According to 1905 Relativity, a single material point must be always at rest
in [Relativity]
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From: harald on 21 May 2010 05:35 On May 21, 1:39 am, va...(a)icmf.inf.cu wrote: > On 20 mayo, 16:43, harald <h...(a)swissonline.ch> wrote: > > > On May 20, 4:28 pm, va...(a)icmf.inf.cu wrote: > > > > On 20 mayo, 08:50, harald <h...(a)swissonline.ch> wrote:> On May 20, 3:19 pm, va...(a)icmf.inf.cu wrote: > > > > > > In his first Relativity paper (30June1905), after declaring the ether > > > > > superfluous, Einstein considers a material point at rest. He uses a > > > > > system of Cartesian coordinates in which the equations of Newtonian > > > > > mechanics and Euclidean geometry hold good. If the massive body is > > > > > alone (and then without a Newtonian gravitational force acting on it), > > > > > it must remains forever at rest in its own centre of mass inertial > > > > > frame. > > > > > RVHG (Rafael Valls Hidalgo-Gato) > > > > > If it were alone, yes. But then a theory about relative motion of > > > > reference systems would certainly be superfluous. ;-) > > > > But who says that the material point must be always alone? Consider > > > the Solar System centre of mass inertial reference frame (SS) and the > > > GPS ECI one. The last can be modelled as a material point that is not > > > alone (is part of the SS one). As a huge experimental evidence put out > > > of any doubt, you can model the SS as a single material point at rest, > > > describing later the Earth (ECI) movement in the SS without any > > > problem at all. In a similar way, all GPS satellite movements > > > (including the ground clock ones) can be described in an ECI modelled > > > as a single material point at rest. > > > Good / so now you do consider a not so alone particle, and even not a > > point if you want to establish time measurements at different places. > > The use of a material point to model part of our Universe as a unique > entity is inherent to Newtonian mechanics since its beginning. You > cant formulate any mechanical law (included the universal gravitation > one) without modelling first all bodies as material points. Of course we can - it's just mathematically very handy to simplify them as points, as far as allowable. > The 1684 > Principia was published only after Newton could prove that an Earth > modelled by a material point in its centre of mass provokes the same > action as the real Earth on bodies at its surface and more far away. > My alone material point at rest can be up to the whole Universe (if it > can be proved composed by a finite quantity of bodies). Ok - that means that your definition of "point" is at odds with mine. Yours isn't "sharp" in any way - http://dictionary.reference.com/browse/point > With Einsteins definition of time, you can synchronize a clock at ANY > point of the space corresponding to ANY centre of mass inertial frame. > I dont understand the meaning of your even not a point. Please, > clear me that in your next post. If you want to set up a Newtonian coordinate system, you need to define at least *two* points; a single coordinate cannot be used to establish time measurements at different places, let alone make a space-time diagram. > > > Do you consider yet superfluous a theory about relative motion of > > > reference systems? Note that the moving system must be always part > > > of the stationary system, and a stationary system moving with > > > respect to a moving system at rest is nothing more that a huge > > > absurd (do you remember Ptolomys Sun going around the Earth?). > > > Following your arguments elsewhere, here we dont care about what you > > think. Einsteins thoery does not prefer one inertial system over the > > other, it is not supporting your theory. > > Long before Einstein, to any body set correspond a unique centre of > mass inertial frame. You never have more than one CM inertial frame to > describe the same body set (the holding of Newtons laws is the > cause). Newton's first law and the related Newtonian coordinate systems do not depend on " unique centre of mass"... > By the way, we are considering here only 1905 Relativity (and > I was born long after that epoch). 1905 Einstein can support only 1905 > Relativity. Exactly, that is what I referred to. His purpose was to show how: "the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good" with the clarification: "In order to render our presentation more precise and to distinguish this system of co-ordinates *verbally* from others which will be introduced hereafter, we call it the ``stationary system.'' " That is at odds with your statement that: > > > "the moving system must be always part > > > of the stationary system, and a stationary system moving with > > > respect to a moving system at rest is nothing more that a huge > > > absurd [..]. Regards, Harald
