The inertial frame concept in 1905 Relativity
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From: PD on 23 Jul 2010 09:37 On Jul 22, 6:44 pm, "Inertial" <relativ...(a)rest.com> wrote: > "PD" wrote in message > > news:be9babb8-7f7b-4600-95c8-c7c7433ada65(a)w30g2000yqw.googlegroups.com... > > >On Jul 22, 11:15 am, va...(a)icmf.inf.cu wrote: > >> When the position of the centre of mass relative to the body set is > >> determined, ONLY the 16 balls are taking into account, you are > >> assuming then in the model that they are the unique existing bodies > >> (that they are the entire universe). > > >To try to explain this further, you worry about the presence of a 17th > >ball outside the system that would affect the center of mass. It does > >NOT affect the center of mass of the system, because the SYSTEM > >specified contains the 16 balls, not the 17th ball. The center of mass > >is calculated using only those masses IN THE system, not all the > >masses available everywhere. The presence of the 17th mass outside the > >system in no way affects the center of mass of the system of 16 balls. > > It sounds like he is advocating the centre-of-mass-of-the-universe as a > special (absolute) frame. It sounds like what he is claiming is that in order to calculate the center of mass of a system, you have to mentally remove the rest of the objects outside the system. He is then claiming that, having done so, there is only one inertial reference frame, with the center of mass fixed at the origin. Both of these ideas are ludicrous.
From: valls on 23 Jul 2010 12:16 On 22 jul, 14:06, PD <thedraperfam...(a)gmail.com> wrote: > On Jul 22, 11:15 am, va...(a)icmf.inf.cu wrote: > > > > > > > On 21 jul, 17:55, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Jul 21, 5:29 pm, va...(a)icmf.inf.cu wrote: > > > > > On 21 jul, 15:50, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > On Jul 21, 3:33 pm, va...(a)icmf.inf.cu wrote: > > > > > > > On 21 jul, 08:27, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > On Jul 21, 8:13 am, va...(a)icmf.inf.cu wrote: > > > > > ........... > > > > > > > > No. Perhaps you don't understand the meaning of "system" in physics. > > > > > > > You can draw an imaginary surface around any collection of objects and > > > > > > > that is a system in physics. Some systems can be (for the purposes of > > > > > > > the analysis at hand) be considered isolated and others not isolated. > > > > > > > Conservation of momentum and conservation of energy are statements > > > > > > > about such systems. > > > > > > > > This in no way presumes that the system is the entire universe. > > > > > > > When you have a center of mass inertial system, you can use it only to > > > > > > describe the bodies taking into account when determining that centre > > > > > > of mass. In your 16 balls system, you cant use it for example to > > > > > > describe an added 17 ball, because the presence of the new ball > > > > > > changes the centre of mass. > > > > > > I'm not talking about adding a 17th ball. I'm talking about the fact > > > > > that the laws of physics are the same in any frame in which the center > > > > > of mass of the 16 balls has a nonzero constant velocity. There are an > > > > > infinite number of such frames. > > > > > I added a new body with the purpose to explain you the implicit > > > > assumption in any center of mass inertial system about being its body > > > > set the entire universe. Taking for granted that you understand it > > > > already, I return to your original 16 balls center of mass inertial > > > > frame. Now you want to put it with a non-zero uniform velocity. > > > > First of all, let's get the language right. > > > The 16 balls is a *system*. It is not the entire universe. It is a > > > physical *system*. > > > Secondly, there is a frame of reference which is NOT the system, in > > > which the center of mass of this system is at rest. This you can call > > > "the center of mass frame" of this system if you like. > > > I dont call anything, I am not the one introducing the centre of mass > > inertial frame concept, it is already in Newtonian mechanics long > > before 1905 Einstein. Yes, you can call the body set (your 16 balls) a > > physical system, a closed one where you can apply conservation laws. > > Or even an open one, if you like, where work, heat and impulse can > cross the boundary of the system. Note you do not have to pretend that > objects outside the system do not exist. > > > If you want now to consider the centre of mass inertial system > > corresponding to that physical system, in the model exists the > > implicit assumption that the physical system is the entire universe. > > Not at all. > We are talking in this thread about inertial frames. If you select for example 16 Jupiters satellites (to simplify things I will assume that Jupiter has only those 16 satellites) you can denote that body set a physical system, but you cant derive from it any inertial frame. You can determine the centre of mass of that system, but it is not related with a centre of mass inertial frame, the presence of Jupiter doesnt permit it. If as gods we now disappear Jupiter, all the relative movements among the satellites surely change a lot, and now we can derive from the system a centre of mass inertial frame. What we are implicitly doing here? Considering a MODEL where the entire universe is only the 16 bodies. We put out Jupiter, but at the start of this comment we consider implicitly that Jupiter and its satellites were the entire