Unmover Mover Outdated?

When digging into the writings of Aristotle, I often wonder if they may be a little outdated. At the time he was developing his theories, there was much less known in the world of physics, and the research capabilities we have today did not exist. Aristotle's basis for the unmoved mover was that a body would remain at rest unless acted on by an outside force, but modern discoveries have proven this untrue. One example cited from Physicist Michio Kaku's book Hyperspace, easily dismisses the argument that objects in motion must be moved by another object. An example he states is that gas molecules may bounce against the walls of a container without requiring anyone or anything to get to get them moving. The movement of these molecules has no definite beginning or end and may be infinite. If this disproves the original reasoning that Aristotle's ideas were founded on, it makes me think that maybe some of his other texts are out of date as well. I am not sure, but this may be the reason I have trouble grasping alot of his concepts, and in general, found Pollan's views to be more easily understood. I am not sure if my criticism of the unmoved mover is exactly right or not, because I don't know if the moving gas molecules are actually acting on something else, causing a chain of motion because I don't know that much about physics. I am interested to see what other people think about this issue. Do you feel that some of Aristotle's books may be outdated, and after the recent discoveries in modern science, some of his reasoning is no longer correct?