A constant speed of light in all reference frames? Surely you can't be serious.
in [Relativity]
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From: Jerry on 3 Mar 2010 08:29 On Mar 3, 6:28 am, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > I understand it and think it is correct. > > My position is that far more people would understand it if it was > explained differently. It is generally accepted by most legitimate posters on these newsgroups that Einstein's original two-postulates axiomatic approach to the development of relativity is somewhat archaic and difficult to follow, to judge by the numerous crackpots who stumble at the very first steps in his derivation. You prefer Bondi's presentation of Milne's derivation, which goes "backwards" starting with the Doppler effect. I also like Bondi's approach which is quite intuitive, but after rederiving all of Einstein's famous results, the reader is left somewhat dangling. How does one proceed from there? Bondi's approach is still, at its core, a classic geometric development of the subject. By analogy: One does not design a skyscraper using Euclid's Elements, and one does not get to General Relativity through either Einstein's original or Milne's "inverted" axiomatic development of relativity. It's just too cumbersome a way to get there. Proceeding forward means presenting Minkowski spacetime. The Minkowski spacetime approach to relativity in essence replaces the two postulates with a single assertion: "The geometry of the universe is accurately described (in low gravity fields) by a four dimensional manifold with properties as follows..." Taylor and Wheeler, which I like and you hate, start with this single "postulate" and spend the rest of the book familiarizing the reader with the implications of this visualization of the universe. If the reader is diligent, by the time they finish the book, Minkowski spacetime will have gone beyond mere mathematical manipulation, but will have become a coherent, consistent, and best of all, highly intuitive mental construct by which the reader apprehends relativity. Your main objection seems to be that Taylor and Wheeler don't bother trying to justify relativity. T&W just want the reader to accept that the battle has been won. Relativity works, so the reader should just get on with learning the most efficient way to work with it, et cetera. You obviously don't like that attitude. Jerry
From: Peter Webb on 3 Mar 2010 09:01 By analogy: One does not design a skyscraper using Euclid's Elements, and one does not get to General Relativity through either Einstein's original or Milne's "inverted" axiomatic development of relativity. It's just too cumbersome a way to get there. Proceeding forward means presenting Minkowski spacetime. The Minkowski spacetime approach to relativity in essence replaces the two postulates with a single assertion: "The geometry of the universe is accurately described (in low gravity fields) by a four dimensional manifold with properties as follows..." ____________________ Its still a very, very long way from Minkowski to GR, and very few people go the whole way. I guess the problem with Minkowski is that its very simple if you understand some quite abstract concepts, specifically matrices, vectors and imaginary numbers (a term I have not used so far in this newsgroup, lest some crackpot size upon it. "Complex numbers" scarcely seems better). If you don't know these concepts reasonably well, you are stuffed, and learning them takes as long as does learning SR itself some other way. Whereas the other approaches are purely algebraic; they are not as self explanatory, but don't involve any even slightly sophisticated maths. And, again, as I think you have pointed out and certainly many others have, that is one of the delights of relativity, that you can derive the same theory and equivalent formulations in so many completely different ways.
From: bert on 3 Mar 2010 09:29 On Mar 2, 9:56 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > On Mar 2, 8:33 pm, Jerry <Cephalobus_alie...(a)comcast.net> wrote: > > > > > > > On Mar 2, 7:06 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > > > > On Mar 2, 5:34 am, Jerry <Cephalobus_alie...(a)comcast.net> wrote: > > > > Special relativity has been established as true within its > > > > domain of applicability. Period. > > > > Your appeal to athority is noted. Some of us don't accept things just > > > because everyone else believes it, particularly when it leads to > > > unexpected results. You would have fit in well with the flat earth > > > society. > > > Not an appeal to authority. Rather, a modest amateur familiarity > > with the literature. > > > I have in my file folders nearly one hundred papers dating from > > the late 1800's to the present dealing with the experimental > > basis of relativity. I have read many more papers than those that > > I own. > > > This is, of course, a very small number compared with the many > > hundreds of papers and subscription journal volumes that I own > > and have read which concern my actual field of work. I know my > > priorities. I am most definitely not a physicist in real life, > > and make no claims to any special expertise. > > > Nevertheless, I imagine that I am probably somewhat more familiar > > with the experimental literature than you. > > > True or false? > > > Jerry > > Seems you have that appeal to athority thing down to a science ;-) > > Bruce- Hide quoted text - > > - Show quoted text - If a photon ever changed its speed it would no longer be a photon TreBert
