The Antennae Galaxies, located about sixty-two million light-years from Earth, take their name from the long, antenna-like arms seen in wide-angle views of the system. These features were produced in the collision.

Interstellar Travel and Post-Humans

MARTIN REES

Martin Rees

Institute of Astronomy, Cambridge, UK

Martin Rees is a cosmologist and space scientist. He has contributed insights to many aspects of stars, black holes, galaxy evolution, the ‘big bang’ and the multiverse. He is based in Cambridge, UK, where he has been Director of the Institute of Astronomy, a Research Professor, and Master of Trinity College. He was President of the Royal Society during 2005–10. In 2005 he was appointed to the UK’s House of Lords. His books include Before the Beginning, Our Final Century, Just Six Numbers, Our Cosmic Habitat, Gravity’s Fatal Attraction, and From Here to Infinity: Scientific Horizons, an expanded version of his BBC Reith Lectures. A further book, What We Still don’t Know, is forthcoming.

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The Earth has existed for forty-five million centuries —and even longer timespans lie ahead before the Sun dies. But even in this vast time-perspective, the present century is special. It is the first when humans may establish communities away from the Earth. And it is the first when they may create electronic intelligences that surpass their own all-round capabilities, and also achieve the ability to bio-engineer their progeny. In this chapter, some aspects of this transition are discussed, along with some even more speculative comments about “post-human” evolution, and the future of the universe itself.

INTRODUCTION

Astronomers like myself are professionally engaged in thinking about huge expanses of space and time. We view our home planet in a cosmic context. We wonder whether there is life elsewhere in the cosmos. But, more significantly, we are mindful of the immense future that lies ahead—the post-human future where our remote descendants may transcend human limitations—here on Earth but (more probably) far beyond. This is my theme in the present chapter.

The stupendous timespans of the evolutionary past are now part of common culture. But the even longer time-horizons that stretch ahead—though familiar to every astronomer —have not permeated our culture to the same extent. Our Sun is less than half way through its life. It formed 4.5 billion years ago, but it has got six billion more before the fuel runs out. It will then flare up, engulfing the inner planets and vaporizing any life that might still remain on Earth. But even after the Sun’s demise, the expanding universe will continue—perhaps forever—destined to become ever colder, ever emptier.

Any creatures witnessing the Sun’s demise six billion years hence will not be human —they will be as different from us as we are from a bug. Post-human evolution could be as prolonged as the Darwinian evolution that has led to us, and even more wonderful—and will have spread far from Earth, even among the stars. Indeed, this conclusion is strengthened when we realize that future evolution will proceed not on the million-year timescale characteristic of Darwinian selection, but at the much accelerated rate allowed by genetic modification and the advance of machine intelligence (and forced by the drastic environmental pressures that would confront any humans who were to construct habitats beyond the Earth). Natural selection may have slowed: its rigors are tempered in civilized countries. But it will be replaced by “directed” evolution. Already, performance enhancing drugs, genetic modification, and cyborg technology are changing human nature, and these are just precursors of more drastic changes.

Darwin himself realized that “No living species will preserve its unaltered likeness into a distant futurity.” We now know that “futurity” extends far further, and alterations can occur far faster than Darwin envisioned. And we know that the cosmos, through which life could spread, offers a far more extensive and varied habitat than he ever imagined. So humans are surely not the terminal branch of an evolutionary tree, but a species that emerged early in the overall roll-call of species, with special promise for diverse evolution—and perhaps of cosmic significance for jump-starting the transition to silicon-based (and potentially immortal) entities that can more readily transcend human limitations.

A SPECIAL CENTURY

For nearly fifty years we have had pictures of the Earth taken from space, showing how its delicate biosphere contrasts with the sterile moonscape where the astronauts left their footprint. These have become iconic, especially for environmentalists. But suppose some aliens had been viewing such an image for our planet’s entire history, what would they have seen?

Over nearly all that immense time, 4.5 billion years, Earth’s appearance would have altered very gradually. The continents drifted; the ice cover waxed and waned; successive species emerged, evolved, and became extinct. But in just a tiny sliver of the Earth’s history—the last one millionth part, a few thousand years—the patterns of vegetation altered much faster than before. This signalled the start of agriculture. The pace of change accelerated as human populations rose. Humanity’s “footprint” got larger because our species became more demanding of resources—and also because of population growth.

Within fifty years—little more than one hundredth of a millionth of the Earth’s age— the carbon dioxide in the atmosphere began to rise anomalously fast. And something else unprecedented happened: rockets launched from the planet’s surface escaped the biosphere completely. Some were propelled into orbits around the Earth; some journeyed to the Moon and planets.