universe. But what about the Sun (and the rest of the universe)? There exists here another implicit assumption, that all external to the Jupiter System provokes in each one of its bodies a sufficiently equal ACCELERATION (that even not needs to be uniform). A little thinking about it will convince you that this is a general rule to decide if any system can be considered the entire universe. And only with that condition you can derive a centre of mass inertial frame from any considered body set. > > I > > explained in detail all this already to you, but you seem not > > understand it yet. I will try again. > > When the position of the centre of mass relative to the body set is > > determined, ONLY the 16 balls are taking into account, you are > > assuming then in the model that they are the unique existing bodies > > (that they are the entire universe). > > Not at all. A center of mass of a SYSTEM is a property of the objects > IN THAT SYSTEM, *regardless* of what lies outside it. You certainly do > not have to assume that there is nothing outside the system to find > the center of mass of a system. > To determine the centre of mass, not; but to derive from it a centre of mass inertial frame, yes. > > > > > > This is nothing new in Physics, > > when 1913 Bohr develops its H atom model, he consider a universe with > > only a proton and an electron, determining their centre of mass at > > rest. Corresponding to any body set exists a unique centre of mass > > inertial frame. You must consider always the exterior of the physical > > system empty, putting a single body there alters the centre of mass (I > > introduced the ball 17 with that purpose). > > > > Now, what I said is that the laws of physics governing this *system* > > > are identical also in any other reference frame in which the center of > > > mass of this system is moving with constant velocity. > > > We are in agreement about the laws of physics being the same in all > > inertial frames. What you dont understand yet is that to have a > > centre of mass moving with a non-zero uniform velocity you need the > > Newtonian absolute inertial frame already put out by 1905 Einstein. > > And this is plainly wrong. > As I explained to you, you can consider the behavior of this system > according to the same laws of physics in any of an INFINITE number of > reference frames, in each of which the center of mass of the system is > moving with constant velocity. This choice is completely arbitrary and > can be done differently by different people thinking about the same > system. This cannot possibly mean that those people are thinking about > different universes. There is only one universe. > Let us consider the Jupiter System of a previous comment. Use your imaginary systems (the Newtonian ones that you insist to consider also present in 1905 Relativity) to put the Jupiter System moving with all possible uniform velocities. All that different views of the Jupiter System are totally imaginary, represent NOTHING in our real universe. In it the Jupiter System has a UNIQUE real movement, the one you can obtain referring it to the real Solar System centre of mass inertial frame. And to describe the internal movements of all the bodies belonging to some centre of mass inertial frame, you must consider always that centre of mass at rest. You are distorting the reality if you put it moving with any other uniform velocity. > > The entire universe can be moving only in the absolute frame.> Note that I am not involving the entire universe in ANY of this. > > > False. Once you talk about a centre of mass inertial frame, in the > > model the body set (or physical system) is already considered the > > entire universe, as I explained in detail to you already twice. > > But you're wrong. A system is not the universe. > You MODEL a part of the real universe as if it were the whole universe. > > I have a system of 16 balls. > > > This system has a center of mass. > > > Then, in your model the 16 balls have no other body in its exterior, > > And that's patently absurd. You have no idea what a system is in > physics. You probably need to revisit freshman physics where this is > defined clearly. > In your MODEL exists only the 16 balls (if you want all of them to be described in an inertial frame), the real whole universe continue existing as always, only partially known by men (thanks to the models they create). > > > > because its presence alters the centre of mass (not exist a 17 ball or > > any other body).> I can look at the coordinates of the center of mass of this system in > > > a reference frame. > > > In 1905 Relativity that reference frame must be the centre of mass > > inertial frame corresponding to your body set. You cant have never > > two different inertial frames derived from the same body set. And only > > in the Newtonian view you can have inertial frames independent from > > bodies.> In one particular reference frame, the coordinates of the center of > > > mass of this system is constant -- the center of mass is stationary. > > > In any other inertial reference frame, the coordinates of the center > > > of mass of this system is moving with constant velocity. > > > For a non-zero uniform velocity, only in the Newtonian view with > > absolute frame, never in the 1905 Relativity one without absolute > > frame. 