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The search for extraterrestrial minds
Aliens are back in the news. Last June, the Office of the Director of National Intelligence in the United States delivered to Congress a report on several thousand sightings of unidentified aerial phenomena (“UFOs” to a previous generation). Although the tenor of the report was predictably inconclusive, many people are already convinced not only that extraterrestrial beings exist, but that they are buzzing around in the skies over our heads.
Whether or not we are alone in the universe is one of the biggest and oldest of the Big Questions of Existence, with roots stretching back into antiquity. The ancient Greek philosopher Democritus argued that if atoms can combine on Earth to form living organisms, then atoms on other worlds must be able to do so too. In a later century, the writer Lucretius expressed the same idea poetically:
If atom stocks are inexhaustible,
Greater than power of living things to count,
If Nature’s same creative power were present too
To throw the atoms into unions – exactly as united now,
Why then confess you must
That other worlds exist in other regions of the sky,
And different tribes of men, kinds of wild beasts.
Democritus’s reasoning is that if the universe is big enough and made of the same material everywhere, then purely by chance life will arise beyond Earth. Today, a common refrain is, “The universe is so vast there must be life out there somewhere!” The argument is simple and obvious, but unfortunately it’s scientifically useless because it gives us no grip on the actual numbers. Astronomers estimate that there could be a billion Earth-like planets in the Milky Way galaxy alone, and there are hundreds of billions of galaxies in the observable universe. Clearly, there is no lack of real estate for alien life to flourish. But habitability on its own isn’t enough. For a habitable planet to become inhabited, life has to arise on it; that is, non-life has to turn into life. Nobody knows how that happens, how a mishmash of chemicals can be transformed into a living cell, with all its awesome organised complexity. It is easy to imagine that the transition requires a dream run of chemical reactions, each individually so specific and so unlikely that the entire sequence would occur only once in a trillion or more trials. Obviously, there was a pathway from non-life to life, or I would not be writing these words now. But how likely was it to occur? If we don’t know what the process was, we simply can’t say how probable it is to happen elsewhere. However good a statistician you may be, you can’t estimate the odds of an unknown process.
One thing is clear, however. If life arose merely from the random shuffling of small molecular building blocks, then it would be a freak accident of staggering improbability and we would almost certainly be alone. When I was a student, that was indeed the prevailing view. “Life seems almost a miracle,” wrote molecular biologist Francis Crick, reflecting on how many special conditions are necessary for it to get going. It was a sentiment echoed by fellow Nobelist Jacques Monod. “The universe was not pregnant with life … man knows at last he is alone in the universe’s unfeeling immensity, out of which he emerged only by chance,” he wrote, pessimistically.
Today, however, few scientists assume that life started from random chemistry. Rather, there would have been a type of canalisation, or fast-tracking process, from disorganised chemicals to living matter – a sort of “life principle” embedded in the laws of physics and chemistry, though it is rarely expressed so starkly. The notion that the laws of nature are somehow rigged in favour of life, implying that the universe is seething with it, has dramatic philosophical implications. It would imbue our existence as biological representatives – the special products of an intrinsically bio-friendly cosmos – with a significance lacking in Monod’s vision of humans as chemical freaks in an otherwise sterile universe. Monod was a staunch atheist, and indeed, a “life principle” seems to flirt with the same sentiment deployed by intelligent design devotees. So, the question of whether or not we are alone in the universe goes far beyond mere scientific curiosity. As astronomer Frank Drake expressed it, the search for life beyond Earth is really a search for ourselves, who we are and how we fit into the great cosmic scheme of things.
