Talk:Time dilation/Archive 5

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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)

"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)

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)

Failed GA

At a quick glance, there are no inline sources. Otherwise, it looks pretty good. Hurricanehink (talk) 04:25, 17 December 2006 (UTC)

Unreadable formulas

I think some formulas in this article does not convey any understanding of time dilation or anything else. I propose to change "'Time dilation at constant acceleration section"' into:

In Special Relativity, time dilation is most simply described in circumstances where relative velocity is unchanging. Nevertheless, the Lorentz equations allow one to calculate proper time and movement in space for any other cases.

The next simple case is movement with constant proper acceleration. Example of such motion is the movement of charge in constant uniform electric field.

Let $t\;$ be the time in an inertial frame subsequently called the rest frame.

Let $x\;$ be a spatial coordinate, and let the direction of the constant acceleration as well as the object's velocity (relative to the rest frame) be parallel to the x-axis. Then the equations can be written in form

${\frac {d^{2}x}{d\tau ^{2}}}=g{\frac {dt}{d\tau }}\;$

${\frac {d^{2}t}{d\tau ^{2}}}={\frac {g}{c^{2}}}{\frac {dx}{d\tau }}\;$

where

$g\;$ is the proper acceleration,

$\tau \;$ is the proper time, hence

$\left(c{\frac {dt}{d\tau }}\right)^{2}-\left({\frac {dx}{d\tau }}\right)^{2}=c^{2}\;$

Uniformly accelerating frame of reference

Assume the object's coordinates at proper time $\tau =0\;$ are $x=0,t=0\;$ and the velocity is $v=0\;$, then the solution of these equations is

$x\ \ ={\frac {c^{2}}{g}}\left(\cosh {\tfrac {g\tau }{c}}-1\right)\;$

$t\ \ \;={\frac {c}{g}}\sinh {\tfrac {g\tau }{c}}\;$

${\frac {dx}{d\tau }}=c\sinh {\tfrac {g\tau }{c}}\;$

${\frac {dt}{d\tau }}=\cosh {\tfrac {g\tau }{c}}\;$

Velocity

${\frac {dx}{dt}}={\frac {dx}{d\tau }}/{\frac {dt}{d\tau }}=c\tanh {\tfrac {g\tau }{c}}\;$

For the trajectory we have the following result

$\left(x+{\frac {c^{2}}{g}}\right)^{2}-c^{2}t^{2}={\frac {c^{4}}{g^{2}}}\;$

--TxAlien 05:59, 19 December 2006 (UTC)

alternate meaning or reference for time dilation (not related to physics)

I have a suggested edit, or perhaps a 2nd entry for time dilation and its meaning (when not discussing physics)

Time dilation is also a perceptual phenomena. That is, time can seem to dilate (slow down) under certain circumstances. It is an effect of some psychoactive drugs, including Marijuana. Perception of time is altered such that much seems to have happened (and much time to have passed), when in actuality little time has passed.

The opposite of time dilation occurs when a person is in the 'flow' state. Being in 'flow' is when completely engrossed and attention is fully engaged in an activity - be it artistic expression or complex problem solving. When time flies, its time contraction.

AlanLeMap 23:14, 29 December 2006 (UTC)Alan Le Map

The correct term is 'time perception' (see Google Scholar) and it certainly does not belong here.

There already is a Wiki article Sense of time.

DVdm 14:03, 30 December 2006 (UTC)

Nonsensical introduction?

It would seem that the edit by 24.149.190.76 has made the introduction nonsensical, but maybe it has some value. I'm not knowledgeable on the subject to evaluate it, but if it does have any value, it certainly doesn't follow the WP:LEAD guideline. I've reverted to this intro. CameronHarris 14:22, 4 March 2007 (UTC)

"In special relativity, the time dilation effect is reciprocal: as observed from the point of view of any two clocks which are in motion with respect to each other, it will be the other party's clocks that is time dilated. (This presumes that the relative motion of both parties is uniform; that is, they do not accelerate with respect to one another during the course of the observations.)

In contrast, gravitational time dilation (as treated in General Relativity) is not reciprocal: an observer at the top of a tower will observe that clocks at ground level tick slower, and observers on the ground will agree. Thus gravitational time dilation is agreed upon by all stationary observers, independent of their altitude."

This part especially doesnt make any sense. What does the reciprical have to do with this? If in special relativity an observer sees someone moving compared to himself, he will see their time dialation in reference to himself. How is that different than in gravitational? If the same observer is at a lower potential than the other person, he will still see that persons time as being the one dialated. Not his own, unless he is looking at his own time from their perspective. You would never see time in your own frame of reference as anything but normal unless you were imagining it from some other perspective regardless of how fast you are moving or what gravitational potenial energy you carry. 192.31.106.35 17:31, 7 September 2007 (UTC)

Time dilation and the sun

The sun's curvature of space-time is greater than the Earth's thus allowing a greater time dilation effect on the sun. When we say that the sun will die out in 6 billions of years, upon which time reference frame do we base our calculus on? Do we take the time dilation effect in consideration?

