If the Universe Is Teeming with Aliens ... WHERE IS EVERYBODY?: Seventy-Five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life

by Stephen Webb

What triggered the transition from complex molecules to entities that can metabolize and reproduce? It might have involved a fluke so rare that it happened only once in the entire Galaxy.

Fermi tried to inculcate this facility in his students. He would demand of them, without warning, answers to seemingly unanswerable questions. How many grains of sand are there on the world’s beaches? How far can a crow fly without stopping? How many atoms of Caesar’s last breath do you inhale with each lungful of air? Such “Fermi questions” (as they are now known) required students to draw upon their understanding of the world and their everyday experience and make rough approximations, rather than rely on bookwork or prior knowledge.

Eubulides of Miletus , who asked: “A man says he is lying; is what he says true or false?”

Sometimes I think we’re alone. Sometimes I think we’re not. In either case, the thought is staggering. Buckminster Fuller

If the scenario Fogg describes is true, then Earth is located within a sphere of influence of one or more advanced ETCs. So why haven’t they taken over? He argues that, in a steady-state era, knowledge will be the most valuable resource.

Advanced ETCs would have a reason to leave a life-bearing planet well alone, if only because the planet will provide a non-renewable source of information.

The Bekenstein Bound Jacob Bekenstein showed how quantum physics places a limit to the amount of information a physical system can code. The uncertainty relations show that the amount of information inside a system of radius (in meters) and mass (in kilograms) can never be greater than the mass multiplied by the radius multiplied by a constant (which has a value of about bits per meter per kilogram). Nature permits a surprising amount of information to be encoded before the Bekenstein bound is reached. For example, a hydrogen atom can encode about 1 Mb of information. A typical human can code about Mb of information—far more information than can be handled by any hard disk in existence. Natural physical systems seem to encode much less information than Nature permits. But the Bekenstein bound gives planetarium designers plenty of opportunity to engineer perfect simulations of varying size and scope. Standard thermodynamic calculations give us the energy required to construct a perfect simulation of any particular size and mass.

A KIII civilization could generate a perfect simulation of a volume with a radius of about 100 AU. This is a large distance, and when I wrote the first edition of this book our civilization was unable to test whether our universe is “real” or the result of a simulation developed by a KIII civilization. But the situation has changed. Voyager 1 is already 127 AU from home and it didn’t bump into a metal wall painted black! We know that we don’t live in a perfect simulation.

We might yet live in a simulation that is less than perfect; after all, only the two Voyager spacecraft have travelled further than 100 AU. The planetarium builders might have scrimped on simulating some aspects of reality in order to extend the boundary of their simulation. But it can’t be a perfect simulation; our instruments can in principle detect the inconsistencies in such a lower-quality simulation.

The Casimir effect —a small attractive force that acts between two uncharged parallel conducting plates brought into close proximity—is the clearest example of the existence of zero-point energy (ZPE). The effect can only be explained in terms of quantum fluctuations of the electromagnetic field.

Some writers suggest there’s an infinite supply of energy in the vacuum and that some day we’ll be able to tap into this ZPE: perhaps we can use ZPE for a propulsion system.

Models of galactic colonization implicitly assume that the important objects out in space are stable, middle-aged, G2-type stars such as the Sun and watery planets such as Earth. But who knows where a civilization much older than ours would choose to live? Even if Earth-like conditions are necessary for the genesis and early evolution of life, once a civilization is technologically advanced and can construct a habitat for itself it might not want to remain on the surface of a planet orbiting a commonplace star. We tend to think ETCs would love to get their hands (tentacles, feelers, whatever) on the prime piece of real estate that is our Solar System, but that might simply be a reflection of our solar and planetary chauvinism. Perhaps the various galactic colonization models aren’t wrong; perhaps they are they simply inapplicable.

Would KII civilizations require stars at all? Perhaps they mine energy from the quantum vacuum or extract energy from black holes.

