A philosopher whose theories on the definition of science have become the standard. It was Popper who argued that science was the gathering of evidence to support or refute a hypothesis. Popper believed that a scientific theory could never be proven. Instead, a theory would be progressively refined to reflect new data, but at no point can this theory be considered, absolute truth, for an exception could appear at any time.

Karl Popper's ideas of science are interpreted as naive and decades out of date by those who study the philosophy of science. Many scientists still cite Popper's older theories as the ultimate authority in how the "business" of science works, that is:
  1. Devise hypothesis. (Perhaps a modification of an existing hypothesis)
  2. Test for falsification. (i.e. Experiment to disprove hypothesis)
  3. Conditional acceptance. (The new theory "wins" until something better comes along.)
  4. Repeat.
In reality, Popper's trials do not describe the actual messy "business" of science, which is brilliantly described in Thomas Kuhn's landmark book, The Structure of Scientific Revolutions. For example, step 2 can be impossible, or the results could be far from clear-cut. What then?

Consider the case where we have two competing theories which can each explain a subset of observations. The orthodoxy explains many data very well, and is quite accepted. But doubts remain about some "outlier" data. Experimental error? A newer, radical theory explains the "outlier" data but perhaps has outlier data of its own. Is the new theory any good? Will it "grow into" something that explains all? Sometimes, a tension develops between supporters of the new theory and those in the orthodoxy. Whose idea "wins" the hearts and minds of scientists? Do we reach some kind of hybrid acceptance? (E.g., Newtonian physics is still extremely useful.) By this stage we have journeyed far from the territory Popper describes.

Kuhn's book coined the famously abused phrase "paradigm shift" to describe scientific revolution as a social phenomenon. Popper's ideas are most relevant for incremental changes to the orthodoxy and cannot explain paradigm shifts.

Some sample paradigms and paradigm shifts.
Sir Karl Raimund Popper (1902-1994)

One of the foremost developers of the philosophy of science. Popper was one of the foremost proponents of the idea that all scientific knowledge cannot be valid unless founded upon empirical observation. In his 1934 book The Logic of Scientific Discovery. In his book Popper argued that all scientific explanations must be falsifiable, or disconfirmed by the presentation of contradictory data. To be scientific, a proposition must be expressed in a form subject to disconfirmation through observing contradictory data. Popper argued that one cannot ‘prove’ a theory through scientific observation. To assert proof is to commit the logical sin of ignoring possible alternative explanations. Rather, a theory advances and grows through surviving repeated attempts at disconfirmation. Data and research methodology used must be made public, so experiments may be independently reproduced. Criticism and peer review are critical parts of the Popperian model. Repetition is also critical, because random events may produce -- or deny-- the expected result. Scientific principles based upon irreproduceable results are inherently unreliable, and thus unscientific in Popper’s view. Knowledge built upon an unreliable foundation must itself be suspect. An open methodology permits peers to point out faults in either logic or methodology, and to suggest improvements.

A good example of the Popperian method in action was when chemists Pons and Fleischmann put forward their cold fusion experiments. The two scientists had achieved dramatically unexpected results in their cold fusion experiment, and chose to announce their results publicly, before peer review. However, no other laboratory was able to reproduce their results, cold fusion became seen as more a fluke or fraud than a real scientific advance.

Popper’s work may be seen as a development that superseded logical positivism, itself a reaction to 19th century mysticism. While knowledge acquired through intuition, induction and other means may prove correct, without controlled observations to confirm or disconfirm there is no basis for asserting correctness. Experiments are to be controlled as tightly as possible, to eliminate extraneous variables.

He also argued that scientific theories must be exhibit parsimony. In other words, they must explain a lot of actions through a simpler logical principle. Theories may be improved only when the proposed improvement explains more than the specific phenomena it was designed to explain Poppers work has influenced many generations of scientists, and his ideas continue to be taught today, His is a difficult standard, particularly in the social sciences. But it represents an ideal which all scientists must strive for.

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