In the absence of any reliable probability estimate, the best that scientists can do is look to see what’s out there – a field known as astrobiology. And they have plenty of subject matter. The closest likely candidate is Mars, long a favourite in the search for life. Mars is not exactly congenial – a freeze-dried desert beneath a pitifully thin atmosphere bathed in deadly ultraviolet rays. Yet it’s not a total write-off. In the past it was warmer and wetter, and could have supported primitive life billions of years ago. It’s not inconceivable that some hardy microbes might still hang out there today, deep underground. Problem is, Earth and Mars are not quarantined. Impacts with planets by asteroids and comets splatter rocks across the solar system. Earth rocks fall on Mars and Mars rocks fall on Earth – dozens of the latter have been collected. Ensconced in a rock, hardy microbes could easily survive the journey from Earth to Mars or vice versa, thus contaminating the other body. If we do eventually find life on Mars, it’s likely to be simply Earth-life that has colonised it. That would be fascinating, but it fails to answer the key question: has life happened more than once? What we really want is to discover a second genesis – a sample of life that has started from scratch, independently of terrestrial life. Just a single example of life not as we know it – just one microbe – would demonstrate a life principle: that life is easy to get going and widespread in the cosmos.
Mars isn’t the only place to look for life in the solar system. Astrobiologists are increasingly enamoured of the icy moons of Jupiter and Saturn. A second genesis could have occurred beneath the frozen crust of one of these bodies. Plumes of gases laden with organic material have been detected spewing from fissures in Saturn’s moon Enceladus, offering an opportunity to sample the moon’s innards with a fly-by probe. Farther afield, thousands of extrasolar planets discovered to date offer potential abodes for life. The trouble is, even the closest stars are much too far away to send probes. Scientists are pinning their hopes on spectroscopic evidence: analysing planetary atmospheres for telltale chemical signatures of biological processes. It is a hugely challenging task, given that the light from a planet is swamped by the glare from its host star. Nevertheless, ambitious plans to tease out the signal from the noise are well advanced.
Searching for ET
Meanwhile, some visionary scientists are focusing their efforts on detecting intelligent life, a project founded by Frank Drake in 1960. The search for extraterrestrial intelligence (SETI) mainly involves sweeping the skies with radio telescopes in the hope of stumbling across some sort of signal or message from an alien civilisation. So far, there has been nothing but an eerie silence.
It’s perhaps no surprise. We lack the capability of detecting the equivalent of Radio National from even the nearest extrasolar planet. To me, radio SETI looks like a lost cause unless ET is deliberately beaming powerful messages directly at us. How likely is that? Not very, unfortunately, even if the galaxy is replete with advanced technological civilisations. The reason is a matter of basic physics. A civilisation located, say, a thousand light years away, will see Earth as it was a thousand years ago, long before the scientific age. Since nothing can travel faster than light, those aliens cannot know by any physical means that we possess radio technology until our own early radio transmissions leaking into space finally reach them in a few hundred years. Why would they try to signal us unless they knew we had radio technology? So, we are in for a long wait. Of course, if ET were just 50 light years away, it’s conceivable we could get a message soon, but SETI scientists doubt there is anyone that close. And even if we did establish two-way communication with such relatively nearby neighbours, the conversation would hardly be a snappy one, with a century delay in receiving replies to our questions.
Frustrating though this is, we don’t need to be informed via a crafted message that we are not alone. We could still draw that conclusion indirectly, by detecting any signs of non-human technology somewhere in the cosmos – known as technosignatures. Figuring out what they might be has become something of a growth industry among astrobiologists.
One much-discussed possibility is alien megastructures. Human technology has had an impact on our planet after just a few centuries – think of global warming and deforestation. A civilisation millions of years old might well have extended its technological footprint beyond its home planet into its astronomical environment. In 1960, the physicist and futurist Freeman Dyson wondered whether an advanced civilisation might build a huge structure around its host star to trap its heat and light – a solar energy project writ large. Searches for such “Dyson spheres” have turned up a few intriguing objects, but so far nothing definitive.
What about all those unidentified aerial phenomena (UAP) sightings? Are they plausible technosignatures? In my view, the answer is no. The issue boils down to the extreme challenges of interstellar voyages. Given that faster-than-light travel is, to the very best of our knowledge, a fantasy, journey times would be daunting and the resources needed to propel a sizeable spacecraft across interstellar space at high speed would be huge. The idea that curious alien tourists would simply pop over from a star system 100 light years away to peruse an upstart intelligent species is ludicrous.
