Re: "The Impossibility of Measuring the Velocity of Light"

Tom Roberts wrote:
>Jerry wrote:
>> a variety of experiments:
>> http://imaginary_nematode.home.comcast.net/
>
>There are A LOT more, referenced in the FAQ:
> http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

My comments relating to the website you quote are as follows. Maybe you
missed them the first, and the second time.
----------------------------------------------------------------------
Maxwell's ether theory predicted that c is the speed of light relative
to the ether. Because of this the speed of the source would not effect
it but the speed of the observer would. This latter prediction proved
false. We tend to attribute that to the MMX but that is really shorthand
for a number of experiments which all said the same thing.

Following MMX there were choices as to which way to go. The two main
ones being:

Choice 1 - Assume that there is no ether. If no ether then c cannot be
the speed relative to the ether leaving two options c = speed relative
to the source or c = speed relative to the observer. The latter is ruled
out because there is no possible causality whereby the speed of the
observer can effect the speed at which light leaves the source and also
because we know that light will leave the source without an observer so
the observer cannot be a crucial element. This then is the no ether
source dependency option. The most prominent theory of this type was
Ritz's. The first thing I note is that TOM does not mention Ritz's
theory so it should not be too difficult for him to justify SR if he
does not admit to any alternative.

Choice 2 - IF you continue to assume light is a wave travelling in the
ether THEN and ONLY THEN can MMX be interpreted as showing that every
observer, for some reason, finds himself stationary w.r.t the ether
which is what both Lorentz and Einstein tried to explain. Lorentz said
that it is an illusion, an observer isn't actually stationary w.r.t the
ether but appears to be because of distortion of his measurement.
Einstein made no attempt to explain it but simply assumed the truth of
it. His second postulate simply describes exactly what an observer
always stationary w.r.t the ether would observe. This then is the basis
of SR.

Now what I would expect in Tom's website is firstly descriptions of
experiments which disprove Maxwell's prediction that an observers speed
relative to the ether effects the measured speed. The MMX et al. This
one does indeed find.

I would then expect him to try and show that Choice 2 [SR] and not
Choice 1 is correct.

A criticism I would make is firstly he describes experiments which
legitimately disprove Maxwell's prediction but then he implies that this
is evidence of SR as if the choice is between Maxwell's ether theory and
SR rather than the choice between source dependent and source
independent theories.

Example

" Bradley (1727) discovered that the images of stars move in small
ellipses. This is explained as aberration due to the earth's motion
around the sun. This is inconsistent with a simple model of light as
waves in an aether which is dragged along by the earth; it is consistent
with SR."

In fact Bradley assumed the speed of light was constant w.r.t the source
and got the first really accurate value of the speed of light. So what
Tom is implying is that because it can be interpreted to be consistent
with relativity it supports relativity while in fact the simplest
interpretation is source dependent theory. A case of 'publication bias'.

"Round-Trip Tests of Light-Speed Isotropy" do not test SR against Ritz's
theory, they are testing the consistency of c. The only relevant section
for me is therefore

"3.3 Tests of Light Speed from Moving Sources".

Tom rightly states that "Experiments Using Cosmological Sources" are
all subject to criticism due to extinction effects in the interstellar
gas. What was accepted as evidence for about 60 years (DeSitters
observation of double stars) was discredited by Fox in 1965.

"Experiments Using Terrestrial Sources"

I am not familiar with all of the experiments but know a little about
two of them.

Beckmann and Mandies, Radio. Sci. 69D (1965), p623.
A moving mirror experiment. It consists of an interferometer - Light
beam split in two, one path goes via a path containing mirrors which can
be rotated, is combined with the other to give interference fringes. The
basic idea is that when the mirrors spin then they become a moving
source and if this produces a speed of c+v that beam will get there
quicker than previous and there will be a shift in the fringes.
The problem is that whichever theory you take a moving source produces
Doppler shift. If you could combine a Doppler shifted beam with a non
Doppler shifted beam you would produce continuously moving fringes. In
this case what they are looking at is strobed continuously moving
fringes and I don't know what one can get from that.

Alvaeger F.J.M. Farley, J. Kjellman and I Wallin, This was once
recommended to me by Franz Heymann as the most convincing evidence of
source independence so I have tried to find out about it. One
problem is that IF light is source dependent the current theory is
wrong. The experiment is highly technical and draws on current theory.
This is worrying in that they may be trying to prove an alternate theory
wrong by drawing on current theory and therefore assuming current theory
is right which therefore assumes the alternate theory is wrong in the
first place. This is not necessarily the case but you should put a
question mark every time I say "Current theory says".

