Known physics defeated by simple puzzle?
in [Relativity]
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From: Ste on 10 Apr 2010 02:25 On 10 Apr, 06:05, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > Well, I asked the question precisely because I wanted an answer to > *that* scenario. If the clocks are already moving (and don't stop > before passing each other), then that really tells me nothing about > what I wanted to know. The purpose of having the clocks stopped at the > beginning and end is that it allows a 'simple' correction for any > propagation delay when testing for synchronisation. > > _______________________________________________ > For SR, you can assume that the change in speed is instantaneous, eg the > speed goes from V to 0 or -V in zero time. While physical objects can't do > that, reference frames certainly can. Yes, as I say in my other post to Inertial, the amount and duration of the acceleration is irrelevant - the answers can be in purely qualitative terms here. > Contrary to what I suspect you > believe, the "twin's paradox" is *not* caused by acceleration of the > travelling twin directly; it is caused by changes in the reference frame in > which the elapsed time is measured, as any non-crank site on the twins > paradox will explain. So you can assume that changes in velocity are > instantaneous. The "twins paradox" is accounted for in some way by the acceleration/ physical "impulse" sustained by the astronaut twin, because that is the variable that is asymmetric between them. I suspect "a change of reference frame" is merely a more obfuscated way of saying the same thing - and if it isn't the same thing, then this "frame" explanation is not an explanation at all. > As I say, I'd also like to discuss the specific scenario that I > raised. Because at least in my scenario, we can agree that they are > both synchronised at the start, and at the end, and that we have > accounted for propagation delays when testing for synchronisation. So > the question is how to interpret what happens in the middle, but > obviously I need you to describe what happens. > > ____________________________________________ > As I understand your experiment, when the clocks are separating they each > see the other clock as running more slowly, and when they are approach they > see the other clock as ticking faster, and the percentage change is the same > as that given by the formula for the Relativistic Doppler Shift. You can > confirm that when you add the outbound and inbound changes together, they > are both re-synchronised when they meet again, as a simple symmetry argument > requires. Yes, but what of "simultaneity"? If we account for Doppler (and, hence, propagation delays), then is there any discrepancy at all in simultaneity? > > After the pass A and B and have their clock readings adjusted, the an A' > > observer would measure B' as ticking slowly (as I described above), and a > > B' > > observer would measure A' as ticking slowly. They will both also see the > > other as showing the 'wrong' time (in particular, from what I think (not > > done the calculations), each frame will measure the other clock as being > > ahead of their own). > > Each frame will measure the other clock as being *ahead*? By any > chance, does the other clock always appear slow when they are sailing > into the distance away from each other, and always appear fast when > approaching each other? > > ______________________________ > Yes. Well that is certainly interesting. So not only does simultaneity change, but the 'direction in which simultaneity moves' depends on the direction of motion?
From: Ste on 10 Apr 2010 02:28 On 10 Apr, 07:11, "Inertial" <relativ...(a)rest.com> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > news:da85279f-24ef-481b-93d0-287ce74db45d(a)y14g2000yqm.googlegroups.com... > > > On 10 Apr, 04:49, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > > wrote: > > > I do wish you'd stop framing the issue as "you're either with us or > > against us". There is obviously some validity to SR - and I've said it > > a million times. > > It cannot be only partly valid > > [...] > > > Incidentally, I > > seem to remember that Terrell (of the "Terrell effect") commented that > > a lot of scientists even in his time (i.e. 50 years after relativity > > had been formulated) still had huge misconceptions about SR. And even > > Newtonian mechanics has not been thrown out - merely reinterpreted to > > show that it gives the correct answers only to certain circumstances > > (which is not how it would have been interpreted in its heyday). > > It is approximately correct .. that is all. It is never completely correct > except when there is no motion involved (which is rather pointless) Indeed, but the point is that Newtonian mechanics has "some validity" (even if a mechanics without movement is useless in practice).
