Dreams of Earth and Sky

by Freeman Dyson

  Hoyle’s wrong theory of the universe had a different status from the other mistakes, because he was a young rebel when he proposed it. The steady-state universe was from the beginning a minority view. The decisive evidence against it was the discovery in 1964 of the microwave radiation pervading the universe. The microwave radiation had been predicted to exist as a relic of the hot big bang. The radiation proved that the hot big bang really happened and that the universe had a violent beginning. After that discovery, Hoyle was almost alone, preaching the steady-state gospel to a small band of disciples.

  Einstein, the last of Livio’s five blunderers, is an exception to all rules. He is widely quoted as saying that his addition of dark energy to the theory of gravitation was his biggest blunder. Livio has carefully examined the evidence and has come to the conclusion that Einstein never made this statement. The evidence points strongly to George Gamow as the guilty party. Gamow was another brilliant blunderer with a reputation for making up colorful stories. Einstein’s real biggest blunder happened when he changed his mind and dropped dark energy from his theory. Nature proved him wrong fifty years after his death, when it revealed that three quarters of the total mass of the universe is dark energy.

  Einstein invented a steady-state model of the universe many years before Hoyle. This steady-state model was discovered recently by a group of Irish scientists in an unpublished Einstein manuscript. Einstein abandoned the idea and never published it, probably because he found that steady-state theories are contrived and artificial. When Hoyle noisily promoted the steady-state cosmology twenty years later, Einstein never mentioned that he had discovered and discarded it long before. Einstein must have recognized it quickly as a brilliant blunder, clever but not likely to be correct. (I am indebted to the Irish scientist Cormac O’Raifeartaigh for information about the discovery of the Einstein manuscript.)

  After reading Livio’s account, I look on the history of science in a new way. In every century and every science, I see brilliant blunders. Isaac Newton’s biggest blunder was his corpuscular theory of light, which had light consisting of a spray of little particles traveling along straight lines. In the nineteenth century, James Clerk Maxwell discovered the laws of electromagnetism and proposed that light consists of electromagnetic waves. In the twentieth, Einstein proved that Newton and Maxwell were both right and both wrong, because light behaves like particles in one situation and like waves in another.

  The chief difference between science and other human enterprises such as warfare and politics is that brilliant blunders in science are less costly. Hannibal’s brilliant crossing of the Alps to invade Italy from the north resulted in the ruin and total destruction of his homeland. Two thousand years later, the brilliant attack on Pearl Harbor cost the Japanese emperor his empire. Even the worst scientific blunders do not do so much damage.

  The worst political blunder in the history of civilization was probably the decision of the emperor of China in the year 1433 to stop exploring the oceans and to destroy the ships capable of exploration and the written records of their voyages. In no way can this blunder be called brilliant. Before the decision, China had a fleet of oceangoing ships bigger and more capable than any European ships. China was roughly level with Europe in scientific knowledge and far ahead in the technologies of printing, navigation, and rocketry. As a consequence of the decision, China fell disastrously behind in science and technology, and is only catching up now after six hundred years. The decision was the result of powerful people pursuing partisan squabbles and neglecting the long-range interests of the empire. This is a disease to which governments of all kinds, including democracies, are dangerously susceptible.

  Another cause of catastrophic blunders is religion. A legendary example of a religious blunder is the story of Tsar Lazar, the king of Serbia in 1389 when his kingdom was invaded by the Turks. He confronted the Turkish army on the fatal battlefield of Kosovo Polje. The story is told in the Serbian national epic The Battle of Kosovo. The Virgin Mary happened to be in Jerusalem at the time when the Turks invaded, and sent a falcon with a message for the tsar. The falcon arrived on the battlefield and told the tsar that he must make a choice between an earthly and a heavenly kingdom. If he chose the earthly kingdom, his army would defeat the Turks and he would continue his reign in Serbia. If he chose the heavenly kingdom, his army would be annihilated and his people would become slaves of the Ottoman Empire. Being a very pious monarch with his mind concentrated on spiritual virtue, the tsar naturally chose the heavenly kingdom, and his people paid for his choice by losing their freedom.

