## Einstein holding Maxwell's equations above Newton's equations

I'm learning electrodynamics and one of the speakers I'm learning from said that when faced with the incompatibility of retaining both Newton's equations (based on mass, distance and time) and Maxwell's equations (based on charge, E and B) unchanged, Einstein had to choose one or the other. The speaker said that Einstein chose Maxwell's equations as definitive, meaning that he kept charge, E and B unchanged. Newton's equations became malleable, so that mass, length and time became malleable. I hope I'm not embellishing his point here.

The speaker added that Einstein's choice was a reinforcement, at least for him, of the fundamental nature of the conversation of charge.

In any event, I hadn't heard this perspective before, and was curious if those more familiar with electrodynamics and the roots of relativity could help explain why Maxwell's equations might hold preference over Newton's equations, or why charge, E and B would go unchanged while mass, time and distance are modified.

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 Recognitions: Science Advisor At the time Einstein formulated special relativity, phenomenon such as length contraction were already known. Additionally, concepts such as transverse and longitudinal mass had already been noted in the 1890's. So Einstein didn't really have a choice; he was merely following experimental evidence.

 Quote by diagopod I'm learning electrodynamics and one of the speakers I'm learning from said that when faced with the incompatibility of retaining both Newton's equations (based on mass, distance and time) and Maxwell's equations (based on charge, E and B) unchanged, Einstein had to choose one or the other. The speaker said that Einstein chose Maxwell's equations as definitive, meaning that he kept charge, E and B unchanged. Newton's equations became malleable, so that mass, length and time became malleable. I hope I'm not embellishing his point here. The speaker added that Einstein's choice was a reinforcement, at least for him, of the fundamental nature of the conversation of charge. In any event, I hadn't heard this perspective before, and was curious if those more familiar with electrodynamics and the roots of relativity could help explain why Maxwell's equations might hold preference over Newton's equations, or why charge, E and B would go unchanged while mass, time and distance are modified.
Most people at Einstein's time tried to coordinate the classical view of spacetime with Maxwell's equations but that gave rise to a lot of problems.Einstein finally discarded the classical view of spacetime and built a new theory upon Maxwell's equations and the special relativitistic principle.

But he did this not because he wanted to.It was because the experiments done by physics before Einstein suggested that this was the only way to solve the problem.

And E、B are not unchanged.They are relativistically covariant.

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## Einstein holding Maxwell's equations above Newton's equations

This is an interesting perspective. Is the person claiming that this was historically how Einstein thought about it, or is this merely the person's own interpretation?

It's true that SR is latent in Maxwell's equations.

On the other hand, I don't really buy this part: "Newton's equations became malleable, so that mass, length and time became malleable." Length and time occur in both Newton's laws and Maxwell's equations. In both cases, the frame-dependence of length and time forces a reinterpretation of the equations, compared to their traditional interpretations. Traditionally, Newton's laws were interpreted in terms of absolute time and instantaneous action at a distance. Traditionally, Maxwell's equations were interpreted in terms of an aether.

And the way we treat mass today is usually that we consider it a frame-independent quantity, just like charge, although it's true that Einstein originally treated mass as being frame-dependent.

 Quote by Nabeshin So Einstein didn't really have a choice; he was merely following experimental evidence.
Thanks for the insight. So does this mean that it would not have been possible for Einstein to have changed Maxwell's equations instead of Newton's to fit the data? Or is my asking such a question perhaps missing the point or otherwise misinterpreting what he did?

 Quote by bcrowell This is an interesting perspective. Is the person claiming that this was historically how Einstein thought about it, or is this merely the person's own interpretation?
He actually didn't specify that, but spoke about it as if this was well-known in the history of science, which I suppose isn't quite true. He said that Einstein had a choice. Either he could keep Newton's equations unscathed, and then he wrote down "(m,l,t)" or keep Maxwell's equations unscathed, and he wrote down "(q,E,B)". He added that Einstein decided that Maxwell's equations could not be wrong, and then he crossed out m,l,t on the board, leaving q,E and B untouched.

