Benjamin Snow

An interesting thought experiment. Where you to suspend the rocks connected by a rope in an empty universe as stipulated, the rope would eventually snap, (if not from decay, as it is a zero-air environment, but the inner cell walls of the plant matter composing the rope could conceivably contain anaerobic extremophiles who could eventually decompose and hence destroy the rope, snapping it. Alternatively, the rope could be untwined or destroyed by a random quantum event, or slight friction in the connection to the rock) we could measure whether the system was rotating by observing if the rocks appear to move away from each other. An non-rotating system would have all object retain their apparent positions regardless of the rope's connection, whereas by the law of inertia, if they were rotating, I am under the impression the rocks would drift apart. Unless the conditions of Newton's experiment involve a constant force to accelerate the rocks rotationally, in which case we could measure the force via the force it exerts on whatever it is exerting it (via Newton's third).
But, and more importantly, assuming you are unable to game the system and determine experimentally if the system is rotating. . . actually, with the whole bucket thing, because of the adhesive and cohesive properties of water, wouldn't you be able to measure the rotation because even if the water didn't form a conical shape, the act of the friction rotating it would disturb the meniscus and surface tension, even if ever-so-slightly. . . but anyways, gaming aside. Ultimate frames of reference. Yeah. I would estimate that over 3 billion people on this planet would argue there is an ultimate frame of reference, that of their god(s), and hence because both history and ideas are subjective (if an individual and I both possess the same flaw in our perception of reality, we would never be able to tell), they could will the bucket taut. Or will it not taut. Vote anyone? Excluding the majority of this planet who choose to be silly, however, because space and time are equivalent and under the current model both were created in a single event (aka el bango grande), which at one point must have originated from a single point, which is observable based on the minute residual drift away from it, this is the ultimate frame of reference. Even in an empty universe, there is a universe, and an event must have created it. We can measure time, and thus space, in the molecular RNA spin of the rope cord, and in the decay of it, and space by the minute particles ejected from said rope. Therefore we can measure the center of the universe, and hence the ultimate frame of reference, at least for this reference. Beyond our own universe, or the hypothetical universe of this thought experiment, we can never observe or hence apply logic. I leave questions to an even more ultimate frame of reference to the aforementioned over 3 billion silly people.

-Ben Snow