Special relativity adandons Maxwell's mechanical interpretation of EM?

[toan]

page 61 in Introduction To Electrodynamics (3rd ed, Griffiths) writes:

"
What exactly is an electric field? ... I encourage you to think of the field as a "real" physical entity, filling the space in the neighborhood of any electric charge. Maxwell himself came to believe that electric and magnetic fields represented actual stresses and strains in an invisible primordial jellylike "ether." Special relativity has forced us to abandon the notion of ether, and with it Maxwell's mechanical interpretation of electromagnetic fields.
"


Can anyone help giving me some basic explanation on: how special relativity abandons the notion of ether and Maxwell's mechanical interpretation of electromagnetic fields? I don't major in relativity but am curious about this statement. Thanks so much.

 

[bcrowell]

Can anyone help giving me some basic explanation on: how special relativity abandons the notion of ether and Maxwell's mechanical interpretation of electromagnetic fields?

The story of how special relativity abolishes the notion of ether is a story that has been told many times by many storytellers. A book I like is Relativity Simply Explained, by Gardner.

The question about Maxwell's mechanical interpretation of electromagnetic fields is a question about the history of science. That is, you can't know the answer to this kind of question without painfully immersing yourself in the confused state of physics knowledge that existed in the middle of the 19th century. This canot be done casually. Physicists try to do this kind of thing causally and are therefore the worst possible people to ask about the history of physics.

 

[ghwellsjr]

Maxwell, like virtually all scientists of his time, believed in an ether that carrried the light waves and suggested an experiment to detect the motion of the Earth through this ether but when Michelson and Morley carried out their famous experiment a few years after his death, they could not detect the expected ether wind. As a result, other scientists figured out that the null result of the MMX could be explained by lengths contracting and time slowing down for the experimental apparatus and they came up with a formula to calculate the effect.

Then they carefully examined Maxwell's equations and discovered that they actually predicted the null result of the MMX which meant that it was fundamentally impossible to measure an ether wind based on Maxwell's equations. You could call this Maxwell's greatest blunder.

Still, scientists persisted in believing in an immovable ether that was essentially the fields that Maxwell's equations defined, even though they had no hope of ever discovering when they would be at rest with respect to this absolute ether.

Then along came Einstein who made the audacious claim that everyone, no matter what their constant relative speed with respect to anyone else or anything else, including the absolute motionless ether, if it existed, could assume that they were, in fact, at rest in the presumed ether, (and so no one could ever measure any ether wind), and as a result, they were not experiencing any lengths contracting or time slowing down for themselves, but everyone else that was moving with respect to themselves would be experiencing lengths contracting and time slowing down for them except they wouldn't know this because all their rulers and clocks would also be similarly affected.

Einstein's idea freed the scientists from having to worry about where or if the ether existed, not because he showed that it cannot exist, but rather that he showed that it could exist by anybody's definition.

Now we say that there is no preferred frame of reference but every inertial frame of reference will have all the same characteristics of an absolute ether rest frame.

 

[Cleonis]

Then they carefully examined Maxwell's equations and discovered that they actually predicted the null result of the MMX which meant that it was fundamentally impossible to measure an ether wind based on Maxwell's equations. You could call this Maxwell's greatest blunder.

I think the above two statements are incorrect, especially the one about Maxwell.

Among the implications of the Maxwell equations (interpreted in terms of a EM-radiation carrying ether) is that if a charged object has a velocity with respect to the ether, then the electric field surrounding that charged particle is deformed from spherical into an oblate spheroid, contracted in the direction of velocity.

If memory serves me: Larmor investigated implications for orbits of electrons (provided one would grant the assumption that electrons follow some orbiting motion.) Larmor's results indicated that for an atom with a velocity with respect to the ether the electron orbit becomes ellipse-shaped rather than circular, contracted in the direction of the velocity. Also the orbit period changes.

The magnitude of the contraction is the one that is in the Lorentz transformation. This is the reason that the Lorentz transformations predate special relativity.


Lorentz proposed the following hypothesis: that all physical effects that allow solid objects to keep their shape transform according to the Lorentz transformations. If that hypothesis is granted then it follows that measuring instruments will contract, making the ether inaccessible to detection. (Also a corresponding time dilation hypothesis must be granted.)

As I understand it: the Maxwell equations by themselves do not imply a null result for MMX. Only when supplemented with the hypothesis that all physical effects that allow solids to keep their shape transform according to the Lorentz transformations.

This was a very audacious hypothesis, which was quite uncalled for in Maxwell's time. By the time of Lorentz experimental evidence was accumulating that pressured physicists to come up with additional hypotheses.

 

[PhilDSP]

I think the above two statements are incorrect, especially the one about Maxwell.

If memory serves me: Larmor investigated implications for orbits of electrons (provided one would grant the assumption that electrons follow some orbiting motion.) Larmor's results indicated that for an atom with a velocity with respect to the ether the electron orbit becomes ellipse-shaped rather than circular, contracted in the direction of the velocity. Also the orbit period changes.

I hadn't heard that Larmor did that. Fitzgerald definitely did with regard to an isolated electron and was that first to do so while Heavyside quantified and further analyzed the situation.

I agree that no fault is due Maxwell. His original equations did not contain the limitations that Heavyside and Gibbs imposed in order to simplify and enforce symmetries. It might be interpreted that Heavyside is the originator of SR though Lorentz, Poincare and Einstein more fully flushed out the consequences. Einstein never considered the equations that Maxwell actually wrote, did he?

 

[toan]

thanks so much. I may need to read some relativity to grasp you guys responses.