Carl Sagan

(born November 9, 1934, died December 20, 1996)

Introduction

Carl Sagan, a modern-day Renaissance man of science, was born in 1934 in New York. After graduating with both a B.A. and a B.S. Degree from the University of Chicago, Sagan completed his M.S. in physics and earned a Ph.D. in astronomy and astrophysics in 1960. Sagan was nominated to join the Smithsonian Astrophysical Observatory in 1962. At the same time, he also worked with the Nobel-prize winner Joshua Lederberg, investigating the origins of life on earth, and taught genetics at Stanford. Sagan then taught astronomy at Harvard until 1968, when he became professor of astronomy and space sciences at Cornell University. He was then appointed director of the laboratory for Planetary Studies. Sagan was awarded the NASA medal for exceptional scientific achievement in 1972, after his hypotheses about Mars were validated by data obtained from the 1971 Mars Mariner expedition. Beginning in 1968, Sagan was editor of Icarus, the international journal of astronomy, and wrote many distinguished books. His works include The Cosmic Connection (1973), which received the Campbell Award for best science book; the Pulitzer-prize winning Dragons of Eden (1977); Broca's Brain (1979), on developments in neurophysiology; and Cosmos (1980), which accompanied his widely-acclaimed television series. In The Nuclear Winter (1983), Sagan explored the unforeseen and devastating physical and chemical effects of even a small-scale nuclear war on the earth's biosphere and life on earth. Personally, I believe that much of Sagan's best humanist writing was done in his later books, especially in Pale Blue Dot (1994), Shadows of Forgotten Ancestors (1992), The Demon-Haunted World (1996), and Billions & Billions (1997--published posthumously).

But Iíd like to start a little earlier...

Ancestry and Biography

A long time ago in a place far, far away, Leib Gruber lived in the village of Sassow on the Bug River. Now located in Ukraine, at the time it was part of the Austro-Hungarian crownland of Galicia. As a young man, the only honest work Carl Saganís grandfather could find was carrying people across the Bug. The customer would mount Leibís back; in his prized boots, the tools of his trade, he would wade out in a shallow stretch of the river and deliver his passenger to the opposite bank. Sometimes the water would reach his waist. There were no bridges, no ferryboats. Horses were too valuable to serve the purpose. Leib was a beast of burden.

It is little wonder to me that he emigrated to New York in 1904, departing in such haste that he left his young wife behind. Family legend has it that he killed a man with his bare hands in a matter of personal honor and boarded ship to avoid the ensuing murder rap. A little more than a year later he sent for Chaiya who, after taking the least expensive passage available, arrived at Ellis Island with only a single dollar to spare. It must have been an ardent reunion, for she conceived a child only weeks after her arrival.

In the Lower East Side of Manhattan there was strong pressure to fit into American life. Leib became Louis, and Chaiya anglicized her name to Clara. She gave her baby a good American name: Rachel Molly Gruber. A few years later, Clara gave birth to a second daughter Tobi, but the stress was too much for her weak heart. Within a month, Clara Gruber, aged 33, was dead of cardiac failure.

Unable or unwilling to face the task of raising two baby daughters by himself, Louis sent Rachel to live with relatives in Austria and put Tobi in an orphanage. Soon afterward he took another wife, Rose Klinghofer. After a few years, Rachel was sent back to rejoin her father and stepmother. Rose received the child with less than open arms, while Rachel viewed her as an impostor, a pod person who had somehow replaced her real mother. She was rebellious and avoided home as much as possible.

Instead, Rachel made many friends. In their company she learned social skills and acquired a fashion sense, eventually becoming something of a trendsetter. In her teens she was the first in her crowd to buy a bathing suit. Apparently too short, as it got her thrown off the boardwalk at Coney Island. She explored New Yorkís high culture, getting into concerts, plays and ballets without money--often by entering at intermission. She was ambitious and very intelligent, completing an equivalency test to receive her high school diploma at a time when relatively few women were educated.

By her mid-twenties, she was bold, brassy and glamorous. At a party she was introduced to a quiet young man. He was skinny, red-haired and covered with freckles. When they went swimming, she gasped at the extent of his splotched flesh, asking "Are you freckled everywhere?" "Everywhere!" he boasted.

