Questions on world-line
in [Relativity]
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From: kenseto on 24 Aug 2006 08:40 "Barry" <sasalobo(a)squaw.ca> wrote in message news:CZ5Hg.10913$EF2.1877(a)newsfe23.lga... > kenseto wrote: > > 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? > > In SR, the motion of an object that gives rise to it's worldline is it's > motion through time at "c". Mmmmm.....motion through time? I think not. > > If the Earth is considered to "stationary" in space, then it's world > line is straight but the moon's worldline (and yours) is a kind of helix. > > If the Sun is considered to "stationary" in space, then it's world line > is straight but the Earth's worldline is a kind of helix. > > > If the Galaxy is considered to "stationary" in space, then it's world > line is straight but the Sun's worldline is a kind of helix. > > Since they can't figure out who is stationary, then they can't figure > out the absolute worldline (i.e. the absolute motion through space). Nobody is stationary (in a state of absolute rest)......however, SR assumes that the observer is in a state of absolute rest and that's why SR asserts that all the clocks moving wrt the observer are running slow and all the rods moving wrt him are contracted. This SR assumption leads to the incompleteness of SR. In real life nobody is in a state of absolute rest. Therefore an observer will see some of the clocks moving wrt him are running slow and some are running fast. Also he will see the light path length of a moving rod can be longer or shorter than the light path length of his rod. This new interpretation leads to a new theory of relativity call IRT (Improve Relativity Theory). IRT includes SRT as a subset. However, unlike SRT, the equations of IRT are valid in all environments, including gravity. A description of IRT is in the following link (page 4): http://www.geocities.com/kn_seto/2005Unficication.pdf Ken Seto
From: kenseto on 24 Aug 2006 09:17 "YBM" <ybmess(a)nooos.fr> wrote in message news:44ece480$0$19781$636a55ce(a)news.free.fr... > kenseto a ?crit : > > "YBM" <ybmess(a)nooos.fr> wrote in message > > news:44ec8a99$0$19782$636a55ce(a)news.free.fr... > > > >>kenseto a ?crit : > >> > >>>The point is: worldline or trajectory in spacetime requires some kind of > >>>motion to happen. In SR there is only relative motion.....does that mean > >>>that worldline of an object is the result of relative motion?? > >> > >>I should be dreaming... You are just about to get it ! > > > > > > RFOTFLOL this idiot falls into the trap.....an object doesn't need any > > reference to have a worldline. > > Well, I'm right not to have bet on that... not that I did believe it > actualy. > > Back to basics : the worldline of Ken Seto is defined in a specific > frame F as the set of the t-uples (x,y,z,t) tagging in F the events > "at time t, Ken Seto is at coordinates (x,y,z)". This is not basic you are talking about relative motion between me and frame F. In my frame of reference my coordinates are (0,0,0) at all time. Why? Because SR and I assumed that I am in a state of rest and all the objects around me are doing the moving. Even though that I assume that I am in a state of rest I still have a worldline. This applies to all the object that are at rest wrt me. Ken Seto
From: Paul B. Andersen on 24 Aug 2006 09:37 Dirk Van de moortel wrote: > "Paul B. Andersen" <paul.b.andersen(a)hiadeletethis.no> wrote in message news:echlqg$7t6$1(a)dolly.uninett.no... >> 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. >> >> Example: >> If you travel in space with a rocket with constant thrust, >> you will have a constant proper acceleration. >> (Assume the mass of of the ship is constant.) >> Your accelerometer shows a constant acceleration of - say 1g. >> This acceleration is absolute, independent of frames of reference. >> >> But your co-ordinate acceleration measured in some inertial frame >> is NOT constant. As your speed in this frame of reference >> (after a year or so) approaches c, your co-ordinate acceleration >> approaches zero. >> >>>> With the exception of the worldline of a particle moving at light >>>> speed, the worldline of a particle is a specific 'curve' (or piecewise >>>> collection of curves and/or line segments) in a specific spacetime >>>> diagram. This curve is generally timelike and not an invariant of a >>>> Lorentz transformation. >>> Wrong again. The worldline is invariant regardless of whether it is >>> spacelike, timelike, or lightlike. >> An interval between two events is timelike if it is >> possible for a massive object to be present at both events. >> The word line of an object is its path through space-time. >> Any interval between events on this world line must thus per >> definition be time-like. >> There is no such thing as a "space-like world line". > > I'd prefer to say that there is no such thing as "an object with a > space-like worldline". > A light signal clearly has a light-like worldline, and a shadow or > the spot of a laser can have a space-like worldline. In that case you would use an unconventional definition of "world-line". > That is of course, unless you prefer to call these lines lightlines > and spotlines :-) Curves in space-time? I looked up a few definitions: Oxford English Dictionary: Physics and Philos. the succession of points in space-time that are occupied by a particle; http://www.answers.com/topic/world-line "The path in space-time traveled by an elementary particle for the time and distance that it retains its identity." In: http://en.wikipedia.org/wiki/World_line I find: "In physics, a world line of an object (approximated as a point in space, e.g. a particle or observer) is the sequence of spacetime events corresponding to the history of the object." and: "In our definition above: world lines are time-like curves in spacetime." but also: "Sometimes, the term world line is loosely used for any curve in spacetime. This terminology causes confusions. More properly, a world line is a curve in spacetime which traces out the (time)history of a particle, observer or small object." I use the "more proper" definition. :-) And then "space-like world-line" is a contradiction in terms. Paul
