm talking about. Paradigm shift is such an overused, clumsy phrase, but it comes close I suppose. Dammit, I'm sure there's a better way to say it, but I just can't think of it. Clarityfiend 06:22, 15 June 2006 (UTC)
The best I can do for you is to call it a "proper time differential". Just be aware that this is a neologism, as I just made it up. So you cannot write a Wikipedia article on it per Wikipedia:avoid neologisms.
The confusion, Clarityfriend, seems to be coming from your use of "deterministic" and "determinism" (which are best known as terms in philosophy dealing with "fate" and "free will") whereas I think the word you wanted to use was "absolute." You're trying to point out the distinction between Newton's view of space and time as having an objective and invariant existence independently of whatever they "contain," as opposed to the Einsteinian view that certain physical principles, while acting according to fixed mathematizable laws, are determined not with reference to such an external absolute space, but rather with reference to the mutual relation of the particular (set of) objects in question: that is, solely with reference to their measured change of position relative to one another, not with reference to a shared common space in which they are both supposed to be embedded. This is traditionally called the contrast between "absolute space" and "relative space." Actually, it would be better put as absolute space, versus the rate of change of certain measurement attributes respecting the different reference objects, with the existence of a "background medium" being regarded as gratuitous metaphysics. (You can see why it isn't put that way.) This is the general Machian "viewpoint," with which Einstein was in sympathy (though not the actual Machian analysis of the situation, which as it happens does include, in effect, what Einstein sets aside). -Scott Dickerson --72.245.1.234 17:11, 5 July 2006 (UTC)

[edit] One thing this article needs

If there is one thing I think this article could do with it is a Graph, showing Time Dilation effects in relation to speed.
I saw a graph like this years ago in an old book and was always interested in it, it showed how much time would appear to slow down if you were in a spaceship travelling at various percentages of the speed of light. I assume the graph was made using the various formulas on this page, it would be really great if someone could create a graph like this for the article.
In case I'm not explaining this well, what I mean specifically is a graph with one axis as speed (in percentages of C), and the other axis as the lengthening of time (i.e. at zero speed 1 second = 1 second, at the Speed of light 1 second = Infinitely long time, at-least I think that's how it goes).
A graph like this would be very useful for people to see at what speeds Time Dilation really starts to affect things, like if I wanted to know say, what would be the dilation at 25% C, then I could just go look (instead of trying to calculate it with those formulas).
--Hibernian 05:53, 19 July 2006 (UTC)

[edit] Real slowdown?!

Someone added about time dilation in general: "The time slowdown is real".

However, such a remark may only be valid in special cases (such as the twin paradox), and depending on what one means with "real". In general, . Thus I object to the abovementioned statement. Either delete or rephrase! Harald88 12:16, 21 July 2006 (UTC)

