In other words, can everything that has real existence, be studied by physics? If so, that’s the same as saying nothing which cannot be studied by physics has real existence. I bring this up because I know someone who asserts this (though I’m omitting his name in case I am misstating his position somehow).
Now when aircraft engineers abstract from real, concrete passengers everything but their average weight, so as to determine how many passengers of average weight can fly on a particular type of plane, no one thinks that the utility of this method shows that actual airline passengers have no features other than their average weight. The abstraction is extremely useful, but hardly provides an exhaustive description of reality. Yet the utility and predictive power of physics is often taken as evidence that it gives us an exhaustive picture of material reality. This sort of argument is like that of the drunk who insists that his keys have to be under the streetlamp, because that is the only place there is light to look for them. That it is difficult to look for the keys elsewhere has absolutely no tendency to show that they are not in fact elsewhere. And that it is difficult to study aspects of material reality not susceptible of the methods of physics does not show that no such aspects exist. The fallacy is extremely obvious when you think about it, but it is committed all the time by otherwise intelligent people, and gains a certain prestige from the frequency of its commission and the status of those who commit it.
Edward Feser, Rediscovering Human Beings, Part 2.