From: Ste on 10 Apr 2010 02:29 On 10 Apr, 06:15, "Inertial" <relativ...(a)rest.com> wrote: > "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote in message > > news:4bc0072f$0$5523$afc38c87(a)news.optusnet.com.au... > > > > > > > > > "Ste" <ste_ro...(a)hotmail.com> wrote in message > >news:e1d473d9-bd92-4373-ac6c-4ec08f157f25(a)z6g2000yqz.googlegroups.com... > > On 10 Apr, 02:26, "Inertial" <relativ...(a)rest.com> wrote: > > >> > Incidentally, if you have two clocks a certain distance apart, > >> > synchronised (obviously, accounting for propagation delays), > > >> Yes .. that is always assumed. > > >> > and > >> > stationary relative to each other, > > >> Yes > > >> > what happens when you accelerate > >> > them towards each other. Does the distant clock appear to slow down, > >> > or speed up? > > >> Acceleration complicates things uncesssarily .. so lets assume no > >> acceleration for simplicity. > > > Well, I asked the question precisely because I wanted an answer to > > *that* scenario. If the clocks are already moving (and don't stop > > before passing each other), then that really tells me nothing about > > what I wanted to know. The purpose of having the clocks stopped at the > > beginning and end is that it allows a 'simple' correction for any > > propagation delay when testing for synchronisation. > > > _______________________________________________ > > For SR, you can assume that the change in speed is instantaneous, eg the > > speed goes from V to 0 or -V in zero time. While physical objects can't do > > that, reference frames certainly can. Contrary to what I suspect you > > believe, the "twin's paradox" is *not* caused by acceleration of the > > travelling twin directly; it is caused by changes in the reference frame > > in which the elapsed time is measured, as any non-crank site on the twins > > paradox will explain. So you can assume that changes in velocity are > > instantaneous. > > >> An equivalent set up is this, with no acceleration invovled, where A, B, > >> A' > >> and B' are all clocks. > > >> A'->v B'<-v > >> A o B > > >> Let A and B be our mutually-at-rest, synchronized clocks (as you > >> mentioned) > > >> Let A' and B' be moving at the same speed (but opposite directions) > >> relative > >> to A and B. > > >> As A' passes A and B' passes B (at the same time according to A and B), > >> we > >> copy the reading from A clock to A' clock, and copy the reading from B > >> clock > >> to B' clock. A' and B' keep moving and arrive together at o, where there > >> times are compared. > > > As I say, I'd also like to discuss the specific scenario that I > > raised. Because at least in my scenario, we can agree that they are > > both synchronised at the start, and at the end, and that we have > > accounted for propagation delays when testing for synchronisation. So > > the question is how to interpret what happens in the middle, but > > obviously I need you to describe what happens. > > > ____________________________________________ > > As I understand your experiment, when the clocks are separating they each > > see the other clock as running more slowly, > > Ticking at the same rate, but see a later time. That is an illusion,of > course > > > and when they are approach they see the other clock as ticking faster, > > There is some optical illusion of that, the actual measurement is slower. > > > and the percentage change is the same as that given by the formula for the > > Relativistic Doppler Shift. You can confirm that when you add the outbound > > and inbound changes together, they are both re-synchronised when they meet > > again, as a simple symmetry argument requires. > > Yeup So which part of this setup is *not* due to an "optical illusion"?
From: Inertial on 10 Apr 2010 02:38 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:dae4fe55-f5fa-419a-bcce-c0236a2d9c37(a)w42g2000yqm.googlegroups.com... > On 10 Apr, 05:51, "Inertial" <relativ...(a)rest.com> wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> >> > what happens when you accelerate >> >> > them towards each other. Does the distant clock appear to slow down, >> >> > or speed up? >> >> >> Acceleration complicates things uncesssarily .. so lets assume no >> >> acceleration for simplicity. >> >> > Well, I asked the question precisely because I wanted an answer to >> > *that* scenario. If the clocks are already moving (and don't stop >> > before passing each other), then that really tells me nothing about >> > what I wanted to know. >> >> Then you don't understand the scenario > > No, Yes. > it's because I want specific answers to specific questions. > There's no point responding to a scenario that I never asked questions > about. That same answer applies >> > The purpose of having the clocks stopped at the >> > beginning and end is that it allows a 'simple' correction for any >> > propagation delay when testing for synchronisation. >> >> That is exactly WHY my scenario below has clocks stopped at the beginning > > But I want them stopped at the end, too. No need .. but if you want you can. It doesn't alter anything. >> > So >> > the question is how to interpret what happens in the middle, but >> > obviously I need you to describe what happens. >> >> Its the same as in my scenario. But in my case there is no need to talk >> about what happens during acceleration, nor specify how long they are >> accelerating for etc etc. The acceleration itself isn't the important >> concept here .. it is the change of rest inertial reference frames. > > It is not important to talk about how much acceleration or for how > long - it suffices that they do accelerate for some period of time, at > the start and at the end. Make the time zero if you like > The point is simply to talk in qualitative > terms about what happens to "simultaneity" between the points at the > start and at the end at which we agree that the clocks are > synchronised. It changes >> >> After the pass A and B and have their clock readings adjusted, the an >> >> A' >> >> observer would measure B' as ticking slowly (as I described above), >> >> and a >> >> B' >> >> observer would measure A' as ticking slowly. They will both also see >> >> the >> >> other as showing the 'wrong' time (in particular, from what I think >> >> (not >> >> done the calculations), each frame will measure the other clock as >> >> being >> >> ahead of their own). >> >> > Each frame will measure the other clock as being *ahead*? >> >> That is what I said >> >> > By any >> > chance, does the other clock always appear slow >> >> I just said it would measure it as ahead. >> >> We are not talking about appearances and optical illusions >> >> > when they are sailing into the distance away from each other, >> > and always appear fast when approaching each other? >> >> We are not talking about appearances and optical illusions > > Just answer the questions Inertial Not ones that are designed by you to divert from the issue [snip more waffle] > So, whether it "appears" slow or is "really" slow, the question is > does it slow down or speed up (whether really or apparently) Two different questions .. two different answers > depending > on whether it is approaching or receding? In other words, if we moved > the clocks in the opposite direction (starting near, and then receding > to a point in the distance)? The clocks always tick at the correct rate .. they are neither fast nor slow in their own frames. A frame moving relative to a clock will measure the clock as ticking slower. Less elapsed time will show between an pair of events for the relatively moving clock than an at-rest clock. That is independent of the direction of the relative motion. I had though we agreed to ignore illusions due to propagation delays. The illusion due to propagation delays is that a clock moving away from you will look like it is running a bit slower, because it takes longer and longer time for the light to reach you. The illusion due to propagation delays is that a clock moving toward you will look like it is running a bit faster, because it takes short and shorter time for the light to reach you. To know what is seen, you need to combine those illusions with what is measured to happen as described. Those illusion do not have any relevance,, unless for some reason you REALLY want to know what an observer at a given location would actually see, as opposed to what is RAALLY going on.
