Is Length Contraction in SR physical??
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From: Ste on 3 Feb 2010 03:08 On 3 Feb, 04:02, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > 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. I think you mean it conflicts with the prevailing philosophy in science.
From: Ste on 3 Feb 2010 03:25 On 3 Feb, 04:08, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > 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. No, it's what I expect from supposed "experts". > You see yourself as a "dissenter". You're not. You do not know enough to > be able to "dissent" in any meaningful way. I am "dissenting", whether or not you accept the dissent as legitimate. And to relate that back, as I say dissent often seems to be met with ridicule and personal hostility, as opposed to simply rebutting contentious claims. > >>>> 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. Well I've already had a long debate with Paul about how to define "science" and "physics", and unless you're suggesting that by expressing a interest and a broad opinion on physics, I'm somehow "pretending to be a physicist", then as I say I'm once again confirmed in my view about the arrogance, loss of touch, and obscuritanism, that physics is currently suffering from. > > - 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'm not calling for anything that is incompatible with observation. > > 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? I was actually talking largely about the arguments that Einstein made about the philosophy of science, since the discussion is about the nature of material reality.
From: Ste on 3 Feb 2010 03:31 On 3 Feb, 05:44, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > Ste wrote: > > "physicists" should be using > > a theory for which there is no definition of "physical", and moreover > > there is no attempt being made to discern it's "physical" basis. > > Define "physical" however you wish, and use it that way. NOTHING about any > theory of physics will change. Nor will the validity of any of their > predictions. All that will change is that you PERSONALLY will feel better. > > But that is not science. It is actually an understanding of the physical nature of things that guides discovery and provides inspiration. If you understand a mathematical procedure without understanding the physical reality, then you're just following by rote that which your betters actually had some insight into.
From: Ste on 3 Feb 2010 03:51 On 3 Feb, 03:16, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > Ste wrote: > > >> I see. So you're the only object in an empty universe. What is your > >> velocity? How do you know that it has that value? > > > That depends on whether the variable can be measured in an observer- > > independent fashion. > > So tell us how one might measure it in an observer-independent fashion. That rests on the question of whether it *can* be measured in an observer-independent fashion, and that in turn rests on understanding the physical nature of the problem. > Tell us how your model may be falsified. If you can't then it's not > science, it's rhetoric. Ah, back to dictating what is and isn't science - so often I'm getting told what is and isn't science, and yet according to Paul science is simply "what scientists do". If all you're doing is making a statement that "I'm not one of you", then that's little better than rhetoric. > >>> The discrepancy between those statements is accounted for by the > >>> fact that I believe in *material reality*, where the measurement of > >>> variables does not necessarily reflect the value of the variable > >>> itself. > > >> And how may your hypothesis of "material reality" be falsified? If > >> it can't then you're in the wrong shop. > > > It can't be falsified. > > Then it's not science and you're wasting everybody's time blathering about > it in science newsgroups. You'll find that every kind of science has aspects that are unfalsifiable. > > That's why I've been spending the last few > > weeks talking to Paul about how any productive endeavour involves > > axioms that are basically irrefutable. > > So you're saying that all of modern engineering is not a productive > endeavor? No, I'm saying it involves certain axioms. > > And before you leap in above your pay grade and accuse me of any sort > > of subjectivity, let's talk about falsification. Why do you hold that > > falsification is necessary? > > Read some Popper. It's basic to the nature of science that if your model > does not contain a means by which it may be falsified then it has no > scientific utility. I have read Popper, and Kuhn, and Lakatos, and others. The question is why science requires falsification - it would be a bit rich, would it not, for you to harp on about falsification without even being able to explain why it is necessary for science. > >>>> I think there may just be a clash regarding an unfounded > >>>> expectation that physical properties "should" be > >>>> observer-independent. Why would this be an expectation? > > >>> Oh I know that is the source of the clash. The reason I expect > >>> observer-independence is because I believe in material reality, > >>> where variables exist independent of observation or measurement. > > >> So measurement is meaningless? The how do you know that those > >> "variables" exist at all? > > > Variables are inferred to exist from variance in observations. > > How do you know that the variance in observations exists if you eschew > measurement? I don't "eschew measurement". What I said is that variables exist independent of measurement.
From: artful on 3 Feb 2010 04:41
On Feb 3, 4:18 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > 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 At first reading you seem to be equating 'physical' with 'frame invariant'. ie. Only things that are not dependent on the observer are physical. But am I right in my assessment that you are really saying that it is only nature / reality itself that is physical. The measurements and calculations we make are parts of our models of reality .. and so are never really 'physical' themselves. The best models (and measurements) for reality are those that are not observer dependent, because physical reality is not observer dependent (ignoring some interpretations of QM :)). In the case of length contraction, what we define as length (roughly speaking: the spatial distance between two simultaneous events in a given time) is contracted .. even though the proper interval is invariant. In both cases they are valid (but different) measurements of the same pair of events. Ken's claim that contraction not being 'physical' means a pole doesn't physically fit between the barn doors at the same time in the barn frame of reference (in the well-known 'paradox'). I guess the issue there is really whether 'between the barn doors at the same time in the barn frame of reference' itself is physical .. as it is observer / frame dependent. Obviously there is *some* 'physical' relationship between the barn doors and pole that means an observer in that frame would measure the pole as being within the barn. How would you best describe that relationship? Is talking about 'between the barn doors at the same time in the barn frame of reference' something valid and meaningful to say? |