[Vo]:ON THE ELECTRODYNAMICS OF MOVING BODIES By A. Einstein
As Dave has mentioned, Einstein's reason for postulating the constancy of c was partly motivated by his examination of the laws of electrodynamics. Here is the introduction to his paper ON THE ELECTRODYNAMICS OF MOVING BODIES. You can see he is bothered by a lack of symmetry in the laws but a lack symmetry does not mean a lack of integrity. The lack of symmetry is an aesthetic judgement. Also he claims the electromotive force has no corresponding energy, but I am not sure why he would say this since it does have a potential energy. Perhaps he expects it to have kinetic energy, but this would reflect an implicit philosophical prejudice against non-mechanical causes. Harry -- ON THE ELECTRODYNAMICS OF MOVING BODIES By A. Einstein June 30, 1905 It is known that Maxwell's electrodynamics--as usually understood at the present time--when applied to moving bodies, leads to asymmetries which do not appear to be inherent in the phenomena. Take, for example, the reciprocal electrodynamic action of a magnet and a conductor. The observable phenomenon here depends only on the relative motion of the conductor and the magnet, whereas the customary view draws a sharp distinction between the two cases in which either the one or the other of these bodies is in motion. For if the magnet is in motion and the conductor at rest, there arises in the neighbourhood of the magnet an electric field with a certain definite energy, producing a current at the places where parts of the conductor are situated. But if the magnet is stationary and the conductor in motion, no electric field arises in the neighbourhood of the magnet. In the conductor, however, we find an electromotive force, to which in itself there is no corresponding energy, but which gives rise--assuming equality of relative motion in the two cases discussed--to electric currents of the same path and intensity as those produced by the electric forces in the former case. Examples of this sort, together with the unsuccessful attempts to discover any motion of the earth relatively to the light medium, suggest that the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest. They suggest rather that, as has already been shown to the first order of small quantities, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good.1 We will raise this conjecture (the purport of which will hereafter be called the Principle of Relativity) to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body. These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell's theory for stationary bodies. The introduction of a luminiferous ether will prove to be superfluous inasmuch as the view here to be developed will not require an absolutely stationary space provided with special properties, nor assign a velocity-vector to a point of the empty space in which electromagnetic processes take place. The theory to be developed is based--like all electrodynamics--on the kinematics of the rigid body, since the assertions of any such theory have to do with the relationships between rigid bodies (systems of co-ordinates), clocks, and electromagnetic processes. Insufficient consideration of this circumstance lies at the root of the difficulties which the electrodynamics of moving bodies at present encounters. The rest of paper is here: https://www.fourmilab.ch/etexts/einstein/specrel/www/
Re: [Vo]:ON THE ELECTRODYNAMICS OF MOVING BODIES By A. Einstein
My view on SR is of course that it can not be possible. But it does give some interesting and correct answers, now impossible is still impossible, but... If we reduce the magnet in Einstein's example to an electromagnet, or better yet just one straight wire carrying a DC current. (or a macro model of this with a pipe and charged balls) And if the coil with relative motion is reduced to just a straight wire... (or a macro model) If the relative motion of the electrons caused them to flatten and pancake (length contraction), then the protons (spherical) field would not cancel the electrons field which has been compressed from length contraction, this would make a voltage appear which would be identical to the motional E-field proposed by Hooper. If we now approached this wire with a second parallel wire, we would now see the electrons moving on a different angle, each electrons pancaking field would now look different, what did look like this || (electric field squashed perpendicular to wire) now looks like this // electric field squashed on a slant. This would cause a voltage to appear along the parallel wire that is approaching our simplified magnet. The direction of this field would be to repel the electrons in this wire from the direction the electrons are moving in the 'magnet' wire. And this is precisely the induction that we would expect from cutting line of magnetic force, the direction is correct and I presume so is the magnitude. If the pickup wire was moving with the electrons in the magnet wire (not typical, but