It was love at first sight. Rachel was enflamed by his red hair and Samuel Sagan was swept away by her vivacious presence. They were married within weeks, on March 4, 1933. As far as their children could determine, they never tired of each other throughout a marriage that lasted 46 years.

The first of their children, Carl Edward Sagan, was born November 9, 1934. He was named after the mother that Rachel never really knew: Clara Gruber.

On a sunny day in 1939 Carl and Rachel, awaiting Samuelís return from work, were watching the Sun set across Lower New York Bay.

"There are people fighting out there, killing each other," she said.

"I know. I can see them" replied Carl.
"No you canít! Theyíre too far away." retorted his mother.

How did she know whether he could see them? Perhaps, he thought, it was just his imagination. But how can you tell when someone is only imagining? It was Carlís first exposure to skepticism.

Soon after, Samuel Sagan patiently explained to Carl about zero as a placeholder in arithmetic, about the wicked-sounding names of big numbers, and about how thereís no biggest number. ("You can always add one," he pointed out). Suddenly Carl was seized by a compulsion to write in sequence all the integers from 1 to 1000. He started the project eagerly, but was surprised at how slowly it went. Before he reached 200, Rachel announced it was time for his bath. A mediator his whole life, his father volunteered to continue the sequence if Carl would cheerfully submit to the bath. By the time he emerged, Sam was approaching 900, and Carl reached 1000 only a little past his normal bedtime. "The magnitude of large numbers has never ceased to impress me."

That same year the family attended the New York Worldís Fair, which offered "a vision of a perfect future made possible by science and technology." Unimagined wonders were demonstrated.

Carlís parents were not scientists, and in fact knew almost nothing about science. But by introducing him simultaneously to skepticism and wonder, they taught him the two uneasily cohabiting modes of thought that are central to the scientific method.

Science Career and Achievement

A survey of the available literature suggests that while Carl Sagan was recognized as a "good" scientist, he was not held in the highest regard by many influential members of the science establishment. Nevertheless, he published over 600 peer-reviewed papers and eighteen books over a career spanning 36 years. Thatís an average of more than a paper per month, which by any measure is prolific.

Sagan almost single-handedly invented the discipline known as exobiology--a probability science which covers the properties that extraterrestrial life might have, the likelihood of the development of intelligent life and SETI, the Search for Extraterrestrial Intelligence. This is an example of the prime motivation for his career--the search for life somewhere else besides the Earth.

Saganís youth was a time of great imagination about the planets, and most especially Mars. Astronomer Percival Lowell--the discoverer of Pluto--was convinced by his telescopic observations that Mars was crisscrossed by what appeared to be a network of immense canals. Lowell imagined them to be the last titanic effort of a dying civilization to irrigate a desiccated planet from its poles. Lowell, wealthy and influential, convinced many scientists and others that Mars was likely an inhabited world. Popular science fiction followed along. Edgar Rice Burroughs--best known as the creator of "Tarzan of the Apes"--spun fantastic yarns in his "Princess of Mars" series, in which gentleman adventurer John Carter of Virginia becomes a superhuman warrior on the red planet. [Both Carl and I read most of these in our youth--riveting stuff for adolescents). The fanciful stories of H.G. Wells were reintroduced to millions when Orson Welles broadcast a radio version of his novel "War of the Worlds" in which highly advanced Martians invade Earth (Welles placed the initial landing site not far from here, in Grovers Mill, NJ).

Partly because of this environment, partly because of his well-developed senses of wonder and curiosity, and partly because of the mentorship of biologist Joshua Lederberg, Sagan devoted his career to projects which had the potential for discovering extraterrestrial life--in any form. (Discourse on Lederberg: Earthlife monotonous to biologists, architecture of proteins & nucleic acids necessary? Universal? Accident? Nobel Laureate in medicine for discovery of sex in E Coli) The study of any ET life would expand the horizons of biology as nothing else has.

