Is Length Contraction in SR physical??
in [Relativity]
|
Prev: Simultaneous events and Einstein's absolute time
Next: New Theory --- The Theory of Quantum Wave Sources
From: J. Clarke on 2 Feb 2010 15:24 Ste wrote: > 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). It still describes, it does not address causes. > 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". Get your PhD and work the problem for a while and maybe _you_ will be the one to crack quantum gravity and collect the Nobel and come up with answers to questions such as these.
From: JT on 2 Feb 2010 15:35 On 2 Feb, 20:14, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 2, 11:54 am, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > > > > On Feb 2, 10:19 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > 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. > > > Sure it is contradictory. > > 1. Physical length is invariant as per the dictionary. > > Really? You'll have to cite a dictionary definition for "physical > length" that includes the word "invariant". > As usual, you are *assuming* connections that ought not to be made. > I'll remind you that "physical" does NOT mean "material". Yes you are correct how could anyone be stupid enough to expect physical to have any connection to a material unit. No here we must embrace the aether, and to really come to the core of subject we have to go into the paranormal and quantum mechanic. There is no spoon........ No, a physical unit could there could be no such thing, such existance would be a ludicrous assertion. Embrace the spoon Ken, it can be heavier then you think..... JT > > > 2. Physical length is observer dependent as per SR . > > Yes, indeed. > > > These are two contradictory definition for Physical Length. > > SR is right. Statement (2) is right. Statement (1) is not right, and > there is no reference you can point to that makes statement (1). It > came out of your head. > > > > > > > Ken Seto > > > > > > 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- Hide quoted text - > > > > - Show quoted text -- Hide quoted text - > > > > - Show quoted text -- Hide quoted text - > > > > - Show quoted text -- Hide quoted text - > > > > - Show quoted text -
From: J. Clarke on 2 Feb 2010 15:32 Ste wrote: > 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. I see. So you're the only object in an empty universe. What is your velocity? How do you know that it has that value? > 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. And how may your hypothesis of "material reality" be falsified? If it can't then you're in the wrong shop. >> 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. What part of his statement are you having trouble with? >>> 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. So measurement is meaningless? The how do you know that those "variables" exist at all? >> 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. So you're advocating an absolute frame of reference. That's fine--if you can sell that you have disproven General Relativity and you will surely win the Nobel. Good luck with that.
From: J. Clarke on 2 Feb 2010 15:34 kenseto(a)erinet.com wrote: > On Feb 2, 10:19 am, PD <thedraperfam...(a)gmail.com> wrote: >> 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. > > > Sure it is contradictory. > 1. Physical length is invariant as per the dictionary. > 2. Physical length is observer dependent as per SR . > These are two contradictory definition for Physical Length. Geez, if you're trying to do physics from a dictionary you really ought to take up a more productive hobby like herding cats or something.
From: Tom Roberts on 2 Feb 2010 16:52
Ste wrote: > 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. The answer is that this is not "physical", this is GEOMETRICAL. Look at a building from directly in front, and it has a given width. Look at it from a front corner and it has a smaller width. There is no "physical cause" of this change, it is purely GEOMETRICAL. In SR, "time dilation" and "length contraction" are likewise purely geometrical -- they are geometrical projections just like the width of that building. Continuing the analogy: there are physical consequences of that change (e.g. the building's width will or won't fit on the film of a given camera). But nothing about the building itself has changed, only the geometrical relationship between building and observer has changed. Similar remarks apply to "time dilation" and "length contraction" -- they can be "physical" for some meanings of the word, and aren't "physical" for other meanings. Extending the analogy: if you want to "model" the building, it's clear that the relevant width is the one marked on the building's plans -- measured parallel to the building's front. It's clear that the possibility of measuring many different "widths" from other points of perspectives is completely irrelevant. Ditto in SR, where proper length and proper time are relevant to modeling phenomena related to a given object, and it is irrelevant that that one can measure other values for "length" and "time" in other frames. > It should be a question taken seriously in > physics. The appropriately related question is taken seriously. And answered easily. But by including a false premise as part of YOUR question (that there is a "physical cause"), you make YOUR question impossible to take seriously. A famous example: When did you stop beating your wife? Tom Roberts |