Nature is not indifferent to the path things take...
Beginning with the Pebbles and People essay we are looking into how human beings can redirect the stream of events, changing the state of the universe to suit their desires (or trying to, bearing in mind the law of unintended consequences). We took a bit of a detour in the Getting Things Done essay to think about how anything gets done at all. Now we are getting to how inanimate matter makes its way through the universe.
We all know what matter is. It is the stuff from which objects are made. We might suppose that inanimate matter would lead a dull and eventless existence but the universe is arranged so that is not necessarily the case. Most of the matter, most of the time is what I will call well behaved, meaning it follows a simple rule in its behavior. Objects large enough to be visible to us interact with their environment in two principle ways. They effect and are affected by the space around them and they exchange photons with one another. Very small objects like atoms and sub-atomic particles have additional ways of interacting with each other that we don't need to deal with here. Basically these interactions hold an object together and give it its physical and chemical characteristics.
The interaction of an object with the space around it is called gravity. In accordance with the general relativity principle, a massive object like Earth significantly curves the spacetime around it. The curved spacetime determines how objects move in the absence of external forces. Experience tells us that a dropped baseball falls freely toward the center of the planet. Of course gravity operates between any pair of objects in the same way so the Moon is also falling toward the center of the Earth, even though its tangential velocity makes that fact less obvious. In fact the path that any object takes when falling freely, without aid or interference, is determined by the curvature of spacetime in the neighborhood.
These paths are called the geodesics of spacetime. I hesitated to use these possibly unfamiliar terms but the glossary will help and the alternative term is worse. The paths Nature chooses for objects, in the absence of interference, is the path of maximal aging and explaining that is another whole story, which we may get to in time.
If an object is responding to the curvature of spacetime but is somehow constrained, it will follow a geodesic as closely as the constraint allows. For example the dropped baseball follows the geodesic that happens to be a straight line through the center of the Earth until it collides with the Earth surface. Thereafter it just lies there, doing its best to follow that geodesic but prevented from moving closer to the center of the planet by all the stuff in the way. If a metal ball is connected by a light rod to a pivot point, making a pendulum, the ball will try to fall to the center of the Earth but the constraint forces it to swing in an arc, constantly overshooting the point of closest approach to the Earth center so it swings back and forth.
I mentioned that the other way objects interact is by exchanging photons with one another. This is just another way to think of electrical forces between objects. Just a quick review of the electric nature of atoms is due here. All atoms consist of a positively charged nucleus surrounded by negatively charged electrons. Normally the number of electrons surrounding the atom equals the number of positive charges in the nucleus, leaving the atom as a whole, electrically neutral.
Now consider two objects, say a few centimeters apart. That distance is so large compared to the separation of the negative and positive charges in the atoms of the objects, that the two objects appear electrically neutral to each other so they have no influence on each other's path. Each object goes coasting along its own geodesic without regard for the other. If their geodesics happen to intersect and if the objects were to arrive at this intersection at the same time, at some point they would come close enough together that the negative electric charges surrounding the atoms of the objects will come close to each other relative to the distance between them and their positive nuclei. The repulsive force between these negative charges will build up rapidly as more and more atoms get involved and the two objects will be forced off their original geodesics and find two new ones that diverge from one another.
That is about the story as far as inanimate lumps of matter go. They drift along whatever geodesic they are on at a fixed speed including possibly zero speed, until something comes along and pushes them off course, changing direction, speed or both. Thereafter they follow a new path until the next bump. Under some circumstances inanimate matter can be induced to behave in much more complicated ways. We will wait until later to examine this situation.
I think that the only way people can alter the future state of the universe is to move small objects in the vicinity, taking them off Nature's preferred path and shifting them to another geodesic in the neighborhood. It is only through the manipulation of matter that human beings exercise their authority over events. The details of how a person decides what moves to make and how those moves are accomplished remain to be explored.