Transcript Document 7194642

Philosophy 226f: Philosophy of Science
Prof. Robert DiSalle ([email protected])
Talbot College 408, 519-661-2111 x85763
Course Website:
http://instruct.uwo.ca/philosophy/226f/
Common ideas about scientific method
Inductivism: Science proceeds by performing experiments
repeatedly, and accumulating observations.
Then it makes inductive generalizations from the accumulated
facts. These are the laws of science. (Francis Bacon)
Hypothetico-Deductivism: Science proceeds by devising
hypothetical models for how nature might really be organized.
Then it deduces the consequences of these models, and
compares them with observation. (cf. The “mechanical
philosophy”)
The Newtonian method of “experimental philosophy”:
Instead of making up theories to explain the facts, find ways to
make the phenomena answer the important theoretical
questions.
Example: Use the laws of motion to impose questions on the
world, such as, “what forces are at work?”
If the laws are assumed to be true, then every acceleration that
we see is telling us something about a force.
Perturbation theory: Any departure from ideal Keplerian
motion in the solar system indicates-- and is a measure of-- the
action of a yet-unaccounted-for force, whose source is a yetunaccounted-for mass.
Phenomenal measures of theoretical magnitudes:
Centrifugal forces as measures of rotational velocity
Keplerian harmonic law:
Ta2 / Tb2 = Ra3 / Rb3
measures the variation of the interplanetary force as 1/R2.
Stability of the planetary orbits also measures the force law.
Agreeing measures of the same magnitude by different
phenomena provide the best possible evidence.
Example: Mercury’s perihelion precession measures the
force to be 1/R2.00000016.
But this disagrees with the measure provided by the other
planets, whose orbits are too stable.
All of this “reasoning from phenomena” presupposes the laws
of motion.
Therefore the laws of motion can’t be the products of such
reasoning.
But what is the status of the laws of motion?
Inductive generalizations?
Deductive consequences of more basic principles?
A priori assumptions of some kind?
Kantian questions about scientific
method:
How has science achieved universal
assent, while philosophy is the subject
of endless dispute?
What distinguishes scientific
reasoning from philosophical
reasoning, so that the former leads to
principles that are necessary and
universal, whereas the latter remains
arbitrary and particular?
How can philosophy start on “the
secure path of a science”?
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Immanuel Kant, 1722-1804
Kant’s “Copernican Revolution”:
The laws of nature don’t describe the way things are in
themselves; they describe conditions that our understanding
imposes upon experience.
“Every effect has a cause” is not a truth about things in
themselves. If it were, we would be right to doubt it.
Instead, it is a rule that the human understanding imposes on
the appearances, in order to submit them to a rule.
Without such rules experience would be impossible. The world
would be a chaos of sensory appearances.
Kant: Scientists like Galileo “comprehended that reason has
insight only into that which it produces itself after a plan of its
own...for otherwise, accidental observations, wth no
previously fixed plan, will never be made to yield a necessary
law….”
“Reason, holding in one had its principles…and in the other
hand the experiments it has devised according to those
principles, must approach nature in order to be taught by it. It
must not, however, do so in the manner of a pupil, who agrees
to everything the teacher says, but of an appointe judge, who
compels the witness to answer the questions which he himself
has phrased…”
Newton’s laws as synthetic a priori principles:
A priori: Known prior to experience
A posteriori: Known by experience only
Analytic propositions: True by definition; the predicate belongs
to the definition of the subject
Synthetic propositions: Joining a new predicate to the subject,
one not contained in its definition
Newton’s laws represent the law of causality as applied to the
entire universe.
Jules Henri Poincaré (1854 -1912)
If the laws of motion were inductive,
they would be easier to revise.
If they were synthetic a priori, they
would be impossible to arrive. We
would not be able to conceive of
alternatives.
They must be another kind of
principle altogether.
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are needed to see this picture.
A triangle whose internal angles sum
to something less than two right
angles
Triangle whose
angles sum to more
than two right
angles
Parallel postulate: Given a line L and a point P not on L, there is
exactly one line through P that does not intersect L.
P
L
Equivalently, if lines L1
and L2 cross a line T, L1
and L2 will meet on that
side of T where their
internal angles with T are
less than two right angles.
T
L1
L2
On a saddle surface, there may be infinitely many lines
through P that do not intersect L.
P
L
On a spherical surface, every line (“great circle”) through P will
intersect L.
L
P
Poincaré: Where do the fundamental principles of geometry get
their appearance of certainty?
How is it that they seem to be universal and necessary, and yet
applicable to the real world?
[Einstein: “To the extent that the principles of geometry apply
to reality, they are uncertain; to the extent that they are certain,
they don’t apply to reality.”]
Could we ever be required to modify them in the face of
experience?
Poincaré: How do we interpret
experience in which triangles seem
non-Euclidean?
What is a non-Euclidean experience?
An experience in which straight lines behave as the “straightest
lines” of a non-Euclidean space.
But what is a straight line? The path of a light ray.
So, how do we distinguish between these two possible
interpretations of our experience?
