I have perhaps a simple question concerning Thomas Aquinas's Third Way of proving God's existence. I've been reading Edward Feser's introductory book to Thomism, and he makes a statement that I'm a little confused by without stating any premises for it. To quote from the book, he writes that "for (again, given at least an Aristotelian conception of possibility) it would be absurd to suggest both that it is possible for every contingent thing to go out of existence together, and yet even over an infinite amount of time this will never in fact occur." Why is this? Especially concerning Thomistic metaphysics, potency can only be actualized by another external cause. Would it not be theoretically possible for no external cause to cause something that which exists to no longer exist? Therefore even over an infinite amount of time it is possible for its potency to not exist to never be actualized?