From: Sorcerer on 24 Aug 2006 10:04 "Paul B. Andersen" <paul.b.andersen(a)hiadeletethis.no> wrote in message news:ecka36$3j6$1(a)dolly.uninett.no... | Dirk Van de moortel wrote: | > "Paul B. Andersen" <paul.b.andersen(a)hiadeletethis.no> wrote in message news:echlqg$7t6$1(a)dolly.uninett.no... | >> 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. | >> | >> Example: | >> If you travel in space with a rocket with constant thrust, | >> you will have a constant proper acceleration. | >> (Assume the mass of of the ship is constant.) | >> Your accelerometer shows a constant acceleration of - say 1g. | >> This acceleration is absolute, independent of frames of reference. | >> | >> But your co-ordinate acceleration measured in some inertial frame | >> is NOT constant. As your speed in this frame of reference | >> (after a year or so) approaches c, your co-ordinate acceleration | >> approaches zero. | >> | >>>> With the exception of the worldline of a particle moving at light | >>>> speed, the worldline of a particle is a specific 'curve' (or piecewise | >>>> collection of curves and/or line segments) in a specific spacetime | >>>> diagram. This curve is generally timelike and not an invariant of a | >>>> Lorentz transformation. | >>> Wrong again. The worldline is invariant regardless of whether it is | >>> spacelike, timelike, or lightlike. | >> An interval between two events is timelike if it is | >> possible for a massive object to be present at both events. | >> The word line of an object is its path through space-time. | >> Any interval between events on this world line must thus per | >> definition be time-like. | >> There is no such thing as a "space-like world line". | > | > I'd prefer to say that there is no such thing as "an object with a | > space-like worldline". | > A light signal clearly has a light-like worldline, and a shadow or | > the spot of a laser can have a space-like worldline. | | In that case you would use an unconventional definition of "world-line". | | > That is of course, unless you prefer to call these lines lightlines | > and spotlines :-) | | Curves in space-time? | | I looked up a few definitions: | | Oxford English Dictionary: | Physics and Philos. the succession of points in space-time | that are occupied by a particle; | | http://www.answers.com/topic/world-line | "The path in space-time traveled by an elementary particle | for the time and distance that it retains its identity." | | In: | http://en.wikipedia.org/wiki/World_line | I find: | "In physics, a world line of an object (approximated as a point in space, | e.g. a particle or observer) is the sequence of spacetime events corresponding | to the history of the object." | and: | "In our definition above: world lines are time-like curves in spacetime." | but also: | "Sometimes, the term world line is loosely used for any curve in spacetime. | This terminology causes confusions. More properly, a world line is a curve | in spacetime which traces out the (time)history of a particle, observer or | small object." | | I use the "more proper" definition. :-) | And then "space-like world-line" is a contradiction in terms. | | Paul "Tom Roberts" <tjroberts137(a)sbcglobal.net> wrote in message news:P4Hqg.60105$Lm5.3167(a)newssvr12.news.prodigy.com... | This is PHYSICS, not math or logic, and "proof" is completely irrelevant. news:ZDmYf.51582$2O6.5573(a)newssvr12.news.prodigy.com " <sigh>", said Humpty Roberts, "The nuances of English. I was discussing the usage of words and not the concepts they represent." news:hG3Sf.54263$H71.9335(a)newssvr13.news.prodigy.com... This is more your level: | Imagine a train leaving one city at 12:00 and arriving in a city 60 | miles to its west at 12:01. Do you really think that train traveled | 3,600 miles per hour? Of course not! This example used two _different_ | coordinate systems for "time", the two timezones of those two cities. To | obtain the speed you _must_ use a single coordinate system; then you'll | realize it traveled just under 60 miles per hour. | Androcles
From: surrealistic-dream on 24 Aug 2006 10:35
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. 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. 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. 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. 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. > However, this whole thing is a math trick. There is no > physical significance to an "instant inertial rest frame co-moving with > an object". In lieu of the math trick, acceleration must be referenced > wrt an absolute space of some kind or wrt the mass distribution in the > universe as Mach insisted, which makes any attempt to develop a > relativity theory hopeless. Just the opposite from Mach, the relativist. > > What this instant inertial frame means essentially, is that any > accelerated motion can be broken down to a series of inertial motions, > something that is totally absurd. This error has been pointed out by > many as back as 300 years ago, before Einstein and SR. It turns out > that while the thinking is wrong the result turns out correct > accidentaly. > > There is no way to define an instant inertial frame because an instant > in the motion of an object cannot be defined. Motion is continuous to > arbitrary accuracy. > > Mike |