Falsifiability

Falsifiability is an essential concept in the [philosophy of science]?. 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.

The nature of the scientific method that Karl Popper stressed is falsifiability; if an explanation can be falsified, then it is scientific and should be tested. If it can't (ie: 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. For any test we might devise, it can be argued that God in his omnipotence chose for the test for fail, or chose for us to perceive that it failed, so there is no possible test that would prove his non-existence.
• 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. Specifically, anyone who denies the conspiracy can simply be made one of the conspirators, and his denial explained as deception.
• 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. An extreme version of this idea is that the world was created ten minutes ago, complete with all of our memories and records and fossils. 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.

Examples of falsifiable theories:

• Laws of physics: At any time, some experiment may behave in a way that violates known "laws" of such things as gravity, electromagnetism, or nuclear interactions. Indeed, Isaac Newton's original laws of motion in their original form were falsified by experiments on the twentieth century, and replaced by more exact theories that hold under more conditions (though Newton's theories are still close enough to be used practically without the modern updates).

• Modern theories of evolution: The theory as a whole could be falsified by finding an anomalous fossil of an advanced life form in rocks dated before that life form or its ancestors could have evolved (for example, finding a mammal in pre-Cambrian sediment). The theory of common descent could be falsified by finding a unique form of Earthly life that was totally unrelated to any existing or fossil form (for example, one not using RNA or proteins). The theory of sexual selection could be falsified by finding an organism with colorful sexual selection markings that was blind.

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