This is Hidden Brain.
I'm Shankar Vedantam.
2,000 years ago, in ancient Greece, a local ruler had a problem.
He suspected his new crown wasn't made of solid gold, but he couldn't prove it.
So he asked the kingdom's most famous mathematician, Archimedes, to investigate.
While pondering the puzzle, Archimedes took a bath.
He filled the tub to the brim, and as he stepped in, the water overflowed.
Archimedes had a flash of insight.
The water that spilled out of the bath reflected the volume of his own body.
He realized that if he put the crown into water, he could measure its volume by seeing how much water was displaced.
He could use this to tell the difference between a crown made of pure gold and one that had impurities.
He was so excited with his discovery that he leaped out of the tub and ran naked through the streets shouting, Eureka!
Eureka!
Which is Greek for, I found it!
I found it!
The famous story of the Eureka moment may or may not have happened.
It was written 200 years after Archimedes died.
But it says something profound about our minds.
A good explanation gives us pleasure.
And when we cannot come up with a good explanation, we feel dissatisfied.