They might live in their generation ships, never feeling the need to set foot (or alien pedal equivalent) on a planetary surface. Most models of galactic colonization have been based on an analogy: the colonization of America by Europeans or of the Pacific islands by Polynesians. Perhaps a better analogy for colonization would be life’s migration from water to land. Just as fish don’t meet fowl perhaps ETCs won’t meet us. Perhaps they colonize space, but they don’t bother to colonize our particular piece of real estate; other places are more attractive to them.

Ćirković presents a handful of reasons why it’s wrong to think of the development of ETCs in imperial terms. First, as we shall see on page 194, there are grounds for supposing that a sophisticated technological civilization is highly likely to make a transition to a postbiological stage. There are various forms this transition could take—perhaps minds are “uploaded” to silicon; carbon-based bodies might merge with metal-based robots; there are many possibilities, as several SF writers have investigated—but, however the transition occurred, various biological imperatives would be called into question.

Solution 23 Information Panspermia There are no foreign lands. It is the traveller only who is foreign. Robert Louis Stevenson, The Silverado Squatters The Armenian mathematical physicist Vahe Gurzadyan has posited an interesting hypothesis: we might inhabit a Galaxy “full of traveling life streams”—strings of bits beamed throughout space. The argument goes as follows.

Gurzadyan showed that with an Arecibo-like antenna it would be possible to transmit the genomes of terrestrial organisms throughout the Milky Way galaxy.

Gurzadyan, then, imagines a type of what might be called “information panspermia”. He describes the possibility of a Galaxy in which ETCs establish a network of self-replicating Bracewell–von Neumann probes and life is propagated not by sending the genomes themselves but by sending the programs that can recover the genomic information. In other words the probes, which could be many light years away from their home planet, would receive coded strings and from those strings reconstitute the full panoply of that planet’s life. Even now, life might be raining down on us. But it would be a strangely desiccated form of life: not living creatures, but rather ghostly strings of information that have the potential to become living.

Besides, really advanced civilizations—as Marvin Minsky pointed out—would consider radiation at any temperature above the cosmic background temperature of 2.7 K to be wasteful. Perhaps an ETC advanced enough to construct a Dyson sphere is advanced enough to squeeze every last drop of useful work out of a star’s radiation, leaving waste heat at a few kelvin. Perhaps Dyson spheres are common but we should be looking for them by searching for points in space that possess a small temperature excess over the microwave background?

(A civilization might even deliberately alter its star’s spectrum in this way to create a beacon. This possibility was first suggested by Drake.

A Frequency for Intergalactic Communication A “natural” frequency for intergalactic communication is represented by where is the observed temperature of the cosmic background radiation, is the Boltzmann constant and is the Planck constant (it thus links the regimes of cosmology and quantum physics). This frequency was originally proposed in 1973 by Drake and Sagan, and independently by Gott in 1982.

The frequency 56.8 GHz is tied to the observed cosmic microwave background, so it’s a universal frequency. If an ETC in a distant high-redshift galaxy

Unfortunately, Earth’s atmosphere has a wide oxygen absorption band at 60 GHz, which means our radio telescopes can’t carry out a search at 56.8 GHz.

Solution 31 Everyone is Listening, No One is Transmitting

If we wanted to send a narrowband signal so it could be detected by a small antenna at a distance of 100 light years, say, then the power required by the transmitter would exceed the present total installed electricity-generating capacity of the world. And 100 light years barely extends beyond our immediate neighborhood.

Even with our present laser technology we can generate a pulse of light that, for a short duration, outshines the Sun.

If an ETC sends a signal to where the star is now, then by the time the light reaches it the star will have moved on. So the transmitting civilization also needs accurate information about the velocities of the target stars. Gathering information about other planetary systems and the precise location and velocity of stars isn’t easy, but neither is it impossible.