Lederberg also got Sagan in the door at NASA. His concern that spacecraft landing on other worlds could contaminate them with earthly microbes got a sympathetic hearing at the fledgling agency in 1958. They made him head of the Space Sciences Boardís exobiology panel. Soon after, Lederberg raised the question of "a NASA contract to do some spadework, mainly consultation, on the generalities of biological probes. Our phone and travel bills are bound to mount, and also I would like to get some help from a young astronomer at Yerkes Observatory (name Carl Sagan) who is well informed and deeply interested in planetary biology. The production of our proposed Handbook of Planetary Biology is really a substantial job and there is some problem in finding a sufficiently informed enthusiast to do the work. Fortunately, Mr. Carl Sagan may be available for some months this summer, and perhaps again after he completes his dissertation in astronomy at Yerkes."

Sagan was soon at work. In his own words: "I sort of glided effortlessly between some kind of late-night bull sessions to advising the government."

Those bull sessions did not significantly slow Saganís paper, titled "Physical Studies of Planets." It was one of the rare instances in which a doctoral thesis is of capital importance, for it contained the first statement of Saganís hypothesis of a greenhouse effect on Venus. At the time, the climate of Venus was thought to be clement, or at least tolerably close to that of Earth, and the planet a candidate for eventual human exploration. But Sagan drew on recent data which showed that Venus radiated strongly at microwave frequencies (explain how this means heat). Calculations showed a surface temperature about 600į F. The problem was explaining this temperature. Venus is completely covered with clouds which bounce more than 70% of the sunlight it receives back into space. Even though it is closer to the sun, Venus absorbs less sunlight than the earth.

Sagan showed that a combination of carbon dioxide and water vapor in the upper atmosphere of Venus would block most of the heat radiated from the surface, keeping it inside the atmosphere and maintaining the hellish temperature (now known to be closer to 900į F. His greenhouse model was immediately taken seriously and did much to make his reputation at the very outset of his career. As we now know, the concept can be applied to many planetary atmospheres--including our own.

Paradoxically, the results of Saganís extensive work on Venus made the planet less interesting to him. Where itís hot enough to melt lead, no life could possibly exist. In the final portion of his thesis, he turned to Jupiter. The atmosphere of the largest planet was thought to contain methane, ammonia, water and hydrogen. It was not lost on Sagan that these gases were the basis of the famous Miller-Urey experiment (digress to explain Miller-Urey). He postulated the likelihood that organic compounds are formed in the Jovian atmosphere and speculated on the possibility that oceans might also exist deep inside the planet. The combination of organic compounds and water meant possible life.

Sagan worked on the first two Mariner probes of Venus, for which he designed an infrared radiometer to measure the heat coming from the surface of the Venusian clouds. The first probe malfunctioned after launch and had to be destroyed, but Mariner 2, launched in 1962, was very successful. Besides supporting Saganís contention that the surface of Venus is blazing hot, it also discovered the solar wind--the first important scientific discovery to be made by a spacecraft.

Some of the highlights of Saganís scientific career:

Science Popularizer

Carl Sagan made his first television appearance in 1961 on a CBS news show on space exploration. Stanford Medical Schoolís Elie Shneour gushed "Carl has created a new field--one bridging the gap between astronomy and biology. He is essentially alone in this field. He is, I believe, the only really fully cognizant scientist who is capable of bridging these two disciplines on a professional level."

One of his greatest popular works was the Cosmos video series, originally filmed in 1980. Cosmos comes from the Greek for "order of the universe."

This is how most people know Carl Sagan. As an enthusiastic and charismatic speaker who expounded about science in a way that virtually anyone could understand. At the end of my presentation we will watch a portion of Cosmos, which was re-released in 1999.

He made 25 appearances on Johnny Carsonís The Tonight Show. A world record for any scientist! Ironically, it was his appearance on The Dick Cavett Show that prompted Carson to request him as a guest in 1973. He was slotted into the last 15 minutes of the 90-minute show, but Carson was so impressed that he invited him back only three weeks later.

New York Magazine wrote:

Sagan launched into a cosmological crash course for adults. It was one of the great reckless solos of late-night television. When Sagan finished and settled back into the eye of the hush that he had generated, one was willing to bet that if a million teenagers had been watching, at least a hundred thousand vowed on the spot to become full-time astronomers.