The only thing one can say for sure in the Alvager et al experiment is
that high energy particles hit a beryllium target and the result was
gamma photons apparently travelling at c relative to the beryllium
target. If you say that the beryllium target is the source then it has
proved nothing at all but 'current theory says' that an interim stage
exists - a pion was created travelling at 0.9999c and this is what
decayed into gamma photons so constituting a moving source.

'According to current theory' A pion, if it exists at all exists for
only 8.4 x 10^-17 s which means that when it decays it does so within
the atomic structure of the beryllium target and does not travel in free
space at all. I don't think we know enough to say what interaction will
take place between the photons and the atomic structure of the Beryllium
before it exits.

I know that in the late 1970s-80s the number of 'fundamental particles'
was rising at an alarming rate until they decided to rationalise and
describe the result of some interactions as 'resonances' rather than
'particles' - OK how do you define a particle? Is a pion a 'real'
particle? As it only exists for 8.4 x 10^-17s there is clearly not
sufficient time to study it and the fact that it is neutral doesn't
exactly help to detect it. Its existence has got to be inferred
indirectly using 'current theory'. As it decays into two photons perhaps
it is simply two photons which have not yet 'disentangled' from each
other? If we had the faintest idea what a photon is we might be able to
answer that.

I have not the original paper but a search on the Internet gave some
information. The apparatus is described as follows:

" Generation of neutral pi-mesons was performed using bombardment of
immovable beryllium target by protons having, after acceleration, the
momentum of 19.2 GeV/co. In the experiment they used gamma quanta flying
at an angle near 6deg to the direction of protons flight. Across the
path of gamma quanta flying out from the beryllium target two deflection
magnets were installed near the beryllium target and one deflection
magnet was installed at a distance near 50 m from the beryllium target."

[In my view a strong magnetic field may invalidate the whole experiment]

"These magnets were intended for deflection of charged particles
generated during bombardment of the target by protons from trajectory of
gamma quanta flight. Before the third deflection magnet a leaden
collimator with diameter of 5 mm was placed."

[the original article apparently does not state the purpose of the lead
collimator. Judging from the scale it is about 2m long with a 5mm hole
down the centre. This has raised the suggestion that all gamma quanta
coming to the detector are secondary gamma quanta retransmitted by the
interior surface of the lead collimator pipe. Note that no experiment
criticising relativity would get through 'peer review' without stating
what part of the apparatus was for. It certainly isn't a level playing
field.] I also recall in another posting in a thread entitled "do
photons travel in straight lines" Tom replied

"Photons to not "travel" in any normal sense of the word, because they
are QUANTUM PARTICLES and not the "tiny bullets" of a simplistic
extrapolation of our everyday experience. Rather than saying they
"travel in straight lines", it is perhaps less violence to the language
to say "they travel in all possible directions at all possible speeds,
and interfere in important ways with themselves and each other". But
even that is overly simplistic."

Yet the experiment quoted appears to expect them to act just like "tiny
bullets" and go down the barrel of a gun without touching the sides.

"After the third deflection magnet gamma quanta passed through a window
in concrete wall, which had thickness of 6 m, and hit a detector of
gamma quanta."

Now here I have a problem. 'Window' to me implies something transparent,
e.g. glass. On a previous thread I pointed out that light travelling at
greater than c entering a solid transparent medium would be expected to
exit at c relative to the window independent of the speed it enters at.
I had the following from Franz Heymann:

"That [the window] was simply a small hole in a concrete shielding wall.
I have seen that hole myself. It was an empty hole in the shield wall
to let the photons through. High energy photons like those in that
experiment cannot penetrate much by way of matter without generating a
shower."

But in the article I am quoting from, it refers to it as "the window of
the vacuum chamber of the accelerator". I am at a loss to understand how
Franz Heymann's 'hole' can retain a vacuum so I assume there is a
'glass' window thick enough to retain a vacuum which for me scuppers the
experiment completely.

Note the other experiments listed are basically similar in type although
I do not claim to have studied them in detail.
-------------------------------------------------------------

4. Tests of Time Dilation and Transverse Doppler Effect.

"The Doppler effect is the observed variation in frequency of a source
when it is observed by a detector that is moving relative to the source.
This effect is most pronounced when the source is moving directly toward
or away from the detector, and in pre-relativity physics its value was
zero for transverse motion (motion perpendicular to the source-detector
line). In SR there is a non-zero Doppler effect for transverse motion,
due to the relative time dilation of the source as seen by the detector.
Measurements of Doppler shifts for sources moving with velocities
approaching c can test the validity of SR's prediction for such
observations, which differs significantly from classical predictions;
the experiments support SR and are in complete disagreement with
non-relativistic predictions".

