Questions on world-line
in [Relativity]
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From: surrealistic-dream on 26 Aug 2006 00:23 Mike wrote: > surrealistic-dream(a)hotmail.com wrote: > > Mike wrote: > > > Paul B. Andersen wrote: > > > > Igor wrote: > > > > > surrealistic-dream(a)hotmail.com wrote: > > > > >> Not true. SR treats accelerations as absolute, but velocites and > > > > >> positions as relative. > > > > > > > > > > Wrong. There is a Lorentz transformation for acceleration also. > > > > > > > > No, it's correct. > > > > But the acceleration that is absolute is the proper acceleration, > > > > that is the acceleration measured in the instant inertial > > > > rest frame of the object. It is the acceleration that is > > > > measured by an accelerometer. This acceleration is absolute, > > > > that is independent of frames of reference. > > > > The co-ordinate acceleration is however frame dependent. > > > > > > The term "absolute" implies a much broader range of possibilities than > > > simply "independent of FoR". It is better to call proper acceleration > > > an invariant. > > > > Einstein claimed that he left acceleration as "absolute" in SR (that > > is, in his generaltization of Newton's mechanics to include > > electrodynamics). Why? well, this is partly semantic and partly > > historical and they go together. Historically "absolute motion" of any > > kind referred to motion with respect to some physically existing space. > > I agree. > > > > To Newton, acceleration only made sense in his theory if one could > > rely on that kind of motion to be with respect to some space in which > > absolute accelerations live. So, of course, Newton took the existence > > of inertial frames as absolute. And later, Einstein found the inertial > > concept wanting, and he introdcued the so-called Principle of > > Equivelence in GR. > > This has nothing to do with absolute motion, i.e. both concepts are > also present in Newtonian mechanics and post-Newtonian formulations. > > > > > Anyway, since you mentioned Mach below, I will address his contribution > > to relativity here. It was Mach, contrary to what you claimed below, > > who got Einstein to doubt the necessity of founding physics on the > > concept of absolute acceleration, meaning accelerations with respect to > > some invisible, unidentifiably space. Instead, he suggested that the > > inertial properties of matter are totally dependent on the distibution > > of matter in the universe. And, since the distribution of matter in the > > universe is happenstance, it is not depedent on the existence of some > > absolute space. > > > > This is a very narrow interpretation. Mach's idea cannot rule out > absolute space. You can still have absolute space and inertia dependent > on mass distribution in the universe. > > > > > Okay, so what is relative about relativity? This: if the equations of > > physics are conceptually founded in some theory on motion with respect > > to some absolute space, such as the space in which absolute > > accelerations live or the space in which absolute velocities live (rest > > space of the ether), then the motion is deemed to be "absolute." But if > > the equations of physics are founded on the notion of objects relative > > to visible (ponderable) matter, the theory is said to be > > "relativistic." Nowadays, physics includes the notion of invisible > > matter/energy but such things are still object like (in the same way > > that ponderable matter is), not space like in the way the the rest > > frame of the ether is. > > You are confusing Relational theories of spacetime and motion with > Relativistic theories. This is a very common mistake. Relativistic > theories do not preclude absolute space. Actually, it is now understood > that the spacetime of SR and GR is absolute. Relational theories > preclude absolute space time but there is no theory at hand which is > founded on purely relational spatiotemporal quantities. It is > impossible to do it since it is impossible to know the mass > distribution function of the universe. Esxpecially when more than 70% > (or 90% nobody knows) is ssome dark matter. > > > > > Einstein's main boasting point for SR, was not E = mc^2, but that he > > got rid of absolute velocities. And his main boasting point of GR was > > not curved spacetime, but that he got rid of absolute accelerations. > > Neither. This is another common misunderstanding. newtonian Mechanics > do not need absolute velocities either. This incorrect reply you made is typical of every reply you made. Newtonian mechanics was NOT a theory of electrodynamics. LET was, and LET is the theory Einstein wanted to replace with SR. But LET used absolute velocties, but SR did not. Einstein said: H. A. Lorentz even discovered the "Lorentz transformation," later called after him, though without recognizing its group character. To him Maxwell's equations in empty space held only for a particular coordinate system distinguished from all other coordinate systems by its state of rest. This was a truly paradoxical situation because the theory seemed to restrict the inertial system more strongly than did classical mechanics. This circumstance, which from the empirical point of view appeared completely unmotivated, was bounded to lead to the theory of special relativity. ---- H. A. Lorentz, Creator and Personality, Ideas and Opinions, p. 75. So, duh, of course Newton's mechanics didn't use absolute velocities, and that was undoubtedly why Einstein thought that any proper generalization of Newton's mechanics to include electrodynamics should also not need absolute velocities. If you're gonna talk about what Einstein was trying to do, be ready to give the specific quote/s with reference/s.
