Falsifiability

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

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.

For example, before the 1960s, there was no way to disprove the proposition that there were little green men living on the other side of the moon. So it wasn't considered a scientific hypothesis. When it became possible to examine the moon closely with spacecraft-mounted cameras, the proposition gained falsifiability, because there was a way to disprove it. Alas, the "moon men" hypothesis's viability lasted only a short time, as an exhaustive photographic survey of the moon showed no evidence of life on the moon.

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 theory of evolution, because it claims that God has nothing to do with the appearance of new species of life. There is no way to falsify their claim, so it's not a scientific hypothesis -- only philosophical conjecture.
• 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. Those who don't believe in God's existence say that the failure of any particular test shows that God doesn't exist. Since any given test can prove and disprove God's existence at the same time, it is unfalsifiable.
• Many conspiracy theories.
• Solipsism?: the belief that the rest of the Universe is only a figment of one's own imagination.
• 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 given the axioms of the system or reducing the negative to a contradiction.
• 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 revivival recently; some modern creationists have extended the argument to light which appears to originate in far-off stars and galaxies.)

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