I have no comments about the demo in the video. However, from what I understand about GR, the important concept is that mass bends space-time (3D space and 1D t

I have no comments about the demo in the video. However, from what I understand about GR, the important concept is that mass bends space-time (3D space and 1D time). Time and space in GR is inseparable. This is an important concept. So the next question is why in GR, the two mass objects gravitated each other. It is because in GR, object follows the geodesics (i.e. straight line, shortest path) in space-time. So imagine, if there is only 1 object, it will follow the geodesics of spacetime with space coordinates being constant and time coordinate is changing with a constant rate. However, if another object is placed near it, it will bend the space time surrounding it. So now, the geodesic is not "straight" anymore. The new geodesic will include changes in the space coordinates ( object moving nearer to each other). So there is actually no pull force of gravity, it justs that the spacetime is curved thus the "straight line" now appears "curved" in our perspective.