On the Future

3

HUMANITY IN A COSMIC PERSPECTIVE

3.1. THE EARTH IN A COSMIC CONTEXT

In 1968, the Apollo 8 astronaut Bill Anders photographed ‘Earthrise’, showing the distant Earth, shining above the lunar horizon. He didn’t realise that it would become an iconic image for the global environmental movement. It revealed Earth’s delicate biosphere, contrasted with the sterile moonscape where Neil Armstrong, one year later, took his ‘one small step’. Another famous image was taken in 1990 by the probe Voyager 1 from a distance of six billion kilometres. The Earth appeared as a ‘pale blue dot’, which inspired Carl Sagan’s thoughts:1

Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.… Every saint and sinner in the history of our species lived there—on a mote of dust suspended in a sunbeam.

Our planet is a lonely speck in the great enveloping cosmic dark. There is no hint that help will come from elsewhere to save us from ourselves—The Earth is the only world known so far to harbor life. Like it or not, for the moment the Earth is where we make our stand.

These sentiments resonate today; indeed, there is serious discussion about how cosmic exploration far beyond the solar system, by machines if not by humans, could become reality—albeit in the remote future. (Voyager 1 is now, after more than forty years, still in the outskirts of the solar system. It will take it tens of thousands of years to reach the nearest star.)

We’ve been aware since Darwin of the Earth’s long history. He concludes On the Origin of Species with these familiar words: ‘Whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved’. We now speculate about equally long time spans stretching into the future, and these will be the themes of this chapter.

Darwin’s ‘simple beginning’—the young Earth—is complex in its chemistry and structure. Astronomers aim to probe still further back than Darwin and the geologists were able to—to the origin of planets, stars, and their constituent atoms.

Our entire solar system condensed from a swirling disc of dusty gas about 4.5 billion years ago. But where did the atoms come from—why are oxygen and iron atoms common, but not gold atoms? Darwin would not have fully understood this question; in his time, the very existence of atoms was controversial. But we now know that not only do we share a common origin, and many genes, with the entire web of life on Earth, but we also are linked to the cosmos. The Sun and stars are nuclear fusion reactors. They derive their power by fusing hydrogen into helium, and then helium into carbon, oxygen, phosphorus, and iron, and other elements in the periodic table. When stars end their lives, they expel ‘processed’ material back into interstellar space (via supernova explosions in the case of heavy stars). Some material is then recycled into new stars. The Sun was one such star.

A typical carbon atom, in one of the trillions of CO2 molecules that we inhale with each breath, has an eventful history stretching back more than five billion years. The atom was perhaps released into the atmosphere when a lump of coal was burned—a lump that was itself the remnant of a tree in a primeval forest two hundred million years ago—and before that had been cycled between the Earth’s crust, biosphere, and oceans ever since our planet’s formation. Tracing back further we would find that the atom was forged in an ancient star that exploded, ejecting carbon atoms that wandered in interstellar space, condensing into a proto–solar system and thence into the young Earth. We are literally the ashes of long-dead stars—or (less romantically) the nuclear waste from the fuel that made stars shine.

Astronomy is an ancient science—perhaps the oldest apart from medicine (and I’d argue the first to do more good than harm—by improving the calendar, timekeeping, and navigation). And for the last few decades cosmic exploration has been on a roll. There are human footprints on the Moon. Robotic probes to other planets have beamed back pictures of fascinating and varied worlds—and landed on some of them. Modern telescopes have enlarged our cosmic horizons. And these telescopes have revealed a ‘zoo’ of extraordinary objects—black holes, neutron stars, and colossal explosions. Our Sun is embedded within our galaxy, the Milky Way, which contains more than a hundred billion stars, all orbiting around a central hub where lurks a massive black hole. And this is just one of one hundred billion galaxies visible through the telescopes. We’ve even detected ‘echoes’ of the ‘big bang’ that triggered our entire expanding universe 13.8 billion years ago. This is how the universe was born—and with it, all the basic particles of nature.

Armchair theorists like myself can claim little credit for this progress; it is owed mainly to improvements in telescopes, spacecraft, and computers. Thanks to these advances we’re starting to understand the chain of events whereby, from a mysterious beginning when everything was squeezed to immense temperatures and densities, atoms, stars, galaxies, and planets emerged—and how on one planet, Earth, atoms assembled into the first living things, initiating the Darwinian evolution that’s led to creatures like us, able to ponder the mystery of it all.

Science is a truly global culture—spanning all boundaries of nationality and faith. That’s especially true of astronomy. The night sky is the most universal feature of our environment. Throughout human history, people all over the world have gazed at the stars—interpreting them in different ways. Just within the last decade the night sky has become vastly more interesting than it was to our ancestors. We’ve learned that most stars aren’t just twinkling points of light but are orbited by planets, just as the Sun is. Amazingly, our galaxy harbours many millions of planets like the Earth—planets that seem habitable. But are they actually inhabited—is there life, even intelligent life, out there? It’s hard to imagine a question of greater importance for understanding our place in the cosmic scheme of things.

It is clear from the extensive media coverage that these issues fascinate millions. It’s gratifying to astronomers (and to those in fields like ecology) that their fields attract such broad popular interest. I’d derive far less satisfaction from my research if I could only discuss it with a few fellow specialists. Moreover, the subject has a positive and nonthreatening image—in contrast to the public ambivalence about, for instance, nuclear science, robotics, or genetics.

