Every interaction is the universe, according to science, is driven by physics, whether or not physics is currently capable of fully explicating the dynamics engineering these actions and reactions. Because physics is responsible for the execution of physical causality and provided physics’ absolute understanding, if it were possible to observe all the actions at any given moment in time, all the subsequent reactions could be predicted using physics. Therefore, if every variable in the universe could be accounted for and all of their reactions predicted, any state of the universe could be predicted, prior or subsequent to that given point in time, by mapping the physics behind the changes.
To understand this concept, visualize a set of three dominos lined up, impervious to external environment influences. Once the first domino has toppled, it is a fact that the third domino will topple because the second will upon being contacted by the first domino, and this could feasibly be shown by a scientist using a computer model frontloaded with the ability to correctly apply physics. But to create such a computer model for the universe, the most intelligent computer the size of the universe would likely be needed, and it would probably be infeasible even then. That, however, does not negate the reality of a deterministic universe, subscribers contest.
Many determinists conclude from this that everything in the universe is “predestined” and randomness does not exist. Additionally, if everything that happens in the universe is simply a physics-based product of that before it, free will does not exist either. The unrelenting forces of physics, these deterministic universe proponents postulate, determines everything from the location of the Milky Way in the universe to the neurochemistry forming your “thoughts” as you read this article. In fact, a reader of this article may have had no other choice but to find and read it since the beginning of time.