Known physics defeated by simple puzzle?
in [Relativity]
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From: Edward Green on 6 Apr 2010 18:52 On Apr 6, 11:39 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 6 Apr, 16:28, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Apr 5, 6:41 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 5 Apr, 22:10, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Apr 5, 3:47 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > I'm happy to make concessions, but I have to be able to ask questions > > > > > and get meaningful answers. The ladder in the barn is a prime example. > > > > > I'm told "the ladder contracts to fit in the barn". > > > > > It contracts to fit the barn in the rest frame of the barn, which is > > > > why the ladder makes no marks on the barn doors when the doors are > > > > shut at the same time. In the rest frame of the ladder, the ladder > > > > does not contract and indeed does not fit inside the barn at all. In > > > > the rest frame of the ladder, the reason why there are no marks on the > > > > barn doors when they are shut is that they were not shut at the same > > > > time in this frame. > > > > This logic is easily defeated Paul, because if we contracted the > > > ladder's length *just* enough so that it marked the door in the barn > > > frame (in other words, the ladder has contracted just enough to manage > > > an interference fit with both doors shut), then this cannot be > > > accounted for in the ladder frame (because, in the ladder frame, if > > > the ladder is *even larger* relative to the barn than when it started, > > > then the ladder could not possibly mark the doors in the same way). > > > I'm not sure what the fuss is. The observation is that the doors are > > shut and open without striking the pole, and this is true in both > > reference frames examined (as well as any other inertial reference > > frame). The account in the ladder frame is, however, not because the > > ladder fits inside the barn. It is exactly as I described above. Why > > is this difficult? > > It isn't difficult for me. I can explain it, in its entirety, in terms > of a "visual effect" and the careful timing of the doors. It's other > people here who keep insisting that it is not a visual effect, and > hence the fuss Taking you at your word (that you can explain it), I wonder if your "visual effect" is not an alternate formulation of SR. But perhaps that has been ruled out already.
From: Sue... on 6 Apr 2010 18:54 On Apr 6, 6:47 pm, Edward Green <spamspamsp...(a)netzero.com> wrote: > On Apr 5, 11:07 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > I still fail to see any plausible explanation for the difference in > > simultaneity, except that it is due to a careful placement of the > > observer and a differential in the delay of propagation. > > The laws of physics are locally Lorentz invariant. That means they > are invariant in form when the coordinates undergo a transformation of > the Lorentz form. This is also known as a change in reference frame. > The form of the transformation involves mixing time and distance. Frayed knot. < if you know about complex numbers you will notice that the space part enters as if it were imaginary R2 = (ct)2 + (ix)2 + (iy)2 + (iz)2 = (ct)2 + (ir)2 where i^2 = -1 as usual. This turns out to be the essence of the fabric (or metric) of spacetime geometry - that space enters in with the imaginary factor i relative to time. >> http://www.aoc.nrao.edu/~smyers/courses/astro12/speedoflight.html Sue... This > is the origin of the change in simultaneity. The identity of form of > the laws of physics under the transformation accounts for each > observer thinking _his_ coordinates are the natural ones. All other > results follow. > > > Incidentally, do the doors shut at different times depending on > > *where* you sit on the ladder? > > No.
From: Sue... on 6 Apr 2010 19:09 On Apr 6, 6:52 pm, Edward Green <spamspamsp...(a)netzero.com> wrote: > On Apr 6, 11:39 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > On 6 Apr, 16:28, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Apr 5, 6:41 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > On 5 Apr, 22:10, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > On Apr 5, 3:47 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > I'm happy to make concessions, but I have to be able to ask questions > > > > > > and get meaningful answers. The ladder in the barn is a prime example. > > > > > > I'm told "the ladder contracts to fit in the barn". > > > > > > It contracts to fit the barn in the rest frame of the barn, which is > > > > > why the ladder makes no marks on the barn doors when the doors are > > > > > shut at the same time. In the rest frame of the ladder, the ladder > > > > > does not contract and indeed does not fit inside the barn at all. In > > > > > the rest frame of the ladder, the reason why there are no marks on the > > > > > barn doors when they are shut is that they were not shut at the same > > > > > time in this frame. > > > > > This logic is easily defeated Paul, because if we contracted the > > > > ladder's length *just* enough so that it marked the door in the barn > > > > frame (in other words, the ladder has contracted just enough to manage > > > > an interference fit with both doors shut), then this cannot be > > > > accounted for in the ladder frame (because, in the ladder frame, if > > > > the ladder is *even larger* relative to the barn than when it started, > > > > then the ladder could not possibly mark the doors in the same way). > > > > I'm not sure what the fuss is. The observation is that the doors are > > > shut and open without striking the pole, and this is true in both > > > reference frames examined (as well as any other inertial reference > > > frame). The account in the ladder frame is, however, not because the > > > ladder fits inside the barn. It is exactly as I described above. Why > > > is this difficult? > > > It isn't difficult for me. I can explain it, in its entirety, in terms > > of a "visual effect" and the careful timing of the doors. It's other > > people here who keep insisting that it is not a visual effect, and > > hence the fuss > > Taking you at your word (that you can explain it), I wonder if your > "visual effect" is not an alternate formulation of SR. But perhaps > that has been ruled out already. About 1907 the formulation changed to a visual derivation. This is why the Quacks will only refer to the 1905 paper. Its well documented here if you can read as fast as you post: http://en.wikipedia.org/wiki/Lorentz_ether_theory Sue...