If I’m on a plane and don’t want to chat with the person in the next seat, a sure conversation stopper is to say ‘I’m a mathematician’. In contrast, saying ‘I’m an astronomer’ often stimulates interest. And the number one inquiry is then usually ‘do you believe in aliens, or are we alone?’ The topic fascinates me too, so I’m always glad to discuss it. And it has another virtue as a conversation starter. Nobody yet knows the answer, so there is less of a barrier between the ‘expert’ and the general inquirer. There’s nothing new about this fascination; but now, for the first time, we have hope of an answer.

Speculations on ‘the plurality of inhabited worlds’ date back to antiquity. From the seventeenth to the nineteenth century, it was widely suspected that the other planets of the solar system were inhabited. The reasoning was more often theological than scientific. Eminent nineteenth-century thinkers argued that life must pervade the cosmos, because otherwise such vast domains of space would seem such a waste of the Creator’s efforts. An amusing critique of such ideas is given in the impressive book Man’s Place in the Universe by Alfred Russel Wallace, the codeveloper of the theory of natural selection.2 Wallace is especially scathing about the physicist David Brewster (remembered by physicists for the ‘Brewster angle’ in optics), who conjectured on such grounds that even the Moon must be inhabited. Brewster argued in his book More Worlds Than One that had the Moon ‘been destined to be merely a lamp to our Earth, there was no occasion to variegate its surface with lofty mountains and extinct volcanoes and cover it with large patches of matter that reflect different quantities of light and give its surface the appearance of continents and seas. It would have been a better lamp had it been a smooth piece of lime or of chalk’.

By the end of the nineteenth century, many astronomers were so convinced that life existed on other planets in the solar system that a prize of one hundred thousand francs was offered to the first person to make contact. And the prize specifically excluded contact with Martians—that was considered far too easy! The erroneous claim that Mars was crisscrossed by canals had been taken as proof positive of intelligent life on the red planet.

The space age brought sobering news. Venus, a cloudy planet that promised a lush tropical swamp-world, turned out to be a crushing, caustic hellhole. Mercury was a pockmarked blistering rock. Even Mars, the most Earthlike planet, is now revealed as a frigid desert with a very thin atmosphere. NASA’s Curiosity probe may, however, have found water. And it detected methane gas burping from below the surface—perhaps from rotting organisms that lived long ago—though there seems no interesting life there now.

In the still-colder objects farther from the Sun, the smart money would be on Europa, one of Jupiter’s moons, and Enceladus, a moon of Saturn. These are covered in ice, and there could be creatures swimming in the oceans beneath; space probes are being planned that will search for them. And there could be exotic life in the methane lakes of Titan, another of Saturn’s moons. But nobody can be optimistic.

Within the solar system, Earth is the Goldilocks planet—not too hot and not too cold. Were it too hot, even the most tenacious life would fry. But if it were too cold, the processes that created and nourished life would have happened far too slowly. The discovery of even vestigial life-forms elsewhere in the solar system would be of epochal importance. That’s because it would tell us that life wasn’t a rare fluke but was widespread in the cosmos. At the moment we know of only one place—Earth—where life began. It is logically possible (indeed, some argue that it’s plausible) that life’s origin requires such special contingencies that it only happened once in our entire galaxy. But if it arose twice within a single planetary system, then it must be common.

(There is one important proviso: before drawing this inference about life’s ubiquity we must be sure that two life-forms emerged independently rather than being transported from one location to another. For that reason, life under Europa’s ice would clinch the case more than life on Mars, because it’s conceivable that we all have Martian ancestry—having evolved from primitive life carried on a rock shot off Mars by an asteroid impact and propelled towards Earth.)

3.2. BEYOND OUR SOLAR SYSTEM

To find promising ‘real estate’ on which life can exist, we must extend our gaze beyond our solar system—beyond the reach of any probe we can devise today. What has transformed and energised the whole field of exobiology is the realisation that most stars are orbited by planets. The Italian monk Giordano Bruno speculated about this in the sixteenth century. From the 1940s onward, astronomers suspected he was correct. An earlier theory that the solar system formed from a filament torn out of the Sun by the gravitational pull of a close-passing star (which would have implied that planetary systems were rare) had by then been discredited. This theory was superseded by the idea that when an interstellar cloud contracted under gravity to form a star, it would, if it were rotating, ‘spin off’ a disc whose constituent gas and dust would agglomerate into planets. But it wasn’t until the 1990s that evidence for exoplanets started to emerge. Most exoplanets are not detected directly; they are inferred through careful observation of the star they’re orbiting. There are two main techniques.

The first is this. If a star is orbited by a planet, then both planet and star move around their centre of mass—what’s called the barycentre. The star, being more massive, moves slower. But the cyclic motion induced by an orbiting planet can be detected by precise study of the starlight, which reveals a changing Doppler effect. The first success came in 1995 when Michel Mayor and Didier Queloz, based at the Observatory of Geneva, found a ‘Jupiter-mass’ planet around the nearby star 51 Pegasi.3 In the subsequent years, more than four hundred exoplanets have been found in this way. This ‘stellar wobble’ technique pertains mainly to ‘giant’ planets—objects the size of Saturn or Jupiter.

