Talk:Twin paradox/Archive 1

message: The explanation involving acceleration is just a red herring. The conclusion (differential aging) is predicted by an equation that does not depend on acceleration and so acceleration is irrelevant. 
: Disagree: this is very thing that made Einstein call it a paradox: if you don't talk about acceleration you cannot differeniate between the twins and you could calculate the same time difference for either twin. It was paradoxical to Einstein, at least, that the very thing that the asymmetry depended on, the acceleration, did not enter the calculation. He resolved the paradox to his satisfaction by making the calculation depend on the acceleration which was equivalent to a gravitational effect. I think we can assume he knew many of the other igenious ways of calculating the time difference presented on this page and I doubt we need more calculations of it from the Lorentz transformations alone. E4mmacro 04:47, 17 December 2005 (UTC)
thread_title: Acceleration is a red herring

message: :It is sometimes claimed that the twin paradox cannot be resolved without the use of general relativity. Indeed, one of the twins must undergo acceleration during the U-turn, and only general relativity can properly describe accellerating observers. Strictly speaking this is true. Special relativity, however, is an excellent approximation to general relativity, except for very strong gravitational fields and large accellerations. If we can make the inertial legs of the trip long enough and the accelleration at the U-turn small enough, the effects of general relativity in the above analysis would amount to very small corrections.
;I don't get this. Why can't accelerating objects be described with special relativity? What difference is there between general and special, as long as the ship isn't traveling cosmological distances or near large masses?
;Also, the point of making the inertial legs of the trip long enough--or the acceleration at the U-turn large enough--is to let you work out the problem with just algebra, instead of calculus, by making the parts of the trip under acceleration a trivial fraction of the whole. You can't do that by making the acceleration small.
;—wwoods 06:32, 20 Nov 2004 (UTC)
thread_title:  Need for general relativity? 

message: On Sept 3 2004, Wodan asked about the quandry of spinning. If spinning is relativistically the same as being stock still while the entire cosmos whirls around about you, then that seems to allow for objcts to be moving at speeds far greater than lightspeed. But what Wodan is overlooking is the fact that in such a scenario (the entire cosmos whirling about you), no specific object is moving faster than lightspeed with respect to any other specific object. So Wodan has confused REAL relative motion with the purely human-concocted construct of moving with respect to a contrived hypothetical x-y-z frame; and those are quite disparate notions! There's no violation of the sanctity of lightspeed in perceiving the entire cosmos as whirling around that way. --ETP 13:34, 16 Dec 2004 (UTC)
thread_title:  spin proviso 

message: Nothing prevents a spatially periodic spacetime in special relativity. It still can be flat. No kidding. It's a boundary condition. It's interesting to consider the Twin Paradox under these circumstances, because the twins can be truly symmetric. That is, in a periodic spacetime, they can meet again without undergoing acceleration. I'm not certain about the resolution of the paradox in this case. However, the  existence in a periodic spacetime of two different light cones connecting the twins, one forward and one back in a 1-D periodic space, may be a clue. -MFR
===Cylindrical Universe===
:E4mmacro 04:33, 18 December 2005 (UTC)
replies: text: E4mmacro 22:54, 18 December 2005 (UTC)
thread_title:  Twins in a Periodic Spacetime 

message: :E4mmacro 04:33, 18 December 2005 (UTC)
thread_title: Cylindrical Universe

message: :E4mmacro 22:54, 18 December 2005 (UTC)
thread_title: Cosmic Censorship?