If they understood astrophysics, the aliens could confidently predict that the biosphere would face doom in a few billion years when the Sun flares up and dies. But could they have predicted this sudden “fever” half way through the Earth’s life—these human-induced alterations occupying, overall, less than a millionth of the Earth’s elapsed lifetime and seemingly occurring with runaway speed?

If they continued to keep watch, what might they witness in the next hundred years? Will the spasm be followed by silence? Will the planet make a transition to sustainability? And, most important of all for the long-term future, will an armada of rockets leaving Earth have led to new communities elsewhere—on Mars and its moons, on asteroids, or freely floating in space?

And we live at a crucial time. Our Earth has existed for forty-five million centuries, and still more lie ahead. But this century may be a defining moment. It is the first in our planet’s history where one species (ours) has Earth’s future in its hands, because of our empowerment by fast-advancing technologies. We humans are entitled to feel uniquely significant, as the first known species with the power (and the responsibility) to mold its own future —and perhaps the future of intelligence in the cosmos.

KEY TECHNOLOGIES

Three new technologies will be crucial in the rest of this century: advanced biotech; artificial intelligence (and the possibility of “cyborg” enhancement); and the ability to explore space. These are all advancing so fast that we cannot confidently predict even to the end of the present century: we must keep our minds open to transformative advances that may now seem science fiction. After all, the smartphone, the web, and their ancillaries pervade our lives today, but they would have seemed magic as little as twenty years ago.

On the bio front, it took fifty years from Crick and Watson’s discovery of the double helix to the sequencing of the human genome. And within just a decade the costs of each such sequencing have fallen by a factor of ten thousand. New techniques for gene editing (e.g., CRISPR) and so-called “gain-of-function” experiments that can make viruses more virulent or transmissible offer great hopes. But they open up new ethical dilemmas, and great fears of misuse, because the relevant expertise will be widespread. (“Biohacking” is already a competitive pursuit among students.) The physicist Freeman Dyson conjectures a time when children will be able to design and create new organisms just as routinely as his generation played with chemistry sets. This is a hugely exciting prospect (especially if we one day wish to “green” alien habitats with plants to flourish there). But on the other hand there is a downside, stemming from the risk of bioerror or bioterror. If it becomes possible to “play God on a kitchen table” (as it were), our ecology, and even our species, may not long survive unscathed.

But what about a second transformative technology: robotics and artificial intelligence (AI)? We are all familiar with the dramatic consequences of Moore’s Law in yielding continuing advances in computer modelling and data processing. Progress in AI has, however, experienced “false dawns” followed by periods of discouragement. But it is currently on a “high,” partly due to exciting advances in what is called generalized machine learning. “Deep Mind” (a small London company now bought up by Google) achieved a remarkable feat early in 2016—its computer beat the world champion in the game of “Go.”

Of course it is twenty years since IBM’s “Deep Blue” beat Kasparov, the world chess champion. But “Deep Blue” was programmed in detail by expert players. In contrast, the Go-playing machine gained expertise by absorbing huge numbers of games and playing itself over and over again. Its designers do not themselves know how the machine makes its decisions.Computers use “brute force” methods and it is the advances in processing power that have allowed generalized machine learning to “take off.” Computers learn to identify dogs, cats, and human faces by “crunching” through millions of images—not the way babies learn. And they learn to translate by reading millions of pages of (for example) multilingual European Union documents (they never get bored!).But advances are patchy. Robots are still clumsier than a child in moving pieces on a real chessboard. They cannot tie your shoelaces or cut your toenails. But sensor technology, speech recognition, information searches, and so forth are advancing apace. They will not just take over manual work (indeed plumbing and gardening will be among the hardest jobs to automate), but routine legal work (conveyancing and suchlike), medical diagnostics, and even surgery.

The big social and economic question is this: will this “second machine age” be like earlier disruptive technologies—the car, for instance—and create as many jobs as it destroyed? Or is it really different this time? These concerns are sufficiently near-term that they are on the political agenda.

But let us speculate further ahead. If robots became less clumsy and limited, they might eventually be able to observe, interpret, and alter their environment as adeptly as we do. They would then truly be perceived as intelligent beings, to which (or to whom) we can relate. Such machines pervade popular culture—in movies like Her, Transcendence, and Ex Machina. Do we have obligations toward them? We worry if our fellow-humans, and even animals, cannot fulfill their natural potential. Should we feel guilty if our robots are frustrated, underemployed or bored?

