The world in whatever-the-next-year-is
Falsifiability or refutability is the logical possibility that an assertion can be contradicted by an observation or the outcome of a physical experiment. That something is “falsifiable” does not mean it is false; rather, that if it is false, then some observation or experiment will produce a reproducible result that is in conflict with it.
For example, the claim “atoms do exist” is unfalsifiable: Even if all observations made so far did not produce an atom, it is still possible that the next observation does. In the same way, “all men are mortal” is unfalsifiable: even if someone is observed who has not died so far, he could still die.
By contrast, “all men are immortal,” is falsifiable by the presentation of just one dead man. Not all statements that are falsifiable in principle are falsifiable in practice. For example, “it will be raining here in one million years” is theoretically falsifiable, but not practically so.
The concept was made popular by Karl Popper, who, in his philosophical criticism of the popular positivist view of the scientific method, concluded that a hypothesis, proposition, or theory talks about the observable only if it is falsifiable. Popper however stressed that unfalsifiable statements are still important in science, and are often implied by falsifiable theories. For example, while “all men are mortal” is unfalsifiable, it is a logical consequence of the falsifiable theory that “every man dies before he reaches the age of 150 years.”