Sorry Tom but that is rubbish. They are completely consistent with
source dependent theory.

Special relativity description:

S ->v ------------------X-----------
|
|
|
|
O

Source S moving along line gives a flash of 'light' at X orthogonal to
observer O. Relativity says the frequency measured by O will be subject
to time dilation. Time is reciprocal of frequency so

fo = f Sqr(1-vv/cc)

Source dependent theory description - Speed of light c w.r.t the
source:

S ->v ------------------X---X'--------
|
|y
|
|
O

With ballistic theory a flash at X will expand in a circle which will
remain centred on the source. When the light reaches O the centre of the
circle has reached X'. If it takes time t for the flash to reach O then

XX' = vt
X'O = ct
Therefore XO = Sqr(cctt - vvtt) -- Pythagoras

The source has moved away from O a distance X'O - XO in time
t so it is moving away at speed

u = [X'O - XO]/t
u = [ct - Sqr(cctt - vvtt)]/t
u = c - Sqr(cc - vv)

Put this into the Doppler equation. For ballistic theory the source is
effectively stationary w.r.t the propagating medium and the observer
moving:
fo = f( 1 - u/c)
= f(1 - [ c - Sqr(cc - vv)]/c)
= f(1 - 1 + Sqr( 1 - vv/cc))
fo = f Sqr(1 - vv/cc)

Exactly the same formula as for SR.

Note that the affect of aberration is that the apparent direction of the
light is XO not X'O as shown below.

Let us start by assuming the source is stationary and the observer
moving. I'm sure we both agree with Einstein that we can do that

SR case
X' X
|
|
|
|
v<-- O'---O


In the SR case the source remains at X but the centre of the circle
moves with the observer so when light reaches O' the centre of the
circle will be at X'. Light is observed as coming from the -y direction.

Source dependent case
X
|
|
|
|
v<-- O'---O

Light leaves X when it is 90deg to O. In the ballistic case the circle
will remain centred at X. At time t the circle reaches O'. O' has moved
away from X such that the Doppler is the same as for 'time dilation' as
shown previously.

Now consider aberration in the ballistic case

\ \ \ \ \*\
\ \ \ \ \ \
\ \ \ \ \ \
\ \ \ \ \ \
\ \ \*\ \ \
\ \ \ \ \ \
\ \ \ \ \ \
\ \ \ \ \ \
\ \ \ \ \ \
\*\ \ \ \ \
v<-- 3 2 1

Imagine light is coming from the direction -y and the observer is moving
in the direction -x at v 1,2,and 3 are successive positions of his
telescope. It must be aimed at an angle as shown in order for him to
observer the source of the light in the -y direction. This apparent
change of direction is termed Aberration.

X
| || || || || |
| || || || ||*|
| || || || || |
| || || ||*|| |
| || || || || |
| || ||*|| || |
| || || || || |
| ||*|| || || |
| || || || || |
|*|| || || || |
v<-- O' 4 3 2 1 O


If we now make the telescope vertical. Light going from X reaching O' is
observed as coming from the -y direction.

So both theories give identical results both in terms of frequency and
apparent direction. The ballistic theory gives a much simpler
explanation.

It is dangerous to assume that the maths of SR and of source dependent
theory is necessarily different. Showing that SR works does not
necessarily imply that it is the only theory which works.

------------------------------------------------------------
5. Tests of the "Twin Paradox"
Haefele and Keating, - Another experiment which got through 'peer
review' and is flawed. There are two things which conflict.

Einstein predicted that a clock on the equator would go slower than a
clock at the pole. Implication is that two clocks at different latitudes
will not keep time. Experiment shows that two clocks at sea level keep
the same time independent of latitude. Cocke explained this. Cocke says
that because the earth is not a sphere, (it bulges at the equator) the
equator is further away from the centre of the earth than the pole and
is therefore at a different gravity potential and if you do a GR
correction for that difference in potential it cancels the SR
prediction. This has implications for H&K. To do a GR correction
according to Cocke you have to take height above a notional sphere with
a diameter equal to that of the pole.

H & K did their corrections for height using the height above sea level
because although they quoted Cocke's paper they obviously didn't read
it. It is clear that Cocke and H&K cannot both be right but there is
some question as to who is. Dr Murray points out that the earth's shape
is not an accident, water moves to produce an equi-potential surface at
mean sea level and it could be argued that H&K were correct to take
height above an equi-potential surface but if that is the case Cocke's
explanation is wrong and the fact that clocks at sea level keep time is
a violation of SR.
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>
>
>Tom Roberts tjroberts@xxxxxxxxxx

--
John Kennaugh
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