Is Length Contraction in SR physical??
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From: PD on 1 Feb 2010 15:52 On Feb 1, 2:49 pm, kenseto <kens...(a)erinet.com> wrote: > 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? No, it does not mean that. Why do you think that "observer dependent" means "not physical"? Lots of physical properties are observer dependent. > 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
From: kenseto on 1 Feb 2010 15:56 On Feb 1, 3:25 pm, "Juan R." González-Álvarez <nowh...(a)canonicalscience.com> wrote: > eric gisse wrote on Mon, 01 Feb 2010 08:08:39 -0800: > > > kens...(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." Hey idiot this does not illustrate length contraction. Ken Seto > > 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/canonicalscienceto...
From: kenseto on 1 Feb 2010 16:33 On Feb 1, 2:03 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. > > It is this discrepancy that I believe Ken is enquiring about.. What I am enquiring about are as follows: 1. Tom Roberts said that length contraction is a geometric projection effect....that means that length contraction is not physical contraction. This means that length contraction is only apparent and not physical. The problem with Tom's approach is that what is "geometric projection" mean physically??? 2. OTOH runts of the SRians such as PD asserts that length contraction is physical....a 80 meter long pole can fit into a 40 meter long barn with both doors close simultaneously for a very brief period. This assertion of length contraction is physical. 3. There seem to be contradictory claims amoung the SRians. I agree with Tom's premise with a twist. I said that the observer assumes that the light path length of his meter stick is assumed to be the physical length of his meter stick. The length contraction formula is used to determine the light path length of a meter stick moving wrt the observer. This explanation eliminates all the paradoxes encounter by the SR assertion that length contraction is physical. Ken Seto
From: crisgoogle on 1 Feb 2010 16:35 On Feb 1, 8:09 am, "Dirk Van de moortel" <dirkvandemoor...(a)nospAm.hotmail.com> wrote: > Igor <thoov...(a)excite.com> wrote in message > > 36f39b8d-b930-487a-9a3d-fbfae25c2...(a)g1g2000yqi.googlegroups.com > > > > > On Feb 1, 9:55 am, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > >> Is Length Contraction in SR physical?? > >> According the most informed SRian, Tom Roberts, the answer to this > >> question is NO. His answer is that length contraction is the geometric > >> projection effect of the length of a moving meter stick onto the SR > >> observer's frame. When a moving meter stick rejoins the stay at home > >> meter stick they will have the same physical length. Furthermore if > >> length contraction is physically real how come SR does not predict > >> length expansion? Is that becasue SR assumes that the observer is in a > >> state of absolute rest? > > > When people walk away from me, they appear to get smaller. Is that > > physical? And no matter which direction, they walk away from me, they > > always get smaller. How come nature doesn't allow them to appear to > > get bigger? > > When Chuck Norris walks away from you, he appears to get bigger. > > Dirk Vdm Naw, you just appear to get smaller =)
From: Peter Webb on 1 Feb 2010 18:22
"kenseto" <kenseto(a)erinet.com> wrote in message news:b53814cc-0c14-476f-bc2c-a88d5532884e(a)u26g2000yqm.googlegroups.com... On Feb 1, 2:03 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. > > It is this discrepancy that I believe Ken is enquiring about.. What I am enquiring about are as follows: 1. Tom Roberts said that length contraction is a geometric projection effect....that means that length contraction is not physical contraction. _______________________ No. You are confusing two different sets of co-ordinates. The length contraction in physical 3D space is real. It can be interpreted as the projection of a 4-vector (space and time) onto 3D space. The 4D vector doesn't change its magnitude, but the 3D projection (which is what we physically measure) certainly does. This means that length contraction is only apparent and not physical. The problem with Tom's approach is that what is "geometric projection" mean physically??? ______________________ Its physical. Any and every physical measurement will show the length has changed. 2. OTOH runts of the SRians such as PD asserts that length contraction is physical....a 80 meter long pole can fit into a 40 meter long barn with both doors close simultaneously for a very brief period. This assertion of length contraction is physical. ________________________ Length contraction is physical. What you have written is meaningless, because you do not describe the frame of reference in which the doors are open "simultaneously". 3. There seem to be contradictory claims amoung the SRians. _________________________ No. People are trying to describe what happens in different ways. These claims are not "contradictory", they are just different ways of explaining the same physical phenomenum. I agree with Tom's premise with a twist. I said that the observer assumes that the light path length of his meter stick is assumed to be the physical length of his meter stick. The length contraction formula is used to determine the light path length of a meter stick moving wrt the observer. This explanation eliminates all the paradoxes encounter by the SR assertion that length contraction is physical. ____________________________ I'm not sure that what you say is "Tom's premise" actually is his premise. Irrespective of that, what you write is wrong; the contraction is actual and not just an artefact of the measuring technology. Ken Seto |