A constant speed of light in all reference frames? Surely you can't be serious.
in [Relativity]
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From: Peter Webb on 4 Mar 2010 04:39 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:8984b4b4-92e9-466a-ad51-20e6b4e815bc(a)u9g2000yqb.googlegroups.com... On 3 Mar, 22:23, "Inertial" <relativ...(a)rest.com> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > news:64d02f70-01e4-44a5-a5ab-41429bf37f71(a)q15g2000yqj.googlegroups.com... > > > I'm sure I said something about the ludicrous assertions that some > > people here have made about the conceptual basis of SR. That is, > > assertions that verge on meaningless, like "rotation into time" as an > > explanation for length contraction. Or even observed time dilation (in > > SR) being "real" as opposed to merely a function of propagation > > delays. But none of this fundamentally challenges SR. > > Time dilation isn't anything to do with propagation delays .. they do NOT > cause time dilation. It IS real in that it has been measured > experimentally. > > Your denial of reality is another trademark of a crackpot. I'm not denying it. I'm saying experiments that involve acceleration are the realm of GR (as I understand it), and that acceleration is the cause of "real" time dilation. We're talking about SR, and therefore we cannot be talking about any experiment that involves acceleration. ________________________________ It is true that you cannot devise an experiment whereby two clocks are together and then separated without at least one of them experiencing acceleration at some point; that unfortunately is a mathematical fact, not a physical one. However, you can make the contribution of acceleration "vanishingly small", by designing thought experiments where the accelerations are very low and slow. Sending a rocket to another star is one such example. More to the point, you don't have to. SR specifically predicts that time dilation will occur. It is fundamental to the whole of SR. You now appear to be claiming that you *don't* believe the twins will be different ages due to simple time dilation in SR, which means you *don't* agree that SR is correct. So, yet again, like the uber-crank you are, you have completely changed your story. Yesterday you believed in the predictions of SR. Now you say you don't. Its called *inability to learn*.
From: Inertial on 4 Mar 2010 04:43 "Peter Webb" <webbfamily(a)DIESPAMDIEoptusnet.com.au> wrote in message news:4b8f7fc6$0$26498$afc38c87(a)news.optusnet.com.au... > > "Ste" <ste_rose0(a)hotmail.com> wrote in message > news:8984b4b4-92e9-466a-ad51-20e6b4e815bc(a)u9g2000yqb.googlegroups.com... > On 3 Mar, 22:23, "Inertial" <relativ...(a)rest.com> wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> news:64d02f70-01e4-44a5-a5ab-41429bf37f71(a)q15g2000yqj.googlegroups.com... >> >> > I'm sure I said something about the ludicrous assertions that some >> > people here have made about the conceptual basis of SR. That is, >> > assertions that verge on meaningless, like "rotation into time" as an >> > explanation for length contraction. Or even observed time dilation (in >> > SR) being "real" as opposed to merely a function of propagation >> > delays. But none of this fundamentally challenges SR. >> >> Time dilation isn't anything to do with propagation delays .. they do NOT >> cause time dilation. It IS real in that it has been measured >> experimentally. >> >> Your denial of reality is another trademark of a crackpot. > > I'm not denying it. I'm saying experiments that involve acceleration > are the realm of GR (as I understand it), and that acceleration is the > cause of "real" time dilation. We're talking about SR, and therefore > we cannot be talking about any experiment that involves acceleration. > > ________________________________ > It is true that you cannot devise an experiment whereby two clocks are > together and then separated without at least one of them experiencing > acceleration at some point; that unfortunately is a mathematical fact, not > a physical one. No .. you can do that without acceleration. But it involves multiple clocks.
