Known physics defeated by simple puzzle?
in [Relativity]
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From: Inertial on 4 Apr 2010 07:38 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:1731685b-72c2-42d2-8f33-ca477d13affc(a)5g2000yqj.googlegroups.com... > On 2 Apr, 16:05, "Inertial" <relativ...(a)rest.com> wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> news:aa6d8cc5-8343-40fb-b960-2693aa6ff4d0(a)z4g2000yqa.googlegroups.com... >> >> >> >> >> >> > On 2 Apr, 02:02, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> >> > wrote: >> >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> >> >> > And just to move to an easier analogy, I don't care how much you >> >> >> > can >> >> >> > accurately quantify something like acoustic Doppler shifting with >> >> >> > an >> >> >> > equation, my question would be this: is the Doppler shift a >> >> >> > product >> >> >> > of >> >> >> > the change of interaction between source and receiver, or is the >> >> >> > source "really" changing frequency by some unknown mechanism? The >> >> >> > answer, of course, is that the Doppler effect is apparent - there >> >> >> > is >> >> >> > nothing inherent about the source that needs to change in order >> >> >> > to >> >> >> > explain the phenomenon. >> >> >> >> The Doppler shift is real. Frequencies really do change. >> >> >> > Yes, but it involves no change in the frequency generated by the >> >> > source. >> >> >> The frequency of the sound depends entirely on the reference frame in >> >> which >> >> it is measured. >> >> > No, the *received* frequency of sound depends on the reference frame. >> > As a human receiver, one can change the *apparent* frequency by >> > changing one's own circumstances (i.e. changing velocity relative to >> > the source), and this *apparent* change does not involve any change in >> > the generating mechanism of the source, and nor does it affect the >> > frequency received at any other receiver. >> >> > At the nub of this is the fact that the audio source, if it is >> > oscillating at say 500Hz a second, continues to do so *no matter what* >> > its relative velocity (at least if we disregard relativistic effects >> > at high velocities for now, for the simplicity of the argument which >> > applies nevertheless). >> >> >> Changing the relative speed of the train definitely changes the >> >> frequency >> >> of >> >> the sound. >> >> >> You can easily verify this yourself. >> >> > You clearly still don't understand the significance of my argument, >> > which is that the *apparent* frequency, as measured by a receiver, can >> > be affected by the receiver's *own* circumstances, as much as by an >> > actual change of frequency at the source. It is significant, to any >> > scientific investigation or understanding, to establish what the >> > *cause* is of the change of received frequency. >> >> >> >> > My question with SR remains the same: is it >> >> >> > "real", or is it an apparent effect. >> >> >> >> Like the Doppler shift, it is both real and apparent. >> >> >> >> As I said already. >> >> >> > It is not "real" in the sense that it involves a change in the >> >> > attributes of the source - it is "apparent" in the sense it involves >> >> > a >> >> > change in the relationship between the source and receiver. >> >> >> That is not what "apparent" vs "real" means, at least in common usage. >> >> > I concede in this particular analogy that the words are not entirely >> > apt, but it is really a sideshow to the real question about "length >> > contraction", where I think it's perfectly reasonable to ask "is the >> > contraction real, or merely apparent". But if you prefer, I can phrase >> > it as "is the contraction mechanical, or visual". >> >> >> The frequency of a sound generated by a moving train definitely does >> >> really >> >> change as its speed changes. Measure it for yourself if you don't >> >> believe >> >> it. >> >> > The frequency generated doesn't change - an observer onboard could >> > attest to that. It is the frequency *received* that changes, depending >> > on the circumstances of the observer. >> >> >> Of course, the frequency that you measure is a function of the >> >> reference >> >> frame in which you measure it. In this respect, the "frequency" of a >> >> sound >> >> is not a precisely defined concept. The normal use is that the >> >> frequency >> >> is >> >> tacitly assumed to be that which is measured at rest. Same as length >> >> in >> >> SR. >> >> When you want to compare frequencies in two different reference >> >> frames, >> >> this >> >> definition breaks down as there are two different possible base frames >> >> for >> >> measurement, and you have to be specific about which reference frame >> >> you >> >> are >> >> measuring frequency in. Same, again, as for length in SR. >> >> > You know, I could explain this same point to a child by saying "the >> > frequency measured depends upon your speed relative the source". >> >> It is not just 'apparent'. The frequency REALLY IS DIFFERENT for each >> observer. > > Then consider another example. OK > I give three people a photographic > filter each, all different colours, and they hold it front of their > eyes. I ask them to look at the sky, and they each comment that the > sky has changed colour. I now ask them "has the sky really changed > colour?". Now how would you interpret my question, and how would you > answer that question? The light reaching them has different colors, because certain frequencies are filtered out. Not a relevant example to SR length contraction.