On Earth, people do travel for tourism, but they also travel for migration and settlement. Is interstellar migration feasible given the vastness of space? It’s true that the universe is very big, making journey times immense, but it’s also very old – nearly 14 billion years. Even without faster-than-light warp drives and other sci-fi devices, there has been plenty of time for an expansionary species to spread out across the entire galaxy. Our solar system is actually relatively young. There were stars and planets around long before Earth came into existence. Any time during our planet’s 4.5-billion-year history, extraterrestrials, or their probes or robotic surrogates, could have descended on Earth and colonised it. Yet they didn’t. Why?
That question was famously posed by the physicist Enrico Fermi in 1950, when the postwar UFO surge was hitting the headlines. Asking “Where is everybody?” Fermi reasoned that, since our planet wasn’t overrun a long time ago, there is probably nobody out there, a conclusion that became known as the Fermi paradox. There are many ways to avoid the paradox – civilisations may be short-lived, or find it easier to set up home on a lifeless planet or to build space colonies. The truth is, we have no way to guess the imperatives or the ethical priorities of a truly alien species. That fact that Earth wasn’t colonised long ago by an expansionary galactic civilisation can’t be used to rule out the possibility that at some stage during our planet’s long history, the solar system may have been visited, maybe not by flesh-and-blood aliens but at least by their space probes.
The possibility of alien technosignatures in our cosmic backyard was thrown into sharp relief four years ago with the arrival in our solar system of a weird object called ’Oumuamua, the first interstellar visitor bigger than a speck ever to be discovered. Its shape and trajectory seemed a bit odd for a comet or asteroid, prompting Harvard astrophysicist Avi Loeb to speculate that it might be some sort of alien artefact, possibly technojunk. Loeb has since launched the Galileo Project, in part to search for more interstellar interlopers, but also to elevate the study of those pesky UAPs that won’t go away after seven decades of aerial antics. Galileo will deploy ground-based telescopes coupled to infrared and radar systems designed to catch a UAP in the act and attempt a positive identification, rather than rely on eyewitness testimonies and vague images.
Meanwhile, we could look for signs of past visitation. The problem then is what traces of alien technology might still be detectable after an astronomical duration? A few years ago, I pointed out that an alien artefact left on the Moon’s surface, which is relatively inert, might remain visible for 100 million years. NASA is currently photographing the lunar terrain from orbit with half-metre resolution. The pictures are posted free on the internet and can be studied by anyone. Artefacts are indeed visible in these images, but, so far, they are all of human origin, such as lunar spacecraft and rovers. Another long-lived technosignature is nuclear waste, which can endure for many millions of years. If we ever found traces of plutonium on the Moon or Mars, it would be a definitive sign that we are not alone, because natural plutonium in our solar system decayed billions of years ago.
The Moon is nearby and convenient to search, but it is not the only candidate for probing. The space engineer James Benford has pointed to a set of recently discovered asteroids locked in the same solar orbit as Earth. Dubbing them “lurkers”, Benford believes they would offer a great venue for an alien probe to monitor our planet. There are also locations in space called Lagrange points where the gravitational fields of the Earth and sun balance out. A spacecraft parked there could maintain station without fuel for a very long time. We might imagine an alien probe that has been dormant for aeons waking up when it detects the stirring of terrestrial technology. In that scenario, the long delay times that would bedevil radio communication with a faraway alien civilisation would be irrelevant – we could converse with the probe in almost real time. Who knows, Encyclopedia Galactica may already be out there, sitting quietly on our cosmic doorstep, waiting for us to log in.
