Is Length Contraction in SR physical??
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From: kenseto on 2 Feb 2010 09:45 On Feb 1, 11:36 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > 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. Right the physical length (or material length) of a ruler does not change no matter who is look 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). This length change is not physical (or material) length change....it is a projection effect or a rotational effect. Much like I see you to be shorter from a distance. BTW no measurement of length contraction ever been made so you do you keep on using the word measure? >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). Right....the proper length of a ruler is the physical or material length of the ruler. It is invarient. > > > 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. I didn't fail to understand anything. You said that in SR length contraction is not physical and I agreed. > > The word "physical" has at least two different meanings that could be applied here: So why bother to invent a new meaning for the word physical that contradicts the dictionary meaning for the word physical??? Why not just stick to the correct meeaning of length contraction in SR: that length contraction is a geometric projection effect??? > 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; I agree. > (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. No both cannot be called physical or material....remember physical length or material length is invariant as you said in A. You invented a new meaning for the word physical that is contradictory to the dictionary meaning for for the word physical or material. B is correct if you said that the geometric projection of a moving rod is contracted. > > When you use the word "physical" without saying what you mean by it, people get > confused. ESPECIALLY YOURSELF. There is no confusion on my part. There is only one correct meaning for the word "physical" and I agree with you that physical length or material length is invariant. Ken Seto > > 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: PD on 2 Feb 2010 10:10 On Feb 1, 10:36 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > 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). Just a small quibble here. "Proper length" is a synonym for "spacetime interval" for space-like-separated events, and the interval is indeed invariant. But the interval is a not strictly a *spatial* quantity, as it involves both space and time coordinates, which is why (in my opinion) interval is a better term than length, proper or otherwise. The purely spatial concept of "length" does not have an invariant form. The interval coincides with a spatial length in one frame only, the rest frame of the object. But there is no invariant *length* (spatial) that is measurable in all frames. There is only a frame- dependent length. This terminological fudwickery is what confuses amateurs like Seto who are looking for a *spatial* quantity (that is, a length in the traditional meaning of that word) that is also "physical" (in the sense of being invariant among inertial frames). There is no such beast. The fact that there is no such beast is what Seto and some others find to be a simply unacceptable aspect of nature. > > > 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. Exactly. Seto thinks they MUST mean the same thing. They don't. > > 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: PD on 2 Feb 2010 10:13 On Feb 2, 7:07 am, Uncle Ben <b...(a)greenba.com> wrote: > On Feb 1, 11:36 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > > > > 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 > > Tom Robrts takes the conservative position on what is "physical." To > be consistent, he would have to deny physicality to kinetic energy and > to the magnetic field of a moving charge. Or even motion itself. Or do > I not understand? > > Uncle Ben Yes, that's what Tom has maintained in discussions with me. In his view, nature cannot depend on coordinate systems, and so what is inherent or physical are those properties that are invariant, and in his view the only fundamental view of physical laws is the one in which they are expressed in terms of invariants and universal constants. This point of view I respect, but I do tend to disagree. I find frame-dependent quantities like kinetic energy and magnetic field to be arguably physical, even if frame-dependent and coordinate- dependent.
From: PD on 2 Feb 2010 10:19 On Feb 2, 8:45 am, kenseto <kens...(a)erinet.com> wrote: > On Feb 1, 11:36 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > > 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. > > Right the physical length (or material length) of a ruler does not > change no matter who is look at it. You are not listening. Tom *just* got through telling you that "physical length" and "material length" are not necessarily synonymous, and yet you just repeated your assumption that they are. > > >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). > > This length change is not physical (or material) length change....it > is a projection effect or a rotational effect. It is not a material effect, but it IS a physical effect. Material and physical do not mean the same thing. > Much like I see you to > be shorter from a distance. BTW no measurement of length contraction > ever been made so you do you keep on using the word measure? > > >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). > > Right....the proper length of a ruler is the physical or material > length of the ruler. It is invarient. > > > > > > 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. > > I didn't fail to understand anything. You said that in SR length > contraction is not physical and I agreed. > > > > > The word "physical" has at least two different meanings that could be applied here: > > So why bother to invent a new meaning for the word physical that > contradicts the dictionary meaning for the word physical??? Words used in physics have more precise meanings than the ones found in the dictionary. If you want to communicate with physicists about physics, then it is extremely important to DROP the meanings of words as listed in the dictionary and LEARN the meanings of those same words as they are used by physicists. > Why not > just stick to the correct meeaning of length contraction in SR: that > length contraction is a geometric projection effect??? > > > 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; > > I agree. > > > (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. > > No both cannot be called physical or material.... They are both physical. Only (A) is material, but (B) is also physical. "Physical" does not mean "material". The electric field of a charged object is not material but it is very physical. > remember physical > length or material length is invariant as you said in A. You invented > a new meaning for the word physical that is contradictory to the > dictionary meaning for for the word physical or material. B is correct > if you said that the geometric projection of a moving rod is > contracted. It is not contradictory. It's just DIFFERENT. Physics uses certain words to have very precise and special meanings that are DIFFERENT than the definitions you will find in the dictionary. > > > > > When you use the word "physical" without saying what you mean by it, people get > > confused. ESPECIALLY YOURSELF. > > There is no confusion on my part. There is only one correct meaning > for the word "physical" and I agree with you that physical length or > material length is invariant. > > Ken Seto > > > > > 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: PD on 2 Feb 2010 10:21
On Feb 2, 7:11 am, JT <jonas.thornv...(a)hotmail.com> wrote: > On 2 Feb, 07:46, Sebastian Garth <sebastianga...(a)gmail.com> wrote: > > > On Feb 1, 8:03 pm, kenseto <kens...(a)erinet.com> wrote: > > > > 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". > > > Not true. Length contraction is a truly physical phenomena which is > > absolutely measurable. Fire two laser beams perpendicularly across the > > front and rear of the moving object; the change in length is not an > > illusion - within the observer's frame of reference, the object indeed > > occupies less space. > > That certainly would mean that distance is observer dependent, Yes, indeed. Why would you believe that it cannot be observer dependent? > two > objects at same distance but with relative measured distance, no it do > not make sense. > > But who cares SR is a silly theory to start with. > > JT |