From: kenseto on 26 Aug 2006 09:05 "YBM" <ybmess(a)nooos.fr> wrote in message news:44efa79f$0$19782$636a55ce(a)news.free.fr... > kenseto a ?crit : > > World line is a path of an object in space traces out by its absolute > > motion. > > Whis this definition, which assumes absolute motion, it is indeed clear > that worldline => absolute motion. > > Note that it is NOT the definition of worldline for the rest of us. SO???? It just mean that the rest of you are wrong. :-) > > > Relative motion between two objects A and B is the vector difference > > of the vector components of A's absolute motion and the vector component of > > B's absolute motion along the line joining A and B. > > For the rest of us relative motion does NOT need to refer to absolute > motion to be defined. Could you provide at least one case where your > definition of relative motion will give another result than the usual > one ? You and I are standing side by side. That means that you and I are in the same state of absolute motion. I accelerated away from you and maintain a constant relative velocity wrt you. My acceleration causes me to have a different state of absolute motion than you and thus a different world line than you. This clearly show that the relative velocity between us is derived from my individual motion. Ken Seto >
From: YBM on 26 Aug 2006 09:19 kenseto a ?crit : > "YBM" <ybmess(a)nooos.fr> wrote in message > news:44efa79f$0$19782$636a55ce(a)news.free.fr... > >>kenseto a ?crit : >> >>>World line is a path of an object in space traces out by its absolute >>>motion. >> >>Whis this definition, which assumes absolute motion, it is indeed clear >>that worldline => absolute motion. >> >>Note that it is NOT the definition of worldline for the rest of us. > > > SO???? It just mean that the rest of you are wrong. :-) > >>>Relative motion between two objects A and B is the vector difference >>>of the vector components of A's absolute motion and the vector component > > of > >>>B's absolute motion along the line joining A and B. >> >>For the rest of us relative motion does NOT need to refer to absolute >>motion to be defined. Could you provide at least one case where your >>definition of relative motion will give another result than the usual >>one ? > > > You and I are standing side by side. That means that you and I are in the > same state of absolute motion. I accelerated away from you and maintain a > constant relative velocity wrt you. My acceleration causes me to have a > different state of absolute motion than you and thus a different world line > than you. This clearly show that the relative velocity between us is derived > from my individual motion. You and I are standing side by side. That means that you and I have a relative velocity of 0. You accelerated away from me, then you change your relative velocity wrt me. Your acceleration causes you to have a different relative velocity wrt me than you had before.