From: Inertial on 4 Mar 2010 04:55 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:4b40c1ce-92fb-47f8-8cec-e97dbde07cd9(a)b7g2000yqd.googlegroups.com... > On 3 Mar, 22:31, "Inertial" <relativ...(a)rest.com> wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> >> and 80 foot ladders can fit through 40 feet barns, >> >> > It remains slightly unclear, but I'm inclined to say no, >> >> Then you do not understand or accept SR. >> >> > although it >> > can certainly be made to appear to happen in certain circumstances. >> >> So if you close the doors simultaneously on a barn and the rod is inside >> you >> think that means it is not REALLY inside? > > The question is of measuring simultaneity. I can accept that, from > certain perspectives, the doors would appear to close simultaneously > with the ladder inside, but that in fact the distant door opened > before the nearest door even shut (and hence the ladder was never > physically inside with both doors shut). This also explains why, from > the ladders perspective, the barn can get apparently *even smaller*, > and yet the ladder can still pass through. > > To conceive of length contraction being real, it would surely be > detectable already, Yeup .. it is .. indirectly. > and moreover it would indicate a preferred frame > of reference No ..it doesn't > (because even from the ladder's frame, the ladder would > have to shrink relative to the barn - No .. it doesn't .. the barn shrinks > which would manifest itself as > the barn growing to apparently twice its real size). Doesn't happen >> >> If, on the other hand, you do not believe in the twin "paradox" >> >> actually >> >> happening, you don't believe in SR. >> >> > We resolved the twins paradox months ago. The astronaut twin undergoes >> > asymmetrical acceleration, and that is why he returns younger. >> >> >> If you do believe the predictions of SR >> >> that one twin is older, then you believe that time dilation is more >> >> than >> >> some mathematical fiction, its what actually happens in the real >> >> world. >> >> > On the contrary. The involvement of acceleration, which is the domain >> > of GR, makes me wonder why this is held to be a paradox in SR at all. >> >> SR handles acceleration just fine > > I doubt it. And you are wrong > Otherwise you'd get a contradiction in the twins paradox. No .. you don't >> > And yes, the acceleration causes real effects for the astronaut twin. >> >> >> So, when relativity predicts that one twin will age more than the >> >> other, >> >> is >> >> this just some mathematical truth, or is it what really happens as >> >> well? >> >> > It really happens, due to acceleration. >> >> >> So, do you believe that SR is correct in its prediction (for example) >> >> that >> >> if one twin were to be sent off into space at 0.9c for 10 years they >> >> would >> >> have aged less on their return than the twin that stayed at home? >> >> > I'm not sure SR does predict this. >> >> Of course it does .. that is the twins paradox you just said you >> understnood >> !! >> >> > As I understand it, GR is required >> > to predict this effect. >> >> Wrong >> >> > The problem for SR was, as I understand it, >> > explaining why SR *doesn't* predict that effect. >> >> It DOES predict it. My god you are SO DAMNED IGNORANT of what you >> ponficiate about. > > As far as I know, Einstein used GR to resolve the paradox, There is no paradox .. and it was part of his 1905 paper on SR > based on > the fact that the astronaut twin undergoes "real" acceleration, > whereas the Earth (and the homebody twin) does not. You don't need ANY acceleration to get a 'twins paradox' result. >> >> Do you agree its correct when it says that an 80 foot ladder could fit >> >> inside a 40 foot barn? >> >> > No, I'm not confident about that prediction. I think it's more likely >> > to be an apparent effect. >> >> What is only 'apparent' about shutting the doors on a barn simultaneously >> with a long rod fully ensloed between them? Do you think it is all done >> with mirrors? > > It doesn't need to be done with mirrors. A person standing at one door > of the barn who observes the doors close simultaneously, would not > observe simultaneity when standing at the other door (when standing at > the other door, he would observe that other door to shut long before > the first door). Hence by careful timing of the doors, and crafty > position of the observer, it can be made to appear that the doors shut > simultaneously while, in fact, they did not. It is not some trick. > And just to be clear, my concept of "simultaneity" is that which would > be simultaneous if information propagated instantaneously. Not required. But if it could be, it would be consistent with SR's notion. Simultaneous means AT THE SAME TIME.
