The real twin paradox.
in [Relativity]
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From: bz on 1 Dec 2007 15:14 "Sue..." <suzysewnshow(a)yahoo.com.au> wrote in news:873636c4-2a93-4f87-88a4-19394f1d85f3(a)e6g2000prf.googlegroups.com: > SR *does* address clocks that are moving toward each other. > "General results of the Theory" random citation by Sue, only relevance is that it mentions SR > http://www.bartleby.com/173/15.html [quote] IT is clear from our previous considerations that the (special) theory of relativity has grown out of electrodynamics and optics. In these fields it has not appreciably altered the predictions of theory, but it has considerably simplified the theoretical structure, i.e. the derivation of laws, and�what is incomparably more important�it has considerably reduced the number of independent hypotheses forming the basis of theory. The special theory of relativity has rendered the Maxwell-Lorentz theory so plausible, that the latter would have been generally accepted by physicists even if experiment had decided less unequivocally in its favour. Classical mechanics required to be modified before it could come into line with the demands of the special theory of relativity. For the main part, however, this modification affects only the laws for rapid motions, in which the velocities of matter v are not very small as compared with the velocity of light. We have experience of such rapid motions only in the case of electrons and ions; for other motions the variations from the laws of classical mechanics are too small to make themselves evident in practice. [unquote] the article goes on to study momentum. It says nothing about clocks that involve momentum keeping time differently from light clocks. It does NOT even INVOLVE time (except as a hidden, unmentioned component of velocity) Sue says that ONLY light clocks obey Einstein-Lorentz time equation. http://en.wikipedia.org/wiki/Proper_time [which 'she' has cited recently as a source of wisdom] show the equations of SR and how they can be derived using GR. It also shows the so-called twin paradox, and how it can be worked. There is no hint that 'proper time' only applies to light clocks. In fact, such a suggestion would seem to be highly 'improper', to me. -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+spr(a)ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
From: colp on 1 Dec 2007 20:23 On Dec 2, 6:10 am, Dono <sa...(a)comcast.net> wrote: > On Nov 30, 11:03 pm, colp <c...(a)solder.ath.cx> wrote: > > > > > > > > > On Dec 1, 6:58 pm, Bryan Olson <fakeaddr...(a)nowhere.org> wrote: > > > > colp wrote: > > > > Bryan Olson wrote: > > > >> colp wrote: > > > >>> What am I making up? > > > [...] > > > >>> For their clocks to be the same time, A must have observed that B's > > > >>> time was compressed at some stage. > > > >>> SR does not describe time compression. > > > >> That you made up. According to SR, A's change it frames will > > > >> result in A seeing B's age jump forward. > > > > > Wrong. SR has nothing to say about non-inertial frames. > > > > > Special relativity (SR) (aka the special theory of relativity) is the > > > > physical theory of measurement in inertial frames of reference > > > > proposed in 1905 by Albert Einstein in his article "On the > > > > Electrodynamics of Moving Bodies". > > > > >http://en.wikipedia.org/wiki/Special_relativity > > > > Reading the page you cite, we find: > > > > Special relativity does not account for gravity, but > > > it can deal with accelerations. > > > How does special relativity deal with accelerations? > > > Cyclotron experiments have shown that, even at accelerations of 10^19 > > g (g = acceleration of gravity at the Earth's surface), clock rates > > are unaffected. Only speed affects clock rates, but not acceleration > > per se. > > >http://metaresearch.org/cosmology/gps-relativity.asp > > http://physics.nmt.edu/~raymond/classes/ph13xbook/node59.html The physics.nmt.edu page describes accelerations in SR. However the page does not describe what time dilation effects occur in an accelerated frame. Such a description is necessary to solve the paradox described in the OP for SR. Describing the experiment from a single inertial frame of refence does not show a paradox as the symmetry of the experiment means that the effects which produce the paradox cancell out. Describing the experiment from the point of view of one of the twins does show the paradox; the twin observes the time dilation of the other twin during both the outbound and return inertial frames, and this effect must be compensated for somehow if a paradox is to be avoided at the end of the experiment when the twin's clocks are observed to tell the same time in a common inertial frame. What is required to solve the paradox is a description of how a twin sees the other twin's clock jump forward.
