Every physical theory postulates the existence of some fundamental constituents of reality that cannot be reduced further.
I've heard one that doesn't. It was agnostic on the subject and speculation on what the reason was for having indefinite layers of 'more fundamental' was outside the scope of the theory (like a 'first cause'). It did qualify as a physical theory (but certainly isn't mine.)
A Wall Street Journal article by Harvard professor of government Harvey Mansfield claims that the social sciences and humanities are inferior to the sciences. The article implicitly urges undergraduates to major in science. From the article:
Do you agree with this? As a game theorist I probably have a rather biased view of the situation. It's certainly true that the ideal of the scientific method is vastly better than the practice of economists, but I think that majoring in economics provides better training for a rationalist than majoring in any of the sciences does.
Economics explicitly considers what it means to be rational. Although it infrequently considers ways in which humans are irrational, I'm under the impression that the hard sciences never do this. Furthermore, because economists can almost never perform replicable experiments we have to rely on what everyone in the profession recognizes as messy data; therefore we’re far more equipped than hard scientists to understand the limits of using statistical inference to draw conclusions from real world situations. Although I have seen no data on this, I bet that a claim by nutritionists that they have found a strong causal link between some X and heart disease would be treated with far more skepticism by the average economist than the average hard scientist.