The Half-Life of Facts

by Samuel Arbesman

  CURRENT

  Published by the Penguin Group

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  First published in 2012 by Current,

  a member of Penguin Group (USA) Inc.

  Copyright © Samuel Arbesman, 2012

  All rights reserved

  LIBRARY OF CONGRESS CATALOGING IN PUBLICATION DATA

  Arbesman, Samuel.

  The half-life of facts : why everything we know has an expiration date / Samuel Arbesman.

  pages ; cm

  Includes bibliographical references and index.

  ISBN 978-1-101-59529-9

  1. Evolution. 2. Science—Philosophy. 3. Probabilities. I. Title.

  Q175.32.E85A74 2012

  501—dc23

  2012019142

  No part of this book may be reproduced, scanned, or distributed in any printed or electronic form without permission. Please do not participate in or encourage piracy of copyrighted materials in violation of the author’s rights. Purchase only authorized editions.

  While the author has made every effort to provide accurate telephone numbers, Internet addresses, and other contact information at the time of publication, neither the publisher nor the author assumes any responsibility for errors, or for changes that occur after publication. Further, the publisher does not have any control over and does not assume any responsibility for author or third-party Web sites or their content.

  TO DEBRA

  CONTENTS

  Title Page

  Copyright

  Dedication

  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

  Acknowledgments

  Notes

  Index

  CHAPTER 1

  The Half-life of Facts

  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 man1 can now be considered as an established fact.”

  But in 1956, Joe Hin Tjio and Albert Levan,2 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 beyond 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 o
ur knowledge—even what each of us has in our head—changes in understandable and systematic ways.

  • • •

  HOW exactly is knowing how knowledge changes actually useful? You may find it interesting to discover that the dinosaurs of our youth—slow, reptilian, and gray-green—are now fast moving, covered in feathers, and the colors of the NBC peacock. But if you don’t have a six-year-old at home, this is probably not going to affect your life in any significant way.

  I could tell you that certain areas of medical knowledge have a churn of less than a half century—well within a single life span—and knowing this can motivate us to constantly brush up on what we know, so we continue to eat healthy or exercise correctly and don’t simply rely on what we were told when we were young. Or I could say that by knowing how language changes, we can better understand the slang and dialect of the generation that follows us.

  But really, practical examples like these, while important (medical knowledge will keep cropping up), are not the main point. Knowing how facts change, how knowledge spreads, or how we adapt to new ideas are all important for a different reason: Knowing how knowledge works can help us make sense of our world. And even more than that, it can allow us to anticipate the shortcomings in what we each might know and help us to plan for these flaws in our knowledge.

  Facts are how we organize and interpret our surroundings. No one learns something new and then holds it entirely independent of what they already know. We incorporate it into the little edifice of personal knowledge that we have been creating in our minds our entire lives. In fact, we even have a phrase for the state of affairs that occurs when we fail to do this: cognitive dissonance.

  Ordering our surroundings is the rule of how we as humans operate. In childhood we give names to our toys, and in adulthood we give names to our species, chemical elements, asteroids, and cities. By naming, or, more broadly, by categorizing, we are creating an order to an otherwise chaotic and frightening world.

  And when we learn facts, we are doing the same thing. Facts—whether about our surroundings, the current state of knowledge, or even ourselves—provide us with a sense of control and a sense of comfort. When we see something out of the corners of our eyes around dusk, we needn’t view it as a creepy bird of the night: We call that a bat, which is a winged nocturnal mammal that “sees” through the use of echolocation and is probably afraid of the bipedal mammals around it. Only half as scary, right?

  But when facts change, we lose a little bit of this control. Suddenly things aren’t quite as they seemed. If doctors didn’t know that smoking was bad for us for decades, we worry about what else doctors are also wrong about today. If I’ve just learned that my parents had completely different—and, for their time, acceptable—parenting techniques from my own, I am a bit concerned about my upbringing. And if I’ve just found out that scientists have discovered hundreds of planets outside the solar system, and I was living with the assumption that there were only a handful, I might be a little shaken, or at the very least somewhat surprised.

  But if we can understand the underlying order and patterns of how facts change, we can better handle all of the uncertainty that’s around us.

  To be clear: I’m using the word fact in an intuitive way—a bit of knowledge that we know, either as individuals or as a society, as something about the state of the world. We generally like our facts to represent an accurate representation of reality, an objective truth, but that’s not always the case.

  Certain fields use fact to mean an objective truth.3 The endeavor of science gets us ever closer to this truth, and many of the shifts in what we know occur only at the fringes of discovery, and are due to our continuous approach to truth. However, I am choosing to use fact in a looser fashion, simply to refer to our individual states of knowledge awareness. This can refer to a scientific fact, even if it might eventually be disproved, or even to a less ambiguous sort of fact, such as the current fastest human runner or the most powerful computer, which are facts about our surroundings.

