Register to reply 
Time paradox 
Share this thread: 
#379
Feb513, 06:40 PM

Sci Advisor
PF Gold
P: 5,027




#380
Feb513, 06:47 PM

P: 1,162

Quote by Austin0
But the assumption of Doppler symmetry and reciprocity are clearly out of thin air and contradictory to classical physics When you say verified experimentally what are you referring to??? .Were the Doppler properties derived directly from Maxwell or were they derived later with the inclusion of the gamma function??? or are you talking about the Lorentz maths derived from them. The gamma function???? When you say "But you don't need SR to derive it" are saying you don't need the Lorentz math which is an integral part of SR??? 


#381
Feb513, 07:35 PM

P: 1,162

Quote by Austin0 View Post
This unambiguously inverts reality. The Doppler effects, symmetry and reciprocity are the end of the line. They are consequences of , not causes of time dilation. Yes there is a correlation between the asymmetry of the observations and the asymmetry of the differential aging but this is a correlation without causation. And is unsurprising because ultimately both the Doppler effects and the final aging are caused by the same thing: The time dilation factor intrinsically resulting from relative motion.. Do you disagree?? so actually the gamma factor does "explain" both the differential aging and the Doppler effects. Even in an SR context , the Twins scenario, the effects directly resulting from relative motion (without the introduction of dilation) are neither symmetric nor reciprocal. Would you agree??? Eg. YOU "Time dilation and length contraction and Einstein simultaneity convention are part of the coordinate expression of a model to explain a range of measurable phenomena: symmetric and reciprocal Doppler, differential aging," ME "so actually the gamma factor does "explain" both the differential aging and the Doppler effects." Here I was explicitly referring to the time dilation aspect of the gamma factor. SO not only are we in agreement but you are supporting my point. Time dilation explains Doppler symmetry not the other way around. "An important one is that symmetric and reciprocal Doppler (along with emitter speed independence of light transmission) implies differential aging" yes i have repeatedly stated that given these assumptions you get differential aging. That is not the question. Which is:Do the Doppler effects explain dilation or does dilation explain the symmetric Doppler effects???Do those effects cause dilation or does dilation cause those effects?? As such they are mathematical descriptions of fundamental phenomena and so precede and determine derivative theorems and coordinate conventions. So i can't really understand a perspective where they are determined by something else other than the intrinsic properties of spacetime???? 


#382
Feb513, 07:35 PM

Sci Advisor
PF Gold
P: 5,027




#383
Feb513, 07:46 PM

Sci Advisor
PF Gold
P: 5,027




#384
Feb513, 08:10 PM

Physics
Sci Advisor
PF Gold
P: 6,051




#385
Feb513, 08:24 PM

Sci Advisor
PF Gold
P: 5,027




#386
Feb513, 09:15 PM

Sci Advisor
PF Gold
P: 1,843




#387
Feb513, 09:19 PM

P: 1,162

would you agree that on an essential level physics is a study of causality?
Quote by Austin0 yes in a sense observables are more fundamental,frame invariant, but observations in themselves have little meaning. That meaning is also derived from our theory , yes??? Quote by Austin0 I said that time dilation resulted from relative motion. relative motion>time dilation>Doppler effect and differential aging You seem to be implying that time dilation and differential aging are unrelated phenomena. That because we cannot observe or quantify time dilation that it is not the same thing. DO you doubt that differential aging is simply the cumulative result of time dilation??? 


#388
Feb513, 09:29 PM

Physics
Sci Advisor
PF Gold
P: 6,051

relative motion > Doppler effect and differential aging Time dilation does not appear because it is framedependent, so it is a convention, not a "real thing" that needs to have a cause. 


#389
Feb513, 09:34 PM

Sci Advisor
PF Gold
P: 5,027




#390
Feb513, 11:47 PM

PF Gold
P: 1,376

I guess I understand Bondi argument just fine as he does not seem to be claiming much. He just says without any argument: "Note that the Principle of Relativity, by insisting on the equivalence of all inertial observers, makes it quite clear that the ratio must be the same whichever of a pair of inertial observers does the transmitting." As I already said he provides no explanation how it can be considered consistent with classical Doppler. And he makes quite clear distinction between classical Doppler and relativistic Doppler contrary to you: "It is trough this rule [PoR] that our work on light differs so sharply from the work on sound where, it will be remembered, the speed of transmitter and receiver relative to the air had also to be taken into account." On the other hand your claim is that one can predict that the travelling twin will be younger than stay at home twin just from PoR and SR second postulate by some shorter route than SR. So I have to "forget" SR and try to understand your argument. And this is a bit complicated as you keep referring to things that I learned from SR as given. 