1905 Einstein never assign a velocity-vector to a point of > > empty space in which electromagnetic processes take place (in the > > Introduction of the 30Jun1905 paper). Inertial frames are denoted by > > him stationary systems. > > > Nothing more good to understand anything that to analyse a real > > example in our world. Consider the GPS ECI. The body set (physical > > system) corresponding to the ECI is only our real Earth and some > > satellites and atomic clocks in them (even the Moon is considered not > > existing in the model). Corresponding to that body set a unique centre > > of mass inertial frame is derived, denoted ECI (Earth Centred Inertial > > system). The rotation of the Earth, the orbit of the satellites, the > > clocks at the Earth surface, absolutely all relevant things that moves > > is described in the same unique inertial frame. And the centre of mass > > of it is considered at REST, and the delay on all clocks owed to > > velocity correspond exactly to the one predicted by the 1905 > > Relativity formula (the same one used by 1905 Einstein in his example > > at the end of paragraph 4 of his 30Jun1905 paper, precisely having as > > the stationary system the same today denoted ECI!). All of this with a > > huge experimental evidence. > > But the centre of the Earth is NOT at rest, anybody knows that it is > > moving with a gravitational centripetal acceleration around the Sun! > > (could say you). And you are right, but that view corresponds to a > > different body set, the Solar System one, with a different centre of > > mass inertial frame (with centre considered also at REST!). In the > > previous case I added the 17 ball to obtain a new centre of mass > > inertial frame, in this case I added to the Earth all the rest of the > > Solar System. > > The ECI and the Solar System are examples of what I denote (many years > > ago) a Hierarchical Inertial System (HIS). The ECI is part of the > > Solar System, low hierarchy HIS compose high hierarchy ones. 1905 > > Relativity lead us to a hierarchical view of our Universe. HIS (1905 > > Relativity stationary systems, inertial frames) are equivalent in the > > sense of the same Physics laws, but hierarchical in the sense of the > > entities described in it. > > > > > OK, a > > > > single question. In the model, with respect to what you pretend to put > > > > the entire universe moving with a non-zero uniform velocity? Only in > > > > the Newtonian mechanics (with absolute frame) you can do that, never > > > > in 1905 Relativity (without absolute frame). > > > > > RVHG (Rafael Valls Hidalgo-Gato)- Hide quoted text - > > > RVHG (Rafael Valls Hidalgo-Gato)- Hide quoted text - > RVHG (Rafael Valls Hidalgo-Gato)
From: valls on 23 Jul 2010 12:36 On 22 jul, 16:20, PD <thedraperfam...(a)gmail.com> wrote: > On Jul 22, 11:15 am, va...(a)icmf.inf.cu wrote: > > > When the position of the centre of mass relative to the body set is > > determined, ONLY the 16 balls are taking into account, you are > > assuming then in the model that they are the unique existing bodies > > (that they are the entire universe). > > To try to explain this further, you worry about the presence of a 17th > ball outside the system that would affect the center of mass. It does > NOT affect the center of mass of the system, because the SYSTEM > specified contains the 16 balls, not the 17th ball. The center of mass > is calculated using only those masses IN THE system, not all the > masses available everywhere. The presence of the 17th mass outside the > system in no way affects the center of mass of the system of 16 balls. But the 17th ball interact with the other 16 changing their velocities and positions, altering then the old 16 balls centre of mass (and determining a new 17 balls centre of mass inertial frame). But even supposing that the old centre of mass is not altered, with it you have no more a centre of mass inertial frame (any body set determines a unique centre of mass inertial frame, that depends on each and all the bodies involved). RVHG (Rafael Valls Hidalgo-Gato)
From: PD on 23 Jul 2010 13:18 On Jul 23, 11:16 am, va...(a)icmf.inf.cu wrote: > On 22 jul, 14:06, PD <thedraperfam...(a)gmail.com> wrote: > > I'm going to top-poste because I think the discussion is well off the rails somewhere, and I'm going to try to go back to some basics. In Newtonian mechanics AND in 1905 relativity, an inertial reference frame is one in which the laws of physics hold true. What this means is that, given a system of bodies, whether that system is isolated or not, you can account for the motions (and in particular, the accelerations) of the bodies as the effect of known interactions, either internal to the system or reaching across the boundary of the system. What the inertial frame does NOT imply is that any one of the bodies in the system need be either stationary or bearing constant velocity. What it also does NOT imply is that the center of mass of the bodies in the system need be either stationary or bearing constant velocity. > > > On Jul 22, 11:15 am, va...(a)icmf.inf.cu wrote: > > > > On 21 jul, 17:55, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Jul 21, 5:29 pm, va...(a)icmf.inf.cu wrote: > > > > > > On 21 jul, 15:50, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Jul 21, 3:33 pm, va...(a)icmf.inf.cu wrote: > > > > > > > > On 21 jul, 08:27, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > On Jul 21, 8:13 am, va...