The Eerie Silence — Paul Davies on the Drake Equation, SETI and Fermi's Paradox

The Eerie Silence – Paul Davies on SETI, the Drake equation and anthropocentrism

A lonely planet

Do you think we’re alone in our galaxy, the Milky Way? So far, and to my personal relief, we are yet to hear so much as a bleep or bloop from any star faring society. So, where is everybody? That’s the big question that physicist Paul Davies explores in his wonderful book, The Eerie Silence.

The absence of evidence

The radius of our galaxy is nearly 53,000 light years long. Even if two distant civilizations existed and shared communicable technologies, it would still take many thousands of years just to say hello. Paul Davies says this is one of the reasons why the Search for Extraterrestrial Intelligence (SETI) requires a truly long-term perspective.

Every attempt that scientists have made to communicate with the great beyond has been “greeted with an eerie silence”. Does that mean we’re alone? As former U.S. defense secretary Donald Rumsfeld once said:

“Simply because you do not have evidence that something exists does not mean that you have evidence that it doesn’t exist… Absence of evidence is not evidence of absence.”.
Donald Rumsfeld. (2002).

From a statistical standpoint, it’s difficult to attach likelihoods to the existence of alternative lifeforms. The problem is that we only have a sample of one when it comes to intelligent life. Even then, there is much about life, intelligence, and technology on Earth that we do not yet understand. So the hunt for evidence and “credibility factors” to substantiate an extraordinary hypothesis continues.

Abandoning anthropocentrism

To tackle SETI, Paul Davies says we have to abandon “the shackles of anthropocentrism”. We tend “to extrapolate from [our] own experience” when thinking about alien life. Unless there are self-organizing and complexity principles we do not yet know about, it seems naïve to expect other advanced civilizations (if they exist) to have evolved in the same way we have.

“SETI is the quintessentially long-term project, … The way forward is to stop viewing alien motives and activities through human eyes. Thinking about SETI requires us to abandon all our presuppositions about the nature of life, mind, civilization, technology, and community destiny. In short, it means thinking the unthinkable.”
Paul Davies. (2010). The Eerie Silence: Are We Alone in the Universe?

Biogenesis in the Goldilocks zone

Speculating on the alien nature is immeasurably difficult. How might extraterrestrial life begin, and where might we find them? Naturally, one starting point is to search for Earth-like planets of similar size, atmosphere, water content, and related characteristics. The implicit assumption here is that there is “a Goldilocks zone” for the emergence of life.

All life on Earth, for example, depends on liquid water. This requirement, Davies notes, “brackets the temperature and pressure range” for terrestrial life. Even hyperthermophiles — microorganisms that grow under very hot temperatures — face “an upper limit of about 130 °C”. Their DNA and proteins begin “to unravel and disintegrate” beyond that threshold.

Should we expect life on another planet to abide by similar rules? As J.B.S Haldane writes in Possible Worlds:

“Now, my own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose… I suspect that there are more things in heaven and earth than are dreamed of, or can be dreamed of, in any philosophy.”
J. B. S. Haldane. (1927). Possible Worlds and Other Essays.

Freakshow or cosmic imperative?

Moreover, just because a planet is habitable doesn’t make it so. If the planet is Earth-like, one still has to ask how likely biogenesis is. Some scientists suggest that life is “a freak side-show”, while others argue that it is a “cosmic imperative”. Of course, scientists have looked for clues to life’s origins on Earth, Mars, and the Moon too. But this introduces three more questions: “the when, where and how of biogenesis”. Could it be that intelligent life is infinitesimally unlikely?

Even if we discovered life on Mars, it mightn’t tell us much about the universality of life (although it might suggest better odds). Davies reminds readers that “Mars and Earth are not quarantined”. Over geologic time, both planets “exchange material in the form of ejected rocks”. So, it’s possible for “terrestrial material… infested with microbes” to find its way to Mars.

“Summing up then, the probability of life emerging from non-life can be placed on a spectrum ranging from infinitesimal ([Jacques] Monod’s position) to almost inevitable ([Christian] de Duve’s position), or anywhere in between.”
Paul Davies. (2010). The Eerie Silence: Are We Alone in the Universe?