Rose and Wright worked out the numbers and made the comparison. They showed that there’s always a break-even distance beyond which it’s better to write. The break-even distance depends upon several factors, but on an astronomical scale it’s never particularly large. Here then is their general conclusion: in terms of energy per bit, it’s overwhelmingly more efficient to write than it is to radiate.

So here is an answer to the Fermi paradox: we’ve been looking for a broadcast when we should have been looking for a message in a bottle. (We might argue, however, that if ETCs would find it so easy to send a physical message then why haven’t we already seen one? Since it would be pointless to hurl a small bottle into space by itself, they would surely attaching a clear, noticeable, persistent beacon to the bottle. Where are the beacons?)

Since the RNA molecule can store a vast amount of information in a small mass, perhaps life itself is the message?

Small Black Holes The smallest possible black hole is about m across—the so-called Planck length. Smaller structures get wiped out by quantum fluctuations. The creation of even the smallest black hole would require energies of around GeV, which is billions of times larger than RHIC energies. And even if it could create such an object, the black hole would evaporate on a timescale of s. There are certainly more pressing things to worry about.

Conan the Bacterium Even a total, all-out, no-holds-barred nuclear war wouldn’t destroy all life on a planet. Consider the organism Deinococcus radiodurans. Scientists first isolated it in 1956 from a can of ground beef; the beef had been radiation-sterilized, but the meat still spoiled. It turns out that D. radiodurans can survive an exposure to gamma-radiation of 1.5 million rads. For comparison, a dose of 1000 rads is usually enough to kill a man.

Not just bacteria would survive; various other organisms could survive a nuclear war. If intelligence is an inevitable outcome of evolution (this is contentious, as we shall see later, but is presumably the viewpoint of those who argue there are a million ETCs in the Galaxy) then the wait for intelligence to emerge after a nuclear holocaust wouldn’t be endless: a few hundreds of millions of years, perhaps. This is an unimaginably vast reach of time on a human scale, but, again, it’s not particularly significant when compared to the age of the Galaxy.

The standard model is stunningly successful; it’s consistent with the results of every subatomic experiment ever made. But the model isn’t complete. It doesn’t incorporate gravity; it applies to only about 4 % of the mass–energy content of the universe, since it doesn’t include dark matter or dark energy; and it contains 19 parameters, the values of which are unexplained and must be inserted “by hand”. Physicists desperately want to find evidence of physics beyond the standard model, but so far no cracks have appeared: the standard model remains solid even though we know, somewhere, it must break down.

We are mining more data and mining less coal.

I mentioned the relevant timescales in chapter 1, but it’s worth repeating them here. We now know that the universe is 13.798 billion years old, give or take 37 million years. Astronomers still don’t have a full understanding of the formation of the first stars, but it seems reasonable to assume that the first Sun-like stars, and thus perhaps the first rocky planets, formed within a billion years after the Big Bang—in other words, about 12.8 billion years ago. If we take Earth as a guide, and assume intelligent life appears 4.5 billion years after a planet forms, then we could argue that the oldest civilizations appeared in the universe 8.3 billion years ago. The oldest stars in our Milky Way galaxy formed roughly 10–11 billion years ago so a similar argument suggests that the oldest neighboring civilizations could quite easily be 5 billion years old. Ray Norris, using an argument based upon stellar evolution, reasoned that the median age of an ETC would be 1.7 billion years. Different astronomers, using different arguments, have argued for a median age somewhere between the Norris figure of 1.7 billion years and the 8.3 billion years mentioned above. The specific age is hardly the point: whether you believe that extraterrestrial civilizations might be 1.7 billion years older than us, 8.3 billion years older or somewhere in between, the take-home message is the following. If ETCs survive natural and home-made catastrophes they are likely to be much, much older than us: the...

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. But, as Richard Feynman once remarked, “there’s plenty of room at the bottom”; in other words, there’s more to explore at small scales than at large scales. Indeed, 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.

