One should assume that with his four causes Aristotle wants to give us some very general starting points for an investigation of reality. Yet, at first sight his four causes (maybe except the efficient cause) seem only applicable for the physical objects of our day-to-day experience.
- The material cause: “that out of which”, e.g., the bronze of a statue.
- The formal cause: “the form”, “the account of what-it-is-to-be”, e.g., the shape of a statue.
- The efficient cause: “the primary source of the change or rest”, e.g., the artisan, the art of bronze-casting the statue, the man who gives advice, the father of the child.
- The final cause: “the end, that for the sake of which a thing is done”, e.g., health is the end of walking, losing weight, purging, drugs, and surgical tools.
(Stanford Encyclopedia of Philosophy, "Aristotle on Causality")
Ok, let's take a light ray as an example:
material cause: umh... 'light stuff'? Pure energy? Electromagnetic radiation? Photons? All that doesn't seem very material...
formal cause: I have no idea... the wavelength of the light, maybe?
efficient cause: ok, that's comparatively easy. If the light came from the sun, the efficient cause would be the sun. On the other hand, let's say the light ray hits a mirror... what now? After hitting the mirror, does the light ray get destroyed and a new light ray comes into existence with the efficient cause 'mirror'? Or is it the same light ray which just got reflected?
final cause: I have no idea.
And now try this for electron or black hole.
Obviously, a metaphysics that only works in middle world is useless. But maybe that's not the case and we just have to understand Aristotle differently. How would one defend him?