message: In the Usenet Physics FAQ discussion of the Twin paradox, it is shown that the magnitude of the difference in proper time can be calculated in as many as four of five different ways, all producing the same answer. 
I favor the most abstract approach, I favor the approach that uses considerations of geometry and symmetry only.
It is possible to account for the difference in proper time on the basis of the invariance of the space-time interval. From the formula for the space-time interval, the following formula can be given for the proper time of a traveller
: d \tau ^2 = dt^2 - dx^2 - dy^2 - dz^2 
This formula expresses an asymmetry: the laziest way to travel a year ahead in time is to just do nothing. You wait a year, and at the end of that, a full year has passed. Alternatively, you can fire up the thrusters of your space-craft, and you can take a longer path through space towards a rendez-vous with the traveller who only waits for a full year to pass. Working up many extra miles of traveling it will take less than a year, say, 11 months, to travel towards a point of rendez-vous with the traveller who is inertial.
The formula expresses that the traveller who remains in the same inertial frame throughout the journey represents some ground level as far as proper time is concerned, somewhat akin to zero Kelvin. No matter what happens, the clocks that are co-moving with a traveller who moves inertially all the time (and stays away from gravitation) are the first to reach the point of a year of proper time. There is no physics that can make a clock count more proper time than that, it is only possible to count less proper time than that, by deviating from moving along a geodesic of Minkowski space-time, by taking "a longer road" towards the rendez-vous point in space-time. The rendez-vous is essential, it closes a loop. Without closure of the loop there is no such thing as being "the first to have counted a year of proper time".
What needs to be calculated is the path-integral of the path that is taken, the path with respect to the inertial frame of reference of the traveller who does nothing. 
Relativity does not explain why time and space are related in this way. What would a universe be like in which taking longer path corresponds to counting more proper time? --Cleon Teunissen | Talk 09:48, 13 Apr 2005 (UTC)
thread_title:  Geodesics and closing a loop 

message: In Special Relativity, there is the upper limit of velocity: the speed of light. Likewise there is an upper limit in the rate of time. 
A clock that moves inertially, and stays away from gravitation, is in step with time at its maximum rate. All clocks that take a longer path through space than the inertially moving clock, are seen to have been in step with time that proceeded at a slower rate than the maximum rate. So when clocks separate and later reunite at a point of rendez-vous, the "wandering" clock is seen to have counted, say, 11 months, instead of the 12 months of the clock that is in step with time-at-its-maximum-rate. 
This does not in any way imply absolute space. The asymmetry in rate of time is subject only to difference in path length, relative to the inertial frame co-moving with the inertially moving traveller.
Still, there is an asymmetry. To focus on that asymmetry I use the following reasoning: all inertial frames are indistinguishable, so I might just as well envision a superposition of the entire group of all inertial frames of reference, and summerize that with the name the inertial frame of reference. I treat the entire symmetry-group of inertial frames of reference as effectively a single frame.
If two clocks separate and later rejoin, there is a loop. And whenever there is a loop, enclosing an area, at least one the the clocks has not moved along a geodesic, and in Minkowski space-time that matters: moving along a geodesic or not is different physics taking place. The geodesics of Minkowski space-time relate to the inertial frame of reference. Minkowski space-time is not a neutral background, it is not just empty space. Minkowski space-time is a physical entity that affects the rate of time of objects moving through it. --Cleon Teunissen | Talk 11:06, 13 Apr 2005 (UTC)
replies: text: There is a possibility that these two references frames may be slighlty different since it has been claimed that the Universe is rotating with respect to the back-ground radiation (Birch, P. 1982 "Is the Universe Rotating", Nature 298, 451). It has also been claimed, on statistical grouns, that we should expect some tiny difference between the matter and radiation reference frames, even if it is not as large a difference as that apparently observed (Macrossan, M. N. 1987 "A thermodynamic origin of a universal mass-angular momentum relationship"Astrophys. Space Sci, 133(2), 403)
Would there be any philosophical objection to assuming this is a privledged reference frame? As long as length contraction and time dilation happened with respect to this frame, the Lorentz transformations will hold between any two inertial frames in which simultaneity is defined by assuming the speed of light is c in that frame. The situation is then identical to all we know about SR - the effects will appear symmetric to all inertial observers as long as they remain unaccelerated. And no one in the privledged reference frame could claim anything special about their inertial frame, except for the theoretical prediction of GR that clocks in their frame will show the greatest age of the universe at the big crunch.
It may seem a retrograde step to say one frame (in our locality) is privileged - so that the contractions and dilations are real with respect to this frame and "apparent" (i.e. arising from a combination of the real effect and the clock synchronisation procedure, relativity of simultaneity) with respect to all other inertial frame. Nevertheless, it might satisfy the "realists" and might even stop the endless discussion. Of course I could be wrong on this, or about the closed universe and co-moving clocks, and wait for enlightenment. E4mmacro 03:20, 17 December 2005 (UTC)
thread_title:  There is no absolute space 

