Known physics defeated by simple puzzle?
in [Relativity]
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From: Sue... on 3 Apr 2010 21:10 On Apr 3, 10:17 am, Ste <ste_ro...(a)hotmail.com> wrote: [...] ============= > > (Also, for the sake of completeness, in GR there *is* a real time > dilation effect, > Indeed a bullet fired at altitude will reach its target in less *time* than a bullet fired at sea level because of a flatter trajectory. http://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment http://en.wikipedia.org/wiki/Noether%27s_theorem#Applications > but that is a discussion for another day, and after > we have nailed down SR.) What? Cart before horse? <<...one of Einstein's two main reasons for abandoning special relativity as a suitable framework for physics was the fact that, no less than Newtonian mechanics, special relativity is based on the unjustified and epistemologically problematical assumption of a preferred class of reference frames, precisely the issue raised by the twins paradox. Today the "special theory" exists only, aside from its historical importance, as a convenient set of widely applicable formulas for important limiting cases of the general theory, but the epistemological foundation of those formulas must be sought in the context of the general theory>> http://www.mathpages.com/rr/s4-07/4-07.htm If you have enough maths to calculate the apparent-power of a motor then you have enough GR to see where SR can be used. http://www.bartleby.com/173/17.html << 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 http://en.wikipedia.org/wiki/Complex_number Sue...
From: Peter Webb on 3 Apr 2010 21:54 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:8b7d62e7-1613-4fea-89bf-34e43b627cbc(a)v20g2000yqv.googlegroups.com... > On 3 Apr, 04:11, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> >> >> > 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. >> >> >> How can you measure a frequency without receiving it? What is this >> >> supposed >> >> to mean? >> >> > You could measure the emitted sound frequency, in this case, by using >> > an electromagnetic (i.e. something like LADAR) measurement of the >> > vibration of the source (and it is that vibration that we know to be >> > the generator of the sound). In this way, we measure the frequency of >> > the sound source, without receiving any sound. >> >> Well, you aren't measuring the frequency of the sound, you are measuring >> the >> frequency with which an object vibrates. > > Yes, which is the frequency of the sound to any sane person! > That statement is correct, along as you define "sane" as "being in the same reference frame as the emitter of the sound". > I think I can finally be sure that you're someone who subscribes to > the philosophy that "a tree does not make a sound if there is no one > around to hear it", but that's not materialism, it's clearly an > idealistic approach. > No, I don't subscribe to that philosophy. > > >> That will allow you to work out the frequency of the sound in the rest >> freame of the emitter, but so what? You could just as easily do this with >> a >> microphone and an oscilloscope next to the speaker, and measure the >> frequency directly. > > Indeed, but the important thing here is that the LADAR measurement is > *invariant* under changes of velocity, and so we can clearly say that > if the receiver changes relative velocity, it is *not* the source that > has changed frequency. The frequency clearly does change depending on the frame in which you measure it. This is observational fact. The frequency at rest is an invariant; the frequency observed in this frame therefore does not change. The rate at which clocks tick clearly does change depending on the frame in which you measure it. This is observational fact. The clock rate at rest is an invariant; the clock rate observed in this frame therefore does not change. > Indeed, one can exceed the speed of sound > completely, and therefore by your logic the source is no longer making > a sound at all, No. I didn't state or imply that at all. > and yet a LADAR measurement verifies that the sound > source is in fact working normally, > and emitting sound in the same > consistent way (in other words, "time" has not stopped or slowed down > at all for the source, any more than "time stops" if you put your > fingers in your ears). > As indeed we can verify that in their rest frame, atomic clocks tick at their correct rate. > > >> The same principle applies in SR, by the way. You can look at an atomic >> clock in some other reference frame and work out the rate at which it is >> ticking in its rest frame. > > Let's stick to sound for now, because I need you to understand the > meaning of my questions first, because there is clearly a disconnect > of understanding. > Well, if you are trying to compare the doppler shift for sound with the relativistic doppler shift, I will continue to make the comparison, you can ignore it if you like. > > >> If you are trying to develop an argument that there is some special >> reference frame for measuring frequency