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Is it possible to have a solid (not moving) reference point in space to determine the movement vector of a object in relation to space? They say everything in space is relative to something else but is it actually possible to create a grid of space which is not in relation to something else but space?

If I had a sensor on a body which detects the amount of time it takes for light to travel in 3 axis with the same distance. The difference in time would create a 3D- vector, would it not? That is relative to space and not to other bodies such as the sun, center of the galaxy or other galaxies. If I travel in a spaceship at 0.5c in the X-axis, but 0 in the Y- and Z-axis and lit a light bulb in the spaceship with a sensor in the X, Y and Z-axis. It would take longer for the light to reach the X sensor. Are these things measurable on earth? How we are actually travelling in relation to space itself.

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    $\begingroup$ You would only measure things in relation to your sensor. The closest you can get to an absolute frame of reference is the CMB rest frame - but that is just another, arbitrarily chosen frame. There simply isn't any absolute frame that is "correct", and relation to space itself is non-sensical. $\endgroup$
    – Polygnome
    Commented Feb 12, 2020 at 13:07
  • $\begingroup$ If you can't share a common reference point, sharing measurements is going to be tricky. You could share your arbitrary point in space, but to do that you'd have to give its position relative to something else (such as yourself), and you're back to square one. $\endgroup$
    – Starfish Prime
    Commented Feb 12, 2020 at 13:11
  • $\begingroup$ @StarfishPrime Yes but for example one could get to approximately 0 movement in relation to space if all sensors indication no movement. We on earth could use that probe as a reference point over time to determine our actual movement through space (and all other things) and build a intergalactic coordinate grid. Telescopes could be positioned at such point a provide exact movement relative to that point. For example is everything moving away in a certain direction at the same time as we move away from each other? Maybe there is no use or even possible to maintain such position. $\endgroup$
    – NeutronCode
    Commented Feb 12, 2020 at 13:29
  • $\begingroup$ @NeutronCode What do you mean by "space itself"? $\endgroup$
    – Organic Marble
    Commented Feb 12, 2020 at 15:22
  • $\begingroup$ @OrganicMarble Mass less particles will always travel from point A to B at the speed c. If I would travel In direction A -> B in a spaceship traveling at 1c where A is the back of my ship and B is the front (on the inside). Standing at A with a laser the light would never reach B. If I instead travel at 0.5 doing the same. A slight delay would occur before the light reaches B. The light would only travel from A to B relative speed of 0.5c before it reaches B. The same effect should be measurable in all speeds even on a very small scale. Should it not? $\endgroup$
    – NeutronCode
    Commented Feb 12, 2020 at 16:06

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If there is an "absolute velocity" to detect, doing so requires something beyond known physics. Your thought experiment is equivalent to the Michelson-Morley experiment, which attempted to measure the motion of the Earth in 1887 and produced a null result. Repetitions of this and other far more sensitive experiments have produced the same result.

Your spacecraft could accelerate in any direction by any amount, and once it has ceased acceleration, you will observe the same results. All inertial frames are equal, velocity only has meaning relative to something, and you will always measure the speed of light relative to yourself to be the same. This is why the Theory of Relativity has its name.

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