Re: [Phys-l] velocity-dependent mass (or not)

[John Denker <jsd@av8n.com>]

On 06/28/2009 01:52 PM, Richard Tarara wrote in part:

> .... I really don't think we are going to give up moving clocks run 
> slow, moving lengths contract, and moving mass increases in our intro books 
> for space-time geometry.  

OK, that's an opinion and a prediction.  Everybody is entitled
to their own opinion.

But I was hoping that the agenda here might aim higher, namely
to persuade people, one way or the other, which way things 
*should* go.  As the saying goes, we are not potted plants.
I like to think we have some say in what happens.

> Of course, my vote only counts when I buy the textbooks!  ;-)

Actually it counts for a lot more than that.  If you adopt
a given book for your course, many copies get bought, with 
other people's money.

> Many of those books are for the seriously math 
> challenged students (ones who can't figure the Carnot Efficiency of an ideal 
> heat engine running between 600 and 300 Kelvin or the amount of work that a 
> 1000 J input produces in a 25% efficient engine).   The 'standard test book' 
> descriptions of the phenomena seem to function OK without somehow totally 
> distorting whatever the 'reality' is--at least many think so.

Have you tried it the other way?  The math required for the
spacetime geometry approach is *less* demanding than the
math involved for the contraction/dilation approach.  And
unless your sights are set so low that rote regurgitation
is the only goal, there is a conceptual layer that comes
before any of the math, and for the spacetime approach that 
is incomparably less challenging.  For crying out loud, the
"standard text book" treats relativity as a collection of
paradoxes!  It emphasizes how weird and counterintuitive
relativity is.  Every such paradox should be a red flag to
the teacher, a warning that the subject is not being presented
properly.  Why tolerate a book that has red flags sticking
out all over the place?

Some guy named Kip once said to me, paradoxes arise from not
formulating the problem correctly.  The goal is to get to the
point where you see things so clearly and express things so
clearly that you cannot even utter a paradox.

On the opposite side of the same coin, any class time spent on
the spacetime approach to relativity reinforces and deepens
the students' understanding of the geometry and trigonometry
of ordinary 3-space, their understanding of vectors, et cetera.
This is important, since many of them will not have much direct 
use for relativity in their future lives.  Therefore the "street
value" of the coursework comes down to gee-whiz value and side
effects.  The gee-whiz value of spacetime (elegant) is *more* 
than the value of a bucket of paradoxes (ugly) ... and the side
effects (geometry, trigonometry, and vectors) are incomparably
more valuable.

The idea that time is the fourth dimension has been around since
1908, i.e. for 101 of the 104 years that relativity has existed.
It is so ingrained in our culture that it is taken for granted in
TV shows, even non-science-oriented shows like /Buffy/.  Why is
it not taken seriously in physics class?

See also next message.