Re: A way to measure OWLS...and verify the constancy of the one way speed of light
- From: Tom Roberts <tjroberts@xxxxxxxxxx>
- Date: Sun, 24 Jul 2005 04:25:36 GMT
C.J. Luke wrote:
Tom Roberts <tjroberts@xxxxxxxxxx> wrote:C.J. Luke wrote:We build an instrument that consists of the following: [...]
This does not measure the one-way speed of light, it measures the round-trip speed of light in a combination of the fiber and the free space between the end of the fiber and the "receiving lens". For different positions of the fiber end there are different proportions of fiber and free space, but it's still a round trip measurement.
Not even close Tom...unless you have a new definiton for round trip
that you could share with us.
Your signal goes out and back -- that makes it a round-trip measurement.
NOTE: I assume the source and detector are co-located, so intitially the fiber loops out and back to its origin. I can no longer see the original post and don't recall if that was stipulated there or not. This makes the discussion simpler, but the conclusion is unchanged even if detector and source are not co-located....
The portion of the trip in the fiber is completely inconsequential to the end result
NOT TRUE! To claim that you must ASSUME that the one-way speed of light inside the fiber is isotropic. But that is directly related to what you are trying to measure.
so I have no idea what
proportions you are talking about above.
Consider the initial situation in which the end of the fiber is right next to the detector. Then the signal goes out and back entirely in the fiber, and its east->west and west->east distances are identical (as are its north->south and south->north distances, which I'll ignore). Now move the end of the fiber some distance to the west -- now the east->west distance in the fiber exceeds the west->east distance in the fiber by EXACTLY the same amount as the west->east distance in air. But still, the total west->east distance equals the total east->west distance. The proportion of the total trip that is in the fiber varies as you move its end: 100%fiber/0%air when the end is next to detector, 50%fiber/50%air when the fiber is fully extended.
My "air" might be vacuum in your original (which I cannot see).
The flight time in the cable
is exactly canceled.
ONLY if you assume isotropy in the propagation in the fiber, which defeats the whole point of the measurement.
The only flight time measured is the flight time
from the end of the cable to the receiving lens.
Not true. You cannot rule out the possibility that light propagates anisotropically in the fiber. In fact, there is an entire class of aether theories in which the one-way speed of light is not isotropic, but the round-trip speed of light is isotropically c in any inertial frame. These theories are all experimentally indistinguishable from SR. They ALL predict anisotropic propagation in the fiber, and that "just so happens" to exactly cancel out the effect you seek (after all, they are experimentally indistinguishable from SR).
NOTE: there is no point in considering theories in which the round-trip speed of light is not isotropic (in the inertial frame of the apparatus), as any such theory is soundly refuted experimentally.
Simple example: Consider the case for which the west->east speed of light is > c (so east->west speed < c, in order to retain an isotropic round-trip speed). As you move the end of the fiber a distance L to the west, the light end->detector travels faster than c and you would expect the time delay to be less than L/c. But you are forgetting that you have also increased the (east->west - west->east) distance the light must travel in the fiber, and it travels more slowly east->west in the fiber than west->east in the fiber. This goes in the opposite direction of the effect you expect; and in fact it cancels it exactly in the class of theories I mentioned above.
bz wrote:
"Martin Hogbin" <goatREMOVETHIS123@xxxxxxxxxx> wrote in
news:dbr83b$a4u$1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx:Imagine replacing the fibre optic with a collection of mirrors.
If you keep the total distance traveled between mirrors constant{exclusive of the point where the fiber /mirror bath is to end} [as the fiber does] then mirrors should work too.
Again, ONLY if you assume that the propagation among the mirrors is isotropic. But Martin's point was that in this case you clearly cannot assume that, as the region among the mirrors is no different from your "measurement region".
Bottom line: one way or another this is a round-trip measurement. For the simple reason that the singal goes out and back. And there are zillions of experiments that show the round-trip speed of light is isotropically c in any inertial frame we have access to.
Tom Roberts tjroberts@xxxxxxxxxx .
- Follow-Ups:
- References:
- Prev by Date: Re: How can this work in relativity?
- Next by Date: Re: How can this work in relativity?
- Previous by thread: Re: A way to measure OWLS...and verify the constancy of the one way speed of light
- Next by thread: Re: A way to measure OWLS...and verify the constancy of the one way speed of light
- Index(es):
Relevant Pages
|