Applying the logic of time dilation, it is wrong said that the sun will become a white dwarf in 6G years since our time here on Earth flows more quickly that the time around the sun (and much quicker than inside the sun's core)

On the sun's surface, the gravitational acceleration is of 27.9g rather than of 1g on the Earth's surface. Such a difference surely must have an impact on how time flows on the sun.

If indeed the sun will last for another 6GY according to our time reference frame, it means that the sun is indeed close to its death but thanks to time-dilation created by its own curvature of space-time, the sun's remaining lifetime is "expanded" up to 6GY.

Here's a shortest explanation:

According to OUR time reference frame: The sun is close to its death but thanks to time dilation, is death is in 6GY for us.

According to the SUN'S time reference frame: The sun has another 6GY of "solar years" meaning that on Earth, thanks to time-dilation, the sun is veeeeeeeeery far from its death.

W.D. Vargen 05:33, 24 March 2007 (UTC)

The effect amounts to two parts in a million at the surface of the Sun. --EMS | Talk 22:20, 24 March 2007 (UTC)

The logic doesnt make sense I believe. If the sun has 6 billion years remaining, which is obviously a length of time in reference to Earth since all of our measurements were made depending on it, then it will die after those 6 billion years. However, you may say that from the perspective of the Sun, time is flowing faster for the less massive bodies (which Earth is included in this); therefore the Sun's remaining time until death is different than that seen on Earth. It doesnt matter how you define the length of time that you are measuring by, it only matters where you are defining that length. Since we make our measurements from our own reference the length of time, 6 billion years, remains what it is. But I may just be misunderstanding the point you are trying to make. 192.31.106.35 17:24, 7 September 2007 (UTC)

Time dilation cannot be said to be a 'fact' or ‘real’.

The alleged effect follows exclusively from theory and the mathematical consequences of the theory. The fact that certain effects predicated by the theory are observed, if they are accurately observed, does not rule out alternate explanations, and certainly does not create a one to one relationship between the theory and reality. Those with the strongest conviction that time dilation is an actual phenomena should check their own premises. To quote:

“ As for "proving" gravitation: You don't do it mathmatically [sic] to begin with. Instead it is the observation that matters. A combination of math and observation comes in when one seeks to verify that a given theory of gravitation is correct. In fact, this also brings up to your last question, since any explanation of gravitation is just a model and not the reality. Even if a given theory is exactly right, there is no way from first principles to prove that gravitation must exist and have exactly certain properties. Given that, any theory of gravitation must be just a theory due to its carrying with itself its own postulates. --EMS | Talk 20:12, 7 February 2007 (UTC “

EMS would be wise to adhere to the excellent standards he illustrates for others, rather than naively wandering away from science and into mysticism in order to preserve a cherished belief.

It is well known that if you synchronize two highly accurate pendulum clocks, one on the highest mountain, and one in the lowest valley, one will run slower than the other … this is a fact. Does this mean that time runs slower at one place than the other? Or to carry it further, let the mountain clock be moved into Earth orbit, will it confirm that time is stopped or runs at an erratic and unpredictable rate in space? Must time do what clocks do? Reductio ad absurdum.

Spin and elucidate your theories as you will. There is no need or justification for advancing them to the level of ‘FACT’. DasV 16:08, 20 April 2007 (UTC)

This talk page is for discussing the article. It is not for discussing your misconceptions and frustrations. DVdm 19:15, 1 May 2007 (UTC)

You need to take a look at the article on fallacy, so that you learn not to resort to one in your dialogues. DasV 20:14, 1 May 2007 (UTC)

Correct the article

phe·nom·e·non

1. a fact, occurrence, or circumstance observed or observable: to study the phenomena of nature.

Time dilation is a 'theoretical' phenomenon predicted by STR.

The article needs to be corrected. DasV 18:51, 1 May 2007 (UTC)

What is the experimental basis of Special Relativity? See some notable literature here: [1]

Specifically about time dilation: See section 4.

DVdm 19:12, 1 May 2007 (UTC)

Providing experimental evidence is not the issue. By that standard Ptolemy's geocentric universe could said to have been a 'fact' before it was proven to be false, as could any number of other theories. The point of an encyclopedia entry is to be accurate, not to be the forum for a debate on experimental evidence.

The theory that the Earth is a hollow sphere does not change to a fact because you circumnavigate it. Even if you circle it a million times it does not become a fact.

Time dilation is predicted by STR. There is evidence that it may be an actual phenomena. It is still theoretical. Why insist that it is a fact? DasV 20:05, 1 May 2007 (UTC)

Other than you we haven't really seen anyone insist at this point.

(1) The article calls time dilation a phenomenon. You seem to object to that, staging some dictionary, describing a phenomenon as a "fact, occurrence, or circumstance observed or observable". Perhaps you only looked at the first two words, but as far as we can see, the dictionary calls a phenomenon a fact or an occurrence or a circumstance, and, presumably in each of these cases, observed or observable. By the way, in this context Webster calls it an observable fact or event.

(2) Anyway, why call it a phenomenon? Most probably because that is how we, members of the human species, behave: we observe something in an accepted and verifiable way, and reach a consensus to call it a phenomenon. If we also happen to have found a theory that explains and predicts (or perhaps merely post-dicts) this 'phenomenon', then that is a nice bonus, even if a few members of the species have problems understanding that theory.

