Is Length Contraction in SR physical??
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From: kenseto on 2 Feb 2010 11:39 On Feb 2, 10:23 am, rotchm <rot...(a)gmail.com> wrote: > > 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. No measurement of length contraction ever been made. Ken Seto > > 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: Ste on 2 Feb 2010 11:39 On 2 Feb, 15:52, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 2, 9:40 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > 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", > > Then I would ask the following questions of you. > Is velocity a physical property? It is *clearly* observer-dependent. Velocity is a physical property that does not vary with observer- perspective, yes. The measurement of velocity is observer-dependent, yes. The discrepancy between those statements is accounted for by the fact that I believe in *material reality*, where the measurement of variables does not necessarily reflect the value of the variable itself. > Having answered that, is kinetic energy a physical property, given > that (at least at low speeds) the kinetic energy is proportional to > the square of the velocity, and so is also clearly observer-dependent. > Having answered that, is the law of conservation of energy, which > includes kinetic energy as one of the contributions to the conserved > sum, a law about physical properties? If not, then what is it a law > about? I'm afraid you'll have to explain what you mean. > > 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". > > I think there may just be a clash regarding an unfounded expectation > that physical properties "should" be observer-independent. Why would > this be an expectation? Oh I know that is the source of the clash. The reason I expect observer-independence is because I believe in material reality, where variables exist independent of observation or measurement. > The reality is that physics is littered with physical properties, > about which there are many laws that seem to hold remarkably well. > Some of those properties are observer-dependent, and some are observer- > independent. There is no rationale required for "why" they are not all > one way or the other, any more than there has to be a reason cited for > "why" all animals are not mammals. There are no properties of the physical world that are "observer- dependent", although the measured value of those properties may depend on the circumstances of the observer.
From: Ste on 2 Feb 2010 11:41 On 2 Feb, 15:59, JT <jonas.thornv...(a)hotmail.com> wrote: > On 2 Feb, 16:25, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > 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-Hidequotedtext - > > > > > - Show quoted text -- Dölj citerad text - > > > - Visa citerad text - > > Yes he should be ashame i mean physical does not even have a > meaningfull definition in SR. > > Shame on you Seto this is common knowledge, both length and time have > no meaningfull definition within SR, it is simply variable units they > are not universal appliance. You seem to think that a unit should be > applicable as a sort of comparisson value that have a equality sign, > no such things exist. The only thing that is "shameful" is that "physicists" should be using a theory for which there is no definition of "physical", and moreover there is no attempt being made to discern it's "physical" basis.
From: Ste on 2 Feb 2010 11:46 On 2 Feb, 16:09, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > Ste wrote: > > 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". > > The "why" is because it is in the nature of spacetime to be that way. > Physics is decriptive. Not according to Paul Draper. Apparently it is necessary that a "scientific theory" be predictive (and therefore prescriptive), not just "explanatory" (i.e. descriptive). In any event, the question of "why" has perhaps been misinterpreted. I really meant "how". That is, what is happening in the physical system to cause a change in measurements which are "observer dependent".
From: rotchm on 2 Feb 2010 12:05
> > 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. > > No measurement of length contraction ever been made. > > Ken Seto Irrelevant to the discussion at hand. As I said, " SR predicts that *if* ... " Direct length measurements have not been perfomed. Direct time, energy, momentum measurements have been performed... but this is not the topic of this thread. The topic is about the words "real" and "physical". > > 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. Have you understood/took my advice on this quote above? |