A Goldilocks universe
The absence of evidence for ET is, as the saying goes, not evidence for absence. We just don’t know one way or the other. It is frustrating that one of the most profound questions to face humanity remains stalled, possibly indefinitely. But even without finding that all-important second genesis, we can still make progress with a deeper issue about life, the universe and everything. Whatever the odds of life existing beyond Earth, the very fact that it exists at all has been the source of some puzzlement to scientists. The reason for this is because the laws of physics and the precise way the universe began seem to be extraordinarily special. To see what this means, imagine playing God and having the power to change some basic features of the universe. You could, for example, make all electrons a bit heavier, or the nuclear forces a bit weaker, or the Big Bang bigger. Calculations suggest that some changes of this nature would have literally lethal consequences, forbidding the chance of any life arising anywhere. In certain cases, just a tiny alteration in one parameter would spell disaster, perhaps because atoms could not form or stars might be unstable. We live, it seems, in a Goldilocks universe, where fundamental physics and cosmology have come out “just right” for life. It looks like a fix. Some theologians have seized on this as evidence that the universe has been designed by God for the express purpose of incubating life.
Before jumping to that conclusion, however, it’s necessary to dig a bit deeper into the concept of laws of nature. The traditional view of the fundamental laws of physics is that they are absolute, immutable and universal, imprinted on the universe at the beginning, like a maker’s hallmark, and good for all eternity. All of which raises the thorny question of their origin. Where did the laws of physics come from and why do they have the intriguingly life-encouraging form that they do?
It’s not possible to separate the origin of the laws of physics from the origin of the universe to which they apply. Cosmologists accept that the universe, at least as we know it, exploded into existence in a Big Bang. There is less agreement, though, on what, if anything, came before it. When I was a student in the 1960s, the simplest account held that the Big Bang was not just the origin of matter but of space and time too. In that case, the question “What happened before the Big Bang?” would be rendered meaningless – there was no “before”. As Stephen Hawking once expressed it, asking what came before the Big Bang is like asking what lies north of the North Pole. There is nothing beyond the North Pole because there is no such place. Likewise, there was nothing before the Big Bang because was no such time.
The idea that time might have had an absolute beginning may appear baffling, but it didn’t start with modern cosmology. In the 5th century, St Augustine of Hippo declared (on theological grounds) that “the world was not made in time, but with time”. An origin of time finds a natural place in Einstein’s general theory of relativity, which provides the mathematical basis for scientific cosmology. Einstein showed that gravity is a warping of space and time, and if gravity becomes strong enough, time (and space) can possess an edge – a boundary where time just stops. The Big Bang is one example, and the inside of a black hole provides another.
But simply asserting that the universe sprang into existence from nothing, without cause, always seemed like an intellectual sleight of hand. So perhaps the universe didn’t have an absolute beginning after all? Could it be that something – maybe not the universe we know and love, but not nothing anyway – has always existed? After all, if the Big Bang was a natural, rather than a supernatural, event, why would it be unique? There could surely be countless bangs scattered throughout space and time, each one incubating a new universe. Ours would then be just one “bubble” universe amid an endless sea of bubbles, a set-up often dubbed “the multiverse”. Each bubble would have a life history – a beginning, a middle and maybe an end – but the entire assemblage could be eternal. The multiverse idea became popular in the 1980s, and cosmologists soon worked up plausible mechanisms to serve as a universe-generator: a physical process that could churn out cosmic bubbles without limit. Outlandish though it may appear, the multiverse of many universes has become the explanation of choice among most cosmologists today as an explanation for why the Big Bang happened.
Armed with the multiverse concept, cosmologists found they had a ready explanation for the weird bio-friendliness of our universe. Although the laws of physics might be fixed for any given universe, maybe they could vary from one universe to the next, each universe possessing its own distinctive hallmark. If the variation from universe to universe were random, then the vast majority of bubble universes would not be Goldilocks versions, and would go unobserved and unlamented. Just by chance, however, here and there would arise a universe with just the right set of properties for life to emerge – like hitting a cosmic jackpot – and it is of course no surprise that we find ourselves living in such a very special universe. Obviously, we couldn’t live in a universe that precluded life.
What’s eating the universe?