DVdm 22:40, 1 May 2007 (UTC)

Well if you like use the Wikipedia definition:

Phenomenon

From Wikipedia, the free encyclopedia A phenomenon (Greek: φαινόμενo, pl. φαινόμενα) is an observable event or, quite literally, something that can be seen. Derived from the noun φαινόμενον (phainomenon, df. appearance), it is also related to the verb φαινειν (phainein, df. to show).

Observe the excellent understanding that EMS has on a ‘phenomenon’: “Even if a given theory is exactly right, there is no way from first principles to prove that gravitation must exist and have exactly certain properties. EMS”

I would disagree only in that ostensive information has a higher degree of certainty ... usually. Subject to the qualification that people readily fool themselves.

The point is the article opens with the statement that Time dilation is a phenomenon. Let’s use your definition to translate the statement into fundamentals: “Time dilation is an observable fact.”

==> Phenomenon does not stand for "observable fact". It stands for "a fact, occurrence, or circumstance observed or observable". Skipping remainder of strawman and turning to last line... DVdm 09:38, 2 May 2007 (UTC)

Is this true? The ‘fact’ is that time dilation is not an observable fact, what is observable is for instance that moving clocks move at different rates with respect to each other. This is certainly observable evidence which coincides with the STR predictions … except that the clocks are not measuring time directly, anymore than any other clocks measure time directly. To extrapolate from what clocks do to what time must do to what bodily processes must do has gone a long ways from the ‘observable fact’ of certain moving clocks moving at different rates, and is simply not factual … it is theoretical. To claim that abstract mathematical descriptions have a one to one relationship with what ‘time’ is in reality simply goes too far. What is observed does not as yet bear that out. The point of science is to differentiate between fact and theory.

Why not be content with the evidence confirming the predications, and continuing to theorize and find observations that agree with the theory? Why would you insist ‘time dilation’ in all its theoretical manifestations be on a one to one basis with the fact that you exist?

Time dilation is a predicted effect ... there is no need to mislead people into thinking otherwise. DasV 23:44, 1 May 2007 (UTC)

==> Time dilation is also an observed effect - see Experiments (section 4).

You seem to feel a need to mislead people into thinking otherwise, but I'm afraid that your failure to understand the theory will not make the phenomena go away. DVdm 09:38, 2 May 2007 (UTC)

It is unfortunate that you do not read your own references. It is not an observed effect. Since you refuse to deal with the issue and can only resort to fallacious arguments I see no point in further discussion with you. Your revisionism which confuses theory and fact should take the next leap and relabel STR as Special Facts of Relativity. Such is one of the reasons that Wikipedia has been reduced to a non-authoritative reference in universities ... it often reflects what contributors would 'like' to believe, rather than the actual mainstream position. DasV 14:08, 2 May 2007 (UTC)

I find it amazing that someone stages a reasonably good definition of phenomenon ("a fact, occurrence, or circumstance observed or observable"), and then accuses people who use that word, that they actually have a completely crippled version (a fact) of that definition in mind. This must be one of the most obvious and easy to spot strawman arguments I have ever seen someone come up with. Congratulations for that. DVdm 15:30, 2 May 2007 (UTC)

“As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality.” Albert Einstein, "Geometry and Experience", January 27, 1921

Enjoy your perspective. I'm quite sure Ptolemy's followers regarded the geocentric universe as a 'fact' also.

==> Here you go with that strawman again. Apart from you, no-one is talking about facts. We are all talking about phenomena, which are, per your own chosen definition, "facts, occurrences, or circumstances observed or observable". You really should at least pretend to try to learn to live with what you brought up yourself. DVdm 17:17, 2 May 2007 (UTC)

> Curious isn't it that each generation is filled with 'experts' who insist that all is correct and all is known, that their beliefs be held as certain as the fact of existence, and therefore there is no need for further experiments ... and then the subsequent generations come along and point out their mistakes. DasV 16:44, 2 May 2007 (UTC)

I guess I missed the experiment where the slowing of bodily processes were observed, though it is said to be part of the 'phenomenon'. But then if it's a 'strawman' he wouldn't have any bodily processes to observe would he? DasV 14:42, 3 May 2007 (UTC)

While looking for experimental evidence for Newton's law of gravity, I guess I missed the experiment where we let go of you from a high tower, to verify whether you would indeed fall. DVdm 14:45, 3 May 2007 (UTC)

Mmmm yes ... Newton's Law 'theory' predicts I would fall ... actually falling would be the observed event. It is not a fact that I 'fall' until I have 'fallen'. This is apparently confusing for some of us. DasV 14:54, 3 May 2007 (UTC)

I am sorry to see that this deteriorated into DVdm trying to be witty. If the common definition of phenomina states that it is an observed effect than obviously this is not an phenomina. How can one observe, which is limited to his frame of reference, any relationship between his own and some other frame of reference without assuming that the other frame of reference treats the observed as his own would if it were occuring there. We can't observe time dialating. We can only observe something that we percieve as another frame of reference's time dialating. —Preceding unsigned comment added by 192.91.171.42 (talk) 18:57, 7 September 2007 (UTC)

No way this is possible?! Am I wrong?

