If the universe is teeming with aliens ... where is everybody?: seventy-five solutions to the fermi paradox and the problem of extraterrestrial life (science and fiction)

"The Russian astrophysicist Nikolai Kardashev proposed a useful way of thinking about such civilizations. He argued that we could classify ETCs in terms of the technology they possessed, and he devised a 3-point scale for measuring the potency of that technology. A Kardashev type 1 civilization, or KI civilization, would be comparable to our own: it could employ the energy resources of a planet. A KII civilization would be far beyond our own: it could employ the energy resources of a star. A KIII civilization could employ the energy resources of an entire galaxy. According to Gillett, then, most ETCs in the Galaxy would be of a KII or KIII type."

"The simplest resolution of the Fermi paradox is that “they”—in other words, intelligent representatives from extraterrestrial civilizations—are already here (or, if they aren’t here now, they were at least here some time in the past). Of the three classes of solution to the paradox, this one is by far the most popular amongst the general public."

"For example, some radionuclides possess half lives measured in millions of years, so if extraterrestrial visitors dumped nuclear waste on the Cretaceous landscape it might leave a trace that we could detect today."

"Several types of orbit are suitable for parking an observational probe, but perhaps the best known are the Lagrangian points. If a small mass is near two much larger orbiting masses, then there are five points at which the small mass can orbit at a fixed distance from the larger masses. These five Lagrangian points mark the positions where the gravitational pull of the two larger masses exactly balances the centripetal force required to rotate with them. Three of the Lagrangian points —L1, L2 and L3—are unstable: nudge the small mass and it will move away from the L point. But L4 and L5 are stable: nudge the small mass and it will return to the L point."

"The space agencies NASA and ESA already make heavy use of parking facilities offered by the Sun–Earth Lagrangian points. If NASA and ESA find it convenient to use those points then perhaps ETCs would do so too. Perhaps we might find probes at Lagrangian points in the Earth–Moon system?"

"at least one dedicated search has been made. Furthermore, astronomers have already studied the L4 and L5 points of the Earth–Moon system, since the points are interesting from a general astronomical viewpoint. In neither the dedicated search nor the general scans was any evidence of probes found."

"The romantic notion of an advanced Martian civilization capable of building canals and launching satellites didn’t survive the 1960s. It was laid to rest when the early Mariner spacecraft flew by at close range, returning photographs that showed none of the canals seen by Lowell. The Viking landers of 1976 and the Pathfinder and Mars Global Surveyor missions of 1997 also failed to find canals. Similarly, the flyby missions saw nothing at all artificial about Phobos."

"If you search through a large collection of random data long enough and hard enough, conveniently ignoring arrangements of the data that are of no interest and not defining beforehand what you are looking for, then eventually you will find something remarkable."

"There are 50 billion billion billion cubic miles of space within a sphere that encloses the orbit of Pluto; and the Solar System extends to the Oort Cloud of comets, almost a light year from the Sun. The chances of finding a small alien artifact by accident are essentially zero. Only if an artifact draws attention to itself—by signaling us, perhaps, or by being in a visible location—will we detect it. We therefore can’t rule out the possibility that observational probes were once in the Solar System nor, indeed, that they are still here. Some would argue that until we can rule out that possibility, there is no Fermi paradox."

"What we can say with confidence, however, is that no evidence for alien artifacts has yet been uncovered."

"The idea that life originated elsewhere and was somehow transported to Earth is an old one. The notion of panspermia —literally “seeds everywhere”—probably dates back to Anaxagoras."

"More recently, researchers have investigated the ability of some extremophiles—microorganisms that can thrive in extremely harsh terrestrial environments—to withstand the conditions found in space. Experiments have shown that extremophilic microorganisms, when protected by microsized carbonaceous grains, can survive hours of intense radiation from a synchrotron source—the equivalent of an accumulated radiation dose from millions of years of solar radiation."

"Ball proposed that ETCs are ubiquitous; many technological civilizations will stagnate or face destruction (from within or without) but some will develop their level of technology over time. Arguing in analogy with terrestrial civilizations, he reasoned that we need only consider the most technologically advanced civilizations. Those ETCs will, in some sense, be in control of the universe because the less advanced will be destroyed, tamed or assimilated. The important question becomes: how will highly developed ETCs choose to exert their power? Arguing in analogy with how mankind exerts its power over the natural world, wherein we set aside wilderness areas, wildlife sanctuaries and zoos so that other species can develop naturally, Ball speculated that Earth is in a wilderness area set aside for us by ETCs. The reason there seems to be no interaction between them and us is that they don’t want to be found—and they have the technological ability to ensure we don’t find them. The zoo scenario involved the idea that advanced ETCs are simply observing us."

