Jeff Jacoby
In astronomy, "Sagan’s number" refers to the number of stars in the observable universe. That’s a value easier to define than to calculate, but in round numbers, according to a 2010 study by Yale astronomer Pieter van Dokkum, it comes to 300,000,000,000,000,000,000,000, or 300 sextillion. (Depending on the meaning of "observable," that number may now be out of date.)
Sagan’s number is named for Carl Sagan, the American astronomer, planetary scientist, cosmologist, and science communicator who died in 1996. He achieved extraordinary renown in the 1970s and 1980s, especially after PBS broadcast his 13-part television series "Cosmos," which became one of the most widely watched series in the history of American public television. (The dazzling volume of the same title produced as a companion to the series was among the best-selling science books ever published.)
His scientific achievements were considerable. He published more than 600 papers and books in the areas of astrobiology, planetary conditions, the origins of life on earth, the greenhouse effect, and extraterrestrial intelligence. He played a role in numerous NASA planetary space probes and helped write the so-called Arecibo message, an interstellar radio signal incorporating information about humanity that was beamed from earth in the direction of the M13 star cluster in 1974. The honors and awards he received numbered in the dozens; they ranged from the NASA Distinguished Public Service Medal to the George Foster Peabody Award for his television work. He was a frequent guest on The Tonight Show with Johnny Carson, and he wrote regularly about science for Parade magazine, a weekly supplement in hundreds of US papers.
As part of his campaign to increase scientific literacy among the general public, Sagan repeatedly emphasized the importance of skepticism and non-dogmatic thinking. He was adamant that extraordinary claims require extraordinary levels of proof and derided pseudoscience and its peddlers. (One of his favorite cartoons, he wrote, showed "a fortune-teller scrutinizing the mark’s palm and gravely concluding: 'You are very gullible.'")
Yet while he cast a cold eye on the supernatural claims of religion, he was equally firm that scientists must not fall in love with scientific claims that aren’t supported by convincing evidence. "If the ideas don’t work, you must throw them away," he wrote in The Demon-Haunted World , the last book he published before his death. "Don’t waste neurons on what doesn’t work. Devote those neurons to new ideas that better explain the data." He warned against succumbing to confirmation bias — what the pioneering 19th-century English physicist Michael Faraday described as the temptation
to seek for such evidence and appearances as are in the favor of our desires, and to disregard those which oppose them. . . . We receive as friendly that which agrees with [us], we resist with dislike that which opposes us; whereas the very reverse is required by every dictate of common sense.
The lure of confirmation bias is if anything more powerful today, when social media and political polarization relentlessly turn scientific matters into culture-war flashpoints. On issues as different as gender identity and COVID-19, too many ideologues on both the right and the left approach public health and science questions through a political lens. News organizations increasingly freeze out or belittle scientific opinions that don’t fit an accepted narrative. Leading politicians support or oppose health-care practices on the basis of party politics.
Were Carl Sagan still alive, he would surely be among those pushing back against such blind antiscientific bias. Alas, he was just 62 when he died from complications brought on by a long struggle with bone marrow disease. But in a recently unearthed speech he gave to the Illinois chapter of the American Civil Liberties Union in 1987, Sagan expressed warnings that are even more relevant today than they were at the time. The speech was obtained and transcribed by Harvard scientist Steven Pinker and civil liberties lawyer Harvey Silverglate, both of Cambridge, Mass., who published it this month in the online journal Quillette.
In his address, write Pinker and Silverglate in a brief introduction, Sagan "spoke prophetically of the irrationality that plagued public discourse, the imperative of international cooperation, the dangers posed by advances in technology, and the threats to free speech and democracy in the United States." If those threats raised concerns in 1987, they have grown dire today. Some excerpts from Sagan’s remarks:
Science has devised a set of rules of thinking, of analysis, which, although there are exceptions in individual cases (scientists being humans just like everybody else), nevertheless, on average, are responsible for the remarkable progress of science.
And you all know, certainly, what these rules are. Things like arguments from authority have little weight. Like contentions have to be demonstrable. Like experiments must be repeatable. Like vigorous substantive debate is encouraged and is considered the lifeblood of science. Like serious critical thinking and skepticism addressed to new and even old claims is not just permissible, but is encouraged, is desirable, is the lifeblood of science. There is a creative tension between openness to new ideas and rigorous skeptical scrutiny.
These are axiomatic to the scientific method, yet they are flouted routinely, even aggressively. Sagan properly noted that "arguments from authority have little weight" — yet how often are controversial matters now declared immune to dispute because "the science is settled" or " 97 percent of scientists agree" or we must "listen to the experts"?
What is true of science is true of everything, Sagan argued. Mistakes are inevitable, which is why it is urgent to allow space for "settled" conclusions to be challenged:
In public affairs, this sort of error-correction machinery in our society is institutionalized in the Constitution. It’s institutionalized, first of all, in the separation of powers, and secondly, in the civil liberties, especially in the first 10 amendments to the Constitution: the Bill of Rights.
The founding fathers mistrusted government power, and they had very good reason to, as do we. This is why they tried to institutionalize the separation of powers, the right to think, the right to speak, to be heard, to assemble, to complain to the government about its abuses, to be able to vote or impeach malefactors out of office. . . .
Despite our best efforts, some things we believe are probably wrong. We certainly are very keen on recognizing the errors of past times and other nations. Why should our nation, why should our time, be different? If there are things that we believe, if there are institutions in our society that are in error, imperfectly conceived or executed, these are potential impediments to our survival. How do we find the errors? How do we correct them?
I maintain: with courage, the scientific method, and the Constitution.
At the intersection of science and public policy, nothing is more hazardous than dogmatism enforced through the squelching of dissenting attitudes. A generation before Sagan voiced his warning, an equally renowned scientist, the theoretical physicist Richard Feynman, raised similar alarms. In a 1955 lecture to the National Academy of Sciences, Feynman — who a few years later would be awarded the Nobel Prize in Physics — addressed what he called "the value of science." He ended with a warning, more desperately needed now than it was then, against closed-mindedness in science and against the urge to demonize those who challenge popular views. "If we want to solve a problem that we have never solved before, we must leave the door to the unknown ajar," Feynman told his listeners.
In the impetuous youth of humanity, we can make grave errors that can stunt our growth for a long time. This we will do if we say we have the answers now, so young and ignorant as we are. If we suppress all discussion, all criticism, proclaiming "This is the answer, my friends; man is saved!" we will doom humanity for a long time to the chains of authority, confined to the limits of our present imagination. It has been done so many times before.
It is our responsibility as scientists, knowing the great progress which comes from a satisfactory philosophy of ignorance, the great progress which is the fruit of freedom of thought, to proclaim the value of this freedom; to teach how doubt is not to be feared but welcomed and discussed; and to demand this freedom as our duty to all coming generations.
Of all scientific values, Sagan and Feynman both knew, the most invaluable is the freedom to doubt. That freedom is no less indispensable to a healthy civic culture. In a universe of 300 sextillion stars, we will never know everything we don’t know. Even here, on the pale blue dot that is the only home humankind has ever known, there are so many unsolved dilemmas, so many questions with only uncertain answers. Those who demand that heterodox thoughts be censored — or self-censored — are playing with fire. For when skeptics aren’t safe, all of us are at risk.
