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Why Alien Life Will Be Robotic

If life off Earth exists it has probably transitioned to machine intelligence.


This September, a team of astronomers noticed that the light from a distant star is flickering in a highly irregular pattern.1 They considered the possibility that comets, debris, and impacts could account for their observations, but each of these explanations was unlikely to varying degrees.2 What their paper didn’t explore, but they and others are beginning to speculate, is that the flickering might be caused by enormous structures built by an advanced civilization—whether the light might be evidence of ET.

In thinking about this possibility, or other similarly suggestive evidence of extraterrestrial life, an image of an alien creature might come to mind—something green, perhaps, or with tentacles or eye stalks. But in this we are probably mistaken. I would argue that any positive identification of ET will very likely not originate from organic or biological life (as Paul Davies has also argued), but from machines.

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Few doubt that machines will gradually surpass more and more of our distinctively human capabilities—or enhance them via cyborg technology. Disagreements are basically about the timescale: the rate of travel, not the direction of travel. The cautious amongst us envisage timescales of centuries rather than decades for these transformations. Be that as it may, the timescales for technological advance are but an instant compared to the timescales of the Darwinian selection that led to humanity’s emergence—and (more relevantly) they are less than a millionth of the vast expanses of time lying ahead. So the outcomes of future technological evolution will surpass humans by as much as we (intellectually) surpass a bug.

Non-biological “brains” may develop insights as far beyond our imaginings as string theory is for a mouse.

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There are, after all, chemical and metabolic limits to the size and processing power of “wet” organic brains. Maybe we’re close to these already. It is remarkable that our brains, which have changed little since our ancestors roamed the African savannah, have allowed us to understand the counterintuitive worlds of the quantum and the cosmos. But there is no reason to think that our comprehension is matched to an understanding of all key features of reality. Scientific frontiers are advancing fast, but we may sometime “hit the buffers.” There may be phenomena crucial to our long-term destiny that we are not aware of, any more than a monkey comprehends the nature of stars and galaxies.

But no such limits constrain silicon-based computers (still less, perhaps, quantum computers): For these, the potential for further development could be as dramatic as the evolution from monocellular organisms to humans. By any definition of “thinking,” the amount and intensity that’s done by organic human-type brains will be utterly swamped by the cerebrations of AI. Abstract thinking by biological brains has underpinned the emergence of all culture and science. But this activity—spanning tens of millennia at most—will be a brief precursor to the more powerful intellects of the inorganic post-human era.

This will be especially true in space, which is a hostile place for biological intelligence. The Earth’s biosphere, in which organic life has symbiotically evolved, is not a constraint for advanced AI. Indeed it is far from optimal—interplanetary and interstellar space will be the preferred arena where robotic fabricators will have the grandest scope for construction, and where non-biological “brains” may develop insights as far beyond our imaginings as string theory is for a mouse.

Consider the development of human space exploration. During this century, the entire solar system—planets, moons, and asteroids—will be explored by flotillas of tiny robotic craft. The next step would be the deployment of large-scale robotic fabricators, which can construct and assemble large structures in space (and fabrication in space will be a better use of materials mined from asteroids or the moon than bringing them back to Earth). The Hubble Telescope’s successors, with huge gossamer-thin mirrors assembled under zero gravity, will further expand our vision of stars, galaxies, and the wider cosmos.

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ROBOT EXPLORER: NASA’s Curiosity Mars rover is one of many robots exploring our solar system in ways that would be difficult for humans. Here, it takes a selfie.NASA

What role will humans play? There’s no denying that NASA’s Curiosity rover, now trundling across Martian craters, may miss startling discoveries that no human geologist could overlook. But robotic techniques are advancing fast, allowing ever more sophisticated unmanned probes, whereas the cost gap between manned and unmanned missions remains huge. The practical case for manned spaceflight gets increasingly weaker with each advance in AI and miniaturization—indeed as a scientist or practical man I see little purpose in sending people into space at all (though as a human being, I’m an enthusiast for manned missions.)

Transit time beyond nearby stars exceeds a human lifetime. Interstellar travel (except for unmanned probes, DNA samples, and so on) is therefore an enterprise for post-humans. They could be silicon-based, or they could be organic creatures who had won the battle with death, or perfected the techniques of hibernation or suspended animation.

Life away from Earth has probably already gone through this transition. Suppose that there are many other planets where life began, and suppose that on some of them Darwinian evolution followed a similar track. Even then, it’s highly unlikely that the key stages would be synchronized. If the emergence of intelligence and technology on a planet lags significantly behind what has happened on Earth (because the planet is younger, or because the “bottlenecks” to complex life have taken longer to negotiate there than here) then that planet would plainly reveal no evidence of ET. But life on a planet around a star older than the sun could have had a head start of a billion years or more. Thus it may already have evolved much of the way toward a dominant machine intelligence.

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Perhaps the galaxy already teems with advanced life, and our descendants will “plug in” to a galactic community.

The history of human technological civilization is measured in centuries—and it may be only one or two more centuries before humans are overtaken or transcended by inorganic intelligence, which will then persist, continuing to evolve, for billions of years. This suggests that if we were to detect ET, it would be far more likely to be inorganic: We would be most unlikely to “catch” alien intelligence in the brief sliver of time when it was still in organic form.

What does this mean for how we search for ET? SETI searches are surely worthwhile, despite the heavy odds against success, because the stakes are so high. They typically seek some electromagnetic transmission that is manifestly artificial. But even if the search succeeded (and few of us would bet more than 1 percent on this), it would still in my view be unlikely that the “signal” would be a decodable message. It would more likely represent a byproduct (or even a malfunction) of some super-complex machine far beyond our comprehension that could trace its lineage back to alien organic beings (which might still exist on their home planet, or might long ago have died out). The only type of intelligence whose messages we could decode would be the (perhaps small) subset that used a technology attuned to our own parochial concepts.

Even if intelligence were widespread in the cosmos, we may only ever recognize a small and atypical fraction of it. Some “brains” may package reality in a fashion that we can’t conceive. Others could be living contemplative lives, perhaps deep under some planetary ocean, doing nothing to reveal their presence. It makes sense to focus searches first on Earth-like planets orbiting long-lived stars.

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But science-fiction authors remind us that there are more exotic alternatives. In particular, the habit of referring to ET as an “alien civilization” may be too restrictive. A “civilization” connotes a society of individuals: In contrast, ET might be a single integrated intelligence. Even if signals were being transmitted, we may not recognize them as artificial because we may not know how to decode them. A radio engineer familiar only with amplitude modulation might have a hard time decoding modern wireless communications. Indeed, compression techniques aim to make the signal as close to noise as possible—insofar as a signal is predictable, there’s scope for more compression.

Perhaps the galaxy already teems with advanced life, and our descendants will “plug in” to a galactic community—as rather “junior members.” On the other hand, Earth’s intricate biosphere may be unique and the searches may fail. This would disappoint the searchers. But it would have an upside. Humans could then be less cosmically modest. Our tiny planet—this pale blue dot floating in space—could be the most important place in the entire cosmos.

We would then be of especially great cosmic significance, for being the transient precursor to the deeper cogitations of another culture—one dominated by machines, extending deep into the future and spreading far beyond Earth.

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Martin Rees is a British cosmologist and astrophysicist. He is also the Astronomer Royal.

The author wishes to acknowledge that portions of this Nautilus article have previously appeared in essays he wrote for other publications.


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1. Boyajian, T.S., et al. Planet hunters X: KIC 8462852—Where’s the flux? Preprint arXiv:1509.03622 (2015).

2. Andersen, R. The most mysterious star in our galaxy. The Atlantic (2015).

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