Is avoiding fine-tuning a useful criterion for looking for new physics?

Cosmological constant and Higgs. People use fine tuning as an argument that there might be a more fundamental theory.

Strongly parameterization dependent.
- Are we unhappy based on our aesthetic options of what a “nice” theory should look like?

Eg. SUSY is “beautiful” for describing connections between many fundamental particles — however so far we have failed to find any experimental evidence for it.

Avoiding fine-tuning in condensed matter is usually the way to go. The description of phases of matter requires only universal data that is independent of any fine-tuning of the microscopic parameters of the theory. In other words, there are several condensed matter systems that are microscopically different but they belong to the same universality class. These means that there are several phases of matter common to a broad range of physical systems. Hence, in the context of condensed matter systems, fine-tuning is usually avoided. In fields like cosmology, avoiding fine-tuning is a reasonable motivation despite the fact that the observable universe seems to be very fine-tuned. Avoiding fine-tuning in cosmology often leads to theories involving many universes. This will correspond to a big conceptual leap that has no supporting evidence, since its been shown that if some of the constants ruling the fundamental interactions are modified slightly,  it is very likely that the life as we know it now wont be able to exist. In cosmology, the theory that describes most of the observable universe has fine-tuning inbuilt. 

It can be, but not always. When there is a competitor theory, fine tuning argument can be useful. However, it is a bad strategy to only focus on fine tuning and reject a theory just based on the fact that it is fine tuned.
Fine-tuning in cosmology may be inevitable, since there is only one universe. Initial conditions of the universe might be fine-tuned. 

Fine-tuning has been useful in the history of particle physics. Maybe in other areas of physics is not as important.

Worked in the past – good track record

Is there an example where fine-tuning has persisted

“environmental” explanations unsatisfactory – know good explanation when you hear it.

\lambda is a big hint

If two theories describe the same phenomena, with the same number of degrees of freedom, then we should decide which one is the true theory by experiment. However, when it is impossible to do an experiment, avoiding fine tuning might be a way to decide which theory is more worth working on. Fine tuning might be a sign that there is a more fundamental theory, and the fine tuning is an artifact of a less fundamental effective description. However, sometimes going to the more fundamental theory requires adding even more fine tuning. Some people take it farther to believe that the most fundamental theory should have only “nice” numbers: small integers, pi, e and so on, and the "ugly", apparently fine-tuned numbers that we measure for various dimensionless parameters in our models are just an artifact of the incomplete effective description.


Comments will be accepted until June 29.