  Seven years after Darwin published The Origin of Species, without any satisfactory explanation of hereditary variations, the Austrian monk Gregor Mendel published his paper “Experiments in Plant Hybridization” in the journal of the Brünn Natural History Society. Mendel had solved Darwin’s problem. He proposed that inheritance is carried by discrete units, later known as genes, that do not blend but are carried unchanged from generation to generation. The Mendelian theory of inheritance fits perfectly with Darwin’s theory of natural selection. Mendel had read Darwin’s book, but Darwin never read Mendel’s paper.

  The essential insight of Mendel was to see that sexual reproduction is a system for introducing randomness into inheritance. In garden peas as in humans, each plant is either male or female, and each offspring has one male and one female parent. Inherited characteristics may be specified by one gene or by several genes. Single-gene characteristics are the simplest to calculate, and Mendel chose them to study. For example, he studied the inheritance of pod color, determined by a single gene that has a version specifying green and a version specifying yellow. Each plant has two copies of the gene, one from each parent. There are three kinds of plants, pure green with two green versions of the gene, pure yellow with two yellow versions, and mixed with one green and one yellow. It happens that only one green gene is required to make a pod green, so that the mixed plants look the same as the pure green plants. Mendel describes this state of affairs by saying that green is dominant and yellow is recessive.

  Mendel did his classic experiment by observing three generations of plants. The first generation was pure green and pure yellow. He crossed them, pure green with pure yellow, so that the second generation was all mixed. He then crossed the second generation with itself, so that the third generation had all mixed parents. Each third-generation plant had one gene from each parent, with an equal chance that each gene would be green or yellow. On the average, the third generation would be one-quarter pure green, one-quarter pure yellow, and one-half mixed. In outward appearance the third generation would be three-quarters green and one-quarter yellow.

  This ratio of 3 between green and yellow in the third generation was the new prediction of Mendel’s theory. Most of his experiments were designed to test this prediction. But Mendel understood very well that the ratio 3 would only hold on the average. Since the offspring chose one gene from each parent and every choice was random, the numbers of green and yellow in the third generation were subject to large statistical fluctuations. To test the theory in a meaningful way, it was essential to understand the statistical fluctuations. Fortunately, Mendel understood statistics.

  Mendel understood that to test the ratio 3 with high accuracy he would need huge numbers of plants. It would take about eight thousand plants in the third generation to be reasonably sure that the observed ratio would be between 2.9 and 3.1. He actually used 8,023 plants in the third generation and obtained the ratio 3.01. He also tested other characteristics besides color, and used altogether 17,290 third-generation plants. His experiments required immense patience, continuing for eight years with meticulous attention to detail. Every plant was carefully isolated to prevent any intruding bee from causing an unintended fertilization. A monastery garden was an ideal location for such experiments.

  In 1866, the year Mendel’s paper was published, but without any knowledge of Mendel, Darwin did exactly the same experiment. Darwin used sn
apdragons instead of peas, and tested the inheritance of flower shape instead of pod color. Like Mendel, he bred three generations of plants and observed the ratio of normal-shaped to star-shaped flowers in the third generation. Unlike Mendel, he had no understanding of statistical fluctuations. He used a total of only 125 third-generation plants and obtained a value of 2.4 for the crucial ratio. This value is within the expected statistical uncertainty, either for a true value of 2 or for a true value of 3, with such a small sample of plants. Darwin did not understand that he would need a much larger sample to obtain a meaningful result.

  Mendel’s sample was sixty-four times larger than Darwin’s, so that Mendel’s statistical uncertainty was eight times smaller. Darwin failed to repeat his experiment with a larger number of plants, and missed his chance to incorporate Mendel’s laws of heredity into his theory of evolution. He had no inkling that a fundamental discovery was within his grasp if he continued the experiment with larger populations. The basic idea of Mendel was that the laws of inheritance would become simple when inheritance was considered as a random process. This idea never occurred to Darwin. That was why Darwin learned nothing from his snapdragon experiment. It remained a brilliant blunder.