We have a long way to go before we really confront these issues. As an indicator of the gap still to be bridged, the Go-playing computer probably consumed several hundreds of kilowatts during the game. The human champion’s brain (which of course can do many other things apart from play a game) consumes about 30 watts—as much as a light bulb.

There is disagreement about the route toward human-level intelligence. Some think we should emulate nature, and reverse-engineer the human brain. Others say that is as misguided as designing a flying machine by copying how birds flap their wings. And philosophers debate whether “consciousness” is special to the wet, organic brains of humans, apes, and dogs—so that robots, even if their intellects seem superhuman, will still lack self-awareness or inner life.

But, either way, we may one day confront in reality scenarios where autonomous robots “ go rogue,” where a “supercomputer” offers its controller dominance of international finance, or where a network could develop a mind of its own. If it could infiltrate the Internet—and the burgeoning “Internet of things”—it could manipulate the rest of the world. It may have goals utterly orthogonal to human wishes—or even treat humans as an encumbrance.

Some AI pundits take this seriously, and think the field already needs guidelines—just as biotech does. But others regard these concerns as premature—and worry less about artificial intelligence than about real stupidity. Be that as it may, it is likely that society will, within this century, be transformed by autonomous robots, even though the jury is out on whether they will still be “idiot savants” or will already display superhuman capabilities.

Back in the 1960s the British mathematician I. J. Good pointed out that superintelligent robots (if sufficiently versatile) could be the last invention that humans need ever make. Once machines had surpassed human capabilities, they could themselves design and assemble a new generation of even more intelligent ones, as well as an array of robotic fabricators that could transform the world physically.

Techno-evangelists like Ray Kurzweil (who now works at Google) predict that intelligent machines will “take over” within fifty years, triggering a global transformation—the so-called “singularity.” For this to happen, processing power is not enough: the computers would need sensors that enabled them to see and hear as well as we do, and the software to process and interpret what their sensors tell them. Kurzweil thinks that humans could transcend biology by merging with computers. In old-style spiritualist parlance, they would “go over to the other side.”

Few doubt that machines will gradually surpass more and more of our distinctively human capacities—or enhance our capabilities via cyborg technology. Disagreements are basically about the timescale: the rate of advance, not the direction of advance. Some think that there will be an “intelligence explosion” during this century. The cautious among us think these transformations may take centuries.

But a timespan of centuries is but an instant compared to the timescales of the Darwinian selection that led to humanity’s emergence. More relevantly, they are less than a millionth of the vast expanses of time lying ahead. So I think it is inevitable that the long-range future lies with machines.There are chemical and metabolic limits to the size and processing power of brains with the kind of “wet” hardware we have inside our skulls. Maybe we humans are close to these limits already. But there are no such constraints on electronic computers (still less, perhaps, on 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 is done by organic human-type brains will be utterly swamped by the cerebrations of AI. Moreover, the evolution toward ever-greater complexity will take place on a technological timescale—far faster than the slow Darwinian selection that has driven evolution on the Earth up till now.

This post-human intelligence will surely spread far beyond the Earth. So I turn next to the prospects for space technology. This is an arena where (despite human spaceflight) robots already have the dominant role.

THE FUTURE OF SPACE TECHNOLOGY

In the last two years we have seen ESA’s “Rosetta” spacecraft land a robot on a comet. And NASA’s “New Horizons” probe has beamed back amazing pictures from Pluto, 10,000 times further away than the Moon. These two instruments were designed and built fifteen years ago: they took five years to construct, and then ten years journeying to their remote targets. Think how much better we could do today.

I would venture a confident forecast that, during this century, the entire Solar System—planets, moons, and asteroids—will be explored and mapped by flotillas of tiny robotic craft. The next step would be space mining and fabrication. (And fabrication in space will be a better use of materials mined from asteroids than bringing them back to Earth.) Every man-made object in space has had to be launched from Earth. But later this century giant robotic fabricators will be able to assemble, in space, huge solar-energy collectors and huge computer networks. 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.

But what role will humans play? There is no denying that NASA’s “Curiosity,” 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 ever weaker with each advance in robots and miniaturization: indeed, as a scientist or practical man, I see little purpose in sending people into space at all. But, as a human being, I am an enthusiast for manned missions. And I am old enough to recall my excitement at the Apollo Program, and Neil Armstrong’s “one small step” on the Moon back in 1969. The last men on the Moon returned in 1972. Since then, hundreds of humans have been into space, but only into low orbit—circling the Earth only a few hundred kilometers about its surface, many in the hugely expensive (but uninspiring) International Space Station.