“The geometry of space is non-Euclidean.”
OR: “Something is happening which prevents light from
propagating in straight lines.”
Poincaré: The two pictures of spatial geometry represent two
ways of saying the same thing.
What we measure is only the displacements of the physical
objects that we use in measurement. The results of those
measurements are open to a number of possible interpretations.
The choice between such interpretations is a matter of
convention.
“Is Euclid’s geometry true?” According to Poincaré, the
question has no meaning.
As well ask whether the metric system is true.
The fundamental laws of physics and physical geometry are not
synthetic a priori principles.
They are not a priori, since alternatives are possible.
They are not synthetic, but are principles of a peculiar kind: they
appear to describe the real world, but in fact they only enunciate
criteria for the description of the world.
Newton’s law of inertia is not a description of nature, but a
criterion that we adopt in order to be able to measure physical
forces.
It can’t be contradicted by the facts, since it is the principle by
which we investigate the facts.
Such principles are “definitions in disguise.”
The hierarchy of science, according to Poincaré:
Every science presupposes more basic sciences, as part of the
language in which it is written. Those are “a priori” with respect
to that particular science.
Logic is presupposed by arithmetic.
Arithmetic is presupposed by geometry.
Geometry is presupposed by physics.
Therefore physics can’t proceed until a geometry is fixed by
convention.
Physics can’t, in turn, force us to revise geometry.
Pierre Duhem:
There are no unrevisable principles in physics. Every principle
is, in effect, an empirical hypothesis.
Holism: An empirical test is always a test of all the principles
that are presupposed in the test.
In chemistry, we can “keep the theory out of the laboratory.” But
in physics, experiments always presuppose a great deal of theory.
When an experiment gives the “wrong” result, there is no certain
way to decide which principle is at fault.
Ernst Mach:
Phenomenalism: Everything that is real is some combination of
“phenomenal elements” apparent to some observer.
The human mind imposes order and regularity among these
elements by identifying large collections of phenomena--even
infinite collections of possible phenomena-- under particular
concepts.
This tendency exhibits the principle of “mental economy”: to
comprehend experience with the least possible expenditure of
mental effort.
This is an adaptive feature of humans as products of evolution.
“Replacing experience by the reproduction of facts in
thought”:
1. Knowledge of general rules replaces the effort of
understanding countless individual cases.
2. Systematic rules substitute for the experience of new cases:
scientific knowledge provides us with a vicarious experience
of evolutionary trial and error.
3. Our theories venture into situations in which ourselves would
be at some risk.
Implications regarding scientific theories:
Laws of nature should not be thought of in the traditional way,
as identifying “powers” or “forces” or “mechanisms” underlying
the phenomena.
Instead, laws simply describe, in the most economical manner
possible, the functional dependencies that exist among various
phenomena.
Example: It is unscientific to speak, following Newton, of
determining the “true motions.” Force is proportional to
acceleration relative to the fixed stars.
The Darwinian theory: Evolution by natural selection
(Blind variation and selective retention)
1. Inherited structural features of all living things are subject
to random variation.
2. Some variations will be more useful than others for
survival in a given environment, and will increase an
organism’s chance of surviving and reproducing.
3. Any environment will have limited resources to support
living populations, while organisms will tend to reproduce
beyond what those resources will support.
4. There must be a struggle for existence which will “select”
variations for survival and inheritance.
Observations supporting Darwin’s view:
1. Geological patterns reveal the earth to be much older than
previously thought, old enough for gradual processes (like
natural selection) to have tremendous effects.
2. Fossil record indicates that numerous variations have existed
and become extinct, and that many present species have
ancestral forms.
3. Artificial selection in domesticated species reveals the same
basic processes at work.
4. Different animal and plant species arise from very slight
variations on a few basic structures.
5. Differentiation reflects differences in environmental
pressures, among forms that are isolated from one another.
Darwin’s empirical premises:
That gradations in the perfection of any organ or instinct, which
we may consider, either do now exist or could have existed,
each good of its kind;
that all organs and instincts are, in ever so slight a degree,
variable;
that there is a struggle for existence leading to the preservation
of each profitable deviation of structure or instinct.
. It is so easy to hide our ignorance under such expressions as
the “plan of creation,” “unity of design,” &c., and to think that
we give an explanation when we only restate a fact. Any one
whose disposition leads him to attach more weight to
unexplained difficulties than to the explanation of a certain
number of facts will certainly reject my theory.
It is interesting to contemplate an entangled bank, clothed with
many plants of many kinds, with birds singing on the bushes,
with various insects flitting about, and with worms crawling
through the damp earth, and to reflect that these elaborately
constructed forms, so different from each other, and dependent on
each other in so complex a manner, have all been produced by
laws acting around us.
Darwin’s fundamental laws:
Growth with Reproduction;
inheritance which is almost implied by reproduction;
Variability from the indirect and direct action of the external
conditions of life, and from use and disuse;
a Ratio of Increase so high as to lead to a Struggle for Life, and
as a consequence to Natural Selection, entailing
Divergence of Character and the Extinction of less-improved
forms.