The Observable / Unobservable Distinction

1. 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?

2. 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”?

3. E.g. can electrons be “observed” using apparatus like cloud chamber:

5. 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.

6. 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.

7. Observing Not observing • Some argue that these events lie on a “smooth continuum”: • How to decide which count as observing and which not?

8. 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

9. Bald? Not bald Bald ? ? ? • 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.

10. ? Unobservable Observable • 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?

11. E.g. Boyle’s Law Directly tested by observing the readings on the apparatus. Molecules postulated are unobservable. 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.

12. T T’ Any relevant observational data • Anti-realists argue that: • Observational data “underdetermine” scientific theories: • If this thesis is true, agnosticism about the unobservable world is vindicated.

13. 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)

14. Example 1: Round Earth vs. Flat Earth Theory

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

17. T + H T’ + H’ any relevant observational data • 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!

18. 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/

19. Before 1987 1987 Implication for Observable but Unobserved Things • Suppose satellite pictures show:

20. Volcanic eruption The camera that took the pictures was faulty Caused by UFO The large crater appearing in 1987 The large crater appearing in 1987 A meteorite struck the moon in 1987 • A common hypothesis: • Many alternative hypotheses are possible, however:

21. 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?

22. 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?

23. T T’ Observational data Theory about unobservable or unobserved entities induction observational data • Underdetermination: • Hence inductive inference from data to theory:

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