At Cornell University where he spent the bulk of his career, Carl became a celebrity of immense proportions. There was enormous competition to register for his classes. And in 1994, the conservative newspaper Cornell Review announced the "I Touched Carl Sagan Contest." A six-pack and a free subscription were offered to the first undergraduate "actually making physical contact with Dr. Sagan."

The contest was closed to undergraduates employed in the Building of Space Sciences, all graduate students, and Mrs. Sagan!

Ironically, Saganís image as a popularizer of science caused him certain problems. As Stephen Jay Gould relates: "Many scientists never appreciated his excellence or his importance to all of us, while a few of the best of us (in a shameful incident at the National Academy of Sciences) actively rejected him."

Superstition and Pseudoscience Debunker

"A fire-breathing dragon lives in my garage"

This is the first statement in one of Saganís most famous arguments about skeptical thinking. He supposes how a reasonable person would respond. But no type of ordinary evidence is available. The dragon is invisible, incorporeal, and breathes heatless fire.

What's the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all? If there's no way to disprove it, no conceivable experiment that would count against it, what does it mean to say that the dragon exists? Inability to invalidate the dragon hypothesis is not at all the same thing as proving it true. Claims that cannot be tested, assertions immune to disproof are veridicially worthless, whatever value they may have in inspiring us or in exciting our sense of wonder. What Sagan asks one to do comes down to believing, in the absence of evidence, on his say-so.

The only thing we learn from this is that something funny is going on inside his head. We wonder what gave him this idea. Was it a dream or hallucination? Why does he take it so seriously? Maybe he needs help.

Suppose we decide to be scrupulously open-minded. We don't outright reject the notion that there's a fire-breathing dragon in his garage. Present evidence is strongly against it, but if new data emerge we're prepared to examine it. Surely it's unfair of Carl to be offended at not being believed; or to criticize us for being stodgy and unimaginative-- merely because you rendered the verdict "not proved."

Sagan sometimes dreamed that he was talking to his parents, and occasionally was seized by an overpowering realization that they didn't really die, that it was all some kind of horrible mistake. There they were, alive and well, his father making wry jokes, his mother earnestly advising him to wear a muffler because the weather is chilly. When he woke up he went through an abbreviated process of mourning all over again. In his words: "Plainly, there's something within me that's ready to believe in life after death. And it's not the least bit interested in whether there's any sober evidence for it."

More than a third of American adults believe that on some level they've made contact with the dead. The number seems to have jumped by 15 percent between 1977 and 1988. A quarter of Americans believe in reincarnation.

But that doesn't mean we should accept the pretensions of a "medium," who claims to channel the spirits of the dear departed, when weíre aware the practice is rife with fraud. We know how much we would like to believe that our parents have just abandoned the husks of their bodies, like insects or snakes molting, and gone somewhere else. Those very feelings might make us easy prey for con artists.

How is it that channelers never give us verifiable information? Why does Alexander the Great never tell us about the exact location of his tomb, Fermat about his Last Theorem, John Wilkes Booth about the Lincoln assassination conspiracy, Hermann Goering about the Reichstag fire? Why don't Sophocles, Democritus, and Aristarchus dictate their lost books? Don't they wish future generations to have access to their masterpieces?

Then there are the annual Whole Life Expos, New Age expositions held in San Francisco. Typically, tens of thousands of people attend. Highly questionable experts tout highly questionable products. Presentations include: "How Trapped Blood Proteins Produce Pain and Suffering." "Crystals, Are They Talismans or Stones?" "As a crystal focuses sound and light waves for radio and television" -- this is a vapid misunderstanding of how radio and television work -- "so may it amplify spiritual vibrations for the attuned human." Or here's one: "Return of the Goddess, a Presentational Ritual." Another: "Synchronicity, the Recognition Experience." That one is given by "Brother Charles." Or, on the next page, "You, Saint-Germain, and Healing Through the Violet Flame.'' It goes on and on, with plenty of ads about "opportunities" -- running the short gamut from the dubious to the spurious -- that are available at the Whole Life Expo.

