The Half-Life of Facts

“An engaging book…It’s a vivid account of the surprising ways in which new facts are accumulated, and how old knowledge is overturned.”

—
Universe Today

“Arbesman’s enthusiasm and humor maintains our interest in subjects many readers may not have encountered before….[
The Half-Life of Facts
] does what popular science should do—both engages and entertains.”

—
Kirkus Reviews

“A fascinating and necessary look at the pace of human knowledge.”

—Maria Popova,
Brain Pickings

“What does it mean to live in a world drowning in facts? Consider
The Half-Life of Facts
the new go-to book on the evolution of science and technology.”

—Tyler Cowen, professor of economics, George Mason University, author of
An Economist Gets Lunch

“
The Half-Life of Facts
is fun and fascinating, filled with wide-ranging stories and subtle insights about how facts are born, dance their dance, and die. In today’s world where knowledge often changes faster than we do, Sam Arbesman’s new book is essential reading.”

—Steven Strogatz, professor of mathematics, Cornell University, author of
The Joy of X

“
The Half-Life of Facts
teaches you that it is possible, in fact, to drink from a fire hose. Samuel Arbesman, an extremely creative scientist and storyteller, explores the paradox that knowledge is tentative in particularly consistent ways. This book unravels the mystery of how we come to know the truth—and how long we can be certain about it.”

—Nicholas A. Christakis, MD, PhD, coauthor of
Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives

“
The Half-Life of Facts
is a rollicking intellectual journey. Sam Arbesman shares his extensive knowledge with infectious enthusiasm and entertaining prose.”

—Michael Mauboussin, chief investment strategist, Legg Mason Capital Management, author of
Think Twice

Samuel Arbesman is an applied mathematician and network scientist. He is a Senior Scholar at the Ewing Marion Kauffman Foundation and a fellow at the Institute for Quantitative Social Science at Harvard University. In addition, he writes for popular audiences as a contributing writer at
Wired
, and his essays about math and science have appeared in places such as
The New York Times
,
The Atlantic
, and the Ideas section of
The Boston Globe.

CHAPTER 1:
The Half-life of Facts

CHAPTER 2:
The Pace of Discovery

CHAPTER 3:
The Asymptote of Truth

CHAPTER 4:
Moore’s Law of Everything

CHAPTER 5:
The Spread of Facts

CHAPTER 6:
Hidden Knowledge

CHAPTER 7:
Fact Phase Transitions

CHAPTER 8:
Mount Everest and the Discovery of Error

CHAPTER 9:
The Human Side of Facts

CHAPTER 10:
At the Edge of What We Know

Afterword

Acknowledgments

Notes

Index

WHEN
my grandfather was in dental school in the late 1930s, he was taught state-of-the-art medical knowledge. He learned all about anatomy, many aspects of biochemistry, and cell biology. He was also taught the number of chromosomes in a human cell. The problem was, he learned that it was forty-eight. Biologists had first visualized the nuclei of human cells in 1912 and counted these forty-eight chromosomes, and it was duly entered into the textbooks. In 1953, a well-known cytologist—someone who studies the interior of cells—even said that “the diploid chromosome number of 48 in man can now be considered as an established fact.”

But in 1956, Joe Hin Tjio and Albert Levan, two researchers working at Memorial Sloan-Kettering Cancer Center in New York and the Cancer Chromosome Laboratory in Sweden, decided to try a recently created technique for looking at cells. After counting over and over, they nearly always got only forty-six chromosomes. Previous researchers, who Tjio and Levan spoke with after receiving their results, turned out to have been having similar problems. These other scientists had even stopped some of their work prematurely, because they could only find forty-six out of the forty-eight chromosomes that they knew had to be there. But Tjio and Levan didn’t make the same assumption. Instead, they made the bold
suggestion that everyone else had been using the wrong number: There are only forty-six chromosomes in a human cell.

Facts change all the time. Smoking has gone from doctor recommended to deadly. Meat used to be good for you, then bad to eat, then good again; now it’s a matter of opinion. The age at which women are told to get mammograms has increased. We used to think that the Earth was the center of the universe, and our planet has since been demoted. I have no idea any longer whether red wine is good for me. And to take another familial example, my father, a dermatologist, told me about a multiple-choice exam he took in medical school that included the same question two years in a row. The answer choices remained exactly the same, but one year the answer was one choice and the next year it was a different one.

Other types of facts, ones about our surroundings, also change. The average Internet connection is far faster now than it was ten years ago. The language of science has gone from Latin to German to English and is certain to change again. Humanity has progressed from a population of less than two billion to more than seven billion people in the past hundred years alone. We have gone from being earthbound to having had humans walk on the moon, and we have sent our artifacts to the boundaries of our solar system. Chess, checkers, and even
Jeopardy!
have gone from being the domains of human experts to ones of computerized mastery.

Our world seems to be in constant flux. With our knowledge changing all the time, even the most informed people can barely keep up. All this change may seem random and overwhelming (Dinosaurs have feathers? When did that happen?), but it turns out there is actually order within the shifting noise. This order is regular and systematic and is one that can be described by science and mathematics.

Knowledge is like radioactivity. If you look at a single atom of uranium, whether it’s going to decay—breaking down and unleashing its energy—is highly unpredictable. It might decay in the next second, or you might have to sit and stare at it for
thousands, or perhaps even millions, of years before it breaks apart.

But when you take a chunk of uranium, itself made up of trillions upon trillions of atoms, suddenly the unpredictable becomes predictable. We know how uranium atoms work in the aggregate. As a group of atoms, uranium is highly regular. When we combine particles together, a rule of probability known as the law of large numbers takes over, and even the behavior of a tiny piece of uranium becomes understandable. If we are patient enough, half of a chunk of uranium will break down in 704 million years, like clockwork. This number—704 million years—is a measurable amount of time, and it is known as the half-life of uranium.

It turns out that facts, when viewed as a large body of knowledge, are just as predictable. Facts, in the aggregate, have half-lives: We can measure the amount of time for half of a subject’s knowledge to be overturned. There is science that explores the rates at which new facts are created, new technologies are developed, and even how facts spread. How knowledge changes can be understood scientifically.

This is a powerful idea. We don’t have to be at sea in a world of changing knowledge. Instead, we can understand how facts grow and change in the aggregate, just like radioactive materials. This book is a guide to the startling notion that our knowledge—even what each of us has in our head—changes in understandable and systematic ways.