From Sabine Hossenfelder at her blog Backreaction:
I was elated when I saw that Gian Francesco Giudice announced the “Dawn of the Post-Naturalness Era,” as the title of his recent paper promises. The craze in particle physics, I thought, might finally come to an end; data brought reason back to Earth after all.
…
I believe what is needed for progress in the foundations of physics is more mathematical rigor. Obsessing about ill-defined criteria like naturalness that don’t even make good working hypotheses isn’t helpful. And it would serve particle physicists well to identify their previous mistakes in order to avoid repeating them. I dearly hope they will not just replace one beauty-criterion by another.
Giudice on the other hand thinks that “we need pure unbridled speculation, driven by imagination and vision.” Which sounds great, except that theoretical particle physics has not exactly suffered from a dearth of speculation. Instead, it has suffered from a lack of sound logic. More.
Rob Sheldon, our physics color commentator, writes to say,
I’m beginning to like Sabine Hossenfelder’s blog–this latest is a critique of a fad in theoretical particle physics called “naturalness”. Briefly, the idea of “naturalness” is that we don’t have enough data to constrain the theories, so we have some sort of Darwinian selection “in theory space”, where two theories that behave nicely in regions we can explore (say, Energy < 14TeV threshold of CERN collider) are compared in regions we can’t explore (say, E>1000 TeV) and the one with better manners is preferred.
Sabine doubts that there is any merit to the hypothetical comparisons of hypothetical theories–not because hypotheticals aren’t real (after all, they may be someday), but because there is an infinite supply of them. So what if your hypotheticals are better than his hypotheticals, there’s an infinite line of contestants to defeat. Thus vendors of “naturalness” must also restrict the venue to truncate the line, and it is that arbitrary choice of venue that makes all objectivity fly out the window.
Sabine concludes:
“I believe what is needed for progress in the foundations of physics is more mathematical rigor. Obsessing about ill-defined criteria like naturalness that don’t even make good working hypotheses isn’t helpful. And it would serve particle physicists well to identify their previous mistakes in order to avoid repeating them. I dearly hope they will not just replace one beauty-criterion by another. Giudice [a founder of naturalness] on the other hand thinks that “we need pure unbridled speculation, driven by imagination and vision.” Which sounds great, except that theoretical particle physics has not exactly suffered from a dearth of speculation. Instead, it has suffered from a lack of sound logic.”
This same argument against naturalness, works for multiverses (as Sabine alludes) as well as Darwinism.
And I don’t want to be a spoilsport, but it applies to “Fine Tuning” arguments equally well, where the conclusion is instead “unnaturalness”. But if “naturalness” is poorly defined, so is “unnaturalness”.
See also: Did Karl Popper really kill particle physics? Would a jury convict him? Rob Sheldon relects on a point made by Sabine Hossenfelder.
and
The multiverse is science’s assisted suicide