easy to imagine) then the protons field would be seen to pancake. This would lead to the opposite voltage gradient (which is seldom looked for or detected) from the wire due to pancaking now being protonic, If this moving wire (moving with the electrons in the other wire) now also moves towards the magnet wire with it's apparent protonic current, the pancaking of the protons would now also slant this way \\ and since electrons are attracted to protons, the voltage induced would be the same. The field would have the same observed induction if it is from electrons moving to our left or protons moving to our right. But what of the electric field from just electron motion, if that is switching from positive to negative, shouldn't there be effects? If we now construct a coil of one magnet wire and we move in a circle along it, we would have an N-machine, or homopolar motor/generator. The Homopolar generator is essentially experiencing induction from the Hooper motional E-field, or from direct charge pancaking. I am unsure, does anyone know if the faster a homopolar generator turns the higher the voltage? Since motion of a disk in an all electromagnetic n-machine (no ferromagnetic help) would have only the slight difference in speed between the electron drift and the protons. So I wonder if such a generator would reach full voltage as extremely slow rpm? If the voltage does keep growing by the electrons moving slightly faster, then this would imply that a coil that not only approaches a magnet but is given a twist should have a larger voltage induced since the pancaking of the electrons would be greater. John On Fri, Feb 21, 2014 at 7:06 AM, H Veeder hveeder...@gmail.com wrote: As Dave has mentioned, Einstein's reason for postulating the constancy of c was partly motivated by his examination of the laws of electrodynamics. Here is the introduction to his paper ON THE ELECTRODYNAMICS OF MOVING BODIES. You can see he is bothered by a lack of symmetry in the laws but a lack symmetry does not mean a lack of integrity. The lack of symmetry is an aesthetic judgement. Also he claims the electromotive force has no corresponding energy, but I am not sure why he would say this since it does have a potential energy. Perhaps he expects it to have kinetic energy, but this would reflect an implicit philosophical prejudice against non-mechanical causes. Harry -- ON THE ELECTRODYNAMICS OF MOVING BODIES By A. Einstein June 30, 1905 It is known that Maxwell's electrodynamics--as usually understood at the present time--when applied to moving bodies, leads to asymmetries which do not appear to be inherent in the phenomena. Take, for example, the reciprocal electrodynamic action of a magnet and a conductor. The observable phenomenon here depends only on the relative motion of the conductor and the magnet, whereas the customary view draws a sharp distinction between the two cases in which either the one or the other of these bodies is in motion. For if the magnet is in motion and the conductor at rest, there arises in the neighbourhood of the magnet an electric field with a certain definite energy, producing a current at the places where parts of the conductor are situated. But if the magnet is stationary and the conductor in motion, no electric field arises in the neighbourhood of the magnet. In the conductor,
Re: [Vo]:ON THE ELECTRODYNAMICS OF MOVING BODIES By A. Einstein
While I would still like to know what voltage a non-ferromagnetic N-machine generator will establish at different RPM's, I looked up and found that Depalma's chart of voltage to RPM in his Sunburst machine was linear, double the RPM produced double the output voltage. This would seem hard to explain (with SR) if the same result were to occur without any ferromagnetism since surely electrons moving at 83001 mm a second compared to protons moving at 83000 mm a second is not going to lead to such a linear or significant voltage increase. At any rate, this result does indicate that movement along a wire or around a magnet does have an impact on the perception of that field, and as such if we take the pancaking view of electrons, if the magnet is rotated as it is thrust toward a coil, you could expect the inductive effect of the magnet to increase as there would be a greater degree of pancaking. Alas I just tried this and it does not work. Indeed it seems that these results are not in keeping with SR, but rather indicate a complex interplay where the magnetic field is not created by relative movement of charges but is somehow absolute. And once the effect appears as magnetic, it seems not to care about change in perspective of what is creating the field and indeed it now appears to be semi-devorces from it's electric origin. We know that the electric field induced by a magnetic field is relative to motion, but at this point we can only speculate that a magnetic field seen around a charge would exist for only some reference frames. Perhaps magnetic fields with their closed loops create their own reference frame, the aether involved in their manifestation may be bound in a way that does not occur for electric fields. As such perhaps the magnetic field from an electric field will be experienced the same for all reference frames since it is relative to the aether. But the magnetic induction is relative to the the aether entrained by the magnetic field? This can be tested by rotating a charged object, if a magnetic field is seen in the stationary frame, is it also evidenced on the rotating frame? I have heard of HV charged disks effecting a compass. John On Fri, Feb 21, 2014 at 8:46 AM, John Berry berry.joh...