I have heard before that Einstein was so convinced of the intrinsic veracity of Maxwell's equations, especially the fixed c for all observers that they seem to necessitate, that he dismissed other interpretations, such as Lorentz's, which argued that m,l and t only appeared to change, and that c only appeared to be the same for all observers, as unsatisfactory. But I'm not sure if this is what this speaker had in mind.

 On the other hand, I don't really buy this part: "Newton's equations became malleable, so that mass, length and time became malleable."
That's probably my misinterpretation of what the speaker said, although this might have been what he meant,judging from the above.

Either way, one thing that does mystify me is how a fixed c for all observers is a logically necessary outcome of Maxwell's equations. Could you help explain? Thanks again for your help

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 Quote by diagopod Either way, one thing that does mystify me is how a fixed c for all observers is a logically necessary outcome of Maxwell's equations. Could you help explain? Thanks again for your help
My interpretation is that Maxwell's equations predict that the speed of light is a function of the permitivity and permeability of space and independent of the velocity of emitter. The last point is the key point. Once you establish that the speed of light is independent of the velocity of the emitter relative to the observer and if you accept that the laws of physics are same in all reference frames, then it follows that the Lorentz transformations are the logical outcome and the consequence of those transformations is that time and space are not absolute.

This was discussed in more detail in this recent thread http://www.physicsforums.com/showthr...=382163&page=8

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 And E、B are not unchanged.They are relativistically covariant.
yes.

 The speaker added that Einstein's choice was a reinforcement, at least for him, of the fundamental nature of the conversation of charge
."

Coulombs law must be modified as well for relativistic effects... so the statement(s) attributed by the OP to his lecturer are inaccurate in a number of respects.

I've tried to find just what Einstein's thinking was as he developed special and general relativity. I don't have a full picture.

 "....why Maxwell's equations might hold preference over Newton's equations..."
Intuition, for one. Einstein was also a founder of quantum mechanics and he sure did NOT like "spooky action at a distance"....Newton "assumed" instantaneous action at a distance and I believe Maxwell's finite fixed speed of light must have appealed to Einstein...

My interpretation is that Maxwell's equations predict that the speed of light is a function of the permitivity and permeability of space and independent of the velocity of emitter."

This might be a key point, however, the "luminiferous ether" was still all the rage when Einstein was in college...According to one account, apparently his old school electromagnetism professor would not even mention the "new" Maxwell's equations...this infuriated Einstein who was apparently "attracted" to the new theory while still an undergraduate.

Lee Smolin, or one other of the big popular physicsts, mentions in a book reading Einstein's original notes (in German) and notes many, many, many fits and starts (errors) but Einstein was very persistent and eventually came around, found his error and proceeded.

I understand that as a teenager Einstein tried to picture what light would look like if he caught up with it...and somehow he came to conclude that the speed of light is constant....I'm guessing Maxwell's theory answered that conundrum for him... then Einstein concluded contrary to thousands of years of science, space and time cannot be constant!

So while he did have many others to "lean on", like Maxwell, Lorentz, Fitzgerald, he also might have choosen the wrong road to follow...his genius seems to have been properly interpreting physical situations.....

 Recognitions: Science Advisor One thing that may have motivated Einstein is the principle of relativity - basically that you can drink coffee on the aeroplane - which we all know is true, and would like to be true (it isn't, at least not in general relativity, but let's stick to special relativity here). I'm not sure if these ideas are exactly correct, but just a sketch for where to look. Newton's mechanics and the prinicple of relativity are compatible. Maxwell's equations and the principle of relativity are compatible. Maxwell's and Newton's equations are not jointly compatible with the principle of relativity. So we must modify Maxwell or Newton or both, if we wish to keep the principle of relativity. Maybe we can justify modifying Newton, if there is no way to modify Maxwell to be compatible with Newton and the principle of relativity. Special relativity is a modification of Newton to be compatible with Maxwell and the principle of relativity. Does anyone know a way to modify Maxwell to be compatible with Newton and the principle of relativity? If that is possible, then Einstein did have a choice whether to modify Newton or Maxwell. If it is not possible, then Einstein had no choice but to modify Newton. (It is possible to keep Newton and Maxwell unmodified, but then the principle of relativity has to go.)