"Indeed, a constant 1 g acceleration would permit humans to circumnavigate the known universe (with a radius of some 13.7 billion light years) in one human lifetime."

Whoa whoa whoa, hold up! If we assume that a human lives to be 100 years old, wouldn't that mean that the maximum distance a human could travel in his lifetime would be less than 100 light years? I mean, a light year is how far light travels in one year, correct? And nothing can travel faster than light, correct? So how is it possible that by traveling at a speed that is close, but not quite the speed, of light, you could travel 13.7 BILLION light years in less than 13.7 billion years?

Am I overlooking something very obvious or am I the only one who sees this?

Yes, you overlooked Length contraction. See if you can figure it out.

DVdm 22:23, 2 May 2007 (UTC)

If my understanding of time dilation is correct, the idea is as follows. If a person travels at the speed of light to reach a place 100 light years away, it will take him 100 years to reach there from our, the stationary viewer's, perspective. But for him, it will feel like he reached there in only a matter of minutes, and thus will have only aged a matter of minutes. However once the ship stops and he gets out, and checks the local time, he will realize that 100 years has indeed passed. 64.236.245.243 16:18, 8 June 2007 (UTC)

No, you can find the answer in the article. Please note that this place is for discussing the article's content and format. Places like sci.physics.relativity might be better suited to help you increase you understanding of this. DVdm 16:26, 8 June 2007 (UTC)

No? No what? What are you saying no to? Copy and pasting the same response for different points makes you sound incoherant. 64.236.245.243 17:41, 8 June 2007 (UTC)

As I already hinted, this is not the place to help you find a way out of your confusion. DVdm 18:25, 8 June 2007 (UTC)

This is a logical fallacy because I'm answering a question in this particular discussion, not asking one. *pats your head* You are confused. 64.236.245.243 18:36, 8 June 2007 (UTC)

It means in theory you can do anything. In reality there are limits. Confusing the two can lead to nonsensical predictions. This most often occurs when the theory is not well understood. DasV 14:49, 3 May 2007 (UTC)

Just trying to understand Time Dilation...

Ok I'm in a spaceship moving close to the speed of light. I am somehow able to look at a stationary clock outside the ship. That clock should appear (to me) to be ticking faster right? 64.236.245.243 16:13, 8 June 2007 (UTC)

No, you can find the answer in the article. Please note that this place is for discussing the article's content and format. Places like sci.physics.relativity might be better suited to help you increase you understanding of this. DVdm 16:26, 8 June 2007 (UTC)

This is comming from the guy who mentioned length contraction in the previous Time Dilation question lol. Don't be a hypocrite. 64.236.245.243 17:39, 8 June 2007 (UTC)

Please Answer The Following Question

In your defintion you state that the time parameters are intervals between events. Suppose we take these events to be the dial readings appearing upon the faces of two clocks. We specify an observer in a stationary frame viewing a moving clock in a moving frame. Now let delta t be the dial readings viewed by the observer in the stationary frame on the face of the moving clock and let delta t zero be the dial readings on the face of the reference clock in the stationary frame. Then according to the time dilation definition equation, the moving clock as viewed by the stationary observer runs fast because if the reference clock reads one hour, the moving clock reads more than one hour, since the gamma factor is greater than one. Hence the statemnt that moving clocks run slow is refuted because the time dilation equation equation states that they run fast in this case. I think you guys have got this wrong. Please explain why the article as written is not a false statement.Electrodynamicist 15:37, 31 July 2007 (UTC)

Your phrase "dial readings appearing upon the faces of two clocks":

If you carefully read the first paragraph, you will notice that it is essential for the equation to be valid, that we are talking about the "time interval between two colocal events for an observer in some inertial frame".

DVdm 15:44, 31 July 2007 (UTC)

I apologise. But I don't know what colocal means. Please explain, why the statement you make is relevant to the question asked.Electrodynamicist 17:01, 31 July 2007 (UTC)

Indeed, apparently the word colocal does not appear in some of the dictionnaries I consulted, so I made a little change to the article. Thanks for spotting this.

Colocal = at the same place. In other words, the events with the time interval $\Delta t_{0}\,$ between them take place on the face of one single clock of an observer in some inertial frame. That is essential for the equation to be valid. The time $\Delta t\,$ between these same events as measured/observed/calculated by another observer in motion with respect to the clock is then larger by the factor gamma. So this observer decides that the other (moving) clock is "running slower".

DVdm 17:20, 31 July 2007 (UTC)

Thank you for this answer. I now understand what colocal, means, but if these "events" are dial readings, then the moving clock is running fast and not slow according to the equation you state. Is this correct or not. A fast clock is one which reads ahead of or greater than the reading of the reference clock.Electrodynamicist 18:10, 31 July 2007 (UTC)

If you carefully check the equation and the precise meaning of the variables, you will see the following:

According to you, your clock has one second between two ticks. According to me, your (moving) clock has more than one second between two ticks, so in a sloppy way, I say that your clock is "running slower than mine".

According to me, my clock has one second between two ticks. According to you, my (moving) clock has more than one second between two ticks, so in a sloppy way, you say that my clock is "running slower than yours".