I edited-in the phrase in question. The objection is validly made, but please consider the following: (1) There seems to be no way to say anything very close to what the common word "real" says without inserting so many qualifiers that the point of using it is obscured. (2) My purpose in using the phrase is to address what I perceive to be a source of confusion in understanding what the theory contends.
The principle competing view is that the phenomenon is "just" a product of the geometry of available measurement technique and should not, by implication or otherwise, be attributed to the state of the measured object. Whether or not this turns out to be the case, it is not an accurate characterization of the Special or General Theories of Relativity as enunciated by Einstein and accepted by his contemporary followers. The competing view does not seem to represent a genuine live controversy, but rather the contention of a small minority outside the physics mainstream--thus not appropriate to the overall approach taken in this article, per Wiki rules. This could change, of course.
It is not accurate to state that, per these theories, "what appears as slowdown in some frames will appear as speeding up in some other frames"--if one uses "frame" in a sense consistent with its prior use in the article, which only addresses constant relative velocity on the part of measurer and measuree. The time-acceleration involved with the twin paradox is assigned, by the theory, to the distinct case of mutual acceleration. (It occurs during the turnaround.) Note that my concern with the above-cited statement involves ambiguity in what the term-of-art "frame" is to refer to. But I think it illustrates the very sort of confusion that I am at pains to alleviate. As the special cases have their own articles, it seems this article ought to present generalities that illustrate the scientifically-revolutionary thrust of the Einsteinian view in its generally accepted interpretation.
And even considering the special cases, the time dilation effect is understood to be a real property of the moving object, and I maintain that it is important to acknowledge that--precisely because it is counter-intuitive.
I say this without prejudice as to the basic question of whether the theories are "truly valid." I wonder that myself. They may not be. Alternatives must receive fair consideration. But non-mainstream objections should not trump a presentation of the theory itself. -Scott Dickerson --69.3.132.12 18:27, 24 July 2006 (UTC)
I doubt that any textbook puts it as you do. making it not only inaccurate but also WP:OR. If I remember well, some books or articles put it as "physical in the corresponding reference frame". Would that convey what you were trying to say? Harald88 21:40, 24 July 2006 (UTC)
Some time ago I uploaded an animation to the wikimedia commons that illustrates the matter that is discussed here. velocity time dilation (This gif-animation is 110 KB in size)
Oops, I had forgotten that I had inserted that animation on this talk page back in january animation with helical worldline
The animation shows two spaceships, one following a straight worldline and the other following a helical worldline that corkscrews around the straight worldline. The animation as a whole is a Minkowski diagram that is co-moving with the object following the straight worldline. For the "blue object" a larger amount of proper time elapses than for the "red object".
However, it is theory dependent whether to state or not that the red clock is slowed down, or even that the time slowdown is real.
The very point of Einsteinian special relativity is that in the setup shown in that animation there is no meaningful correlation to be found between the plane of simultaneity of the blue spaceship and the plane of simultaneity of the red ship. The plane of simultaneity of the red ship cannot be spatially extended in such a way that it contacts the worldline of the blue ship in a selfconsistent way, which rules out a comparison.
Strictly speaking, it is beyond the scope of Einsteinian special relaivity to state whether the red clock is slowed down. All that the theory states is that when the two spaceships rejoin after having travelled on worldlines of differing length, they will on comparison see that the blue clock has counted a larger amount of proper time.
I like the animation, and would welcome it inside this article. BTW, I disagree with your last remark: in SRT the reference clock is in the inertial frame and compared to that the red clock has retarded. That is, in standard English, "slowdown". Even when looking at it from other inertial frames, the red clock has slowed down relative to the blue clock, and the blue clock hasn't changed its rate during the experiment. Therefore I agree with Einstein when he wrote that that clock "must go more slowly". Harald88 20:10, 25 July 2006 (UTC)
It is very common in physics writing to not adhere to strict formulation all the time, for that would disrupt the flow of language too much. Without the context, it cannot be assessed whether this Einstein quote is originally intended as a principal statement, or as physics shorthand in the flow of the narrative. --Cleonis | Talk 22:38, 25 July 2006 (UTC)
In view of my remark below about Einstein's relative reality, I agree that such remarks are open for interpretation. Which doesn't change the fact that in SRT that effect is "absolute" (in both meanings of that word). Harald88 06:28, 26 July 2006 (UTC)
Of course, this strictness is very awkward for writing introductory material about relativistic physics. I am keen to avoid teaching the beginner things that he must later unlearn again, but this ties me down on all sides. Some authors decide to oversimplify some things, in order to get at least something across. --Cleonis | Talk 15:37, 25 July 2006 (UTC)
That last sentence appies to my efforts, the point of dispute being the "over." It's a basic question regarding not only Wiki but encyclopediae in general--do you provide "in a nutshell" versions for the casual or nonexpert inquirer, or offer something more precise and technical--but definitely harder for the typical inquirer to grasp? My own suggestion is that both be provided--a simplified, Asimov-type intro, followed by a more technical, less summary presentation. As written so far, this article does do both, though (to partially address the objections raised above) it might be better to completely separate them as a "part One"/"part Two".
Commentators on Einstein (I recognize that that isn't a "cite") express his negative attitude toward ("gratuitous") metaphysics. Raising the "but is it real" question may cross the line. My question is: does this snippet of metaphysics lead the reader further from the theory than the alternative of allowing him to assume the more-intuitive converse?
No OR is presented here. My goal is to provide a fair and clear exposition of the specifically Einsteinian interpretation of the phenomenon: not just the math and experimental confirmations, but the significant change in the physical wordview following upon a fundamental-spacetime interpretation (the expressed view of Minkowski and Einstein) as opposed to an artefact-of-measurement interpretation.
I'll acknowledge, certainly, that the project of centering an article on "Time Dilation" on Einstein's theories is a defeasible choice. Let's see some "Be Bold" alternatives, and discuss them. -Scott Dickerson--69.3.132.12 18:10, 25 July 2006 (UTC)
It's my personal experience that oversimplification easily leads to long-lasting misinterpretation. In particular, I only started to correctly understand SRT after reading the original papers. Careful phrasing isn't necessarily overly technical or complicated.
Note also that Einstein had a peculiar understanding of "real": for him (in 1905), real is what one measures, even if (as with time dilation!) what one measures is in part stipulated by convention.
Moreover, why single out the rather obscure Einsteinian interpretation, and omit the Lorentzian interpretation which is much more straightforward and easier to understand?
To me it makes more sense to have a box with varying interpretations (Einstein, Lorentz, Minkowski) than overly simple explanations.
As you didn't comment on my suggestion, I'll try to modify the statement in question to something almost as simple but not self-contradictory (as it is now). - Harald88 19:19, 25 July 2006 (UTC)