@gmail.com wrote: My view on SR is of course that it can not be possible. But it does give some interesting and correct answers, now impossible is still impossible, but... If we reduce the magnet in Einstein's example to an electromagnet, or better yet just one straight wire carrying a DC current. (or a macro model of this with a pipe and charged balls) And if the coil with relative motion is reduced to just a straight wire... (or a macro model) If the relative motion of the electrons caused them to flatten and pancake (length contraction), then the protons (spherical) field would not cancel the electrons field which has been compressed from length contraction, this would make a voltage appear which would be identical to the motional E-field proposed by Hooper. If we now approached this wire with a second parallel wire, we would now see the electrons moving on a different angle, each electrons pancaking field would now look different, what did look like this || (electric field squashed perpendicular to wire) now looks like this // electric field squashed on a slant. This would cause a voltage to appear along the parallel wire that is approaching our simplified magnet. The direction of this field would be to repel the electrons in this wire from the direction the electrons are moving in the 'magnet' wire. And this is precisely the induction that we would expect from cutting line of magnetic force, the direction is correct and I presume so is the magnitude. If the pickup wire was moving with the electrons in the magnet wire (not typical, but easy to imagine) then the protons field would be seen to pancake. This would lead to the opposite voltage gradient (which is seldom looked for or detected) from the wire due to pancaking now being protonic, If this moving wire (moving with the electrons in the other wire) now also moves towards the magnet wire with it's apparent protonic current, the pancaking of the protons would now also slant this way \\ and since electrons are attracted to protons, the voltage induced would be the same. The field would have the same observed induction if it is from electrons moving to our left or protons moving to our right. But what of the electric field from just electron motion, if that is switching from positive to negative, shouldn't there be effects? If we now construct a coil of one magnet wire and we move in a circle along it, we would have an N-machine, or homopolar motor/generator. The Homopolar generator is essentially experiencing induction from the Hooper motional E-field, or from direct charge pancaking. I am unsure, does anyone know if the faster a homopolar generator turns
Re: [Vo]:ON THE ELECTRODYNAMICS OF MOVING BODIES By A. Einstein
On Thu, Feb 20, 2014 at 10:06 AM, H Veeder hveeder...@gmail.com wrote: As Dave has mentioned, Einstein's reason for postulating the constancy of c was partly motivated by his examination of the laws of electrodynamics. ... Here is the introduction to his paper ON THE ELECTRODYNAMICS OF MOVING BODIES. That's a remarkable paper to read. Einstein proposes two bold postulates -- (1) let the velocity of light be constant; (2) let physical laws apply to any bodies in the same manner, no matter what system of coordinates and uniform translation (as well as (3), let space be homogenous). The reader is not told why he should go along with the speed of light one, and you can imagine that people didn't want to suspend disbelief on that one at first. But then Einstein goes on to derive a bunch of remarkable mathematical results from these postulates that make sense of Maxwell's equations, the Doppler effect, the movement of an electron, and so on. You can also see E = mc^2 implied in the equation for the energy of the motion of an electron, towards the end. Occasionally there is a statement that might possibly be experimentally verified. I doubt this system appeared to Einstein as though by way of revelation, at least at first. Along the lines of what Harry suggests, I'm guessing that he was irritated by the different ways in which electric and magnetic fields were being calculated at the time, depending upon whether a system was at motion or at rest, and that this was the thread in the sweater that, when he pulled at, kept on unravelling, until at some point he found himself looking at a very different system from the one he at first anticipated. Eric