I hope some people now living will walk on Mars—as an adventure, and as a step toward the stars. They may be Chinese: China has the resources, the dirigiste government, and maybe the willingness to undertake an Apollo-style program. And China would need to aim at Mars, not just at the Moon, if it wanted to assert its superpower status by a “space spectacular”: a rerun of what the US achieved fifty years earlier would not proclaim parity.

Unless motivated by pure prestige and bankrolled by superpowers, manned missions beyond the Moon will need perforce to be cut-price ventures, accepting high risks—perhaps even “one-way tickets.” These missions will be privately funded; no Western governmental agency would expose civilians to such hazards. There would, despite the risks, be many volunteers—driven by the same motives as early explorers, mountaineers, and the like. Private companies already offer orbital flights. Wealthy adventurers are signing up for a week-long trip round the far side of the Moon—voyaging further from Earth than anyone has been before (but avoiding the greater challenge of a Moon landing and blast-off). I am told they have sold a ticket for the second flight but not for the first flight. And Denis Tito, a former astronaut and entrepreneur, may not be crazy in planning to send people to Mars and back—without landing. This would involve five hundred stressful days cooped up in a capsule. The ideal crew would be a stable middle-aged couple—old enough to be relaxed about a high dose of radiation. And there is another scheme that would allow you to land on Mars, but then to stay there—no return ticket.

We should surely acclaim these private-enterprise efforts in space—they can tolerate higher risks than a Western government could impose on publicly funded civilians, and thereby cut costs compared to NASA or ESA. But they should be promoted as adventures or extreme sports—the phrase “space tourism” should be avoided. It lulls people into unrealistic confidence.

By 2100 courageous pioneers in the mold of (say) Felix Baumgartner, who broke the sound barrier in free fall from a high-altitude balloon, may have established “bases” independent from the Earth—on Mars, or maybe on asteroids. Elon Musk himself (aged forty-four) says he wants to die on Mars—but not on impact. Development of self-sustaining communities remote from the Earth would also ensure that advanced life would survive, even if the worst conceivable catastrophe befell our planet.

But do not ever expect mass emigration from Earth. Nowhere in our Solar System offers an environment even as clement as the Antarctic or the top of Everest. It is a dangerous delusion to think that space offers an escape from Earth’s problems. There is no “Planet B.”

The Kepler satellite owes its name to Johannes Kepler. Its mission was to seek planets outside the Solar System. It was launched from Cape Canaveral on the morning of March 6, 2009. The mission concluded four years later, on August 15, 2013.

Indeed, Space is an inherently hostile environment for humans. For that reason, even though we may wish to regulate genetic and cyborg technology on Earth, we should surely wish the space pioneers good luck in using all such techniques to adapt to different atmospheres, different g-forces, and so on. This might be the first step toward divergence into a new species: the beginning of the post-human era.

Human exploration will be restricted to the planets and moons of our Solar System. This is because the transit time to other stars, using known technology, exceeds a human lifetime. And it will remain so even if futuristic forms of propulsion can be developed and deployed—involving nuclear power, matter-antimatter annihilation, or pressure from giant laser beams. Interstellar travel (except for unmanned probes, DNA samples, and so on) is therefore an enterprise for post-humans. They could be organic creatures (or cyborgs) who had won the battle with death, or perfected the techniques of hibernation or suspended animation. A journey lasting thousands of years is a doddle if you are near-immortal and not constrained to a human lifespan.

And machines of human intelligence could spread still further. Indeed, the Earth’s biosphere, in which organic life has symbiotically evolved, is not essential sustenance for advanced AI. Indeed it is far from optimal: interplanetary and interstellar space, a hostile environment for humans, will be the preferred arena where nonbiological “brains” may, in the far future, construct huge artifacts by mining moons and asteroids. And where these post-human intellects will develop insights as far beyond our imaginings as string theory is for a mouse.

These considerations have a transformational impact on our perception of Earth’s cosmic significance. Even if intelligent life were unique to the Earth, we need not conclude that life is a trivial irrelevance in a vast cosmos. It may seems so today, but in the billions of years lying ahead, post-human species or artifacts would have abundant time to spread through the entire Galaxy.

But are we unique, or is there intelligent life out there already?

DOES ALIEN LIFE EXIST AND HOW CAN WE FIND IT?

