It is trivial using an Arduino and laser to measure the speed of light round trip. I’m aware of the Sagnac effect formula I have verified it experimentally. I have 2 atomic clocks.
IANAP, but I’m pretty sure no one has figured out a way to measure the one-way speed of light; thus far, all measurements of the speed of light measure the roundtrip speed.
It may even be impossible to do so.
And because of this, it’s possible (though unlikely) the foward speed toward the mirror is different than the return speed.
People have tried within a certain precision. Many experts agree with you.
youtube/watch?v=pTn6Ewhb27k
https://www.reddit.com/r/Physics/comments/jljj5s/why_no_one_has_measured_the_speed_of_light/
I’ve lowered my expectations to 1%. This changes the question?
If you have two synchronized clocks, can’t you just set up a pulsed light source far away, and turn it on at a pre-set time, and measure how long it takes for the pulse to arrive?
No.
Why not?
You must synchronize them when they are adjacent. If you move them slowly, far apart, they will drift. If you move them at 1/4 speed of light they will no longer be in sync. You cannot calculate this change without first assuming light is the same speed in both directions.
Synchronize them when they are far apart.
How? You cannot assume the speed of light is the same in both directions.
Well, I have to admit I haven’t pondered all the nuances of this experiment, but it seems to me that if you have two clocks some distance from one another, it should be possible to transmit a timecode from one and receive it at the other, and measure to phase difference. Then it’s a simple matter of compensating for this difference.
It’s been a long time since I studied relativity, so I’m probably missing something obvious.
The video in my link above explains it.
I don’t see that you posted a link, but I did find this:
Here’s a simple idea:
The 2 atomic clocks are miles away on earth. They are not synchronized but drift apart by 1ppb. Up to 1ns per second. Send the laser both directions. Simply compare the time elapsed in one direction to the other direction. Are they the same?
You must send the data before you subtract the numbers. You can write it on a piece of paper.
Only in a very solipsistic sense. It’s possible that the one-way speed of light is different in different directions and the Universe is conspiring against us to hide this fact, but if you’re going to posit that the Universe is conspiring against you, you might as well at least come up with a more interesting conspiracy.
Sounds pretty easy to me unless you move the goalposts and specify it must be the speed of light in a vacuum.
My simple idea above does seem easy. 1.00003 = speed air / speed vacuum
This misses the point. It doesn’t matter if the clocks are synchronized or drift by a known, fixed amount. That’s basically the same thing in the end.
One problem - how are you sending this data back? Presumably with a signal of known velocity (probably the speed of light) from one of the clocks back to you? I.e. you’re measuring the two-way speed of light with this method plus adding a bit of measurement error due to the time to make the measurement, encode it, and transmit it back. Instead of one two-way measurement, you’re now comparing 2 two-way measurements. Fuzzy ones, at that.
Another problem: why would the elapsed time be the same? You know the distance to each of these clocks is identical? How? I.e. how do you know the distances are the same in a way that does not require already assuming knowing the speed of light or relying on a two-way measurement already?
There has been an optical experiment measuring the Sagnac Effect for a large part of the Earth, enclosing the axis of rotation, but it was at higher latitudes, and not at the equator. There is enough fibre connecting the world that this is a doable thing. Of course, this still only yields a two way time for light itself, but does measure the offsets due to rotation.
I can’t remember the reference to the experiment off the top of my head. Which is annoying. But the numbers that came out were pretty good IIRC.
What if you run a parallel experiment?
A timed round trip one. The second leg has another clock at twice the distance of the round trip one. Arrange for the beam from the round trip one to also pass on to the second clock detector. Set the clocks by a beam split at the same point as the reflector for the round trip portion.
A sloppy explanation but you get the idea.