Possible ‘twins’ of Earth are specially interesting: planets the same size as ours, orbiting other Sun-like stars, on orbits with temperatures such that water neither boils nor stays frozen. But detecting these—hundreds of times less massive than Jupiter—is a real challenge. They induce wobbles of merely centimetres per second in their parent star—this motion has hitherto been too small for the Doppler method to detect (though the instrumentation advances apace).

But there’s a second technique: we can look for the planets’ shadows. A star would appear to dim slightly when a planet was ‘in transit’ in front of it; these dimmings would repeat at regular intervals. Such data reveal two things: the interval between successive dimmings tells us the length of the planet’s year, and the amplitude of the dimming tells us what fraction of the star’s light a planet blocks out during the transit, and therefore how big it is.

The most important search (so far) for transiting planets was carried out by a NASA spacecraft named after astronomer Johannes Kepler,4 which spent more than three years measuring the brightness of 150,000 stars, to a precision of one part in 100,000—it did this once or more times an hour for each star. Kepler found thousands of transiting planets, some no bigger than Earth. The prime mover behind the Kepler project was Bill Borucki, an American engineer who had worked for NASA since 1964. He conceived the concept in the 1980s and doggedly pursued it despite funding setbacks and initial scepticism from many in the community of ‘established’ astronomers. His triumphant success—achieved when he was already in his seventies—deserves special acclaim. It reminds us of how much even the ‘purest’ science owes to the instrument builders.

There is variety among the already discovered exoplanets. Some are on eccentric orbits. And one planet has four suns in its sky; it is orbiting a binary star, which is orbited by another binary star. This discovery involved amateur ‘planet hunters’; any enthusiast had the chance to access Kepler data from some stars, and the human eye was able to pick out ‘dips’ in the stars’ brightness (which occurred less regularly than in the case when a planet orbits a single star).

There’s a planet orbiting the nearest star, Proxima Centauri, which is only four light years from Earth. Proxima Centauri is a so-called M dwarf star, about a hundred times fainter than our Sun. In 2017 a team led by the Belgian astronomer Michaël Gillon discovered a miniature solar system around another M dwarf;5 seven planets, with ‘years’ lasting from 1.5 to 18.8 Earth days, are orbiting around it. The outer three are in the habitable zone. They’d be spectacular places to live. Viewed from the surface of one of the planets, the others would swing fast across the sky, looming as large as our Moon does to us. But they’re very un-Earthly. They’re probably tidally locked so that they present the same face to their star—one hemisphere in perpetual light; the other always dark. (In the unlikely event that it harboured intelligent life, a kind of ‘segregation’ might prevail—the astronomers quarantined in one hemisphere, everyone else in the other!) But it’s likely that their atmospheres have been stripped away by the intense magnetic flaring that is common on M dwarf stars, rendering them less propitious for life.

The known exoplanets are nearly all inferred indirectly, by detecting their effect on the motions or brightness of the stars they’re orbiting. We’d really like to see them directly but that’s hard. To realise just how hard, suppose that aliens existed, and that 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. The shade of blue would be slightly different, depending on whether the Pacific Ocean or the Eurasian land mass was facing them. The alien astronomers could infer the length of our day, the seasons, the existence of continents and oceans, and the climate. By analysing the faint light, the astronomers could infer that the Earth had a green surface and an oxygenated atmosphere.

Today, the largest terrestrial telescopes are built by international consortia. They are mushrooming on Mauna Kea (Hawai‘i) and under the clear dry skies of the high Andes in Chile. And South Africa not only has one of the world’s largest optical telescopes but will also have a leadership role, along with Australia, in constructing the world’s largest radio telescope, the Square Kilometre Array. A telescope now being built on a Chilean mountaintop by European astronomers will have the required sensitivity to pick up light from planets the same size as Earth orbiting other sun-like stars. It’s called the European Extremely Large Telescope (E-ELT)—literal rather than imaginative nomenclature! Newton’s first reflecting telescope had a 10-centimeter-diameter mirror; the E-ELT will be 39 meters—a mosaic of small mirrors with a total collecting area more than a hundred thousand times larger.

From the statistics of planets around the nearby stars studied so far, we can infer that the entire Milky Way harbours around a billion planets that are ‘Earthlike’ in the sense that they are about the size of Earth and at a distance from their parent star such that water can exist, neither boiling away nor staying permanently frozen. We’d expect a variety: some might be ‘waterworlds’, completely covered with oceans; others might (like Venus) have been heated and sterilised by an extreme ‘greenhouse effect’.

How many of these planets might harbour life-forms far more interesting and exotic than anything we might find on Mars—even something that could be called intelligent? We don’t know what the odds are. Indeed, we can’t yet exclude the possibility that life’s origin—the emergence, from a chemical ‘mix’, of a metabolising and reproducing entity—involved a fluke so rare that it happened only once in our entire galaxy. On the other hand, this crucial transition might have been almost inevitable given the ‘right’ environment. We just don’t know—nor do we know if the DNA/RNA chemistry of terrestrial life is the only possibility, or just one chemical basis among many options that could be realised elsewhere. Nor, even more fundamentally, do we know whether liquid water really is crucial. If there were a chemical path whereby life could emerge in the cold methane lakes of Titan, our definition of ‘habitable planets’ would be very much broader.