Distraught cancer victims make pilgrimages to the Philippines, where "psychic surgeons," having palmed bits of chicken liver or goat heart, pretend to reach into the patient's innards and withdraw the diseased tissue, which is then triumphantly displayed. Leaders of Western democracies regularly consult astrologers and mystics before making decisions of state. Under public pressure for results, police with an unsolved murder or a missing body on their hands consult ESP "experts" (who never guess better than expected by common sense, but the police, the ESPers say, keep calling). A clairvoyance gap with adversary nations is announced, and the Central Intelligence Agency, under Congressional prodding, spends tax money to find out whether submarines in the ocean depths can be located by thinking hard at them. A "psychic" -- using pendulums over maps and dowsing rods in airplanes -- purports to find new mineral deposits; an Australian mining company pays him top dollar up front, none of it returnable in the event of failure, and a share in the exploitation of ores in the event of success. Nothing is discovered. Statues of Jesus or murals of Mary are spotted with moisture, and thousands of kindhearted people convince themselves that they have witnessed a miracle.

These are all cases of proved or presumptive baloney. A deception arises, sometimes innocently but collaboratively, sometimes with cynical premeditation. Usually the victim is caught up in a powerful emotion -- wonder, fear, greed, grief. Credulous acceptance of baloney can cost you money; that's what P. T. Barnum meant when he said, "There's a sucker born every minute." But it can be much more dangerous than that, and when governments and societies lose the capacity for critical thinking, the results can be catastrophic -- however sympathetic we may be to those who have bought the baloney.

In science we may start with experimental results, data, observations, measurements, "facts." We invent, if we can, a rich array of possible explanations and systematically confront each explanation with the facts. In the course of their training, scientists are equipped with a baloney detection kit. The kit is brought out as a matter of course whenever new ideas are offered for consideration. If the new idea survives examination by the tools in our kit, we grant it warm, although tentative, acceptance. If you're so inclined, if you don't want to buy baloney even when it's reassuring to do so, there are precautions that can be taken; there's a tried-and-true, consumer-tested method.

What's in the kit? Tools for skeptical thinking.

What skeptical thinking boils down to is the means to construct, and to understand, a reasoned argument and -- especially important -- to recognize a fallacious or fraudulent argument. The question is not whether we like the conclusion that emerges out of a train of reasoning, but whether the conclusion follows from the premise or starting point and whether that premise is true.

Among the tools:
- Wherever possible there must be independent confirmation of the "facts."

- Encourage substantive debate on the evidence by knowledgeable proponents of all points of view. Arguments from authority carry little weight -- "authorities" have made mistakes in the past. They will do so again in the future. Perhaps a better way to say it is that in science there are no authorities; at most, there are experts.

- Spin more than one hypothesis. If there's something to be explained, think of all the different ways in which it could be explained. Then think of tests by which you might systematically disprove each of the alternatives. What survives, the hypothesis that resists disproof in this Darwinian selection among "multiple working hypotheses," has a much better chance of being the right answer than if you had simply run with the first idea that caught your fancy. This is a problem that affects jury trials. Retrospective studies show that some jurors make up their minds very early -- perhaps during opening arguments -- and then retain the evidence that seems to support their initial impressions and reject the contrary evidence. The method of alternative working hypotheses is not running in their heads.

- Try not to get overly attached to a hypothesis just because it's yours. It's only a way station in the pursuit of knowledge. Ask yourself why you like the idea. Compare it fairly with the alternatives. See if you can find reasons for rejecting it. If you don't, others will.

- Quantify. If whatever it is you're explaining has some measure, some numerical quantity attached to it, you'll be much better able to discriminate among competing hypotheses. What is vague and qualitative is open to many explanations. Of course there are truths to be sought in the many qualitative issues we are obliged to confront, but finding them is more challenging.

- If there's a chain of argument, every link in the chain must work (including the premise) -- not just most of them.

- Occam's Razor. This convenient rule-of-thumb urges us when faced with two hypotheses that explain the data equally well to choose the simpler.

- Falsifiability. Always ask whether the hypothesis can be, at least in principle, falsified. Propositions that are untestable, unfalsifiable are not worth much. Consider the grand idea that our Universe and everything in it is just an elementary particle -- an electron, say -- in a much bigger Cosmos. But if we can never acquire information from outside our Universe, is not the idea incapable of disproof? You must be able to check assertions out. Inveterate skeptics must be given the chance to follow your reasoning, to duplicate your experiments and see if they get the same result.

