If one interprets "physically" like positivists, there can be no physical argument against it - if the theory predicts the observable facts, everything is fine, and the number of epicycles does not matter. A preference for a theory with less parameters goes already beyond positivism, it has to rely on Popperian (philosophical) empirical content (predictive power).

In real physics, this is what the experimenters have to do - observe more "epicycles", more of the lowest order terms. And it is the job of the theoreticians to try to find a new theory which allows to get rid of all the epicycles already found.

What one has to expect is that trying to find new epicycles will fail beyond a critical length. Think about some lattice regularization as a typical theory where the continous approximation, similar to atomic theory, fails below the critical distance. If what you can "see" is, say, 1000 times the critical length, anything will look yet smooth and you will succeed with a few lowest order terms of an effective theory. At 100 times you will already need much more terms, at 10 times it will start to fail completely, and at the critical length itself even the lowest 10000 terms will not save the game.

So, roughly, if you need one more term to explain the observations, expect that you are already near the critical length where everything will fail, and you need a new theory.

In some sense, gravity is simply that first nontrivial (non-renormalizable) lowest order term, and the Planck length is the corresponding prediction where we see that it cannot be ignored anymore in QFT computations. And where we have, therefore, to expect that the theory starts to fail completely too.

This post imported from StackExchange Physics at 2017-09-16 17:56 (UTC), posted by SE-user Schmelzer