Falsifiability is an essential concept in the [philosophy of science]
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For an assertion to be falsifiable, there must exist some theoretical physical experiment
or observation that would convince the observer that the assertion is false.
For example, the assertion "All crows are black" could be falsified by observing a
red crow.
Karl Popper stressed that the scientific method is based on falsifiability; if an explanation can be falsified, then it is scientific and should be tested. If it can't (that is, it is unfalsifiable), then it is entirely outside the realm of science and totally irrelevant to it.
Scientists and philosophers generally try to resolve issues of reliability of evidence and falsifiability with Occam's Razor, but this is often inconclusive in practice.
Some examples of things that are unfalsifiable are:
- The existence or non-existence of God. This is unfalsifiable because it is unable to be consistently tested. Those who believe in the existence of God note that God is able to make decisions, and thus would decide whether to cooperate with any test devised by humans. If we conceived of any test that would prove to us that God did not exist, proponents could argue that God in his omnipotence caused the test to fail, or caused us to observe its failure. There is, therefore, no way to falsify the "God" hypothesis.
- Many conspiracy theories. These are unfalsifiable because the nature of most conspiracy theories require that the conspiracy to be strong enough to generate evidence that shows the conspiracy does not exist. In particular, if any person denies the conspiracy or purports to show that is doesn't exist, the theorist can simply add him to the alleged conspirators. Within the conspiracy theory belief system, conspiracies can only be proven as true, not disproven.
- Solipsism?: the belief that the rest of the Universe is only a figment of one's own imagination. This is not falsifiable, because to a solipsist, there is no evidence that can prove anything.
- Tautology?: statements which are necessarily true without any knowledge of the world, such as "All green things are green." Proving mathematical theorems involves reducing them to tautologies, which can be mechanically proven as true given the axioms of the system or reducing the negative to a contradiction. This is unfalsifiable, because any evidence given is ignored in the proof process.
- Supernatural? creation of the world. This has been called the "Omphalos" hypothesis, after the title of a 1857 book by Philip Henry Gosse in which he argued that in order for the world to be "functional", God must have created the Earth with mountains, canyons, etc.; trees with growth rings; Adam and Eve with hair, fingernails, and navels ("omphalos" is Greek for "navel"), and that therefore no evidence we can see of the presumed age of the world can be taken as reliable. (The idea has seen some revival in the twentieth century by modern creationists who have extended the argument to light which appears to originate in far-off stars and galaxies.)
- The "ten minutes ago creation". This is the idea that the entire world came into existence ten minutes ago, exactly as it is right now, with the appearance of a history, people with memories, etc. This is unfalsifiable because to be falsifiable, one would have to be able to control time and be able to compare entire universes.
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