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I just stumbled across the following....seems Einstein surely would have known about this in the early 1900's....but who accepted it and who did not is another question....

In PART VI of his 1864 paper which is entitled 'ELECTROMAGNETIC THEORY OF LIGHT'[2], Maxwell combined displacement current with some of the other equations of electromagnetism and he obtained a wave equation with a speed equal to the speed of light. He commented:

 The agreement of the results seems to show that light and magnetism are affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws.[3]
http://en.wikipedia.org/wiki/Electro..._wave_equation

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This seems to substantiate that ether WAS still popular at the time Einstein launched SR...and maybe even after:

 Contemporary scientists were aware of the problems, but aether theory was so entrenched in physical law by this point that it was simply assumed to exist. In 1908 Oliver Lodge gave a speech in behalf of Lord Rayleigh [6] to the Royal Institution on this topic, in which he outlined its physical properties, and then attempted to offer reasons why they were not impossible. Nevertheless he was also aware of the criticisms, and quoted Lord Salisbury as saying that "aether is little more than a nominative case of the verb to undulate". Others criticized it as an "English invention", although Rayleigh jokingly corrected them to state it was actually an invention of the Royal Institution.[citation needed] By the early 20th Century, aether theory was in trouble. A series of increasingly complex experiments had been carried out in the late 1800s to try to detect the motion of earth through the aether, and had failed to do so. A range of proposed aether-dragging theories could explain the null result but these were more complex, and tended to use arbitrary-looking coefficients and physical assumptions. Lorentz and Fitzgerald offered within the framework of Lorentz ether theory a more elegant solution to how the motion of an absolute aether could be undetectable (length contraction), but if their equations were correct, the new special theory of relativity (1905) could generate the same mathematics without referring to an aether at all.
http://en.wikipedia.org/wiki/Luminiferous_ether

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Did not realize it was that early:

 The Michelson–Morley experiment was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University. Its results are generally considered to be the first strong evidence against the theory of a luminiferous aether.
http://en.wikipedia.org/wiki/Michael...ley_experiment

Anyway, Einstein appears to have had lots of choices....depending on what information he had (this WAS before Al Gore's invention of the internet, after all)

 Quote by kev My interpretation is that Maxwell's equations predict that the speed of light is a function of the permitivity and permeability of space and independent of the velocity of emitter. The last point is the key point.
Thanks kev. I suppose what I still need guidance on is what aspect of Maxwell's equations necessitate that all observers will measure c to be the same, regardless of the velocity of the source of the emitter relative to them. I'm familiar w/ Maxwell's laws at this point, and to some degree the wave equations, Poynting vector and so on, but it's still not clear to me how they necessitate the "independent of the velocity of the emitter" part of the above. Could you help explain if you have time or point me to an explanation perhaps?
Thanks again for your help.

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 Quote by diagopod Thanks kev. I suppose what I still need guidance on is what aspect of Maxwell's equations necessitate that all observers will measure c to be the same, regardless of the velocity of the source of the emitter relative to them. I'm familiar w/ Maxwell's laws at this point, and to some degree the wave equations, Poynting vector and so on, but it's still not clear to me how they necessitate the "independent of the velocity of the emitter" part of the above. Could you help explain if you have time or point me to an explanation perhaps? Thanks again for your help.
If permittivity and permeability of space are Lorentz invariant, then they will give the same value when measured in any intertial frame and the constancy of locally measured c follows. Now, one of the LT invariants of the EM field is $-4E\cdot B$. If we make a leap and say that E depends linearly on $\epsilon_0$ and B depends on $\mu_0$ then the product $\epsilon_0\mu_0$ is an invariant. That is speculative but gives the right answer.

 Recognitions: Homework Help Science Advisor You also have to consider that Einstein had the Maxwell's Equations t-shirt. It's interesting how close Maxwell came to inventing SR, not sure if it was the acceptance of the aether or he was just happy being a millionaire VC on his yacht that stopped him going further.

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