Re: A way to measure OWLS...and verify the constancy of the one way speed of light

Tom Roberts <tjroberts@xxxxxxxxxx> wrote in
news:dc5oh5$je2@xxxxxxxxxxxxxxxxxxxxxxxx:

> bz wrote:
>> Make it simpler. Use an oscilliscope, a laser diode, a 1000 meter
>> length of fibre cable and a photo diode.
>> Use a pulse generator, you might save money by using the square wave
>> calibration signal that most scopes have built in.
>> You measure the time delay introduced by the fiber cable. You make sure
>> that moving the cable around [without moving the end of the cable away
>> from the photodiode] has no effect on the delay introduced by the
>> cable.
>
> This merely establishes that the round-trip speed within the cable does
> not depend on its orientation. It says nothing at all about the
> difference between east->west propagation compared to west->east
> propagation in the cable, it ONLY shows that east->west->east
> propagation is the same as west->east->west propagation (and other
> orientations as well), in the cable.
>
>
>> You then start to move the end of the cable away from the photodiode
>> and measure the INCREASE in delay.
>> That increase is the one way speed of light.
>
> Not true. You make the same mistake that the C.J.Luke keeps making --
> you forget that in moving the cable end to the west you change the
> amount of east->west vs west->east traveling the signal makes within the
> cable.

We are comparing the speed of light in two very different media. It is
unlikely that something will effect BOTH speeds by the same amount.

>
> In fact, for a change dL to the west, the time delay dt is:
>
> dt = c1*dL + c2*dL - c3*dL
>
> where c1 is OWLS(west->east in vacuum/air), c2 is OWLS(east->west in
> cable), and c3 is OWLS(west->east in cable).

scope
laser--------fiber---------------------------------\
diode.............................................-/
East West
length fiber is constant. distance diode-fiber is variable.
deltat = c1 * delta distance - (cw * lw + ce * le)
but lc (length of cable) = lw (length to the west + le (length to the east)

deltat = c1 * delta distance - ce le + cw(le -lc)
if ce = cw
deltat = c1 * delta distance - cw lc
if cw is constant
deltat = c1 * delta distance - a constant.


> Only if c2=c3 can you get
> the answer you desire, and you have no way to establish that equality
> (i.e. isotropy of OWLS in the cable).

I don't really care very much. If it appears to be constant, I will be happy.

> There is no possible variation of this technique that can avoid this
> problem. For the simple reason that this is INHERENTLY a round-trip
> measurement, and no round-trip measurement can establish anything about
> OWLS.

You perform the test with your cable moved outward in many different
directions.

If you find that the delta delay is only dependent on distance between photo
diode and the end of the cable, then it doesn't matter that part of your
apparatus is has the signal traveling two ways, the ONLY part where the
testing of light [in a vacuum] is taking place is between the end of the
fiber and the photo diode. Everything else remains 'constant' and drops out
of any calculations.

> Note that the observed isotropy in TWLS measurements puts a constraint
> on any anisotropy in OWLS, but that constraint is rather loose, and
> certainly doesn't require OWLS to be isotropic.







--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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