From: Peter Webb on 4 Mar 2010 05:10 > 3) This does not explain why atomic clocks on a jet register different > times AFTER being brought to rest than do their counterparts which > have been at rest the entire time--or why the difference in time that > they register is exactly consistant with the predictions of > relativity. Indeed, because SR doesn't deal with acceleration. ______________________ No, that is not true. The effects of acceleration are absolutely inconsequential compared to those deriving from SR time dilation. > I know this isn't the first time this has been told to you, although > maybe not all at once. Do you just not pay any attention at all to > what anybody tells you? I pay attention. It's just that I've been asking for weeks for an explanation for this assertion that time slows down in SR above and beyond the "apparent" effect due to propagation delays, and all I keep getting in return is a bald assertion that this is the case, even though I've made it quite clear that I do not find this bald assertion believable. ________________________ OK. Do you believe that you could be sitting inside a 40 foot barn and there is an 80 foot ladder contained within? That you would actually see it fully contained? And every measurement you took, including physically measuring it with a ruler, would show a length of less than 40 feet? And in the twins "paradox", do you believe that one twin would actually be older, independent of any effects of acceleration but deriving purely from classical SR time dilation? These are both predictions of SR. Do you agree with these predictions? How would you explain the fact that one twin is older on propagation delay? And this is nothing to do with acceleration, the contribution from that is vanishingly small, it is a function of the specific and definite prediction of SR that time slows when you travel fast. Independent of GR, SR predicts that time dilation will occur; if you believe it does, then you believe this part of SR, if you don't you don't believe in SR. So do you? And the fact that one twin is demonstrably older than the other could not possibly be an artifact of "propagation delays", could it?
From: Ste on 4 Mar 2010 05:34
On 3 Mar, 22:59, PD <thedraperfam...(a)gmail.com> wrote: > On Mar 3, 11:52 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > On 3 Mar, 12:30, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > > wrote: > > > > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > > > >> You say you are here to learn about SR. > > > > > I am here to learn more about the *conceptual basis* of SR. > > > > Minkowksi space time? > > > No. > > How about just spacetime, then, for which there is both a conceptual > description and a mathematical description? No. I would go as far as saying I don't want another word said about spacetime as a means of answering any of my questions. If an explanation falls back on appealing to the truth of even a single equation, then the explanation is defective as an answer to my questions. > > > >> Do you believe SR is true? > > > > > I accept it's mathematical form has some obvious truth, yes. > > > > Do you believe that it correctly predicts the results of every experiment > > > that it claims to? That clocks run slower, > > > No. In SR, clocks *appear* to run slower as you are increasing your > > distance from the clock. The effect is entirely apparent in SR. > > That's not the extent of what SR claims. Muons in a circulating ring > exhibit time dilation, though they are not receding from the clock at > all, for example. What they exhibit is a longer half-life. But I'm not sure that a single variable, time, has been isolated here. Firstly, there is constant acceleration if the particle is in a ring (and it seems unarguable that acceleration causes some kind of real change in behaviour at an atomic level). Secondly, were an observer travelling along with the muon, he may also report an increased half-life, as against if he and the muon were stationary relative to the ring - possibly because the cause of decay, which is assumed to be random, is actually influenced by the fact that the environment (as perceived by the muon) is spinning at relativistic speeds. There is certainly a need to account for this behaviour, but I am not sure it is accounted for by time dilation as opposed to the physical reality that the muon really is decaying slower. > > > and 80 foot ladders can fit through 40 feet barns, > > > It remains slightly unclear, but I'm inclined to say no, although it > > can certainly be made to appear to happen in certain circumstances. > > I would be cautious about inclinations. It is pretty easy to make the > distinction between "appears to" and "does". For example, if I hold > the doors of the barn open to admit the pole, and at a carefully > chosen moment, briefly close both barn doors simultaneously and then > open them again, in such a way that I can verify that the both ends of > the pole had entered the barn before I closed both doors, then I can > be pretty sure that the pole