# Is there any threat to the results of our effective field theories from unknown higher energy theories?

We use renormalization arguments (and experiments) to change the couplings of a theory and suppress the higher energy physics (saying things like “whatever the fundamental theory, this will be true of the low energy theory.”). And we then get some set of fields, correlation functions, etc. My question is just about the possibility of, say, a theory of quantum gravity that compromises the renormalization arguments we’d been using to determine the sensitivity of EFTs to the space of possible high energy theories. So, perhaps the actual theory wasn’t included in the high energy theory space?

• For one, we know EFTs are useful because we have experimental data to compare its predictions with (and dispel any serious doubts about its usefulness). Theory must explain data, not the other way round. – Avantgarde Oct 16 '18 at 20:33
• @Avantgarde Interesting! I wonder if someone might respond by asking “how do you know that you’ve found the right theory, when other theories might explain the data just as well?” And what the response to them would be. – Hanguk Oct 16 '18 at 20:39
• There is no 'right' theory when one talks about EFTs. The Schrödinger equation is not predictive for $p<m$ while the Dirac equation is (because it is relativistic). But it doesn't mean that one is right and the other is wrong; they are both useful, in their own regimes of validity. – Avantgarde Oct 16 '18 at 21:04
• I might be misinterpreting you here, but I meant to include the regimes of validity in that question. So, we have a low energy theory of quantum gravity valid at scales below the Planck scale. And then someone poses the question I first asked and the one I asked in response to you. – Hanguk Oct 16 '18 at 21:19