Half a century has now passed since the discovery of supersymmetry. During this time the subject has developed enormously, with stupendous advances on many fronts, some of which are also documented in this book. Supersymmetry has been a major driving force of developments in mathematical physics and pure mathematics. So it is definitely here to stay! Nevertheless, we now (in 2023) have to face up to the fact that supersymmetry, at least in the form championed over many years, is off the table as a realistic option for real life particle physics. 15 years of LHC searches have not produced a shred of evidence for superpartners of any kind. Quite to the contrary, the integrated results from LHC strongly indicate that the SM could happily live up to the Planck scale more or less as is, and without supersymmetry or other major modifications.It is funny how physicists can persist with ideas that have no hope of finding any connection to the real world.
So what keeps them going? A misguided notion that they are following an Einsteinian ideal.
Independently of whether the ideas sketched above are on the right track or not, I remain attached to the Einsteinian point of view that we should try to understand and explain first of all our universe and our low energy world, and that in the end there should emerge a more or less unique answer. I believe that 50 years of supersymmetry have brought us a wee bit closer to this goal, though not as close as many would have wished. Of course, this point of view runs counter to currently prevalent views according to which the only way out of the vacuum dilemma of string theory is the multiverse. But if Nature must pick the ‘right’ answer at random from a huge (> 10272,000 ?) number of possibilities, I see no hope that we would ever be able to confirm or refute such a theory.I don't see how supersymmetry could be getting us closer to any goal, or that the multiverse could be a way out of anything.
Already in 1929, and in connection with his first attempts at unification, Albert Einstein published an article in which he states with wonderful and characteristic lucidity what the criteria should be of a ‘good’ unified theory: (1) to describe as far as possible all phenomena and their inherent links, and (2) to do so on the basis of a minimal number of assumptions and logically independent basic concepts. The second of these goals, also known as the principle of Occam’s razor, he refers to as “logical unity” (“logische Einheitlichkeit”), and goes on to say: “Roughly but truthfully, one might say: we not only want to understand how Nature works, but we are also after the perhaps utopian and presumptuous goal of understanding why Nature is the way it is, and not otherwise.”This is why I wrote an anti-Einstein book. Einstein's views were bad enough, but his followers quote him to justify absurd research programs.
Update: Sean M. Carroll made some comments in his recent AMA podcast, similar to this paper. That is, supersymmetry was invented to solve certain technical theoretical mysteries in high-energy physics. Had that been valid, supersymmetric particles would have been discodvered at the LHC collider. The LHC determined that no such particle exists. However he insists that supersymmetry is not dead, because theorists still study it, and because there could be supersymmetric particles that are beyond the range of what anyone can observe.