Is Length Contraction in SR physical??
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From: rotchm on 2 Feb 2010 10:23 > Hey idiot there is disagreement. You give two meaning for physical > that contradict each other. Ken, their own personal definitions of "physical" might not be the same. But their personal definitions are not part of SR. These SRians are using different definitions for some concepts, but they are using the same math/theory in the same way with the same conclusions. The Lor. Contraction cannot be said to be real or physical if you do not define those terms first. SR does not define those terms. SR predicts that if you measure the length of a moving rod, the *value* obtained will be less than its rest length. That value is "real" in the sense that that value is a real number; is part of the set of the Reals. So, my advice to you is DO NOT WORRY ABOUT THE CONCEPTS OF "REAL" OR "PHYSICAL". These words are not part of the theory of SR, only part of some different dialects.
From: PD on 2 Feb 2010 10:24 On Feb 1, 8:19 pm, artful <artful...(a)hotmail.com> wrote: > 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. Here I'll bring up the same point I raised with Tom. To me, an "intrinisic" property is one that is frame-independent. A system can have an intrinsic mass. Two events can have an intrinsic interval. But to call a spatial length that has a certain value only in the object's rest frame is to me not an intrinsic anything, because as soon as you change the frame, that spatial length changes value. To me, length (and to be precise, 3-length) is no more an intrinsic property than 3-velocity. > 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: Ste on 2 Feb 2010 10:24 On 1 Feb, 19:14, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 1, 1:03 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > 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. I am aware of the point you make. What you're saying basically is that physicists are always careful to stretch the elastic object as much as the elastic ruler - and they only guarantee consistent results if this stretching is also done consistently, otherwise a conversion factor is required. But the question remains, what is the *physical* cause of the discrepancy when the object to be measured is moving differently from the measuring equipment. It should be a question taken seriously in physics.
From: PD on 2 Feb 2010 10:25 On Feb 2, 7:55 am, kenseto <kens...(a)erinet.com> wrote: > On Feb 1, 6:38 pm, artful <artful...(a)hotmail.com> wrote: > > > On Feb 2, 1:55 am, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > Is Length Contraction in SR physical?? > > > Define 'physical' > > Look up the dictionary. That's a bad idea. The definitions listed in a dictionary for words that are special in physics are usually NOT the meaning of those terms as used in physics. > > > > > > According the most informed SRian, Tom Roberts, the answer to this > > > question is NO. > > > I doubt that > > You are not qualified. > > > > > > 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. > > > No .. it can be MODELLED by geometry > > So Modelled by geometry is not physical. > > > > > > When a moving meter stick rejoins the stay at home > > > meter stick they will have the same physical length > > > Irrelevant > > So there was no physcial contraction. > > > > > > Furthermore if > > > length contraction is physically real how come SR does not predict > > > length expansion? > > > How come something can't be slower than at rest? > > No object in the universe is in a state of absolute rest. > > > > > > Is that becasue SR assumes that the observer is in a > > > state of absolute rest? > > > No. Just rest relative to himself .. everything else is either also > > at rest, or has a non-zero speed > > ROTFLOL....at rest relative to himself is a oxymoron statement. > > > > > > So what does it mean when SR says that a moving meter stick is > > > contracted? > > > That is it measured as shorter (eg if you measure poles by whether > > they fit inside a barn, then the pole is shorter) > > No measurement of physical length contraction due to relative motion > ever been made. > > > > > > The answer: > > > You wouldn't know > > > > 1. An SR observer assumes that the light path length of his meter > > > stick is the same as the physical length of his meter stick. > > > Nonsense > > You are nonsense. > > > > > > 2. Using this standard the light path length of a meter stick moving > > > wrt an SR observer is shorter than the light path length of the stay > > > at home meter stick. Why? Because light generated at the front end of > > > the stick will reach the rear end of the stick sooner for a moving > > > meter stick (c+v) according to the stay at home SR observer. > > > Totally irrelevant > > You are totally irrelevant. > > > > > > 3. So according to the SR observer the light path length of a moving > > > meter stick is as follows: > > > L' = L_o/gamma. > > > Nonsense > > You are nonsense. > > > > > > 4. The above interpretation avoids all the paradoxes that arise due > > > to > > > the bogus interpretation that a moving meter stick is physically > > > contracted. > > > There are no paradoxes > > There are paradoxes if length contraction is physical. You are an > idiot. > > Ken Seto > > > > > > However, the above interpretation is incomplete. Why? > > > Because it is nonsense and wrong > > > > Because the > > > light path length of a meter stick moving wrt the observer may be > > > longer than the observer's meter stick. In that case the light path > > > length of such meter stick is calculated as follows: > > > L' = L_o(gamma) > > > This interpretation is included in a new theory of relativity called > > > Improved Relativity Theory (IRT). IRT includes SRT as subset. > > > Which is nonsense > > > > However, > > > the equations of IRT are valid in all environments, including > > > gravity. > > > Nonsense is nonsense no matter where you use it > > > > A complete description of IRT is available in the following link:http://www.modelmechanics.org/2008irt.dtg.pdf-Hide quoted text - > > > - Show quoted text -
From: Ste on 2 Feb 2010 10:40
On 1 Feb, 20:52, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 1, 2:49 pm, kenseto <kens...(a)erinet.com> wrote: > > > 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. Because for anyone who believes in material reality, physical properties should not be "observer dependent", and if physical properties do indeed seem to change depending on how they are observed, then there should be some coherent explanation for it rather than just a statement that things are "observer dependent", which in most people's minds rather leaves the glaring question "why". |