The Sagan Paradox Chapter 9: GOLDILOCKS IN OUR COSMIC NEIGHBORHOOD

The article moves from the general historical context of SETI to a specific, modern candidate for life, then to a mysterious signal from that candidate, critiquing the scientific response to potential extraterrestrial signals, presenting an alternative theory for the signal, and finally broadening the discussion to the overall limitations of the SETI methodology.

A Sagan-Sized Question

For decades, the search for extraterrestrial life was haunted by a daunting sense of scale. In a 1969 lecture that laid the foundation for modern UFO skepticism, Carl Sagan imagined our cosmic neighbors searching for us by a random principle: sending a spaceship to any old star and simply hoping for the best. More often than not, he assumed, they would find nothing. The universe was a colossal haystack, and intelligent life was a single, lonely needle.

It is a triumph of modern astronomy that this picture has been completely overturned. Today, we know of promising candidates for life-bearing planets right in our cosmic backyard. The proverbial haystack, it turns out, might just be a needle factory.

Proxima b’s orbit is in the habitable zone, but it doesn’t necessarily have to be habitable.

From Random Hopes to Targeted Searches

We are no longer searching blindly. Armed not with metal detectors but with powerful telescopes, we can pinpoint the most likely worlds to harbor life. An intelligent civilization on Earth would not send probes randomly into the void; we would send them to these promising targets. And there are many.

In 2016, astronomers discovered one such target: Proxima Centauri b in the Alpha Centauri system: a potentially habitable planet orbiting the closest star to our sun, a mere 4.2 light-years away. While its parent star’s fierce solar winds make surface picnics unlikely, life could theoretically thrive in subterranean shelters.

In an unrealized project, NASA studied in 1987 the possibility of reaching the orbit of Proxima Centauri b within just 100 years at 4.5% the speed of light. This project was named Longshot, and it was about sending an unmanned probe using nuclear propulsion.

If our initial observations of such a world prove inconclusive in the search for life, what would we do? We would do what we are already doing with Mars: we would send probe after probe until we could be certain. Why would an alien intelligence, having discovered a promising blue dot called Earth, be any different? And from a distance, what do our own Martian space probes look like, if not unidentified flying objects?

Human spacecraft approaches Mars, Enlargement of oil on canvas panel for NASA Headquarters. By Don Davis.

A Tantalizing Whisper from Proxima b

In a remarkable coincidence, just as we began to focus on Proxima b in the search for extraterrestrial life, a potential signal emerged from its direction. In April and May of 2019, the Parkes radio telescope in Australia detected a strange, narrow-band radio emission. Dubbed Breakthrough Listen Candidate 1 (BLC1), initially it was classified as a possible sign from an alien civilization.

Parkes Radio Telescope, by Diceman Stephen West, CC BY-SA 3.0, via Wikimedia Commons

The signal’s characteristics were puzzling. Its Doppler shift—the change in its frequency—appeared to be the opposite of what would be expected from the planet’s orbit. Curiously, the signal appeared 10 days after a major solar flare from Proxima Centauri, though no link has been established. The primary investigators were two interns, Shane Smith and Sofia Sheikh. They worked cautiously to rule out terrestrial interference.

Some senior researchers did review the results but found nothing of note.


Long Delay

The BLC-1 signal was first reported publicly 1.5 years after its detection, and only because it was leaked to The Guardian newspaper. The public then had to wait another year for the final results. People were puzzled by the secrecy which fueled speculation.

Delays in announcing a discovery—or non-discovery—within SETI and astronomy are standard practice. Data are not released to the public until they have been verified. For instance, when radio stars were first discovered in 1967, it took two years before the discovery was published. The scientists held on to their data until they found what they considered a plausible natural explanation. The supposed Pulsar mechanism remains a mystery to this day.

This delay practice by SETI can give the impression that data are withheld until “natural explanations” have been found; radio-frequency interference (RFI) is one such explanation.