These key issues may soon be clarified. The origin of life is now attracting stronger interest; it’s no longer deemed to be one of those ultrachallenging problems (consciousness, for instance, is still in this category) which, though manifestly important, don’t seem timely or tractable—and are relegated to the ‘too difficult’ box. Understanding life’s beginnings is important not only for assessing the likelihood of alien life but also because life’s emergence on Earth is still a mystery.

We should be open-minded about where in the cosmos life might emerge and what forms it could take—and devote some thought to non-Earthlike life in non-Earthlike locations. Even here on Earth, life survives in the most inhospitable places—in black caves where sunlight has been blocked for thousands of years, inside arid desert rocks, deep underground, and around hot vents in the deepest ocean bed. But it makes sense to start with what we know (the ‘searching under the streetlight’ strategy) and to deploy all available techniques to discover whether any Earthlike exoplanet atmospheres display evidence for a biosphere. Clues should come, in the next decade or two, from the deep space James Webb Space Telescope and from the E-ELT and similar giant telescopes on the ground that will come on line in the 2020s.

Even these next-generation telescopes will have a hard job separating out the spectrum of the planet’s atmosphere from the spectrum of the brighter central star. But, looking beyond midcentury, one can imagine an array of vast space telescopes, each with gossamer-thin kilometre-scale mirrors, being assembled in deep space by robotic fabricators. By 2068, the centenary of the Apollo 8 ‘Earthrise’ photo, such an instrument could give us an even more inspirational image: another Earth orbiting a distant star.

3.3. SPACEFLIGHT—MANNED AND UNMANNED

Among my favourite things to read during my childhood (in England, way back in the 1950s), was a comic called the Eagle, especially the adventures of ‘Dan Dare—Pilot of the Future’—where the brilliant artwork depicted orbiting cities, jet packs, and alien invaders. When spaceflight became real, the suits worn by NASA astronauts (and their Soviet ‘cosmonaut’ counterparts) were therefore familiar, as were the routines of launching, docking, and so forth. My generation avidly followed the succession of heroic pioneering exploits: Yuri Gagarin’s first orbital flight, Alexey Leonov’s first space walk, and then, of course, the lunar landings. I recall a visit to my home town by John Glenn, the first American to go into orbit. He was asked what he was thinking while in the rocket’s nose cone, awaiting launch. He responded, ‘I was thinking that there were twenty thousand parts in this rocket, and each was made by the lowest bidder’. (Glenn later became a US senator, and, later still, the oldest astronaut when, at age seventy-seven, he became part of the STS-95 Space Shuttle crew.)

Only twelve years elapsed between the flight of the Soviet Sputnik 1—the first artificial object to go into orbit—and the historic ‘one small step’ on the lunar surface in 1969. I never look at the Moon without being reminded of Neil Armstrong and Buzz Aldrin. Their exploits seem even more heroic in retrospect, when we realise how they depended on primitive computing and untested equipment. Indeed, President Nixon’s speechwriter William Safire had drafted a eulogy to be given if the astronauts had crash-landed on the Moon or were stranded there:

Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace. [They] know that there is no hope for their recovery. But they also know that there is hope for mankind in their sacrifice.

The Apollo programme remains, a half century later, the high point of human ventures into space. It was a ‘space race’ against the Russians—a contest in superpower rivalry. Had that momentum been maintained, there would surely be footprints on Mars by now; that’s what our generation expected. However, once that race was won, there was no motivation for continuing the requisite expenditure. In the 1960s, NASA absorbed more than 4 percent of the US federal budget. The current figure is 0.6 percent. Today’s young people know Americans landed men on the Moon. They know the Egyptians built pyramids. But these enterprises seem like ancient history, motivated by almost equally bizarre national goals.

Hundreds more have ventured into space in the ensuing decades—but, anticlimactically, they have done no more than circle the Earth in low orbit. The International Space Station (ISS) was probably the most expensive artefact ever constructed. Its cost, plus that of the shuttles whose main purpose was to service it (though they have now been decommissioned) ran well into twelve figures. The scientific and technical payoff from the ISS hasn’t been negligible, but it has been less cost effective than unmanned missions. Nor are these voyages inspiring in the way that the pioneering Russian and US space exploits were. The ISS only makes news when something goes wrong: when the loo fails, for instance; or when astronauts perform ‘stunts’, such as the Canadian Chris Hadfield’s guitar playing and singing.

The hiatus in manned space exploration exemplifies that when there’s no economic or political demand, what is actually done is far less than what could be achieved. (Supersonic flight is another example—the Concorde airliner went the way of the dinosaurs. In contrast, the spin-offs from IT have advanced, and spread globally, far faster than forecasters and management gurus predicted.)

Space technology has nonetheless burgeoned in the last four decades. We depend routinely on orbiting satellites for communication, satnav, environmental monitoring, surveillance, and weather forecasting. These services mainly use spacecraft that, though unmanned, are expensive and elaborate. But there is a growing market for relatively inexpensive miniaturised satellites, the demand for which several private companies are aiming to meet.