Undiscovered emergent laws

While scientists have a good understanding of evolution, the origin of life itself remains a mystery. Many theories exist today, from clay crystals to primordial soup. While experiments like Urey-Miller’s ‘early-Earth simulations’ provide potential hints, there remains much to learn. I share Davies’ fascination on the topic:

“To a physicist like me, life looks to be little short of magic: all those dumb molecules conspiring to achieve such clever things! How do they do it? There is no orchestrator, no choreographer directing the performance, no esprit de corps, no collective will, no life force — just mindless atoms pushing and pulling on each other, kicked about by random thermal fluctuations. Yet the end product is an exquisite and highly distinctive form of order.”
Paul Davies. (2010). The Eerie Silence: Are We Alone in the Universe?

Davies points out that there may be additional emergent laws that we’re yet to discover — laws that describe the properties of self-organizing complex systems, and the conditions and propensity for biogenesis to occur. The author parallels this to John Conway’s The Game of Life (or cellular automata games), in which a simple set of rules can generate a “rich and complex ecology of shapes that move and interact”.

Multiple trees of life

We know today that three “distinct bushes” — bacteria, archaea and eukaryotes — “branched apart” from “the trunk of the tree [of life]” many billions of years ago. Davies wonders whether a “fourth bush”, separate tree, or entire forest, awaits discovery. Indeed, evidence in favor of multiple origins of life on Earth would have profound implications for biology and SETI by extension.

Scientists have gone looking for multiple origins, undiscovered bushels and “weird life” in exotic environments. Thus far, even unusual microbes, like extremophiles, come from our standard tree of life. They’ve simply adapted to extreme conditions on Earth. The absence of evidence, however, is not evidence of absence.

The directionality of intelligence

So far, we’ve talked mostly about the origin of life. What SETI is interested in is the search for intelligent life. Even if primitive life is abundant, the emergence and persistence of intelligence might not be.

Many would argue that intelligence confers an evolutionary advantage. Indeed, the encephalization quotient (animal brain to body ratio) has exhibited “an accelerating trend” towards intelligence over the last several million years. And so, it seems reasonable for intelligence to flourish if given enough time. (The operative, of course, is ‘given enough time’. Some of us are still waiting for our workplaces and governments to make smart decisions. One might wonder if intelligence even real!)

Evolution, however, doesn’t exhibit foresight. Cumulative adaptation is the result of chance mutations that nature selects “simply on the basis of what works best at the time”. Rising intelligence and complexity may generate “an illusion of directionality” where none exists. (For more on this topic, I recommend Richard Dawkin’s The Blind Watchmaker)

“Life becomes more complex on average over time, not because it is subtly directed towards complexity, but merely because it is randomly exploring the range of possibilities, most of which are more complex than the starting state. [Stephen Jay] Gould believed that the ‘progressive’ misconception is exacerbated by the metaphor of the tree of life first used by Darwin, which has a clear direction (up), whereas a bush would be a more fitting metaphor. Summarizing this viewpoint, one might say that life simply ‘makes it up as it goes along’. And intelligence is just one of those things it made up.”
Paul Davies. (2010). The Eerie Silence: Are We Alone in the Universe?

Convergent evolution

Insects, mammals, and birds have evolved eyes, limbs, and wings, many times over. Should we expect convergent evolution in intelligence? Compared to eyes and wings, at least, nature required much more time to ‘discover’ intelligence. And prior to the discovery of fire, humans were relatively marginal animals. Perhaps, under alternate starting conditions, Sapien-like intelligence might not have come about. Or maybe another brainy animal on the periphery would evolve to fill the intelligence niche. It’s hard to say with a small sample size.

“The upshot of these arguments is that there is wide scope for disagreement. There may be a deep law of nature that drives living systems towards greater complexity, with big brains and intelligence being one consequence. But no such law is known to science, in spite of the widespread belief that it may exist. It is also possible that evolutionary convergence is so strong, and advanced intelligence has such good pervasive survival value, that it will sooner or later inevitably evolve, barring major calamities.”
Paul Davies. (2010). The Eerie Silence: Are We Alone in the Universe?

