[music-dsp][ot] DSP vs analog circuits

Yaakov Stein yaakov_s at Rad.co.il
Sun Nov 4 00:54:43 EST 2001


> The title of the landmark SR paper is "On The Electrodynamics Of Moving
Bodies".  
> It is not a consequence of Maxwell's equations that C is constant in all
moving frames of reference.  
> It was that assumption by Einstein that led to the proper view of
kinematics in part I of the
> paper and from that new kinematics to part II which established the proper
view of electrodynamics 
> which allowed Maxwell's equations to be the same in all moving frames of
reference.  

I would suggest going back and reading the paper again,
or reading Einstein's "The Meaning of Relativity" or any similar text.

Although I don't have the paper here before me
and it has been quite a few years since I have looked at it,
what I recall is the following.

Einstein shows that the Galilean transformation between reference frames
is incompatible with Maxwell's equations, and then goes on to find the
transformation between reference frames, namely the Lorentz transformation.
(He even calls the equations the Lorentz-Maxwell equations, 
I am not sure if he uses that term in the 1905 paper,
but he certainly does in other places).

The Lorentz transformation forces the speed of light to be the same in all
reference frames (or at least in STR terms all reference frames traveling
at constant velocity with respect to each other).
For example, if two light beams are traveling head on,
and one measures the other's speed,
it will find C and not 2C.

It is actually very easy to see that Maxwell infers that C is constant
(independent of frame) even without Einstein's paper.
The equations only admit wave solutions with speed C
(this is how Maxwell figured out that light is electromagnetic radiation!)
no matter what frame you are in.

BTW - concerning your first point that Einstein "must have known"
about Michelson-Morley, don't forget that he was a patent clerk
cut off from the mainstream academic world.
If he says he didn't know about it, I would tend to believe him.
It certainly would have strengthened his argument to mention the fact.
Don't forget that he had a hard time getting it published,
and that mentioning that it solved a major problem in physics
would have made it eagerly sort after.


Jonathan (Y) Stein   author at dspcsp.com


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