# Can a beam splitter be used to measure Earth's absolute motion through space?

Let say the Earth is not moving through space...Then a beam splitter that refracts the beam into 2 new created beams at an angle of 90° towards reflectors which will reflect the beams at 180° again to the splitter will be eventually touched by these reflected beams. But in the case the Earth is moving, and we know it is moving just to not fall into the Sun for example...then the reflected beams will not end their journeys into the splitter but a little bit away from it due to a bit of path traveled by the Earth during the time the 2 reflected beams reach again the splitter. So as we know the speed of light and the geometry of the setup of that virtual experiment we should figure out the absolute speed of Earth?

• Absolute motion doesn't exist. Commented Feb 21, 2023 at 20:45
• @DavidWhite Please, suggest an edit but not to change the aim of the question... Commented Feb 21, 2023 at 20:48
• My whole point is that the question cannot be answered as stated. Only relative motion can be measured, and there is no unique stationary reference point from which to make the measurement that you allude to. Commented Feb 21, 2023 at 20:59
• How is this different from en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment ? Commented Feb 21, 2023 at 22:59
• Are you reinventing the Michaelson interferometer? If you weren't aware of it and came up with this experiment from first principles, that's impressive. Commented Apr 26, 2023 at 5:05