Is Length Contraction in SR physical??
in [Relativity]
|
Prev: Simultaneous events and Einstein's absolute time
Next: New Theory --- The Theory of Quantum Wave Sources
From: kenseto on 8 Feb 2010 10:08 On Feb 7, 10:41 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > Certainly, if *you're* familiar with all this experimental evidence, > then surely you can either point out where the evidence (not theory) > contradicts my hypothesis, or on the other hand concede that the > evidence would not discern between existing interpretations and mine. > > ____________________________________ > I have now posted exactly what you are asking for three times. Here it is a > fourth time: > > http://www2.slac.stanford.edu/vvc/theory/relativity.html > > It clearly states what would be observed in SLAC if length contraction of > the track did not occur, states the impact of relativistic shortening of the > track, and then states that the experimental results are exactly as are > predicted using SR's length contraction, and are not as predicted if length > contraction did not occur. There is an alternate explanation for the SLAC experiment.....the particle gains in life time when accelerated and this is interpreted as length contraction. Ken Seto > > Why do you keep complaining that there is no experimental support for length > contraction, when I have given you an extremely reputable site which > provides exactly that? > > BTW, the same is true of any particle accelerator built in the last 50 > years. > > People who doubt SR seem to forget that we routinely accelerate particles > close to the speed of light in countless particle accelerators world-wide > every day, and precisely measure resulting speeds, energies and momenta. > These accelerators simply would not work if SR was wrong.
From: PD on 8 Feb 2010 11:20 On Feb 6, 11:33 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 7 Feb, 03:54, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 6, 8:52 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > The only thing that is required is to note at the detector X or the > > > > detector Y whether the signals from the events arrive at the same time > > > > or at different times. This is a point decision. It is a yes or no > > > > question. "Signal from A just arrived at X. Did signal from B arrive > > > > at X at the same time? Yes or no." > > > > If detection is instantaneous (i.e. if a photon is absorbed > > > instantaneously), then it is possible for A and B to be simultaneous > > > according to both X and Y. However, if detection is not instantaneous, > > > then it is *not* possible. > > > I didn't say "according to both X and Y". What I said in fact was the > > opposite. Please reread. > > What I did say is that X is *right* in concluding that A and B are > > simultaneous, based on the procedure we established as reliable. > > But the procedure isn't reliable! I've said that repeatedly. It isn't reliable for what? For driving a consensus between X and Y? Is that a necessary requirement? Why? Let's revisit the procedure. If you were going to try to determine whether two events are simultaneous, according to a *particular* observer, then our suggested procedure is as follows: 1. Position a detector midway between the two events, where "midway" can be established at any time by directly measuring the length between the marks left by the events and the mark at the location of the detector. Let's amend this to say that this can be repeated on two occasions to determine that the "midway" condition has not changed. 2. Have the events send a signal known to travel with equal speeds toward the detector. The equality of the speeds can be established at any time by reproducing the signal and directly measuring the distance covered by the signal per unit time. (Note that (1) and (2) unambiguously determine that the propagation delay is the same from both events.) 3. Determine whether the signals from the events arrive at the detector at the same time or at different times. If the signals arrive at the same time, then from that information the correct conclusion is that the original events were simultaneous. If the signals arrive at different times, then from that information the correct conclusion is that the original events were not simultaneous. You agreed earlier that this procedure should be sufficient for determining the simultaneity of spatially separated events, according to a particular observer. Now you seem not so sure. What's the source of your sudden reservation? What procedure would you otherwise propose for determining the simultaneity of two spatially separated events? > > > Also, Y is *right* in concluding that A and B are not simultaneous, > > based on the same reliable procedure. > > The procedure is not reliable! > > > But yes, photons are absorbed instantaneously, or at least MUCH faster > > than the propagation delay for the signals to arrive. > > Indeed. > > > > > If the answer is yes, and if we ALSO know that the distance from X to > > > > A is the same as the distance from X to B (which we can check later if > > > > we wish), and if we ALSO know that the signal speeds from A and B are > > > > the same (which we can check later if we wish), then we KNOW the > > > > events A and B were simultaneous, even though they happened some time > > > > ago. Likewise, if the answer is no, then we KNOW the events A and B > > > > were not simultaneous, even though they happened some time ago. > > > > As I say, there is a third way here: the answer is "no", and we know > > > that the events were indeed simultaneous. > > > How would you derive from the procedure we agreed upon, where the > > answer to the relevant condition is "no", that the events were > > nevertheless simultaneous? > > We didn't agree on the procedure. I said from the very beginning that > it was not reliable because it fails to take into account the fact > that detection is not an instantaneous process > > > On what basis would you come to that conclusion. > > Because as I've said, the absorbtion/detection of the photon requires > a time interval, and although X and Y can be equidistant from both > events *at a single instant*, they