Scientific theories are marvelous structures built out of scientific concepts ("vocabularies"), laws, empirical facts, and logical entailments. They are not, as "creationists" say of evolution, mere unconfirmed "facts." The word "theory" has a vastly different meaning to the scientist than it does in everyday discourse, (as I explain in my "Creationism and the Devolution of the Intellect"). To the scientist, "facts" are ingredients of theories. And as theories encompass more observed and confirmed facts and formulate new "laws," this theoretical growth reverberates throughout the entire theoretical system. Thus, for example, post-Darwinian discoveries in genetics, bio-chemistry and paleontology have not "refuted" evolution, they have enriched and expanded it.
Robust scientific theories are characterized by their scope of application (comprehensiveness) -- another manifestation of their structure and coherence. Thus, for example, "natural selection" explains such diverse phenomena as dated sequence of fossils, comparative anatomy and physiology, comparative species, DNA, declining potency of insecticides and antibiotics. Similarly, Einstein's theory of relativity explains observations at the working end of particle accelerators, nuclear and thermonuclear reactions, the behavior of clocks on spaceships, astronomical observations, and the apparent bending of light near massive objects (e.g., during a solar eclipse).
Science is Empirical.
A scientific investigation "begins" and "ends" in experience. A scientist might find, in the field or his laboratory, an interesting phenomenon worthy of investigation. For example, Darwin found varieties of finches on the Galapagos Islands and the South American mainland. Why both the variety and the similarities? And Wilhelm Roentgen accidentally made a momentous discovery while experimenting with X-Rays in his laboratory. In a desk drawer below his apparatus, a key was placed atop an unexposed photographic plate. He later discovered an image of the key on the plate. How come? His search for an answer led to X-Ray photography.
Darwin and Roentgen developed hypotheses ("hunches") to explain these experienced phenomena. Some failed to "pan out" in experience, so new hypotheses were formed. Eventually, they came up with hypotheses which, in conjunction with settled scientific concepts and data, predicted events which were empirically confirmed by experiments and observations.
Scientific theory and laws are not made up of "hunches." And yet creative imagination ("hunches") can play an important role in scientific investigation. Legend has it that Archimedes came upon the concept of specific gravity while taking a bath. (Did he really? Who knows? Who cares? The story is illustrative, not scientific). James Watson tells us that the idea of the double helix came to him as he recalled his boyhood exploration of the spiral staircase at a lighthouse. And Einstein thought of relativity as he was riding a Zurich trolley and contemplated the "relative motion" of a passenger walking in the trolley.
But when the scientific community demanded confirmation of the theory of DNA, Crick and Watson did not look to lighthouses. Nor did Einstein demonstrate Special Relativity with a trolley car. These insights were the beginning, not the end, of scientific inquiry. The inquiry "ended" with empirical confirmation in the laboratory or the field.
Scientific assertions are Falsifiable.
For any statement whatever in the body of science, we know what it would be like for that statement to be false. (I exclude "formal" statements: e.g., definitions, logical rules and tautologies, which lack external empirical reference -- a technical point which I won't elaborate here). It is thus possible, in principle, to describe a refutation of a scientific claim. In other words, scientific statements, hypotheses and theories are falsifiable -- not "false," but falsifiable. The distinction is crucial.
To put it another way, for an hypothesis, prediction or confirmation to have scientific meaning, one must be prepared to say, "expect to find such-and-such empirical conditions in the world, to the exclusion of other describable conditions." If you find these conditions, your statement has been proven true of this particular "real nature," and not some "fanciful nature." For example, Galileo determined that a free-falling object falls at a distance of d = gt2 (with "d" for distance, "t" for time, and "g" for a gravitational constant at the Earth's surface). Not 1/4g or 1/3g, but 1/2g. And not time cubed, or time to the 2.5 power, but time squared. In other words, that simple equation describes one sort of nature to the exclusion of an infinitude of other "natures" described by different formulas. But experimentation and observation has proven that Galileo's formula applies to the "nature" we live in. In short, the free-fall formula is falsifiable. We can easily describe how it might be false but have determined experimentally that it is true.
Similarly, in Eddington's famous 1919 eclipse experiment, Einstein's theory of relativity predicted that star near the eclipse would appear in a precisely defined location, and not in any other location in the night sky (a falsification). And sure enough, it appeared where predicted by the relativity theory. Confirmation!
In contrast, dogmas give us unfalsifiable assertions. Once in a debate with an evangelical minister, I asked: "Why should I believe that the Bible is the inerrant truth, and that I must believe in Jesus Christ to be saved?" He replied, "just you wait -- when you die and face your maker, then you will find out." Of course, that challenge was utterly unfalsifiable to anyone alive, which is to say, to anyone at all. Similarly, economic dogmas, which are "theory rich," have an "explanation" (after the fact) for every and any developments in the national economy. And if one theory in the economist's kit of tools won't work, he has another that will. What such an economist cannot do is describe a turn in the economy that would disprove his dogma. In short, unfalsifiable assertions, because they describe every possible world, describe nothing unique about the world we live in, which is to say that they "describe" nothing at all.
(The Falsifiability rule has been challenged by many reputable philosophers of science. My blunt reply: they are correct, but so what? Falsifiability remains as a robust and essential, albeit imperfect, criterion, as I explain in this supplementary note).
Scientific assertions are fallible.
An important implication of the falsifiability rule, is what Charles Peirce called "Falliblism." Because every scientific statement is falsifiable, we must be forever open to the possibility (however remote) that some new observation or experiment will prove it wrong. The "falliblist" says, in effect, that "while I have strong beliefs, I am forever prepared to change these beliefs if confronted with compelling evidence to the contrary."
We have often heard that "science has been proven to be wrong in the past." True enough! But what has discovered and corrected scientific error? Science of course. Again, as a human institution, science is imperfect -- which is to say, "fallible." But science is far and away the best remedy for the imperfections of science.
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