Is Length Contraction in SR physical??
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From: Peter Webb on 2 Feb 2010 23:08 > > You are the one presenting some radical new theory which if true will set > the Physics world on its ear and gain you the Nobel. If you can't do the > math then perhaps you shouldn't be pretending to be a physicist. I'm not pretending to be a physicist - __________________________ And yet you claim that all physicists are wrong about SR. and I find it comical that you think "reality" is a "radical new theory". I know Einstein basically made many of the arguments that I'm making. ______________________________ I would be amazed if you and Einstein agreed on anything to do with physics. However, this is easily tested. Produce a quote you have made in this thread, and a quote from Einstein, which show the same "basic argument".
From: YBM on 2 Feb 2010 23:19 Ste a �crit : > On 3 Feb, 02:51, artful <artful...(a)hotmail.com> wrote: >> On Feb 3, 12:02 pm, Ste <ste_ro...(a)hotmail.com> wrote: >> >> >> >> >> >>> On 2 Feb, 20:10, PD <thedraperfam...(a)gmail.com> wrote: >>>> On Feb 2, 9:24 am, Ste <ste_ro...(a)hotmail.com> wrote: >>>>> But the question remains, what is the *physical* cause of the >>>>> discrepancy when the object to be measured is moving differently from >>>>> the measuring equipment. It should be a question taken seriously in >>>>> physics. >>>> And it is. >>>> I will give you just a sketch, meant to inspire further investigation, >>>> not to teach. >>>> The physical cause is traced to the *meaning* of the physical property >>>> length, which is the difference in the locations of the endpoints of >>>> something, where those locations are measured *simultaneously*. The >>>> importance of the simultaneity becomes apparent if you try to measure >>>> the locations of the endpoints of, say, a moving car and attribute the >>>> difference to the length. Then in turn, it becomes clear that length >>>> is frame-dependent if simultaneity is frame-dependent -- the frame- >>>> dependence of simultaneity is the physical cause of the frame- >>>> dependence of length. >>> Ah, now I know this is the difference between us. I hold that >>> "simultaneity" is *not* frame dependent. >>>> So now the question becomes, what is the >>>> physical reason for the frame-dependence of simultaneity? This in turn >>>> is traced to the *meaning* of simultaneity, and how we would know that >>>> two spatially separated events are simultaneous; this in turn hinges >>>> on the synchronous arrival of equal-speed signals from the events at >>>> the midpoint between the events. From here it is relatively simple to >>>> show that the frame-independence of the speed of light *demands* that >>>> for a given pair of events, that definition of simultaneity will be >>>> satisfied in one reference frame and not in another reference frame. >>>> That is, the frame-independence of the speed of light is the physical >>>> cause of the frame-dependence of simultaneity, which in turn is the >>>> physical cause of the frame-dependence of length. So then the question >>>> is, what is the physical cause of the frame-independence of the speed >>>> of light? The answer to this question has to do with the hyperbolic >>>> structure of space-time and the fact that causal relationships are >>>> limited to a region of spacetime called the past- and future-light >>>> cones. This hyperbolic structure of space and time is thus the >>>> physical cause of the frame-independence of the speed of light, which >>>> is in turn the physical cause of the frame-dependence of simultaneity, >>>> which in turn is the physical cause of the frame-dependence of length. >>>> To expand this in a way that would be compellingly easy to follow >>>> would take more pages than I'm willing to invest. Fortunately, this is >>>> done in numerous books designed to explain these things in a >>>> compellingly easy-to-follow fashion. Would you like some >>>> recommendations? >>> You have in fact answered the whole of my question here Paul. The >>> difference lies in our concepts of "simultaneity". As I said, my >>> concept of "simultaneous" is "those events which occur at the same >>> instant, and would be observed to do so universally, *if* information >>> about the occurence of those events could be conveyed instantaneously". >> Simultaneity issues in SR are nothing to do with instantly conveying >> information. >> >> According to SR your concept of simultaneity being universal does not >> hold in reality (as nice and simple and idea as it is). > > I disagree. Then you could be interesteed by this (espacially bibiography) : http://plato.stanford.edu/entries/spacetime-convensimul/ > You seem to be saying that if a tree falls in the woods > and no one is around to hear it It's not what he is saying. Please pay attention.
