54 pages • 1 hour read
Carl SaganPale Blue Dot: A Vision of the Human Future in Space
Nonfiction | Book | Adult | Published in 1994A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 19-22Chapter Summaries & Analyses
Chapter 19 Summary: “Remaking the Planets”
The rest of Pale Blue Dot turns to the future. Chapter 19 concerns terraforming and the possibility of humans living on other worlds. The chapter opens with the first mention of “terraforming” in print: the 1942 science-fiction short story “Collision Orbit,” by Jack Williamson for Astounding Science Fiction. The story is about humans living on an asteroid, and Sagan weighs Williamson’s imagination against what might be possible. While Sagan doubts artificial gravity will be possible, the idea of living on other planets inside domes or underground caverns full of oxygen are scientific possibilities. Williamson imagines a power source of antimatter; while Sagan acknowledges that little is known about generating antimatter, he does not reject the possibility of running a colony or engine using the gamma rays emitted by matter and antimatter interactions. He also considers other possible power sources such as solar, deuterium, tritium, and fusion reactors.
Sagan considers the possibilities of engineering a planet’s surface and atmosphere for human life. He claims that he was the first person to discuss terraforming as a possibility in a scientific publication, writing on Venus in 1961. That article, written before humans knew about the acidic clouds and extreme surface temperature, suggested methods for reversing Venus’s greenhouse effect by removing carbon dioxide from the atmosphere. Sagan suggests that now the only way to engineer Venus to be cooler would be nuclear winter or the collision of a moon, asteroid, or comet made mostly of ice.
Sagan is more optimistic about living on Mars. Mars has sunlight and water, enough to suggest that domed enclosures could be possible. He observes that humans already know how to change environments at global scales because we are doing so, negatively, on Earth. We know how to cause global warming on Mars, too, through the introduction of carbon dioxide and ammonia, and Sagan believes that with enough time and expense Mars’s surface temperatures could become as warm as an Earth winter. Similarly, he suggests Saturn’s moon Titan could be terraformed through nuclear fusion applied to the surface. But all these options are impossible until we learn more about these places and develop cost-effective ways of traveling there.
Sagan ends the chapter imagining what settling other worlds would look like. It would be a familiar process for humans, Sagan believes, looking back on the history (and especially the American history) of homesteading. He expects the first pioneers will be sent by Earth governments and then eventually earn independence and develop a unique culture. But he also wonders if humans will be capable of such an undertaking: “Can we, who have made such a mess of this world, be trusted with others?” (283). If we know enough to terraform any planet, shouldn’t we first apply that engineering to repair Earth?
Chapter 20 Summary: “Darkness”
Chapter 20 is about the search for extraterrestrial life, from Earth, via radio. There are an estimated 400 billion stars in the Milky Way; some percentage of those stars have planets, and some tiny percentage of those planets might have been or will one day be able to support life. We can communicate into that vastness with radio. Mostly, we listen.
Sagan introduces some of the organizations dedicated to this work, starting with the Search for Extraterrestrial Intelligence (SETI), which began in 1960. A man in West Virginia listened via radio telescope to nearby stars and heard a signal (which would turn out to be military aircraft on Earth). That false positive was still encouraging enough to inspire others to borrow time on other radio telescopes. The Planetary Society, a nonprofit started by Bruce Murray, then director of the Jet Propulsion Laboratory, Sagan, and others (and originally supported by Steven Spielberg), started the Megachannel ExtraTerrestrial Assay (META). META used radio telescopes in Massachusetts and Buenos Aires to listen to a new section of the sky each day, changing its frequencies to compensate for Earth’s rotation. META would be replaced by BETA. NASA started its SETI program in 1992, but it only lasted a year. Other private enterprises have taken up the reins. People keep trying, and there have been many false alarms. Nothing has been confirmed, which is also why it is so difficult to fund: “SETI is one of those search programs irritating to those who want well-defined cost/benefit ratios” (299).
These programs listen on frequencies near 1420 megahertz because hydrogen, the most abundant atom in the universe, releases radio waves at this frequency. Sagan argues that anyone scientifically minded would try this frequency when looking for other intelligent life. A seven-year study by META, which Sagan was involved with, yielded 11 notable “events” that satisfy every requirement except one: none of the signals were found a second time. There was no way to know what percentage was due to astronomical phenomena or Earth interference. If any are alien intelligence, it would suggest, due to the short time that humans have been listening, that there are millions of alien civilizations out there. Sagan confesses that finding anything is an extremely long shot. But he also notes that such a discovery has the power to transform Earth. “It would be the last of the Great Demotions, a rite of passage for our species and a transforming event in the ancient quest to discover our place in the Universe” (300-01).
Chapter 21 Summary: “To the Sky!”
Chapter 21 opens with a gesture to midcentury visionaries: Konstantin Tsiolkovsky and Robert H. Goddard. Both are rocket scientists who discussed the possibility of using rockets to travel in space when it was still considered ridiculous to believe in such a thing.
Sagan then talks about the importance of the current moment. He writes to future generations that will decide the direction of humanity. He tempers the notion that our moment is special, citing a more cosmic perspective. But he also defines the end of the 20th century as the first time our species becomes a true danger to itself through the burning of fossil fuels, use of CFCs, nuclear and bioweapons, and an ongoing hesitancy to act on the threat of comets and asteroids. This precipice of self-destruction coincides with another new possibility: traveling to other planets. Sagan writes that it seems unlikely governments will suddenly change from thinking short-term to thinking long-term. But he also notes that humans have done the impossible before, and “our leverage on the future is high just now” (305).