Note that measuring when an event takes place on a local clock is very easy and straightforward: just take the reading. On the other hand, measuring when an event takes place on a remote clock is far less easy. It takes (1) having sent a light signal, (2) receiving an echo, reading the times of those two local events on your local clock, and taking the average of those times. So, measuring a time interval between two events on a remote (and possibly even moving) clock takes four local events.

It's really all a question of how things are defined and measured. A useful (and probably less surprising) analogy: when we look at each other through a small gap between our fingers, according to me, you have a smaller opening angle than I have, and according to you, I have a smaller opening angle than you have.

DVdm 08:24, 1 August 2007 (UTC)

I am sorry but I did not understand the answer at all. The only part I understood was "It's really all a question of how things are defined and measured". This is a simple problem. It states that when clock dial readings are used to define what you call events, the equation which you give asserts that the moving clock runs fast. So there is a need to define your events so that this problem does not arise. However, since most events are defined in terms of some concept of clock dial time, this may not be an easy thing to do. I suggest consulting Einstein's 1905 paper in which the correct definition of time dilation is given.Electrodynamicist 13:04, 1 August 2007 (UTC)

I am sorry that you don't understand the answer, but this is not the place to teach you. As I suggested when talking to some of your alter-egos, places like sci.physics.relativity might be better suited to help you increase you understanding of this. Good luck. DVdm 16:07, 1 August 2007 (UTC)

That settles it. The current article is incorrect and is in need of revision. It should state Einstein's 1905 definition of time dilation as the correct equation instead of the current equation. Since the current article does not do this it, must be incorrect.Electrodynamicist 18:43, 1 August 2007 (UTC)

Yes, your failing to understand a simple concept certainly settles something :-)

But seriously, you really need another kind of soapbox to vent your frustrations. Really, I recommend you go back to sci.physics.relativity. That place has been specially created for people with problems like yours.

Cheers and good luck. DVdm 18:49, 1 August 2007 (UTC)

This question has a very simple answer. Go and read Einstein's papers. Is that too much to ask? If you would actually study what he says, then you will understand the problem and be able to give a correct definition of time dilation. But refusing to do that simple thing is not a positive response.Electrodynamicist 21:08, 1 August 2007 (UTC)

According to "The Classical Theory Of Fields" Landau and Lifshitz page 8, "...the proper time of a moving object is always less than the corresponding interval in the rest system." This shows that your definition is false. Please change to agree with this authority. 72.64.58.30 20:28, 5 August 2007 (UTC

Oh, by the way. In Electrodynamics and Classical Theory of Fields, by A. O. Barut, page 22 it says:"...time lags behind in the moving frame relative to the rest frame..." See my question above. Please explain this in your discussion.72.64.58.30 20:50, 5 August 2007 (UTC)

"This shows that your definetion is false" ==> the fact that you write this (and I'm not referring to the "dyslexic" typo) shows that you honestly haven't got a clue what you are dealing with. This is becoming really embarrassing. Please stop this - you'll hurt yourself. DVdm 21:03, 5 August 2007 (UTC)

Your definition of time dilation is false. In your equation delta t and delta zero must be measured by an observer in the stationary frame with reference to the same stationary clock. The time interval in the moving frame is assumed to be the ticks on a moving clock running at the same rate as the reference clock in the stationary frame. In order for the stationary observer to conclude that the moving clock is slow the time interval of the moving frame clock, which he observes in his frame by comparasion to his reference clock, must be longer than the same interval on his reference clock. Hence the comparasion requires that the same clock be used to compare both time intervals. It is an assumption of the theory that the proper time of the moving frame clock is the same as the proper time of the stationary frame clock. So the observer sees that the moving clock appears slow when he observes the time interval between ticks on the moving clock in comparasion with his reference clock. A crucial assumption of the theory is that both clocks run at the same rate and therefore record the same proper time. 72.84.67.171 21:34, 5 August 2007 (UTC)

Let'e see: The article specifies that $\Delta t_{0}$ time as measured using the "stationary" clock (so that the events are "colocal"), whils $\Delta t$ is time a measured using the "moving" clock. You then turn around and demand that the time interval be measured using the same clock. Excuse me for waying so, but a clock cannot be time dilated with respect to itself. Your demand can have no effect other than to ruin this exercise (which I suspect is your goal here). --EMS | Talk 04:34, 6 August 2007 (UTC)

Ed, I wouldn't bother trying to explain anymore. It will just bounce. DVdm 08:48, 6 August 2007 (UTC)

Let me repeat this again so that you will understand it. According to your definition, the moving clock is running fast. So you made a mistake. You need to go back to the textbooks and read them more carefully. 72.64.62.72 12:30, 7 August 2007 (UTC)

I quote from Foundations Of Physics by Lindsay an Margenau page 340. "...the indicated time interval on the clock that is considered to be moving is shorter than the time interval on the clock considered stationary for the same two events." Your definition states the opposite, so it is false.72.64.62.72 16:03, 7 August 2007 (UTC)

The part that you quoted suggests that the two events in question happen at the same place in the rest frame of what they call the stationary clock. Can you quote the relevant part that clearly defines the two events? DVdm 16:39, 7 August 2007 (UTC)

