Known physics defeated by simple puzzle?
in [Relativity]
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From: J. Clarke on 17 Feb 2010 09:51 dlzc wrote: > Dear Peter Webb: > > On Feb 16, 3:35 pm, "Peter Webb" > <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: >> "dlzc" <dl...(a)cox.net> wrote in message >> news:61cef5d0-9103-4e95-b9bb-a81eeb738aab(a)b1g2000prc.googlegroups.com... >> On Feb 16, 6:46 am, Ste <ste_ro...(a)hotmail.com> wrote: >> >>> On 16 Feb, 03:40, mpalenik <markpale...(a)gmail.com> wrote: >> ... >>>> You've brought the detector at rest with respect >>>> to the source. They're now both in the same >>>> reference frame. The only way SR says that you >>>> should observe anything "unusual" is if the >>>> source and detector are moving with respect to >>>> each other. >> >>> Perhaps. But what is confusing me is this >>> "constant speed of light" postulate. >> >> This postulate is superfluous. The constancy of >> the speed of light is the result of Maxwell's >> equations (the laws of physics that are the >> same, regardless of source speed), and has >> good agreement with reality, with the proviso >> that only the two-way speed of light can >> ever be measured. >> >> ________________________________ >> Huh? The one way speed of light has been >> measured many times. > > Using a clock synchronization procedure that is equivalent to > Einstein's method, which establishes a "two-way light measured > experiment space". So all they can return is an average TWLS. > >> The first reasonably accurate measurement of >> the speed of light was in fact a one way >> measurement; the timing of the occultations of >> Jupiter's moons. > > Given a TWLS measurement of Juptier's orbital radius, Earth's, the > moon's, and angles Sun to Jupiter, and all the *inferred / impressed* > TWLS geometry... Make some reasonable assumptions about the difference in speed in different directions and then calculate the effect on the measurement based on the motion of Jupiter's moons and get back to us.
From: Ste on 17 Feb 2010 10:13 On 16 Feb, 14:31, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 16, 7:46 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > I'm not trying to prove anything. I'm trying to form some sort of > > consistent picture in my own head of how this setup behaves under > > different transformations. > > Another terminology issue here. The setup as described is undergoing > an acceleration or two. It therefore changes from being at rest in one > reference frame to being at rest in another reference frame. > "Transformations", as in the context Galilean transformations or > Lorentz transformations, is the relationship between the descriptions > of this system in those reference frames, but it does not mean the > physical process of the acceleration of the system itself. > > Do you understand the terminology? I'm not sure. If you're asking whether I considered "transformation" synonymous with "acceleration", the answer is no. I basically meant transformation in the sense that I have always know it, that is, "a movement of some sort", including translation, rotation, reflection, etc. > > > You've brought the > > > detector at rest with respect to the source. They're now both in the > > > same reference frame. The only way SR says that you should observe > > > anything "unusual" is if the source and detector are moving with > > > respect to each other. > > > Perhaps. But what is confusing me is this "constant speed of light" > > postulate. > > What is confusing about it? > Keep in mind that the constancy of the speed of light is something > that is experimentally, unambiguously confirmed. Well, I'm working through my confusion with my simple scenarios, so I won't rehash the same questions as I've already asked previously. > > > Translations in relativity--or in fact, even in pure mathematics--are > > > very different things than rotations, and picking the detector up and > > > putting it somewhere else without changing the speed is a pure > > > translation. You don't even need relativity in this scenario, where > > > everything is at rest with respect to everything else. > > > Yes, but we're going to get to the bit where relativity is required in > > a moment. > > > Now, let us suppose we have two source and two detectors again: > > > D1 D2 D3 > > > S1 S2 S3 > > > S1 and D1 are stationary in the frame, and do not move. D2 is also > > stationary in the frame. S2, S3, and D3 are all moving in the y+ > > direction (i.e. same as the previous scenario) at a constant speed > > (which is close to 'c'). Just to be sure we understand, the same setup > > a few moments back in time would have looked like this: > > > D1 D2 > > > D3 > > > S1 > > > S2 S3 > > > Now, when all sources come into line with each other (as per the first > > illustration above), a pulse is emitted towards the respective > > detectors. After emission, S2 would continue towards D2, but in > > reality we remove S2 from the picture before any collision (and we've > > already established that any transformation of the sources after > > emission has no effect on photons already emitted). > > > Now, based on the previous scenario, I presume that in SR, D3 receives > > its pulse long after D1. However, this time, does D2 receive its pulse > > at the same time as D1? > > The answer again depends on which reference frame you want the answer > in. I am guessing, but need confirmation, that the answer you want is > in the frame in which S1, D1, and D2 continue to be at rest? Yep.