message: Not using GR seems silly -- as I understand it, GR has no problem with special references frames; the "co-moving clocks" (in free fall from the moment of the Big Bang to the Big Crunch) will age the greatest (show the greatest age in the closed Universe) from creation to destruction. All other clocks, moving with respect to the co-moving clocks will experience a shorter life from bang to crunch. You could find (approximately) this reference frame in your locality by finding the frame in which the entire Universe appears the most symmetrical; or you could find the reference frame in which the Doppler shift of the cosmic micro-wave background radiation is isotropic (this has already been done?) 
: There is a possibility that these two references frames may be slighlty different since it has been claimed that the Universe is rotating with respect to the back-ground radiation (Birch, P. 1982 "Is the Universe Rotating", Nature 298, 451). It has also been claimed, on statistical grouns, that we should expect some tiny difference between the matter and radiation reference frames, even if it is not as large a difference as that apparently observed (Macrossan, M. N. 1987 "A thermodynamic origin of a universal mass-angular momentum relationship"Astrophys. Space Sci, 133(2), 403)
Would there be any philosophical objection to assuming this is a privledged reference frame? As long as length contraction and time dilation happened with respect to this frame, the Lorentz transformations will hold between any two inertial frames in which simultaneity is defined by assuming the speed of light is c in that frame. The situation is then identical to all we know about SR - the effects will appear symmetric to all inertial observers as long as they remain unaccelerated. And no one in the privledged reference frame could claim anything special about their inertial frame, except for the theoretical prediction of GR that clocks in their frame will show the greatest age of the universe at the big crunch.
It may seem a retrograde step to say one frame (in our locality) is privileged - so that the contractions and dilations are real with respect to this frame and "apparent" (i.e. arising from a combination of the real effect and the clock synchronisation procedure, relativity of simultaneity) with respect to all other inertial frame. Nevertheless, it might satisfy the "realists" and might even stop the endless discussion. Of course I could be wrong on this, or about the closed universe and co-moving clocks, and wait for enlightenment. E4mmacro 03:20, 17 December 2005 (UTC)
thread_title: Somethig like "absolute space": Privileged frames OK in GR?

message: ...and you dont need General Relativity.
And it can be explained without complex calculations.
Consider a Ten Year Trip.
The observer on the Ship sees the earth receeding for 5 years and converging for 5 years.
The observer on earth sees the ship receeding for longer than five years because at the point he turns around light takes a long time to reach earth. The return journey seems a lot faster as from the earths viewpoint
he is chasing his own light.
Now with two different times of visible receeding and converging we have 
two different results. Put them into standard special relativity calculations and no paradox exists.
At the point the ship switches intertial frames(turns around). He has a totally different view of when past events occured on earth.
:In the Twin paradox, one must distinguish between two kinds of suspicion: (1) Are we baffled because there is an inconsistency in the theoretical framework of relativistic physics? (2) The theory is self-consistent, but incomplete.
:Its number (2). The twins are traveling with portable atomic clocks and at the point of rendez-vous the clock of the twin who has travelled has counted less cycles. In the end all clocks, including biologial and mechanical clocks, measure rate of time because the underlying quantumprocesses happen in time. This shows that relativistic physics deals for a 100% with quantumbehavior. It is sometimes said that relativistic physics 'describes macroscopic phenomena' and that quantum physics 'describes the microscopic world of quantum particles', but the Twin paradox brings into focus the reality that quantumbehavior is affected by space-time geometry.
:In order to complete the theory a quantumphysical model would have to be found that predicts the physics of Minkowski space-time on the basis of more fundamental physics. --Cleon Teunissen | Talk 14:45, 29 Apr 2005 (UTC)
thread_title:  There is no Paradox 

