Era

19th Century

1800 – 1900

Beginner

Ages 8+, no background needed.

EconomicsPrincipleFamousBeginner

80% of results come from 20% of effort. 80% of bugs from 20% of code. Is this a law of nature, or a coincidence with a catchy ratio?

18966 min read

PsychologyEffectBeginner

A doctor proved handwashing saved lives. He had the data. The medical profession ignored him for twenty years. Why does evidence trigger resistance?

18476 min read

ProbabilityBeginner

You reach into one of three boxes and pull out a gold coin. The chance the other coin in that box is gold is not one half.

188910 min read

Curious teenagers and general adult readers.

AstronomyIntermediate

If the universe is infinite and full of stars, every line of sight should end on one. So why is the night sky dark?

1610 (Kepler), 1744 (de Chéseaux), 1823 (Olbers)17 min read

EconomicsIntermediate

Build an engine that burns less coal and the country ends up burning more coal. This was noticed in 1865 and has not stopped.

186518 min read

Undergraduate level in the relevant field.

PhysicsFamousAdvanced

A tiny creature sorting fast molecules from slow ones appears to make heat flow the wrong way, for free, forever.

1867 (letter to Tait), 1871 (published in Theory of Heat)18 min read

MathematicsAdvanced

There are more numbers between 0 and 1 than there are whole numbers in all of eternity. Both lists are infinite.

189116 min read

EconomicsAdvanced

Some things sell more as the price goes up, and the people buying them are behaving perfectly sensibly.

1895 (Marshall's third edition); 2008 (first credible field evidence)18 min read