Speaking of the Munich conference "Why trust a theory?" a philosopher of science named Massimo Pigliucci (MP)provided an extensive account of the first day's talks.
Here are excerpts of his summary of the first two talks of the day---by David Gross and Carlo Rovelli:
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So, let us get started with
David Gross, talking on “What is a theory?” Gross began by noticing that philosophy and physics have, ahem, “grown apart” over the years — citing the now classic quote by Richard Feynman about philosophy, birds, and ornithology. Gross himself said, however, that he envies the pioneers of quantum mechanics and relativity, who were well versed in philosophy, and he still thinks there is much the two fields can say to each other.
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The crucial issue is strategy, not ideology: we shouldn’t be discussing what science is or is not — since the scientific method itself evolves continuously — but rather what works and what doesn’t. One of the reasons for this meeting is that physics makes predictions that are far out of the current limits of experimentation, around the energy level at which all forces, including gravity, unify (10^28 eV, the Planck scale).
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Theorists may give up, or they may play with extrapolation, or toy models (i.e., thought experiments). They could also adopt strategies from other fields, like mathematics, where beauty is a criterion for success. [Uhm, that’s pretty dangerous territory…]
String “theory” (framework, really) started about 47 years ago out of a data fitting problem, and it didn’t even feature strings at the time, as it initially was a theory of the behavior of gauge mesons. Then people immediately realized that string theory “must” contain gravity, and it is this sort of unexpected theoretical consequences that have kept the excitement going.
But string theory isn’t really a theory — you can’t write its equations on a t-shirt, after all! String theory and quantum field theory are, according to Gross, part of a larger framework. The problem is that we don’t have any idea of how the framework in question picks the Standard Model, hence connecting to experimentally based physics. Here, Gross also thinks, is perhaps where philosophers — who are used to think carefully — may help.
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Gross thinks that the “no alternatives argument” introduced by Dawid (see below) is a powerful one in favor of string theory, as it is not easy to change a framework. [I guess Kuhn would call these paradigms?] There is also an “unexpected explanatory power” argument based on the fact that the string framework connects elegantly with a number of other known notions in physics. Finally, there is the “meta-inductive argument,” according to which past speculative but strongly supported (by the physics community) theories have turned out to be correct. As I said, these are the argument actually advanced by the conference organizer, Richard Dawid, so I’ll return to them shortly below.
[Some of the testiness underlying the conference became briefly evident during an exchange between the next speaker, Rovelli, and Gross. Rovelli pointed out that Gross had gone way over time, and asked whether the organizers would take time out of his talk or from dinner. To which Gross replied that he will surely interrupt Rovelli’s talk too. And he did, somewhat rudely I must say, follow up on his threat. Ouch.]
Next was
Carlo Rovelli, on “Non-empirical confirmation: just a cover-up for the failures of string theory?” He started out by saying that Dawid makes good points in his paper on non-empirical confirmation, about the analyzability of the context of discovery, for instance. But also that Dawid confuses the context of discovery with the context of validation. [Smells of Popper here.] He also confuses descriptive and normative philosophy of science, misreading the history of string theory, since the latter has failed by the lights of its own stated criteria for validation.
Rovelli traced the distinction between context of discovery and of validation to Reichenbach (1938). The time between the two can be very long, as for instance between the publication of Copernicus and Galileo’s books on the structure of the solar system (1543 vs 1610).
[Rovelli has a good general point, though I must also signal that modern philosophers of science do not make a sharp distinction between the two contexts, as discovery and validation are continuously interacting processes.]
Theoretical work is guided by preliminary appraisal, i.e. weak evaluation. This aids the decision of whether to take the theory seriously enough to develop it and test it further. Dawid’s criteria are good as preliminary, weak evaluations of string theory. But they fail as validations.
Rovelli, amusingly, quotes Lakatos [an influential student of Popper]: “It is no success of Newtonian theory that stones, when dropped, fall towards the Earth.” The speaker then listed a good number of past theories that seemed very promising, and yet turned out to be very clearly wrong.
String theory itself set out validation criteria early on in its history: computing the parameters of the Standard Model from first principles, for instance, or deriving the existence of three families (of particles) from first principles, or predicting the sign of the cosmological constant, or predicting new particles to be discovered at LHC energy levels, or low energy supersymmetry, and so forth. According to Rovelli, all of these failed, turning string theorists into the mythical fox who argued she didn’t really like the grapes, once it was clear that she couldn’t reach them… [Nice classical reference to Aesop!]
There are alternatives, like loop quantum gravity (which actually
can be written on a t-shirt!). For Rovelli this is just as not yet validated as string theory, but at the least its existence rejects the oft-made claim that string theory is the only game in town. He also cautioned about confusing “tenure in major universities with consensus of the scientific community,” pointing out that Gross won the Nobel and has a position at a major university because of his non-string work.
Rovelli concluded by pointing out that claiming that a theory is valid even though no experiment has confirmed it destroys the confidence that society has in science, and it also misleads young scientists into embracing sterile research programs. [Lakatos would have called them “degenerate.”]
After coffee break it was
Dawid’s turn with “Non-empirical Confirmation.” Though his focus is on string theory, his ideas are applicable to other frameworks as well. He began by acknowledging that the theory hasn’t found empirical confirmation for quite some time, and moreover that this state of affairs may continue long into the future. Nevertheless, ...
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https://platofootnote.wordpress.com/2015/12/08/why-trust-a-theory-part-i/
http://www.whytrustatheory2015.philosophie.uni-muenchen.de/index.html
http://www.whytrustatheory2015.philosophie.uni-muenchen.de/program/index.html
http://www.whytrustatheory2015.philosophie.uni-muenchen.de/media/index.html