message: i have too many questions on the twin paradox, like 30 or something, but all i want to know is that has people really resolved all the situation that you can ever make up about the paradox? and is it even easy to fully learn the whole thing and never think its inconsistent again? because i read from lots of places but i can still think up of new situations where it doesnt make sense
thanks for your help
-protecter
* Yes, it is absolutely resolved, and has been for some decades.  You can make up new situations that are difficult to understand intuitively (as the Twin Paradox always has been), but they make perfect sense when expressed within the mathematical framework of relativity.  The Twin Paradox is taught in every undergraduate class on Special Relativity these days; it is in no way controversial, it's simply a fun problem that illustrates the importance of inertial reference frames.  --LostLeviathan 01:13, 17 October 2005 (UTC)
thread_title:  question 

message: As far as I know, Doppler effect (both classical and relativistic),
concerns the change in perceived frequency of a wave if the source of the wave is moving with respect to me, or if I'm moving with respect to the source. I don't understand the statement .."according to relativistic Doppler effect 1 second for one of the two brothers is seen as 3.7 seconds lapsed for the other". For me is a mistery, and for You?
 Demaag 16:24, 21 October 2005 (UTC)
replies: text: One draws a distinction between time dilation and the doppler effect.  Time dilation is the perceived rate of time between the moving clock, and a clock at the same place that isn't moving with respect to the observers frame.  This is to be contrasted with directly observing (via, say, a telescope) the moving clock:  such an observation is subject to the doppler effect (which has the time-dilation built into it).  The alternative explanation to the supposed paradox, which is far easier to comprehend and is an easier lead in to the simpler space-time interval explanation, is based on both twins literally looking at each other, so it the doppler effect is used.  mdf 00:02, 22 October 2005 (UTC)
thread_title:  Alternative resolution of paradox 

message: I've never studied physics, except to read a few popular books.  I want to understand this problem.  I've looked up many many web pages to try to get at the nature of it.  None of them are satisfying; they explain some of the basic physics without getting at the heart of what is bothering people that makes this seem paradoxical.  I keep wanting to put something in lay terms so it's a little plainer for 99% of us.
Here's what I understand:
Whereas relative motion within an inertial frame of reference is symmetrical, acceleration is not.  If my spaceship accelerates, it is doing it on its own, not in relation to the Earth.  Thus, the Earth doesn't accelerate.  Acceleration moves you from one inertial frame to another.
The problem:  Why?  Why should my acceleration be something I can do alone, and not necessarily in a symmetrical relation to anything else?  Doesn't that imply absolute space?
This is at the heart of the confusion.
Don't say "but really what's happening is that the traveling twin is shifting frames but the Earth twin isn't."  That doesn't answer WHY the Earth isn't the one shifting frames and the twin isn't.
People want to understand why, why is there assymetry, why something can accelerate apparently separate from everything else when we keep being told everything is relative.  Someone please answer this.
(Above by anon)
You really need to ask yourself why after reading the page and the linked-to physics FAQ, you did not use "inertial reference frame" instead of "absolute space" in your question, in which case, you would have answered your own question.  As for teaching this to laymen, they neither believe in absolute space nor inertial reference frames, so good luck with that.Jok2000 23:33, 23 October 2005 (UTC)
thread_title:  Why 

message: sorry for the stupid question but this is really interesting and i was just wondering, does this mean that if I could travel to the end of the universe and back at the speed of light it would take only a second for me (provided I didnt hit anything).. although when I got back to earth it would now be 30 billion A.D. ??? 202.161.26.89 16:01, 26 October 2005 (UTC)
thread_title: Travelling at the speed of light