“Ultimately, I think we’ll be able to convince ourselves that BLC-1 is interference.”

– Andrew Siemion, SETI Principal Investigator for Breakthrough Listen

Within the SETI community, Siemion’s statement exemplifies scientific humility and the cautious process necessary to distinguish genuine signals from interference. Outside SETI, analogous statements can be understood as masking underlying biases or reluctance to accept paradigm-shifting discoveries. This highlights how context influences the interpretation of such remarks.


How long did Earth listen for the BLC-1 signal?

Breakthrough Listen reserved 30 hours on the Parkes telescope to observe Proxima Centauri, but the putative signal was detected during only about three of those hours—roughly 10 % of the total observing time.

During the next six months the team logged another 39 hours of follow-up observations. Out of the 4,320 hours in that half-year, just 0.9 % was spent searching for a repeat—about one-tenth of the effort devoted to the original scan.

The question remains: Was a longer campaign warranted? More generally, aren’t extended observing campaigns in radio-astronomical SETI necessary? We cannot presume that extraterrestrial civilizations broadcast continuous signals; those transmissions may be the only ones we ever detect, and even then only by chance.

BLC-1 has underscored that, when practicable, observations of potential technosignatures should be conducted from at least two different observing sites simultaneously. That this wasn’t done in the case of BLC-1 is inexplicable.

What would be the worst case when announcing the discovery of extraterrestrial technological intelligence?

A mass panic? That later investigations prove the discovery to be wrong and it has to be retracted? Thus discrediting the field of SETI? Or that humankind no longer occupies the pinnacle of evolution in the Cosmos? Would this discovery temper humankinds worst instincts, such as warfare, to the detriment of despotic rulers?


A “Galactic Communications Grid” and BLC-1

At first glance, detecting a narrowband radio signal (e.g., BLC-1) from Proxima Centauri—the star system next door—seems fantastically unlikely. Astrophysicist Jason T. Wright countered that, from an engineering standpoint, Proxima is exactly where we should expect to find such a transmission.

If a galactic communication network exists, Proxima would be the most likely “last mile” transmitter to the Solar System. Instead of every civilization trying to beam powerful, targeted messages to every other star system they want to contact, they would establish a network of communication nodes or relays.


Proxima as the Solar System’s “Cell Tower”

Proxima as the Solar System’s “Cell Tower”
In this scenario, Proxima Centauri—the closest star to our Solar System—serves as the logical “cell tower.” A message intended for our region of space would be routed through the galactic network to the Proxima Centauri system. A transmitter located there would then handle the “last mile” broadcast to the Solar System.

These nodes in the Galactic Communications Grid would need to ping each other regularly. But since radio waves travel at the speed of light, a single ping would take over eight years (accounting for the 4.24-light-year distance and signal processing time). Given this limitation, perhaps there’s another way to communicate with extraterrestrial intelligence (ETI)?

The speed of light is fixed for electromagnetic radio waves—but what about physical objects? And I’m not primarily referring to warp technology, but rather to objects that might already be here.


The Trouble with SETI

ET to SETI: can you hear us now?
ET to SETI: can you hear us now?

 SETI’s foundational premise is that extraterrestrial civilizations would likely be light-years away, not operating stealthily in Earth’s atmosphere. The hundreds of thousands of reported UFO sighting are perceived by SETI as being mostly the product of wishful thinking, misinterpretations and fakes.

Because UAPs/UFOs have no confirmed extraterrestrial link, SETI has no scientific basis for allocating resources to them. Consequently, no scientific efforts are undertaken to attempt contact with UAPs by radio or other signalling methods (e.g., lasers).

To qualify as a genuine ETI radio signal, the signal must come from far away and its detection must be reproducible. Otherwise it risks being classified as interference outright.

Highly directional, sensitive radio telescopes are not suited for close-range communication. For this reason, the Contact Project has suggested involving amateur radio operators (hams), whose omnidirectional antennas could be used in communication attempts with UAPs.