From: paparios on 1 Dec 2007 21:12 On 1 dic, 22:23, colp <c...(a)solder.ath.cx> wrote: > On Dec 2, 6:10 am, Dono <sa...(a)comcast.net> wrote: > > > > > On Nov 30, 11:03 pm, colp <c...(a)solder.ath.cx> wrote: > > > > On Dec 1, 6:58 pm, Bryan Olson <fakeaddr...(a)nowhere.org> wrote: > > > > > colp wrote: > Describing the experiment from the point of view of one of the twins > does show the paradox; the twin observes the time dilation of the > other twin during both the outbound and return inertial frames, and > this effect must be compensated for somehow if a paradox is to be > avoided at the end of the experiment when the twin's clocks are > observed to tell the same time in a common inertial frame. > > What is required to solve the paradox is a description of how a twin > sees the other twin's clock jump forward. None of the twins can (realistically) see anything from the other twin but the signals he receives. This is a really problem of communication of information. That is the reason why a geometric view helps to see what is going on. That is the reason why using a third twin, who stays at Earth, eases the drawings and understanding of the problem (any frame of reference can be used with the same results but using the Earth frame helps). From the graphic representation, one can see that each travelling twin experiences time dilation, with respect to the Earth frame, both in the outward and inward legs of the trip, the effect being caused by them moving at relativistic speeds. Information received by one of the twins from the other two, is clearly dependent on whether his ship is going outward (and so the signals take a longer time to reach him) or coming inward (where signals take less time to reach him). Final result: both travelling twins arrive back to Earth having experienced the same length of time (according to their local clocks), but during the trip they "saw" the signals coming from the other twin doing strange changes of rates (very slow in the first part of the trip, then quite normal in the middle part and, finally, quite fast in the last part. Those observations say nothing with respect to the time dilation experienced (as it has been pointed out they will notice nothing peculiar in their voyages), which finally manifest itself when both twins compare their clocks with the third twin who remained at Earth, observing that they are indeed younger. Acceleration is not really relevant in this problem, as long as the acceleration period is small with respect to the inertial period (just a little bit over a couple of years of acceleration at 1 g will take the ship to near 0.99c, or shorter if larger g's are used). Miguel Rios
From: colp on 1 Dec 2007 23:31 On Dec 2, 3:12 pm, "papar...(a)gmail.com" <papar...(a)gmail.com> wrote: > On 1 dic, 22:23, colp <c...(a)solder.ath.cx> wrote: > > > > > On Dec 2, 6:10 am, Dono <sa...(a)comcast.net> wrote: > > > > On Nov 30, 11:03 pm, colp <c...(a)solder.ath.cx> wrote: > > > > > On Dec 1, 6:58 pm, Bryan Olson <fakeaddr...(a)nowhere.org> wrote: > > > > > > colp wrote: > > Describing the experiment from the point of view of one of the twins > > does show the paradox; the twin observes the time dilation of the > > other twin during both the outbound and return inertial frames, and > > this effect must be compensated for somehow if a paradox is to be > > avoided at the end of the experiment when the twin's clocks are > > observed to tell the same time in a common inertial frame. > > > What is required to solve the paradox is a description of how a twin > > sees the other twin's clock jump forward. > > None of the twins can (realistically) see anything from the other twin > but the signals he receives. These signals can be described as clock ticks. According to SR, while the twins are in inertial frames the ticks that are sent by the other twin will be sent at a slower rate than the ticks that are sent from the twin's local clock. It doesn't matter how long it takes for the tick signals to get from one twin to another. All that matters is that the rate that the ticks are generated by the other twin is slower becuase of the time dilation while they are in inertial frames. Every signal than is sent must be received by the other twin in the experiment. > This is a really problem of communication > of information. That is the reason why a geometric view helps to see > what is going on. You're talking about Minkowski diagrams, right? > That is the reason why using a third twin, who stays > at Earth, eases the drawings