The Shaky Throne: String Theory, Inflationary Cosmology, and The Very Idea of Scientific Explanation.

Thomas Kuhn is most well known for developing a model of scientific revolutions, the plural is important, which to no small degree considers sociological factors to be significant to any explanation of the shift from normal to revolutionary science. One of the more controversial of Kuhn’s claims, flowing from the incommensurability thesis, was that not only are scientific revolutions instances of revolution *within* science, but they are also revolutions *of* science, given that standards of theory appraisal are internal to a prevailing paradigm, according to Kuhn. That view flows from the plural, for it strikes against the view that there has been only one scientific revolution namely *the* scientific revolution of the 17th century.

An interesting feature of contemporary theoretical physics, both within high energy particle physics and cosmology, is claims made by proponents of string theory and inflationary cosmology that they are engaging in not only a revolution within science but a fundamental epistemic shift of science. Their claim rests on the view that science hitherto has been characterised by Popperian falsifiability, whereas they possess a prior reasons for being right usually ones to do with beauty, consistency and completeness. They are right because they must be right, even though no clear empirical benchmark yet exists that could falsify the theory.

But what if, rather, the erstwhile revolutionaries are really the conservatives defending an outlook with little to no credence, “not even wrong” as it were, from an established position within the hierarchy of science against an increasingly confident, though ostracised, band of critics who really are the revolutionaries of the piece? Following in the spirit, rather than the footprints, of Kuhn we are invited to consider some of the possible sociological, noncognitive, forces at play, both within and without science.

The critics of the established position in particle physics and cosmology assert that the prevailing view, of string theory and inflation theory, represents a type of collective irrationality. One should stress that although the hitherto lack of empirical testability is a key issue, the critics themselves are not Popperian for the issue is the in principle absence of any criteria of empirical testability. The critique of Popper, long ago made and accepted within the philosophy of science, then becomes an epistemic device to justify theoretical approaches that in principle are not amenable to empirical testability. Furthermore, to make matters worse, the critics allege that string theorists and inflationary cosmologists stand contrary to their preferred a prior cognitive criteria, beauty and the like, for they no longer are in possession of a beautiful and consistent theory. Perhaps at an earlier time both were in possession of a certain elegance and beauty, but that is the problem with beauty. It can bedazzle the beholder long after it has passed.

One can, broadly speaking, think of two causes underlying collective irrationality. The first are manifestations of innate cognitive biases that can inhibit collective understanding, and the second are sociological whereby expressions of institutional interest even, indeed especially, rational ones, lead to collective irrationality.

The two, of course, can coexist. Consider, for instance, financial crises. The “animal spirits,” as Keynes put it, can lead to collective irrationality through herd behaviour and, moreover, cognitive biases under conditions of uncertainty can prevent the rational assessment of risk. Regarding the sociological, systemic risk is a good example of an externality for individual financial institutions, quite rationally in pursuit of short term profit, under price the risk of systemic collapse when engaging in trades which can and does lead to systemic financial crises.

The same can apply to science, and some claim that fundamental physics currently exhibits a type of collective irrationality through what’s called “multiverse mania.” The multiverse refers to the supposition, deriving from both particle physics and cosmology, that there exists a “cosmic landscape” of universes each with their own fundamental physics. The key physical parameters of our universe, such as the values of the constants of nature, can be explained upon the basis of the anthropic principle.

Critics of multiverse mania argue that the two key theories that underpin it, string theory within particle physics and inflation within cosmology, in principle are beyond empirical testability, that they, in fact, make no testable empirical predictions, and that to remain consistent with the nature that we know they are required to engage in special pleading, such as invoking the anthropic principle. Hence, as far as fundamental physics goes, science, on the critical account, is exhibiting a type of collective irrationality.

It is not hard to see that the critics are not naïve Popperians. The issue, I would argue, concerns not so much falsifiability or testability but rather explanation. The big advance made by the scientific revolution was that it replaced a concern for developing coverage of data with concern for depth of explanation through idealisation and abstraction, if need be at the cost of common sense. Multiverse mania, to no small degree, trades on this but one can see that this is not justified. To be sure spacetime dimensions beyond the four strikes against common sense, but that doesn’t mean that it also offers an explanation of nature. String theory and inflation theory are not scientific because they in principle provide no explanation, let alone depth of explanation, for the universe we inhabit. Ours is as likely as any other, and our existence selects its properties. That explains nothing.

Explanation, not testability, is the matter that makes both contrary to science.

To be sure there have been good intellectual reasons for adopting both string theory and inflationary cosmology. The first superstring revolution, as it is called, in the 1980s led to a finite theory of quantum gravity. However, that came at the cost of many spacetime dimensions and a plurality of theories. The second superstring revolution promised a unification of those theories by showing that they are dual aspects of the one underlying theory. But that too came at a cost, namely the multiverse. Inflationary cosmology offered to sweep away the anomalies of cosmology left unanswered by the hot big bang model, such as the horizon and flatness problems. However, it soon became clear, through eternal inflation, that this too led to the multiverse.