The San Francisco–based company PlanetLab has developed and launched swarms of shoebox-sized spacecraft with the collective mission of giving repeated imaging and global coverage, albeit at not-specially-sharp resolution (3–5 metres): the mantra (with only slight exaggeration) is to observe every tree in the world every day. Eighty-eight of the craft were launched in 2017 as payload on a single Indian rocket; Russian and US rockets have been used to launch more, as well as a fleet of somewhat larger and more elaborately equipped SkySats (each weighing 100 kilograms). For much sharper resolution, a larger satellite with more elaborate optics is needed, but there is nonetheless a commercial market for the data from these tiny ‘cubesats’ to monitor crops, construction sites, fishing boats, and suchlike; they are also useful for planning a response to disasters. Even smaller wafer-thin satellites can now be deployed—exploiting the technology that has emerged from the colossal investment in consumer microelectronics.

Telescopes in space offer astronomy a huge boost. Orbiting far above the blurring and absorptive effects of Earth’s atmosphere, they have beamed back sharp images from the remotest parts of the cosmos. They have surveyed the sky in infrared, UV, X-ray, and gamma ray bands that don’t penetrate the atmosphere and therefore can’t be observed from the ground. They have revealed evidence for black holes and other exotica and have probed with high precision the ‘afterglow of creation’—the microwaves pervading all space whose properties hold clues to the very beginning, when the entire observable cosmos was squeezed to microscopic size.

Of more immediate public appeal are the findings from spacecraft that have journeyed to all the planets of the solar system. NASA’s New Horizons beamed back amazing pictures from Pluto, ten thousand times farther away than the Moon. And the European Space Agency’s Rosetta landed a robot on a comet. These spacecraft took five years to design and build and then nearly ten years journeying to their remote targets. The Cassini probe spent thirteen years studying Saturn and its moons and was even more venerable; more than twenty years elapsed between its launch and its final plunge into Saturn in late 2017. It is not hard to envisage how much more sophisticated today’s follow-ups to these missions could be.

During this century, the entire solar system—planets, moons, and asteroids—will be explored and mapped by fleets of tiny robotic space probes, interacting with each other like a flock of birds. Giant robotic fabricators will be able to construct, in space, solar energy collectors and other objects. The Hubble telescope’s successors, with oversize mirrors assembled in zero gravity, will further expand our vision of exoplanets, stars, galaxies, and the wider cosmos. The next step would be space mining and fabrication.

But will there be a role for humans? There’s no denying that NASA’s Curiosity, a vehicle the size of a small car that has since 2011 been trundling across a giant Martian crater, may miss startling discoveries that no human geologist could overlook. But machine learning is advancing fast, as is sensor technology. In contrast, the cost gap between manned and unmanned missions remains outsized. The practical case for manned spaceflight gets ever weaker with each advance in robots and miniaturisation.

If there were a revival of the ‘Apollo spirit’ and a renewed urge to build on its legacy, a permanently manned lunar base would be a credible next step. Its construction could be accomplished by robots—bringing supplies from Earth and mining some from the Moon. An especially propitious site is the Shackleton crater, at the lunar south pole, 21 kilometres across and with a rim 4 kilometres high. Because of the crater’s location, its rim is always in sunlight and so escapes the extreme monthly temperature contrasts experienced on almost all the Moon’s surface. Moreover, there may be a lot of ice in the crater’s perpetually dark interior—crucial, of course, for sustaining a ‘colony’.

It would make sense to build mainly on the half of the Moon that faces the Earth. But there is one exception: astronomers would like a giant telescope on the far side because it would then be shielded from the artificial emission from the Earth—offering a great advantage to radio astronomers seeking to detect very faint cosmic emissions.

NASA’s manned space programme, ever since Apollo, has been constrained by public and political pressure to be risk-averse. The space shuttle failed twice in 135 launches. Astronauts or test pilots would willingly accept this level of risk—less than 2 percent. But the shuttle had, unwisely, been promoted as a safe vehicle for civilians (and a female schoolteacher, Christa McAuliffe, in the NASA Teacher in Space Project, was one of the casualties of the Challenger disaster). Each failure caused a national trauma in the United States and was followed by a hiatus while costly efforts were made (with very limited effect) to reduce risks still further.

I hope some people now living will walk on Mars—as an adventure, and as a step towards the stars. But NASA will confront political obstacles in achieving this goal within a feasible budget. China has the resources, the dirigiste government, and maybe the willingness to undertake an Apollo-style programme. If it wanted to assert its superpower status by a ‘space spectacular’ and to proclaim parity, China would need to leapfrog, rather than just rerun, what the United States had achieved fifty years earlier. It already plans a ‘first’ by landing on the far side of the Moon. A clearer-cut ‘great leap forward’ would involve footprints on Mars, not just on the Moon.

Leaving aside the Chinese, I think the future of manned spaceflight lies with privately funded adventurers, prepared to participate in a cut-price programme far riskier than western nations could impose on publicly supported civilians. SpaceX, led by Elon Musk (who also builds Tesla electric cars), or the rival effort, Blue Origin, bankrolled by Jeff Bezos, founder of Amazon, have berthed craft at the space station and will soon offer orbital flights to paying customers. These ventures—bringing a Silicon Valley culture into a domain long dominated by NASA and a few aerospace conglomerates—have shown it’s possible to recover and reuse the launch rocket’s first stage—presaging real cost savings. They have innovated and improved rocketry far faster than NASA or ESA has done—a SpaceX Falcon rocket is able to put a fifty-ton payload into orbit. The future role of the national agencies will be attenuated—becoming more akin to an airport than to an airline.