I now changed it, but as I remained close to 69.3.132.12's version, it's perhaps more complex than needed. I hesitate to replace it by a remark that a change of speed of a moving clock results in a change of clock rate, according to all observers in uniform motion - only, there is disagreement about the sign and magnitude. That's more compact, and perhaps simpler to understand. Or, as another alternative, we may use Cleonis'animation and pinpoint that although it's "relative" between inertial frames, the velocity time dilation can be as "absolute" as gravitational time dilation. Harald88 20:12, 25 July 2006 (UTC)

No comments?? Aren't we discussing how to present this? Harald88 20:47, 28 July 2006 (UTC)

[edit] The question of what is inherent in the phenomena

I quote and paste from above:

(2) My purpose in using the phrase is to address what I perceive to be a source of confusion in understanding what the theory contends. [...] And even considering the special cases, the time dilation effect is understood to be a real property of the moving object, and I maintain that it is important to acknowledge that--precisely because it is counter-intuitive. -Scott Dickerson --69.3.132.12 18:27, 24 July 2006 (UTC)

I presume you are referring to the following kind of error. Some authors throw sand in their readers eyes by suggesting that the frequency shift in accordance with time dilation can be understood along the same lines as classical doppler shift.

The animation symmetric velocity time dilation, that is already in the article, is designed to avoid any association with classical Doppler effect. That animation is designed to hammer in the point that a distinction between "being stationary" and "having a velocity" does not enter special relativity, the symmetry is unconditional. As regards the time dilation; all observers will agree that on reception of exchanged signals the greens will count half the frequency of what the reds emitted as counted in red time, and vice versa.

The animation non-symmetric velocity time dilation (the helical worldline) is again designed to avoid any association with classical Doppler shift. All observers will agree that for the reds a smaller amount of proper time elapses than for the blues. That is, this difference in amount of lapse of proper time is invariant under coordinate transformation between inertial coordinate systems.

