Source of Gravitational Attraction


What actually causes the force of gravity?


Well... The short answer is that I do not exactly know. In the absence of knowledge I have sometimes found it convenient to create a little mental image that helps me think about effects without going too far into causes. Let me make up a story that is almost certainly not completely true but may contain some true elements and which may help you think about the nature of gravity.

The universe we inhabit has three observable dimensions. Let's call them the left-right, front-back and up-down dimensions. There is a fourth dimension which is perpendicular to all three of these called the time dimension. The observable dimensions have no absolute reference point. We can only measure relative distances along these. Along the time dimension we seem to be drifting at a fixed rate measured relative an event that happened about 16 billion years ago, the so-called big bang.

Now to compensate for our lack of ability to visualize more than three dimensions, lets imagine a universe in which there is only one observable dimension, say left-right and the time dimension running perpendicular to it. The inhabitants of this dimensionally challenged universe would be aware of the distance between them but not of their uniform motion along the time dimension. If this whole two-dimensional space were flat then the motion along the time dimension would not have any effect on the distances between objects. Things would just drift along in parallel lines unless some force was applied to move them closer together or farther apart.

longitudesSuppose however that the whole two-dimensional universe lay on the surface of a three dimensional sphere rather than on a plane. Then the curvature of the space would cause the lines that were parallel when the space was flat, to look like lines of longitude on the earth. Now the drift along the time dimension would have an effect on the distance between objects. The inhabitants would be forced to propose some sort of force between objects tending to bring them all together.

If then in our universe the four-dimensional space composed of three observable dimensions and unobservable time dimension were curved, lying on the five-dimensional equivalent of a sphere, might we not be tempted to make up a force to account for the tendency of things to be drawn together as time passes. Perhaps we could call it gravity.