The Observable / Unobservable Distinction

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The Observable / Unobservable Distinction

• Anti-realism depends crucially on this
  distinction the epistemological thesis.
• A somewhat confusing distinction
• Observable / theoretical distinction
• Can we divide our language into a theoretical and
  non-theoretical part?
• Can we classify objects and events into
  observable and unobservable ones?

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• Some relevant questions
• Is the line drawing the observable/unobservable
  distinction arbitrary?
• Is this distinction epistemologically
  significant?
• Does this distinction really exist?
• Is everything observable in principle?

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• E.g. can electrons be observed using apparatus
  like cloud chamber

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• It seems that cloud chambers only allow us to
  detect electrons, but not observe them.
• E.g. a jet aircraft can only be detected by the
  trail left behind.

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• But how to distinguish between observation and
  detection? Would it be arbitrary?
• Consider these sequence of events looking at
  something
• with the naked eye,
• through a window,
• through a pair of strong glasses,
• through binoculars,
• through an ordinary microscope,
• through an electron microscope, and so on.

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• Some argue that these events lie on a smooth
  continuum
• How to decide which count as observing and which
  not?

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• E.g. can a biologist observe microorganisms
  with a high-powered microscope, or can she only
  detect their presence?
• Detection relies heavily on theory.
• Interpreting this image also relies on theory.
• Theory-ladenness of detection / observation

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• So how much theory-ladenness is needed to draw
  the line? Arbitrary?
• Yet some retort that this argument only shows
  that observable is a vague concept.

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• The same applies to observable
• Vagueness seems only to set an upper limit on the
  precision with which antirealists can formulate
  their position.
• What do you think?

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The Underdetermination Argument

• Why is knowledge of unobservables impossible?
• Consider again the kinetic theory of gases
• Observational data constitute the ultimate
  evidence for claims about unobservable entities.

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• Anti-realists argue that
• Observational data underdetermine scientific
  theories
• If this thesis is true, agnosticism about the
  unobservable world is vindicated.

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• Underdetermination the Duhem-Quine thesis
• Pierre Duhem (1861-1916)
• French philosopher, historian
• W. V. O. Quine (1908-2000)
• American philosopher, logician
• Recall some previous points
• Negative evidence does not prove conclusively
  that a theory is incorrect.
• (Theory T Auxiliary Hypothesis H) ?
  Implication I
• ? I
  ___.
• ? (T H)

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• Example 1 Round Earth vs. Flat Earth Theory

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• Example 2 The discovery of Neptune
• Newtons theory of gravitation wrongly predicted
  the orbit of Uranus.
• Some scientists tried to rescue Newtons theory
  by postulating the existence of an unknown
  planet.
• Neptune was finally discovered at almost the
  exact place and time as predicted.

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• The Duhem-Quine thesis
• Any theoretical claim T can consistently be
  retained in the face of contrary evidence by
  making adjustments elsewhere in our web of
  beliefs.
• (T H) ? I (T H) ? ?I
• Underdetermination

Both T and T can always be retained!
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• Besides observational data, recall the criteria
  of adequacy (pragmatic virtues) for choosing
  theories
• Simplicity, conservatism, fruitfulness, scope.
• But are such criteria relevant to the truth of
  theories, or at least to their probable truth?
• What do you think?
• Reference
• Simplicity from the Stanford Encyclopedia of
  Philosophy
• http//plato.stanford.edu/entries/simplicity/

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Implication for Observable but Unobserved Things

• Suppose satellite pictures show

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• A common hypothesis
• Many alternative hypotheses are possible, however

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• The Duhem-Quine thesis guarantees that all these
  hypotheses can be sustained come what may.
• Hence underdetermination again!
• Only knowledge of actually observed things is
  possible?!
• But what about knowledge of
• dinosaurs,
• continental drift,
• formation of the Earth,
• and many other things in science?

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• Seems to be a reductio ad absurdum.
• Knowledge of the unobservable world seems
  possible after all.
• But a version of the problem of induction still
  persists
• The problem of induction
• How to justify inductive inferences - on which
  scientific knowledge heavily depend?
• Uniformity of Nature Assumption (UNA)
• No consensus.
• Scientific knowledge is ultimately founded on
  faith towards UNA?

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• Underdetermination
• Hence inductive inference from data to theory

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• Final remarks
• The underdetermination argument does raise a real
  difficult problem.
• But it seems that there is no special difficulty
  about unobservable entities.
• Problem of inductive knowledge for all sorts of
  objects.