in which it is invariant, then >> you >> are completely correct. Exactly the same applies in SR; there is a >> reference >> frame for measuring length in which it is invariant, and that is the rest >> frame of the object. > > No, I'm trying to develop an argument that when a person asks "has > time really slowed down", they're not asking you to issue a crude > report of what you detect with your senses (in other words, report > simply what *appears* to be the case), but on the contrary they are > asking you to employ your powers of thought, your knowledge of theory, > your years of learning and experience, to make a meaningful > *interpretation* of what is already apparent to everyone. > Well, if you visit a particle accelerator, its pretty obvious that relativistic effects do occur. If you want an "interpretation" of why this is so, I would recommend you study Minkowski space time. > Ironically, I was expecting you to react harshly to my "spaceship on > the monitor" question, but in the event you accepted that what appears > on the monitor is not necessarily a representation of "real objects" > with "real attributes", but is a cunning visual trick which merely > makes it *appear* that a spaceship is in the sky. > Glad I could answer your question to your complete satisfaction. > The same is true of my questions about special relativity. When I ask > "does time really slow down", I'm asking you to interpret the crude > observations, and hypothesise about what is *really* happening, > independent of our ability to measure what is happening. > Time really does slow down. The travelling twin is younger. The more youthful appearance of the travelling twin is not an optical illusion, they really are younger. > In developing this argument, the analogy with sound is a brilliant > analogy from my perspective, because sound manifests the same Dopper > shifting and time dilatory effects. But the ace is that we still have > LADAR to fall back on in order to make measurements of the source, and > even though the sound source time dilates when measured with the ear > (or a microphone), we can verify with LADAR that it is indeed still > vibrating at the same frequency, so we *know* that "time itself" has > *not* slowed down at all (and the effect is merely due to propagation > delays in the sound medium). > A sound of frequency 120 Hz is heard in some reference frame. By measuring the difference in speed between the emitter and the source, we can calculate using the equations for Doppler Shift (or even directly observe) that the frequency in the emitters frame would be 100 Hz. A clock is observed ticking at 120 Hz in some reference frame. By measuring the difference in speed between the emitter and the source, we can calculate using the equations of SR (or even directly observe) that the clock rate in the emitters frame would be 100 Hz. > (Also, for the sake of completeness, in GR there *is* a real time > dilation effect, but that is a discussion for another day, and after > we have nailed down SR.) > You know nothing about SR, and given that GR is far, far more complex and uses mathematics far more advanced than Minkowski, you know nothing about GR. > > >> >> > 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). >> >> >> Yes. >> >> >> Similarly, an atomic clock travelling at 0.9c continues to tick at >> >> exactly >> >> the same rate in its own inertial frame of reference. >> >> > Lol. No no no. The sound source continues to oscillate at 500Hz >> > according to *all* observers, no matter what speed they are travelling >> > at. (For the sake of this argument, we are confining possible speeds >> > to within the speed of sound). >> >> "Sound source" ? >> >> Do you by that mean the frequency of the sound measured by an observer >> stationary with respect to the train? If so, the same applies in SR. >> >> If "sound source" does not mean that, what does it mean? > > The "frequency of the sound source" means "the frequency of > oscillation at the source". The beauty with a sound source is that we > can measure the oscillations (and hence, the "sound source frequency") > with light instead of sound. > > (And to hedge my bets for the umpteenth time, at relativistic speeds, > even the LADAR method would fall down, because electromagnetic > propagation delays would also start to become dominant. But the point > of the argument is merely to illustrate that what is "apparent" is not > the same as what is "real".) > Huh? Are you saying that the frequency of a sound does not depend on the relative motion of the emiter and receiver? Try standing next to a train line and measure the frequency of the sound. You will rapidly see that it *does* depend on relative motion; this is an observed fact. > > >> >> >> 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. >> >> >> That is correct, except that the effect is not just "apparent", it is >> >> real, >> >> as can be easily verified by measuring it. >> >> >> A tone which is emitted in a moving trains reference frame at 100 Hz >> >> might >> >> be measured in a stationary frame as being 120 