If I were an American, I would not support NASA’s manned programme—I would argue that inspirationally led private companies should ‘front’ all manned missions as cut-price high-risk ventures. There would still be many volunteers—some perhaps even accepting ‘one-way tickets’—driven by the same motives as early explorers, mountaineers, and the like. Indeed, it is time to eschew the mind-set that space ventures should be national (even international) projects—along with pretentious rhetoric where the word ‘we’ is used to denote the whole of humanity. There are some endeavours—tackling climate change, for instance—that can’t be done without concerted international action. The exploitation of space need not be of this nature; it may need some public regulation, but the impetus can be private or corporate.

There are plans for week-long trips round the far side of the Moon—voyaging farther from Earth than anyone has gone before (but avoiding the greater challenge of a Moon landing and blast-off). A ticket has been sold (I’m told) for the second such flight but not the first. And Dennis Tito, an entrepreneur and former astronaut, has proposed, when a new heavy-lift launcher is available, to send people to Mars and back—without landing. This would require five hundred days in isolated confinement. The ideal crew would be a stable middle-aged couple—old enough to not be bothered about the high dose of radiation accumulated on the trip.

The phrase space tourism should be avoided. It lulls people into believing that such ventures are routine and low risk. And if that’s the perception, the inevitable accidents will be as traumatic as those of the space shuttle. These exploits must be ‘sold’ as dangerous sports, or intrepid exploration.

The most crucial impediment to space flight, in Earth’s orbit and for those venturing farther, stems from the intrinsic inefficiency of chemical fuel and the consequent requirement for launchers to carry a weight of fuel far exceeding that of the payload. So long as we are dependent on chemical fuels, interplanetary travel will remain a challenge. Nuclear power could be transformative. By allowing much higher in-course speeds, it would drastically cut the transit times to Mars or the asteroids (reducing not only astronauts’ boredom but also their exposure to damaging radiation).

Greater efficiency would be achieved if the fuel supply could be on the ground and not carried into space. For instance, it might be technically possible to propel spacecraft into orbit via a ‘space elevator’—a carbon-fibre rope 30,000 kilometres long anchored to the Earth (and powered from the ground), extending vertically up beyond the distance of a geostationary orbit so that it is held taut by centrifugal forces. An alternative scheme envisages a powerful laser beam generated on Earth that pushes on a ‘sail’ attached to the spacecraft; this might be feasible for lightweight space probes and could in principle accelerate them to 20 percent of the speed of light.6

Incidentally, more efficient on-board fuel could transform manned spaceflight from a high-precision to an almost unskilled operation. Driving a car would be a difficult enterprise if, as at present for space voyages, one had to programme the entire journey in detail beforehand, with minimal opportunities for steering along the way. If there were an abundance of fuel for midcourse corrections (and to brake and accelerate at will), then interplanetary navigation would be a low-skill task—simpler, even, than steering a car or ship, in that the destination is always in clear view.

By 2100 thrill seekers in the mould of (say) Felix Baumgartner (the Austrian skydiver who in 2012 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 (born in 1971) of SpaceX says he wants to die on Mars—but not on impact. But don’t ever expect mass emigration from Earth. And here I disagree strongly with Musk and with my late Cambridge colleague Stephen Hawking, who enthuse about rapid build-up of large-scale Martian communities. It’s a dangerous delusion to think that space offers an escape from Earth’s problems. We’ve got to solve these problems here. Coping with climate change may seem daunting, but it’s a doddle compared to terraforming Mars. No place in our solar system offers an environment even as clement as the Antarctic or the top of Everest. There’s no ‘Planet B’ for ordinary risk-averse people.

But we (and our progeny here on Earth) should cheer on the brave space adventurers, because they will have a pivotal role in spearheading the posthuman future and determining what happens in the twenty-second century and beyond.

3.4. TOWARDS A POST-HUMAN ERA?

Why will these space adventurers be so important? The space environment is inherently hostile for humans. So, because they will be ill-adapted to their new habitat, the pioneer explorers will have a more compelling incentive than those of us on Earth to redesign themselves. They’ll harness the super-powerful genetic and cyborg technologies that will be developed in coming decades. These techniques will be, one hopes, heavily regulated on Earth, on prudential and ethical grounds, but ‘settlers’ on Mars will be far beyond the clutches of the regulators. We should wish them good luck in modifying their progeny to adapt to alien environments. This might be the first step towards divergence into a new species. Genetic modification would be supplemented by cyborg technology—indeed there may be a transition to fully inorganic intelligences. So, it’s these space-faring adventurers, not those of us comfortably adapted to life on Earth, who will spearhead the posthuman era.

Before setting out from Earth, space voyagers, whatever their destination, would know what to expect at journey’s end; robotic probes would have preceded them. The European explorers in earlier centuries who ventured across the Pacific went into the unknown to a far greater extent than any future explorers would (and faced more terrifying dangers)—there were no precursor expeditions to make maps, as there would be for space ventures. Future space-farers will always be able to communicate with Earth (albeit with a time lag). If precursor probes have revealed that there are wonders to explore, there will be a compelling motive—just as Captain Cook was incentivised by the biodiversity and beauties of the Pacific islands. But if there is nothing but sterility out there, the voyages might be better left to robotic fabricators.

