"Then the bucket starts to rotate, and the water surface will immediately begin to change." "Then the central mass's spin angular momentum and the surrounding mass's orbital angular momentum will conform to a certain function, which means the sum of all rotational inertias of matter in the universe equals zero." Friends who have studied graduate-level physics should know. Xu Yun's explanation is based on the intrinsic reference point theory, which is very friendly to beginners. This means setting the reference frame within the target region's boundary as the intrinsic reference point of this region, where each space within is stationary relative to this reference frame. The intrinsic reference point, as a whole, shares a common motion, and the acceleration caused by various external forces is equivalent. Therefore, the positional relationship of intrinsic reference points remains unchanged. Suppose the intrinsic reference point spontaneously generates a static point and analyzes its force and motion conditions to keep it stationary. Then its force and acceleration balance and cancel each other. As for the second example Xu Yun mentioned, it's actually an astronomical concept called "dragging effect," belonging to the cutting-edge theory of spacetime curvature. Actually, in later generations. The final blow to Little Niu's bucket theory came from an extremely long experiment lasting 48 years called Gravity Probe B. Its core purpose was to precisely measure geodetic drift and inertial frame dragging near Earth to quantitatively test the General Theory of Relativity. The main apparatus was an extremely precise gyroscope placed on a satellite with a circular orbit passing over Earth's poles. Orbiting at an altitude of 642 kilometers, it measured the rotation of the gyroscope axis concerning the background of the starry sky. According to calculations from the General Theory of Relativity. The geodetic drift and inertial frame dragging effects on the satellite's gyroscope axis are respectively 1.8 thousandths of a degree per year and 1.1 ten-thousandths of a degree per year. Gravity Probe B was led by Professor Everitt of Stanford University, running from 1963 to 2011. The first 45 years were funded by NASA, marking it as NASA's longest-supported project, costing a total of 750 million US Dollars. In the recent three years, it was funded by a Saudi Prince who earned his PhD degree at Stanford University, costing over 30 million US Dollars. What? You ask why the early 45 years cost 750 million, and the recent three years cost only 30 million? Don't ask; if you do, the answer is inflation. Certainly. Despite the gravy inherent in this plan, the final capital implemented is still a very large figure. However, despite the tremendous time and financial expenditure by Gravity Probe B, its results were less than ideal. According to the original claimed goals. Gravity Probe B could provide geodetic drift data with accuracy reaching 0.01%, and inertial frame dragging data with accuracy reaching 1%. Yet, the final result's accuracy was only 0.28% and 19%, both more than twenty times less precise than expected. But on the other hand. Although the accuracy differences were significant, it still successfully debunked the conclusion of "Once an axis of a gyroscope with no external interference points in a certain direction of the background starry sky, it will always maintain this direction" in a straightforward manner with its gyroscope. Thus, Little Niu's absolute spacetime view was completely negated in reality—combined with theoretical arguments, this count as a definitive conclusion. Incidentally. Reaching a 1% accuracy in inertial frame dragging data. But the final result's accuracy was only 0.28% and 19%, more than twenty times less precise than expected. But on the other hand. Although the accuracy differences were significant, it still successfully debunked the conclusion that "Once an axis of a gyroscope with no external interference points in a certain direction of the background starry sky, it will always maintain this direction" in a straightforward manner with its gyroscope. Thus, combining theoretical arguments, this counts as a definitive conclusion. Incidentally.