Is Length Contraction in SR physical??
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From: Sam Wormley on 1 Feb 2010 13:14 On 2/1/10 8:55 AM, kenseto(a)erinet.com wrote: > Is Length Contraction in SR physical?? Length contraction, time dilation and relativistic mass are observer dependent!
From: Ste on 1 Feb 2010 14:03 On 1 Feb, 17:25, PD <thedraperfam...(a)gmail.com> wrote: > > 2. Secondly, he did NOT say that the length contraction is not > physical. What he did say is that the word "physical" has an ambiguous > meaning at best and does not mean what you think it means. What he did > say is that physics deals with what is MEASURED, and what is measured > is therefore physical in that sense. It was you and ONLY you that said > that if it is a geometric effect (which it is), then it CANNOT be > called a physical effect. Tom did not make that statement. You did. I think others will contend that "what is measured" does not necessarily relate to a physical reality. After all, if I have an elastic meter ruler, and apply various amounts of tension to it, then the measurement of an object can be changed without any "physical" change in that object. On the other hand, if the object to be measured is also elastic, and I apply the same amount of tension to the object as well as to the meter ruler, then there are "physical" changes even though there is no change in the measurement. It is this discrepancy that I believe Ken is enquiring about..
From: PD on 1 Feb 2010 14:14 On Feb 1, 1:03 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 1 Feb, 17:25, PD <thedraperfam...(a)gmail.com> wrote: > > > > > 2. Secondly, he did NOT say that the length contraction is not > > physical. What he did say is that the word "physical" has an ambiguous > > meaning at best and does not mean what you think it means. What he did > > say is that physics deals with what is MEASURED, and what is measured > > is therefore physical in that sense. It was you and ONLY you that said > > that if it is a geometric effect (which it is), then it CANNOT be > > called a physical effect. Tom did not make that statement. You did. > > I think others will contend that "what is measured" does not > necessarily relate to a physical reality. After all, if I have an > elastic meter ruler, and apply various amounts of tension to it, then > the measurement of an object can be changed without any "physical" > change in that object. On the other hand, if the object to be measured > is also elastic, and I apply the same amount of tension to the object > as well as to the meter ruler, then there are "physical" changes even > though there is no change in the measurement. This is why we have standards of measurement. A standard is defined so that a replicable process conducted *locally* yields the same measurement when measured again. Thus if you measure the half-life of an isotope locally with this clock, and you measure the half-life of a different sample of the same isotope over there with a clock that is local to that sample, you should get the same number. Now, the local criterion is important and it is built into the standards, because it can be shown (and this is what Einstein showed) that standards applied nonlocally with the expectation that they would yield common results is an expectation that violates the known laws of physics. This connection between the two statements is not obvious to the amateur but is extremely important. > It is this discrepancy that I believe Ken is enquiring about..
From: "Juan R." González-Álvarez on 1 Feb 2010 15:25 eric gisse wrote on Mon, 01 Feb 2010 08:08:39 -0800: > kenseto(a)erinet.com wrote: > >> Is Length Contraction in SR physical?? > > No, just as it has been explained to you repeatedly since the mid 90's. > > [...] From Tom Roberts page: "At this time there are no direct tests of length contraction, as measuring the length of a moving object to the precision required has not been feasible. There is, however, a demonstration that it occurs: A current-carrying wire is observed to be electrically neutral in its rest frame, and a nearby charged particle at rest in that frame is unaffected by the current. A nearby charged particle that is moving parallel to the wire, however, is subject to a magnetic force that is related to its speed relative to the wire. If one considers the situation in the rest frame of a charge moving with the drift velocity of the electrons in the wire, the force is purely electrostatic due to the different length contractions of the positive and negative charges in the wire (the former are fixed relative to the wire, while the latter are mobile with drift velocities of a few mm per second). This approach gives the correct quantitative value of the magnetic force in the wire frame." P.S: Do you want your new 'brilliant' post to be added to your profile as USENET crackpot? :-D P.P.S: Newsgroup sniped by Eric re-added to the reply. -- http://www.canonicalscience.org/ BLOG: http://www.canonicalscience.org/en/publicationzone/canonicalsciencetoday/canonicalsciencetoday.html
From: kenseto on 1 Feb 2010 15:49
On Feb 1, 1:14 pm, Sam Wormley <sworml...(a)gmail.com> wrote: > On 2/1/10 8:55 AM, kens...(a)erinet.com wrote: > > > Is Length Contraction in SR physical?? > > Length contraction, time dilation and relativistic mass are > observer dependent! So does that mean that length contraction is not physical? IOW an 80 meter pole can't fit into a 40 meter barn with the doors at the front and the rear close simultaneously.....Right? . I agree with what you said :-) Ken Seto |