Both theories, the critics assert, not only do not make testable empirical predictions but they are challenged by current observation, and that on interestingly similar grounds. With string theory a key empirical challenge is the continued failure of the Large Hadron Collider to find evidence of “natural” supersymmetry, and for inflation observation appears to rule out “natural” versions of inflationary expansion. They both, as noted, also lead to the multiverse and hence the epistemic shift. The empirical problems of natural supersymmetry and inflation, notice, also are of relevance to the criteria of elegance and beauty.

What might account for this state of affairs? One of the more oft stated explanations focuses on the lack of new experimental data that takes us beyond the standard model in particle physics, so inviting higher superstitions, to borrow a useful and insightful term from Helge Kragh, given that when the cat is away, namely nature, the mice shall play. That explanation ignores two points, firstly the current experimental state of play discussed above which is problematical for both strings and inflation, and secondly that whatever the situation might be in particle physics the same cannot be said for cosmology.

It is often stated that from the 1980s, pretty much at the same time that inflation became the standard paradigm, cosmology transitioned from an almost purely theoretical enterprise into an empirical science. Notice that is the opposite of the picture painted in high energy particle physics, yet multiverse mania rules the roost. This seems to demonstrate to us that the dearth of experiment beyond the standard model cannot be a complete explanation of the current state of affairs. Also, during the renaissance of general relativity in the 1960s and 1970s, much work proceeded in the absence of experimental data yet that did not lead to an epistemic shift within cosmology of the multiverse variety. The situation, then, seemingly is the exact opposite of that in particle physics. When experiment was further removed from theory than today cosmology firmly had its feet on the ground as it were, but when it became an empirical science so theory increasingly exhibited higher superstition.

That is quite peculiar, both intrinsically but also with respect to the usual explanation for higher superstition in particle physics. One possible noncognitive explanation for this lies with the culture of post-war particle physics, especially in the United States. The origins of inflationary cosmology can be found in a certain marriage of cosmology with particle physics, so it shouldn’t be too surprising to see what had become the prevailing culture, of faith fashion and fantasy to steal Roger Penrose’s phraseology, within particle physics increasingly spread to theoretical cosmology. Perhaps there is something there.

Should the critics of multiverse mania be right, surely noncognitive factors would, to whatever degree, be needed to explain this curious phase in the history of science.

We tend to think of physics as the king of the sciences, a view that has had a strong influence in philosophy especially with physicalist conceptions of naturalism. Iwan Morus in an interesting study, that should be more widely read, has pointed out that physics became king relatively recently basically in the mid to late 19th century. Physics is a diverse discipline, there’s more to physics than high energy particle physics, so whatever type of physics should become hegemonic within the discipline should, naturally, inherit not just the throne of science but the throne of knowledge itself.

There surely could not be any doubt that upon the throne sits physics and the crown jewels very much consists of particle physics, especially after World War Two. I would argue that the Manhattan Project and the Cold War played an important role here although there would have been antecedents (think of both as exponentially expanding tendencies already existent), so factors outside of science were, partly, surely at play. But the Cold War bubble, to continue the analogy with inflationary cosmology, by the 1970s most definitely burst, and the bursting of the bubble also coincided with the onset of the neoliberal era which has had a negative effect on universities and research. This might partly explain why multiverse mania manifests itself so readily in the media, popular culture and the like, largely at the behest of scientists themselves, as it provides justification for continued support for theoretical particle physics at a time of neoliberal discipline. Even space physics by now, as demonstrated in Trump’s budget proposal, is not immune to the neoliberal lash.

The erstwhile revolutionaries are defending the throne which is to say that they are defenders of an established hierarchy. It may well be the case that high energy particle physics has exhausted its intellectual potential and that fundamental advances in physics will come when the discipline overcomes the higher superstitions of string theory and inflationary cosmology, in which case the defenders of the traditional conception of science bequeathed to us from the scientific revolution would become the true revolutionaries as the explanatory power of physics deepens.

Consider one possible example. Some that criticise inflationary cosmology have revived bouncing cosmologies whereby the universe exhibits cycles of contraction and expansion, rather than having a singular big bang origin, which can dispense with a postulated period in the universe’s history, known as the Planck epoch, governed by a theory of quantum gravity. If that’s so, that takes away one argument for developing a theory of quantum gravity a quest that has dominated physics even more than string theory and inflationary cosmology. The history of science may one day record this quest as the cognitive side of the ledger distorting theoretical physics.

Perhaps, in short, there are two overriding factors at play one cognitive the other noncognitive and they both have coincided during the same period of scientific history. The first is the quest for quantum gravity, and the second is the bursting of the post cold war bubble in theoretical physics.

I don’t think I have articulated this rather well, that is looked at it with sufficient depth and subtlety, so I will revisit this topic from time to time to further clarify my thinking.