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 6 Mar 2010 08:18 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:e75f3463-ac9f-4b6c-ac9f-52b8622956a0(a)z4g2000yqa.googlegroups.com... On 5 Mar, 14:46, mpalenik <markpale...(a)gmail.com> wrote: > On Mar 5, 3:55 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > So what you're saying (and I had recognised this problem before you > > said it) is that it is the "original" position of emission that > > matters? > > > And the "original" position changes depending on the frame (i.e. in > > the source frame, the source does not move, whereas in the receiver > > frame, the sources are constantly moving from their "original" > > positions)? > > Right. The sources send out one pulse at one particular point in > time. The only thing that matters is where they were located when > they sent out that pulse. That location is the "source" of the pulse. Ok. But one observation I would make first is that, I presume, from the source inertial frame, both the rising and falling edges of the wave have the same origin. However, in the receiver inertial frame, the rising edge does not have the same origin as the falling edge - so there is a lack of symmetry between what is being described in these inertial frames. _____________________________________ No, they can still be symmetric, and the choice of origin is arbitrary. The rising and falling edges of the photon's E field (which I assume you are talking about) is a complete red herring in the context of this thread; this is what gives rise to the Relativistic Doppler Effect, but you seem to be discussing time dilation generally, and this is not tied to using light - you would get the same answers using neutrinos for signalling, and as far as we know they don't "wave" at all. Secondly, we talk of the sources being in a "particular place" when the pulse is emitted, and yet by your own argument they are not in a "particular place" at all - in one frame, the sources are in the same place at all times, and in the other frame, the sources are never in the same place for more than an instant. So is it really meaningful to talk of the "place of origin" of the source as a well-defined, single point in space and time? ____________________________________ Well yes, it is, but in a somewhat more abstract sense than in Newton. Individuals in their own co-ordinate systems in 3D space will measure these differently, but they are the same point in spacetime viewed from different angles. Much earlier on, somebody replied to a question about the ladder/barn paradox by pointing out that an 80 foot high ladder can fit under a 10 foot high door by rotating it. As you live in a world where speeds near c are uncommon, its as if every ladder you have ever seen is standing upright and you had no idea they could be tilted. You are now asking a question which use of this analogy will help answer. If your question "is it really meaningful to talk about a single well defined origin for an event" was translated as "is it really meaningful to talk about the *height* of a ladder", the answer is no, because by tilting it you can have whatever height you want. OTOH, if it is translated as "is it really meaningful to talk about the *length* of a ladder", the answer is yes because this is invariant; an 80 foot ladder lying flat on the ground is still 80 feet long, even if it has almost zero height. HTH. Really, I do hope this helps; if you take the time to frame half decent questions civilly I will take the time to give you half decent answers, civilly.
From: Jerry on 6 Mar 2010 09:21 On Mar 6, 6:26 am, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > More generally, you are missing the difference between LET and SR. LET > compared to SR is a bit like Kepler's laws of planetary motion compared to > Newton's laws of gravity. Mathematically, inverse square laws imply > elliptical orbits (and Kepler's equal area formula), and Kepler's laws > require inverse square forces for gravity. You could say that Kepler is > mathematically identical to Newton for calculating planetary motion, because > you could derive the inverse square law purely from Kepler. Just as you can > derive time dilation purely from LET. > > What Newton did, in a sense, is create a model of the solar system which > obeys the same physical laws as Kepler, but did so using a completely > different starting point and framework. Newton and Kepler predict exactly > the same kinds of orbits, but Kepler's laws of planetary movement are not > the same as Newton's law of gravity, even though mathematically they produce > exactly the same orbits. > > A very similar relationship exists between SR and LET. SR in a sense > "explains" LET, just as Newton "explained" Kepler. > > Kepler's laws were statements about what is observed, Newton explains why > these observations occurred. LET was statements about what was observed, SR > explains why these observations occur. > > When Newton's law of gravity came out, it did not invalidate Kepler, and nor > did it even make any new predictions concerning elliptical orbits. It did > explain however why Kepler's laws were in a sense correct. Physicists did > not say immediately after Newton that Kepler was wrong, or his equations > were wrong (and indeed they produce mathematically identical elliptical > orbits). Newton just told a whole lot more of the story a lot more clearly, > and Newton's laws were immediately taken as more fundamental and useful than > Kepler. > > When SR came out, it did not invalidate LET, and nor did it even make any > new predictions concerning time dilation. It did explain however why LET's > equations were in a sense correct. Physicists did not say immediately after > SR that LET was wrong, or its equations are wrong (and indeed they produce > mathematically identical time dilation). SR just told a whole lot more of > the story a lot more clearly, and SR was immediately taken as more > fundamental and useful than LET. > > Had Kepler known calculus, he could have worked out that the acceleration of > a planet is proportional to the inverse square of the distance, and > eventually got Newton's law of gravity, which is implicit in elliptical > orbits. He didn't. More to the point, he had no explanation of why his laws > held; they were empirical and not theoretical in that they described the > results of experiments, but provided no theoretical framework. > > Similarly, if Lorentz and the others had considered the relationships > between energy and momentum in the right way, they would have got e=mc^2. > They didn't. More to the point, Lorentz had no explanation of why the > various transforms worked, they were empirical and not theoretical in that > described the results of experiments, but provided no theoretical framework. > > You can use LET to calculate time dilation, just as you can use Kepler to > calculate orbits. But that doesn't mean that Kepler's theories are the same > as Newton's, or that LET is the same as SR. An excellent analogy that I've never seen before!!! I'll remember it. Jerry
