Falsifiability

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Philosophy of science

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If you can't test your theory, it's probably bullshit.
—Maddox, How to tell if you believe in bullshit[1]

Falsifiability is the ability of a theory—a working framework for explaining and predicting natural phenomena—to have its falsity demonstrated by overwhelming evidence through experiments or observations.[2] The ability to evaluate theories against observations is essential to the scientific method, and as such, the falsifiability of theories is key to this and is the prime test for whether a proposition or theory can be described as scientific. Put simply, if a theory cannot be falsified, there is no point in even examining the evidence.

Contents

[edit] Philosophy of science

Falsifiability is one of the bedrocks of science.

All scientific knowledge and theories are based on two things: observation and consistent logic. A theory is a logical explanation for observations. A good, scientific theory also proposes a set of new observations that could test a theory's power to explain. Once technology, time or funding catches up with the theory, these observations can be made, which can either support or invalidate the theory. This ability to be tested, and the potential for the theory to be invalidated by the experiment, is the essence of falsifiability.

It has been argued, most notably by Karl Popper, that the scientific method demands that a theory must at least in principle be falsifiable in order for it to be valid as science. This requirement was Popper's solution to the demarcation problem, or what is and what is not science. Popper's view is not widely acceptable in contemporary philosophy of science. However, that does not mean that falsifiability is not important. Falsifiability is a virtue in a scientific theory. Evolution, for example, is theoretically falsifiable - "fossil rabbits in the Precambrian", as J.B.S. Haldane once said - whereas intelligent design is not, mostly because it makes no predictions that can actually be tested.

Thus, we obtain a process:

  • A theory is a well substantiated explanation for some aspect of nature; it is different from a hypothesis.
  • A hypothesis or conjecture is an idea that a researcher believes may be true. The researcher can test this idea using the scientific method.
  • Scientists constantly investigate even highly supported theories.
  • If evidence is found that contradicts a theory, the theory must be discarded or revised.

[edit] Naive falsificationism and the Duhem-Quine Thesis

The Duhem-Quine Thesis is something of a conflation of the ideas of Pierre Duhem and W.V.O. Quine. In short, it states that it is impossible to test or falsify a hypothesis in isolation for two reasons. Firstly, the hypothesis relies on a number of supporting assumptions. For example, does the exposure of the Piltdown Man fraud falsify the validity of that fossil alone or all of evolutionary theory?

Secondly, a discrepancy between theory and data does not necessarily falsify the theory. For example, in the early 19th century, scientists discovered discrepancies between the orbit of Uranus as predicted by Newton's theory of gravity and the orbit which was actually observed. However this discrepancy between theory and evidence was not considered a falsification of the theory; in time the discrepancy was resolved through the discovery of Neptune. In the late 19th century a similar discrepancy was discovered in the orbit of Mercury. This time, however, this discrepancy did lead to the falsification of Newtonian gravity; the discrepancy could only be resolved when Einstein proposed his amended theory of gravity. Scientists will typically not consider a theory as falsified simply because of the existence of discrepancies between theoretical predictions and observations, even if those discrepancies remain unexplained for a long time; in fact attempting to account for such discrepancies is what motivates a lot of scientific research.

The Duhem-Quine Thesis is often contrasted with or considered to modify "naive" or "Popperian" falsificationism.[3]

[edit] Lakatos and research programs

Imre Lakatos further extended Popperian falsification and the Duhem-Quine Thesis with his concept of "research programs." Lakatos defined extensively developed theories and techniques in a field as the "hard core" of a research program. Around this hard core is a "protective belt" of auxiliary hypothesis and modified or ad hoc assumptions added by scientists to protect the core of the program from falsification. While the protective belt is auxiliary and ad hoc, this does not necessarily translate to "bad" in Lakatos' view. If the protective belt leads to the discovery of new facts made by novel predictions, this leads to what Lakatos called a "progressive research program." A "degenerative research program" is one in which the protective belt grows but leads to no new discoveries, merely acting as a way to cover up the flaws of the hard core.[4][5]

[edit] Examples

Until the twentieth century Newton's laws of motion were

  • a) scientific and
  • b) believed to be true.

Newton's laws allowed us to make specific predictions regarding such things as the trajectories of artillery projectiles or the orbits of planets. These predictions were observed to hold most of the time, but in some cases such as the orbit of Mercury there were observations that contradicted predictions based on Newton's laws. This led to their modification and replacement by relativity, which, rather than being a complete rejection of the Newton's laws, was a clarification and refinement that allowed them to hold true in a greater range of observable circumstances. It was the specific predictions made by Newton's laws that allowed scientists to test them, and eventually replace them. This happened because the predictions made Newton's laws falsifiable.

