🚀 go-pugleaf

On Tue, 25 Dec 2007 02:29:16 -0800 (PST), Pentcho Valev
<pvalev@yahoo.com> wrote:

>One can never know how exactly silly Einsteinans draw their
>conclusions but at least one can guess. So this Eric Baird may have
>decided to get rid of special relativity after reading the following
>two texts:
>
>http://www.pitt.edu/~jdnorton/Goodies/rel_of_sim/index.html
>John Norton: "But an emission theory is precluded in special
>relativity by the part of the light postulate that asserts that the
>velocity of light is independent of the velocity of the emitter."
>
>http://press.princeton.edu/chapters/i6272.html
>John Stachel: "Not only is the theory [of relativity] COMPATIBLE WITH
>AN EMISSION THEORY OF RADIATION, since it implies that the velocity of
>light is always the same relative to its source; the theory also
>requires that radiation transfer mass between an emitter and an
>absorber, reinforcing Einstein's light quantum hypothesis that
>radiation manifests a particulate structure under certain
>circumstances."
>
>Eric Baird's possible conclusion: "Master John Norton clearly says the
>emission theory is incompatible with special relativity whereas Master
>John Stachel says it is compatible with "the theory". The only
>solution to the problem is to abandon special relativity and continue
>to worship, as fiercely as possible, general relativity."
>
>Pentcho Valev
>pvalev@yahoo.com


No ... since my name's being brought up here, I should point out that
I'm not aware of having been influenced by either Stachel or Norton.
The line of reasoning above doesn't really represent my position.

:Me and GR: 
I //do// like the idea of a theory that corresponds to the most
general definition possible of the general principle of relativity ...
but I think that parts of our current implementation of a general
theory suck, and suck badly. I think that some of our textbook GR
definitions suck, too. I certainly don't worship our current
//implementation// of a general theory, I think that if we went back
and redesigned the thing from scratch, it could potentially be pretty
damned good, but I'm not especially fond of what we have right now. 

:Me and ET: 
My attitude to standard emission theory isn't too dissimilar to
Einstein's: I think that in some ways the historical implementation of
emission theory was actually a lot better than is generally
recognised, but it had a whopping great problem in that it wasn't
obviously compatible with wave theory. "Simple" emission theory seemed
to suggest that different signals from differently-moving sources
could travel along the same path at the same time with different
speeds, which made wave-particle duality a much more difficult thing
to implement.   

Emission theory was "relativistic" in the sense that there was no
absolute preferred frame for the speed of light, and it worked well at
the "emitter end", but it created problems at the "observer end". 
These difficulties manifested themselves in three classes of effect
that we might expect to have seen according to emission theory, but
which people didn't seem to see in practice: 

::EFFECT #1::
A star's atmosphere consists of particles moving with different
velocities. If atmospheric particles that were originally moving
towards us gave off light that propagated across the intervening
distance faster than those from particles originally moving away from
us, then, since the first category of light should appear blueshifted
by the approach velocity of the emitting particle, and the other light
should be redshifted by recession velocity, then ... if the star was
also moving directly across our field of vision, we'd probably expect
to see the pattern of "faster" and "slower" light arriving at our
location to make moving stars appear to show a sort of "rainbow"
streaking effect. 

::EFFECT #2::
Similarly, if these differently-Doppler-shifted components moved at
different speeds, we might expect to see coloured fringes during an
eclipse. Newton seems to have asked astronomers about this effect, and
been told that it hadn't been noticed.

::EFFECT #3::
In simple emission theory, if light emitted by an approaching star
moved through space towards us faster than that from a receding star,
then, when we observed a double-star system whose rotation plane was
at an angle to us, we might expect to see apparent timing
irregularities in the orbit, with magnitudes that would be expected to
scale with distance. At a certain distance, we might see the images of
both stars seeming to pass through each other, or the "fast" and
"slow" light thrown out by a single star at different points in its
orbit might arrive at our location at the same time, making the star
appear to be in two places at once. We might expect this effect to
cause our view of distant double-star systems to be significantly
scrambled, Willem deSitter described a survey of systems (in ~1913)
and pointed out that no "significant" effect of this sort had been
seen.