"The zoo scenario has been criticized on several grounds. A major drawback to my mind is that it leads us nowhere: it’s not a testable hypothesis."

"Stephen Baxter has proposed an interesting variant on the zoo scenario. He calls it the planetarium hypothesis. The speculation is far wilder than Ball’s idea, but it merits the term “hypothesis” rather than “scenario” because it offers testable predictions. Is it possible, Baxter asks, that the world we live in is a simulation—a virtual-reality “planetarium” engineered to present us with the illusion that the universe is devoid of intelligent life?"

"The planetarium hypothesis taken to extreme is similar to solipsism. The true solipsist believes that everything he experiences—people, events, objects—is part of the content of his consciousness, rather than an external reality in which we all share. It’s not just that his is the only mind that exists. (The sole survivor of some planet-wide catastrophe might be correct if he believed his was the only mind, and yet he wouldn’t necessarily be a solipsist.) Rather, the true solipsist in principle can attach no meaning to the idea that other minds experience thoughts and emotions. It’s an egocentric view of the universe. The most extreme planetarium, therefore, would have an ETC generate an artificial universe directly into my consciousness. The universe appears to me to be empty because an ETC, for some reason, wants to fool me into so thinking."

"Occam’s razor gives us a reason for rejecting all these planetaria. Suppose you throw a ball and watch its parabolic path: you’ll conclude the ball is an autonomous object obeying Newton’s law of gravity. The alternative—that some system (whether an individual consciousness or a sophisticated virtual-reality generator) contains laws that simulate the properties of the ball and its motion under gravity—is a more complex explanation of the same phenomenon. Both explanations fit the observations. But Occam’s razor tells us to use the simplest explanation, which in this case is that the ball is “real”. It has an autonomous existence. We can make the same argument regarding our observations of the universe."

"Baxter points out that a fundamental requirement of a planetarium is that scientific experiments should always yield consistent results."

"The planetarium hypothesis defies both Occam’s razor and our basic intuition about how the universe works."

"In the decades to come, as we explore more of the universe and test the fabric of reality at ever-larger distance scales, we will either find an inconsistency in the simulation or be forced to accept that the universe is “real”."

"since ETCs are likely to be far in advance of us, they’ll be almost omniscient, omnipotent beings. We’d think of them as gods. Many SETI scientists would disagree: an ETC’s technology might indeed be so far advanced that it is, to use Clarke’s phrase, indistinguishable from magic, but surely we know enough to consider these beings as master engineers. At worst, we’d look on them as thaumaturgists. We know enough not to think of them as gods."

"the laws of physics don’t forbid interstellar travel, but they don’t make it easy."

"First assumption: a civilization can appear at any point in unoccupied space with some small probability. Second, and crucially, all civilizations have the same natural lifetime, , after which they start to die. (The authors believe the universal cause of the death of civilizations would be the loss of “basic functions—knowledge functions”. In other words, having learned all it can about itself and its environment a civilization has no desire to continue. It withers, dies.) Third: if one civilization makes contact with another then the lifetime of both increases by a time : the contact generates new things to learn, new conversations to be had, a spur to further development."

"In the bonus stimulated model a civilization is represented by a square of cells, with the central square being the birthplace of the civilization. The model can be defined as a cellular automaton by casting the assumptions in the form of transition rules. The first rule is that a new civilization can be born in any empty cell; the probability of birth is and the civilization begins as a single cell. The second rule is that, with each tick of the clock, the civilization changes size by one layer of cells on each side: if the civilization is younger than then it increases in size; if the civilization is older than then it decreases in size; and when the size becomes zero, in other words when there are no more cells, then the civilization is dead. Third rule: if a growing civilization meets another civilization—which in this model means that a cell has to belong to both civilizations—then the lifetime of both civilizations is increased by the bonus time ; if there are several civilizations in a cluster then they all get the bonus time. The subsequent development of each civilization is as in the second rule."

"Models of galactic colonization based on diffusion (such as the Newman–Sagan proposal), percolation (the Landis proposal) or cellular automata (Bezsudnov and Snarski) make statements about the migratory behavior of species that are assumed to hold true over timescales measured in hundreds of thousands or even millions of years. Colin McInnes developed a model of migration that only needs to hold true over a period of a few millennia in order to account for the lack of extraterrestrial visitors here on Earth. It’s a rather bleak resolution of the Fermi paradox; unfortunately, when one considers the behavior of the human species, it seems rather plausible."

