# Can you measure the one-way speed of light using gravity?

I recently learned that you can't measure the speed of light one way, only back and forth. I thought you might be able to use gravity to measure the speed one way.

If you have to stations at the same altitude and shine a laser from one station to another, then see how far the beam of light has dropped. You can then use the acceleretation of gravity and calculate how long it took for the light to get to the station. When we know the time we can use that to calculate the speed of light.

For example if the light dropped 20m we know that the light took about 2 seconds to reach the station.

I know it would very hard to measure accurately but I just want to know if it would theoretically possible.

• see how far the beam of light has dropped - how? What's your reference? Gravity curves space. Dec 31, 2021 at 17:24
• would this be useful astronomy.stackexchange.com/questions/11592/… Jan 1 at 16:46

A non-Lorentz coordinate transformation on Minkowski space can always change one-way speeds in various directions (exercise for OP: write down a transformation law that changes the speed of light in positive $$x^1$$ and negative $$x^1$$ directions).