From: Inertial on 10 Apr 2010 02:39
"Ste" <ste_rose0(a)hotmail.com> wrote in message news:9ad034ee-f382-4349-aaf3-dd58d93dd669(a)w42g2000yqm.googlegroups.com... > On 10 Apr, 06:05, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> Well, I asked the question precisely because I wanted an answer to >> *that* scenario. If the clocks are already moving (and don't stop >> before passing each other), then that really tells me nothing about >> what I wanted to know. The purpose of having the clocks stopped at the >> beginning and end is that it allows a 'simple' correction for any >> propagation delay when testing for synchronisation. >> >> _______________________________________________ >> For SR, you can assume that the change in speed is instantaneous, eg the >> speed goes from V to 0 or -V in zero time. While physical objects can't >> do >> that, reference frames certainly can. > > Yes, as I say in my other post to Inertial, the amount and duration of > the acceleration is irrelevant - the answers can be in purely > qualitative terms here. > > > >> Contrary to what I suspect you >> believe, the "twin's paradox" is *not* caused by acceleration of the >> travelling twin directly; it is caused by changes in the reference frame >> in >> which the elapsed time is measured, as any non-crank site on the twins >> paradox will explain. So you can assume that changes in velocity are >> instantaneous. > > The "twins paradox" is accounted for in some way by the acceleration/ > physical "impulse" sustained by the astronaut twin, because that is > the variable that is asymmetric between them. I suspect "a change of > reference frame" is merely a more obfuscated way of saying the same > thing - and if it isn't the same thing, then this "frame" explanation > is not an explanation at all. No .. it is explained by change in reference frame. Acceleration is simply one way to cause that. >> As I say, I'd also like to discuss the specific scenario that I >> raised. Because at least in my scenario, we can agree that they are >> both synchronised at the start, and at the end, and that we have >> accounted for propagation delays when testing for synchronisation. So >> the question is how to interpret what happens in the middle, but >> obviously I need you to describe what happens. >> >> ____________________________________________ >> As I understand your experiment, when the clocks are separating they each >> see the other clock as running more slowly, and when they are approach >> they >> see the other clock as ticking faster, and the percentage change is the >> same >> as that given by the formula for the Relativistic Doppler Shift. You can >> confirm that when you add the outbound and inbound changes together, they >> are both re-synchronised when they meet again, as a simple symmetry >> argument >> requires. > > Yes, but what of "simultaneity"? If we account for Doppler (and, > hence, propagation delays), then is there any discrepancy at all in > simultaneity? Yes. >> > After the pass A and B and have their clock readings adjusted, the an >> > A' >> > observer would measure B' as ticking slowly (as I described above), and >> > a >> > B' >> > observer would measure A' as ticking slowly. They will both also see >> > the >> > other as showing the 'wrong' time (in particular, from what I think >> > (not >> > done the calculations), each frame will measure the other clock as >> > being >> > ahead of their own). >> >> Each frame will measure the other clock as being *ahead*? By any >> chance, does the other clock always appear slow when they are sailing >> into the distance away from each other, and always appear fast when >> approaching each other? >> >> ______________________________ >> Yes. > > Well that is certainly interesting. So not only does simultaneity > change, but the 'direction in which simultaneity moves' depends on the > direction of motion? No .. you are talking now about optical illusions. You are VERY confused .. or (I suspect) deliberately confusing the issue. |