The two time intervals must be compared to the same or to an identical clock. Otherwise you can not say anything about which clock is slow or fast.72.64.62.72 21:49, 7 August 2007 (UTC)

I repeat: can you quote the relevant part that clearly defines the two events? DVdm 22:00, 7 August 2007 (UTC)

I have cited textbooks and journal articles that should be sufficient for you to determine the answer as to why you are mistaken in your definition. I would also strongly suggest that you read Einstein's 1907 paper.72.64.62.72 18:56, 8 August 2007 (UTC)

I am just browsing but I believe there is a flaw in these two statements. 'According to you, your clock has one second between two ticks. According to me, your (moving) clock has more than one second between two ticks, so in a sloppy way, I say that your clock is "running slower than mine". According to me, my clock has one second between two ticks. According to you, my (moving) clock has more than one second between two ticks, so in a sloppy way, you say that my clock is "running slower than yours".' If according to 'me', 'my' clock has one second between two ticks and according to 'you' 'my' moving clock has more than one second to two ticks; this does not mean that to 'you' 'my' clock is running slower. In fact the first sentence has no direct relationship to the remaining two sentences because you switched frame of reference. A more accurate way of saying it might be that according 'you', when 'my' clock is in 'your' frame of reference it takes one second for two ticks to occur. This first sentence is always true...and therefore it has no relationship to the other sentences. Any time the reader and clock are in the same frame of reference, there will be one second between two ticks. A comparison of slower or faster can only be made through the same frame of reference. If you only see that the moving person's clock takes more than one second between two ticks you cant assume his clock is the same as yours when it is inside your frame. —Preceding unsigned comment added by 192.91.171.42 (talk) 18:51, 7 September 2007 (UTC)

Lack of citation in First section

To DVdm:

The main issue is that there is no citation at all. How do we know it was not written by a crank? For example in A.P. French "Special Relativity" 1968 p.100, in essence, it states that you need 3 clocks to see what is going on, which is discussed to death on the twin paradox page. Anyway, for years this page has contained very cranky stuff. Why do you delete citations of other articles? Jok2000 18:23, 28 October 2007 (UTC)

Hi Jok2000, I deleted your first fact request because the fact is explained in the definitions of the first section, and I undid your second edit because it made the concept frame of reference point to twin paradox, whereas the latter is much narrower a concept than time dilation and even more so than frame of reference. I.m.o. the introduction has sufficient pointers to other wiki articles, although it might be a good idea to have an extra wikilink to the time dilation section in the main article on special relativity.

And of course, if it is written by a crank, it will be quickly (or at best ultimately) reverted :-). I admit it's a while ago since I had a complete read of the article, but do you see cranky stuff in its current state? Cheers, DVdm 18:53, 28 October 2007 (UTC)

Er, the article has been pretty much devoid of citation (using the "ref" tags) for 3 years running. Jok2000 23:46, 28 October 2007 (UTC)

Ah, you mean actual <ref>tags</ref>. Yes, I agree that the article could use a few more of those. But at least the article is stable. :-) DVdm 07:56, 29 October 2007 (UTC)

Phrasing of 2nd paragraph

In the 1st bullet of the 2nd paragraph of the article itself, where it says, "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", it would be more accurate to replace "are found to be running slower" with "are observed to be running slower". The reasons for this (important) word change are well stated by what follows in the article itself.

In the 2nd bullet, one would not make an analogous change to "In general relativity, clocks at lower potentials in a gravitational field — such as in proximity to a planet — are found to be running slower" as that would be a change for the worse. The reasons for the different wordings is well stated in the 3rd and 4th bullets. Since I have not yet read the history of this article, I will let someone who has been involved in developing this article make the change - or if there is a consensus against and rationale for not changing, please put in the Discussion. Otherwise, I'll assume it hasn't been considered one way or the other and change it, after a week passes, to flush out other views. (Jok2000's comments below have been addressed.) TwPx 04:00, 7 November 2007 (UTC)

They have not been addressed. You have not provided a citation that justifies removing the word "found". Actually, this is ridiculous. I have no stated position aside from WP:V so far. Jok2000 20:46, 9 November 2007 (UTC)

Jok2000, as I have read the history of this article and another, I have been impressed by your politeness and sincere desire to get it right. So my apologies for obviously pushing the wrong button by my "have been addressed" comment above. I was not saying it as arguer AND judge. I was just noting in the main section that I had seen your subsequent comment below and had responded to it and, hence, my intent to do the change had not been subsequently changed by your comment.

