I see, if you’ll bear with me for a moment I shall endeavor to explain why it’s not incredulity that leads to that conclusion. https://twitter.com/illjord/status/1299331507111288832

First off, we are not talking here of causality in the temporal sense, but in the ontological sense. The “first (or efficient) cause” is a sustaining cause of the world here and now and at any moment at which the world exists at all. 2/

In this argument, what is key is the distinction between instrumental and principal causality, an instrumental cause is one that derives whatever causal power it has from something else. A good example of this is a pen writing letters on a page. 3/

The pen has no power to write on its own, it relies on the hand that is holding it. So the pen is an instrumental cause in that it (through the ink inside of it) makes letters appear on the page, but it derives it’s causality from the hand holding it. 4/

A principal cause is one that does have its causal power inherently. The hand in our example can be thought of for purposes of illustration as such a cause, though of course ultimately it is not, since its power to move the pen depends on other factors. 5/

At the end of the day there can be only one cause which is principal or non-instrumental in an unqualified sense, namely a cause which is purely actual and thus need not be actualized in any way whatsoever by anything else. 6/

This is a series ordered “per se” all the causes in such a series other than the first are instrumental in this way that they are said to be ordered per se or “essentially,” 7/

for their being causes at all depends essentially on the activity of that which uses them as instruments. The simultaneous nature of an essentially (or per se) ordered causal series is what necessitates the “imperishability” of the “first cause.” 8/

the distinction between causal series ordered in fieri (or per accidens) and causal series ordered in esse (or per se) are what the Thomistic arguments (like other Scholastic cosmological arguments) crucially depend. 9/

A misunderstanding on this point is what leads to the cosmological incoherence you referenced. End.

Addendum: I should note however, that the argument doesn’t rest on simultaneity as such. It rests on the instrumentality of the members of a causal series ordered per se, and instrumentality does require an uncaused cause.

Addendum II: ultimately a first cause is first in the sense of being metaphysically ultimate or fundamental, and not (necessarily) in the sense of standing at the head of some temporal or even non-temporal queue.