Is Length Contraction in SR physical??
in [Relativity]
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From: Ste on 3 Feb 2010 18:39 On 3 Feb, 20:51, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 2, 7:02 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > Ah, now I know this is the difference between us. I hold that > > "simultaneity" is *not* frame dependent. > > But it is, according to the *definition* of simultaneity, and > experimental evidence. But this is where the difference is between 'real (or absolute) simultaneity' (i.e. what most people, other than physicists, understand by the word), and 'observed simultaneity' (which is *not* what most people mean by the word). What I find quite surprising is that I'm perfectly able to make sense of 'the relativity of observed simultaneity' within an absolute framework, and yet for others here the idea of absolute simultaneity is basically absurd. > Insisting that it is *not* frame dependent is to either declare that > there is something wrong with the tested laws of physics or that there > is something wrong with the experimental evidence. No, it's to declare that there is something wrong with the philosophy of physics. > In which case, one would be naturally tempted to ask how it is you > KNOW that simultaneity is not frame-dependent, other than it being an > article of faith? It is, as you say, an article of faith - I might, after all, just be a brain in a vat, or you might be a figment of my imagination... As I keep making clear, I have axioms, and materialism is one of them. > If you would like, we can discuss both the unambiguous definition of > simultaneity and the experimental evidence that shows that your belief > is not matched by observation. This evidence fully accounts for > propagation time. It's apparent to me that you've never been educated > on this. I'd be interested to discuss experimental evidence. Incidentally, the evidence might account for propagation time, but does it account for propagation distance? > > 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". > > Two comments: > - Propagation time can be accounted for, and it IS in the analysis > alluded to above, and it is STILL true that after this accounting, two > events that are simultaneous in one frame CANNOT be simultaneous in > another frame, according to the laws of physics. When you talk of "reference frames", you're identifying a problem that I recognise as a problem of *measurement*, not a statement about the 'real world'. However I am interested to hear how a finite speed of light means events that are observed as simultaneous in one reference frame cannot be observed as simultaneous in another - because after a few minutes of thinking, I can definitely conceive of a situation where events do remain simultaneous in more than one reference frame. > - Aside from this, it is the laws of nature that say that information > cannot be passed instantaneously. Thus, it is a smallish bit of > foolishness to attempt to describe how nature works if only the laws > of nature were not in effect. Not really. If you define the "event" as "the source of the information", then by definition the event occurs before information of it is received. You appear to be saying events do not happen until they are observed (presumably by a "conscious" observer) - which cannot be the view of a materialist.
From: YBM on 3 Feb 2010 18:56 Ste a �crit : > However I am interested to hear how a finite speed of light means > events that are observed as simultaneous in one reference frame cannot > be observed as simultaneous in another This is NOT the case. This is not especially because of *finite* speed of light that simultaneity is relative. Like most cranks of this group you seem to think that SR is just about visual effects when it is quite the opposite. Precisely in the classical derivation of SR this is the *invariance* of light speed NOT its *finiteness* which implies relativity of simultaneity. Moreover it is now very well known that SR does not even need this to be derived. It has been said to you, you could have checked this, you didn't, you just refused to believe it. Fine, it's your faith. > - because after a few minutes > of thinking, I can definitely conceive of a situation where events do > remain simultaneous in more than one reference frame. It won't work, trying to figure out why *by yourself* would be a very good way to study SR.