TwPx 00:01, 14 November 2007 (UTC)

I disagree, some of the experiments listed involve moving a clock around and bringing it back and looking at the two clocks. That would be a finding. Going through the pain of synchronizing GPS satellites' clocks using transmitted signals, now that's an observation. Jok2000 04:14, 7 November 2007 (UTC)

"Found" is certainly correct for clocks that are brought back, but it's inaccurate for clocks that are in inertial motion - slowness is in that case no absolute. Thus the addition of for example "measured" is certainly an improvement eventhough it makes that sentence a little more complex. I'll be bold about it and make that little change. Harald88 12:47, 11 November 2007 (UTC)

Your 1st sentence is correct (e.g., J.C. Hafele and R.E. Keating, Science 177, 166 (1972)). However, just as in the Twin Paradox debate, there is great debate about what was the cause of that net proper time difference - so your position is assuming that one of a number of different positions is correct. (By the way, the position that you side with is currently a small minority position, if published papers are a good measure - not that that rules it out.) Hence, there are unresolved, to say the least, theoretical problems with your position. In addition, the GPS, VBLI and NASA data sets argue against your position - if need be, I and others can go into greater detail. In addition, Special Relativity says that both A and B will observe the other's clock to be running slow. So that says it is unquestionaly correct to use the suggested "observe".

I didn't understand what you meant by "Going through the pain of synchronizing GPS satellites' clocks ...", but, from the context, I think you were suggesting that saying that gravitational time dilation is on shakier ground than SRT time dilation on the "observed" vs "found" issue. That's incorrect. The physical, asymmetric difference in clock rates as a function of the difference in gravitational potential was shown to virtually everyone's satisfaction (e.g., Pound, R. V.; Rebka Jr. G. A. (November 1, 1959). "Gravitational Red-Shift in Nuclear Resonance", Physical Review Letters 3 (9): 439-441, R.V. Pound and J.L. Snider, Phys. Rev. 140, B788 (1965)) - well before GPS sattelites .

Also, your argument is in direct contraction to bullets 3 & 4 of the article itself. As I look at the rest of the article, I now see that the three references I gave above are also mentioned in the body of the article which is good as they are the classics and quite relevant. Hence, consistent acceptance of your arguments would require a significant re-write of the current article.

TwPx 18:01, 7 November 2007 (UTC)

Voice of a Distant Star

Time dilation plays an integral part of the story in the short anime film Voices of a Distant Star. Young lovers are separated when one decides to enlist in a six month tour of the galaxy and the other ages many years.

That wasn't time dilation. The girl traveled by way of a wormhole to a distant location, many light-years away. There was no time-dilation, it's just that it took many years for her messages to reach him back on Earth. I removed it. Nik42 06:54, 8 November 2007 (UTC)

"Stationary"?

The reference to "stationary" in this article when discussing special relativity is inadvisable. Among other things, it is extremely misleading to the naive reader as it conjures up the idea that there is some special frame, as in aether theory, against which (absolute) velocity is measured - even if that was not what was meant or explicitly stated. Einstein and special relativity are quite clear that all inertial frames are on equal footing and to claim that one frame, even in the context of one example, is a special ("stationary") frame is, at the very least, misleading.

I see that some here understand this: "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" - Cleonis

In particular, there is absolutely no justification to claim, "The Einsteinian takes seriously the thesis that all motion is indeed relative to some actual (if specified only by implication) "benchmark" that is regarded as stationary, ...".

Hence, I would recommend changing such references and would plan to do so after, of course, waiting for persuasive feedback.

As it happens, "stationary" is also used in the article when discussing GRT and as such is not subject to the above comments. The quote is "Thus gravitational time dilation is agreed upon by all stationary observers, independent of their altitude". As a minor note, I think it would be clearer to delete "stationary" from that sentence. (It's usually dropped as the key for agreement is not the observer's motion relative to the observed, but the observed's motion relative to one another or rather their lack of or negligible relative motion.) TwPx 03:00, 14 November 2007 (UTC)

There is a responsibility at Wikipedia to keep things in layman's terms. Using the word "putative" in front of "stationary" is a clue that there is more to it for those who wish to read on further. This way the article increases in complexity for those who want to make the effort of reading on. Jok2000 21:47, 14 November 2007 (UTC)

Observers on the ground will NOT agree

"an observer at the top of a tower will observe that clocks at ground level tick slower, and observers on the ground will agree."

I see this has been brought up but I don't see an explanation and experiments cited in the article seem to dispute it completely. Shouldn't we remove that line?

If the clock is moving slower due to time dilation from gravitational effects the observer next to the clock will be in the same gravitational field and therefore the same realm of time as the clock. So no, the observers on the ground will NOT agree with the person on the tower. Observers on the ground will see their own clock as moving at the normal rate while the clock on the tower will appear to be moving fast. Observers on the tower will see their clock run at the normal rate while the clock on the ground will appear to be moving slow.

"Hafele and Keating, in 1971, flew cesium atomic clocks east and west around the Earth in commercial airliners, to compare the elapsed time against that of a clock that remained at the US Naval Observatory. Two opposite effects came in to play. The clocks were expected to age more quickly (show a larger elapsed time) than the reference clock, since they were in a higher (weaker) gravitational potential for most of the trip (c.f. Pound, Rebka). But also, contrastingly, the moving clocks were expected to age more slowly because of the speed of their travel. The gravitational effect was the larger, and the clocks suffered a net gain in elapsed time. To within experimental error, the net gain was consistent with the difference between the predicted gravitational gain and the predicted velocity time loss."

Cyberben3d 17:28, 14 November 2007 (UTC)

I did not write the quoted sentence in the article, but let me confirm that it is correct. I think the problem maybe that you, Cyberben3d, are interpreting it differently than it was intended to read and how I, as a first time reader of it, interpret it. It's correct in the limited assertion that both observers will agree that the clock on the ground ticks slower than the clock in the tower.