From: Mike on 26 Aug 2006 13:51 surrealistic-dream(a)hotmail.com wrote: > Mike wrote: > > surrealistic-dream(a)hotmail.com wrote: > > > Mike wrote: > > > > Paul B. Andersen wrote: > > > > > Igor wrote: > > > > > > surrealistic-dream(a)hotmail.com wrote: > > > > > >> Not true. SR treats accelerations as absolute, but velocites and > > > > > >> positions as relative. > > > > > > > > > > > > Wrong. There is a Lorentz transformation for acceleration also. > > > > > > > > > > No, it's correct. > > > > > But the acceleration that is absolute is the proper acceleration, > > > > > that is the acceleration measured in the instant inertial > > > > > rest frame of the object. It is the acceleration that is > > > > > measured by an accelerometer. This acceleration is absolute, > > > > > that is independent of frames of reference. > > > > > The co-ordinate acceleration is however frame dependent. > > > > > > > > The term "absolute" implies a much broader range of possibilities than > > > > simply "independent of FoR". It is better to call proper acceleration > > > > an invariant. > > > > > > Einstein claimed that he left acceleration as "absolute" in SR (that > > > is, in his generaltization of Newton's mechanics to include > > > electrodynamics). Why? well, this is partly semantic and partly > > > historical and they go together. Historically "absolute motion" of any > > > kind referred to motion with respect to some physically existing space. > > > > I agree. > > > > > > > To Newton, acceleration only made sense in his theory if one could > > > rely on that kind of motion to be with respect to some space in which > > > absolute accelerations live. So, of course, Newton took the existence > > > of inertial frames as absolute. And later, Einstein found the inertial > > > concept wanting, and he introdcued the so-called Principle of > > > Equivelence in GR. > > > > This has nothing to do with absolute motion, i.e. both concepts are > > also present in Newtonian mechanics and post-Newtonian formulations. > > > > > > > > Anyway, since you mentioned Mach below, I will address his contribution > > > to relativity here. It was Mach, contrary to what you claimed below, > > > who got Einstein to doubt the necessity of founding physics on the > > > concept of absolute acceleration, meaning accelerations with respect to > > > some invisible, unidentifiably space. Instead, he suggested that the > > > inertial properties of matter are totally dependent on the distibution > > > of matter in the universe. And, since the distribution of matter in the > > > universe is happenstance, it is not depedent on the existence of some > > > absolute space. > > > > > > > This is a very narrow interpretation. Mach's idea cannot rule out > > absolute space. You can still have absolute space and inertia dependent > > on mass distribution in the universe. > > > > > > > > > Okay, so what is relative about relativity? This: if the equations of > > > physics are conceptually founded in some theory on motion with respect > > > to some absolute space, such as the space in which absolute > > > accelerations live or the space in which absolute velocities live (rest > > > space of the ether), then the motion is deemed to be "absolute." But if > > > the equations of physics are founded on the notion of objects relative > > > to visible (ponderable) matter, the theory is said to be > > > "relativistic." Nowadays, physics includes the notion of invisible > > > matter/energy but such things are still object like (in the same way > > > that ponderable matter is), not space like in the way the the rest > > > frame of the ether is. > > > > You are confusing Relational theories of spacetime and motion with > > Relativistic theories. This is a very common mistake. Relativistic > > theories do not preclude absolute space. Actually, it is now understood > > that the spacetime of SR and GR is absolute. Relational theories > > preclude absolute space time but there is no theory at hand which is > > founded on purely relational spatiotemporal quantities. It is > > impossible to do it since it is impossible to know the mass > > distribution function of the universe. Esxpecially when more than 70% > > (or 90% nobody knows) is ssome dark matter. > > > > > > > > Einstein's main boasting point for SR, was not E = mc^2, but that he > > > got rid of absolute velocities. And his main boasting point of GR was > > > not curved spacetime, but that he got rid of absolute accelerations. > > > > Neither. This is another common misunderstanding. newtonian Mechanics > > do not need absolute velocities either. > > This incorrect reply you made is typical of every reply you made. > Newtonian mechanics was NOT a theory of electrodynamics. LET was, and > LET is the theory Einstein wanted to replace with