Newton’s Bucket demonstrates relative motion the sense that there are a number of different frames of reference possible to measure the spin of the bucket and water in relation to. Whether the water moves in relation to objects around it, the earth, celestial bodies, or the entirety of the universe, one can judge whether or not it is rotating.

I personally can’t help but be torn on the debate of an ultimate frame of reference. I believe that yes motion is measurable with relative perspectives. The relative frame of reference is determined by the purpose and intention of the given motion. Contrary I can see the logic behind an ultimate frame of reference. I agree with Eric that with our current scientific knowledge of the universe there is sufficient evidence that it has an origin and began at a certain point in which gave us the reference of time. I think that the universe, that includes all of the mass available to us, can be considered as the “ultimate” frame of reference. In a sense every possible frame of reference lies within this “ultimate” frame, it is all-inclusive. Against the argument that the universe itself could be rotating in relation to something greater I believe that the only thing we can be “absolute” about is what we know is true and proven. Another, larger, frame of reference may be discovered someday in which this all-inclusive frame of reference can be reevaluated. But until then we should let these theories alter what we know.