There may be simple organisms on Mars, or perhaps freeze-dried remnants of creatures that lived early in the planet’s history; and there could be life, too, swimming in the ice-covered oceans of Jupiter’s moon Europa, or Saturn’s moon Enceladus. But few would bet on it; and certainly nobody expects a complex biosphere in such locations. For that, we must look to the distant stars—far beyond the range of any probe we can now construct. And here the prospects are far brighter: we have recognized that there are, within our Milky Way Galaxy, millions—even billions—of planets resembling the young Earth.

In the last twenty years (and especially in the last five) the night sky has become far more interesting, and far more enticing to explorers, than it was to our forbears. Astronomers have discovered that many stars—perhaps even most—are orbited by retinues of planets, just like the Sun is. These planets are not detected directly. Instead, they reveal their presence by effects on their parent star that can be detected by precise measurements: small periodic motions in the star induced by an orbiting planet’s gravity, and slight recurrent dimmings in a star’s brightness when a planet transits in front of it, blocking out a small fraction of the star’s light.

NASA’s “Kepler” spacecraft monitored the brightness of 150,000 stars with high enough precision to detect transits of planets no bigger than the Earth. Some stars are known to be orbited by as many as seven planets, and it is already clear that planetary systems display a surprising variety: our own Solar System may be far from typical. In some systems, planets as big as Jupiter are orbiting so close to their star that their “year” lasts only a few days. Proxima Centauri, the nearest star, is orbited by a planet only a few times heavier than the Earth. This star is much fainter than our Sun. Consequently, even though the planet is orbiting so close that its “year” is only eleven days, it has a temperature such that liquid water could exist without boiling away. Some planets are on eccentric orbits. And there is one planet orbiting a binary star, which is itself orbited by another binary star: it would have four “suns” in its sky. But there is special interest in possible “twins” of our Earth—planets the same size as ours, orbiting other Sun-like stars, on orbits with temperatures such that water neither boils nor stays frozen. These exo-planets have been inferred indirectly, by detecting their effect on the brightness or motions of the stars they are orbiting around.

But we would really like to see these planets directly—not just their shadows. And that is hard. To realize just how hard, suppose an alien astronomer with a powerful telescope was viewing the Earth from (say) thirty light-years away—the distance of a nearby star. Our planet would seem, in Carl Sagan’s phrase, a “pale blue dot,” very close to a star (our Sun) that outshines it by many billions: a firefly next to a searchlight. But if the aliens could detect the Earth at all, they could learn quite a bit about it. The shade of blue would be slightly different, depending on whether the Pacific ocean or the Eurasian land mass was facing them. They could infer the length of the “day,” the seasons, whether there are oceans, the gross topography, and the climate. By analyzing the faint light, they could infer that the Earth had a biosphere.

Our present telescopes do not allow us to infer much about Earthlike planets (though they are able to resolve the light from “Jupiters” around nearby stars. But firmer cues will surely come, in the next decade, from the James Webb Space Telescope (a space telescope with a 6.5-meter-diameter mirror, due to be launched in 2018). Better still could be the next generation of giant ground-based telescopes. Within fifty years, the unimaginatively named E-ELT (“European Extremely Large Telescope”) being constructed on a mountain-top in Chile, with a mosaic mirror thirty-nine meters across, will be able to draw such inferences about planets the same size as our Earth, orbiting other Sun-like stars. (And there are two somewhat smaller US telescopes in gestation too.)

But do we expect alien life on these extra-solar planets? Many are “habitable,” but that does not mean that they are inhabited, even by the most primitive life forms, let alone by anything that we would deem “advanced” or “intelligent.” We do not know how life began on our planet—it is still a mystery what caused the transition from complex chemistry to the first replicating and metabolizing entities that would be deemed to be “alive.” This transition could have involved an incredibly rare fluke. On the other hand, something similar could have happened on many of these other “Earths.” The origin of life has long been realized to be one of the “Everest problems” of science. But until recently it has been deemed too challenging, and has not attracted many top-rate scientists. But that has now changed. I am hopeful that biochemists will offer clues within the next decade or two. We shall then know how likely life’s emergence was, and where best to look. And also whether there is something very special about the DNA/RNA basis of terrestrial life, or whether alien creatures could exist whose bodies and metabolism are based on very different chemistry.

In considering the possibilities of life elsewhere, we should surely, in our present state of ignorance, be open-minded about where it might emerge and what forms it could take. It is important not to dismiss the possibility of non-Earthlike life in non-Earthlike locations, But it plainly makes sense to start with what we know (the “searching under the street light” strategy) and to deploy all available techniques to discover whether any exo-planet atmospheres display evidence for a biosphere—or for any life at all.

