I would argue that modern knowledge of physics only bolsters Aquinas’ argument.
First, I want to thank you for your analysis.
Now let’s get down to it.
Aquinas’ argument doesn’t only encompass those things which are actually changing, it also deals with those things that have the potential to change, to be changed, or to be different from what they are. This encompasses everything from your puddle, to the foundational laws of physics that govern the structure of the universe.
This paragraph has an error in it. The “laws” of the universe are not ontologically existing phenomena, they are our
explanations of the observed events. As our understanding grows the explanation will have to be modified. This has nothing to do with the concept of “change”.
All things which exist in this universe appear to be contingent, there are forces external to themselves which govern their current state.
This is the same incorrect generalization from the particular to the whole that Aquinas committed. And you introduced another concept: “contingent”. This concept needs to be defined. Does it mean that things could be “different”? Like a water molecule does not “have to” contain one oxygen and two hydrogen atoms? Or that a hydrogen atom does not “have to” contain exactly one proton and one electron?
There is no evidence that anything in the whole of material existence is not acted on and influenced by external forces.
This is a strange “double negative”.
The basic building blocks of the universe are what they are. They cannot change even if external forces act upon them. It is quite possible that our current understanding of the concept “basic” needs to be refined. But the
basic building blocks do not change, only our understanding of them.
D: An infinite regression of changes is impossible, given that, with infinite “moments” of change prior to the current one, it would be impossible to ever reach the current point of change in the line of changes. (If there is an infinite distance to travel before I reach my current location, then I can never reach where I am because there is an infinite distance to travel before I get here.)
This argument contains an incorrect understanding of the concept of “time” and the incorrect understanding of the mathematical concept of “convergent series”. In the times of Zeno people simply could not imagine a convergent series, where infinitely many changes will result in a finite amount. But that is just abstract mathematics, which is not applicable to physics.
The error you commit comes from the incorrect understanding of “time”. Time and space used to be understood as absolute phenomena, an unchanging “box” of the Newtonian universe, which contains the physical universe. This understanding has been discarded with the Einsteinian model of space-time-matter-energy where time is not an independent variable any more.