cannot both maintain equidistance > *over an interval of time*. > > > > > Do you agree that those are the right conclusions, based on the yes or > > > > no question above, and given that the other conditions can be > > > > established? > > > > No. I think your mistake is in assuming that both the photon and > > > detector have an absolutely zero diameter (and therefore detection > > > occurs as soon as the surface of the zero-diameter objects touch). In > > > reality, nothing in space will have a diameter of zero. > > > I don't know why you think diameter has anything to do with it. Note > > the size of the distance between A and X and between B and X. If a > > detector is 1.5 mm across, do you think this is going to be a dominant > > effect? > > No, I'm talking about the diameter of the photon and the atom. As I > say, the visualisation I have is somewhat like two bubbles in water, > and clearly if they are forced together so that they become one > bubble, that is not an instantaneous process. Certainly, the bubbles > do not merge merely at the first instant their (idealised spherical) > surfaces touch - they must be actually forced together until their > surface tension breaks. > > Having thought about it for a moment however, I realise that my > previous argument might not be wholly relevant or may be speculative > (although it embodies some likely factors that may be relevant in the > real world). You can theoretically (in particular, in the absence of > gravity) bring about absorbtion of photons from both events > simultaneously for both A and B, assuming that the photons and the > atoms maintain a constant speed as they impact and are absorbed by the > atom. Let me ask you this. If your physical process can be established to take no more than, say, 2 picoseconds, and the arrival of the signals at the detectors is seen to be different by at least 2 microseconds, would it be established that the original signals were not simultaneous? > > However, I've formulated a slightly different argument based on the > same principle of detection requiring a time interval. Once detection > has taken place, a signal must then be sent that tells the detection- > system to check whether the events are an equal amount of distance > away. By time *this* signal is being acted upon, the events are no > longer equidistant from the observer. > > As I say though, the ultimate argument with this scenario Paul is that > equidistance is not maintained over the measurement interval, and so > each detector is subject to non-symmetric factors that influence the > measurement. But it is, because I can make the measurement of equidistance at ANY TIME after the events. > > > The signal starts at the location of the > > event, where it leaves a mark, and the signal stops at the location of > > the detector, where there is also a mark. Then we can certainly > > measure the distance between the marks at our leisure, no? > > Indeed. But real world measurements do not happen this way. On the contrary. We shall arrange this so this is so.
From: PD on 8 Feb 2010 11:24 On Feb 6, 11:38 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 7 Feb, 03:57, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 6, 9:02 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > Secondly, we can determine whether any part of the pole was outside > > > > > > the barn when those doors were closed by looking for the marks the > > > > > > ends of the pole would have made on the door. In the absence of those > > > > > > marks, we can safely conclude that the entire pole was inside the barn > > > > > > at the time the doors were closed. > > > > > > Agreed. I would expect this test is definitive, were it possible to > > > > > carry out. > > > > > And this has been tested in equivalent experiment. Documented. > > > > Has it really? Which experiment was that, because my sources say that > > > length contraction has *never* been experimentally observed. > > > I already told you the answer to that. Please look again. > > No it hasn't Paul. The experiment you describe, or anything like it, > has not been carried out, and the literature makes this clear that > physical length contraction has not been observed experimentally. What literature are you referring to? The experiments I described at FNAL and ISR, have certainly been carried out. > > > > > Seto does not read experimental papers, because he finds them > > > > confusing. So instead he believes what makes sense to him, rather than > > > > letting experimental results tell him something different. > > > > You have to concede at least the possibility Paul that the reason Ken > > > finds them confusing, and so do I, is because *we* can see that they > > > rest on certain assumptions. That is, assumptions that you've > > > internalised, and assumptions which me and Ken reject. > > > In Seto's case, it has more to do with thinking that SR says something > > it does not. I haven't yet figured out whether you are in the same > > boat. > > The only assumptions I make are those that have testable consequences. > > Which ones of those do you think I have that you reject? > > At least one of the assumptions to which I refer is that observation > reflects reality. Science is about relationships between measurable phenomena, that is, the observed ones. If you believe science is about "real" properties which are unmeasurable but are nevertheless there, then I would ask how you would deduce anything quantitative about them, or in fact how you would test that your deductions are in fact accurate? If you then claim that it is not necessary to test them, and is only sufficient to be reasonably certain that one's intuitions about them are correct, then I can pretty flatly say that what you are talking about no longer has any resemblance to science. > So if length contraction is observed, it must be > "real", but in my view this is as childish as saying you're 12 feet > tall simply because you're looking into a curved mirror. > > As I say, I am quite firmly of the view that SR describes the > behaviour of EMR - in other words, it describes what you see with your > eyes - and says nothing about physical reality.
