The output — is it caused by the program? Or by the user input? Or by the computer? Or by the electric current?

Each of these things — if not quite another one — may be referred to as the relevant cause, depending on context.

In physics it has become common practice to take the laws of nature as fundamental causes. If we describe an event in a way that clearly shows the effective laws of nature, then we explicate it physically.

So we say, in the framework of mechanics, that a body principally moves linearly uniformly, as long as no forces act upon it. Nobody reasonably involved in that matter still asks “why?“.

But here, in the framework of these investigations, we take the next — maybe just small — step. We declare the moving body to be a special case of a thing, saying that every thing multiplies.

This is a law — and cause of all kinds of events.