SETI with directional AND omnidirectional antennas, for far-and close-range Rx/Tx searches

Scientific Observational Attempts to Detect UAPs/UFOs

Harvard astrophysicist Avi Loeb has been leading the Galileo Project, one branch of his project is the detection of possible radio emissions from UAPs.

With new observatories online Avi Loeb is challenging the scientific establishment by taking UAPs seriously.

He sensationally declared he’s looking for intelligent life in deep space, blasting: “I’m interested in intelligence in outer space because I don’t find it very often here on Earth!”

The definition of his job is simple. “What is it to be a scientist?” he asks. “As far as I’m concerned, it’s the privilege of being curious.” It is this foundational principle that now drives one of the most ambitious and controversial scientific endeavors of our time: the Galileo Project. In an age of polarized opinion, the project aims to rise above the noise by focusing on a single, unimpeachable authority. “In science,” he declares, “the arbitrator is the physical reality.”

The project, which is now in full swing in the summer of 2025, was born from a frustration with a scientific community he sees as often too quick to dismiss the unknown. The turning point was the baffling 2017 interstellar visitor, ‘Oumuamua. Its strange, flat shape and its acceleration away from the sun without a visible cometary tail led him to suggest it could be an artifact of an alien technology. The backlash was swift. He recalls a colleague, an expert on rocks, confiding that ‘Oumuamua was “so weird I wish it never existed”—a statement project leader Avi Loeb sees as the antithesis of scientific curiosity.

Just A Friendly Hello: Contact Project Proposes a Continuous, Worldwide Omnidirectional Beacon to Engage Nearby Extraterrestrial Visitors

ContactProject.org: Is humanity ready for contact with extraterrestrial intelligence?

ETI is already near Earth, either in the form of drones, UAPs, or UFOs—whatever you prefer to call them. That is the premise of the Contact Project. The project proposal is therefore simple: instead of broadcasting a pinpointed message to a potential civilization far, far away, we can use simple, inexpensive, and widely available omnidirectional antennas to invite communication from objects or phenomena in Earth orbit. Moreover, this effort should not be limited to a short period of time; it should be sustained and undertaken with the broad agreement of people on every continent.

The message in the Contact Project might resemble the following:

“A Beacon in the Galaxy: Updated Arecibo Message for Potential FAST and SETI Projects” https://arxiv.org/abs/2203.04288, by Jonathan H. Jiang, Hanjie Li, Matthew Chong, Qitian Jin, Philip E. Rosen, Xiaoming Jiang, Kristen A. Fahy, Stuart F. Taylor, Zhihui Kong, Jamilah Hah, Zong-Hong Zhu.

A potential ETI is, of course, capable of decoding any human transmission we are already broadcasting, but the point of the Contact Project is to address ETI directly, acknowledge their presence, and actively seek contact.

Demonstrating such openness would prove humankind’s readiness for contact. By doing so, we would not be giving away anything new—such as our position—beyond what we already broadcast. It would simply be a friendly hello, as envisioned by the Contact Project organization.

Flaws in the Dark Forest Game Theory: A Closer Look

“I don’t know why you say goodbye, I say hello.”
The Beatles ‧ 1967

Why Liu Cixin’s Chilling Vision May Exaggerate the Dangers – ​in Space and on Earth

Dark Forest Hypothesis

1. A Tale of Two Dark Forests

Liu Cixin’s award-winning trilogy Remembrance of Earth’s Past (commonly called The Three-Body Problem series) popularized the Dark Forest Hypothesis: in a universe where every civilization fears annihilation and resources appear scarce, the safest strategy is absolute silenceor a pre-emptive strike on anything that betrays its position.

Initial Dark Forest Assumptions (click for full PDF here)

Yet, just as children often overestimate the terrors of a literal dark forest, adults may be overestimating the hazards of its cosmic counterpart. Both fears rest on questionable assumptions about scarcity, detectability, and universal hostility.


