[Phys-L] history of relativity

[John Denker <jsd@av8n.com>]

On 11/18/2015 03:57 PM, Jeffrey Schnick wrote:

> http://www.quantum-field-theory.net/einstein-didnt-say/
>  Is that page a bunch of nonsense?

That page says some true things that aren't very important,
plus some untrue things that aren't very important.  The title
of the article is "EINSTEIN DIDN'T SAY THAT" which covers a
lot of ground.  You could write an article "Einstein didn't
say X" every day for a year, with a different "X" each time.
Each one would be true, but I'm not sure that would be the
best use of your time.

Rather than picking on the cited article in particular, let's
just write down some actual factual facts.  You should have 
no trouble verifying the following:

1638 -- Galileo:  
          The principle of relativity.
          Reference frames.
          Physics is invariant with respect to change of reference
          frame with uniform straight-line motion.
          Clear and unmistakable exposition.
          Remains correct and unchanged to this day.

1862 -- Maxwell equations:
          Privileged role for the speed of light.
          Equations are consistent with special relativity,
          i.e. Lorentz covariant, although nobody understood
          what this meant at the time.

1887 -- Michelson and Morley:  No "ether drift".
          Speed of light the same in all directions.

1887 onwards -- Discussions involving Voigt, FitzGerald, Larmor,
          Lorentz, Heaviside, and others.

1889 -- FitzGerald contraction.
          Salvages consistency between Michelson, Morely,
          Maxwell, and Galileo.

1892 -- Lorentz transformations.
          More detailed than the 1889 FitzGerald version.

Early 1905 -- Poincaré shows that the transformations form a
          closed group, which he names the Lorentz group.
          It has some interesting properties;  in particular,
          rotations are a subgroup, but boosts are not.  The
          commutator of two boosts is a rotation.

June 1905 -- Einstein reverses the argument.  Previously the
          constancy of the speed of light was a consequence of
          experiment and a consequence of the FitzGerald-Lorentz
          transformation.  Now he showed that the transformations
          could be derived as a consequence of the constancy of
          the speed of light.

1908 -- Minkowski:  Spacetime.
          The four-dimensional continuum.
          Non-Euclidean geometry.
          Four-vectors.
          Spacetime diagrams.
          Constant speed of light returns to being a consequence of
          the theory, not a postulate.

          Einstein initially calls it "überflüssige Gelehrsamkeit"
          (superfluous learnedness).  However, before long he gets
          with the program and bases all of his later work on it.

1915 -- Einstein: General relativity.
          Accelerated frames; principle of equivalence.
          Relativistic gravitation.

===========================================

At this point you should be asking, what did Einstein actually contribute
to the theory of special relativity?  As I see it, not much.  There was
a period of 3 years out of the last 375 years where Einstein's approach
to SR was the most elegant.  As of today, everything useful we know about
SR was done by somebody other than Einstein.  His idea of /postulating/
c=const was an original and clever idea, but not state-of-the-art in
the post-1908 world.

Meanwhile, practically everybody you meet "knows for sure" that SR is 
/Einstein's/ theory of relativity.  It's as if Galileo, FitzGerald, 
Minkowski, and a whole bunch of other guys never existed.  It's insane.

As Thomas Kuhn and others have pointed out, most physicists are lousy
historians.

This is extra-insane because if you grab some guy who has been out of
school for a few years and ask him what he remembers from high-school
and/or college physics, mostly what he remembers are the historical
anecdotes.  (Sometimes he tells you that "mass is equal to force times
uhhh, errr, something-or-other" ... but usually not even that.)  If he
remembers anything at all, it may be the story about Galileo dropping 
stuff from the leaning tower of Pisa.  Nevermind that the guy cannot 
explain why that's important, and nevermind that there's not one iota
of historical evidence for that story ... that's what the guy remembers.
Either that or some similar anecdote.

I find it odd that what the course actually teaches usually isn't what
it claims to be teaching.