Organic creatures need a planetary surface environment, but if posthumans make the transition to fully inorganic intelligences, they won’t need an atmosphere. And they may prefer zero-g, especially for constructing extensive but lightweight habitats. So it’s in deep space—not on Earth, or even on Mars—that nonbiological ‘brains’ may develop powers that humans can’t even imagine. The timescales for technological advance are but an instant compared to the timescales of the Darwinian natural selection that led to humanity’s emergence—and (more relevantly) they are less than a millionth of the vast expanses of cosmic time lying ahead. The outcomes of future technological evolution could surpass humans by as much as we (intellectually) surpass slime mould.

It’s likely that ‘inorganics’—intelligent electronic robots—will eventually gain dominance. This is because there are chemical and metabolic limits to the size and processing power of ‘wet’ organic brains. Maybe we’re close to these already. But no such limits constrain electronic computers (still less, perhaps, quantum computers). So, 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. We are perhaps near the end of Darwinian evolution, but a faster process, artificially directed enhancement of intelligence, is only just beginning. It will happen fastest away from the Earth—I wouldn’t expect (and certainly wouldn’t wish for) such rapid changes in humanity here on Earth though our survival will depend on ensuring that the AI on Earth remains ‘benevolent’.

Philosophers debate whether ‘consciousness’ is special to the organic brains of humans, apes, and dogs. Might it be that robots, even if their intellects seem superhuman, will still lack self-awareness or inner life? The answer to this question crucially affects how we react to their ‘takeover’. If the machines are zombies, we would not accord their experiences the same value as ours, and the posthuman future would seem bleak. But if they are conscious, why should we not welcome the prospect of their future hegemony?

The scenarios I’ve just described would have the consequence—a boost to human self-esteem—that even if life had originated only on the Earth, it need not remain a trivial feature of the cosmos; humans may be closer to the beginning than to the end of a process whereby ever more complex intelligence spreads through the galaxy. The leap to neighbouring stars is just an early step in this process. Interstellar voyages—or even intergalactic voyages—would hold no terrors for near-immortals.

Even though we are not the terminal branch of an evolutionary tree, we humans could claim truly cosmic significance for jump-starting the transition to electronic (and potentially immortal) entities, spreading their influence far beyond the Earth, and far transcending our limitations.

But the motives and the ethical constraints will then depend on the answer to one great astronomical question: Is there life—intelligent life—out there already?

3.5. ALIEN INTELLIGENCE?

Firm evidence for vegetation, primitive bugs, or bacteria on an exoplanet would be significant. But the thing that really fuels popular imagination is the prospect of advanced life—the ‘aliens’ familiar from science fiction.7

Even if primitive life were common, ‘advanced’ life may not be—its emergence may depend on many contingencies. The course of evolution on Earth was influenced by phases of glaciation, our planet’s tectonic history, asteroid impacts, and so forth. Several authors have speculated about evolutionary ‘bottlenecks’—key stages that are hard to transit. Perhaps the transition to multicellular life (which took two billion years on Earth) is one of these. Or the ‘bottleneck’ could come later. If, for instance, the dinosaurs hadn’t been wiped out, the chain of mammalian evolution that led to humans may have been foreclosed; we can’t predict whether another species would have taken our role. Some evolutionists regard the emergence of intelligence as an unlikely contingency, even in a complex biosphere.

Perhaps, more ominously, there could be a ‘bottleneck’ at our own evolutionary stage—the stage we’re at during this century, when intelligent life develops powerful technology. The long-term prognosis for ‘Earth-sourced’ life depends on whether humans survive this phase—despite vulnerability to the kinds of hazards I’ve addressed in earlier chapters. This does not require that no terminal catastrophe ever befalls the Earth—only that, before that happens, some humans or artefacts have spread beyond their home planet.

As I’ve emphasised, we know too little about how life emerged to be able to say whether alien intelligence is likely or not. The cosmos could be teeming with varieties of complex life; if so, we could aspire to be minor members of a ‘galactic club’. On the other hand, the emergence of intelligence may require such a rare chain of events—like winning a lottery—that it has not occurred anywhere else. That will disappoint those searching for aliens but would imply that our Earth could be the most important place in the galaxy, and that its future is of cosmic consequence.

It would plainly be a momentous discovery to detect any cosmic ‘signal’ that was manifestly artificial—radio ‘beeps’, or flashes of light from some celestial laser scanning the Earth. Searches for extraterrestrial intelligence (SETI) are worthwhile, even if the odds seem stacked against success, because the stakes are so high. Earlier searches led by Frank Drake, Carl Sagan, Nikolai Kardashev, and others didn’t find anything artificial. But they were very limited—it’s like claiming that there’s no life in the oceans after analysing one glassful of seawater. That’s why we should welcome the launch of Breakthrough Listen, a ten-year commitment by Yuri Milner, a Russian investor, to buy time on the world’s best radio telescopes and develop instruments to scan the sky in a more comprehensive and sustained fashion than before. The searches will cover a wide range of radio and microwave frequencies, using specially developed signal processing equipment. And they will be supplemented by searches for ‘flashes’ of visible light or X-rays that don’t seem to have a natural origin. Moreover, the advent of social media and citizen science will enable a global community of enthusiasts to download data and participate in this cosmic quest.