From: kenseto on 6 Mar 2010 09:29 On Mar 5, 12:12 am, "Inertial" <relativ...(a)rest.com> wrote: > "Bruce Richmond" <bsr3...(a)my-deja.com> wrote in message > > news:7806715d-93d2-49ff-ad67-6dac8ea64d8c(a)e7g2000yqf.googlegroups.com... > > > > > > > On Mar 4, 10:48 am, PD <thedraperfam...(a)gmail.com> wrote: > >> On Mar 3, 10:59 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > > >> > On Mar 3, 11:21 am, PD <thedraperfam...(a)gmail.com> wrote: > > >> > > 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. > > >> > Well you are going to have problems with that. There is no way to > >> > *know* that the speed is the same both ways. > > >> Yes, there is. That's what isotropy experiments have determined. I'm > >> surprised you weren't aware of this. > > > Do you mean like this one? > > >http://mysite.verizon.net/cephalobus_alienus/papers/Gagnon_et_al_1988... > > > The author is kind enough to point out problems in some similar > > experiments, while failing to notice any in his own. > > > For example, has he made any assumption about contraction of his > > equipment in the direction of motion? Tom Roberts has written posts > > in this group showing where some of these experiments are in effect > > two way measurements. > > >> > That is why Einstein > >> > wrote, "But it is not possible without further assumption to compare, > >> > in respect of time, an event at A with an event at B. We have so far > >> > defined only an ``A time'' and a ``B time.'' We have not defined a > >> > common ``time'' for A and B, for the latter cannot be defined at all > >> > unless we establish by definition that the ``time'' required by light > >> > to travel from A to B equals the ``time'' it requires to travel from B > >> > to A." > > >> > > 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. > > >> > Assuming the speed of light is the same in both directions. > > >> Which is an experimentally confirmed fact. Done well after Einstein's > >> comments on the matter, by the way. > > > Provide a link to an experiment and I'll take a look. > > >> > > 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. > > >> > No need. Lorentz showed how all frames could measure the speed of > >> > light to be c. That in effect confirms the second postulate, which is > >> > the stumbling block for many. > > >> Well then, you are just *choosing* what you would like to believe. In > >> this case, lodging a complaint against relativity that it is not well > >> explained, when you are not interested in pursuing a better > >> explanation, having settled on LET instead, is a bit on the > >> disingenuous side. > > > You are reading more into that than what I wrote. I am not choosing > > LET over SR. They use the same math > > Yes > > > and I consider them two > > interpertations of the same thing. > > Not at all. Very different as far as how they explain reality > > LET has and required a fixed (theoretically undetectable) aether in a fixed > absolute frame. > SR does not specify nor require anything about an aether > > LET has objects physically compressed due to absolute motion thru the aether > SR has no absolute motion, so objects are not affected by such motion > > LET has processes physically slowed due to absolute motion thru the aether > SR has no absolute motion, so processes are not affected by such motion > > LET has a side-effect of the speed of light being measured as the same in > all frames of reference, due to measuring with compressed rulers and slowed > clocks, even though its only really has that speed relative to the aether, > SR has no absolute compression and slowing, and the speed of light really is > c > > LET has a side-effect of an appearance of the lorentz transforms holding on > measured values, due to measuring with compressed rulers and slowed clocks. > SR has no absolute compression and slowing, so the lorentz transform hold > > > The LET interpertation had the > > advantage, for me, of showing how c + or - v could end up being > > measured c in all frames. > > In SR there is no c+v or c-v, because there is no fixed absolute aether > frame in which light really travels at c. Then why did Einstein say that M' is runshing toward the light front from the front (c+v) and receding away from the light front from the rear (c-v)?? Ken Seto > > > Given that was possible I no longer had any > > problem accepting the second postulate. Eventually I became aware > > that the second postulate wasn't so much an assumption as a > > stipulation. We will consider the speed of light to be our standard. > > No .. it is an observed fact. Not a stipulation > > > Recently I have been going back and re-reading some of the books I > > have bought over the years to see if I can come to grips with some of > > the modern interpertations of SR. After thinking about it for awhile > > I have realized that my objections about the changing definition of c > > were petty/anal. > > :) Always a good conclusion to reach .. it shows you really are thinking > and learning and advancing. > > > An analogy would be that there used to be 24 hours > > in a day, 60 minutes in an hour, and 60 seconds in a minute. Now we > > have defined a second as so many transitions of an atom, and can > > measure the variation in the length of a day. The new way is better. > > That it is not in perfect agreement with the old doesn't change much. > > There was nothing sacred about the old. So yes, an old dog can be > > taught new tricks :) > > > Bruce > > And several points up my estimation ladder for doing so and admitting it > :):)- Hide quoted text - > > - Show quoted text -
From: waldofj on 6 Mar 2010 09:46 > > In SR there is no c+v or c-v, because there is no fixed absolute aether > > frame in which light really travels at c. > > Then why did Einstein say that M' is runshing toward the light front > from the front (c+v) and receding away from the light front from the > rear (c-v)?? > > Ken Seto that is from the point of view of the observer on the ground and it's called closing speed (c + v) and separating speed (c - v). Why is that so difficult to understand?
From: rotchm on 6 Mar 2010 09:48
>LET was statements about what was observed, SR > explains why these observations occur. Hmmm, the opposite is generally said. SR is a math theory which predicts outcomes of observations. LET is a physical theory, predicting and dynamically explaining the outcome. This is often pointed out in the literature and in some scholarly books on SR. |