While Sagan advocates for saving Earth first, he also argues for the importance of settling other worlds. Settling on other planets would ensure the survival of the species. The more chances humans have, the greater the diversity of human futures, the more likely some humans will survive what comes next. While he pauses a moment to consider what right humans have to other worlds, especially places like Titan where life might emerge, he believes that this time our motivations won’t be religion or greed. We will homestead transnationally and ethically. He ends the chapter with a call to increase space exploration: “On behalf of Earthlife, I urge that, with full knowledge of our limitations, we vastly increase our knowledge of the solar system and then begin to settle other worlds” (312).
Chapter 22 Summary: “Tiptoeing Through the Milky Way”
The final chapter addresses possible limitations to humanity’s future. Sagan follows the structure of his early chapters by starting with ancient humans. Sagan cites theories that humanity has peaked, that science and technology will not continue to improve exponentially, that humanity has already produced its best artistic masterpieces, and that the liberal democratic world government, with all its dangers of fascism and ethnic hatred, is the endpoint of political history. To this, Sagan responds that the solar system will catalyze changes yet unforeseen. He argues that space travel will renew human potential: “Exploring the solar system and homesteading other worlds constitutes the beginning, much more than the end, of history” (318).
For the first time, Sagan acknowledges that his techno-optimism often constitutes magical thinking. He calls it potentially “too much Buck Rogers” (315). Much of our technology was developed without consideration for negative implications; Sagan writes, “we have become powerful without becoming commensurately wise” (316). But he also notes that there is no turning back. Even if we throttled civilization back to simpler times, humans would eventually return to this moment, and all the while asteroids and comets could find their way to Earth before defense systems exist. Our only hope is outer space. It is a dangerous path, and our solar system, too, will one day become uninhabitable. But it is the only option if humanity hopes to survive millennia.
Sagan imagines human colonies so far out they eventually break ties with Earth politically and culturally. Some colonies might remain nomadic, moving from world to world and burning resources. Humans might one day settle on the worldlets of the Oort Cloud, so far past Neptune that it is halfway to the next closest star. They might be happier in smaller groups than they were as citizens of a global civilization. Sagan then imagines a propulsion technology that allows humans to fly through space at a speed that would take one day to get to Mars, less than two weeks to Pluto, only a year to the Oort Cloud, and only a few years to the newest stars. And he talks about other kinds of destinations: the site of our star’s “gravitational lensing,” about 550 astronomical units from Earth, where radio waves are naturally boosted; brown dwarfs which, if they exist, might be stars cool enough for human visitation; and black holes, which if visited would tell us a great deal about the universe.
Sagan believes that in the decades after his book is published, we will learn about many more potential places to visit. “If you’re young,” he writes, “it’s just possible that we will be taking our first steps on near-Earth asteroids and Mars during your lifetime” (329). Going father will take longer, and by then, the human species will have changed. We will have become wiser for having turned our attention to the stars. There will have been other scientific advancements, in psychology, for instance. Looking at how much we’ve learned in recent decades, how quickly we innovated from airplane to Moon landing, and even how quickly we evolved from amphibious fish to apes to astronomers, it is difficult to imagine humans slowing down.
Finally, Sagan returns to religion. He notes that, due to the limitations of the speed of light, much of our exploration and research into the universe will take generations. Even if alien civilizations intercept Earth broadcasts of the mid-20th century, the fastest we can expect a response would be centuries from now. It will take a long time and a lot of faith, but he believes science will be what one day leads us to true religion: feeling at home in the universe (334).
Chapters 19-22 Analysis
By the end of the book, Sagan has repeatedly teased and gestured to the possibility of human settlement on other worlds. He repeats the ideas across chapters. His thesis is clear: Humans should imagine this future and make choices toward it. Sagan also suggests that humans will thrive and be happier if they are homesteading again. The “frontier thesis” developed by Frederick Jackson Turner in 1893, proposes that the process of exploring and then settling a wilderness makes a population more individualist and democratic. The process and related popular imagery renew the country or group’s investment in developing a culture of its own. Sagan imagines that smaller groups of human settlers will be happier on the planetary frontier in part because of this individuation process and because he claims there is an evolutionary imperative for humans to desire small group identities rather than global or even national identities. Sagan offers no evidence to support these claims, and the history behind the “frontier thesis” is suspect. After all, the American frontier was not unsettled and often required violence, and settlement involved extensive violence against preceding inhabitants.
The search for intelligent life in the universe persists as a theme throughout Pale Blue Dot. But at every step of the way, Sagan uses statistics and logic to undermine the likelihood of finding life elsewhere. Alien life is a topic that captures the public imagination, so Sagan uses it to animate human exploration of a potentially lifeless expanse. Sagan supports the search for alien intelligence. He supports all efforts to learn more about the Milky Way and notes that humans would have much to learn about themselves and their future if intelligent life were discovered. But he also notes the sheer unlikelihood that, even if intelligent alien civilizations existed or existed, connections between those civilizations can be made. Space is too big. Thus, the search for other civilizations throughout Pale Blue Dot reads more like a rhetorical move compared to Sagan’s calls for asteroid defense, future settlement, and an increased understanding of Earth.
The final chapter is the first time that Sagan acknowledges his so-called “Buck Rogers” optimism. The book assumes technology will not only continue to develop at a rapid pace but will also remain safe: “We’re on the cusp of technology, near the midpoint between impossible and routine” (284). However, even after raising concerns in the last chapter, Sagan immediately returns to a faith that “we will get better at going into space” (311). More than that, he believes that, as technology improves, the appropriate safeguards will develop along with it. There is very little consideration of the way technologies can reinforce biases and inequalities. His faith that humans will become wiser and fairer in the ensuing decades is hopeful but arguably naïve.