  Mendel made a brilliant blunder of a different kind. He published his laws of heredity, with a full account of the experiments on which the laws were based, in 1866, seven years after Darwin had published The Origin of Species. Mendel was familiar with Darwin’s ideas and was well aware that his own discoveries would give powerful support to Darwin’s theory of natural selection as the cause of evolution. Mendelian inheritance by random variation would provide the raw material for Darwinian selection to work on.

  Mendel had to make a fateful choice. If he chose to call Darwin’s attention to his work, Darwin would have understood its importance, and Mendel would inevitably have become involved in the acrimonious public disputes that were raging all over Europe about Darwin’s ideas. If Mendel chose to remain silent, he could continue to pursue his true vocation, to serve his God as a monk and later as the abbot of his monastery. Like Tsar Lazar five hundred years earlier, he had to choose between worldly fame and divine service. Being the man he was, he chose divine service. Unfortunately, his God played a cruel joke on him, giving him divine gifts as a scientist and mediocre talents as an abbot. He abandoned the chance to be a world-famous scientist and became an unsuccessful religious administrator.

  Darwin’s blindness and Mendel’s reticence combined to delay the progress of science by thirty years. But thirty years is a short time in the history of science. In the end, after both men were dead and their personal shortcomings forgotten, their partial visions of the truth came together to create the modern theory of evolution. Thomas Hunt Morgan at Columbia University understood that the fruit fly Drosophila was a far better tool than the garden pea and the snapdragon for studying heredity. Fruit flies breed much faster and are more easily handled in large numbers. With fruit flies, Morgan could go far beyond Mendel in exploring the world of genetics.

  In my own life as a scientist, there was one occasion when I felt that a deep secret of nature had been revealed to me. This was my personal brilliant blunder. I remember it with joy, even though my dreams of glory were shattered. It was a blissful experience. It arose out of work that I did with my colleague Andrew Lenard from Indiana University, investigating the stability of ordinary matter. We proved by a laborious mathematical calculation that ordinary matter is stable. The physical basis of stability is the exclusion principle, a law of nature saying that two electrons can never be in the same state. Matter is stable against collapse because every atom contains electrons and the electrons resist being squeezed together.

  My blunder began when I tried to extend the stability argument to other kinds of particles besides electrons. We can divide particles into two types in three different ways. A particle may be electrically charged or neutral. It may be weakly or strongly interacting. And it may belong to one of two types that we call fermions and bosons in honor of the Italian physicist Enrico Fermi and the Indian physicist Satyendra Bose. Fermions obey the exclusion principle and bosons do not. So each particle has eight possible ways to make the three choices. For example, the electron is a charged weak fermion. The light quantum is a neutral weak boson. The famous particle predicted by Peter Higgs, and discovered in 2012 at the European Center for Nuclear Research (CERN), is a neutral strong boson.

  I observed in 1967 that seven of the eight possible combinations were seen in nature. The one combination that had never been seen was a charged weak boson. The missing type of particle would be like an electron without the exclusion principle. Next, I observed that our proof of the stability of matter would fail if electrons without the exclusion principle existed. So I jumped to the conclusion that a charged weak boson could not exist in a stable universe. This was a new law of nature that I had discovered. I published it quietly in a mathematical journal.

  I knew that my theory flatly contradicted the prevailing wisdom. The prevailing wisdom was the unified theory of weak and electromagnetic interactions proposed by my friends Steven Weinberg and Abdus Salam. Weinberg and Salam predicted the existence of a new particle as a carrier of weak interactions. They called the new particle W. The W particle had to be a charged weak boson, precisely the combination that I had declared impossible. Nature, speaking through an experiment at CERN in Geneva, would decide who was right.