2. How Dark Is the Cosmic ForestReally?

2.1 Abundant Resources
Asteroid mining makes most “resource wars” unnecessary.
– Example: NASA’s current Psyche mission targets a metal-rich asteroid whose contents have often been cited – though the estimate is highly speculative – as being worth about $100,000 quadrillion.
– Lower gravity and higher ore purity mean it is far easier to extract metals in space than to invade a habitable planet.

• Science-fiction authors anticipated this logic well before the 1970s, from Garrett P. Serviss (1898) to Isaac Asimov (1953) and Poul Anderson (1963-65).


2.2 Alternative Solutions to the Fermi Paradox

The silence we observe could stem from:
the brevity of civilizations’ effective ‘radio window‘ (50-70 years);
the Sanctuary Hypothesis (ETI nurture developing planets without revealing themselves);
crewed or uncrewed craft-based exploration rather than radio beacons (compare UAP/UFO debate). These sightings challenge the premise of universal silence.

ABC 7 NEWS, December 2024

2.3 Humanity Has Already Broadcast

Humankind has been broadcasting TV and radio signals since the 1930s. These signals can be received hundreds of light-years away. This may have triggered ETs curiosity.

Then, between 1945 and 1961, Earth detonated more than 2,000 nuclear devices. Each blast produced an electromagnetic pulse (EMP) strong enough to be detected light-years away.

If an advanced civilization had been listening to early broadcasts of the Olympics, for instance, they’d have been surprised to see Earth suddenly erupting in artificial, high-energy flashes at irregular intervals.

The most powerful explosion was ten billion times stronger than the Arecibo broadcast message and could have been received anywhere in the Milky Way, which may contain 300–500 million habitable planets.

In effect, we have already shouted our existence into the forest; worrying about a polite radio greeting now is like closing the barn door after the horse has bolted.

The Ostrich Problem: Silence Isn’t Safety

If ETIs detected our radio signature, broadcast or EMP, but hear no follow-up, they might assume:

  • We’re hiding (suspicious).
  • We’re unstable (dangerous).
  • We’re ignorant (vulnerable).

3. Game-Theory Revisions: Three Big “What-Ifs”

Here are some of the big “what ifs” that challenge the whole “hide or attack” idea:

3.1 Mutually Assured Destruction (MAD) on a cosmic scale
If retaliation is credibleand especially if the cost of failure is extinction – first strikes lose their appeal, exactly as they did with Cold War nuclear strategy. Think about our own history with nuclear weapons. The concept of Mutually Assured Destruction (MAD) is a huge deterrent. What if that applies on a cosmic scale too? Let’s say there’s a certain chance of a successful attack. And, crucially, if an attack fails, the attacking civilization faces a really nasty consequence – let’s call it the disaster of retaliation. We’re talking about something far worse than just wasting resources.

Here’s how that changes the math for choosing to “Attack”:

If one civilization tries to hit another:

There’s a certain chance it pulls it off. The attacker survives, though it still pays the cost of the attack, while the other civilization is wiped out.

But, there’s also a chance the attack completely flops. In that nightmare scenario, the attacker is the one facing the disaster of retaliation (or even total annihilation if the other civilization hits back hard), and the target is still around and really angry.

So, when you consider whether to attack, you have to weigh these probabilities. If the chance of a successful attack is low, or if the disaster of retaliation is utterly catastrophic (like in MAD), then the appeal of attacking first plummets. It might even make more sense to just stay hidden, which totally undermines the “attack first” logic.

Flaws in the Dark Forest game theory

3.2 The Impossibility of Hiding

Sufficiently advanced telescopes detect radio signatures and other technosignatures whether or not we transmit on purpose. Admittedly, humankind has only transmitted purposefully for only a bit over 67 hours in its entire history. But this doesn’t reduce over a century of radio and TV signals that are already out there. Within this 130 light-year bubble (260 light-years across) there exist between 700-1,140 habitable worlds. If stealth is futile, the strategic game reduces to “communicate or attack,” and communication becomes the cheaper, more mature, safer option.