(a)icmf.inf.cu wrote: > > > > > > ........... > > > > > > > > > No. Perhaps you don't understand the meaning of "system" in physics. > > > > > > > > You can draw an imaginary surface around any collection of objects and > > > > > > > > that is a system in physics. Some systems can be (for the purposes of > > > > > > > > the analysis at hand) be considered isolated and others not isolated. > > > > > > > > Conservation of momentum and conservation of energy are statements > > > > > > > > about such systems. > > > > > > > > > This in no way presumes that the system is the entire universe. > > > > > > > > When you have a center of mass inertial system, you can use it only to > > > > > > > describe the bodies taking into account when determining that centre > > > > > > > of mass. In your 16 balls system, you cant use it for example to > > > > > > > describe an added 17 ball, because the presence of the new ball > > > > > > > changes the centre of mass. > > > > > > > I'm not talking about adding a 17th ball. I'm talking about the fact > > > > > > that the laws of physics are the same in any frame in which the center > > > > > > of mass of the 16 balls has a nonzero constant velocity. There are an > > > > > > infinite number of such frames. > > > > > > I added a new body with the purpose to explain you the implicit > > > > > assumption in any center of mass inertial system about being its body > > > > > set the entire universe. Taking for granted that you understand it > > > > > already, I return to your original 16 balls center of mass inertial > > > > > frame. Now you want to put it with a non-zero uniform velocity. > > > > > First of all, let's get the language right. > > > > The 16 balls is a *system*. It is not the entire universe. It is a > > > > physical *system*. > > > > Secondly, there is a frame of reference which is NOT the system, in > > > > which the center of mass of this system is at rest. This you can call > > > > "the center of mass frame" of this system if you like. > > > > I dont call anything, I am not the one introducing the centre of mass > > > inertial frame concept, it is already in Newtonian mechanics long > > > before 1905 Einstein. Yes, you can call the body set (your 16 balls) a > > > physical system, a closed one where you can apply conservation laws. > > > Or even an open one, if you like, where work, heat and impulse can > > cross the boundary of the system. Note you do not have to pretend that > > objects outside the system do not exist. > > > > If you want now to consider the centre of mass inertial system > > > corresponding to that physical system, in the model exists the > > > implicit assumption that the physical system is the entire universe. > > > Not at all. > > We are talking in this thread about inertial frames. If you select for > example 16 Jupiters satellites (to simplify things I will assume that > Jupiter has only those 16 satellites) you can denote that body set a > physical system, but you cant derive from it any inertial frame. You > can determine the centre of mass of that system, but it is not related > with a centre of mass inertial frame, the presence of Jupiter doesnt > permit it. If as gods we now disappear Jupiter, all the relative > movements among the satellites surely change a lot, and now we can > derive from the system a centre of mass inertial frame. What we are > implicitly doing here? Considering a MODEL where the entire universe > is only the 16 bodies. We put out Jupiter, but at the start of this > comment we consider implicitly that Jupiter and its satellites were > the entire universe. But what about the Sun (and the rest of the > universe)? There exists here another implicit assumption, that all > external to the Jupiter System provokes in each one of its bodies a > sufficiently equal ACCELERATION (that even not needs to be uniform). A > little thinking about it will convince you that this is a general rule > to decide if any system can be considered the entire universe. And > only with that condition you can derive a centre of mass inertial > frame from any considered body set.> > I > > > explained in detail all this already to you, but you seem not > > > understand it yet. I will try again. > > > When the position of the centre of mass relative to the body set is > > > determined, ONLY the 16 balls are taking into account, you are > > > assuming then in the model that they are the unique existing bodies > > > (that they are the entire universe). > > > Not at all. A center of mass of a SYSTEM is a property of the objects > > IN THAT SYSTEM, *regardless* of what lies outside it. You certainly do > > not have to assume that there is nothing outside the system to find > > the center of mass of a system. > > To determine the centre of mass, not; but to derive from it a centre > of mass inertial frame, yes. > > > > > > > > This is nothing new in Physics, > > > when 1913 Bohr develops its H atom model, he consider a universe with > > > only a proton and an electron, determining their centre of mass at > > > rest. Corresponding to any body set exists a unique centre of mass > > > inertial frame. You must consider always the exterior of the physical > > > system empty, putting a single body there alters the centre of mass (I > > > introduced the ball 17 with that purpose). > > > > > Now, what I said is that the laws of physics governing this *system* > > > > are identical also in any other reference frame in which the center of > > > > mass of this system is moving with constant velocity. > > > > We are in agreement about the laws of physics being the same in all > > > inertial frames. What you dont understand yet is that to have a > > > centre of mass moving with a non-zero uniform velocity you need the > > > Newtonian absolute inertial frame already put out by 1905 Einstein. > > > And