Re: Relativity: An orientation for beginners

On Jun 13, 2:41 pm, Uncle Ben <b...@xxxxxxxxxxx> wrote:
What kind of lunacy prompted Einstein to say
the speed of light from A to B is c-v,
the speed of light from B to A is c+v,
the "time" each way is the same?

-- John Parker, aka Androcles

This is a question that our friend Androcles has asked almost every
day for as many years as he has infected sci.physics.relativity.  I
have not examined every response he has received.  Responses to
Androcles have dwindled in these years, as wise folks have recognized
the uselessness of trying to reason with him.

But there is a steady stream of new people who come to the newsgroup
seeking some help in understanding the mysteries of relativity.

Recently a university professor from an Asian country joined us with
these questions (in perfect English).  I shall respect his privacy and
leave him nameless, but at first he was somewhat seduced by the
confidence and self-assurance of the critics here, including
Androcles, into believing that there is still -- after more than 100
years -- some controversy as to the truth, or at least utility, of
Special Relativity.

So I think it useful from time to time to answer the question
Androcles eternally poses.  In the process we may give the new person
some hint as to why some of us who work or have worked professionally
in physics are inclined to edit the question and to replace the word
"lunacy" with the word "genius."

One can understand the puzzlement that the question raises in the
innocent mind.  One needs to understand Einstein's motive in proposing
such concepts, a motive which arises from the history of physics. The
Nineteenth Century saw a revolution created by James Clerk Maxwell's
brilliant synthesis of a coherent theory of electromagnetism. Maxwell
unified the earlier findings of Coulomb and Ampere and others, and
adding a new term of his own, the
"displacement current" purely on the grounds of mathematical symmetry,
created the theory represented by "Maxwell's equations of
electrodynamics."

In so doing, Maxwell unified the theories of electricity, magnetism,
and optics. His equations implied the existence of electromagnetic
waves which travel at the same speed
known to be that of light in a vacuum.  Such genius was not to appear
again for the thirty years to the work of Einstein.

There was a problem, however. Electromagnetic theory involves a speed-
dependent force:  The force on a current-carrying wire near a
stationary magnetic exists only when the wire is moving. Moving with
respect to what?

And Maxwell implied a different phenomenon to explain what happens
when it is the magnet that is moving and not the wire!

And that is the least of the matter:

Using the conventional wisdom everyone grows up with about time and
space, Maxwell's discovery seemed to imply that the light waves are,
as are all waves with which we are familiar, waves in a medium.  Not
only was there a medium, but that medium miraculously pervades all
space, so as to bring the light of stars to us over unimaginable
distances.

And ultimately, such a medium would constitute a frame of reference
with respect to which motion could be measured absolutely, not
relatively as Galileo had taught. Wonderful!

Furthermore, we should be able to measure the speed of the Earth
through this universal medium.  We could place ourselves in absolute
space, with who knows what implications for science and perhaps
religion.

Michelson and Morley set up a sensitive interferometer in the basement
of Adelbert Hall at what is now Case-Western Reserve University to do
just that. They spent years searching for signs of our motion through
the light medium. The mystery was that they always found nothing -- no
motion. (Emission theory can explain this result, but it has fatal
problems in other ways.)

My job is finished. The reader has now been prepared to consult
Einstein's world-shaking paper of 1905 titled "On the electrodynamics
of moving bodies."

If one reads from the Introduction through only the first "Kinematical
Part," actually only its subsections 1 and 2, he will encounter the
reasoning behind the claims that so disturb Androcles and other
critics.  The English translations are good and the prose, simple and
elegant. The intelligent reader can  the grasp the unbelievable
audacity of Einstein, who resolves these problems only at the expense
of giving up ideas about space and time that we are deceived into
thinking we are born with. Give it time to sink in.

Hundreds of experiments later have persuaded reluctant professionals
in physics that Einstein was correct. No better competing theory has
been found. On its foundation Einstein went on to create his theory of
gravity, General Relativity, which also has not been surpassed on the
scale of the entire universe. At the level of the very small, SR has
supported the discovery of Quantum Electrodynamics, which is the most
precise predictor of fundamental constants of nature yet known.

The world has benefitted from Einstein's work and the work of his
successors by giving us nuclear power, high-energy particle
accelerators, GPS, and many other marvels.  We have also had to deal
with nuclear weapons.

A sceptic can be forgiven for not accepting Einstein's results.
Unless one has spent years studying experimental investigations by
hundreds of physicists, some of whom have been almost as sceptical as
Androcles, relativity is hard to swallow.

But the evidence is there, and when it is Nature that speaks to us,
the wise will listen.

-------------------

References:

1. Einstein's paper:

http://www.fourmilab.ch/etexts/einstein/specrel/www/

2. Experimental evidence for SR:

http://math.ucr.edu/hyome/baez/Relativity/SR/experiments.html

This massive collection is the work of Tom Roberts and collaborators.
Tom is one of the very few professionals to spend time on our
newsgroup to teach us more about relativity.

Uncle Ben

In my haste to post my paper, I mis-stated the motor principle.
The current-carrying wire near the magnet does NOT have to be moving
in order to experience a force. The charge in the wire is already
moving.

.

Relevant Pages

  • Corrected: Orientation for beginnners in relativity
    ... What kind of lunacy prompted Einstein to say ... This is a question that our friend Androcles has asked almost every ... as are all waves with which we are familiar, waves in a medium. ... Einstein's world-shaking paper of 1905 titled "On the electrodynamics ...
    (sci.physics.relativity)
  • Relativity: An orientation for beginners
    ... This is a question that our friend Androcles has asked almost every ... again for the thirty years to the work of Einstein. ... as are all waves with which we are familiar, waves in a medium. ... Einstein's world-shaking paper of 1905 titled "On the electrodynamics ...
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  • Re: SRs velocity addition -- ANY Experimental Evidence?
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  • Re: SRs velocity addition -- ANY Experimental Evidence?
    ... | "Androcles" wrote in message ... |> If the presence of a medium the signal will travel at its characteristic ... |> a truck) relative to the air and the police car is in park, ...
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  • Re: 1c+1c Closing Velocity...,answer to Henri Wilson
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    (sci.physics.relativity)