The Dark Forest idea hinges on the ability to stay hidden. But what if detection is inevitable? Imagine super-advanced telescopes that can spot signs of life without anyone broadcasting a thing. In that case, the “Hide” strategy basically becomes the same as “Broadcast” – you’re going to be found either way. The whole benefit of trying to hide just disappears.

If being detected while hiding is as bad as outright annihilation, then:
– If both civilizations hide → annihilation.
– If one hides and one broadcasts → annihilation.
– If one hides and one attacks → annihilation.

This scenario pretty much pulls “Hide” off the table as a viable survival strategy. It forces civilizations into a choice between broadcasting or attacking, since there’s no real hiding place left.

3.3 Civilizational Diversity
Assuming every species is paranoid and violent ignores the probability distribution of motives. If even a modest fraction are cooperative, expected-value calculations tilt toward cautious outreach rather than universal suppression.

“Our ability to reach unity in diversity will be the beauty and the test of our civilization”, Mahatma Gandhi

Perhaps the biggest assumption of the Dark Forest is that every civilization out there is a paranoid, aggressive killer. But is that realistic? We can think about different “types” of players in our cosmic game. What if there’s a certain probability that a civilization is hostile, and also a probability that it’s cooperative?

Now, the overall benefit of broadcasting changes dramatically, depending on who you meet. It’s a blend of the risk of annihilation if you meet a hostile civilization, and the potential benefit of survival and cooperation if you meet a friendly one.

If the probability of encountering a cooperative civilization is high enough, and the benefits of cooperation are truly significant, then suddenly, broadcasting might actually be a better bet than attacking. It opens the door to the idea that some civilizations might actually try to say “hello” rather than “kaboom.”

So, while the Dark Forest is a chilling thought experiment, these added factors suggest the universe might be a bit more complex than just a cosmic shooting gallery.


4. Earth’s Own “Dark Forests”: Fear vs. Fact

U.S. National Parks​millions of annual visits into true wilderness​average roughly 0.11 deaths per 100,000 recreational visits. The leading causes are drownings (20.9%), car accidents (17.3%), medical events (12%), and suicides (12.4%), not wolf packs or bear maulings.

A global study of carnivore attacks from 1950 to 2019 documented 5,440 attacks, with about one in three being fatal. Likewise, tiger attacks in India average 34 deaths per year; direct wildlife fatalities in the United States hover around eight. Our imagination inflates the danger of forests much as it inflates the peril of first contact.

Star Trek: First Contact

In the Star Trek movie “First Contact,” the Dark Forest of the human heart (causing a nuclear Armageddon) proved much more dangerous than the meeting with the Vulcan emissary.


5. Why Would ETIs Attack Us?

Possible motives beyond resources:

  • First-strike paranoia (fear of future competition).
  • Ideological conflict (ethics, expansionism).
  • Scientific curiosity (studying emerging civilizations).

But if aliens wanted resources, they’d mine asteroids, not Earth. (Take that, Zecharia Sitchinyour ancient alien gold-mining slaves theory doesn’t hold up when space is full of purer, easier-to-extract metals.)


6. UAPs & the Pentagon’s Admission: Are They Already Here?

If Unidentified Anomalous Phenomena (UAPs) are extraterrestrial probes:

  • They’ve seen our nukes, satellites, and wars.
  • Silence may look like hostility.
  • controlled message (math, music, science) could be safer than ambiguity.

7. Synthesis: From Paranoia to Policy

  • Accept the beacon we have already lit (Radio and TV bubble, nuclear tests) and
  • Send cautious, non-threatening signals (math, art, science).
  • Study apparent probes (UAPs/UFOs) with scientific rigor, but get out of the denial-loop.
  • Prepare a diplomatic framework​a “UN for exocivilizations” – ​before we need it.
  • Invest in asteroid-mining technology; abundance is the best antidote to resource anxiety.