message: The confusion around this paradox is incredible! Besides the effects, described bei Lorentz transformation, mentioned by A.Einstein in his famous paper, e.g. time dilation, there is nothing to be confused, except Langevins misinterpretation.
Relativity doesn't say that there is no absolut room, but, it doesn't matter. The fact is: speed is symmetric. Terra measures the speed of Stella, relative to herself. This measurement is independent of any unaccelerated movement relative to any other object. Without violation of generality, as well Terra, as Stella can be seen to have speed 0. But, to measure speed, you have to measure distance and time. Time measuring instruments we call clocks. Space measuring instruments can be two stars. Terra and Stella measure the relative speed in relation to speed of light. Terra and Stella can very easily answer the question, who "moves": They independently measure the distance of the stars and the one, who measures the smalest distance, moves. In very coincidence with Lorentz tranformation.
Where is the problem? Why all the confusion? Just plain thinking. ErNa 14:30, 27 October 2005 (UTC)
thread_title:  Incredible! 

message: Part of the problem is that for the people explaining the solution, the intuition has already been ingrained, so they have a hard time relating to those people for whom it isn't.  This is generally a problem with teaching:  the teacher has a hard time thinking from the students' perspective.  Both need to switch mental frames of reference to understand where the other is coming from.
It took me a lot of work to understand - not because I couldn't 'get it,' but because no one doing the explaining got at the heart of the paradox as I saw it.  It's resolvable with a basic understanding of concepts of physics, but for those of us who don't have such a background, Wikipedia doesn't help much.  Every article on physics is written from the perspective of someone who already understands basic physics, so that most of us have no place to begin learning.  So, for the benefit of those who are confused, the following might be helpful, coming not from a physics prof but a physics pauper:
:Motion itself is mutual, symmetrical (relative).  Both twins recede from each other.  Even during acceleration, both move apart from each other, at an increasing rate.
:However, "moving apart at an increasing rate" does not equal "mutual acceleration."  These ideas seem equal, since "moving apart" itself is mutual.  However, acceleration is something different than motion.  Both can be moving apart at an increasing rate, and yet only one be accelerating.  I think this is the heart of the confusion.
:To understand why only one accelerates requires an understanding of inertia.  Imagine 100 motionless planets sitting in space.  One starts revolving. Its motion is relative to the other planets, but only it has changed anything.  Acceleration is not a relative thing, but rather a force-driven thing.  
:Acceleration breaks the symmetry.  You can talk about inertial reference frames if you like, but they're not at the heart of the misunderstanding.  You can even do away with acceleration, but then you no longer have a twin taking a trip (unless she "beams over" to the ship traveling in the opposite direction, in which case the change of spaceships breaks the symmetry).
I wish something in this article would explain it this way.  It really shouldn't be that hard to write articles that assume the reader knows little.  Otherwise us physics paupers get lost travelling through endless links, and pretty soon what we thought was minutes turns into hours, as if the Earth has suddenly aged below us.24.64.223.203 04:07, 28 October 2005 (UTC)
replies: text: I tried to give you a hint, what the misunderstanding in Twin Paradox is and where it comes from. But it was reverted: William M. Connolley (Talk) (rv to Mathbot. I didn't find ErNa's additions helpful.) May be, he knows, what really happens or he just didn't understand. ErNa 12:18, 30 October 2005 (UTC)
thread_title:  The Physics Prof and the Pauper 

