An atomic clock emits a nano-bullet that moves at a given speed through a vacuum pipe to another atomic clock at a given moment. The other atomic clock records the instant at which the bullet reaches and calculates the time of another atomic clock based on the known speed and distance. Sync the clock and repeat the back and forth comparisons. The data match shows that the clock time coincides.
With such a synchronous clock, can we measure the unidirectional speed of light unchanged?
Many aeroplanes now navigate using optical gyroscopes (Sagnac interferometer) where a beam of light is split and sent in opposite directions around a fibre optic.
A direct measurement of the Sagnac effect between the separate light beams as the aircraft turns provides highly accurate data about the state of the craft.
This is in effect your experiment but using a single clock, which will not need synchronising.
The output of the experiment will measure the interference between light waves from the two beams.
Your philosophical task will be to understand if the mutual interference results from a shift in the speed of light or a shift in the apparent (relative)wavelength of individual beams.
The overwhelming view in the scientific community at large is that the wavelength changes, as the device rotates, the speed of light remains constant.
The device works regardless of the cause so in my mind there is no difference.
Mr. Wu,
Ni How,
This is an interesting question. In principle you propose to compare the speed of light with another speed and try to see if the ratio between one speed and the other speed stays the same. When you shoot the nano bullet you have to make sure that this process is reliable constant and it should not depend on the speed of light. I assume that the process of shooting is an electromagnetic process. So how can you be sure that the nano bullet speed is independent of the local speed of light in the same direction?
Regards,
Paul Gradenwitz
light speed in vacuum cannot be measured, because if one puts light into the voidadge the vacuum wouldn`t be empty anymore!
This explanation of vacuum makes me remember a cartoon where people needed to travel from earth to a far away place. Then one earthling asked the aliens why they were waiting. The answer was: they needed to empty the transfer channel from light so that there would be no light barrier in the speed. I was delighted by the smart solution for faster than light travel. If it could work?
Regards,
Paul Gradenwitz
I stand in awe at the willingness of researchers on this site to redefine fundamentals such as vacuum with negligent ease.
Make the word mean something else and you can prove whatever you like.
dear T.H. Ray, that`s right: vacuum does not exist! so the axiom about c is and will be an axiom. axioms needn`t demonstrations (according to maths)
dear Ian, to build a theory it is necessary first to assume (axioms). for instance: assume that light speed in vacuum is c. and some more. then one can start. and see what we`ve got (RT). similarily, one can assume (as axiom) that c is a limit for speeds; an unreachable limit. then build the theory and see what we`ve got now. note: axioms need no demonstration.
To the original question: the two-way speed of light can clearly be measured with no issues: a light beam goes from source A to mirror B at distance L and then back to source A. A clock at A measures the time elapsed and always finds 2L/c, with c independent of reference frame.
So far, this is experiment, well confirmed in many different ways.
One-way speed of light always has some kind of problem, since we need to say when two distant clocks mark the same time. It turns out that it is a consistent convention to assume that clocks can be synchronised in such a way as to make the one-way speed of light constant.
However, to make contact with those who mentioned the Sagnac effect, this consistency only holds in *inertial* reference frames, not in rotating ones. In rotating reference frames, or other non-inertial frames, you generally cannot consistently synchronise clocks in such a way as to have a constant one-way speed of light.
measure versus confirm: has anybody asked about changing conditions (from measuring to confirm experiment of 1st measuring)?
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