From: valls on 21 May 2010 06:18 On 20 mayo, 19:30, "Dono." <sa...(a)comcast.net> wrote: > On May 20, 4:39 pm, va...(a)icmf.inf.cu wrote: > > > and I was born long after that epoch). > > Judging by your advanced level of senility, this isn't true. Hello Dono, you don't finish yet to calculate the Sun's trajectory in the ECI? I am still waiting for it. RVHG (Rafael Valls Hidalgo-Gato)
From: valls on 21 May 2010 07:01 On 20 mayo, 21:42, "Inertial" <relativ...(a)rest.com> wrote: > <va...(a)icmf.inf.cu> wrote in message > > news:c13b9123-0513-4072-8dc5-54557b8cfaf5(a)y12g2000vbr.googlegroups.com... > > > In his first Relativity paper (30June1905), after declaring the ether > > superfluous, Einstein considers a material point at rest. He uses a > > system of Cartesian coordinates in which the equations of Newtonian > > mechanics and Euclidean geometry hold good. If the massive body is > > alone (and then without a Newtonian gravitational force acting on it), > > it must remains forever at rest in its own centre of mass inertial > > frame. > > RVHG (Rafael Valls Hidalgo-Gato) > > Yeup .. do you think that is a problem? Not for me, but maybe for other persons. In the Newtonian view (with absolute space and time), a single material point can have any constant velocity v in an infinite quantity of different inertial frames. In the 1905 Einsteinian view (without absolute space and time), the same single material point can have only the constant velocity v=0 in a unique inertial frame. Are we in agreement about that? RVHG (Rafael Valls Hidalgo-Gato)
From: valls on 21 May 2010 07:27 On 20 mayo, 13:09, PD <thedraperfam...(a)gmail.com> wrote: > On May 20, 8:19 am, va...(a)icmf.inf.cu wrote: > > > In his first Relativity paper (30June1905), after declaring the ether > > superfluous, Einstein considers a material point at rest. He uses a > > system of Cartesian coordinates in which the equations of Newtonian > > mechanics and Euclidean geometry hold good. If the massive body is > > alone (and then without a Newtonian gravitational force acting on it), > > it must remains forever at rest in its own centre of mass inertial > > frame. > > Yes. So? > > Every object lives in an infinite multitude of frames. The ones that > have constant velocity with the frame you just described, plus this > frame itself, constitutes the set of inertial frames. > If we apply that to the single material point case, the result is an infinite number of inertial frames where the single material point can be moving with any velocity v. Once the ether is put out by 1905 Einstein (and with it the Newtonian absolute space and time), can you explain to me with respect to what a single material point can have then a velocity different from zero? > The question of interest is what is the relationship between various > physical properties, as measured in different inertial frames? Yes, but before addressing that we must put clear which are the inertial frames involved. RVHG (Rafael Valls Hidalgo-Gato)
From: Greg Neill on 21 May 2010 08:15
valls(a)icmf.inf.cu wrote: > On 20 mayo, 13:09, PD <thedraperfam...(a)gmail.com> wrote: >> On May 20, 8:19 am, va...(a)icmf.inf.cu wrote: >> >>> In his first Relativity paper (30June1905), after declaring the ether >>> superfluous, Einstein considers a material point at rest. He uses a >>> system of Cartesian coordinates in which the equations of Newtonian >>> mechanics and Euclidean geometry hold good. If the massive body is >>> alone (and then without a Newtonian gravitational force acting on it), >>> it must remains forever at rest in its own centre of mass inertial >>> frame. >> >> Yes. So? >> >> Every object lives in an infinite multitude of frames. The ones that >> have constant velocity with the frame you just described, plus this >> frame itself, constitutes the set of inertial frames. >> > If we apply that to the single material point case, the result is an > infinite number of inertial frames where the single material point can > be moving with any velocity v. Once the ether is put out by 1905 > Einstein (and with it the Newtonian absolute space and time), can you > explain to me with respect to what a single material point can have > then a velocity different from zero? A single material point can have any desired velocity simply by choosing a suitable frame of reference (for the observer) that is not identical to the frame of reference in which the particle is at rest. A frame of reference is not a material thing, it is a coordinate system construction. You have proposed a thought experiment where a universe contains but one single particle and a (presumably) discorporate, purely theoretical observer. This "observer" can be in any frame of reference that you choose. >> The question of interest is what is the relationship between various >> physical properties, as measured in different inertial frames? > Yes, but before addressing that we must put clear which are the > inertial frames involved. All of them. They are purely theoretical so they are cheap and easy to deploy. Pin one to your "material point" and another to your observer (even if he's purely theoretical in your gedanken universe). |