Even if simple life is common, it is of course a separate question whether it is likely to evolve into anything we might recognize as intelligent—whether Darwin’s writ runs through the wider cosmos. Perhaps the cosmos teems with life; on the other hand, our Earth could be unique among the billions of planets that surely exist.

But if intelligence did emerge on some of these worlds, it could have had a head start if it emerged on a planet around a star older then the Sun, or it could have evolved faster than it did here. Consequently life elsewhere could have already achieved capabilities far exceeding our own.

Such thoughts have led to renewed interest in seeking evidence for “ET,” or extraterrestrial. Indeed a Russian investor, Yuri Milner, has committed 100 million dollars, over the next decade, to upgrading such searches. I would rate the chances of success as, at best, a few percent. But a detection would be so important—not just for science but for our perception of humanity’s place in the cosmos—that it is surely worth the gamble.

Conjectures about advanced or intelligent life are, of course, far more shaky than those about simple life. The firmest guesses that we can make are based on what has happened on Earth, and what might develop in the far future from Earth-based life.

It would plainly be a momentous discovery to detect any “signal” that was manifestly artificial: it would indicate that there are entities elsewhere in the cosmos manifesting evidence of intelligence and technology. If there were to be a detection, what might its originators be like? In popular culture, aliens are generally depicted as vaguely humanoid—generally bipedal, though maybe with tentacles, or eyes on stalks. Perhaps such creatures exist. But I would argue that they are not the kind of alien intelligence that we should be expecting.

The changing perspective on the future of life on Earth that I have described earlier in this chapter is highly relevant to any discussion of SETI (or Search for Extraterrestrial Intelligence) and suggests that we should expect something very different. The recent advances in computational power and robotics have led to growing interest in the possibility that artificial intelligence could in the coming decades achieve (and exceed) human capabilities over a wider range of conceptual and physical tasks. This is leading to a greater understanding of learning, thinking, and creativity and has stimulated debate on the nature of consciousness (is it an “emergent” property or something more special?). It has also led to some fascinating speculation by ethicists and philosophers on what forms of inorganic intelligence might be created by us.

Suppose that there are many other planets where life began; and suppose that on some of them Darwinian evolution followed a similar track to what happened here on Earth. Even then, it is 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—from single cell to multicellular organisms, for instance—have taken longer to negotiate there than here) then that planet would plainly reveal no evidence of ET. But life on some planets could have developed faster. Moreover, on a planet around a star older than the Sun, it could have had a head start of a billion years or more.

The history of human technological civilization is measured in centuries—and it may be only a few more centuries before humans are overtaken or transcended by inorganic intelligence. And—most importantly—this inorganic intelligence could then persist, continuing to evolve, for billions of years. Such considerations suggest that if we were to detect ET, we would be most unlikely to “catch” alien intelligence in the brief sliver of time when it was still in organic form. It is far more likely that it would have had a head start and would long ago have transitioned into electronic (and inorganic) forms.

So an ET signal, if we were to find it, would more likely come not from organic or biological life, not from an alien “civilization,” but from immensely intricate and powerful electronic brains. In particular, the habit of referring to “alien civilizations” may be too restrictive. A “civilization” connotes a society of individuals: in contrast, ET might be a single integrated intelligence. What does this mean for SETI searches? These are surely worthwhile, despite the heavy odds against success because the stakes are so high. That is why we should surely acclaim the launch of Yuri Milner’s “Breakthrough Listen” project, which will carry out the world’s deepest and broadest search for alien technological life using several of the world’s largest radio and optical telescopes. The project involves dedicating to the program twenty to twenty-five percent of the time on two of the world’s biggest steerable radio dishes: those at Green Bank, West Virginia, in the United States, and at Parkes in Australia. Hopefully other instruments such as the Arecibo Observatory (the huge dish carved in the ground in Puerto Rico) will join the quest. These telescopes will be used to search for non-natural radio transmissions from nearby and distant stars, from the plane of the Milky Way, from the Galactic Center and from nearby galaxies. They will seek narrow-band emission of a kind that could not arise from any natural cosmic source. They will search over a wide frequency range from 100 MHz to 50 GHz using advanced signal processing equipment developed by a team centered on UC Berkeley.

This project builds on a tradition of radio-astronomical SETI dating back fifty years. But of course there could be evidence in other wavebands. For instance, laser pulses would be a good way to communicate over interstellar distances. And very powerful laser beams offer a possible advanced technique for accelerating spacecraft to high speed. These would be even more conspicuous. And that is why the Breakthrough Listen project will use optical telescopes as well.