#391
Feb713, 08:50 AM

PF Gold
P: 4,688




#392
Feb713, 09:09 PM

P: 1,162

Quote by Austin0
Quote by Austin0 Quote by Austin0 The Doppler effects, symmetry and reciprocity >time dilation instead of time dilation>Doppler effects, symmetry and reciprocity which is what I said. Quote by Austin0 But what does that bare value tell us about what is being measured other than that you may not want to stick your fingers in it? What does the word temperature or heat even mean without a theory? A molecular model, mechanics,etc, etc. With Doppler the theoretical context in this case is SR . According to which it appears that the observed values are the result of two distinct factors relative motion and the dilation factor. Now the quantitative evaluation of the relative effect of these components is of course conventional and not to be understood as having any absolute significance quantitatively. but you seem to want to throw out this understanding completely. Not only the implication that time dilation is a phenomenon which exists independent of convention but also the fundamental kinematics involved in this analysis and understanding. You missed this one; Quote by Austin0 Quote by Austin0 That those rates are not "real" ( don't occur) until a clock is transported and returned ? That the returning twins age is only a "real thing" after he arrives and it becomes observable?? Do you think that the existence of phenomena is dependent on or determined by convention? Quote by Austin0 View Post Ultimately the asymmetry, the difference in signals received is solely dependent on the actual difference in the number of signals sent at the sources. YES? This difference in number must be spread out over the course of travel ...........Agreed? This seems to lead to two inevitable inferences: 1)There must be differences in relative rates during that transit. The fact that we can't quantify or locate these differences in a frame independent way during transit does not negate the conclusion they must occur somewhere in that course. 2) These differences occur at the sources. Simply mechanisms (observers and clocks) and relative motion. No other intermediate factors or influences. You agreed that differential aging was a consequence of relative motion, yes/ Well differential aging is a process occurring over time. As a process it is a difference in rates (biological or mechanical) over intervals. Time dilation by definition ,,,yes"??? 


#393
Feb713, 10:39 PM

Sci Advisor
PF Gold
P: 5,027

With (2), I have a big problem. You say differential aging is a process occurring over time. Whose time? The only objective time is the time along each world line. If I draw lines on a piece of paper, we don't talk about length occurring over length. If two curves on a plane have different lengths, we don't say one of them accumulated length faster, or more length per length. We say nothing more than one is longer. That is all we can say of world lines. 


#394
Feb713, 11:05 PM

PF Gold
P: 1,376

And when it cames to the point where one should invoke PoR (reverse sender and receiver) and two Dopplers are not equal any more all the explanations are cut short with this sentence: "Note that the Principle of Relativity, by insisting on the equivalence of all inertial observers, makes it quite clear that the ratio must be the same whichever of a pair of inertial observers does the transmitting." 


#395
Feb713, 11:09 PM

Sci Advisor
PF Gold
P: 5,027

Theories don't cause anything. They explain observations.
Doppler symmetry exists independent of theory, and, if observed, is sufficient to predict differential aging (which might then be observed). Doppler symmetry and reciprocity is sufficient to derive the gamma factor of differential aging, without deriving Lorentz transform or even assuming invariance of light speed (if you don't assume this, you allow that the c in gamma could be frame dependent and not necessarily isotropic). SR is a theory which explains a whole range of phenomena in a unified way. That is what is great about it. But it doesn't cause anything. Within SR, you can, but in no way need to invoke time dilation to explain Doppler. If you look at SR as Einstein did, you have assumptions: (POR applies to all phenomenon including light = can't detect aether, if it exists (I am building in invariance of light speed into this); speed of light is independent of emitter speed). From these, plus a convention, you derive Lorentz transform and the full machinery of SR. Also, from these, without the convention, and without bothering to derive Lorentz transform or time dilation, you can derive symmetry and reciprocity of Doppler, and from that differential aging by gamma factor. It thus seems tendentious to insist the time dilation is the explanation (let alone cause!) of Doppler symmetry and reciprocity. 


#396
Feb713, 11:15 PM

Physics
Sci Advisor
PF Gold
P: 6,051

[tex]\frac{\omega}{\omega_0} = \sqrt{\frac{1 + v}{1  v}}[/tex] where [itex]v[/itex] is the relative velocity of the observer *towards* the source (i.e., positive v is velocity towards, negative v is velocity away). Now tell me, where in that formula does time dilation appear? To answer your questions as you pose them, obviously if gravity (spacetime curvature, whatever) is present, there is another causal factor involved; in the case of static objects (i.e., no relative motion), the causality would be: varying gravitational potential > differential aging Since the situation is static, two observers at different altitudes can establish the same simultaneity convention by exchanging light signals; and when they do, they will find that the one who is higher up experiences more ticks of his own clock between two of the exchanged light signals than the one who is lower down. So there is a set of direct observables corresponding to differential aging in this case even though the two observers don't ever actually meet. Note, by the way, that this is a key difference from the flat spacetime case; in flat spacetime it is impossible for two observers who remain at rest relative to each other to have differential aging. If two such observers in flat spacetime run the above experiment (exchanging light signals to establish the same simultaneity convention), they will find that both of their clocks tick the same number of ticks between light signals. And if they are in relative motion, they can't synchronize their clocks this way; so the only way they have of detecting differential aging is to actually meet up and compare clocks. If we take quantum mechanics into account, of course, we can no longer always make the effects of observations negligible; but I don't think we need to open that can of worms here. PAllen already commented on the rest of your post; I agree with what he said. 


Register to reply 
Related Discussions  
Time paradox (?)  Special & General Relativity  7  
Time paradox?  Special & General Relativity  2  
Name for a particular time travel paradox  General Discussion  1  
Waiting time paradox  Set Theory, Logic, Probability, Statistics  1  
Silly time paradox  General Discussion  17 