Roger Penrose Challenges Popper’s Falsifiability Criteria

Many years ago I read Roger Penrose’s books and found that he had a strong challenge to Popper’s demarcation of science-based on falsifiability. This is a challenge I feel is worth discussing and understanding better, so I quote it here:

Karl Popper provided a reasonable-looking criterion for the scientific admissibility of a proposed theory, namely that it be observationally refutable. But I fear that this is too stringent a criterion and definitely too idealistic a view of science in this modern world of ‘big science.’

Let me take the example of supersymmetry in modern particle physics. …it is a central ingredient of string theory. Its status among theoreticians these days is so strong that it is almost considered to be part of today’s ‘standard’ particle-physics model. Yet, it has no (serious) experimental support, as things stand. [At least when this was written back in 2005.] The theory predicts ‘superpartners’ for all the observed fundamental particles of Nature, but none of these has so far been observed. The reason that they have not, according to supersymmetry theorists, is that a symmetry-breaking mechanism (of unknown nature) causes the superpartners to be so massive that the energies needed to create them are still beyond the scope of present-day accelerators. With increased energy capabilities, the superpartners might be found, and a new landmark in physical theory would be thereby achieved, with important implications for the future. But suppose that still no superpartners are actually found. Would this disprove the supersymmetry idea? Not at all. It could (and probably would) be argued that there had simply been too much optimism about the smallness of the degree of symmetry breaking, and even higher energies would be needed to find the missing superpartners.

We see that it is not so easy to dislodge a popular theoretical idea through the traditional scientific method of crucial experimentation, even if that idea happened to actually be wrong. …

Does the ‘un-Popperian’ character of such models make them unacceptable as scientific theories? I think that such a stringent Popperian judgment would be definitely to harsh. For an intriguing example, recall Direac’s argument ([in section] 28.2 [of his book]) that the mere existence of a single magnetic monopole somewhere in the cosmos would provide an explanation for the fact that each particle in the universe has an electric charge that is an integral multiple of some fixed value (as is indeed observed). The theory which asserts that such a monopole exists somewhere is distinctly un-Popperian. That theory could be established by the discovery of such a particle, but it appears not to be refutable, as Popper’s criterion would require; for, if that theory is wrong, no matter how long experimenters search in vain, their inability to find a monopole would not disprove the theory! Yet that theory is certainly a scientific one, well worth of serious consideration.

Roger Penrose in Road to Reality, p. 1020-1021

The reason we added supersymmetry to modern particle physics was to solve problems that we knew of no other way to solve. Yet supersymmetry can’t be falsified by experiment. (Or so Penrose is claiming.) The only real way to ‘refute’ supersymmetry would be to propose a better theory that solved the original problem in a better way. So Deutsch’s 2016 Logic of Experimental Tests is relevant here because he points out that falsification (by experiment at least) is actually impossible outside of a theory-to-theory comparison thanks to the Duhem-Quine thesis. This is a strong example of Deutsch’s thesis.

There is an interesting epistemological problem here, however, that Deutsch didn’t resolve. Let’s say we did find a magnetic monopole in nature or that we did find a superpartner via a collider. What role would the discovery play epistemologically? At a minimum, it seems to inform us that physics with supersymmetry is a better explanation than physics without supersymmetry. Yet there is no ‘falsifying case’ here. Physics without supersymmetry doesn’t actively predict that there are no monopoles, for example.

But then how would that not at least tentatively be a case of “corroborating” (or, if you prefer “strengthening”) the theory? What epistemological role does “verification” or “evidence” like this play in Popper’s theory?

3 Replies to “Roger Penrose Challenges Popper’s Falsifiability Criteria”

  1. I don’t understand Penrose’s problem. Super-symmetry is a conjecture, for which no significant test has been found. Just like lots of other conjectures. The fact that lots of theoreticians “like it” could hardly be more irrelevant, most of their “theories” are just untested conjectures as well. Real scientific theories have been tested, and have consequences in the real world. The only consequences of the conjectures mentioned above is that they keep some really smart people employed, and result in the destruction of whole forests of trees to make the paper on which their speculations about these conjectures are printed. And we haven’t even gotten to Multi-verses,

    1. Allan, do this as a simple thought experiment. Pretend a monopole was found in nature. Would you still see super-symmetry as ‘merely a conjecture’ and not a ‘theory’? Or would you then consider it now a ‘theory’ because it’s now been ‘tested’?

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