Philosophy 226f: Philosophy of Science Prof. Robert DiSalle
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: Mercurys 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 cant 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? QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Immanuel Kant, 1722-1804 Kants Copernican Revolution:
The laws of nature dont 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 principlesand 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
Newtons 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 Newtons laws represent the law of causality as applied to the entire universe.
Jules Henri Poincar (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.
QuickTime and a TIFF (Uncompressed) decompressor 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 Poincar: 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 dont apply to reality.] Could we ever be required to modify them in the face of experience? Poincar: 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.
Poincar: 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 Euclids geometry true? According to Poincar, 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. Newtons 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 cant 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 Poincar: 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 cant proceed until a geometry is fixed by convention.
Physics cant, 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 organisms 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 Darwins 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. Darwins 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. Darwins 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.
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