From: Timo Nieminen on 6 Apr 2010 19:30 On Tue, 6 Apr 2010, Edward Green wrote: > On Apr 6, 11:39 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > It isn't difficult for me. I can explain it, in its entirety, in terms > > of a "visual effect" and the careful timing of the doors. It's other > > people here who keep insisting that it is not a visual effect, and > > hence the fuss > > Taking you at your word (that you can explain it), I wonder if your > "visual effect" is not an alternate formulation of SR. But perhaps > that has been ruled out already. No, "visual effect" isn't an alternative formulation. But it's easy to get the idea that it is from the language used, especially that Most Evil Word, "observer". The usual usage of "observer" in SR means "coordinate system" or "reference frame", not "somebody who sits there and looks around" which we might expect from other usage of the term. "As seen by observer X" means "as measured using synchronised clocks in coordinate system X". The coordinate system extends over all space, and the question of "where is the observer located" doesn't apply. So, it doesn't matter where the observer sits on the ladder or stands in the barn, or at which door they stand, since "observer" doesn't mean that kind of real observer. That said, it's quite possible to include real observers, who sit and look around, in SR, taking the finite propagation speed of signals into account. You get interesting optical effects. Exercise for the reader: Consider a pole of length L, moving directly towards or away from an observer (a real observer!) at speed v. 1. What is the length L' of the pole, as measured in a coordinate system in which the observer is at rest (i.e., the observer's rest frame)? Does this depend on whether it is moving towards or away from the observer? Why or why not? 2. How long does the pole appear to be when the observer _looks_ at it? (We can assume there are little flags or lights on the ends, so that the ends can be clearly seen). What is this apparent length for motion towards and away from the observer? 3. Can the observer see the Lorentz contraction of the pole? -- Timo
From: Inertial on 6 Apr 2010 19:35
"Ste" <ste_rose0(a)hotmail.com> wrote in message news:2de6401c-02e2-4047-ae0c-6bbc299e035b(a)u34g2000yqu.googlegroups.com... > Btw I just wanted to post this again, and invite responses from > anyone: > > > On 6 Apr, 01:15, Ste <ste_ro...(a)hotmail.com> wrote: >> On 5 Apr, 22:57, PD <thedraperfam...(a)gmail.com> wrote: >> >> > On Apr 5, 4:29 pm, Ste <ste_ro...(a)hotmail.com> wrote: >> >> > > I do not see how this can work, >> > > unless the clocks themselves fall out of synchronisation (and hence >> > > are not actually measuring the same periods of time as each other). >> >> > The clocks' synchronization can be (and is) checked both before and >> > after the operations described above and verified to still hold, so >> > your supposition of what must have happened is ruled out. >> >> Not necessarily. If both slowed in the middle of the operation, then >> they would still be synchronised with each at the end, but it would >> utterly confound any calculation about simultaneity, unless you also >> knew by how much the other clock had slowed and when. >> >> To give you an example, if I have two clocks stationary relative to >> each other and ten light-seconds apart, and I suddenly slow both >> clocks to half-speed (in other words, ticking once for every two >> previous ticks), then according to each clock, the other one speeds up >> to double speed, No. There is a visual illusion due to delays in the information arriving. But we would NOT say that either speeds up according to the other. Just as there is a visual illusion that the clocks are not in sync when they actually are. |