and understanding of the problem (any > frame of reference can be used with the same results but using the > Earth frame helps). The paradox isn't apparent when the events are viewed from a single inertial frame. Minkowski diagrams represent events according to such a frame. > From the graphic representation, one can see that > each travelling twin experiences time dilation, with respect to the > Earth frame, both in the outward and inward legs of the trip, the > effect being caused by them moving at relativistic speeds. Information > received by one of the twins from the other two, is clearly dependent > on whether his ship is going outward (and so the signals take a longer > time to reach him) or coming inward (where signals take less time to > reach him). Final result: both travelling twins arrive back to Earth > having experienced the same length of time (according to their local > clocks), but during the trip they "saw" the signals coming from the > other twin doing strange changes of rates (very slow in the first part > of the trip, then quite normal in the middle part and, finally, quite > fast in the last part. Those observations say nothing with respect to > the time dilation experienced (as it has been pointed out they will > notice nothing peculiar in their voyages), which finally manifest > itself when both twins compare their clocks with the third twin who > remained at Earth, observing that they are indeed younger. The fact that the twins are younger than a third twin at the end isn't the paradoxical aspect of the experiment. > Acceleration is not really relevant in this problem, as long as the > acceleration period is small with respect to the inertial period (just > a little bit over a couple of years of acceleration at 1 g will take > the ship to near 0.99c, or shorter if larger g's are used). The importance of acceleration is that it is the only situation where a twin might be able to experience an effect which compensates for the time dilation of the other twin. The consideration of acceleration is necessary because it must have an effect if the explanation of the classic paradox is true. In the classic paradox, acceleration is used as an argument against symmetry, in which either twin could have been considered to be the travelling twin. Paradoxically, <grin>, acceleration is not used to quantify time dilation in the classic case, only velocity. (According to the argument presented at http://en.wikipedia.org/wiki/Twin_paradox#Resolution_of_the_paradox_in_special_relativity)
From: Dono on 2 Dec 2007 00:10
On Dec 1, 5:23 pm, colp <c...(a)solder.ath.cx> wrote: > On Dec 2, 6:10 am, Dono <sa...(a)comcast.net> wrote: > > > > > On Nov 30, 11:03 pm, colp <c...(a)solder.ath.cx> wrote: > > > > On Dec 1, 6:58 pm, Bryan Olson <fakeaddr...(a)nowhere.org> wrote: > > > > > colp wrote: > > > > > Bryan Olson wrote: > > > > >> colp wrote: > > > > >>> What am I making up? > > > > [...] > > > > >>> For their clocks to be the same time, A must have observed that B's > > > > >>> time was compressed at some stage. > > > > >>> SR does not describe time compression. > > > > >> That you made up. According to SR, A's change it frames will > > > > >> result in A seeing B's age jump forward. > > > > > > Wrong. SR has nothing to say about non-inertial frames. > > > > > > Special relativity (SR) (aka the special theory of relativity) is the > > > > > physical theory of measurement in inertial frames of reference > > > > > proposed in 1905 by Albert Einstein in his article "On the > > > > > Electrodynamics of Moving Bodies". > > > > > >http://en.wikipedia.org/wiki/Special_relativity > > > > > Reading the page you cite, we find: > > > > > Special relativity does not account for gravity, but > > > > it can deal with accelerations. > > > > How does special relativity deal with accelerations? > > > > Cyclotron experiments have shown that, even at accelerations of 10^19 > > > g (g = acceleration of gravity at the Earth's surface), clock rates > > > are unaffected. Only speed affects clock rates, but not acceleration > > > per se. > > > >http://metaresearch.org/cosmology/gps-relativity.asp > > >http://physics.nmt.edu/~raymond/classes/ph13xbook/node59.html > > The physics.nmt.edu page describes accelerations in SR. However the > page does not describe what time dilation effects occur in an > accelerated frame. Such a description is necessary to solve the > paradox described in the OP for SR. > http://en.wikipedia.org/wiki/Twin_paradox#Accelerated_rocket_calculation |