From: Ste on 17 Feb 2010 10:20 On 16 Feb, 23:21, "Inertial" <relativ...(a)rest.com> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > news:e6adef4c-9c7e-421a-8a35-097ef868a9e4(a)k19g2000yqc.googlegroups.com... > > > > > > > On 16 Feb, 03:40, mpalenik <markpale...(a)gmail.com> wrote: > >> On Feb 15, 6:49 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > >> > On 15 Feb, 23:05, "Inertial" <relativ...(a)rest.com> wrote: > > >> > > "mpalenik" <markpale...(a)gmail.com> wrote in message > > >> > >news:90a5859a-7eaf-41ef-bda5-133028662cf0(a)h17g2000vbd.googlegroups.com... > > >> > > > On Feb 15, 4:09 pm, PD <thedraperfam...(a)gmail.com> wrote: > >> > > >> On Feb 15, 2:41 pm, dlzc <dl...(a)cox.net> wrote: > > >> > > >> > Dear PD: > > >> > > >> > On Feb 15, 12:20 pm, PD <thedraperfam...(a)gmail.com> wrote: > >> > > >> > ... > > >> > > >> > > I'm sorry, I misrepresented the diagram. They would arrive at > >> > > >> > > different times but there would be no red/blue-shifting. > > >> > > >> > The emitters are in a rest frame, and the detectors are (later) > >> > > >> > in a > >> > > >> > frame with +v and -v. Better think again. > > >> > > >> > Same situation would obtain the S1 and D2 were stationary, D1 > >> > > >> > and D2 > >> > > >> > were moving at v, and the pulses were sent through some form of > >> > > >> > clock > >> > > >> > synchronization (no more complex than obtaining "rigid" > >> > > >> > geometry). > > >> > > >> > David A. Smith > > >> > > >> Perhaps I don't understand the (revised) picture, either. > >> > > >> My understanding was that S1, D1, S2 and D2 are initially all at > >> > > >> rest > >> > > >> in a common reference frame. Then, after emission, they are all > >> > > >> briefly accelerated in the same direction and in the plane of the > >> > > >> apparatus, and then brought back to rest in the initial reference > >> > > >> frame. In this case, the whole apparatus has been simply displaced > >> > > >> while the photons are in transit. > > >> > > > Yes, this is the revised picture. For some reason, I was thinking > >> > > > the > >> > > > motion was supposed to be perpendicular to the plane of the > >> > > > apparatus, > >> > > > but when I thought about it later, I specifically remembered a post > >> > > > from Ste where he said this was not the case (that he meant "up", > >> > > > as > >> > > > in "up on the screen"). This is how I understand the description > >> > > > as > >> > > > well. > > >> > > Its much simpler now. The pulses arrive at different times, because > >> > > the > >> > > detectors have been moved (one closer to where pulses was emitted, > >> > > the other > >> > > further way from it). And no doppler as the detectors are at rest > >> > > again by > >> > > the time the pulses gets to it. > > >> > So do we have a consensus on the matter then? The pulse has an > >> > independent existence from its source so that, once emitted, a > >> > translation of the actual source does not translate the 'apparent' > >> > source of a pulse already in flight? > > >> I'm not sure what you're trying to prove here. > > > I'm not trying to prove anything. I'm trying to form some sort of > > consistent picture in my own head of how this setup behaves under > > different transformations. > > >> You've brought the > >> detector at rest with respect to the source. They're now both in the > >> same reference frame. The only way SR says that you should observe > >> anything "unusual" is if the source and detector are moving with > >> respect to each other. > > > Perhaps. But what is confusing me is this "constant speed of light" > > postulate. > > >> Translations in relativity--or in fact, even in pure mathematics--are > >> very different things than rotations, and picking the detector up and > >> putting it somewhere else without changing the speed is a pure > >> translation. You don't even need relativity in this scenario, where > >> everything is at rest with respect to everything else. > > > Yes, but we're going to get to the bit where relativity is required in > > a moment. > > > Now, let us suppose we have two source and two detectors again: > > > D1 D2 D3 > > > S1 S2 S3 > > > S1 and D1 are stationary in the frame, and do not move. D2 is also > > stationary in the frame. S2, S3, and D3 are all moving in the y+ > > direction (i.e. same as the previous scenario) at a constant speed > > (which is close to 'c'). Just to be sure we understand, the same setup > > a few moments back in time would have looked like this: > > > D1 D2 > > > D3 > > > S1 > > > S2 S3 > > Your diagram contradicts your description .. you show in the diagram that S1 > and D1 have moved apart (as have S3 and D3), but you said they do not. D3, > S2 and S3 have also moved to the left. I think you need to draw your > diagram again. No, I think you need to look at the diagram in a monospaced font.