The universe may contain dangers, but the data​from asteroid economics to wilderness safety statistics – ​suggests we routinely overrate them. Instead of cowering in silence, humanity should engage with the cosmos thoughtfully. We must do so armed with game-theoretic prudence, technological optimism, and a clear appreciation of how rarely the monsters in our dark forests turn out to be real. 

Stop Whispering, Start Strategizing!

The Dark Forest Game Theory Equations (PDF)


References:

National Park Service. (n.d.). Deaths in National Parks. U.S. National Park Service. Retrieved June 14, 2025, from https://www.nps.gov/aboutus/mortality-data.htm

Skylis, M. B. (2024, February 27). Data Reveal How People Die in National Parks. Backpacker. Retrieved June 14, 2025, from https://www.backpacker.com/survival/deaths-in-national-parks/

Handwerk, B. (2023, January 31). What 70 Years of Data Says About Where Predators Kill Humans. Smithsonian Magazine. Retrieved June 14, 2025, from https://www.smithsonianmag.com/science-nature/where-lions-and-tigers-and-wolves-attack-and-kill-humans-180981539

Conover, M. R. (2019). Numbers of Human Fatalities, Injuries, and Illnesses in the United States Due to Wildlife. Human–Wildlife Interactions, 13(2), 12. Retrieved June 14, 2025, from https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1544&context=hwi


APPENDIX: THE THREE BODY PROBLEM in brief

tl;dr

Liu Cixin’s *Remembrance of Earth’s Past* trilogy, commonly known as “The Three-Body Problem” series, is a sweeping hard science fiction epic that explores humanity’s first contact with an alien civilization and the existential threats that follow.


1. The Three-Body Problem (三体):
humanity learns an invasion fleet will arrive in 450 years; physics itself is sabotaged by proton-sized “sophons.”

Initial Setup & The Cultural Revolution:
The story begins in China during the tumultuous Cultural Revolution, where astrophysicist Ye Wenjie witnesses the brutal death of her father. Disillusioned with humanity, she is later recruited to a secret military project called “Red Coast,” a deep-space listening station. There, she discovers a method to amplify radio signals using the sun and, in a moment of profound despair, broadcasts a message into space, essentially inviting alien intervention.

Present Day Mystery:
Decades later, in the early 21st century, a series of mysterious suicides among prominent scientists plagues the world. Detective Shi Qiang (Da Shi) investigates, collaborating with nanotechnologist Wang Miao. Wang becomes entangled with a mysterious online VR game called “Three Body,” which simulates a chaotic planet experiencing extreme climatic shifts due to the gravitational pull of three suns.

The Trisolarans Revealed:
Through the game and his investigation, Wang uncovers a vast conspiracy: the Earth-Trisolaris Organization (ETO), a secret society formed by humans who worship the Trisolarans and desire Earth’s destruction. The Trisolarans are the inhabitants of the chaotic “Three-Body” planet. Their civilization has been repeatedly destroyed by their unpredictable system, leading them to seek a new, stable home – Earth. They are on their way, but their fleet will take approximately 450 years to arrive.

Sophon Blockade:
To prevent humanity from developing technology capable of resisting their invasion, the Trisolarans deploy “sophons” – proton-sized supercomputers that unfold into higher dimensions, act as omnipresent spies, and subtly disrupt fundamental physics research on Earth, creating the illusion that science is failing. The first book ends with humanity aware of the impending invasion but hamstrung by the sophon blockade.


2. The Dark Forest (黑暗森林):
Luo Ji invents cosmic MAD – threatening to broadcast Trisolaris’s coordinatesand forces a temporary peace.

The Crisis Era and Wallfacers: With the Trisolaran invasion fleet on its way and sophons making all human communications transparent to the aliens, humanity enters the “Crisis Era.” To develop secret strategies, the United Nations designates four “Wallfacers” – individuals granted immense resources and autonomy to devise plans that remain entirely within their own minds, impenetrable by sophons.

