Is Length Contraction in SR physical??
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From: artful on 1 Feb 2010 21:17 On Feb 2, 1:03 pm, kenseto <kens...(a)erinet.com> wrote: > On Feb 1, 6:22 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > wrote: > > > > > > > "kenseto" <kens...(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. > > I suggest that you go argue with your SR brother Tom Roberts. He said: > "Generally, they would consider a "physical length contraction" to > mean that the object ITSELF gets > physically shorter. This is manifestly not so in SR". > > Ken Seto There is no disagreement here .. we non-crackpots are saying the same things here. You simply don't understand enough of the physics to see that we are agreeing with each other and disagreeing with you.
From: artful on 1 Feb 2010 21:19 On Feb 2, 1:11 pm, kenseto <kens...(a)erinet.com> wrote: > On Feb 1, 8:04 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 1, 3:33 pm, kenseto <kens...(a)erinet.com> wrote: > > > > 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. > > > No, it does NOT mean that. Have you asked Tom whether that's what he > > means? > > > > The problem with Tom's approach is that what is > > > "geometric projection" mean physically??? > > > Now it's apparent you don't know WHAT he means. > > > > 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. > > > That depends on what you mean by "physical". Does it mean that some > > interaction compressed the rod to make it shorter? No, it does not > > mean that. The pole STILL fits in the barn without requiring that. > > I suggest that you go argue with your SR brother Tom Roberts. He said: > "Generally, they would consider a "physical length contraction" to > mean that the object ITSELF gets > physically shorter. This is manifestly not so in SR." We all agree with that. > See that? He said that in SR the object ITSELF does not get physically > shorter Its own intrinsic length doesn't change .. no. No compression takes place in its own frame. however, it occupies less space in a relatively moving frame. That is something physically measureable in that other frame > and you contradicted him by insisting that the object does get > physically shorter.....btw no compression is inferred in this > discussion. We are all in agreement (other than you).
From: Peter Webb on 1 Feb 2010 22:45 "kenseto" <kenseto(a)erinet.com> wrote in message news:e6a1fa4d-a136-4ded-bbf5-fcab36d86cfb(a)g29g2000yqe.googlegroups.com... On Feb 1, 6:22 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > "kenseto" <kens...(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. I suggest that you go argue with your SR brother Tom Roberts. He said: "Generally, they would consider a "physical length contraction" to mean that the object ITSELF gets physically shorter. This is manifestly not so in SR". ___________________________ I'm not answering questions from Tom Roberts, I am answering your questions. And nor am I responsible for what Mr Roberts's posts. Do you have any more questions, or have I answered them to your satisfaction?
From: Tom Roberts on 1 Feb 2010 23:36 kenseto wrote: > On Feb 1, 6:42 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: >> This is a LINGUISTIC issue. When someone asks "Is length contraction in SR >> physical?", they invariably don't have a definite meaning of "physical" in mind >> (if they did, they could answer the question themselves). Generally, they would >> consider a "physical length contraction" to mean that the object ITSELF gets >> physically shorter. This is manifestly not so in SR. But it is indeed what >> kenseto has repeatedly failed to understand. > > The general public know what physical length means.....the length of a > ruler is physical. You clearly haven't a clue. In SR, length is most definitely not "physical" in the usual sense. In the USUAL sense, physical attributes of an object do not change with the way someone looks at it. But the length of an object DOES change with the way one looks at the object (i.e. which inertial frame one uses to measure its length). The related PHYSICAL attribute is proper length -- that is an attribute of an object that is intrinsic to the object (and does not change with how one looks at it -- it is an invariant). > If you don't like the word physical how about > "material" length contraction? In any case you stated above that > material length contraction does not occur in SR and I agree with that > fully. So I don't know why you accused me of repeatly failed to > understand!!!!!! Indeed, you clearly do not understand why I say you fail to understand this, because you STILL don't understand it. Your statement three sentences earlier ("the length of a ruler is physical") CONTRADICTS your claim here. The word "physical" has at least two different meanings that could be applied here: A) the object itself contracts B) the object itself does not change, but the measurements have physical consequences (such as a long pole fitting in a short barn when moving rapidly enough wrt the barn). (A) is not correct in SR; (B) is correct in SR. Both COULD be called "physical" so one MUST specify what they mean when they use that word in this context. When you use the word "physical" without saying what you mean by it, people get confused. ESPECIALLY YOURSELF. Ditto for "material"-- changing the word does not change the problem. > BTW your SR brothers PD and other disagree with you. They insisted > that a moving meter stick itself gets physically (materially) > shorter. Again you demonstrate your inability to read or understand. PD most definitely did NOT say that. I'm not sure what "others" you mean. In any case, you _REALLY_ _REALLY_ _REALLY_ need to learn how to read. You have no hope whatsoever of understanding subtle concepts like SR until you learn how to read. [I give up. It's hopeless until you LEARN how to read.] Tom Roberts
From: Sam Wormley on 2 Feb 2010 00:12
On 2/1/10 2:49 PM, kenseto 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? 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 Real is what is measured Seto. GPS works. Particle accelerators work. Special and general relativity predictions have never been contradicted by observations. Relativistic effects are observer dependent! |