Re: [Phys-l] how to prove relativity

[John Denker <jsd@av8n.com>]

On 05/28/2010 10:15 AM, Paul Lulai wrote in part:

> > The teacher and his wife (PhD in experimental psychology) have been
> > going back and forth for years about the 
> > idea of special relativity, specifically time dilation.  She insists 
> > that the ideas produced are ridiculous, can never be tested, etc.  
> > When I point out the experimental evidence such as muons in the 
> > atmosphere, difference in clocks moving at different speeds, and the 
> > fact that GPS uses special relativity to help pinpoint location has 
> > not helped to persuade her.  Does anyone know of any experiments that 
> > could be easily interpreted by a non- physics person (She has never 
> > taken a physics course and I have never taken a psychology course) to
> help convince her?
> > And finally are there any good definitions for time out there?

Two answers;  two rather different answers:

1) It has been a dictum in philosophy for 2300 years to "save the
phenomena".  Or as D.P. Moynihan put it more recently, "Everybody
is entitled to their own opinions, but not their own facts."

I don't know if this applies to experimental psychology, but it
should.

The fact is, if you carry a clock around the world, it comes back
with a shifted time, shifted relative to a stay-at-home clock.
If somebody tries to argue that the clock is in some way "broken", 
then carry multiple clocks, all based on different physical principles, 
and observe that they are all shifted by the same amount.  Lucy, you
have some 'splainin to do!  I don't believe in coincidences like this.  
Also, the clocks are shifted differently for eastbound trips and 
westbound trips.  There is nothing special about "atomic" clocks;
all sufficiently-accurate clocks behave the same way.  So the claim 
that the clocks are merely "broken" is indefensible.  The clocks 
are trying to tell you something fundamental about the geometry 
and trigonometry of spacetime.

2) On the other hand, let us now pass from observable phenomena
to the question of how to model the observations, and how to 
explain them.  This involves pedagogy, and indeed psychology.  
Facts are facts, but the choice of model is a matter of opinion, 
and opinions may differ.

Now, for more than 100 years, enlightened opinion has *not*
favored the idea of "time dilation".  Surely we agree that
rotating an ordinary ruler does not change "the" length (i.e.
proper length) of the ruler ... although it may change the
length of the ruler's shadow, or the length of the ruler's
projection along this-or-that line of sight.  Again, it has
been understood for 2300 years that the shadow of a thing
is not the same as the thing itself, and sometimes you can
infer the existence of a thing even if you have seen only
the shadow, not the thing itself.

By the same token, for more than 100 years, enlightened 
opinion has held that boosting a clock does not change
"the" rate (i.e. proper rate) of the clock ... although
it may change the projection of the rate along this-or-that
frame of reference.  In other words, the idea of "time
dilation" is a pre-spacetime idea whose usefulness expired 
more than 100 years ago.  It is as dead as phlogiston.

So if somebody says there is no such thing as time 
dilation, and that observing clocks and muons does not 
suffice to "prove" time dilation, I agree with them!  
This is discussed in detail at
  http://www.av8n.com/physics/odometer.pdf

  Note that I would not use that document to _introduce_
  anyone to the topic of relativity, because it spends
  far too much time contrasting the wrong approach with
  the right approach.  In an introductory situation, I
  would avoid like the plague any mention of time dilation,
  length contraction, or non-constant mass.

It is an interesting behavioral question as to why people
who really ought to know better keep putting long-dead
ideas into textbooks.  Maybe a good experimental psychologist
could help us answer this question.