On the night of 15 August 1971, the dollar stopped being a claim on gold. After that, everyday money was a promise, and the issuer could make more promises whenever the old ones felt heavy. Money you can audit still exists. A supply nobody can quietly dilute is not a myth. Most people keep the melting kind anyway, because the person next to them does. A herd feels like safety. The old word for that is sheep.

Worth knowing

Sound money is real. People stay with the kind that melts because the herd does.

Nixon Ends Convertibility of U.S. Dollars to Gold and Announces Wage/Price Controls · Federal Reserve History · 1971

This one is the shelf's own note on money. Read the whole story.

Euclid's proof that there are infinitely many primes is short. Suppose the list of primes ended. Multiply them all and add one. That number is not divisible by any prime on the list, so either it is a new prime or it has a prime factor you missed. Either way the list was not finished. There is no last prime. The shelf does not close.

Worth knowing

There is no largest prime. Euclid's argument is a one-page proof of an endless list.

Euclid's Theorems · Wolfram MathWorld · Year unknown

Voyager 1 carries a golden record. It is a disk of sounds and images: greetings in many languages, music, and a map that says where the sender lived. The craft has left the heliosphere. The record is not a distress call. It is a note in a bottle, written by people who knew the reader might not exist, and sent it anyway.

Worth knowing

The golden record is a greeting sent with no promise of a reader.

The Golden Record · NASA Jet Propulsion Laboratory · 1977

Ludwig van Beethoven was already losing his hearing when he wrote much of the music he is known for, and he was profoundly deaf by the Ninth Symphony. He was not remembering a concert he could still hear in the room. He was composing from a trained inner ear, and from the page. The premiere happened. He had to be turned around to see the applause.

Worth knowing

The Ninth was written by a man who could no longer hear the room.

Ludwig van Beethoven · Encyclopaedia Britannica · 1824

In the 1840s Ignaz Semmelweis noticed that women died of childbed fever far more often in the doctors' ward than in the midwives' ward. The doctors came from the autopsy room. He ordered handwashing in chlorine solution. Deaths fell. Colleagues were insulted by the implication, and the practice spread slowly. The evidence arrived before the welcome.

Worth knowing

Handwashing cut deaths before the profession was ready to believe why.

Ignaz Semmelweis · Encyclopaedia Britannica · 1847

On the island of Yap, some money was stone, cut into disks too large to carry. One famous disk sank in a storm and was never recovered. People went on counting it. The owner had not lost the claim, because everyone still agreed whose stone it was. The rock was on the sea floor. The record of the rock was the money.

Worth knowing

Money can be a shared record of a thing, not the thing you can pick up.

Money Mischief · Milton Friedman · 1992

Chocolate began as a bitter drink in Mesoamerica, made from cacao, often spiced, and not sweetened with sugar. The bar on a modern shelf is a later invention: sugar, milk, and a European sweet tooth rearranged a ceremonial drink into a confection. If the old cup tastes strange to you, that is because you learned the dessert, not the plant.

Worth knowing

Chocolate was a bitter drink long before it was a sweet bar.

A Brief History of Chocolate · Smithsonian Magazine · 2015

Occam's razor is not a proof that the simple story is true. It is a preference: do not add an assumption you do not need. Two explanations can both fit the facts. The razor says to start with the one that invents less. Nature is allowed to be complicated. The razor is a rule for us, so we do not decorate a theory with our favorite extra causes.

Worth knowing

Prefer the explanation that assumes less. That is a habit, not a guarantee.

Simplicity · Stanford Encyclopedia of Philosophy · 2016