Hz. This is as real as >> >> a >> >> tone >> >> of 120 Hz directly emitted from a stationary train. There is not test >> >> which >> >> can tell them about; none. >> >> > You mean except a test that measures the oscillation of the sound >> > source with light instead of sound? You lack imagination Peter. >> >> No. I mean a test of the frequency of the sound that is received. > > But we're not interested in what is received, because what is received > is a product of more than one variable. What we are interested in is > ascertaining the sound source frequency, and isolating it as an > invariant. If we know that the sound source is invariant, then we know > that the cause of the Doppler shifting is the propagation delay. > No, you know the reason that the frequency is different is because the frequency is a function of the relative speed. There *is* an invariant, which is the frequency measured in the rest frame of the emitter. In SR, we know that the rate at which you measure a clock tick differs because the length is a function of the relative speed. There *is* an invariant, which is the rate at which the clock ticks measured in the reference frame of the emitter. > But if we *didn't* know that the sound source was invariant, then the > apparent Doppler shifting Doppler shift is not "apparent". It is "real". The frequency really does change depending on your speed relative to the emitter. > it could just as easily be (the usual kind > of) Doppler shifting, or it could easily be a change in the source > frequency caused by some unknown mechanical interaction between the > source and receiver that causes the source to change frequency when > the receiver moves. > You should Google "doppler shift" if you really don't know the cause of the frequency change. > Or to put it another way, imagine I am stood at the side of the road > singing. You are approaching me in a car at a constant speed. You > notice that on your approach, my voice has a certain tone. But as you > pass, the tone drops. Now, did the tone of my voice "really" drop, The frequency depends on the frame in which you measure it. In the frame of the receiver, the tone changed. In the frame of the emitter, the tone is unchanged. (Just like in SR). > or > is it Doppler shifting? Or in other words, did I intentionally drop > the tone of my voice as you passed, or did I keep the tone of my voice > constant and the "drop" you heard was the Doppler effect? > > > >> >> > It is significant, to any >> >> > scientific investigation or understanding, to establish what the >> >> > *cause* is of the change of received frequency. >> >> >> Relative motion. We all know that already. >> >> > Yes, but with sound it's easy to understand (in common sense >> > mechanical terms) *why* relative motion causes Doppler shifting, and >> > it's also clear (at least to me) that the effect is apparent, and does >> > not involve a change in the frequency of the source. >> >> Its not just "apparent", its also real. As I keep saying - and is easily >> verified - the frequency of the sound really does change. You can measure >> the frequency using an oscilloscope and easily verify this for yourself. > > It is as "real" as the spaceship on the monitor - in other words, you > can see it, and everyone else watching the monitor can see it, but it > is not "real" at all. > Cosmic. > > > >> > The problem with >> > SR is I keep getting told that there *is* an actual change at the >> > source. >> >> I don't know what other people have told you, and I would be saddened if >> anybosy used these exact words, as they are so vague as to be >> meaningless. >> >> What you *should* have been told is that: >> >> 1. Length is a relative concept, as it depends upon the frame of >> reference >> in which it is measured. >> >> 2. Frequency is a relative concept, as it depends on the frame of >> reference >> in which it is measured. > > But when I ask "does the length *really* contract?", I keep getting > told either "yes", or I keep getting asked "what do you mean 'real'?". > I don't know exactly what other people have told you. > And when I speculate that, in SR, the time dilation and length > contraction effects are a product of propagation delays (like they are > with sound), I keep getting told "no, no, no, it is nothing to do with > electromagnetic propagation delays". Its not. >And indeed, some posters have > even gone as far as saying that an 80 foot ladder would fit in a 40 > foot barn with both doors closed (and again, they insist that it is > not an optical illusion, it *really* would fit inside). > It does. > So, I'm sure you can understand my confusion. > Yes, you don't understand SR. > > >> >> >> >> > 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". >> >> >> Mechanical. It does not depend on visually observing objects. The twin >> >> who >> >> stays at home ages faster; its not some optical illusion they have >> >> wrinkles >> >> when the travelling twin does not. Every day SR is tested in particle >> >> accelerators; AFAIK none of these depend upon "seeing" a particle >> >> being >> >> emitted