- #31
Darwin123
- 732
- 3
If Newton's Laws as written in Principia were precisely true, applying to both ordinary matter and this hypothetical ether scientists believed in, the electric and magnetic constants could be constant only for an observer in the inertial frame where the ether is stationary. There would be a one specific frame where Maxwell's equations could be written in the simplest form. It didn't matter whether or not there really is an ether. By the logical argument that you just gave, Maxwell's equations could be written in a simple form in only one frame. I will call this hypothetical unique frame the "ether frame", even though there may be no ether. If Newton's Laws are precisely valid, the constants are not invariant because the change for observers other than the ether frame.Boorglar said:
This also assumes that the measuring instruments are unaffected by the motion relative to the ether frame. This si consistent with Principia. However, Maxwell's equations may not be consistent with Principia. More on that later.
Maxwell's equations would not be valid as currently written in any other frame except one. An experimenter moving at a nonzero constant velocity with respect to that one frame would find different electric and magnetic constants from those of that one "proper frame". In fact, he would probably have to replace those constant numbers by constant matrices.
There was no experiment that showed this wouldn't be true. However, what bothered Einstein is the idea that the "constants" would be different for two observers moving at a constant velocity with respect to each other.
To visualize the problem, imaging that you moving at the speed of light with reference to the "ether frame". Suppose you hold up a mirror that relative to your eyes is in the direction of motion. You couldn't see your reflection! You also probably drop dead since your body has evolved for the electromagnetic constants being what they are on earth.
So this bothered Einstein. However, there is another reason to doubt the Principia. The reason is that the forces that hold bodies together are largely electromagnetic. Therefore, their dimensions and even their movements have to be affected by this speed relative to the ether!
Imagine that extended bodies are held together by a combination of electromagnetic and nonelectromagnetic forces. Our bodies contain a number of electrically charged particles. Using the laws of electromagnetic forces, it is easy to see that when in motion one particle will apply a force to the other particle. You can use the Law of Biot and Savart, the Lortentz force law, and anything else you want. Motion with respect to the ether frame will cause a stress on the extent body that will affect both its dimensions and its motion. For instance, an electrical coil moving with respect to the ether frame should experience a torque. Furthermore, a material that is not birefringen should show birefringence if it is in motion relative to the ether frame.
Efforts were made to measure this stress. There were two scientists, Raleight and Brace, that tried to measure the force on an electrical coil caused by the Earth's motion. This was an experiment not as well known as the Michaelson-Morley experiment. They had a null result that was just as important.
Experimental results indicated that Principia couldn't hold for electrical measurements.The motion of an electrical coil doesn't cause a torque on itself! A nonbirefringent material is nonbirefringent at all speeds!
I got the references to this from a paper by Lorentz. However, I have never found a copy of these experiments. They are just as important as the Michaelson Morley experiment. Yet, I can't find a copy. Maybe you will have better luck.
Null result on measuring the birefringence of an isotropic material in motion.
1) Rayleigh, Phil. Mag. 6(4), 678 (1902).
2) Brace, Phil. Mag. 6(7), 317 (1904)
Null result on measuring the torque on an electrical coil:
3) Troughton and Noble, Roy. Soc. Trans. A 202, 165 (1903).
Experiments 1-3 showed clearly that Principia was faulty.
The problem comes about because measuring instruments are extended bodies! Suppose and observer calibrates his measuring instruments, both rulers and clocks, in the ether frame. Some other observer moving at a constant velocity relative to the first observer grabs those measuring instruments, and accelerates them to his velocity. The internal forces will distort those measuring instruments!
He may try to calibrate them by a series of timing experiments. However, most timing experiments require synchronization of clocks using electrically charged particles. Thus, it appears impossible to calibrate measuring instruments that contain electrically charged particles or electromagnetic radiation.This includes every measuring instrument ever invented, then and now! The presence of nonelectromagnetic forces doesn't change things, because some distortion remains as long as any electromagnetic force is used.
Furthermore, there is a contradiction if both Principia and Maxwell's equations are used. The third law of motion is written in present tense. So Principia implies that the action and the reaction have to occur simultaneously. Maxwell's equations implies a delay in electromagnetic forces consistent with the speed of light. So they both can't be true under all conditions. Either Principia or Maxwell's equations or both are a little bit wrong.
H. A. Lorentz did a complete analysis on how the electromagnetic stress of motion would effect rulers and clocks. It turned out that the rulers and clocks would behave just as Einstein described in special relativity.
However, I will just write down the names of these articles where H. A. Lorentz put down his theory of electrons.
4) "Electromagnetic phenomena in a system moving with any velocity smaller than that of light," by Hendrik Lorentz. Proceedings of the Royal Netherlands Academy of Arts and Sciences, 809-831 (1904).
5) "The Theory of Electrons" by Hendrik Lorentz (1915).
There are copies of 4 and 5 free on the Internet. Someone on this forum listed them.
Lorentz only varied from Principia in one regard. He assumed that the forces holding things together have a minimum delay given by the speed of light. It is this delay that makes the measuring instruments act in a "relativistic" way.
In any case, your conundrum is resolved when you consider the stress in a measuring instrument caused by the motion of the measuring instrument. The atomic components of clocks and rulers interact with each other to distort the measurements in a way consistent with relativity.
If all forces are Lorentz invariant, then the changes in the dynamics of the particles that comprise a measuring instrument causes the measurements to determine the same electromagnetic constants in any frame. Furthermore, the speed of light delay in the forces makes it impossible to determine which of the frames is an ether frame.
Last edited: