Experimental Testing of Physical Theories by Caitlin Mace - HPS 2103 Spring 2022
DUHEM: PHYSICAL THEORY
AND EXPERIMENT
CAITLIN MACE, HPS 2103 SPRING 2022
1
THE EXPERIMENTAL TESTING OF A
THEORY DOES NOT HAVE THE SAME
LOGICAL SIMPLICITY IN PHYSICS
AS IN PHYSIOLOGY
•
Claude Bernard (Physiologist): experimental method depends on intellectual and moral
conditions requiring freedom of mind, detachment, absence of animosity.
•
As opposed to those who seek to confirm their own or destroy others’ theories.
•
But in physics, theory-independence of observation is unachievable.
•
Concrete apparatus on which the physicist tests
•
Schematic and abstract apparatus on which the physicist reasons
•
Theory substitutes the latter for the former
2
Basis of Holism
AN EXPERIMENT IN PHYSICS CAN
NEVER CONDEMN AN ISOLATED
HYPOTHESIS BUT ONLY A WHOLE
THEORETICAL GROUP
•
Physicists implicitly accepts a theory complex when conducting or reporting on an experiment.
•
Experiments of application: experiment draws on theories
•
Experiments of testing: given a P, derive experimental predictions from P, bring about the
experimental conditions which should bring about P. If the prediction fails, P is false.
•
Theory Complex (consisting of P
1
… P
n
) Observation
~Observation
_______________________________________________________________________________________________________________________________________________________
∴ ~P
4
Invalid
(Holist Underdetermination)
3
A “CRUCIAL EXPERIMENT” IS
IMPOSSIBLE IN PHYSICS
•
Hypothesis 1 (H
1
) or Hypothesis 2 (H
2
)
H
1
Observation; H
2
~Observation
Observation
∴ ~H
2
_________________________________________________________________________________________________
∴ H
1
•
Theory Complex 1 (C
1
) or Theory Complex 2 (C
2
)
•
More critically, “Shall we dare to assert that no other hypothesis is imaginable?” (265).
•
Problem of unconceived alternatives > contrastive underdetermination
Reduction to absurdity;
crucial experiment
showing H
1
to be an
indisputable truth
4
CRITICISM OF THE NEWTONIAN
METHOD
•
H
1
Observation
1
; H
2
Observation
2
; … H
n
Observation
n
Observation
1
, Observation
2
, … Observation
n
until certainty
∴ H
1,
H
2, …
H
n
are laws (justified by observation) or mathematical corollaries deduced from laws
Via induction and generalization, derive principles.
_________________________________________________________________________________________________
∴ Theory complex (directly demonstrated)
•
But in the example, the principles are neither deduced from nor are inductive
generalizations of the laws.
•
More critically, Kepler’s laws are approximate, permitting an infinity of translations from its
symbolic form, and Newton’s theory is presupposed when translating Kepler’s laws.
5
ARE CERTAIN POSTULATES OF
PHYSICAL THEORY INCAPABLE OF
BEING REFUTED?
•
Assertion in question (Édouard Le Roy): “Certain fundamental hypotheses of physical theory
cannot be contradicted by any experiment, because they constitute in reality
definitions
, and
because certain expressions in the physicist’s usage take their meaning only through them” (271).
•
So, given some law in which
X
is defined by
O
, if
O
is not observed, this entails either
1.
The definition is right, but since
O
was not observed, we should reject the broader theory
from which our definition is derived.
2.
The link between our
O
and what was observed was not established, and the definition
should be altered.
•
The second is more reasonable, but implies that some hypotheses are forever warranted, which
the history of science tells us isn’t the case.
6
ON HYPOTHESES WHOSE
STATEMENT HAS NO
EXPERIMENTAL MEANING
•
Assertion in question (Poincaré): the principles of mechanics “ […] cannot be refuted by
experiment because
the operation which would claim to compare them with the facts would have no
meaning
” (274).
•
Such hypotheses are essential foundations of theories and have no meaning isolated from the
theory they figure in.
•
E.g., ‘The center of gravity of an isolated system can have only a uniform rectilinear motion.’
•
But, again, when the day comes that the theory should be rejected, such principles will crumble
alongside it.
•
“Hypotheses which by themselves have no physical meaning undergo experimental testing in
exactly the same manner as other hypotheses” (277).
7
GOOD SENSE IS THE JUDGE OF
HYPOTHESES WHICH OUGHT TO BE
ABANDONED
•
Given holism about theories under experimental examination, how are weak spots identified?
•
“No absolute principle directs this inquiry, which different physicists may conduct in very
different ways without having the right to accuse one another of illogicality” (277), and further,
“reasons of good sense do not impose themselves with the same implacable rigor that the
prescriptions of logic do” (278).
•
Good sense requires moral conditions of impartiality and judgments made on good faith; thus,
we are led back to the conclusions of Claude Bernard.
8
MY ANALYSIS
1.
Duhem addressed principles of reasoning
that govern comparison of theory with facts:
•
Falsification
•
Reduction to absurdity
•
Observation and induction
•
(Holistic comparison)
a)
These methods were shown to be mistaken
(or invalid), yet might good sense require
them?
b)
Perhaps these are better ways of being
irrational?
1.
Regarding Duhem’s Holism:
2.
Regarding Duhem’s Holism:
“Hypotheses which by themselves have no
physical meaning undergo experimental
testing in exactly the same manner as other
hypotheses” (277).
Might we think perhaps more risky
hypotheses with physical meaning are under
more serious analysis than secured auxiliary
hypotheses?
Holism is too strong, but we should think
that it is not easy to tell which part of a
theory should be rejected.
9
MY ANALYSIS (CONT.)
Crucial Experiment:
1.
Pretend the star
did not
appear to change
position. What in Einstein’s theory would
have been refuted? Just those parts unique
to the theory? Would some scientists try
to protect it nonetheless?
2.
The experiment served as a confirmation;
was it part of an eliminative inference
refuting Newtonian mechanics?
10
Retrieved from: https://sciencemeetsfaith.wordpress.com/2018/05/29/arthur-s-eddington-
and-the-bending-of-light/
DISCUSSION GEMS
1.
Is my analysis correct?
2.
What is Duhem right about? Where
might he be wrong?
3.
Do Duhem’s concerns extend beyond
physics? To what extent?
Integration of history and philosophy
of science
Gives us holism, problem of
underdetermination, and problem of
unconceived alternatives all in simple
terms.
Street cred
11
A detailed examination of the relationship between experimental testing and theoretical complexity in physics, exploring the limitations and implications of conducting experiments within the framework of complex theories. The content delves into the challenges faced by physicists in distinguishing between valid and invalid observations, the concept of theory complexes, and the impossibility of a single crucial experiment in physics. The critical analysis extends to the Newtonian method, highlighting the difficulties in deriving principles from laws and the interplay between Kepler's laws and Newton's theory.
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Presentation Transcript
D U H E M : P H YS I C A L T H E O RY A N D E X P E R I M E N T C A I T L I N M A C E , H P S 2 1 0 3 S P R I N G 2 0 2 2 1
T H E E X P E R I M E N TA L T E S T I N G O F A T H E O RY D O E S N OT H AV E T H E S A M E LO G I C A L S I M P L I C I T Y I N P H YS I C S A S I N P H YS I O LO G Y Claude Bernard (Physiologist): experimental method depends on intellectual and moral conditions requiring freedom of mind, detachment, absence of animosity. As opposed to those who seek to confirm their own or destroy others theories. But in physics, theory-independence of observation is unachievable. Concrete apparatus on which the physicist tests Schematic and abstract apparatus on which the physicist reasons Theory substitutes the latter for the former Basis of Holism 2
A N E X P E R I M E N T I N P H YS I C S C A N N E V E R C O N D E M N A N I S O L AT E D H Y P OT H E S I S B U T O N LY A W H O L E T H E O R E T I C A L G RO U P Physicists implicitly accepts a theory complex when conducting or reporting on an experiment. Experiments of application: experiment draws on theories Experiments of testing: given a P, derive experimental predictions from P, bring about the experimental conditions which should bring about P. If the prediction fails, P is false. Theory Complex (consisting of P1 Pn) Observation ~Observation Invalid _______________________________________________________________________________________________________________________________________________________ (Holist Underdetermination) ~P4 3
A CRUCIAL EXPERIMENT IS IMPOSSIBLE IN PHYSIC S Hypothesis 1 (H1) or Hypothesis 2 (H2) H1 Observation; H2 ~Observation Observation Reduction to absurdity; crucial experiment showing H1 to be an indisputable truth ~H2 _________________________________________________________________________________________________ H1 Theory Complex 1 (C1) or Theory Complex 2 (C2) More critically, Shall we dare to assert that no other hypothesis is imaginable? (265). Problem of unconceived alternatives > contrastive underdetermination 4
CRITICISM OF THE NEWTONIAN METHOD H1 Observation1; H2 Observation2; Hn Observationn Observation1, Observation2, Observationn until certainty H1, H2, Hn are laws (justified by observation) or mathematical corollaries deduced from laws Via induction and generalization, derive principles. _________________________________________________________________________________________________ Theory complex (directly demonstrated) But in the example, the principles are neither deduced from nor are inductive generalizations of the laws. More critically, Kepler s laws are approximate, permitting an infinity of translations from its symbolic form, and Newton s theory is presupposed when translating Kepler s laws. 5
A R E C E RTA I N P O S T U L AT E S O F P H YS I C A L T H E O RY I N C A PA B L E O F B E I N G R E F U T E D ? Assertion in question ( douard Le Roy): Certain fundamental hypotheses of physical theory cannot be contradicted by any experiment, because they constitute in reality definitions, and because certain expressions in the physicist s usage take their meaning only through them (271). So, given some law in which X is defined by O, if O is not observed, this entails either 1. The definition is right, but since O was not observed, we should reject the broader theory from which our definition is derived. 2. The link between our O and what was observed was not established, and the definition should be altered. The second is more reasonable, but implies that some hypotheses are forever warranted, which the history of science tells us isn t the case. 6
O N H Y P OT H E S E S W H O S E S TAT E M E N T H A S N O E X P E R I M E N TA L M E A N I N G Assertion in question (Poincar ): the principles of mechanics [ ] cannot be refuted by experiment because the operation which would claim to compare them with the facts would have no meaning (274). Such hypotheses are essential foundations of theories and have no meaning isolated from the theory they figure in. E.g., The center of gravity of an isolated system can have only a uniform rectilinear motion. But, again, when the day comes that the theory should be rejected, such principles will crumble alongside it. Hypotheses which by themselves have no physical meaning undergo experimental testing in exactly the same manner as other hypotheses (277). 7
G O O D S E N S E I S T H E J U D G E O F H Y P OT H E S E S W H I C H O U G H T TO B E A B A N D O N E D Given holism about theories under experimental examination, how are weak spots identified? No absolute principle directs this inquiry, which different physicists may conduct in very different ways without having the right to accuse one another of illogicality (277), and further, reasons of good sense do not impose themselves with the same implacable rigor that the prescriptions of logic do (278). Good sense requires moral conditions of impartiality and judgments made on good faith; thus, we are led back to the conclusions of Claude Bernard. 8
MY ANALYSIS 1. Duhem addressed principles of reasoning that govern comparison of theory with facts: Falsification Reduction to absurdity Observation and induction (Holistic comparison) a) These methods were shown to be mistaken (or invalid), yet might good sense require them? b) Perhaps these are better ways of being irrational? 1. 2. Regarding Duhem s Holism: Regarding Duhem s Holism: Hypotheses which by themselves have no physical meaning undergo experimental testing in exactly the same manner as other hypotheses (277). Might we think perhaps more risky hypotheses with physical meaning are under more serious analysis than secured auxiliary hypotheses? Holism is too strong, but we should think that it is not easy to tell which part of a theory should be rejected. 9
MY ANALYSIS (CONT.) Crucial Experiment: 1. Pretend the star did not appear to change position. What in Einstein s theory would have been refuted? Just those parts unique to the theory? Would some scientists try to protect it nonetheless? 2. The experiment served as a confirmation; was it part of an eliminative inference refuting Newtonian mechanics? Retrieved from: https://sciencemeetsfaith.wordpress.com/2018/05/29/arthur-s-eddington- and-the-bending-of-light/ 10
DISCUSSION GEMS 1. Is my analysis correct? Integration of history and philosophy of science 2. What is Duhem right about? Where might he be wrong? Gives us holism, problem of underdetermination, and problem of unconceived alternatives all in simple terms. 3. Do Duhem s concerns extend beyond physics? To what extent? Street cred 11