was wholly in the barn. I can also then > check whether there were any strike marks on the barn doors where the > pole would have struck them. If there are none, then this pretty well > unambiguously tells you the pole WAS inside the barn, not just > appeared to be inside the barn. If you think those events (no marks on > the barn doors, both doors closed simultaneously after entry of the > pole) can be observed while still maintaining the pole does not fit in > the barn, you'll have to explain to me how this is. This door-marking test is nice in principle, and I agree that the results would be conclusive. However I fear it is not a test that is implementable in practice with real materials. > > > and that the speed of light is measured the same in > > > every intertial frame of reference and this speed is independent of the > > > speed of the emitter, receiver, and underlying medium of transmission? > > > Yes. I think I've been able to reconcile this partially, but only > > vaguely and within a definitely non-standard conceptual framework, and > > it is forced to completely dispense with any corpuscular form of > > matter, and instead relies wholly on fields. Unfortunately it's > > probably the sort of thing that physicists spend their lives thinking > > about and never quite put their finger on. > > Aha. I hope you did not sprain your wrist while hand-waving. Lol. > > > If you believe all of those things, then you are saying more than "SR has > > > some obvious truths in its mathematical form" you are saying it is an > > > accurate portrayal of reality - ie, what happens when you conduct those > > > experiments, what physically and actually happens, is exactly as predicted > > > by Relativity. > > > I think we all agree that SR portrays reality, but none of us seem to > > be able to agree on what kind of reality it portrays. > > Do you believe there is more than one kind of reality? Namely, do you > believe there is a reality that matches your expectations for the > orderliness of that reality, and another reality that does not > necessarily meet those expectations? I'm a materialist (i.e. realist). You can't be a materialist and believe in more than one kind of reality. > > > If, on the other hand, you do not believe in the twin "paradox" actually > > > happening, you don't believe in SR. > > > We resolved the twins paradox months ago. The astronaut twin undergoes > > asymmetrical acceleration, and that is why he returns younger. > > Yes, but that is still very much the prediction of SR. I didn't realise SR could cope with acceleration. I thought that was what GR was required for? > > > If you do believe the predictions of SR > > > that one twin is older, then you believe that time dilation is more than > > > some mathematical fiction, its what actually happens in the real world. > > > On the contrary. The involvement of acceleration, which is the domain > > of GR, makes me wonder why this is held to be a paradox in SR at all. > > This is incorrect. SR can handle acceleration just fine. What matters > here, and what marks the difference between the twins, is the > straightness of the path (a special term called "worldline" in > physics) in spacetime. Straighter paths consume longer "proper > time" (another specialized term in physics). Yes, and off we go into la-la land again. (I know exactly what you're describing, but it is the most obtuse way of describing the essential physical reality.) > > And yes, the acceleration causes real effects for the astronaut twin. > > Yes indeed, and it is remarkable that the effects are precisely in the > quantity that is predicted by SR. I need some clarification Paul. My understanding is that SR does not deal with acceleration - one must "reanchor" the frame of reference each time velocity changes. Now is that correct or not? > > > You seem to agree they are "mathematical truths". Do you also agree those > > > equations correctly predict the outcomes of real world experiments, which > > > means they are far more than simply "mathematical truths"? > > > The question is of interpreting the mathematical predictions. As I say > > above, there is a difference between what is real and what is merely > > apparent. > > See above regarding the pole and the barn. In terms of the > observations given, you'll have to explain to me how the pole would > have really NOT fit into the barn (but only apparently) and been > consistent with the observations noted. Ok. We have an observer standing by a door of the barn. We call this the near door. The other door is the distant door. Now, we close the distant door, and then reopen it. Then we send the ladder in (at relativistic speeds). The observer watches the ladder go in. Then we close the near door behind the ladder. The propagation delays from the distant door mean that, according to the observer standing by the near door, the doors are closing simultaneously, but in fact the distant door had closed and reopened before the ladder had even entered the barn. Hence the ladder fits apparently, but not really. |