"An automaton can reproduce itself as follows. The program first tells the constructor to make a copy of the program’s instructions and place the copy in a holder. It then tells the constructor to make a copy of itself with a clear memory bank. Finally, it tells the constructor to move the copy of the program from the holder to the memory bank. The result is a reproduction of the original device. The reproduction can function in the same environment as the original and is itself capable of self-reproduction."

"In a lecture first given in 1948, he discussed the relevance of self-reproducing automata to the question of life. He argued that a living cell, when it reproduces, must follow the same basic operations as a self-reproducing automaton. Within living cells, there must be a constructor and there must be a program. He was right. We now know that nucleic acids play the role of the program and proteins play the role of the constructor. All of us are self-reproducing automata."

"A spaceship containing a sufficient number of human couples, the appropriate life support systems, stored knowledge in the form of large databases and a sophisticated onboard factory would constitute a Bracewell–von Neumann probe."

"Since colonization of the Galaxy by probe seems straightforward, at least on paper, some authors argue that there’s an inevitable motivation for an ETC to engage in colonization: if we don’t do it, some other species will. Stake your claim early, in other words. (This sort of argument might have appealed to von Neumann, who was a strong proponent of the nuclear first strike. In an interview with a Time magazine reporter, von Neumann said: “If you say why not bomb them tomorrow, I say, why not today? If you say five o’clock, I say at one o‘clock.” We must be grateful that, in the 1950s and 1960s, wiser counsel than von Neumann’s prevailed.)"

"Consider two strings, each containing a trillion characters. The first string starts “101010…” and continues in that way until the trillionth character is reached; the second string starts “x9Y$m&…” and carries on in a seemingly randomly pattern. The Kolmogorov complexity of strings such as these is defined as the minimum length in bits of a binary-coded program that describes the string. The Kolmogorov complexity of the first string is small because one requires only a short program to describe it: in words, the program could be something along the lines of “Print alternating sequence of 1s and 0s, starting with 1 and ending after the trillionth digit”. The Kolmogorov complexity of the second string is large because there’s no obvious way of compressing the information it contains; any program describing the string would likely be as long as the string itself. Gurzadyan argued that the Kolmogorov complexity of the human genome—indeed, of the totality of terrestrial life—is relatively low. There’s a vast amount of genetic information contained in the millions of species on Earth, but the program that describes that information might be much smaller."

"Kepler “objects of interest” (KOI) are those stars that are known to possess planets and that are judged to be most amenable to the presence of Earth-like life. Targeted searches of KOI have already taken place, and more will surely follow."

"Many mathematicians, perhaps most of them, subscribe at least tacitly to Platonism. The Platonic philosophy holds that mathematics and mathematical laws exist in some sort of ideal form outside the realm of space and time. The work of a pure mathematician is therefore akin to that of a gold prospector; a mathematician searches for nuggets of pre-existing absolute mathematical truth. Mathematics is discovered, not invented."

"since the ability to make rapid judgments based upon the perceived numbers of objects is so clearly useful, we might expect animals to possess some sort of “number sense”. There is indeed evidence that rats and raccoons, chickens and chimpanzees can make rudimentary numerical judgments."

"Could a solution to the Fermi paradox be that other civilizations develop other systems of mathematics—systems that are useful for the local conditions in which they find themselves but inapplicable for use in building interstellar communication or propulsion devices?"

"As a resolution to the paradox this suffers from the same difficulty as several others: even if it applies to some civilizations (and many would deny even that possibility), it surely can’t apply to all civilizations."

"But even if we detect a message, could we decode the contents? Consider the Voynich Manuscript. In 1912, Wilfred Voynich, a collector, claimed to have bought a 234-page book from the Jesuit College at the Villa Mondragone, Frascati, in Italy. It presently resides in the Rare Book Room at the Library of Yale University, where its less romantic catalog name is MS 408. The book is about the size of a modern-day paperback, and is bound in a soft, ivory-colored vellum. Many Voynich scholars believe the book was written some time between the 13 century and 1608; radiocarbon dating suggests that the vellum was made from animal that was alive in the early 15 century. And this is pretty much everything we know about the manuscript: it was written in a language or code that no one has yet deciphered."

"Whatever information the Voynich Manuscript contains, we know it was written by a human being in the not too distant past. So the author had the same sensory inputs as the rest of us; a cultural background that is recognizable, if not identical to our own; human emotions that drove him (or her) in exactly the same way they drive us. And yet he (or she) wrote a book we can’t decipher. If such a situation can occur with a member of our own species, what chance do we have of understanding a message from an ETC?"