==========

:SALVAGING EMISSION THEORY?
On a more conciliatory note, I do think that an updated //form// of
emission theory may well be workable, if we invoke gravitomagnetic
arguments as a way of explaining a compensating mechanism for the
local regulation of lightspeeds. 

A velocity-equivalent gravitomagnetic effect would seem to fix
emission-theory's "wave" problem, and also fix the three experimental
issues above.
In that sort of "revised" emission theory, light would initially be
thrown off from an emitter at c(EMITTER), but as it left the immediate
influence of the emitting body, the influence of that body on the
signal's speed would quickly fade, and as it approached the observer,
the increasing gravitomagnetic influence of the observing body's mass
would ensure that the light finally arrived with a speed of
c(observer). This would bypass deSitter's disproof of emission theory,
because the influence of the star's velocity on the speed of its
signals would then only be "significant" over a vanishingly-short
section of the signal's total journey.

If we were prepared to make make that sort of "gravitomagnetic"
modification to emission theory, the "revised" theory would seem to be
immune to the usual objections to ET. However, some people would then
feel that the suggested lightspeed-regulation mechanism is just an
arbitrary "fix" unless we could also come up with a wider set of
arguments justifying why this sort of regulatory gravitomagnetic
mechanism ought to be there. We'd nominally have an emission theory
superimposed on a "velocity-warped" lightbeam metric, but the bulk of
the final theory would then have to deal with the way that the
gravitomagnetic effects operate, rather than on how simple signals
propagate through that metric. 

To still be calling it "emission theory" at that point might be a bit
unhelpful. 

====

:SR's SECOND POSTULATE:
I do think that there are some general arguments in favour of the sort
of lightspeed-regulation effect mentioned above, but most relativity
people probably won't like them, because these arguments also tend to
undermine the geometrical basis of the special theory. 

Special relativity's second postulate is //nominally// that all legal
inertial observers are allowed to claim that the speed of light is
constant w.r.t. them ...
... but the way that SR //implements// lightspeed constancy is more
specific ... it presumes that lightspeed is //globally// constant for
the theory's observers, and that the lightbeam-geometry of a region
containing a collection of differently-moving bodies is therefore
necessarily "flat". That rules out the alternative possibility of a
relativistic light-dragging model. Special relativity's use of
language (and its math) depends on the idea that the sort of
complicating gravitomagnetic effects above (which would turn the
exercise into a curved-space or curved-spacetime problem) don't exist.
SR people sometimes say that we "know" that these variations don't
exist, because we "know" that the speed of light is constant, and that
this is supported by experiment ... 
... but actually, experiments such as Fizeau's indicate that
measurable short-range lightspeed-dependencies do seem to exist in
real life, between the speed of light and the speed of the emitter,
observer and any other masses in the neighbourhood. 

These effects seem to be short-range. They show up in signals sent
between moving conglomerations of atoms, and in these situations we
tend to respond, not by saying that SR's lightspeed model is basically
wrong, but by saying that that special relativity doesn't claim
validity for particulate-matter effects. Unfortunately, all observers
and objects in the real world would seem to be made of particulate
matter, so SR's second postulate, in the way that SR applies it, would
only seem to be truly valid for "unphysical" bodies whose behaviour
doesn't actually correspond to the behaviour of real bodies in our own
universe. 

IMO, SR may yet turn out to be the correct answer to the wrong
question. If we accept that the moving matter does seem to interact
with light, and we interpret SR's second postulate to mean that the
speed of light only has to be //locally// constant, then the result
isn't necessarily special relativity. 

If we drop the "traditional" idea of global c-constancy and apply a
more GR-style concept of local c-constancy in its place, then we still
seem to be able to arrive at a GR-like geometrical theory of
gravitation, but it becomes quite difficult to difficult to justify
saying that that theory ought to reduce to special relativity.

If real particles are expected to have mass and energy, and are
expected to be associated with curvature, then it's more difficult to
justify the existence of a zero-curvature solution as real physics. 

Special relativity might conceivably turn out to be a null solution -
mathematically pretty, but not guaranteed to be foundation theory.

=Erk= (Eric Baird)
www.relativitybook.com

:   " But why would anyone be interested in getting exact solutions 
:    of such an ephemeral set of equations? "
:  - Einstein, on his own general theory of relativity