SETI searches seek electromagnetic transmissions—in any band—that are manifestly artificial. But even if the search succeeded (and few of us would bet more than one percent on this), it would still, in my view, be unlikely that the “signal” would be a decodable message, intentionally aimed at us. It would more likely be just a by-product (or even a malfunction) of some super-complex machine far beyond our comprehension that could trace its lineage back to alien organic beings. (These beings 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 signals were being intentionally 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 is scope for more compression, and more energy saving in the transmission. So we may fail to recognize a meaningful message even if it is detected.

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 cannot conceive. Others could be living contemplative lives—deep under some planetary ocean or floating freely in space—doing nothing to reveal their presence.

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, our Earth 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. Moreover, we would be living at a unique time in our planet’s history: our species would have cosmic significance, for being the transient precursor to a culture dominated by machines, extending deep into the future and spreading far beyond Earth. Even if we are now alone in the universe (which would be a disappointment, of course, for the SETI program) this would not mean that life would forever be a trivial “pollutant” of the cosmos, Our planet’s future would then be of cosmic importance, not “merely” a matter of concern for us humans.

The Breakthrough Listen project may not settle this momentous question. But it gives us a small chance of doing so—and the stakes are so high that even that small chance is worth far more than zero.

A MOTIVATION FOR INTERSTELLAR TRAVEL

As I have emphasized earlier, interstellar travel is inherently of long duration, and is, therefore, in my view, an enterprise for post-humans, evolved from our species not via natural selection but by design. 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. Even those of us who do not buy the idea of a singularity by mid-century would expect a sustained, if not enhanced, rate of innovation in biotech, nanotech, and information science—leading to entities with superhuman intellect within a few centuries. The first voyagers to the stars will not be human, and maybe not even organic. They will be creatures whose life cycle is matched to the voyage: the aeons involved in traversing the Galaxy are not daunting to immortal beings.

Before setting out from Earth the voyagers would know what to expect at journey’s end, and what destinations would be most promising. Such information will have come from studies using giant futuristic telescopes. Most importantly of all, they will know whether their destination is lifeless or inhabited, and robotic probes will have sought out already existing biospheres, or planets that could be terraformed to render them habitable.

It could happen, but would there be sufficient motive? Would even the most intrepid leave the Solar System? We cannot predict what inscrutable goals might drive post-humans. But the motive would surely be weaker if it turned out that biospheres were rare. The European explorers in earlier centuries who ventured across the Pacific were going into the unknown to a far greater extent than any future explorers would be (and facing more terrifying dangers): there were no precursor expeditions to make maps, as there surely would be for space ventures. Future space-farers would always be able to communicate with Earth (albeit with a time lag). If precursor probes have revealed that there are, indeed, wonders to explore, there will be a compelling motive—just as Captain Cook was motivated by the biodiversity and beauty of the Pacific islands. But if there is nothing but sterility out there, the motive will be simply expansionist—in resources and energy. And that might be better left to robotic fabricators.

And it might be too anthropocentric to limit attention to Earthlike planets. Science-fiction writers have other ideas—balloon-like creatures floating in the dense atmospheres of Jupiter-like planets, swarms of intelligent insects, nanoscale robots, and so on. Perhaps life can flourish even on a planet flung into the frozen darkness of interstellar space, whose main warmth comes from internal radioactivity (the process that heats the Earth’s core). And if advanced ET exists, it will most likely not be on a planet at all, but freely floating in interstellar space. Indeed, no life will survive on a planet whose central Sun-like star flares up when its hydrogen fuel is exhausted, and blows off its outer layers. Such considerations remind us of the transience of inhabited worlds (and life’s imperative to escape their bonds eventually).

Maybe we will one day find ET. On the other hand, SETI searches may fail; Earth’s intricate biosphere may be unique. But that would not render life a cosmic sideshow. Evolution is just beginning. Our Solar System is barely middle-aged and if humans avoid self-destruction, the post-human era beckons. Intelligent entities—descended from Earthly life—could spread through the entire Galaxy, evolving into a teeming complexity far beyond what we can even conceive. If so, our tiny planet—this pale blue dot floating in space—could be the most important place in the entire Galaxy, and the first interstellar voyagers from Earth would brave a mission that would resonate through the entire Galaxy and perhaps beyond.

“FAST-FORWARD” TO THE END OF TIME

In cosmological terms (or indeed in a Darwinian timeframe) a millennium is but an instant. So let us “fast-forward” not for a few centuries, nor even for a few millennia, but for an “astronomical” timescale millions of times longer than that. The “ecology” of stellar births and deaths in our Galaxy will proceed gradually more slowly, until jolted by the “environmental shock” of an impact with Andromeda, maybe four billion years hence. The debris of our Galaxy, Andromeda, and their smaller companions, which constitute the so-called Local Group, will thereafter aggregate into one amorphous galaxy.

