Limitations to Underdetermination of Theory Building and their Role in Fundamental Physics

1. Limitations to Underdetermination of Theory Building and their Role in Fundamental Physics Richard Dawid

2. Empirical Confirmation and Fundamental Physics • In various ways, fundamental physics today has problems to connect to empirical testing. • Gap between characteristic energy scales and range of experiments. (GUTs, SUGRA, Strings...) • fundamental conceptual problems, which prevent empirical predictions. (Strings in particular) • Theoretical scenarios where a large part of the conjectured structure seems to be unobservable in principle. (multiverses) • The situation cannot be expected to change in the foreseeable future.

3. The Theories‘ Status • According to a canonical understanding empirically unconfirmed theories are mere hypotheses. However: + Theories do have a stable development and play the role of well established theories over decades. + A close interdependence between various fields(strings, inflation, part. phys. model building) stabilizes the overall system. + Physicists working on empirically unconfirmed theories in several cases do have substantial trust in their theory‘s viability. (strings, inflation) • Physicists from other fields and philosophers of science tend to be more sceptical. => The canonical understanding of theory assessment may not be adequate for grasping the status quo of fundamental physics

4. Underdetermination of Scientific TheoryBuilding by all possibleevidenceavaillableevidence logically ampliatively

5. The Canonical Understanding ofTheoryAssessment • Theoryconfirmationisbased on empiricaltesting. • Theoreticalreasoningcan‘treplaceempiricaltestingbecauseofscientific underdetermination. • Considerationsaboutscientific underdetermination, in particularaboutthelikelihoodof unconceived alternatives, do not play a significantrole in determining a theory‘sscientificstatus. • Ifwe find a theorytobeconsistently predictively successful, wedon‘thavetothinkaboutpossible unconceived alternatives • Ifnoempiricalconfirmationfor a theoryisfound, assessmentsof underdetermination don‘thelpeither.

6. String Theory & Scientific Underdetermination • String Theory, 35 years after it was firstproposed, remainstheoreticallyincompleteandempiricallyunconfirmed. • Nevertheless, itishighlyinfluentialandconsideredtrustworthybyitsexponents. ? Why? • Trust in thetheoryisbased on theoreticalarguments. • Claim: Thosearguments all amountto assertionsoflimitationstoscientific underdetermination. • Twotypesofargumentsofthatkind: external & internal.

7. External Arguments for ST’s Viability Directly implying limitations to ScU: • Argument of no choice. Directly against ScU’s significance, indirectly for limit. to it: • Meta-inductive argumentof success of consistency-driven theory dynamics in particle physics. • Surprisingexplanatory connections which emerge even though ST was not devised to produce them. All these kinds of argument are known from other scientific fields. They get particularly strong in ST, however.

8. Internal Arguments for ST’s Viability build on Uniqueness Claims • Structural Uniqueness : further theory succession would be implausible under certain conditions. => Final Theory Claim • Final theory Claims also based on - full unification. - lower limit to distance scales due to T-duality. ! Int. arg. arise only in ST. As they rely on its validity, they are circular. ! Combined with ext. arg., they strengthen the case for ST’s viability. Expecting further theory succession implies an assumption of scientific underdetermination. Final theory claims work against it.

9. Interpretation • Constructing a consistent theory becomes so difficult that successes in that direction carry increasing weight. • The general format of the scientific process changes: succession of limited but fully developed theories ==> improving a universal theory without concrete perspective of completion. • Both developments create an environment that suggests strong limitations to scientific underdetermination. • Assessment of scientific underdetermination plays a more central role in theory assessment.

10. A Critical Method or Self-Fulfilling Prophesy? Theories can be questioned and rejected based on theoretical theory assessment. • New theoretical alternatives may be found. • Consistency problems may arise. • No theoretical progress for a long time raises the question whether the theory has a coherent form. • Empirical data can serve as an indirect „test“ of the viability of assessments of underdetermination. • If predictions are confirmed, they strengthen the general case for AoU. • If they are refuted, they weaken the general case for it.

11. The Status ofEmpiricallyUnconfirmedTheories • Assessment of scientific underdetermination can never fully replace empirical confirmation. • However, it may make sense to take it as a strategy for establishing scientific knowledge about the world in the absence of empir. data. • AoU can establish an intermediate epistemic status for theories that lies between „empirically confirmed“ and „pure hypothesis”. (Maxwell thought about such an intermediate status for atomism in the 1870s) • A new concept of theory assessment emerges where AoU is one important pillar. ! New conception is not based on an outright inconcistency of the old one but solely on arguments of plausibility and coherence.

12. Underdetermination and Scientific Realism • Stanford and Hoyningen-Huene: The threat of unconceived alternatives implies the rejection of scientific realism. • If assessments of the likelihood of unconceived alternatives are part of science, the philosopher of science may use the scientist‘s assessment to retain access to a realist interpretation of scientific theories. • One crucial question: What is the conceptual framework within which scientific underdetermination is being assessed and how can that framework be legitimated itself?