Attractive though this multiverse theory may be, it strikes many scientists as a speculation too far. In most variants of the theory, the bubbles move apart from each other much faster than they expand, so cannot be directly observed, even in principle. But other possibilities have been discussed. If there is evidence for something beyond, or before, the Big Bang, it’s likely to be found in the sea of radiation that bathes the universe, known as the cosmic microwave background (CMB). Detected accidently by two radio engineers in 1964, the CMB is best envisaged as the afterglow of the Big Bang. Although the intense heat of the primordial explosion has faded over time as the universe expanded, it still pervades all of space and has been intensively studied using satellites, the most recent of which is the Planck satellite of the European Space Agency. The purpose of the observations is to create heat maps of the sky in fine detail.
Although these maps show the CMB to be astonishingly uniform, there are very slight variations in temperature of a few parts per million. Etched into these patterns are important clues about the birth pangs of the universe a split second after its origin. If the universe originated from a single, simple Big Bang, then there should be distinctive statistical features in the CMB that can be calculated in detail using a branch of physics known as quantum mechanics. The satellite data matches the predicted features extremely well. But not perfectly. There remain a number of peculiar anomalies. For example, there is a small but definite difference in the amount of radiation between opposite hemispheres of the sky, and an unlikely alignment of the largest scale temperature variations.
Perhaps the oddest of all the anomalies lies in the direction of the constellation Eridanus, where there is a vast cold patch, as if a cosmic giant has taken a huge bite out of the universe. This super-void seems like a scar or blemish on an otherwise near-perfect cosmos, a flaw hinting that the notion of a simple Big Bang might be wrong. The cosmologist Laura Mersini-Houghton has suggested that the cold patch was produced by another bubble universe crashing into ours, a cosmic encounter awesome to contemplate. In similar vein, Roger Penrose, who won last year’s Nobel Prize in Physics, is convinced there is evidence in the CMB of enormous black holes from an epoch that preceded the Big Bang. Recently, the physicist Abhay Ashtekar has done some detailed calculations applying quantum mechanics to gravitation, and thinks he can account for the CMB anomalies as the product of a “big bounce”. Ashtekar suggests that before the Big Bang the universe was contracting until it reached a state of maximal compression, at which point quantum effects kicked in and initiated the current expansion phase.
If the cold patch is a type of portal into a region beyond, or before, our universe, a pressing question then arises. There is some controversial evidence advanced by John Webb, formerly of the University of New South Wales, that the force of electromagnetism might vary slightly across the universe. Apart from that, the laws of physics seem to be remarkably the same wherever we look. But if we can somehow peer beyond our universe, might we glimpse signs that the laws of physics there differ from those in our textbooks, even by a small amount? Such a discovery would have sweeping implications, suggesting the life-encouraging laws of our universe are not fixed and absolute, or the product of intelligent design, but a Goldilocks-type statistical fluke.
Why can we make sense of it all?
The multiverse explanation for cosmic bio-friendliness is easy to grasp and extremely popular with cosmologists (who generally don’t like intelligent designers), but it leaves out something of great significance. The Goldilocks argument hinges on a selection effect: a universe that is observed is a universe with life-encouraging laws able to spawn observers. And while it is true that we are observers of the universe, we are much more than that. When it comes to the great drama of nature, we don’t just “watch the show”, we have pretty much unravelled the plot, which is to say that humans have come to understand the cosmos. How is it that we are able to do this? It remains a profound enigma. As Einstein once remarked, the most incomprehensible thing about the universe is that it’s comprehensible.
To get a feel for what is involved, consider the role of mathematics. Science is so successful, people take it for granted that scientists and engineers can use mathematics to work out in advance how things will behave in the real world. Newton’s laws, for example, enable us to compute the trajectory of a spacecraft going to Mars; Maxwell’s equations of electromagnetism can be used to calculate the propagation of radio waves; quantum mechanics predicts when a chemical bond will form.