message: :: (Commentary Note: For once, special relativity makes a simple claim which anyone could, in principle check.Whether a man looks older than his twin, who is standing next to him, is a fact which can be observed and agreed upon by all persons, whatever their state of motion. Furthermore, the development of the twins' bodies could be determined at definite stages of the experiment. If the experiment were, specifically, to send a twin to another star known to be 50 light-years away, and return immediately - at speeds close to light-speed - we could wait on earth for fifty years to pass and then photograph the home-dwelling twin. The travelling twin could photograph himself when he approaches the star. These two images could be compared when the traveller returns.
::Matters become interesting if there are four clones (such as Armadilloes produce). Bill stays at home while Tom, Chris, and Harry set off to the distant star. According to Einstein, the metabolic clocks of the travellers are all similarly slowed. Tom is soon homesick and comes back to Earth in a lifeboat, using its jets to slow down and then return. Presumably he now lives out his life at the same rate as Bill. Chris completes the mission, and eventually comes back, almost unchanged. Harry also gets homesick whilst still near Sol, but he makes an unfortunate mistake - he sets his lifeboat jets going 180 degrees the wrong way. He goes even faster towards the target-star, and comes back even younger than Chris. Now concentrate on the space-ship in deep-space. A general observer does not have to know anything about the existence of the Earth or its state of motion. Thus,an alien might first notice the space-travellers as a curious piece of debris. He sees inside three entities together. He then sees two of the entities accelerate away from the third, in opposite directions. Because the observer thinks like Einstein, he will expect to see the two accelerated entities - Tom and Harry - both living life more slowly than Chris. However we have shown that (1) according to the common observation that everything on the Earth has a similar clock-time, Tom will be living faster than Chris; and (2) according to Einstein's rules, Harry will be living slower than Chris. The curious alien can come to Earth and observe the brothers at the end of all the travelling. We can be sure that his expectations will be confounded. Unless, that is, there is an ABSOLUTE state of rest as an ultimate reference.)
The above argument assumes the alien is at rest relative to Chris, in which case if the alien, tom & harry "return" to chris, everything works.  You can't have it both ways.  Either you know of the earth, or you don't.Jok2000 16:48, 12 November 2005 (UTC)
thread_title:  5 object supposed paradox added by anon 

message: Consider the hidden assumption in the elegant Doppler shift calculation of the age difference. We assume that the twin who turns around, immediately sees a Doppler shift in his image of the stay-at-home brother (and the rest of the universe). The stay-at-home twin has to wait quite some time before he sees the change in Doppler shift in the image of his brother. We then explain the asymmetry by saying the travelling-brother is accelerating; that it is not the rest of the Universe and all the radiation in it that is accelerating. The paradox for SR is that we invoke accleration but say the time difference is not a function of the acceleration; and we do not say how we know the rest of the Universe is not accelerating, except to say that it doesn't feel the inertial force the travelling twin feels (i.e we say that the Universe isn't accelerating but do not, in SR, take the next step and try to explain this.) E4mmacro 04:22, 17 December 2005 (UTC)
thread_title: The Doppler shift calculation

message: All animals are created equal, but some are more equal. ;-> All electrons are created equal, but, are some created more equal? I create an electron-positron pair during a collider experiment. These electrons are born in an very relativistic atmosphere! But, if I catch them, slow them down, there will never be a difference to those electron, that existed since ever and a day. Did Einstein ever say: a inertial frame at absolute rest doesn't exist or did he say: the physical laws are the same, whenever coordinates of space and time form an inertial system? More relative then "there is no absolute frame" is: "it doesn't matter". René Descartes invented "good faith": god created mankind with the ability to understand the world. ErNa 20:31, 12 November 2005 (UTC)
thread_title:  An Animals Farm 