From: PD on 8 Feb 2010 11:30 On Feb 7, 3:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 7 Feb, 05:55, mpalenik <markpale...(a)gmail.com> wrote: > > > > > On Feb 7, 12:38 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > As I say, I am quite firmly of the view that SR describes the > > > behaviour of EMR - in other words, it describes what you see with your > > > eyes - and says nothing about physical reality.- Hide quoted text - > > > Respond to my post that has the link to my second picture before you > > respond to this, but here's something for you to consider. > > > Special relativity predicts that an object will undergo length > > contraction in its direction of motion. Any observer "at rest" at any > > location should observe this length contraction. > > > Say that a car drives past you close to the speed of light. You take > > a picture exactly at the instant when the center of the car is > > directly in front of you. Since the two ends of the car are > > equidistant from you, if propagation delay were the only thing going > > on, you should not see any sort of length contraction in the > > photograph. But SR still predicts that the car should be contracted > > in its direction of motion, independant of the location of the > > observer. > > Indeed. I don't totally rule out physical length contraction, but I > would require a physical, classical, explanation first. I don't know why you think that physical models MUST meet your criteria of "physical" (how YOU understand that term rather than how physicists understand that term) and "classical" in order to be acceptable to you. Note that the REQUIREMENT you impose that the explanation be classical is simply an assertion that anything that does not meet the classical mold is not to be entertained as viable. This is a personal choice on your part that you will ONLY believe that which meets the classical physics mold and simply NOT BELIEVE anything else. Therefore your secondary demand that physicists owe it to the public to explain their understanding of the natural world in a simple and compelling way becomes completely compromised by your insistence that this explanation follow YOUR imposed criterion of fitting the classical mold before you'd believe it. Basically, this is the juxtaposition of "I don't believe it and you can't make me" with "But you owe it to me to try and make me." Sorry, but you'll find just about anyone will tire of that chain-yanking exercise pretty quickly. > I simply don't > accept the argument of "rotation into time".
From: PD on 8 Feb 2010 11:35
On Feb 8, 4:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 8 Feb, 04:29, mpalenik <markpale...(a)gmail.com> wrote: > > > On Feb 7, 11:16 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > But let me ask you, how is the decay event detected?- Hide quoted text - > > > Is it really that hard to click the link?http://www2.slac.stanford.edu/vvc/detectors.html > > > Just so you know, it's not done by sending a beam of light at the > > particle or anything like that, which would be nearly impossible to do > > anyway. > > I had a quick glance at some of the pages and links on that site, and > it seems to be aimed at 8-year-old children, or the sort of summary > you'd expect to find in a newspaper - as though anyone in this > discussion here ought to care that "the complete detector weights > 4,000 tons and stands six stories tall". I'll remind you that this is PRECISELY the sort of explanation you think physicists owe the "ordinary man". When an example of that is given to you, you sniff at it. When references aimed at a more specialized audience were given to you, you sniffed at that as well, saying that they were not comprehensible to the "ordinary man". It seems you are content to sniff at anything that is offered to you, and that you are content to just see whether folks will leap if you hold a hoop up. It also seems that experimental evidence is not compelling to you in any event, since you maintain that what is observed does not correspond to what is reality, and that what reality is should be the concern of physicists even if it is not measurable. > > To reiterate, if you want to have a serious discussion, then provide > *real evidence*, and expect me to ask some questions. |