The commitment of Einsteinian special relativity is that among the quantities that can be measured, only the measurables that are invariant under coordinate transformation (between inertial coordinate systems) qualify as candidates for being inherent in the phenomena. The values of measurables that are variant under coordinate transformation (such as spatial distance and velocity) are regarded as artifacts of the particular choice of inertial coordinate system. (I sorely regret that special relativity isn't called 'invariance theory'. That name is ever so appropriate)

An example: if two objects collide and stick together after the collision, some of the kinetic energy converts to heat in the process. The amount of energy converted to heat is invariant under Lorentz transformation; singling out that aspect as inherent to the phenomenon of collision. The foremost invariance of special relativity is the invariance of proper time. Proper time is invariant under Lorentz transformation, and thus seen as an inherent quantity. On the other hand, relative velocity is not invariant under Lorentz transformation. That puts relative velocity in the category of artifacts of the particular choice of coordinate system. --Cleonis | Talk 14:31, 26 July 2006 (UTC)

I'll endorse the gist of what you're saying, Cleonis. I see now that, by my saying that the dilation phenomenon is "real" "for the object," I'm obscuring the fact that the dilation is not detected-as-such within the object (ie, the ship seen by the "stationary" reference as in relative motion), but is "real" as measured by the stationary observer, who is then allowed to "impute" the slowdown to the mover. Jeez, its a mark of how radical this stuff is, that all manner of common words are shown to be derived from defeasible assumptions not straightforwardly applicable to the elements of the situation in question. --As Einstein, following Minkowski, admitted with pride.
I think (in your "sand-throwing" reference) you HAVE pinpointed the basis of my concern. The new phrasing strikes me as an improvement over my own.
The Lorentz transformations are clearly the definite statement of "what happens." But then there's the interpretation, which many inquirers are looking for. Wasn't it Lorentz who advocated a purely "mechanistic" interpretation of the details?--preserving the aether hypothesis by maintaining that absolute motion through the medium induces longitudinal compression as a direct consequence via a resultant nonisotropy in the spatial distribution of the charges' fields? (Adopting that approach has implications for interpreting time dilation.) That's an early interpretation rejected by Einstein. But I wonder if I'm confusing Lorentz with Eddington.
One last point: Animation is a valuable supplement, but I know for a fact that a significant percent of our likely inquirers don't easily grasp concepts presented in that manner. So it's still important to make the words sing too. Whether we've accomplished that is still open to challenge. But the present form does look pretty good.
Maybe we should insert a box: SERIOUS INQUIRERS PLEASE SEE ACCOMPANYING DISCUSSION!-Scott Dickerson --69.3.132.12 16:51, 26 July 2006 (UTC)
Historians of science describe that Lorentz acquired a full grasp of the commitment of einsteinian relativity, but he expressed a personal preference for a Lorentzian view.
I like to distinguish theories in terms of what does and does not enter the theory. In the case of a Lorentz-type theory, the concept of velocity with respect to the aether enters the theory as a necessary element. Additional hypotheses are devised to account for the fact that attempts to find evidence of velocity with respect to the aether have all failed. In the case of Einsteinian special relativity, such a thing as velocity with respect to spacetime does not enter the theory in the first place. That is where Einsteinian special relativity departs from Lorentz-type theories.
What does enter special relativity is difference in spatial distance travelled, and intimately connected with that, it is key in special relativity that acceleration with respect to spacetime is an operative factor. That is what the helical worldline animation is about. The red ship is accelerating with respect to spacetime, and as a consequence of that symmetry is broken.