Your argument doesn't seem to debate that point. You are correct that the two observers will see things differently in that both will see their own clock as ticking at a "normal" rate, but that is not in contradiction to the quote's claim.

I see that you are already familar with the original citation, Pound, R. V.; Rebka Jr. G. A. (November 1, 1959). "Gravitational Red-Shift in Nuclear Resonance", Physical Review Letters 3 (9): 439-441, supporting the quote.

TwPx 19:44, 14 November 2007 (UTC)

Problem with the article that is misleading readers

There is a problem with the article that is misleading readers. It is NOT pointed out that the sign of the 'Delta T' is dependent upon direction of motion. Dilation is NOT the only choice.
The Lorentz-Einstein time transformation equation can be written t' = gamma (t - vx/c^2)
And this form makes it clear that the sign of the correction depends on the sign of v.
Normal convention has v as positive when the distance is growing and v as negative when the distance is shrinking.
x is, of course, the location on the x axis or the distance between the observer and the object being studied.
You will also notice that relativistic time correction can involve dilation or contraction, matching the relativistic Doppler effects.
The idea that 'ALL moving clocks run slower than our clock' is incorrect. Only those moving away run slower.
Those moving toward us will appear to be ticking faster than our clock to us.
This SOLVES the 'paradox' in the symmetric acceleration example by removing the apparent problem some see because they do not realize that relativity can compress the time (as WE see it) of an oncoming object.
N5bz (talk) 20:27, 27 November 2007 (UTC)

With the usual definition (see article) for time dilation to come into play, the x in the equation t' = gamma (t - vx/c^2) is supposed to be 0, meaning that the clock is at rest in the unprimed coordinate system (x,t). In that case the equation reduces to t' = gamma t, meaning that the time between the 0-tick and the t-tick on that clock is measured to be t' in the primed coordinate system (x',t') in which the clock is moving, t' being larger than t by the factor gamma, hence the term time dilation. DVdm (talk) 22:34, 27 November 2007 (UTC)

Perhaps I am wrong. I thought that x and v were measured in the unprimed frame and refered to the

distance to the OTHER clock, and the velocity of the OTHER clock as measured in the stationary frame.

[quote from AE 1905 paper]

Now to the origin of one of the two systems (k) let a constant velocity v be imparted in the direction of the increasing x of the other stationary system (K), and let this velocity be communicated to the axes of the co-ordinates, the relevant measuring-rod, and the clocks. To any time of the stationary system K there then will correspond a definite position of the axes of the moving system, and from reasons of symmetry we are entitled to assume that the motion of k may be such that the axes of the moving system are at the time t (this “t” always denotes a time of the stationary system) parallel to the axes of the stationary system.

[unquote]

so the velocity and distance traveled are as measured in the stationary system but they are of the moving object. And he is talking about something moving AWAY at v. "in the direction of increasing x".

[quote]

Further, we imagine one of the clocks which are qualified to mark the time t when at rest relatively to the stationary system, and the time tau when at rest relatively to the moving system, to be located at the origin of the co-ordinates of K, and so adjusted that it marks the time tau. What is the rate of this clock, when viewed from the stationary system? Between the quantities x, t, and tau, which refer to the position of the clock, we have, evidently, x = vt and tau = gamma (1-vx/c^2).

[end quote][note: I substituted gamma for 1/sqrt(1-v^2/c^2) in this quote]

[quote]

whence it follows that the time marked by the clock (viewed in the stationary system) is slowed....

[unquote]

So I read AE as speaking about a clock that is moving AWAY at v. So, unless I am misreading badly, the x means the distance (as measured in K) of THE MOVING CLOCK. And v is the velocity of same as measured in K.

The fact that AE has not bothered to explain the case where the clock is approaching the origin of K at -v and is located at x does not seem to me to imply that Tau will ALWAYS be less than t.

I think he just expected us to understand that tau could be greater or less than t, depending on sign of v.

I suspect that if we start his derivation using '-v in direction of decreasing x' we will derive exactly the same equation as he did using 'v in the direction of increasing x'.

But perhaps I am misreading. --N5bz (talk) 00:09, 28 November 2007 (UTC)

Perhaps you're just a bit confused by the inevitable multitude of choices of variables notation. For a clear understanding I'd refer to the section Time dilation and length contraction in the main Special relativity article, and then review the definition (using slightly different notation) in the overview of this article.

If you have a clear understanding of that, then keep in mind that above (with your choice of the equation t' = gamma (t - vx/c^2) ), we have implicit deltas, meaning that (x,t) = (x',t') = (0,0) is the event of coincidence of the two origins, such that in terms of the deltas, we have Delta(x) = x-0, Delta(t) = t-0, Delta(x') = x'-0, Delta(t') = t'-0.

If this does not help, since this article content/format talk page is not the place to explain such things, perhaps you could go to a Usenet forum like for instance sci.physics.relativity, where surely you will find someone who will help you. Good luck. - DVdm (talk) 09:22, 28 November 2007 (UTC)