From: Sue... on 4 Apr 2010 08:10 On Apr 4, 2:52 am, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > "Sue..." <suzysewns...(a)yahoo.com.au> wrote in message > > news:af2773f5-640d-4e4b-a490-cc091d6d2912(a)z7g2000yqb.googlegroups.com... > On Apr 4, 12:25 am, "Peter Webb" > > > >But this is true of > > > every other frame, even moving ones. If you take a measurement in any > > > frame, then that measurement is always invariant within that frame. > > ==================== > > > > > But its not invariant across frames. > > > In the reference frame of the train, the tone is *always* 100 Hz. > > > In other reference frames, the frequency depends upon the relative motion. > > That is clocks (plural) > > Write this on the back of your hand so you > can tell when you have broken your experiment: > > << Einstein's relativity principle states that: > > All inertial frames are totally equivalent > for the performance of all physical experiments. > > In other words, it is impossible to perform a physical > experiment which differentiates in any fundamental sense > between different inertial frames. > > My egg takes 3 min to boil flying north. > Your egg takes 3 min to boil flying south. > > 2 eggs. > 2 clocks. > > Sue... > > __________________________________ > You should see a doctor. You are babbling nonsense. Coming from your side of Alice's mirror, I'll take that as a compliment. :-) Sue...
From: Ste on 4 Apr 2010 08:36 On 4 Apr, 12:38, "Inertial" <relativ...(a)rest.com> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > > I give three people a photographic > > filter each, all different colours, and they hold it front of their > > eyes. I ask them to look at the sky, and they each comment that the > > sky has changed colour. I now ask them "has the sky really changed > > colour?". Now how would you interpret my question, and how would you > > answer that question? > > The light reaching them has different colors, because certain frequencies > are filtered out. So when I ask "has the *sky* changed colour?" you will say "no"?
From: Inertial on 4 Apr 2010 09:10 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:9b9f09c2-c45f-4169-9aa6-ba7a107de57f(a)k19g2000yqn.googlegroups.com... > On 4 Apr, 12:38, "Inertial" <relativ...(a)rest.com> wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> > I give three people a photographic >> > filter each, all different colours, and they hold it front of their >> > eyes. I ask them to look at the sky, and they each comment that the >> > sky has changed colour. I now ask them "has the sky really changed >> > colour?". Now how would you interpret my question, and how would you >> > answer that question? >> >> The light reaching them has different colors, because certain frequencies >> are filtered out. > > So when I ask "has the *sky* changed colour?" you will say "no"? Each sees a different color .. there is no change to the color of the sky itself, only in the frequencies of light allowed to reach the observers. The different color is an illusions that the filters create. The length contraction is not an illusions caused by any 'filters'
From: Peter Webb on 4 Apr 2010 09:15
"Ste" <ste_rose0(a)hotmail.com> wrote in message news:9b9f09c2-c45f-4169-9aa6-ba7a107de57f(a)k19g2000yqn.googlegroups.com... > On 4 Apr, 12:38, "Inertial" <relativ...(a)rest.com> wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> > I give three people a photographic >> > filter each, all different colours, and they hold it front of their >> > eyes. I ask them to look at the sky, and they each comment that the >> > sky has changed colour. I now ask them "has the sky really changed >> > colour?". Now how would you interpret my question, and how would you >> > answer that question? >> >> The light reaching them has different colors, because certain frequencies >> are filtered out. > > So when I ask "has the *sky* changed colour?" you will say "no"? Just sticking my 2 cents worth in here. I'm not sure I understand what you mean by the term "the colour of the sky" in this context. You seem to want it to mean two different things. If you define it to mean the colour seen by an observer looking through filters, then the colour does change. If you define it to mean the colour seen by an observer not looking through filters, then the colour doesn't change. So when you say "the colour of the sky", how are you defining this term in the context of this experiment? |