"One problem with signal recognition is the following: physicists have shown that if a message is sent electromagnetically and has been encoded for optimal efficiency, then an observer who is ignorant of the coding scheme will find the message indistinguishable from blackbody radiation."

"Well, in 2004 Christopher Rose (a professor of electrical engineering at Rutgers University) and Gregory Wright (an astrophysicist) took a communications-theory approach to the question of interstellar communication. In particular, they dropped the requirement that information had to be sent at the fastest possible speed and then investigated how much energy would be required to send a message. Their result was startlingly clear but counter-intuitive (at least, it was counter-intuitive to me): from an energy perspective it makes much more sense to write down a message on some material and hurl it into space than it does to broadcast the message. Sending a physical message has the added advantage that if the message is intercepted and decoded then the entirety of the information gets through, without the need for repetition: you can guarantee the recipient has a chance of watching the whole of Chinatown rather than risk them seeing just the final few seconds."

"just before it went live in 2008 there were lawsuits filed in various courts, protests at the European Commission and death threats aimed at members of the LHC team. All the worries expressed about previous collider experiments were trotted out before the LHC began operations, along with another possibility: that particle collisions might generate monopoles—hypothetical particles that are, in essence, isolated magnetic poles. Physicists at CERN patiently answered the worries, but to my mind that was unnecessary. As Rees and Hut remarked when discussing the possibility that the Tevatron might collapse the vacuum, the LHC isn’t doing anything that Nature isn’t already doing daily and on a much larger scale. High-energy particles collide with nuclei in Earth’s atmosphere all the time. Fortunately the lawsuits and the fearmongering got nowhere, and in 2012 the LHC made one of the great achievements of 21st century science when it discovered the Higgs boson."

"In 2003, for example, the planetary scientist David Stevenson published a (tongue-in-cheek) proposal to investigate Earth’s core. The idea was to use nuclear weapons to open a crack in Earth’s crust and then fill the crack with molten iron containing a probe. The iron would fall under gravity and eventually reach Earth’s core, carrying the probe with it. In case anyone was dreaming of actually doing this, Ćirković and Cathcart pointed out that it would be a rather dangerous activity: large deposits of carbon dioxide could be released, causing a global warming effect much greater than mankind is producing. Earth might end up like Venus."

"One element of any future nanotechnology is likely to be the nanorobot—nanobot, for short. We should welcome the coming of the nanobots because they have the potential to improve health care: they’ll diagnose medical problems at an early stage, monitor the body’s processes and target the delivery of drugs."

"As Asimov was fond of pointing out, when man invented the sword he also invented the hand guard so that one’s fingers didn’t slither down the blade when one thrust at an opponent."

"The Human Genome Project, which was founded formally in 1990, made a rough draft of the genome available in 2000 at a cost of a couple of billion pounds; when I published the first edition of this book, the cost of sequencing a human-sized genome had fallen to about sixty million pounds; the equivalent cost today is about four thousand pounds and soon cost simply won’t be an issue. Progress in genomic sequencing is following a path that makes Moore’s law seem tardy. It seems certain that within a few decades the billions of individuals here on Earth will have the capacity, if they so wish, to create artificial life."

"any population of several billion will contain individuals who are insane, hateful or vengeful: we have plenty of such people among us right now. The difference is that in a few years those people will be able to create pathogens that target those possessing the “wrong” number of X chromosomes, “too high” a production of melanin, or otherwise “undesirable” genetic traits. The equal-opportunities misanthrope could unleash an engineered bioweapon to kill us all. So Cooper offers this as a possible resolution of the paradox: any spacefaring civilization will possess a knowledge of how to destroy its own type of life, and it’s likely that one individual from the billions that make up the civilization will—for whatever reason—apply that knowledge."

"What’s required is that Goldilocks “just right” object, a planet on which water is free to flow and work its magic. Earth is clearly a Goldilocks planet in this respect, but it’s not immediately obvious why Earth possesses the surface temperature it does. Clearly, Earth receives energy from the Sun and that warms our planet—but then why isn’t the Moon at the same temperature as Earth? After all, both Earth and Moon are the same distance from the Sun."