Suppose that there are many other planets where life began, and that on some of them Darwinian evolution followed a similar track to what has happened here. Even then, it’s highly unlikely that the key stages would be synchronised. If the emergence of intelligence and technology on a planet lagged significantly behind what has happened on Earth (because the planet is younger, or because the ‘bottlenecks’ have taken longer to negotiate), then that planet would reveal no evidence of ET. But around a star older than the Sun, life could have had a head start of a billion years or more.

The history of human technological civilisation is measured in millennia (at most)—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. If ‘organic’ human-level intelligence is, generically, just a brief interlude before the machines take over, we would be most unlikely to ‘catch’ alien intelligence in the brief sliver of time when it was still in organic form. Were we to detect ET, it would be far more likely to be electronic.

But even if the search succeeded, it would still be improbable that the ‘signal’ would be a decodable message. It would more likely represent a by-product (or even a malfunction) of some supercomplex 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. So, could we tell whether a signal is intended as a message or just some ‘leakage’? Could we build up communication?

The philosopher Ludwig Wittgenstein said, ‘If a lion could speak, we couldn’t understand him’. Would the ‘culture gap’ with aliens be unbridgeable? I don’t think it necessarily would be. After all, if they managed to communicate, they would share with us an understanding of physics, mathematics, and astronomy. They may come from planet Zog and have seven tentacles; they may be metallic and electronic. But they would be made of similar atoms to us; they would (if they had eyes) stare out at the same cosmos and trace their origins back to the same hot dense beginning—the ‘big bang’ around 13.8 billion years ago. But there’s no hope for snappy repartee—if they exist, they would be so far away that exchanging messages would take decades, or even centuries.

Even if intelligence were widespread in the cosmos, we may only ever recognise 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 energy-conserving lives, doing nothing to reveal their presence. It makes sense to focus searches first on Earthlike planets orbiting long-lived stars. But science fiction authors remind us that there are more exotic alternatives. In particular, the habit of referring to an ‘alien civilisation’ may be too restrictive. A ‘civilisation’ connotes a society of individuals; in contrast, ET might be a single integrated intelligence. Even if signals were being transmitted, we may not recognise them as artificial because we may not know how to decode them. A veteran 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.

The focus has been on the radio part of the spectrum. But of course, in our state of ignorance about what might be out there, we should explore all wavebands; we should look in the optical and X-ray band and also be alert for other evidence of nonnatural phenomena or activity. One might seek evidence for artificially created molecules such as CFCs in an exoplanet atmosphere, or else for massive artefacts such as a Dyson sphere. (This idea, due to Freeman Dyson, envisions that an energy-profligate civilisation might harness all the energy of its parent star by surrounding it with photovoltaic cells, and that the ‘waste heat’ would emerge as infrared emission.) And it’s worth looking for artefacts within our solar system; maybe we can rule out visits by human-scale aliens, but if an extraterrestrial civilisation had mastered nanotechnology and transferred its intelligence to machines, the ‘invasion’ might consist of a swarm of microscopic probes that could have evaded notice. It’s even worth keeping an eye open for especially shiny or oddly shaped objects lurking among the asteroids. But it would of course be easier to send a radio or laser signal than to traverse the mind-boggling distances of interstellar space.

I don’t think even the optimistic SETI searchers would rate the chance of success as more than a few percent—and most of us are more pessimistic. But it’s so fascinating that it seems worth a gamble—we’d all like to see searches begun in our lifetime. And there are two familiar maxims that pertain to this quest: ‘Extraordinary claims will require extraordinary evidence’, and, ‘Absence of evidence isn’t evidence of absence’.

Also, we have to realise just how surprising some natural phenomena can be. For instance, in 1967 Cambridge astronomers found regular radio ‘beeps’, repeating several times a second. Could this have been an alien transmission? Some were open to accepting this option, but soon it became clear that these beeps came from a hitherto undetected kind of very dense object: neutron stars, which are only a few kilometres across and spin at several revs per second (sometimes several hundred), sending a ‘lighthouse beam’ of radiation towards us from deep space. The study of neutron stars—of which thousands are now known—has proved an especially exciting and fruitful topic because they manifest extreme physics, where nature has created conditions that we could never simulate in the laboratory.8 More recently, a new and still perplexing class of ‘radio bursts’ has been discovered, emitting even more powerfully than pulsars,⁹ but the general disposition is to seek natural explanations for them.

SETI depends on private philanthropy. The failure to get public funds surprises me. If I were up before a government committee, I’d feel less vulnerable and more at ease defending a SETI project than seeking funds for a vast new particle accelerator. That’s because many thousands of those watching movies of the Star Wars genre would be happy if some of the tax revenues they generated were hypothecated for SETI.

Perhaps we’ll one day find evidence of alien intelligence—or even (though this is less likely) ‘plug in’ to some cosmic mind. 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 for humanity’s long-term resonance. Our solar system is barely middle-aged, and if humans avoid self-destruction within the next century, the posthuman era beckons. Intelligence from Earth 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 cosmos.

Either way, our cosmic habitat—this immense firmament of stars and galaxies—seems ‘designed’ or ‘tuned’ to be an abode for life. From a simple big bang, amazing complexity has unfolded, leading to our emergence. Even if we are now alone in the universe, we may not be the culmination of this ‘drive’ towards complexity and consciousness. This tells us something very profound about nature’s laws—and motivates a brief excursion, in the following chapters, out to the broadest horizons in time and space that cosmologists conceive.