Theories and Data.
How they interact in exploring Reality
Uppsala, April 2010
Andreas Bartels
Institut für Philosophie, Universität Bonn
[email protected]
Outline
1. Theories as Means of Interpreting and Discovering
Data.
2. Three Problems for the Epistemic Interaction
between Theories and Data.
3. Theory-Ladeness of Observation: Vice or Virtue?
4. Glymour‘s Bootstrap Theory of Confirmation
5. Empirical Underdetermination: A Problem for
Theory-Selection?
6. Why believe in Theories?
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1. Theories as Means of Interpreting and
Discovering Data
Scientific Theories (Models) fulfill two main functions
with respect to empirical Data:
First, they provide a net of theoretical relations by
which we may interpret the Data.
For example, by embedding Data into the standard
model of cosmology (sometimes by identifying the
data as fulfilling certain theoretical predictions, as
in the case of microwave background radiation),
some otherwise contingent and unrelated facts will
be located at a particular place within the causal net
of the model.
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1. Theories as Means …
Data, when integrated into a theory by theoretical
interpretation, get some evidential status with
respect to other parts of the theory. Their further
exploration may produce confirmations (or
disconfirmations) of theoretical relations of the
theory.
Example: Are there inhomogeneities in the microwave
background radiation (MBR) compatible with the
homogeneity assumption of the idealized model and
with the observed amount of inhomogeneity of
matter distribution in the actual universe?
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1. Theories as Means …
Disagreement between Theory and Data may be
compensated by the introduction of additional
objects or mechanisms.
Example: The existence of dark matter may
compensate the fact that the measured temperature
inhomogeneities of MBR are smaller than to be
expected if all matter would interact with light.
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1. Theories as Means …
Data do not only confirm or disconfirm a theory
qualitatively, they can also be used to specify the
values of theoretical parameters and thereby to test
the theory in a quantitative way.
Example: Statistical analysis of MBR allows to measure
space curvature. Global flatness of space leads to
specification of the age of the universe.
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1. Theories as Means …
Theories interact with Data not only in a descriptive or
puzzle solving dimension (interpretation,
confirmation, specification), but
There is a further explorative function of theories
which is responsible for research dynamics.
Theories do not only describe reality, but they are also
means for exploring reality (discovery of novel data).
Example: Predictions of dark matter and dark energy
(theoretical requirements based on critical density
and on expansion rate).
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2. Three Problems for the Epistemic Interaction
between Theories and Data
Data specify and (dis-)confirm Theories
Epistemic value of that interaction depends on how
independent the Data are from the Theory. Only independent
Data supply genuine information about the validity of Theories.
Theories interpret Data
Epistemic value depends on how well selected the theory is
from the set of theoretical alternatives by means of the Data.
Theories predict or require (not yet discovered) Data
Epistemic value depends on the reasons for believing in
predicting theories (instead only in collections of Data).
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2. Three Problems …
That the conditions on which the epistemic value of
theory-data interaction depends are fulfilled, is far
from obvious. The following three problems cast
serious doubts that this is the case:
Theory-Ladeness of Observation.
Empirical Underdetermination of Theories.
Challenge: Empirical Knowledge restricted to the
collection of evidences of a theory?
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3. Theory-Ladeness of Observation. Vice or
Virtue?
When Feyerabend, Hanson, Kuhn et. al. rejected the classical
logico-empiricist programme in philosophy of science, they
referred to the ‚Theory-Ladeness of Observations‘ in order to
demonstrate the falsity of this programme.
That a type of observation is theory-laden, means that
the values of the corresponding observational
variable can be determined only by means of
presupposing some of the hypotheses of the theory.
If so, observations of that sort cannot be an impartial
judge on the validity of the theory. Verifying the
observation then already means (partly) accepting
the validity of the theory.
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3. Theory-Ladeness …
Examples for Theory-ladeness:
Galileo‘s tower: That the stone comes down to the
ground at the tower‘s foot, can tell for or against the
hypothesis of the rotating earth, depending on
whether the principle of circular inertia is
presupposed or not.
Hubble-constant: Determination presupposes the
relativistic interpretation of redshift data.
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3. Theory-Ladeness …
Could the problem be circumvented by extracting ‚raw
data‘ from ‚interpreted data‘?
This can be done, but row data would not confirm or
disconfirm any theory, according to the bootstrap
conception of confirmation. At least some variables
within theoretical hypothesis have to be determined
by means of observational parameters plus other
theoretical hypotheses. Thus the logic of bootstrapconfirmation requires Data to be ‚laden‘ by
theoretical hypotheses.
In that sense, theory-ladeness is not a vice, but a virtue
of Data. It makes data able to confirm theories.
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4. Glymour‘s Bootstrap Theory of Confirmation
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4. Glymour‘s Bootstrap Theory of Confirmation
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5. Empirical Underdetermination. A Problem for
Theory Selection?
Empirical Underdetermination: The existence of
alternative theories that possess an identical body of
observational consequences.
According to the Hypothetico-Deductive (HD)-approach
of confirmation, such alternative theories are equally
well confirmed by their consequences.
The situation is different according to the Bootstrapaccount: The internal structures of the competing
theories decide, which theory is better confirmed by
the data.
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5. Empirical Underdetermination …
Thus, even if two theories can explain exactly the same
observations, it can be rational to prefer one of them,
if its hypotheses are better confirmed by the data.
Example (Glymour: Theory and Evidence 1980):
„Copernican theory is superior to Ptolemaic
astronomy. There are properties of the bodies of the
solar system that are presupposed by both theories,
but that are indeterminable in Ptolemaic theory
whereas they can be determined within Copernican
theory“
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5. Empirical Underdetermination …
In Copernican theory – contrary to Ptolemaic theory –
the orbital periods of the inferior planets can be
determined (from the orbital period of the earth and
from the synodic periods of these planets, which are
observable). Only Copernican theory can thus
determine the order and distances from the sun of
the inferior planets, whereas the order of Venus and
Mercury is indeterminate in Ptolemaic theory.
Thus hypotheses about the order and distances of the
planets can be tested in Copernican theory, whereas
Ptolemaic theory provides no means for testing any
particular hypothesis about their order from
observations.
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5. Empirical Underdetermination …
Theories do not necessarily have equal empirical
validity, if the body of observational evidences is the
same for them. It depends from the internal
structures of the theories, which hypotheses can be
confirmed by which Data.
‚Empirically equivalent‘ theories may draw different
degree of confirmation from the Data and thus
selection between them can be rational:
„If the bootstrap strategy is a rational one, then
positional astronomy provided rational grounds for
preferring Copernican theory to Ptolemaic theory“
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6. Why believe in Theories?
Why not prefer the body of observational evidences of
a theory as representing our empirical knowledge –
why not believe in the data themselves instead of
believing in a theory that has uncertain degree of
confirmation?
Answer:
This super-empiricism would not be rational, if
confirmational status decides on the rationality of
theory preference. Theories are better warranted by
the evidence than is their collection of observational
evidences alone. Thus we should prefer theories to
their bodies of evidences.
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6. Why believe in Theories?
Why are theories better warranted by their evidence?
Answer: Confirmation is ‚spread‘ over the theory, but
not over the body of evidences
There is no sentence within the whole body of
consequences that is tested by the evidence and
that entails all sentences in the collection, but there
are such sentences in a theory.
„Evidence which tests the fundamental principles of
the theory, with respect to the theory, will fail to test
all of the observational consequences of the theory
with respect to the observational consequences of
the theory“ (Glymour 1980)
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