Special relativity is a theory of motion. Conceivably, a physicist may attempt to formulate a theory of motion in which it is assumed that space and time are just a container, a passive background in which physics events take place. Clearly, special relativity does not fall in that category. In special relativity, the background that the physics is embedded in, known as Minkowski spacetime, is a participant in the physics taking place. If you are in a spaceship, and you make a U-turn (allowing you to rejoin your twin brother), making the U-turn is a phase of accelerating with respect to the background you are embedded in. According to special relativity, the consequences of the phase of acceleration-induced symmetry breaking are irreversable. (For example, the twin brother who has flown away and rejoined cannot undo what he has done.)
As I wrote before, the commitment of einsteinian special relativity is to the invariants of special relativity. These invariants follow from the dual requirement that velocity with respect to spacetime does not enter the theory, and that acceleration with respect to spacetime does enter the theory. --Cleonis | Talk 21:25, 26 July 2006 (UTC)
I have to correct myself.
The decision to adopt the Lorentz transformations as the fundamental transformations entails acceptence of all the logical implications of the Lorentz transformations. Foremost among these logical implications is that acceleration with respect to spacetime is an operative factor.
In pre-relativistic physics, position in space did not enter the theory. Space, time and aether were regarded as symmetrical for position. In 1905 Einstein showed that this could be moved up one notch. (With velocity as first derivative of position as a notch, and acceleration, second derivative of position, as the next notch). Spacetime is regarde as symmetrical for inertial velocity, so inertial velocity does not and should not to enter the theory. --Cleonis | Talk 11:08, 27 July 2006 (UTC)
Your last metaphysical assertion is contradicted by SRT's equations themselves ("the physics"): in SRT the observed effects are a function of inertial velocity (and explicitly *not* of acceleration), just as in GRT the observed effects are a function of gravitational potential.
BTW, I look forward to practical reactions to my different suggestions above, instead of another newsgroup discussion... Harald88 20:47, 28 July 2006 (UTC)
More precisely: velocity with respect to spacetime does not enter SRT.
As to practical suggestions: I think the article should avoid teaching things that the reader must later unlearn again. What can be observed in for example non-symmetric velocity time dilation is that when the two spaceships rejoin the spaceship that has traveled a longer spatial distance has had a smaller amount of lapse of proper time. It is speculative metaphysics to claim that one clock has run slower than the other; one has no opportunity to actually observe such a slowdown. Clocks can only be compared if they are both moving inertially and are co-moving. I never use words like 'slower' or 'slowed down', I only use the expression 'difference in amount of lapse of proper time'.
Of course, all this boils down to the incompatibility of Lorentz-type theories and einsteinian relativity. The scientific community has opted to follow einsteinian special relativity. However, in physics writing usage of metaphors is unavoidable, and as the metaphors root in concepts from daily life the metaphors have an unintended Lorentzian flavor to them. Unfortunately, that leaves room for the erroneous perception that the Lorentzian view is alive in the physics community.
I don't edit the time dilation article because I think a separate article is superfluous. The natural place to cover time dilation is the special relativity article. I agree that if that is my view, I shouldn't have posted comments on the time dilation talk page in the first place. --Cleonis | Talk 22:03, 28 July 2006 (UTC)
The speed v is of course defined relative to the inertial frame of choice, and not relative to spacetime.
Einstein used the term "slower" in exactly the way most people who are newly introduced to this subject will understand it, and it's not a problem (I think) to state the same in a well defined and unambiguous language (I think to have done so; if not please point out what is wrong about it). And to get back to the original argument of Scott: it's certainly not understandable to a novice what "difference in amount of lapse of proper time" means, while most people would understand "slower" to mean just that, if they understood the meaning of the words. BTW, the "scientific community" (which itself can't make choices anyway) would be unscientific if it would "choose" for something that can't be tested by the scientific method. Thus, let's hope that your last assertion is erroneous! ;-) Harald88 21:33, 2 August 2006 (UTC)

[edit] "Einstein's account?"

