Re: one way light speed


Tom Roberts wrote:
nobody1357@xxxxxxxxxxxxx wrote:
I have been told a few times that all measurements of light speed are
two way and I can't think of an experiment setup which can show a
different result if one way speed differed in two directions.

Take two clocks separated by some distance, with a light source and
detector at each such that the clocks can record the time of emission
and arrival of light pulses. Watch the variation in the time difference
for successive pulses sent between them as the apparatus rotates. If the
one-way speed of light varies for different orientations, the time
difference for propagating light pulses will likewise vary.

This has been done: see the FAQ for references to Cialdea, to Krisher et
al, and to Torr and Kolen, plus the other experiments listed under
"one-way tests of light-speed isotropy".

Exercise: there is a hidden assumption in claiming this
experiment measures one-way light speed anisotropy. Explain
what it is. Discuss implications.


So, if
one way speed can never be measured, doesn't this mean it has no effect
on laws of nature and in a sense it doesn't exist like aether?

It can be measured. But _interpreting_ the measurement is complicated by
the fact that the two clocks must be synchronized; _any_ method can be
use to synchronize them, and the results depend directly on the method used.

This is merely one more instance of why in modern science we don't do
experiments to "measure things", we use them to TEST THEORIES. In
testing a theory applied to a one-way measurement, the method of clock
synchronization must be included in the analysis, and for all viable
physical theories it will cancel out (an arbitrary human choice like
clock synchronization cannot affect any physical phenomena).


Suppose
I'm saying that speed of light is infinite in this direction and c/2 in
the opposite direction, what can disprove this claim?

The above experiment could do so. Note that what you claim is not
enough, and you must describe how the one-way speed of light varies with
orientation. The fact that rotations come back to the same orientation
after an angle of 2pi puts rather strong constraints on how it can vary
with orientation. Indeed, for the outrageously large variation you
suppose even a second-order experiment like the MMX could refute it
(because you cannot make the anisotropy vary with orientation in such a
way that the MMX would not detect it in some orientations).

You will probably claim that the authors of the following paper are
crackpots!

Search for anisotropic light propagation as a function of laser
beam alignment relative to the Earth's velocity vector
astro-ph/0608223

"The results obtained with both methods show that the course of
the light rays are affected by the motion of the Earth, and
a predominant quantity of first order with a $\Delta c/c=-\beta
(1+2a)\cos \theta$ signature with $a=-0.4106\pm 0.0225$ describes
well the experimental results. This result differs in a amount
of 18% from the Special Relativity Theory prediction and that
supplies the value of $a=-1/2$ (isotropy)."

Marcel Luttgens




If this can be
disproved, one way speed of light can be measured. But it would also
mean there is no speed limit in one direction and c/2 speed limit in
opposite direction, and energy required to change direction of speed of
a particle would be different in two directions. This is not so in
particle accelerators so isn't this indirect proof that one way speed
has to be the same in all directions?

The variation of accelerators with orientation would have truly enormous
errorbars and would not be much of a test.


Imagine a particle accelerator that is not a circle but a very long
line. This can not accelerate a particle faster than c in any
direction. Clock sychronization does determine how the speed of this
particle is measured, but with an array of clocks sychronized the same
way, it is measured that succesive accelerations do not cause equal
speed increase, so there is a speed limit, which is not infinite. If
this particle is put in a race with light, it arrives just after light,
so this speed limit is the same as one way speed of light. So at least
it is certain that one way speed of light can not be inifinite in any
direction, correct?

Yes. But MANY other observations show the speed of light is not infinite
in any direction.


Tom Roberts

.

Relevant Pages

  • Re: one way light speed
    ... detector at each such that the clocks can record the time of emission ... But _interpreting_ the measurement is complicated by ... The fact that rotations come back to the same orientation ... a particle would be different in two directions. ...
    (sci.physics.relativity)
  • Re: one way light speed
    ... detector at each such that the clocks can record the time of emission ... But _interpreting_ the measurement is complicated by ... The fact that rotations come back to the same orientation ... a particle would be different in two directions. ...
    (sci.physics.relativity)
  • Re: one way light speed
    ... detector at each such that the clocks can record the time of emission ... But _interpreting_ the measurement is complicated by ... clock synchronization cannot affect any physical phenomena). ... The fact that rotations come back to the same orientation ...
    (sci.physics.relativity)
  • Re: one way light speed
    ... Take two clocks separated by some distance, with a light source and detector at each such that the clocks can record the time of emission and arrival of light pulses. ... In testing a theory applied to a one-way measurement, the method of clock synchronization must be included in the analysis, and for all viable physical theories it will cancel out. ... The fact that rotations come back to the same orientation after an angle of 2pi puts rather strong constraints on how it can vary with orientation. ... a particle would be different in two directions. ...
    (sci.physics.relativity)
  • Re: one way light speed
    ... or two clocks to measure the one-way speed. ... In the case of a one-clock two-way measurement the, ... synchronisation by slow transport. ... a particle would be different in two directions. ...
    (sci.physics.relativity)
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