There are more such principles which Iíve skipped for brevity.

Antiwar Activist

Nuclear Winter

Except for fools and madmen, everyone knows that nuclear war would he an unprecedented human catastrophe. A more or less typical strategic warhead has a yield of 2 megatons, the explosive equivalent of 2 million tons of TNT. But 2 million tons of TNT is about the same as all the bombs exploded in World War II -- a single bomb with the explosive power of the entire Second World War but compressed into a few seconds of time and an area 30 or 40 miles across Ö

In technical studies of the consequences of nuclear weapons explosions, there has been a dangerous tendency to underestimate the results. This is partly due to a tradition of conservatism which generally works well in science but which is of more dubious applicability when the lives of billions of people are at stake. In the Bravo test of March 1, 1954, a 15-megaton thermonuclear bomb was exploded on Bikini Atoll. It had about double the yield expected, and there was an unanticipated last-minute shift in the wind direction. As a result, deadly radioactive fallout came down on Rongelap in the Marshall Islands, more than 200 kilometers away. Most all the children on Rongelap subsequently developed thyroid nodules and lesions, and other long-term medical problems, due to the radioactive fallout.

Likewise, in 1973, it was discovered that high-yield airbursts will chemically burn the nitrogen in the upper air, converting it into oxides of nitrogen; these, in turn, combine with and destroy the protective ozone in the Earth's stratosphere. The surface of the Earth is shielded from deadly solar ultraviolet radiation by a layer of ozone so tenuous that, were it brought down to sea level, it would be only 3 millimeters thick. Partial destruction of this ozone layer can have serious consequences for the biology of the entire planet.

These discoveries, and others like them, were made by chance. They were largely unexpected. And now another consequence -- by far the most dire -- has been uncovered, again more or less by accident.

The U.S. Mariner 9 spacecraft, the first vehicle to orbit another planet, arrived at Mars in late 1971. The planet was enveloped in a global dust storm. As the fine particles slowly fell out, we were able to measure temperature changes in the atmosphere and on the surface. Soon it became clear what had happened:

The dust, lofted by high winds off the desert into the upper Martian atmosphere, had absorbed the incoming sunlight and prevented much of it from reaching the ground. Heated by the sunlight, the dust warmed the adjacent air. But the surface, enveloped in partial darkness, became much chillier than usual. Months later, after the dust fell out of the atmosphere, the upper air cooled and the surface warmed, both returning to their normal conditions. We were able to calculate accurately, from how much dust there was in the atmosphere, how cool the Martian surface ought to have been.

Afterwards, I and my colleagues, James B. Pollack and Brian Toon of NASA's Ames Research Center, were eager to apply these insights to the Earth. In a volcanic explosion, dust aerosols are lofted into the high atmosphere. We calculated by how much the Earth's global temperature should decline after a major volcanic explosion and found that our results (generally a fraction of a degree) were in good accord with actual measurements. Joining forces with Richard Turco, who has studied the effects of nuclear weapons for many years, we then began to turn our attention to the climatic effects of nuclear war.

Groundburst -- at hardened missile silos, for example -- generate fine dust. Airbursts -- over cities and unhardened military installations -- make fires and therefore smoke. The amount of dust and soot generated depends on the conduct of the war, the yields of the weapons employed and the ratio of groundbursts to airbursts. So we ran computer models for several dozen different nuclear war scenarios. Our baseline case, as in many other studies, was a 5000-megaton war with only a modest fraction of the yield (20 percent) expended on urban or industrial targets. Our job, for each case, was to follow the dust and smoke generated, see how much sunlight was absorbed and by how much the temperatures changed, figure out how the particles spread in longitude and latitude, and calculate how long before it all fell out in the air back onto the surface. Since the radioactivity would be attached to these same fine particles, our calculations also revealed the extent and timing of the subsequent radioactive fallout.

Some of what I am about to describe is horrifying. I know, because it horrifies me. There is a tendency -- psychiatrists call it "denial" -- to put it out of our minds, not to think about it. But if we are to deal intelligently, wisely, with the nuclear arms race, then we must steel ourselves to contemplate the horrors of nuclear war.