message: I wonder, if anyone ever set up a real symmetric sitution: Two individuals are separated by a very big distance, lets say: 1 LJ. They like to know, if they are twins. So they exchange information with the help of coded light signals. This information is the sequence of the acids in their DNA. It takes one year to send the code. After they completed the broadcasting, they compare the now incoming signal to the local information and after one year they now: I am his twin. Again they send an acknowledge and after a second year they both know, that both know: we are twins. This is symmetry. And now we can modify the experiment: After starting to send the code, both immediately accelerate to speed c/2 towards the other. What happens if no time dilation takes place (non constant speed of  light?): after one year they meet in the middle. And just completed transmission of the information. So the shake hands and know, they are twins. Now we can make a similar experiment with c= const. And other similar experiment with unsymmetrical situations: One accelerated, the other not. And this will show to us, that it is not possible to change ones point of view as one likes it without consequences. We talk about physical experiment, not about womd. ErNa 08:23, 2 December 2005 (UTC)
replies: text: Post it in sci.physics.relativity (Google groups) complete with your calculation, and I (or someone else) will show you there what calculation error you made. This is not the place for it. Harald88 19:12, 2 December 2005 (UTC)
replies: text: No, I didn't make an error, I just said, wether or not RT is right, there has to be a symmetric experiment and after discussing (that is, understanding) it, we introduce a slight asymmetrie and will see, what happens. I just wanted to show, that we should not start from an asymmetric situation and prove, that she is symmetric, but go the different way. ok, ok, ErNa 20:54, 2 December 2005 (UTC)

text: No, the twin paradox is not about asymmetry. It is about misinterpretation of SRT. This has to become clear in the article. ErNa 12:51, 3 December 2005 (UTC)
replies: text:  That's mistaken according to Einstein; and this article is both terribly incomplete as well as biased as long as his POV as the reactions on that are not included, as explained above. I'll now economise my time for such editing work, instead of trying to explain either SRT or the Twin paradox to you on this Talk page. By for now Harald88 14:48, 3 December 2005 (UTC)
thread_title:  Real symmetry 

message: See http://fr.wikipedia.org/wiki/Paradoxe_des_jumeaux, under Le choix du repère inertiel.
On that point the French page is more advanced than the English version, but they still omitted the objections against the GRT solution.  Harald88 18:46, 3 December 2005 (UTC)
thread_title:  According to the French Wikipedia, GRT solved the paradox 

message: The above peculiar phrase can be found in the article. It doesn't seem to be really fitting and I see no good reason to have that phrase. Anyone who can motivate what that phrase is doing there and how it is helpful? It's not in the remarks of the editions. Harald88 16:49, 4 December 2005 (UTC)
thread_title:  "This can actually be accomplished through the use of the Frenet-Serret formulas." 

message: I finally obtained the paper by Langevin; it's in several important details significantly different from what some writers claim about it - apparently Langevin didn't consider it of paradoxical nature, and later authors so much disliked his argumentation that they misrepresented it! Happily, this does not affect the introduction as it stands now. If someone wants a copy (PDF, 2.4 Mb, French), just ask and I will send it. Harald88 21:02, 6 December 2005 (UTC)
thread_title:  The paper by Langevin 

message: After 10 days silence on the above topics related to how "twin paradox" originated as well as silence to the same question on sci.physics.research, I think that we may, at least for the time being, work with these papers as providing the origin of the Twin paradox. This could run the risk of being criticized of "original research", if presented as Wikipedia conclusion and loose from any peer reviewed article. 
However, it can be presented as received factual information about the origin of the Twin/Clock paradox (BTW it may be useful to add the info that they are the same thing), and happily the corresponding logical conclusion turns out to be nothing new. Ives claimed in "The aberration of Clocks and the Clock Paradox" JOSA 27 p.305, 1937:
"The "clock paradox" is a consequence of a sweeping and unqualified application of the hypothesis that relative motion of matter is the only operative factor." 
Thus I have in mind to write a paragraph titled "The origin of the clock paradox" starting with that remark, and adding the historical information that we have and which corraborates it.
Next we should write a paragraph that summarizes the differing opinions of scientists on this matter, exclusively based on cited reference of peer reviewed papers in high quality journals (there is plenty of that). 
Note that I push strongly that we stick to what is availabe in literature, in order to avoid the mess of adding text that is just personal (and possibly confused) opinions of Wikipedia editors. Harald88 15:32, 17 December 2005 (UTC)
thread_title:  additional paragraphs to fill the information hole 

message: Substituted at 20:55, 4 May 2016 (UTC)
thread_title: Assessment comment