Luo Ji and Cosmic Sociology:
Among the Wallfacers is the initially reluctant and cynical astrophysicist Luo Ji. Unlike the others, he doesn’t have a clear military or scientific background. He slowly develops the “Dark Forest Hypothesis” (based on insights from Ye Wenjie): the universe is a “dark forest” filled with advanced civilizations, each acting as a silent, paranoid hunter. Any civilization that reveals its location becomes a target for pre-emptive destruction, as there’s no way to guarantee another civilization’s intentions are benign, and rapid technological explosion makes any unknown a potential existential threat.

The Deterrence Era:
Luo Ji’s seemingly bizarre actions as a Wallfacer lead to his plan: he threatens to broadcast the coordinates of the Trisolaran home system to the entire galaxy, a suicidal act that would doom both Trisolaris and Earth (due to Earth’s proximity). This threat, known as “Dark Forest Deterrence,” forces the Trisolarans into an uneasy peace, as they realize Luo Ji can enact mutual annihilation. This ushers in the “Deterrence Era,” a fragile peace enforced by the constant threat of a “Swordholder” (Luo Ji) initiating the broadcast.

The Great Fleet Annihilation:
Humanity flourishes during this era, building powerful space fleets, believing they have achieved parity with the Trisolarans. However, when the first Trisolaran probe (“the Droplet”) finally arrives, it effortlessly annihilates Earth’s entire space armada, revealing the vast technological superiority of the Trisolarans and shattering humanity’s hubris.


3. Death’s End (死神永生):
deterrence fails, higher-dimensional weapons collapse the Solar System, and the protagonists ultimately sacrifice themselves so the universe can “bounce” and begin anew.

New Challenges and the Swordholder:
The Deterrence Era continues, but Luo Ji is aging, and a new “Swordholder” must be chosen. The burden falls upon Cheng Xin, a kind and compassionate aerospace engineer. Her appointment is a calculated move by the Trisolarans, who correctly predict her moral nature will prevent her from activating the deterrence in a crisis. When the Trisolarans test the deterrence by attacking Earth’s broadcast stations, Cheng Xin hesitates, allowing them to take control of Earth.

Humanity’s Flight and Cosmic Revelations:
A few human starships that had escaped the initial Droplet attack (including one that had gone rogue much earlier) manage to broadcast the Trisolaran coordinates, leading to the destruction of the Trisolaran home system by a higher-dimensional alien weapon. Earth, however, is then also targeted by a “Dark Forest” attack.

Dimensional Collapse and Universe’s End:
Humanity faces escalating cosmic threats, including:

Two-Dimensional Attacks:
The ultimate “Dark Forest” weapon, a “photoid,” collapses the Solar System into two dimensions, an irreversible process that kills almost all of humanity.

Light-Speed Travel:
Cheng Xin and a few others escape on a light-speed capable ship. They encounter the former “brain-only” ambassador, Yun Tianming, who sends cryptic fairy tales that contain vital information about higher-dimensional physics and the nature of the universe.

Micro-Universes and The Big Bounce:
The narrative expands to encompass the universe’s ultimate fate. It’s revealed that advanced civilizations, to survive cosmic catastrophes like dimensional collapse, create “mini-universes.” However, the proliferation of these mini-universes is draining mass from the main universe, preventing its “Big Bounce” (a theoretical cyclical collapse and rebirth).

The Final Choice:
Ultimately, Cheng Xin and a few companions, after millennia of wandering the cosmos and witnessing countless cosmic events and the end of the universe itself, are faced with a profound choice: contribute their own remaining mass to the main universe’s rebirth, effectively ceasing to exist, or remain in their isolated mini-universe. They choose to return their mass, hoping to contribute to the cycle of universal renewal.

The trilogy is renowned for its grand scale, complex scientific concepts, and unflinching exploration of humanity’s place in a vast, indifferent, and dangerous cosmos. It presents a grim, yet intellectually stimulating, vision of interstellar survival.