From: PD on 17 Feb 2010 10:53 On Feb 17, 9:13 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 16 Feb, 14:31, PD <thedraperfam...(a)gmail.com> wrote: > > > On Feb 16, 7:46 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > I'm not trying to prove anything. I'm trying to form some sort of > > > consistent picture in my own head of how this setup behaves under > > > different transformations. > > > Another terminology issue here. The setup as described is undergoing > > an acceleration or two. It therefore changes from being at rest in one > > reference frame to being at rest in another reference frame. > > "Transformations", as in the context Galilean transformations or > > Lorentz transformations, is the relationship between the descriptions > > of this system in those reference frames, but it does not mean the > > physical process of the acceleration of the system itself. > > > Do you understand the terminology? > > I'm not sure. If you're asking whether I considered "transformation" > synonymous with "acceleration", the answer is no. I basically meant > transformation in the sense that I have always know it, that is, "a > movement of some sort", including translation, rotation, reflection, > etc. You're confusing two things. Translation, rotation, reflection, etc. do not necessarily imply movement of any objects. I'll give you an example from everyday experience. In map-and-compass orienteering, you have to decide whether you are using true north or magnetic north, and the two can vary significantly. Thus if you're at one place and you want to go to another place, the coordinates of the new place and the bearing you would choose would depend on this decision. Changing map coordinates and bearing from one kind of north to the other kind is a rotation. But this doesn't mean that you or your destination have moved. It only means that the coordinates or bearing by which you specify WHERE the destination is have changed. As another example, a Lorentz transformation tells you how to view the *same* objects undergoing the *same* events but from the perspective of two different observers moving relative to each other. This does not involve MOVING the objects or altering the events, or even moving an observer from one state to another. All it is talking about is how to translate the *description* of those events according to one observer into the description of the those events by the other observer. > > > > > You've brought the > > > > detector at rest with respect to the source. They're now both in the > > > > same reference frame. The only way SR says that you should observe > > > > anything "unusual" is if the source and detector are moving with > > > > respect to each other. > > > > Perhaps. But what is confusing me is this "constant speed of light" > > > postulate. > > > What is confusing about it? > > Keep in mind that the constancy of the speed of light is something > > that is experimentally, unambiguously confirmed. > > Well, I'm working through my confusion with my simple scenarios, so I > won't rehash the same questions as I've already asked previously. > > > > > > > Translations in relativity--or in fact, even in pure mathematics--are > > > > very different things than rotations, and picking the detector up and > > > > putting it somewhere else without changing the speed is a pure > > > > translation. You don't even need relativity in this scenario, where > > > > everything is at rest with respect to everything else. > > > > Yes, but we're going to get to the bit where relativity is required in > > > a moment. > > > > Now, let us suppose we have two source and two detectors again: > > > > D1 D2 D3 > > > > S1 S2 S3 > > > > S1 and D1 are stationary in the frame, and do not move. D2 is also > > > stationary in the frame. S2, S3, and D3 are all moving in the y+ > > > direction (i.e. same as