Limitations to Underdetermination
of Theory Building and their Role in
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
The Theories‘ Status
- According to a canonical understanding empirically unconfirmed
theories are mere hypotheses.
+ 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,
• Physicists from other fields and philosophers of science tend to be
=> The canonical understanding of theory assessment may not be
adequate for grasping the status quo of fundamental physics
Underdetermination of Scientific Theory Building
by all possible evidence availlable evidence
ampliatively Quine [‚reasons for Sklar, Stanford,
indet. of transl.‘] Hoyningen-Huene
van Fraassen (transient underdet.)
The Canonical Understanding of Theory Assessment
• Theory confirmation is based on empirical testing.
• Theoretical reasoning can‘t replace empirical testing because
of scientific underdetermination.
• Considerations about scientific underdetermination, in
particular about the likelihood of unconceived alternatives, do
not play a significant role in determining a theory‘s scientific
– If we find a theory to be consistently predictively successful, we don‘t
have to think about possible unconceived alternatives
– If no empirical confirmation for a theory is found, assessments of
underdetermination don‘t help either.
String Theory & Scientific Underdetermination
• String Theory, 35 years after it was first proposed, remains
theoretically incomplete and empirically unconfirmed.
• Nevertheless, it is highly influential and considered
trustworthy by its exponents.
• Trust in the theory is based on theoretical arguments.
• Claim: Those arguments all amount to
assertions of limitations to scientific underdetermination.
• Two types of arguments of that kind: external & internal.
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 argument of success of consistency-driven
theory dynamics in particle physics.
• Surprising explanatory 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.
Internal Arguments for ST’s Viability build on
• 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.
• 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.
A Critical Method or Self-Fulfilling Prophesy?
Theories can be questioned and rejected based on theoretical
• 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.
The Status of Empirically Unconfirmed Theories
• Assessment of scientific underdetermination can never fully replace
• 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
• A new concept of theory assessment emerges where AoU is one
! New conception is not based on an outright inconcistency of the old
one but solely on arguments of plausibility and coherence.
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?