this is plainly wrong. > > As I explained to you, you can consider the behavior of this system > > according to the same laws of physics in any of an INFINITE number of > > reference frames, in each of which the center of mass of the system is > > moving with constant velocity. This choice is completely arbitrary and > > can be done differently by different people thinking about the same > > system. This cannot possibly mean that those people are thinking about > > different universes. There is only one universe. > > Let us consider the Jupiter System of a previous comment. Use your > imaginary systems (the Newtonian ones that you insist to consider also > present in 1905 Relativity) to put the Jupiter System moving with all > possible uniform velocities. All that different views of the Jupiter > System are totally imaginary, represent NOTHING in our real universe. > In it the Jupiter System has a UNIQUE real movement, the one you can > obtain referring it to the real Solar System centre of mass inertial > frame. And to describe the internal movements of all the bodies > belonging to some centre of mass inertial frame, you must consider > always that centre of mass at rest. You are distorting the reality if > you put it moving with any other uniform velocity.> > The entire universe can be moving only in the absolute frame.> Note that I am not involving the entire universe in ANY of this. > > > > False. Once you talk about a centre of mass inertial frame, in the > > > model the body set (or physical system) is already considered the > > > entire universe, as I explained in detail to you already twice. > > > But you're wrong. A system is not the universe. > > You MODEL a part of the real universe as if it were the whole > universe.> > I have a system of 16 balls. > > > > This system has a center of mass. > > > > Then, in your model the 16 balls have no other body in its exterior, > > > And that's patently absurd. You have no idea what a system is in > > physics. You probably need to revisit freshman physics where this is > > defined clearly. > > In your MODEL exists only the 16 balls (if you want all of them to be > described in an inertial frame), the real whole universe continue > existing as always, only partially known by men (thanks to the models > they create). > > > > > > > > because its presence alters the centre of mass (not exist a 17 ball or > > > any other body).> I can look at the coordinates of the center of mass of this system in > > > > a reference frame. > > > > In 1905 Relativity that reference frame must be the centre of mass > > > inertial frame corresponding to your body set. You cant have never > > > two different inertial frames derived from the same body set. And only > > > in the Newtonian view you can have inertial frames independent from > > > bodies.> In one particular reference frame, the coordinates of the center of > > > > mass of this system is constant -- the center of mass is stationary.. > > > > In any other inertial reference frame, the coordinates of the center > > > > of mass of this system is moving with constant velocity. > > > > For a non-zero uniform velocity, only in the Newtonian view with > > > absolute frame, never in the 1905 Relativity one without absolute > > > frame. 1905 Einstein never assign a velocity-vector to a point of > > > empty space in which electromagnetic processes take place (in the > > > Introduction of the 30Jun1905 paper). Inertial frames are denoted by > > > him stationary systems. > > > > Nothing more good to understand anything that to analyse a real > > > example in our world. Consider the GPS ECI. The body set (physical > > > system) corresponding to the ECI is only our real Earth and some > > > satellites and atomic clocks in them (even the Moon is considered not > > > existing in the model). Corresponding to that body set a unique centre > > > of mass inertial frame is derived, denoted ECI (Earth Centred- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -... > > read more »
From: PD on 23 Jul 2010 13:19
On Jul 23, 11:36 am, va...(a)icmf.inf.cu wrote: > On 22 jul, 16:20, PD <thedraperfam...(a)gmail.com> wrote:> On Jul 22, 11:15 am, va...(a)icmf.inf.cu wrote: > > > > When the position of the centre of mass relative to the body set is > > > determined, ONLY the 16 balls are taking into account, you are > > > assuming then in the model that they are the unique existing bodies > > > (that they are the entire universe). > > > To try to explain this further, you worry about the presence of a 17th > > ball outside the system that would affect the center of mass. It does > > NOT affect the center of mass of the system, because the SYSTEM > > specified contains the 16 balls, not the 17th ball. The center of mass > > is calculated using only those masses IN THE system, not all the > > masses available everywhere. The presence of the 17th mass outside the > > system in no way affects the center of mass of the system of 16 balls. > > But the 17th ball interact with the other 16 changing their velocities > and positions, Yes. > altering then the old 16 balls centre of mass You mean changing the LOCATION of the center of mass of this system. Yes. >(and > determining a new 17 balls centre of mass inertial frame). But even > supposing that the old centre of mass is not altered, with it you have > no more a centre of mass inertial frame (any body set determines a > unique centre of mass inertial frame, that depends on each and all the > bodies involved). > > RVHG (Rafael Valls Hidalgo-Gato) |