From: J. Clarke on 2 Feb 2010 23:02 Ste wrote: > On 2 Feb, 23:52, "J. Clarke" <jclarke.use...(a)cox.net> wrote: >> >> Physicists deal with what is observed. If you want to "take a leap >> and start talking about reality" as if "reality" is something other >> than what is observable, then you're in the wrong shop. > > I'm sure I would want to go as far as saying that there are aspects of > reality that are not observable, but I would say there are aspects of > reality that are not easily measurable, or not measurable at all. Well that's nice. But it's not physics.
From: J. Clarke on 2 Feb 2010 23:08 Ste wrote: > On 2 Feb, 23:50, "J. Clarke" <jclarke.use...(a)cox.net> wrote: >> Ste wrote: >> >>> You shouldn't need *any* maths to describe in broad terms what this >>> "length contraction" is all about, and in any event anyone who >>> understands their subject should be able to sum it up in a few >>> sentences. It should not be this complex Paul, and the fact that it >>> is simply demonstrates that science has lapsed into obscuritanism. >> >> Lemme guess--you've got a degree in "education"? > > I don't, but even if I did I don't see what difference it would make. > Incidentally the sort of responses you're making should be interesting > for Paul, because it reinforces what I said about how it appears any > dissent is met with ridicule and hostility. Your "in any event anyone who understands their subject should be able to sum it up in a few sentences" is what one expects from schoolteachers, not from people who have climbed the whole immense edifice of quantum theory or general relativity. You see yourself as a "dissenter". You're not. You do not know enough to be able to "dissent" in any meaningful way. >>>> By all means, put such a scheme together. Be sure to show where the >>>> factor of 1/sqrt(1-v^2/c^2) comes from in such an explanation, >>>> because that part is quantitatively checked. >> >>> I'll let you do the maths Paul - that is, after all, the virtue of a >>> *co-operative endeavour*, where different people bring different >>> skills to the table. >> >> You are the one presenting some radical new theory which if true >> will set the Physics world on its ear and gain you the Nobel. If you >> can't do the math then perhaps you shouldn't be pretending to be a >> physicist. > > I'm not pretending to be a physicist. Well, actually you are. > - and I find it comical that you > think "reality" is a "radical new theory". When "reality" is calling for something that is incompatible with well established, tested, validated models, then it is radical. If you don't understand that then you should not be surprised when you meet with ridicule. > I know Einstein basically > made many of the arguments that I'm making. In that case, since the currently accepted model in physics is that of Einstein, you don't have anything new to bring to the party, do you?
From: Tom Roberts on 3 Feb 2010 00:18
Uncle Ben wrote: > On Feb 1, 11:36 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: >> [...] > > Tom Robrts takes the conservative position on what is "physical." Hmmm. I tried not to make any statement about what is or is not "physical", because that word is too ambiguous. To me it is irrelevant whether one considers this or that quantity to be "physical". What is important is whether or not a given quantity can be an appropriate model for some physical phenomenon. For that, it's QUITE CLEAR that no coordinate-dependent quantity can be a valid model of any physical phenomenon, as arbitrary human choices cannot possibly affect physical phenomena. Nor can the perspective from which one looks at an object affect the object itself. Coordinates are, of course, arbitrary human choices that define the perspective one uses to look at and describe objects and situations. > To > be consistent, he would have to deny physicality to kinetic energy and > to the magnetic field of a moving charge. Or even motion itself. I deny that any of those can be valid models for physical phenomena. I make no statement about their "physicality" -- arguments over word meanings are uninteresting (but inappropriate word meanings must be dealt with before the real discussion can even begin). In every case I know of, if you analyze the physical situation sufficiently well, you will find an appropriate quantity that is a valid model for the physical phenomena in question. For instance, when considering a collision between two particles, don't use kinetic energy, use the Mandelstamm s (total energy squared in their center-of-momentum frame); instead of magnetic field, use the Maxwell 2-form; instead of motion, use the particles' individual trajectories. Tensor and geometric analysis provide methods to analyze all situations of interest in a coordinate-free manner. This is one of the major lessons of GR (but it took about a half-century to sink in). > Or do > I not understand? The issue is more subtle than you seem to think. It is not merely about the meanings of words, or about what is or is not "physical", it is about what types of quantities can be used to model physical phenomena. Tom Roberts |