SR. But LET used > absolute velocties, but SR did not. No, I think you are talking about things you do not understand well. Neither NM nor LET require absolute velocities to determine state of motion. The introduction of absolute velocities in these theories is done solely on the basis of defining the structure of spacetime and consequently, the metaphysics of these theories. Einstein's bold step was to introduce the invariance of the speed of light in all globally inertial reference frames. But this has consequences only in the way observer A determines the motion of observer B and vice versa. I never said NM was a theory of electrodynamics. LET does not "use" absolute velocities, it postulates them but the way it is formulated in modern times does not require them to determine state of motion. Einstein realized this and thought absolute velocities were absolete in an extension of mechanics to electrodynamics. Furtermore, the important thing to understand is that Einstein never disputed absolute space. He just insisted absolute velocities are not required. something that was already known but nobody was as convincing. > > Einstein said: > > H. A. Lorentz even discovered the "Lorentz transformation," > later called after him, though without recognizing its group > character. To him Maxwell's equations in empty space held > only for a particular coordinate system distinguished from > all other coordinate systems by its state of rest. This was > a truly paradoxical situation because the theory seemed to > restrict the inertial system m
From: Igor on 26 Aug 2006 13:54
kenseto wrote: > "Igor" <thoovler(a)excite.com> wrote in message > news:1156525443.210500.226300(a)75g2000cwc.googlegroups.com... > > > > kenseto wrote: > > > "Igor" <thoovler(a)excite.com> wrote in message > > > news:1156435588.287603.157960(a)p79g2000cwp.googlegroups.com... > > > > > > > > kenseto wrote: > > > > > "Igor" <thoovler(a)excite.com> wrote in message > > > > > news:1156353371.333406.159360(a)i42g2000cwa.googlegroups.com... > > > > > > > > > > > > kenseto wrote: > > > > > > > "Igor" <thoovler(a)excite.com> wrote in message > > > > > > > news:1156349832.759078.175940(a)74g2000cwt.googlegroups.com... > > > > > > > > > > > > > > > > kenseto wrote: > > > > > > > > > "Igor" <thoovler(a)excite.com> wrote in message > > > > > > > > > > news:1156265582.026355.324580(a)p79g2000cwp.googlegroups.com... > > > > > > > > > > > > The worldline is invariant. Motion is relative. That's all there > is > > > > > > to it. Beyond that, I don't really understand what you're even > > > asking. > > > > > > > > > > > What I am asking is: what motion of an object that gives rise to it > > > > > worldline? Is it the object's absolute motion (individual motion)? > If > > > not > > > > > why not? > > > > > > > > > > Ken Seto > > > > > > > > Ask Galileo. This is not just an issue with SR. You might want to > > > > reprase your question as "How can motion in space be relative and > still > > > > have a well-defined trajectory?" > > > > > > > Of course it is an issue with SR. SR claims that there is only relative > > > motion and the fact that each object has its own world line refute this > > > claim. The world line of an object is due to the individual motion of > the > > > object in space. > > > > But Galileo claimed the exact same thing, except with invariant time. > > So it's not strictly a SR thing. Thus, the notion of relative motion > > has been around since the 17th century. So how can you have relative > > motion and still have a well-defined trajectory? > > SO???? Both Galileo and SR failed to recognize that world line is the result > of absolute motion and relative motion between A abnd B is the vector > components difference of the vector component of A's absolute motion and the > vector component of B's absolute motion along the line joining A and B. > > > It's simple. How the > > motion is described is entirely dependent on the coordinate system, > > hence relative motion, but all inertial observers must see the same > > trajectory. > > > But relative motion is derived from the absolute motions of the interacting > objects. > All inertial observers do not see the same world line for the same object. > > Ken Seto Not only do all inertial observers see the same world line in SR, all non-inertial observers see the same world line in GR. You obviously don't know what you are talking about. But it's not my problem. You claim there is absolute motion. How do you get to that? Even prior to SR, most reasonable believers in absolute motion still had it tied down to relative motion WRT the aether. How can you believe in absolute motion when simple everyday experiences can shoot it down? And one more thing, how you model any such absolute motion mathematically? It can't be done. |