The results of our calculations astonished us. In the baseline case, the amount of sunlight at the ground was reduced to a few percent of normal-much darker, in daylight, than in a heavy overcast and too dark for plants to make a living from photosynthesis. At least in the Northern Hemisphere, where the great preponderance of strategic targets lies, an unbroken and deadly gloom would persist for weeks.

Even more unexpected were the temperatures calculated. In the baseline case, land temperatures, except for narrow strips of coastline, dropped to minus 250 Celsius (minus 13 degrees Fahrenheit) and stayed below freezing for months -- even for a summer war. (Because the atmospheric structure becomes much more stable as the upper atmosphere is heated and the low air is cooled, we may have severely underestimated how long the cold and the dark would last.) The oceans, a significant heat reservoir, would not freeze, however, and a major ice age would probably not be triggered. But because the temperatures would drop so catastrophically, virtually all crops and farm animals, at least in the Northern Hemisphere, would be destroyed, as would most varieties of uncultivated or domesticated food supplies. Most of the human survivors would starve.

This horrifying discovery prompted Sagan into action against nuclear testing. He helped organize three of the largest demonstrations of nonviolent civil disobedience at the Nevada Nuclear test site. He was twice arrested there for demonstrating against continued American testing of nuclear weapons in the face of the Soviet unilateral moratorium. He opposed Ronald Reagan's Star Wars scheme from the moment he proposed it -- on grounds that are now widely accepted. During the last ten years of his life, he spoke out around the world to warn about greenhouse warming and depletion of the ozone layer.

Through his success in organizing physicists to communicate the message about the nature of the nuclear winter that would predictably result from the deployment of hydrogen bombs, Carl Sagan, more than any other one person, may have been responsible for the avoidance of nuclear war in our lifetime.

Rational Humanist

Near the end of his life Sagan told of being asked by a student, "Now that you have successfully debunked everything that we have been taught to believe about the human role and origin in the Universe, what is there left for us?" His answer for the student, and for all human beings, was "Do something worthwhile with this amazing life while you have it!"

Did Carl Sagan in fact merely tear down old beliefs without putting anything better in their place? Far from it! He left behind a treasure trove of published works which put the lie to that accusation. His life was dedicated, not to tearing down, but to building a positive, integrated world view capable of providing better guidance for human beings in the centuries to come than ancient inherited mythologies could ever do.

He was worried about the welfare of a humankind that was being forced to navigate the perilous waters of the future with one foot aboard the seaworthy craft of science and the other embedded in the quicksand of mysticism along the shore. "We compartmentalize", he said, referring even to the highly schooled among us. "Some scientists do this too, effortlessly stepping between the skeptical world of science and the credulous world of religious belief without missing a beat....But we cannot have science in bits and pieces, applying it where we feel safe and ignoring it where we feel threatened." He explained that science is a way of thinking much more than it is a body of knowledge. It provides an integrated, yet evolving and open-ended, frame of reference for making sense out of experience -- all experience.

Sagan admitted that the results of scientific inquiry can never be the "Truths" or "the essence of reality" claimed by mystics and purportedly embodied in the mythologies of most religions. This means that they cannot offer us the illusion of certainty that so many religious natures seem to crave. But they are by far the best that fallible humans can hope for. Sagan quoted Einstein's famous comment that, "All of our science, measured against reality, is primitive and childlike -- and yet it is the most precious thing we have. He warned that there are already many signs that American culture may be on the verge of forsaking science for mysticism, and thereby sliding back almost without noticing it into superstition and the darkness that engulfed our demon-haunted world for thirteen centuries after the fall of Rome.

He also deplored the way that popular tabloids contribute to a confusion of pseudoscience with science by their concerted attempt to make science (the very instrument of skeptical inquiry) appear to confirm ancient faiths and popular occult propositions, all of which are devised in such a way that they are neither subject to disconfirmation nor amenable to rational discussion. The latter are limbic, right-hemisphere-inspired doctrines, Sagan said. Although natural human responses to the complexity of our surroundings, they are fatally limited if not subject to the intervention of the fully functioning neocortex -- a left-hemispheric reason that works over the world's inputs as they are actually experienced.

