Re: [Phys-l] three central misconceptions about relativity

[Moses Fayngold <moshfarlan@yahoo.com>]

  The so-called "relativistic paradoxes" are not within Relativity itself. They are merely the conflicts between the relativistic effects and our everyday life intuition (and the same is true about Quantum-Mechanical paradoxes). Such conflicts usually do not appear in Classical Mechanics or Classical Electrodynamics simply because the latter are mostly within our classical intuition. It is hard to believe that some professional physicists do not understand this simple distinction.
  I disagree with Hugh Haskell and John Denker that avoiding paradoxes makes the good teaching of Relativity. In my view, to shove the known and widely spread misconceptions under the rug is the worst possible approach to teaching. And vice versa, srutinizing and resolving the paradoxes shows Relativity as the vibrant science about the real world rather than just an elegant but highly abstract intellectual curiosity. The space-time geometry is beautiful, but it is precisely the length contraction and time dilation effects that make this geometry. To deny the reality of these effects or relativistic mass confirmed by overwhelming scientific evidence makes as much sense as denying the existence of life in teaching Molecular Genetics. 
  Also, I do not see anything horrible in using the terms like 3-velocity or 3-force as long as we alert the students to possible ambiguities associated with the use of language. We measure 3-velocity and 3-force, not 4-velocity and 4-force. Unfortunately, any term may turn out to be misleading. The "reduced velocity" suggested by John Denker, may lead students to think that there is something abstract but really valuable named 4-velocity, and what we actually measure is just 4-velocity with reduced value. 
 
Moses Fayngold,
NJIT       


________________________________
From: John Denker <jsd@av8n.com>
To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
Sent: Thursday, October 13, 2011 4:31 PM
Subject: [Phys-l] three central misconceptions about relativity

On 09/28/2011 02:10 PM, Hugh Haskell wrote:
> I agree with JD that one should never raise misconceptions ... in class. If 
> you bring up a common preconception then it is more likely to imprint 
> on other students and reinforce in those already suffering from it. 
> As John says, its best to teach the correct conceptions and ignore 
> the incorrect ones--until they are raised by a student.

I think just about everybody would agree with that principle.

Alas, the practice does not always follow the principle.

In particular, in some quarters it is fashionable to teach
relativity by introducing "paradoxes" to be analyzed.  This
makes absolutely no sense to me.
-- We don't introduce mechanics in terms of mechanical
  paradoxes.
-- We don't introduce electrostatics in terms of electrostatic
  paradoxes.
-- et cetera ...

... so why why why do some folks cook up relativity misconceptions
and foist them on students?  I'm talking about problems involving
poles in barns, and things like that.  The statement of the problem
seems designed to teach people to think about relativity the wrong
way.  That is, if you think about relativity the right way, you would
never dream of formulating the problem that way.  It's like asking
about a flying unicorn ten miles north of the north pole.


I know it is bad manners to speculate about other people's motives.
Once upon a time I suspected some people were just bragging about
how tough they were and how smart they were, because they knew
about this incredibly weird and paradoxical theory.  However, I
don't think that anymore.  I think they just have no clue about
how relativity really works.

The laws of physics -- when properly stated -- do not contain any
paradoxes, so far as we know.  In contrast, if you mis-state the
laws, you can cook up all sorts of paradoxes ... but why would
you want to?

As I see it, special relativity is not paradoxical.  It's not even
weird.  It's just the geometry and trigonometry of spacetime.

IMHO it is a tremendous mistake to portray special relativity as
weird and paradoxical.  It is a disservice to students.

We can agree that contracted rulers are weird, and dilated clocks
are weird, and velocity-dependent mass is weird ... but those
things are not part of relativity, and haven't been for more than
100 years.  They are as dead as phlogiston.

As Thomas Kuhn pointed out, phlogiston was not a dumb idea in its
day.  However, its day ended a long time ago.



That brings us to another misconception, namely the idea that the
development of special relativity began and ended with Einstein's
1905 paper.

Every so often, somebody casually mentions Galileo's principle
of relativity, and some nitwit corrects him: "You meant Einstein's
principle of relativity".  That really makes my hair stand on end.
The fact is, Galileo enunciated the principle of relativity with
magnificent clarity in 1632.  That gives him 273 years of priority.
I'm also quite sure that Einstein wasn't the first to discuss
Lorentz contractions.  (For that matter, Lorentz wasn't either.)

As of 1901, Poincaré and Lorentz knew more about relativity than 
Galileo ever did. As of 1905, Einstein knew more about relativity 
than Poincaré and Lorentz did. As of 1908, Minkowski knew more 
about relativity than Einstein did. This is how science works. 
Newton said he stood on the shoulders of giants. 

There are a lot of people (including some on this list) who
advocate using the history of science to motivate and organize
the teaching of science.  They say history is important.  Well,
I say history is sufficiently important that when you tell the 
story, you should tell what really happened, not some fractured 
fairy tale.

This has direct pedagogical consequences:  Just because Einstein
used contracted rulers and dilated clocks in 1905 doesn't mean
that is a good idea.  In fact it is a terrible idea.  Every minute
spent learning about such things is at least two minutes wasted,
because you will have to unlearn it before you can achieve any
real understanding of relativity.

This also has consequences that extend outside the classroom
... consequences that are (for most people) far more serious
than anything having to do with relativity per se.  Let me
explain:

I have spent many years as a manager.  This includes helping to
set up collaborations.  As you might imagine, it is hard to get
a not-so-famous person to collaborate with a famous person, if
the expectation is that no matter what happens, the famous
person will get all the credit.  This is a big problem, and it
hurts the big shots as well as the little shots, and hurts the
organization as a whole, by making it hard to set up collaborations.

Any big-shot with any sense will be ultra-scrupulous to give
credit to collaborators, but it's never enough.  I have personally
experienced this problem from the big-shot point of view, from
the little-shot point of view, and from the bystander / manager
point of view.  I guarantee you, it is nasty all around.

This is really a Big Deal for me.  When I invite somebody to
give a colloquium on the subject of quasars, you can be sure
I invite Jocelyn Bell.

I beg all of you, please, don't mess this up.  Most people don't 
really need to know much about special relativity, but they do
need to know how to collaborate.

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

Summary:

Galileo originated the principle of relativity.  Minkowski
originated the idea of spacetime.

Special relativity is not weird or paradoxical.  Using paradoxes
to explain relativity is a Bad Idea.

Special relativity is the geometry and trigonometry of spacetime.
Contracted rulers are a Bad Idea.  Dilated clocks are a Bad Idea.
Velocity-dependent mass is a Bad Idea.
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