But the mathematical dimension of science goes far beyond a shorthand way to catalogue regularities. It can be used to uncover new and unexpected connections at a very deep level, leading to discoveries that could not be predicted any other way. Antimatter, black holes, the Higgs boson particle, gravitational waves: they are all things we would never know existed were it not for the abstract manipulations of mathematical relationships.
Sometimes it takes decades of cutting-edge experimentation to confirm what theoretical physicists predicted from their arcane calculations. Gravitational waves, for example, were discovered a hundred years after Einstein predicted them, and then only by building huge machines called laser interferometers with such sensitivity that they can measure movements of a suspended mirror less than the distance across an atomic nucleus. Who would have guessed that ghostly ripples in the fabric of space are traversing us at the speed of light all the time? Now, with the aid of their giant gravitational wave detectors, astronomers can spot these ethereal vibrations and use them to open up a new window on the universe. Gravitational wave astronomy will in turn lead to yet more discoveries and uncover more connections in the elaborate network of explanation we call science.
The oddity in this account of scientific progress is that mathematics is a rational construct of the human mind, yet for some unknown reason it is found to align beautifully with the deep order in nature. There is no absolute reason for nature to have a straightforward mathematical subtext in the first place. And even if it does, there is no reason why humans should be capable of comprehending it. After all, you can’t tell from daily experience that the disparate physical systems making up the natural world are linked, deep down, by a network of coded mathematical relationships. When you see an apple fall, you see a falling apple, not a set of differential equations linking the motion of the apple to the motion of the Moon – as Newton deduced using abstract reasoning. That is already more than we could reasonably expect. But what is even more remarkable is that relatively straightforward mathematics – the sort most students learn in school – can be used to accurately explain the large-scale properties of the universe, starting with a Big Bang and expanding to what we see today. Even after a lifetime in science, I am still astonished that three or four compact equations capture the essential features of cosmology.
How has it come about that human beings are privy to nature’s subtle and elegant scheme, to the encrypted relationships linking all of nature into a coherent functional web? Somehow the universe has engineered not just its own awareness but its own comprehension. Mindless, blundering atoms have conspired to spawn beings who are able to engage with the totality of the cosmos and the silent mathematical tune to which it dances.
Is this just a quirk of one offbeat species called homo sapiens inhabiting an anonymous cosmic outpost, or something reflected in the overall nature of the universe? If indeed we are not alone, are there alien beings who have likewise decoded the mathematical subtext of nature and uncovered the hidden network of interconnecting principles? Could it be that not merely life, not merely intelligence, but comprehension is built into the organisation of the cosmos?
It is an inspiring thought. How might we find out? Several years ago, the Tidbinbilla radio dish was used to transmit “a message to the aliens” as part of Australian Science Week. Sadly, most of the content was fairly banal. I had a small involvement because, at the time, I was chair of the SETI Post-Detection Taskgroup. This august body was set up by the International Academy of Astronautics to deliberate on what humanity should do in the event of contact with an extraterrestrial civilisation. Part of its brief was to mull over the implications of us trying to signal extraterrestrials, and what sort of information we should transmit.
In thinking this through, I came up with a very definite suggestion. We should send the number 0.0072973525693 (roughly 1/137, converted to binary for convenience). Why? What’s so special about that number? Well, it is known to every physicist as the quantity that determines the strength of the electromagnetic force at the atomic level. To know about it requires an understanding of both quantum mechanics and the theory of relativity, and the manner in which they interweave. It provides one of the most striking examples of the rational web of nature accessible to the human mind and would immediately tell an advanced civilisation that we have decrypted a big chunk of the coded rules that make the universe tick. If, conversely, we picked up a radio message from across the galaxy containing that number, or one of a handful of others describing the fundamental workings of physics, we would immediately know that we are not alone. But more importantly, we would know that the universe had built not just life, not just minds, but minds that can make sense of the world in which they are embedded. And not merely on Earth, but everywhere. We could then celebrate our existence as beings who are truly at home in the universe.
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