From: Ste on 3 Feb 2010 19:05 On 3 Feb, 21:21, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 2, 5:09 pm, Ste <ste_ro...(a)hotmail.com> 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. > > I'm sorry, but I find this whole expectation that "everything should > be so simple that it can be explained to anyone in a few sentences" to > be just crapola. It isn't true in chemistry, it isn't true in > molecular biology, it isn't true in architecture, it isn't true in > auto mechanics, it isn't true in musical composition. I agree it isn't true that the entire subject should be be able to be summed up in a few sentences. What I'm saying is that it's most rundimentary concepts should be sum-uppable in a few sentences. If I were describing the essentials of an internal combustion engine, for example, I might draw a simple diagram of a bore and a piston, and point to where the explosion happens. If further questions are asked, I can pad this out with further detail, without any overhaul of the fundamental concept that I started with. And the same is true of chemistry - assuming someone understands magnetism, then I can explain ionic bonding in terms of two "magnetic" atoms. And then I can move onto biology, and explain the heart in terms of a simple expansion and contraction of a cavity - and then briefly explain how a heart valve works so that the expansion and contraction actually pumps blood in one direction. > Furthermore, the attitude that "Well, if you CAN'T explain it in a > satisfactory way to anyone who asks in just a few sentences, then you > are guilty of obscuritanism," is similarly crapola. No that's not what I'm saying. What I'm saying is that you shouldn't need a degree in maths and another in physics to broadly answer "does a ladder moving at speed fit inside a garage". > Not every body of knowledge should be expected to be grasped by anyone > in just a few sentences. There is a reason why people spend years to > become reasonably expert in an area, and not just a month. I agree. As I say, I'm not saying there is no need for expertise, but the value of expertise is in accuracy, nuance, etc. > > > No, sir. You are not following. There is no mechanical shrinking of > > > the clock that is going on. > > > If there is no "mechanical shrinking", then I interpret this to mean > > the contraction of lengths is *apparent*, not "real". > > Then again you are using your own private understandings of the term > "apparent" and "real" and not those shared by physicists. I don't know > why you would expect physicists to explain things using YOUR > understandings of these terms. I'm not expecting physicists to explain things using my terms. I'm expecting them to work with me while I translate their terms into my own. > > 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. > > I'm sorry but that's crapola too. I refer you to an anecdote, archived > from this newsgroup by a kindly soul:http://users.telenet.be/vdmoortel/dirk/Physics/Gems/WhatItTakes.html Indeed, but unlike that chap I haven't yet waltzed into a physics department claiming to have all the answers. What is more, I know my strengths and I see no reason not to play to them - one does not expect a musician to be able to craft an instrument, a dancer to construct a stage, or a cartoonist to understand the paper-making process.
From: Ste on 3 Feb 2010 19:15 On 3 Feb, 21:30, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 3, 1:55 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > Also "it is the theory that decides what you > > can observe" - I've been trying to hammer that one home with Paul for > > the past few weeks. > > And that is also an unwise comment that is not thought highly of by > physicists. And yes, I know who said it. Not everything he said is > right. I'm not saying everything he said is right, but what I'm emphasising is that I'm not saying anything that even respected physicists haven't said before, and just because certain philosophical approaches are out of fashion in physics at the moment is irrelevant to me. > > And to describe both me and Einstein: "I have no particular talent - I > > am merely inquisitive" or "It's not that I'm so smart, it's just that > > I stay with problems longer". > > Please do not underestimate the work that Einstein put in or the > skills that he mastered along the way. Please do not overestimate > yourself, especially in light of how little work and how few skills > you are willing to apply. I don't underestimate the work Einstein put in - on the contrary, I'm *emphasising* the work he put in over any supposed "brilliance". And I don't overestimate myself. > > The fact is, I'm able to conduct a reasonable debate with experts > > because, for the past month, I've gone to bed thinking about physics, > > and I've woken up thinking about physics, and I've spent most spare > > hours thinking or reading about physics. > > No, I'm sorry. The world is RIFE with people who believe that doing > physics involves just having a rough intuitive grasp of things, a > reasonably sharp wit, and the willingness to ponder for a while. They > are deluded. That's not what I said at all. > You have been able to engage in reasonable debate here because, and > solely because, there are people here who are willing to try to inform > you of some things you are sorely misinformed about. Indeed, which is exactly what I came here for.
From: Ste on 3 Feb 2010 19:38
On 3 Feb, 21:44, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 2, 7:13 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > Then let's start with the basics. > > > Let's suppose there is, as you claim, an observer-independent value of > > > the speed of your coffee cup right now. > > > For a different observer, that coffee cup will be measured to have a > > > value of velocity that is different than the observer-independent > > > value. > > > What is happening in the physical system of the coffee cup and that > > > observer to yield a different measured value of velocity? > > > Nothing (i.e. nothing of relevance here) is physically happening to > > the coffee cup. The difference is in the circumstances of the > > observer. > > The measured velocity OF THE coffee cup is observer-dependent. So what > is physically happening in the system containing the coffee cup and > the observer to alter the real value of the velocity to the measured > velocity? Answer precisely, please. I'm not quite sure what you mean. Clearly, the measured velocity can change if *either* the cup or the observer changes velocity. You can infer which (i.e. one or both) has changed velocity by the effects of inertia (the coffee with slop over the edge, for example, if it is the cup that physically changes velocity). > I'm choosing as simple a case as possible, so that you can explain > what is going on physically simply and in a few sentences. To use your > own challenge, if you cannot do this, then perhaps your understanding > of this very simple situation is not as good as you think. Indeed. > However, I'm willing to even relax the "in a few sentences" criterion > that you have insisted on. Explain what is going on physically, > elaborately and using as much detail as necessary. You know, clarification questions don't count. ;) |