What would show it wrong?

About this video

At a fair, a fortune teller looks at Teo's hand and says: "Something important will happen to you soon." A week later Teo gets a good mark in a test, and says she was right. On the same day, the weather forecast says: "Rain here tomorrow, between 2 and 4 in the afternoon." Which claim told him more?

Think of what could have happened to Teo that week: a good mark, a bad mark, a new friend, a lost key, a cold, a birthday party. Every one of them would count as "something important". Nothing that could happen would show the fortune teller wrong. That sounds like a strength, but it is a weakness: a claim that fits whatever happens tells you nothing about what will happen.

The forecast names a place, a day and two hours. If tomorrow afternoon is dry, it was wrong, and everyone can see it. A claim that some result could show to be false is called falsifiable. That doesn't mean false: the forecast may well be right. It means the claim takes a risk. The philosopher Karl Popper made the idea famous in the 1930s: what makes a claim scientific is that it could fail a test, and hasn't. Each test a risky claim passes counts, because it could have failed; a claim that can't fail can't pass a test either. So ask of any claim: what would show this to be wrong? This video goes with the Could It Be Proved Wrong? lesson of Science Level 1 on Knaph.

Transcript

1. 0:00A fortune teller and a weather forecast. Which one tells you more?
2. 0:05Something important will happen. A good mark? A cold? A party? All of them count.
3. 0:11Nothing could ever show it wrong. So it tells you nothing.
4. 0:17Rain tomorrow, two to four. A dry afternoon would show it wrong.
5. 0:23So ask, what would show this wrong? Each test passed counts.
6. 0:29A useful claim is one the world could prove wrong.