  The decision did not come quickly. It took the experimenters fifteen years to build a new machine and use it to search for the W particle. But the decision, when it came, was final. Large numbers of W particles were seen, with the properties predicted by Weinberg and Salam. With hindsight I could see several reasons why my stability argument would not apply to W particles. They are too massive and too short-lived to be a constituent of anything that resembles ordinary matter. I quickly forgot my disappointment and shared the joy of Weinberg and Salam in their well-deserved triumph. As my mother taught me long ago, the key to enjoyment of any sport is to be a good loser.

  In Livio’s list of brilliant blunderers, Darwin and Einstein were good losers, Kelvin and Pauling were not so good, and Hoyle was the worst. The greatest scientists are the best losers. That is one of the reasons why we love the game. As Einstein said, God is sophisticated but not malicious. Nature never loses, and she plays fair.

  Note added in 2014: Several readers wrote indignant letters complaining because I accused great scientists of blundering. I replied to them as follows:

  Thank you for your comments on my review. I learn more from people who disagree with me than from those who agree.… The main cause of disagreement in this case is a different understanding of the word “blunder.” To me and to Mario Livio the word carries no blame. We use it in a joking fashion to refer to any proposal or opinion that turns out to be wrong or ignorant. To you the word seems to be judgmental, as if committing a blunder were committing a crime. To me, the main value of Mario Livio’s book is to make blunders respectable.

  *Brilliant Blunders: From Darwin to Einstein—Colossal Mistakes by Great Scientists That Changed Our Understanding of Life and the Universe (Simon and Schuster, 2013).

  SOURCES

  The essays in this book were originally published as follows:

  “Our Biotech Future,” The New York Review of Books, July 19, 2007

  The letter responding to “Our Biotech Future” was published in The New York Review of Books, September 27, 2007, and is reprinted here with the permission of Wendall Berry.

  “Writing Nature’s Greatest Book,” The New York Review of Books, October 19, 2006

  “Rocket Man,” The New York Review of Books, January 17, 2008

  The letter responding to “Rocket Man” was published in The New York Review of Books, February 14, 2008, and is reprinted here with the permission of Bernard Lytton.

  “The Dream of Scientific Brotherhood,” The New York Review of Books, May 10, 2007

  “Working for the Revolu
tion,” The New York Review of Books, October 25, 2007

  “The Question of Global Warming,” The New York Review of Books, June 12, 2008

  The letter responding to “The Question of Global Warming” was published in The New York Review of Books, October 9, 2008, and is reprinted here with the permission of Robert M. May.

  “Struggle for the Islands,” The New York Review of Books, October 23, 2008

  “Leaping into the Grand Unknown,” The New York Review of Books, April 9, 2009

  The letter responding to “Leaping into the Grand Unknown” is reprinted here with the permission of Frank Wilczek.

  “When Science and Poetry Were Friends,” The New York Review of Books, August 13, 2009

  “What Price Glory?,” The New York Review of Books, June 10, 2010

  The letter responding to “What Price Glory?” is reprinted here with the permission of Steven Weinberg.

  “Silent Quantum Genius,” The New York Review of Books, February 25, 2010

  “The Case for Far-Out Possibilities,” The New York Review of Books, November 10, 2011

  “Science on the Rampage,” The New York Review of Books, April 5, 2012

  “How We Know,” The New York Review of Books, March 10, 2011

  “The ‘Dramatic Picture’ of Richard Feynman,” The New York Review of Books, July 14, 2011

  “How to Dispel Your Illusions,” The New York Review of Books, December 22, 2011

  The letter responding to “How to Dispel Your Illusions” was published in The New York Review of Books, January 12, 2012, and is reprinted here with the permission of Daniel Kahneman.

  “What Can You Really Know?,” The New York Review of Books, November 8, 2012

  “Oppenheimer: The Shape of Genius,” The New York Review of Books, August 15, 2013