Re: [Phys-l] Modern Physics

[John Denker <jsd@av8n.com>]

On 03/11/2007 05:24 PM, Krishna Chowdary wrote:

> If you're going for a separate text on Special Relativity, French is ok.
> But I _have_ to suggest that you check out Spacetime Physics, by Taylor
> (same one as above) and Wheeler.  I don't think you'll be disappointed.

Amen, brother.

Actually, I might go even farther in the same direction.  I
reckon the vast majority of the folks on this list teach a
course that touches on relativity at some point in the year,
and would benefit from reading and occasionally re-reading
Taylor & Wheeler.

Going even yet farther, in all courses (not just "modern physics"
courses) I would recommend:
 a) As the main text, choose something that takes the "spacetime"
  approach to relativity, or failing that,
 b) supplement with something that does.


There is a nice survey of the pedagogical situation by Gary Oas:
  "On the abuse and use of relativistic mass"
  http://arxiv.org/PS_cache/physics/pdf/0504/0504110.pdf

which (among other things) lists a number of texts and shows
whether they manage to avoid "relativistic mass".  Most of
the "modern physics" texts do manage ... and the other texts
seem to be drifting in the right direction.

However, "relativistic mass" isn't the whole problem;  we must
also consider FitzGerald-Lorentz contracted "length" and dilated
"time" which are IMHO just as archaic and unenlightened as
"relativistic mass".  Alas I don't know of any work (comparable
to Oas) that surveys textbooks for their treatment of these issues.

Help stomp out contracted rulers!  Help stomp out dilated clocks!
Help stomp out velocity-dependent mass!

Next year is the 100th anniversary of Minkowski's epochal work,
"Raum und Zeit".  If you're going to teach "modern physics" in
2008, there can hardly be anything more appropriate than to
teach relativity the ways the pros do it ... *not* the way the
gen-ed textbooks do it.

Help stomp out contracted rulers!  Help stomp out dilated clocks!
Help stomp out velocity-dependent mass!

> ... looking for texts that are good *and* freely available,

Well, the following aren't texts, let alone "good" texts, but they
are freely available and stake out a /modern/ (i.e. post-1908)
view of relativity, in terms of invariant rulers, invariant clocks,
and invariant mass:
  http://www.av8n.com/physics/odometer.pdf
  http://www.av8n.com/physics/spacetime-trig.pdf
  http://www.av8n.com/physics/spacetime-acceleration.htm


===========================
Here's an amusing spacetime exercise that I just now added to my
"acceleration in spacetime" page:

Suppose Joe sets up an electric field that is uniform in the lab
frame, uniform over all times and places of interest. Let the electric
field vector point in the x1 direction. Let Moe be comoving with a
free particle of mass m and charge q that is initially at rest and
thereafter accelerates under the influence of the field.

    Exercise: Find the proper acceleration as a function of time.

    Note: As usual, there are multiple ways of solving the problem
          … some of them more elegant than others.

    Huge hint: There is a way to solve this problem in your head.

For details, including two methods of solution, see
  http://www.av8n.com/physics/spacetime-acceleration.htm#sec-lorentz

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

There is of course more to "modern physics" than just spacetime.
There were multiple revolutions in physics that took place around
the turn of the last century:
 -- radioactivity
 -- statistical mechanics, and an atomistic description of matter
 -- special relativity and spacetime
 -- superconductivity
 -- general relativity
 -- quantum mechanics
... and then there's the even more-modern stuff, including
 -- nuclear reactions (reactors, bombs, stars, ...)
 -- elementary particles
 -- transistors
 -- lasers
 -- etc. etc.

This is of course waaay too much to cover in a one-year "modern
physics" course.  You could spend an entire year trying to make
sense of statistical thermodynamics.  And beware that there are
many textbooks out there just loaded with misconceptions about
thermodynamics.  Far and away the best book I've seen is Kittel
& Kroemer, _Thermal Physics_.  Indeed it's the only thermo book
I don't find absolutely infuriating ... and even so it's not
perfect (e.g. abuse of inexact differentials).  Every teacher
should read K&K, if only to see just how different it is from
the usual textbook presentation.  Also, here's my attempt to do
things right:
  http://www.av8n.com/physics/thermo-laws.htm

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

When it comes to quantum mechanics, almost no matter what text is
adopted, it is common to supplement it with Feynman volume III.
Presumably only physics majors are taking the modern physics course,
and all physics majors should own a copy of Feynman, so there's no
downside to requiring it.  The upside is tremendous:  it's elegant,
it's incisive, it's beautifully written....


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

Finally, not just the choice of text but also the whole syllabus
and the whole character of the course depends on whether the
"mathematical methods of physics" course is a prerequisite,
corequisite, or neither.

In a perfect world, I would like to see it be a corequisite,
since the math can be awfully dry in the absence of physical
applications ... and the physics can be awfully mysterious in
the absence of the proper mathematical foundations.

   I've seen the corequisite idea used to great effect at the
   freshman level, where the calculus course was beautifully
   dovetailed with the calculus-based physics course.

   OTOH I've also seen it fail miserably, where neither the
   physics professor and the math professor would condescend to
   cover certain topics that didn't interest them.  They did
   the old after-you-my-dear-Alphonse you-first-my-dear-Gaston
   schtick.

If it's neither a prerequisite nor a corequisite, then you need
to go shopping for *two* texts.  And maybe for a psychiatrist.