As the universe expands the observable universe gets emptier and more lonely. Distant galaxies will not only move further away, but recede faster and faster until they disappear—rather as objects falling into a black hole encounter a horizon, beyond which they are lost from view and causal contact.

But the remnants of our Local Group could continue for far longer—time enough, perhaps, for all the atoms that were once in stars and gas to be transformed into structures as intricate as a living organism or a silicon chip but on a cosmic scale. But even these speculations are in a sense conservative. I have assumed that the universe itself will expand, at a rate that no future entities have power to alter. And that everything is in principle understandable as a manifestation of the basic laws governing particles, space and time that have been disclosed by twenty-first-century science. Some speculative scientists envisage stellar-scale engineering to create black holes and wormholes—concepts far beyond any technological capability that we can envisage, but not in violation of these basic physical laws. But are there new “laws” awaiting discovery? And will the present “laws” be immutable, even to an intelligence able to draw on galactic-scale resources? We are well aware that our knowledge of space and time is incomplete. Einstein’s relativity and the quantum principle are the two pillars of twentieth-century physics, but a theory that unifies them is unfinished business for twenty-first-century physicists. Current ideas suggest that there are mysteries even in what might seem the simplest entity of all—“mere” empty space. Space may have a rich structure, but on scales a trillion trillion times smaller than an atom. According to the string theory, each “point” in our ordinary space, if viewed with this magnification, would be revealed as a tightly wound origami in several extra dimensions. Such a theory will perhaps tell us why empty space can exert the “push” that causes the cosmic expansion to accelerate; and whether that “push” will indeed continue forever or could be reversed. It will also allow us to model the very beginning—an epoch where densities are so extreme that quantum fluctuations can shake the entire universe—and learn whether our big bang was the only one.

The same fundamental laws apply throughout the entire domain we can survey with our telescopes. Atoms in the most distant observable galaxies seem, from spectral evidence, identical to atoms studied in laboratories on Earth. But what we have traditionally called “the universe”—the aftermath of “our” big bang—may be just one island, just one patch of space of time, in a perhaps infinite archipelago. There may have been an infinity of big bangs, not just one. Each constituent of this “multiverse” cooled down differently, ending up governed by different laws. Just as Earth is a very special planet among zillions of others, so—on a far grander scale—our big bang was also a very special one. In this hugely expanded cosmic perspective, the laws of Einstein and the quantum could be mere parochial bylaws governing our cosmic patch. Space and time may have a structure as intricate as the fauna of a rich ecosystem, but on a scale far larger than the horizon of our observations. Our current concept of physical reality could be as constricted, in relation to the whole, as the perspective of the Earth available to a plankton whose “universe” is a spoonful of water.

And that is not all: there is a final disconcerting twist. Post-human intelligence (whether in organic form, or in autonomously evolving artifacts) will develop hyper-computers with the processing power to simulate living things—even entire worlds. Perhaps advanced beings could thereby surpass the best “special effects” in movies or computer games so vastly that they could simulate a universe fully as complex as the one we perceive ourselves to be in. Maybe these kinds of superintelligences already exist elsewhere in the multiverse—in universes that are older than ours, or better tuned for the evolution of intelligence. What would these superintelligences do with their hyper-computers? They could create virtual universes vastly outnumbering the “real” ones. So perhaps we are “artificial life” in a virtual universe. This concept opens up the possibility of a new kind of “virtual time travel,” because the advanced beings creating the simulation can, in effect, rerun the past. It is not a time-loop in a traditional sense: it is a reconstruction of the past, allowing advanced beings to explore their history.

Possibilities once in the realms of science fiction have shifted into serious scientific debate. From the very first moments of the big bang to the mind-blowing possibilities for alien life, parallel universes, and beyond, scientists are led to worlds even weirder than most fiction writers envisage. We have intimations of deeper links between life, consciousness, and physical reality. It is remarkable that our brains, which have changed little since our ancestors roamed the African savannah, have allowed us to understand the counter-intuitive 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 at sometime “hit the buffers.” Some of these insights may have to await post-human intelligence. There may be phenomena, crucial to life’s long-term destiny, that we are not aware of, any more than a monkey comprehends the nature of stars and galaxies.

If our remote descendants reach the stars, they will surely far surpass us not only in lifespan, but in insight as well as technology.

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