From: PD on 3 Mar 2010 11:21 On Mar 2, 8:12 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > > > It is not a function of finite propagation speeds, this we know, > > because we took into account the finite propagation speeds in our > > procedure for determining simultaneity/nonsimultaneity. Do you not > > remember that? > > I beg to differ. It is not a "mere" or "simple" function of finite > propagation speed, but it *is* a function of it IMO. RoS only took it > into account by allowing us to use different time coordinates in each > frame. If the speed of light was infinite there would be no RoS. > I disagree. All that is needed in relativity of simultaneity is a signal speed that can be VERIFIED to be the same from both events by either observer. Since the distance from the events to the observer is equal, as verifiable at any time by each observer, we learn from this that each observer KNOWS the propagation delays from each event to the observer are equal. This acknowledges the propagation delays completely, but simply allows for verification that they are the same. Then the determination of simultaneity or nonsimultaneity of the original events is completely unambiguous: If the observer receives both signals at the same time, then (because the propagation delays are the same) the original events were simultaneous; if the observer receives both signals at different times, then (because the propagation delays are the same) the original events were nonsimultaneous. Then the frame-dependence of simultaneity follows directly from the experimental *observation* that for the same pair of events, one observer correctly and unambiguously concludes the events were simultaneous, and the other observer correctly and unambiguously concludes the events were nonsimultaneous. You've mentioned in the past that you found your disbelief in relativity stems from being unable to find a good, understandable explanation of it. I invite you to read back on this thread where I was trying to explain to Ste (who has a similar complaint) how this comes about.
From: PD on 3 Mar 2010 11:43
On Mar 3, 3:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 2 Mar, 18:37, PD <thedraperfam...(a)gmail.com> wrote: > > > On Mar 2, 11:23 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > The point about emphasising the similarities between science and > > > religion is to combat some of the more absolute assertions about the > > > nature and value of science. In reality, what you really have is two > > > religions at war, where 99% can be the same and yet both insist that > > > the remaining 1% difference is a fundamental difference. > > > Gee, I happen to think that the scientific method on one side, and the > > belief in a supernatural entity on the other, are more than "1%" > > insignificant differences. > > Religious believers always do insist this. Many of the major religions > of the world share in common a God, much of their scripture, and most > of their prophets, and yet all insist that the remaining differences > are fundamental. Indeed, if you go to somewhere like Afghanistan, to > the outside eye the people apparently share a common religion, and yet > the mere difference of emphasis on some small aspects of scripture are > enough for the proponents of differing interpretations to consider > their differences fundamental. I don't understand what you're trying to argue. I've told you that I believe that the difference between science and religion is not a 1% and insignificant difference. You tell me something about what religious folks believe about their religions, as though that has any bearing on what I told you about the significance of the difference between science and religion. Are you trying to tell me that because what you consider a 1% difference between religions is not considered a 1% difference by religious folks, that this somehow maps to what you consider to be a 1% difference between science and religion? What about the 1% difference between mammals and reptiles? > > > > And certainly, one can discuss the differences between science and > > > religion, and its significance, but the debate certainly *cannot* be > > > conducted in terms of sayng that science invariably produces more > > > truth, or is more functional, or is more objective, or involves less > > > faith at its core. > > > Who said that science invariably produces more truth, or is more > > functional, or is more objective? I certainly have never told you > > that. > > You have certainly said that it is more functional - perhaps in a > slightly different way of saying it's "useful". I certainly did not say that science is more functional or useful than religion. > And of course, I'm not > just addressing the specific things that you've said, but instead > setting out my case in a more general way. Science is, after all, not > just you. Nevertheless, you are tossing up strawmen as though I've maintained that they are true, and I've never told you they are. > > > > > > I personally think it's more convenient to compare and contrast, > > > > > rather than trying to establish a definition for either religion or > > > > > science. Indeed, attempts to establish a consistent definition of > > > > > science, by men better than me, have time and again died a thousand > > > > > deaths. > > > > > By that approach, one could easily be convinced that cows are > > > > reptiles, no? > > > > Indeed. But if people are determined to focus on the differences, the > > > question is why. > > > To decide if a cow is a reptile, which I believe was the question at > > hand. No, I'm sorry, it was to decide if science is a religion. Same > > thing, more or less. > > I think I missed your point. > > > > If you want cow's milk to drink, then it's convenient > > > to distinguish between cows and reptiles. But people are less clear > > > about why they want science and not traditional religion. > > > Who said people want science and not traditional religion? > > I said that. Then say "I am less clear why I want science and not traditional religion." I don't believe the generalization you made applies, and it certainly does not apply to me. |