Philosophy
Falsifiability
Quick fact
Karl Popper used the example of 'all swans are white' – a single black swan falsifies it. In contrast, the claim 'invisible unicorns exist' cannot be falsified, making it unscientific.
Why this is interesting
Imagine a claim that no matter what evidence you find, it can never be proven wrong. Is that good science? Why do some theories, like astrology, persist despite failing all tests, while others, like Newtonian gravity, are revised when new evidence emerges?