Scott rephrased some of the text into "Einstein's account of time dilation" (and it's not clear if it's really Einstein's). In contrast, we already achieved an opinion-neutral account of time dilation such as happens to be the case in special relativity (which is on purpose neutral about such opinions), and above we proposed to make a separate box in which we would sketch different opinions about the physical cause. I plan to do so, in which case Einstein's opinion will move into that box, and the main text will be opinion-neutral. Harald88 21:58, 2 August 2006 (UTC)

Here's the question I have, and I don't have any investment one way or another--but I think it needs to be clarified. Just what is the typical inquirer who seeks out this page really looking for? My assumption is that they want something like the standard account (not the standard opaque wording, mind you) found in the usual college undergraduate physics tests, or perhaps in any of the many popularizations available, from Asimov to Weinberg. (The basics, that is, not the newest speculations--that can be another article.) Now if I'm just plain out of date, and such accounts of "time dilation" no longer present it in the context of the concept of spacetime as (popularly) set forth by Einstein himself, or by Born, Bondi, Wheeler--all of them crediting Einstein and explicitly presenting these issues in the context of the views he championed, in contrast to what is called the Newtonian view--then by all means, let's have just an historical reference to AE's role and no more. But don't inquirers demand "why" as well as "what"? (As in: But WHY does it work like that?) And much as we (like Einstein!) may deprecate gratuitous metaphysics, the only "why" with much currency at all seems to be that offered through the spacetime conceptual framework draw directly from Einstein. I'm one of those people who contends that "metaphysics" can never be set aside: we can either bring it forward and acknowledge it, or leave it obscurely resident and unchallenged. There is no account (at least, none understandable by nonmathematicians) that doesn't incorporate a range of extratheoretical assumptions embedded right in the foundations of the theory. All of which is to say: that's why I've made express references to AE and SR. Still...if someone can find a way to address the questions in the minds of likely inquirers without Einstein as the underlying interpretive frame, I'm ready to be astonished. -Scott Dickerson --207.200.116.13 20:04, 5 August 2006 (UTC)
Hi Scott, usually physics textbooks do an effort not to make claims that can't be corroborated. Moreover, their purpose is not to inform the students about speculations and philosophoes, but to enable them to calculate and make predictions. Or, as you imply yourself, they are rather silent about the metaphysics. Einstein gave a good example of such silence in 1905 by remaining vague about possible causes: SRT is on purpose not built on a hypothetical physical explanation or model, instead it's a principle theory.
I expect that many people who come to this article will expect to be first of all informed about the physics. Thus my plan to give metaphysics a presence, but keep it opticlly separated from the physics. Harald88 18:47, 8 August 2006 (UTC)
Hi Scott, your question is perfectly valid, of course. The expectation pattern is that science answers the why-questions. I feel deeply impressed by science when the physical explanation moves my understanding to a deeper level. In the case of time dilation, the why it works the way it works is not known, and there are no leads in what direction that "why" is to be sought. It's an enigma.
I have noticed that in the case of special relativity many authors tend to lose themselves in circular reasoning. Theorem B is derived from A, theorem C is derived from B, and then theorem C is derived from A. An example of that is the section Simple inference of time dilation Of course the mathematical formula is derived correctly there, but the verb 'to infer' suggest that those diagrams with propagating light are somehow informative in a deeper sense, which they aren't. What happens in the section 'simple inference of time dilation' is that it is based on reversing cause and effect. Light and matter are in motion in spacetime and the nature of motion in spacetime is such that it gives rise to relativistic effects. My supposition is that authors (subconsciously) prefer a presentation with circular reasoning to stating explicitly: "the why is an enigma".
Personally, I think the two axioms that Einstein presented in his 1905 article are unsuitable for an exposition of special relativity. I favor taking the physical properties of motion in spacetime as the starting point, and derive everything from that. Specifically, that means that the invariance of the spacetime interval is taken as principle of physics, with everything else presented as following from that principle. I wrote a user subpage article about Special relativity to inform other wikipedians how I see special relativity. The backbone of that article is the invariance of the spacetime interval. --Cleonis | Talk 23:19, 7 August 2006 (UTC)
I think we understand one another's point of view fairly well. Presenting the phenomenon as a consequence of Interval invariance is attractive in many ways. And to be frank, the more I consider just what I mean by "Einstein's appproach to spacetime", the less sure I am of what sort of treatment would satisfy me. It may be more a question of how the article could be structured than anything else: I'd like to see an introductory paragraph which summarizes how the "commonsense" view of Newton with regard to space and time (which of course wasn't "commonsense" when he promulgated it) has been modified by the Einstein-Minkowski generalization. FROM THIS we proceed onward into the notion of "interval," as something derived from that newer general view. I suppose I fear that what is proposed is to just set forth "interval" as a "given" with a (seemingly) arbitrary definition, and then forge ahead applying it to time dilation. An inquiring reader like me immediately starts resisting, thinking things like--"So just what IS this 'interval' thing? Some kind of object? A piece of spacetime? A mathematical fiction? I just wanna know why time slows down!" My thought is that by starting with just a few sentences making clear and explicit that, yes, this really is a new concept that came out of some very basic rethinking of our assumptions in the early 20th century (itself an integration and fusion of 19th-Century speculations and geometry development)--by doing that, discomfort will be lessened. But my concerns may be needless. (The preceding is actually what I meant by wanting-the-Why. Not an eternal metaphysical Why, unanswerable, but rather "Why did the physicists end up thinking about it this way?") Harald, I recognize that this business may not address your separate objections. -Scott Dickerson --207.200.116.13 23:54, 7 August 2006 (UTC)
Scott, indeed it would be a mistake to lable the Poincare-Minkowski invariance approach as "Einstein's". Moreover, it would also be a mistake to confuse a mathematical approach with a philosophy about "what really happens". Poincare distinguished between those two matters, while Minkowski proposed that space and time are "of the same substance". There is certainly no concensus about these largely philosophical things (that's is normal!). I don't necessarily disagree with writing an article about such philosophies, but it looks to me a subject that deserves to have an article devoted to it - it goes far beyond the subject matter of this article. Anyway, if I understand you well, that's not exactly what you ask for. But probably the answer on your last question is again a matter of opinion... Harald88 18:47, 8 August 2006 (UTC)