Humanists will be interested in what Carl Sagan had to say about religion. In one of his earliest books he spelled out the basis of his scientific agnosticism, as applied to religious belief:

"Those who raise questions about the God hypothesis and the soul hypothesis are by no means all atheists. Considering the enormous emotional energies with which the subject is invested, a questing, courageous and open mind seems to be essential for narrowing our collective ignorance on the subject [of the existence of god]."

Sagan distinguished clearly between mysticism and spirituality. While mysticism is concerned with matters of magic, the occult, the supersensual and Ďessentially unknowable,í spirit is something quite different, he maintained. "It comes from the Latin word 'to breathe'. What we breathe is air, which is certainly matter, however thin. Despite usage to the contrary, there is no necessary implication in the word 'spirituality' that we are talking about anything other than matter (including the realm of matter of which the brain is made) or anything outside the realm of science...Science is not only compatible with spirituality; it is a profound source of spirituality...The notion that science and spirituality are somehow mutually exclusive does a profound disservice to both."

Family Life

Carl Sagan married three times. First, to Lynn Alexander (now Lynn Margulis, a famous scientist in her own right) in June 1957, second to Linda Salzmann in April 1968, and finally Ann Druyan, June 1981.

Only Annie, as he called her, truly held his heart, and only she was able to to bring Carl down from the cosmos to face his humanity. She helped him restart relationships with his two older sons and make amends to Lynn for his previously chauvinistic behavior.

Druyan was Saganís partner for the last two decades of his life. She helped him enormously with Cosmos and his novel turned screenplay, Contact. The main character of the latter, Ellie Arroway, is named after Eleanor Roosevelt, whom Druyan admired. And it was she who broached the idea of putting Chuck Berryís music on the record launched with the Voyager planetary probes. With Annie, Sagan wrote on subjects other than cosmology, dealing with evolution, pseudoscience and philosophy in his later years.

Eulogies

Carl Sagan died of pneumonia early in the morning of December 20, 1996. It was a complication caused by radiation treatments for myelodysplasia, a disease of the bone marrow.

On his third try, he had married well. As he left the world, Annie Druyan gave him the undivided attention he had always desired. To Annie, even the heat emanating from his fevered skin was welcome proof that he was still with her. She kissed him and rubbed her face against his, to make an indelible memory of the moment. "What a wonderfully lived life," she said, gripping his hand tightly. Over and over she repeated: "With pride and joy in our love, I let you go. Without fear. June 1st. June 1st. For keeps."

Stephen Jay Gould:

I would epitomize Carl Sagan's excellence and integrity in three points. First, in an age characterized by the fusion of high and pop culture, Carl moved comfortably across the entire spectrum while never compromising scientific content. He could joke with Johnny Carson, compose a column for Parade, and write a science fiction novel while maintaining an active laboratory and publishing technical papers. He had foibles aplenty; don't we all? We joked about his emphatic pronunciation of "billions," and my young son (much to Carl's amusement) called Cosmos the "stick-head-up show" because Carl always looked up dreamily into the heavens. But the public watched, loved, and learned. Second, for all his pizzazz and charisma, Carl always spoke for true science against the plethora of irrationalisms that surround us. He conveyed one consistent message: real science is so damned exciting, transforming, and provable; why would anyone prefer the undocumentable nonsense of astrology, alien abductions, and so forth? Third, he bridged the gaps between our various cultures by showing the personal, humanistic, and artistic side of scientific activity. I will never, for example, forget his excellent treatment of Hypatia, a great woman, philosopher, and mathematician, martyred in Alexandria in A.D. 415.

Ray Bohlin:

Sagan was awarded the Peabody Award and an Emmy for his stunningly influential public television series, Cosmos. The accompanying book by the same title is the best-selling science book ever published in the English language. He earned the Pulitzer Prize for his book Dragons of Eden on the evolution of human intelligence, and numerous other awards and honorary degrees. He is the most read scientific author in the world, and upon awarding him their highest honor, the National Science Foundation heralded his gifts to mankind as "infinite."