Maxwell's Equations: Solving a Puzzlement for Bob

[Wannabeagenius]

Hi All,

I understand that at the turn of the twentieth century, Physicists were rather smug and thought that they knew all there was to know; however, as I understand it, there was a glaring problem with one of the main laws of Physics, namely that all the laws of Physics are the same in all Inertial Reference frames.

I'm specifically referring to Maxwell's equations which show the speed of light to be a universal constant but this was not the case in all Inertial Reference frames as defined classically.

Please clarify this puzzlement for me.

Thank you,
Bob

 

[HallsofIvy]

I'm not sure what puzzle you are talking about. Actually, the point you cite in your paragraph is little more fundamental than that. What is often called "Gallilean relativity" is based on an idea Galilleo himself mentioned: If you are completely inside a closed car, no windows, moving in a straight line, at a constant speed, no acceleration, without any bumping (which would be an acceleration), there would be no experiment you could do which would tell you how fast you are moving or if you are moving at all.

But, by the middle of the 19th century, physicists knew that the force exerted on a charged particle by a magnetic field depended on the particles speed (this led to Maxwell's equations). That seemed to imply that you could do an experiment, involving electro-magnetic forces, that Galileo knew nothing about, inside a closed cart, that would tell you how fast you were going. Not "how fast relative to some outside reference" but just "how fast"- and that speed would be absolute rather than relative to some reference.

Naturally, scientists of the time were anxious to do such an experiment. But ordinary "electric" and "magnetic" measurements were just not precise enough. Since light is an "electro-magnetic" phenomenon (this is where Maxwells equation come in again since they can be manipulated to show that waves in electro-magnetic fields propogate at the speed of light), and light measurements can be made very accurately, scientists tried using light. In 1887, Michaelson and Morley finally did such an experiment- and it gave a null result. That is, Galileo was stillright. Even electro-magnetic experiments, in a closed environment, could tell how fast that closed environment was moving or if it was moving at all. The explanation of how that could be reconciled with Maxwell's laws was the special theory of relativity.

 

[Meir Achuz]

"I understand that at the turn of the twentieth century, Physicists were rather smug and thought that they knew all there was to know;" is an apocryphal statement based on an out of context quote of one (too) senior physicist. As you intimate, most theoretical physicists were seriously troubled by a number of unsolved problems. Understanding how two moving charges interacted was one of the major unsolved problems. This is why the title of Einstein's relativity paper was "The Electrodynamics of Moving Bodies".

 

[Wannabeagenius]

"I understand that at the turn of the twentieth century, Physicists were rather smug and thought that they knew all there was to know;" is an apocryphal statement based on an out of context quote of one (too) senior physicist. As you intimate, most theoretical physicists were seriously troubled by a number of unsolved problems. Understanding how two moving charges interacted was one of the major unsolved problems. This is why the title of Einstein's relativity paper was "The Electrodynamics of Moving Bodies".

OK and thank you!

Now I know that it's a myth that physicists at the time thought that the only thing left to do in Physics was to add more decimal places to the constants of Physics such as G.

I guess this isn't as ridiculous as Newton being hit on the head with an apple!

Bob

 

[Meir Achuz]

The apple story was originally related by someone who recalled Newton telling him about it.