[edit] Is it falsifiable?

A simple procedure can be used to determine whether or not a hypothesis or conjecture is scientific and falsifiable. What would be an example of something that, if observed, would contradict the hypothesis? If this question cannot be answered, then the conjecture is not scientific. In addition, a good test of a theory is that it is able to make predictions about some future event. For example, Einstein's ideas about relativity predicted specific things that would be observed during a total solar eclipse. When the eclipse came, the predictions were confirmed, something which strongly supported his theory.

Logically, the two applications are the same thing. A theory useful in practice is not defined by what it allows, but by what it disallows, because that is where its predictive power lies. For example, Newton's theory of gravity says that the force of universal attraction cannot act in any other way except in accordance to the inverse square formula. If a theory allows anything whatsoever to happen (e.g. via Goddidit), it can make no useful predictions, and conversely, if a theory says that an event cannot happen, then such an event would falsify the theory — and practical uses of the theory can rely on the fact that this event will never happen.

[edit] Unfalsifiable ideas

The invisible and non-existent look very alike.
—Delos Banning McKown

A science stopper is a hypothesis that makes no testable or useful predictions and therefore prevents any science from being performed based on that hypothesis. It is usually viewed as a very bad thing and a consequence of poorly formulated ideas that fail to grasp concepts such as falsifiability and methodological naturalism.

Real science and scientists are unaffected by so-called science stoppers. Although it infuriates proponents of a young earth and so-called intelligent design, peer review journals, universities, and institutions that fund scientific research pay no attention to crackpot pseudoscientific theories. In fact, science is a highly conservative activity that has a very high bar for the acceptance, or even notice, of new hypotheses and theories.

[edit] Creationism

See the main article on this topic: Falsifiability of creationism

Creationism is not falsifiable as its proponents base the conjecture on a human text (the Bible) which provides accounts of creation and other events that cannot be tested by observation or experiment but are instead accepted as infallible truth. This is one of the primary characteristics of pseudoscience. No matter what evidence is presented, there is no way that creationism can be contradicted. Even when evolution in action is observed, creationism always allows for an after-the-fact justification of the inconsistent observation with an argument to authority. Put differently, for any possible observation you can imagine Creationism can explain away both that observation and its opposite. Only an observation proving that God does not exist would undermine the theory, and obviously that is impossible. Since no observation is allowed to contradict creationism and it has no predictive value, it is not science.

It is important to remember that just because a theory is falsifiable it may never be falsified, contrary to some anti-evolutionist thought. Theory is neither the opposite of "fact" nor a synonym for "hunch" or "hypothesis". "Theory" is a scientific term of art; a theory is a hypothesis which has been able to withstand repeated falsification attempts to the point of being generally accepted by the practicing scientific community. Even though details about the exact way evolution occurred are debated, evolution is almost universally accepted by scientists. Despite this fact, scientists would reconsider evolution if suddenly observations seemed to contradict its principles and falsify the idea. Note however that when a new observation contradicts a well established theory it is usually rational to treat the single observation, not the established theory, as suspect (unless and until it can be verified and replicated).

Willingness to reexamine facts objectively is the key difference between a scientist and a theologian.

[edit] Deductive argument for falsifiability

[edit] Informal

Scientific theories can usually be thought of as a series of statements and deductions which infer whether or not some observation will be made. This view is commonly called the hypothetico-deductive model. Now let us apply this model to the concept of falsifiability. Let's say some theory deduces that some observations will be made. This theory thus becomes verifiable, but not necessarily falsifiable. Now, let's analyze what happens in two cases. In the first case, if the observations deduced by the theory aren't made, the theory is negated (or rejected, in other terms). In the second case, the observations which are deduced by the theory aren't made, and yet, the theory isn't negated. The latter case fails the test of falsifiability. Not only that, this theory also violates the basic rules of logic - it proves both the theory and its negation. Thus, this theory is logically inconsistent. If we consider accepting logically inconsistent theories as futile, this argument makes a case for the criterion of falsifiability.

[edit] Formal

Let T be a formal theory which denotes a scientific conjecture in the context of the hypothetico-deductive model. Let O be a set of first-order propositions denoting observations which can be deduced from the formal theory T.

A scientific conjecture T is said to be consistent if and only if: \forall o\in O[(T\vdash o)\wedge (\neg T\vdash \neg o)].

Falsifiability can be expressed formally as the following condition: [\exists o\in O (\neg o)] \rightarrow (\neg T)

Falsifiability is thus a necessary condition for a scientific theory being consistent.

[edit] See also

[edit] Footnotes

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