the previous scenario) at a constant speed > > > (which is close to 'c'). Just to be sure we understand, the same setup > > > a few moments back in time would have looked like this: > > > > D1 D2 > > > > D3 > > > > S1 > > > > S2 S3 > > > > Now, when all sources come into line with each other (as per the first > > > illustration above), a pulse is emitted towards the respective > > > detectors. After emission, S2 would continue towards D2, but in > > > reality we remove S2 from the picture before any collision (and we've > > > already established that any transformation of the sources after > > > emission has no effect on photons already emitted). > > > > Now, based on the previous scenario, I presume that in SR, D3 receives > > > its pulse long after D1. However, this time, does D2 receive its pulse > > > at the same time as D1? Yes, and yes. > > > The answer again depends on which reference frame you want the answer > > in. I am guessing, but need confirmation, that the answer you want is > > in the frame in which S1, D1, and D2 continue to be at rest? > > Yep.
From: jbriggs444 on 17 Feb 2010 11:21
On Feb 17, 10:13 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 16 Feb, 14:31, PD <thedraperfam...(a)gmail.com> wrote: > > > On Feb 16, 7:46 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > I'm not trying to prove anything. I'm trying to form some sort of > > > consistent picture in my own head of how this setup behaves under > > > different transformations. > > > Another terminology issue here. The setup as described is undergoing > > an acceleration or two. It therefore changes from being at rest in one > > reference frame to being at rest in another reference frame. > > "Transformations", as in the context Galilean transformations or > > Lorentz transformations, is the relationship between the descriptions > > of this system in those reference frames, but it does not mean the > > physical process of the acceleration of the system itself. > > > Do you understand the terminology? > > I'm not sure. If you're asking whether I considered "transformation" > synonymous with "acceleration", the answer is no. I basically meant > transformation in the sense that I have always know it, that is, "a > movement of some sort", including translation, rotation, reflection, > etc. That is not the sense in which physicists use the word. A "coordinate system transformation" does NOT involve any movement at all. Let us take a simple example. Little Red Riding Hood has a house in the woods. So does Grandma. There is a trail between the two houses. Assume that the trail is 1 mile long. It need not be straight. Little Red Riding Hood can put coordinates on the trail, starting with her house at coordinate value 0 and Grandma's house at coordinate value 1. Grandma can put coordinates on the trail starting with her house at coordinate value 1 and Little Red Riding Hood's house at coordinate value 0. The Big Bad Wolf can put coordinates on the trail starting from his hiding point at coordinate value 0 back to Little Red's house at coordinate value -0.3 and forward to Grandma's house at coordinate value +0.7 [Let us agree for the moment to ignore any shortcuts that the Wolf knows about] A "coordinate system transformation" is the process of taking coordinates expressed in one coordinate scheme and re-expressing them in a different scheme. When you switch from one coordinate system to another, coordinates change but nothing "moves". Red 0 0.3 1 Grandma 1 -0.7 0 Wolf -0.3 0 0.7 If, for instance, the Big Bad Wolf decides to adopt Red's coordinates instead of his own, he immediately goes from coordinate value 0.0 (Wolf) to coordinate value 0.3 (Red). But he's still sitting in his hiding place. He hasn't moved. He's just decided to use a different coordinate system. (This is an example of translation) And if Grandma decides to adopt Red's frame, she goes from coordinate value 0.0 (Grandma) to coordinate value 1.0 (Red). But she's still puttering around in the kitchen baking cookies. (This is an example of a reflection plus a translation) I've avoided "rotation" and "re-scaling" for simplicity. This is what coordinate systems and "frames of reference" are all about. Different ways of assigning coordinate values to positions (and times). Different ways of putting numbers on the same underlying physical reality. |