"We have the atmosphere to thank for Earth’s temperate nature. Earth receives energy from the Sun at a variety of electromagnetic wavelengths—ultraviolet, visible and near-infrared. Almost all of this energy passes straight through the atmosphere and about half of it is absorbed at Earth’s surface, which subsequently becomes warm. Any warm surface will radiate simply because it’s warm, and the peak wavelength of the radiation depends upon the surface’s temperature. In the case of Earth, most of the thermal radiation it emits is in the far infrared region. Here’s the wonderful thing: the chemical make-up of Earth’s atmosphere is such that it’s almost transparent to the incoming short-wavelength ultraviolet, visible and near-infrared radiation but it’s almost opaque to the outgoing longer-wavelength far-infrared radiation. The radiation emitted by Earth’s surface is absorbed by the atmosphere, which then re-radiates it—and the radiation that’s emitted downwards is absorbed by Earth’s surface. Our atmosphere thus keeps us warm. Not only that, the atmosphere has a moderating effect; winds carry heat from the equator to the poles and from the day side of the planet to the night side. Without an atmosphere, there would surely be no life on Earth."

"First, fossil fuels constitute a finite resource. An inexorable increase in energy demand will eventually exhaust fuel reserves. If our access to fossil fuels were to end abruptly, right now, the consequences would be unthinkable. Our civilization would collapse. One suggested resolution of the Fermi paradox, then, is that the inevitable depletion of fossil fuels means that civilizations never make it into deep space. They collapse before they can colonize a world that contains more energy resources."

"It’s already safer, cheaper and more practical to explore Mars using telepresence than it is to attempt to send manned craft. We can even do science at a distance. For example, if a rover found alien microbial life hiding under the sands of Mars then we wouldn’t need to send astronauts to investigate: genome sequencers inside the rover could transmit genetic information back to Earth and we could reconstruct the life form in labs using biological printers."

"Lampton’s take on the Fermi paradox, therefore, is that all technologically based societies eventually make a transition: pre-transition societies are motivated by colonization, conquest and trade; post-transition societies are driven by information. A post-transition society doesn’t have to “be there” if it has a complete but remote knowledge of “there”. When an individual from a posttransition society really wants to visit “there”, it need simply construct a local simulation. If such a societal transition occurs on a short timescale compared to the colonization timescale—and if we extrapolate current trends here on Earth that would appear to be likely—then the paradox disappears."

"The Intelligence Principle implies that given enough time—and ETCs will have had enough time—biologically based intelligence will create artificial intelligence. The products of biological evolution will be replaced by, or will merge with, their machine progeny. Stapledonian thinking suggests that we might live in a postbiological universe."

"The Cambridge cosmologist John Barrow has introduced a scale of inward manipulation, which one can argue would be just as applicable to ETCs as the Kardashev energy scale. A civilization at the BI level of advancement can manipulate objects at its own size, or about 1 m (assuming that intelligent beings exist, as we do, at this size). A BII civilization can work with objects at the  m scale, which would allow it to manipulate genes. A BIII civilization can work with objects at the  m scale, which would allow it to manipulate molecules. Barrow argues that human civilization is now at the BIV level, since various technological advances are allowing us to manipulate individual atoms at the  m scale."

"there are 35 orders of magnitude between the human scale of 1 m and the smallest possible scale defined by quantum physics—the Planck scale; there are “only” 26 orders of magnitude between the human scale and the size of the observable universe."

"Perhaps, then, as ETCs advance in sophistication they choose to investigate the microworld instead of, or at least in addition to, the macroworld. A better classification of ETCs might be their ability to manipulate smaller and smaller length scales. On the Barrow scale a BV civilization could manipulate atomic nuclei (and thus work at the  m distance range); a BVI civilization could manipulate elementary particles ( m); and a B civilization could manipulate the structure of spacetime itself ( m)."

"Vidal argues that black holes are “attractors for intelligence”: KII–B civilizations will be drawn to using these extreme objects. With our current level of understanding it’s impossible to state what such an advanced civilization would choose to do with their black holes, but it’s interesting to speculate. Advanced civilizations might, for example, use black holes to store or extract energy—various mechanisms have been proposed for extracting energy from black holes, and they often have excellent efficiency. Or they might use them for science: a black hole gravitational lens could form the basis of a hugely powerful telescope."

"The argument simply requires there to be some number of critical yet unlikely steps on the road to intelligence, with each step only possible after earlier earlier steps in the sequence have taken place. The eminent evolutionary biologist Ernst Mayr once listed over a dozen such steps; other scientists have suggested the number might be even greater, particularly if certain physical and astronomical coincidences are added to the list. The status of these various steps can, of course, be contested. Some of the evolutionary steps we call “difficult” might not be hurdles at all. We regard a particular evolutionary step as being difficult if it occurred only once in Earth’s history, but some steps probably could be taken only once—the competition they stimulated would have made a second occurrence redundant. On the other hand, some steps probably were genuinely improbable. For example, if a particular critical step required several otherwise worthless mutations to take place at the same time, then it would make sense to regard the step as a fluke."