and "seeing" it smash into a target and then measuring the >> >> difference in time of visual observations. They use mechanical >> >> processes - >> >> eg interactions with physical matter - to measure times. >> >> > Yes, but I'm still not sure this is true, not least because you either >> > don't understand what I mean by the difference between "real" and >> > "apparent", or at any rate you don't see the significance of the >> > question. >> >> Correct. I don't understand what you mean by "real" and "apparent". My >> "apparent" height - as measured at rest with a tape measure - is 178 cms. >> What is my "real" height? How is it different? > > No, your *real* height is 178cms, and it is mechanically invariant. > However your apparent height, measured visually (i.e. > electromagnetically), can be manipulated in all sorts of ways. If I > step back from you, you appear to shrink. If one of us lies down on > the floor, you appear to shrink. If your image goes through a > refracting lens, your apparent height can change in all sorts of ways. > > Indeed, I recall hearing the other week that a handful of blind people > who have been given rudimentary brain implants that give them sight > for the first time, struggle at first because they are not accustomed > to correcting for the "apparent" effects of perspective, as objects of > fixed size appear to visually grow and shrink. > Perhaps if you were to give a definition of "real" vs "apparent"? > > >> >> >> 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. >> >> >> The frequency in an inertial frame is constant. Same as lengths and >> >> times >> >> in >> >> SR. >> >> >> > It is the frequency *received* that changes, depending >> >> > on the circumstances of the observer. >> >> >> Yes. Frequency depends on the frame of reference in which it is >> >> measured. >> >> > No, the *received* frequency depends on the relative velocity. The >> > *source* frequency doesn't. >> >> The length of an object in SR in its rest frame doesn't vary either. The >> length in other frames does. How is this different to the frequency of a >> sound? > > It isn't different from sound, as far as I can tell. The point is that > it's real length does not change at all, and hence the 80 foot ladder > *never* fits in the barn with both doors *really* closed, although it > can be made to *appear* to do so. Gee, again, your argument seems to hinge on what is "real" vs what is "apparent"; you better define those terms or there is enormous scope for misunderstanding.
From: Sue... on 3 Apr 2010 22:08 On Apr 3, 9:54 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: ================== > > Well, if you visit a particle accelerator, its pretty obvious that > relativistic effects do occur. I believe a new record was set on 30 March 2010. Would you happen to have the relativistic calculations that show the energy? Sue...
From: Peter Webb on 3 Apr 2010 22:12 "Sue..." <suzysewnshow(a)yahoo.com.au> wrote in message news:0e0454c7-85ca-4783-b10d-2e5372612f9c(a)n34g2000yqb.googlegroups.com... On Apr 3, 9:54 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: ================== > > Well, if you visit a particle accelerator, its pretty obvious that > relativistic effects do occur. I believe a new record was set on 30 March 2010. Would you happen to have the relativistic calculations that show the energy? _________________________________ No. But if you know the mass of the particle and its speed, I can work out its energy in the frame of reference in which you measure the speed by plugging it into a very simple formula. Note that you should be careful when talking about the kinetic energy of a particle; it is frame dependent, and *not* invariant under changes of frame, so a statement about energy must be qualified with the frame in which it is measured.
From: Sue... on 3 Apr 2010 22:27
On Apr 3, 10:12 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > "Sue..." <suzysewns...(a)yahoo.com.au> wrote in message > > news:0e0454c7-85ca-4783-b10d-2e5372612f9c(a)n34g2000yqb.googlegroups.com... > On Apr 3, 9:54 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > wrote: > > ================== > > > > > Well, if you visit a particle accelerator, its pretty obvious that > > relativistic effects do occur. > > I believe a new record was set on 30 March 2010. > Would you happen to have the relativistic calculations > that show the energy? > > _________________________________ > No. But if you know the mass of the particle and its speed, I can work out > its energy in the frame of reference in which you measure the speed by > plugging it into a very simple formula. Is this what you need? proton mass = 1.67262158 × 10-27 kilograms relative speed 1.999999982 times the speed of light. Note that you should be careful when > talking about the kinetic energy of a particle; it is frame dependent, and > *not* invariant under changes of frame, so a statement about energy must be > qualified with the frame in which it is measured. I would assume a calorimeter in the laboratory frame but I have not researched it. Sue... |