"Original Ideas"

Albro Swift wrote:
 The equivalence of mass and energy emerges very naturally from 
 the principle of relativity, and forms a coherent whole, especially 
 with the general theory, but in an ether theory the equivalence of 
 mass and energy is a distinct anomaly.

Alan Pendleton wrote:
 One solution that has been proposed ... is that mass is energy 
 traveling around in a closed loop, while the energy we see as 
 energy is traveling in a straight line. I don�t claim that this 
 is the way things really are; I use it as an example of an 
 original idea.

An original idea?  I assume you mean original with every freshman
physics student who ever lived... but never mind.  The point at 
issue was the heuristic value of relativity in *suggesting* the
equivalence of mass and energy in the first place, not merely 
being able to accommodate it by some "original idea".   One can 
take ANY theory and augment it with some particular mechanistic 
model of matter and energy that yields mass-energy transmutability
with the c^2 proportionality, but the point is that within the
relativistic program this striking result emerges independently 
of any particular model of matter, and it arises as a natural
consequence, without any additional ad hoc assumptions.  In fact,
it would be difficult for relativity to survive if the relation
between mass and energy were anything else.  The relativity 
principle allows very few "degrees of freedom" is things like 
this, which explains why it was so unusually effective at leading 
to new predictions and theoretical outlooks.  And of course, even
though such a rigid theory stands exposed on every front to
experimental falsification, its predictions have been consistently
corroborated by experiment.  Thus, the point of the text to which 
you responded is that mass-energy equivalence stands as an example 
of the immense heuristic power of the relativity principle, as
emphasized by Lorentz, Planck, and others.


Alan Pendleton wrote:
 The fact that you personally cannot come up with an elegant aether 
 theory does not mean that no one ever will.

That "fact" is not in evidence, but in any case, we were not
comparing current relativity theory with some unspecified future
theory, we were comparing relativity with its past and present
rivals, and explaining why the relativity principle has come to
be so widely accepted, and why it is so highly valued.


Albro Swift wrote:
 Likewise, the equivalence between inertial and gravitational mass,
 ... in perfect accord with the principles of general relativity, 
 must appear simply as an accident in an ether theory, or any other 
 theory with an absolute time axis.

Alan Pendleton wrote:
It is currently unexplained by aether theory. It is also unexplained
by GR; it is assumed as a postulate by GR. 

Once again, I fear the point has eluded you.  The equivalence of
inertial and gravitational mass is taken by general relativity not
just as some incidental thing to be explained by some "original idea"
that is logically independent of the basic theory itself, but rather
it is incorporated as a fundamental and extremely rigid principle of
the theory.  The wonder is that from this principle flows predictions
about the rate of energy loss of rotating binary star systems via
gravitational waves, and those predictions have been supported by
observations.  Thus it is another example of the heuristic power
of the principles that Einstein selected and on which the theory
of relativity is based.

No one questions that you can take any arbitrary theory and dream 
up some ways of imposing inertia-gravity equivalence (either 
exact or approximate) and mass-energy equivalence (either exact 
or approximate), but what we seek in an observationally viable
physical theory is unity, coherence, and heuristic power.  These
are all exhibited by the theories that Einstein based on the
relativity principle and the equivalence principle.  It is far
from clear that any number of "original ideas" tacked on to an
ether theory to make it mimic relativity will result in a 
theoretical framework that surpasses relativity in conceptual 
unity, coherence, and heuristic power.


Alan Pendleton wrote:
 There is a long list of experiments which have demonstrated a violation 
 of Lorentz covariance. The observed violations are always explained 
 away somehow...

The performance and analysis of experiments and experimental results
requires a mature judgement.  As Poincare (or maybe it was Bryan
Wallace) said, it is equally convenient to believe everything or to
doubt everything, because both relieve us of the requirement to think.

When performing experiments we are seeking to determine the exact
behavior of objects in perfectly defined circumstances, trying to
separate the world into distinct operational phenomena, but in fact
it is very difficult (viz, impossible) to establish perfectly defined
circumstances, and our instruments are also physical entities that 
are hard to perfectly isolate from extraneous influences.  Also, we
can make mistakes.  This is why judegement is required when evaluating
experimental results.  On the one hand, we don't want to discount a
small discrepancy that could be a real systematic effect (e.g., the
slight errors in the orbit of Mars noted by Kepler, and maybe a
slight "background noise" in microwave receivers, etc), but on the
other hand we cannot deny that noise and extraneous results WILL
occur from time to time, so if we allow any such result to invalidate
our current hypothesis we will never be able to maintain ANY
hypothesis.  Thus we need a set of criteria, including such things
as "repeatability", with which to assess the weight of available
evidence at any given time.

Needless to say, anyone who found an experiment that repeatably
gave significant results in clear conflict with the relativity
principle would be awarded a Nobel prize, which I believe carries 
with it a considerable cash stipend, and is also a babe magnet.  
Thus, we certainly need not worry that there is insufficient
motivation for experimenters to detect such a phenomenon.  I 
stand by my statement: There are no (known) physical phenomena 
that demonstrate a violation of Lorentz covariance.


Alan Pendleton wrote:
 Why then, do I still think that GR is, as one writer whose name 
 escapes me memorably put it, "eyewash"? Because it lacks another 
 criterion high on my list: computational simplicity.

That's a highly anthropocentric criterion, and of course it's
inherently subjective.  What's computationally simple for you may
not be simple for someone else.  For example, if a chimp applied
your criterion he would be limiting himself to a class of theories
that are probably not very comprehensive.  From our perspective, his
knowledge of the universe is limited by his mental capacity for
handling "computationally difficult" ideas.  The more complexity
and subtlety his brain can handle, the more comprehensive can be
his understanding.

Now, it's conceivable that the universe has some finite level of
"computational depth", and that we (humans) have already surpassed 
it in our mental abilities, so that we're now actually in danger of
making theories that are more computationally difficult than they 
need to be for a full representation of "what's going on".  But I 
seriously doubt it.

Nevertheless, this is an interesting cultural point.  As people
continue to strive to develop and refine the most comprehensive
physical theories their brains can handle, it seems inevitable that
the "state of the art" will reside some place near the upper limit
of the capacity of the smartest individuals in the population, 
which, due to inveitable variations, is presumably ABOVE the 
upper limit of the majority of the population.  In such a situation,
what is the majority of the population to do?  We might actually
PREFER a theory that is LESS comprehensive than the "state of the
art" (according to the experts), simply because we can understand 
it, and it is "computationally simple".  

Note that I'm not just referring here to a practical preference,
e.g., using Newtonian formulas rather than GR because they're
computationally simpler, I'm saying that those of us who don't 
(can't) understand GR would actually prefer to think that GR is 
WRONG, and that the theory we can understand and compute with is
RIGHT.  This could lead to all sorts of cultural lines being 
drawn, and endless disputes between "elitist defenders of ivory 
tower nonsense" versus "crackpot laypersons who couldn't find 
their butts with both hands", and so on.