[edit] Popular Culture

Time dilation is used in The Matrix (called bullet-time by the directors) to exaggerate the speed of the "Agents" and Neo, as well as to further establish the fact that something is not right about the Matrix, relative to the real world.

Surely the above statement has nothing to do with time dilation in the sense of Einstein’s theories of relativity.

Since the “bullet-time” sequences take place in virtual reality they cannot have anything to do with real matter moving at speeds close to the speed of light. They merely represent Neo’s ability to manipulate the computer generated reality in which he finds himself as he sees fit consequent on his recognition that his movements in the virtual world have nothing to do with the strength of his own muscles – or indeed the movement of physical matter within a physical universe and thus the known laws of physics.

I fail to see how the “phenomenon” has any relevance to time dilation. Can anyone justify its continued presence?

I fail to see the entire point of the Popular Culture section. It clearly is a load of nonsense and misconceptions, originated in the minds of those who clearly know knothing about the subject. I would vote for removing the entire section. DVdm 20:23, 16 October 2006 (UTC)
I agree entirely. Orange112 20:35, 16 October 2006 (UTC)
Well, the phenomenon does appear in a number of fictional works and reference to such appearances could make the article significantly more relevant and accessible to many readers. To the lay reader, pages of calculations and diagrams of space travel probably convey very little by comparison to a simple example of something with which they are probably already quite familiar.
I see no reason in principle why such a section should not be included – reference to Planet of the Apes appears earlier on in the text for example, (though not in the actual Popular Culture section for some reason).
Clearly if anything does remain, the section needs a cleanup by someone who is familiar with not only the item of popular culture but also the subject matter itself. Practically this may well mean that much of the current section is removed but I think it would be beneficial to the article as a whole if something of the section remained and was supplemented at a later date with further, bona fide, examples of the phenomenon in popular culture. --62.173.76.218 15:33, 17 October 2006 (UTC)
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