The Drake equation

Even if intelligent life exists elsewhere, how likely is it for them to achieve interstellar communications? We’re now entering the realm of SETI. Sadly, the further we go, the more uncertain everything becomes. The Drake Equation, however, can help us to “catalog [our] ignorance”. The equation, first formulated by astronomer Frank Drake in 1961, is described as follows:

N = R^* f_p n_e f_l f_i f_c L

Where:

N is the number of communicable civilizations across the galaxy.
R^* is the “rate of formation of sun-like stars in the galaxy”.
f_pis the “fraction of those stars with planets”.
n_e is the “average number of Earth-like planets in each planetary system”.
f_l is the “fraction of those planets on which life emerges”. Davies says this is “the really hard part”.
f_i is the “fraction of planets with life on which intelligence evolves”.
f_c is the “fraction of those planets on which technological civilization and the ability to communicate emerges”.
L is the “average lifetime of a communicating civilization.”

Cataloguing our ignorance

Scientists have reasonably good estimates for R^*, f_p, and n_e. “The really hard part”, Davies says, are our estimates for f_l, f_i, f_c, and L. Carl Sagan, ever the optimist, assumed that f_l = 1. Drake’s original assumptions, likewise, produced a result of N = 10,000 — that there are around 10,000 civilizations in the Milky Way with interstellar communications today. Do remember, however, that our assumptions behind the last four variables are uncertain. (As an aside, you have to admire Frank Drake’s lifelong commitment to finding aliens. As Davies notes in a 2012 public lecture, it takes resilience to dedicate your life to a scientific cause without any hits.)

“All we have to go on is life on Earth – a sample of one. … In other words, life on Earth had to get going pretty fast, or there wouldn’t have been enough time for intelligent observers like us to hit the scene before the sun became a red giant. So, life’s prompt appearance on Earth may not after all be indicative of the general situation; it could have been a highly atypical set of events which has been selected for observation and scrutiny by the very observers it created.”
Paul Davies. (2010). The Eerie Silence: Are We Alone in the Universe?

Civilizations at the Great Filter

As an economist, our assumption about L is most interesting to me. Davies “[sees] no reason why” an advanced civilization, once established, cannot “endure for an extraordinary length of time”. Civilization in this sense mustn’t necessarily be biological in design. Synthetic intelligence, for example, may propagate across the cosmos someday. Many people, I suspect, would disagree with Davies’ optimism. Our nuclear arsenal, for example, might bring about a second Stone Age. Perhaps Mother Nature will play her hand if we cannot resolve the sustainability challenge. More generally, it’s possible that intelligent civilizations “are inherently unstable” by nature.

Fermi’s paradox

If the galaxy is buzzing with life, shouldn’t aliens have visited Earth by now? Indeed, life on Earth began around 3 to 4 billion years ago. If you gave an advanced civilization a billion-year head start, they’d have ample time to spread across the Milky Way. Yet things in space remain eerily silent. As Physicist Enrico Fermi famously asked, “where is everybody?”

Fermi’s paradox, however, rests on the assumption that advanced civilizations are forever expanding. But galactic expansion is expensive. It seems more reasonable, Davies says, to expect “a patchwork quilt of diverse local cultures”. Some colonies may “expand rapidly”, while others remain “content to consolidate”. To me, this sounds like the early murmurings of galactic ecology and economics — an exciting field of research, I’m sure, many years from now.

In Davies’ view, extra-terrestrials are more “likely to be post-biological in nature”, where “biological intelligence is only a transitory phenomenon”. If you think about it, synthetic intelligences seem better equipped for space faring and long voyages. Ultimately, though, when it comes to SETI, Davies says we should “expect the unexpected”. This must be an unsatisfying answer for some. But it creates a wonderful void for science fiction to fill, don’t you think?

References

Davies, Paul. (2010). The Eerie Silence: Renewing Our Search for Alien Intelligence.
Davies, Paul. (2016). The Cosmos Might Be Mostly Devoid of Life. Scientific American.
Davies, Paul. (2012). The Eerie Silence: Are We Alone in The Universe? Public Lecture Series. Australia National University.
Sierra, Leonor. (2016). Are We Alone in the Universe? Revisiting the Drake Equation. Exoplanet Exploration. NASA.

The Eerie Silence — Paul Davies on SETI, the Drake Equation, and Anthropocentrism