  This will not satisfy everyone, but there are two reasons for this choice. The first is to avoid being drawn down some sort of epistemological rabbit hole, which is likely to be more than a little confusing. To paraphrase Justice Potter Stewart, many of us know a fact when we see one. But second, and more important, it turns out that lots of different types of knowledge change in similar ways. While some facts are about approaching truth and some are about our changing surroundings, we can only see the similarities clearly in how they operate by bundling all of these types of facts together.4

  And there’s one simple way to organize facts, even before we understand all the math and science behind how knowledge changes. We can organize what we know by the rate at which it changes.

  Imagine we have all the facts in the world—those pieces of knowledge that contain all that we know—lined up according to how often they change. On the far left we have the fast-changing facts, the ones that are constantly in flux. These are things such as what the weather will be tomorrow or what the stock market close was yesterday. And on the far right we have the very slow-changing facts, the ones that for all practical purposes are constant. These are facts such as the number of continents on the planet or the number of fingers on a human hand.

  In between we have the facts that change, but not too quickly—and are therefore that much more maddening to deal with. These facts might change over the course of years or decades or a single lifetime. How many billions of people are on the planet is one of these. I learned five billion in school, and we just recently crossed seven billion, as of 2012. My grandfather, who was born in 1917, learned there were fewer than two billion. The number of planets outside the solar system that have been discovered, or, for that matter, the number of planets in our own solar system, is also in this category. What we know about dinosaurs is in this group of facts, as is the average speed of a computer. The vast majority of what we know seems to fall into this category, which I call mesofacts5—facts that change at the meso-, or middle, timescale.

  Lots of our scientific knowledge consist of mesofacts. For example, the number of known chemical elements is a mesofact. If, as a baby boomer, you learned high school chemistry in 1970, and then, as we all are apt to do, did not take care to brush up on your chemistry periodically, you would not realize that there are at least 12 new elements in the periodic table, bringing the total up to 118. Over a tenth of the elements have been discovered since you graduated high school. And all that dinosaur knowledge I’ve mentioned is also made up of mesofacts.

  Technology is full of mesofacts too, from the increase in transportation speeds to the changes in how we store information—from floppy disk to the cloud. The height of the tallest skyscraper has also steadily increased over time due to improving technology.

  World records are constantly being broken in the realms of human ability, and we recently have begun to be humbled by machines, as they rack up wins against us in more and more games once deemed too complex for computers, from Othello and checkers to chess. All mesofacts.

  Mesofacts are all around us and just acknowledging their existence is useful. It can help eliminate part of the surprise in our lives.

  If my grandfather had been told in dental school that a specific fraction of the knowledge he learned there would become obsolete soon after he graduated, this could at least provide an anchor for his uncertainty. It would prevent dentists of his generation from being surprised by basic biological facts, or from working with outdated knowledge. In fact, many medical schools now do this: They embrace the mesofacts of medicine, teaching physicians that changing knowledge is the rule rather than the exception.

  But simply knowing that knowledge changes like this isn’t enough. We would end up going a little crazy as we frantically tried to keep up with the ever-changing facts around us, forever living on some sort of informational treadmill. But it doesn’t have t
o be this way, because there are patterns: Facts change in regular and mathematically understandable ways. And only by knowing the pattern of our knowledge’s evolution can we be better prepared for its change.

  • • •

  THERE are mathematical regularities behind the headlines of changing scientific knowledge. We accumulate scientific knowledge like clockwork, with the result that facts are overturned at regular intervals in our quest to better understand the world. Similarly, the growth and change of technological knowledge, from processing power to information storage, are also part of the universe of facts that change with regularity. And of course these two areas—science and technology—affect many other factual aspects of our lives: from the spread of disease, to how we travel, and even to the increase in computer viruses on the Internet. All of these areas of knowledge change systematically.

  But just as the creation of facts operates according to certain scientific principles, so too does the spread of knowledge; how each of us hears of new information, or how error gets dispelled, adheres to the rules of mathematics. And due to a new understanding of cognitive biases, much of what each of us knows, even as it changes, now has a clear structure: These shifts obey certain scientific patterns that are explicable by findings in cognitive science.

  This is not to say that we can understand everything. Much in the world is shocking and unexpected, and we still have to deal with these new facts when we become aware of them. But by and large there are ways to understand how our knowledge changes, ways to bring order to the chaos of ever-changing facts.

  William Macneile Dixon, a British professor of literature in the late nineteenth and early twentieth centuries, once wrote, “The facts of the present won’t sit still for a portrait. They are constantly vibrating, full of clutter and confusion.”

  We now understand how vibrations work, due to physics. We’re no longer confused by the fact that plucking a guitar string somehow gives rise to order and music. It’s time we do the same thing for the fluctuations in what we know as well, and recognize that there’s an order to all of our changing knowledge. This book is a guide to the science behind the vibrations in the facts around us.