The Sagan Paradox, Chapter 5: Cosmos Eating Space Probes and Sagan’s Response

SELF-REPLICATING PROBES

In the context of the Extraterrestrial Intelligence Search, in 1980 the mathematical physicist and cosmologist Frank J. Tipler published a paper, “Extraterrestrial intelligent beings do not exist.”

Tipler sought a universal principle to explain the Fermi Paradox: the apparent absence of extraterrestrial beings on Earth. He contended that if extraterrestrial intelligent beings existed, then their manifestations would be obvious. Conversely, since there is no evidence of their presence, they do not exist.

Von Neumann Probes

Frank Tipler argued that if any extraterrestrial civilization ever built self-replicating von Neumann starprobes, those probes would grow exponentially. They would fill the galaxy in a few million years. Since we don’t see them here, Tipler concluded there are no other intelligent civilizations.

  • Tipler assumed each probe would land on a new world and make just one or a few copies before moving on. However, he had no reason to limit its reproduction so drastically.

  • Even if each probe were only 10 grams and doubled once per decade, in about 150 generations we’d have the mass of an entire galaxy. This conversion to machines would be on the order of 1 followed by 54 zeros grams (1 quindecillion tons). Moreover, this transformation would occur in less than 15 million years.

  • Because we see no evidence of such galaxy-eating machines anywhere, Tipler said no one else ever invented them. Therefore, no one else is out there.


SAGAN’S RESPONSE

Carl Sagan pondered the arithmetic of Tipler’s solipsist argument. His response is a classic in the realm of science and philosophy. He draws attention to the limitations of our current knowledge and the vastness of the universe. By stating, “Absence of evidence is not evidence of absence,” Sagan cautioned against jumping to conclusions based on what we don’t know.

Sagan and William I. Newman challenged Tipler’s assumptions and conclusions, proposing a more realistic colonization model based on population growth and organization. This alternative model estimates a galaxy-crossing time of approximately one billion years, significantly longer than Tipler’s few million years.

Sagan further suggests that self-replicating probes are subject to evolutionary divergence, imposing unacceptable risks to altruistic extraterrestrial intelligent life (ETI). The ETI only communicate with other ETI through signals. This argument assumes that self-replicating machines are essentially uncontrollable because they must evolve.

Sagan and Newman also propose that the emergence of powerful weapons of mass destruction may impose a universal brake on unchecked expansion. This could potentially limit the spread of advanced civilizations. Ultimately, they emphasize the importance of experimentation in resolving the Fermi Paradox. Systematic searches using radio telescopes and other tools are necessary to settle the question of whether we are alone in the universe.


Terrestrial Shortsightedness

Imagine New York in 1894, its streets choked with the clatter of hooves. Its futurists were drowned in calculations of manure. They predicted that by 1944 New York would drown in horse manure.

The futurists only saw linearity: more carriages, more waste, an apocalypse of filth. However, they could not fathom the silent revolution already stirring—the internal combustion engine, the horseless carriage—a paradigm shift that would render their equations relics.

So too might we falter when envisioning the starfarers of tomorrow. To assume interstellar travel or contact must devour suns is to chain possibility to the physics of this moment. What of the technologies unimagined? The spacetime shortcuts, the dark energy harnessed, the self-replicating probes born of nanoengineering? The cosmos whispers of mysteries we have yet to decode.

Carl Sagan may have cautioned Tipler that his reasoning could mirror that of the horse-cart prophets. One may fail to see beyond the boundaries of the known. The universe is not merely a puzzle to solve with present tools. It is also a frontier that reshapes the solver. As we once tamed fire and split the atom, so too might we one day dance with the fabric of spacetime itself. The answer to the Fermi paradox may not lie in the scarcity of civilizations. It may lie in the humility of our assumptions.

After all, the stars are not merely endpoints. They are teachers. Their greatest lesson might be this: To traverse the light-years, we must first learn to think in ways as boundless as the dark between galaxies.