if all motion is relative, how do we know the Earth isn’t stationary with everything else in the Universe rotating around us, albeit in a right weird and in uniform way.
In: Physics
You *can* indeed assume a reference frame where the Earth is stationary. However, the earth interacts with other celestial bodies (most importantly with the sun via gravity), and would thus immediately go into motion in that reference frame. So you cannot *maintain* the stationariness of the Earth in any reference frame.
Because the same theories that tell us all motion is relative also tell us that you cannot be stationary. In order to not move, you’d have to be stationary relative to some special fixed point in the Universe. No such point exists, entirely because if it *did* exist, then the speed of light would be fixed relative to that point, and thus anything moving would see a change in the speed of light relative to them.
In reality, it’s been repeatedly shown via experiments that it does not matter where you are, what direction you’re traveling in, or what speed you’re going; light will *always* move at **exactly** C (in vacuum) relative to you.
*ununiform way… Darn Amazon fire auto correct & me not catching it
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