In his PhD thesis, presented in 2013, the Belgian philosopher Clément Vidal argues that ETC development can best be discussed using a two-dimensional metric that combines the Kardashev and Barrow scales. In particular, he argues that SETI researchers should consider what it might mean if civilizations were at the KII–B level—civilizations that could harness the energy of a star and manipulate spacetime. If a civilization has the capacity to manipulate spacetime then its technology will be able to work with black holes —regions of spacetime from which nothing can escape.

Vidal argues that black holes are “attractors for intelligence”:

In a paper published in 2012, in the journal Acta Astronautica, John Smart argues that advanced civilizations do indeed hit a technological singularity but that it’s possible to predict where that singularity will take them. Smart agrees with Vidal (see Solution 46) that black holes are attractors for intelligence: we don’t see advanced civilizations because they disappear into black holes. This is the transcension hypothesis.

The literature contains several types of anthropic reasoning, corresponding to several anthropic principles each with different shades of meaning. According to Carter, the weak anthropic principle (WAP) is that “what we can expect to observe must be restricted by the conditions necessary for our presence as observers.” The WAP seems almost tautologous. The strong anthropic principle (SAP), on the other hand, is more contentious: “the universe (and hence the fundamental parameters on which it depends) must be such as to admit the creation of observers within it at some stage.” Barrow and Tipler, in a classic book, also discuss the final anthropic principle (FAP), which they define as “intelligent information-processing must come into existence in the universe and, once it comes into existence, it will never die out”.

Soon after the Big Bang, the universe contained essentially only hydrogen and helium (in the ratio 75% to 25%). There were small amounts of lithium, and even smaller traces of beryllium and boron, but that was all. To an astronomer, then, the universe consists of hydrogen, helium and everything else; all the elements heavier than hydrogen and helium—the “everything else”—are called metals. Now, the biochemistry of terrestrial organisms, and the biochemistry of any extraterrestrial organisms we can plausibly imagine, depends crucially on six elements: hydrogen (H), sulfur (S), phosphorus (P), oxygen (O), nitrogen (N) and carbon (C). In astronomical terminology, therefore, life depends upon hydrogen and the five metals SPONC. However,

Gamma-Ray Bursts

A GRB pours out more energy in a few seconds than the Sun will generate in its entire lifetime.

Metabolism takes place through the catalytic action of enzymes: without enzymes, the various biochemical reactions that take place in cells simply wouldn’t happen. In turn, enzymes are made of proteins. Proteins are therefore a vital constituent of life—at least here on Earth. As we shall see later, the instructions for creating the various proteins necessary for a cell’s existence are contained in its deoxyribonucleic acid (DNA), while the biochemical machinery of protein synthesis is based on its ribonucleic acid (RNA). In shorthand form: DNA makes RNA makes proteins.

A. As I write this, biologists have announced the production of semisynthetic bacteria whose engineered DNA contain two extra letters, X and Y. In other words, these modified E. coli cells have a third base pair—these cells are a new type of life.

There are several types of RNA, each performing different tasks, and we shall meet three of them—messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA) —below.

Until this explosion of creativity the three extant hominid species appear to have been equally stagnant. Why the sudden change for us humans? There are several possible explanations. Perhaps the development of language triggered the creative explosion. Perhaps the explosion occurred much earlier, but artifacts prior to 40,000 years ago weren’t well preserved. Perhaps the humans of more than 40,000 years ago were anatomically modern, but lacked a modern brain. Perhaps cultural knowledge accumulated slowly until, 40,000 years ago, it passed a critical threshold. Perhaps the exceptionally long stage of human child development, and the play that children engage in, enabled humans to envision their environment in new and creative ways. Perhaps a constellation of factors was involved. We don’t know. But if whatever caused this explosion of creativity was a fluke, an accident, then we might expect the number of communicating ETCs to be small.

Many difficulties which nature throws in our way may be smoothed away by the exercise of intelligence. Livy, Histories, Book XXV, Sec. 11