The Aliens Are Coming!

by Ben Miller

  H = K log W

  Where K is a constant. Wait a minute! That’s uncannily reminiscent of Boltzmann’s formula for the entropy of a group of particles with W possible configurations, each of which is equally likely:

  S = k log W

  So what’s going on?

  SOD’S LAW

  On the face of it, the progression seems unlikely. At one end, nineteenth-century physicists were looking for a way to improve the efficiencies of steam engines. At the other end, twentieth-century engineers were looking for a way to improve the efficiency of communication devices. Extraordinarily, they both turned out to be working on the same problem. Entropy, S, being our uncertainty about the microscopic configuration of a physical system, and entropy, H, being our uncertainty about the configuration of the letters in a message, are connected.

  The link is information. When we calculate the entropy of a group of atoms, we can think of it either as our uncertainty as to which one of its possible W configurations it is actually in, or as how uncertain we are as to the content of a message that completely describes that configuration. Boltzmann entropy is, in fact, a special case of Shannon entropy.

  So what does this mean? Well, for a start, it means that entropy is the enemy of information. The greater the entropy of a system, the less we know about the content of any message it might contain. But on a deeper level it means that information is more than just books, DVDs, and hard drives; it is a fundamental property of matter. A sugar molecule, a photon of light, an edition of The Times: All of them contain information. That information may have to do with the location of individual atoms, or the location of George Clooney’s wedding; it’s all the same to the universe. It simply doesn’t care for it.

  Now we start to understand the true nature of the Second Law. Energy dissipates. The entropy of the universe always increases, corrupting information, increasing disorder, and dispersing heat. Now we see why those fossilized grains in the Allan Hills meteorite are so striking, and, indeed, why all life-forms are so magically unusual; they contain an extremely high degree of order, far greater than could arrive by chance. From stromatolite colonies of cyanobacteria, to Venus flytraps, ants’ nests, and bridge clubs, life-forms constantly cheat the Second Law of Thermodynamics. From a world bent on chaos they concentrate energy, order, and information.

  Life is shit, and then you die. Everyone is promoted to a position of incompetence. If something can go wrong, it will go wrong. These are all statements of the Second Law, and they are so ingrained in us that they feel like second nature. The joy that we feel when we tidy up the office, write a letter, or hold a newborn baby is a vaulting ecstasy at momentarily defying the Second Law of Thermodynamics. We know that it can’t last, but somehow that makes it all the more sweet. We got one past the goalie. We passed the flaming torch of information, despite the best efforts of the universe. Life goes on.

  We know, of course, that in the long run it’s probably not good news. Life is swimming against the tide of creation, and it can’t last forever. In a moment, I’m going to let the Laws of Thermodynamics run to their inevitable conclusion, but first we need to answer the all-important question: How does life do it? If the universe is painstakingly eradicating information wherever it can find it, how did life manage to get started, and how has it managed to become ever more complex?

  INSANE IN THE MEMBRANE

  For once I’m going to give a straight answer to a straight question: cells. The fundamental building block of all life on Earth is an ingenious way of piggybacking the Laws of Thermodynamics. All life on Earth is made up of cells, and they all have one thing in common. They have a means of keeping their insides separate from their outsides.

  On the face of it, a cell membrane might not be the sexiest of features. There are other, far more photogenic things to get excited about like nuclei, Golgi bodies, and mitochondria, but arguably none of them would ever manage to scratch a living without something to protect them from the big bad world. As Claude Shannon might see it, a cell membrane is a great way of separating a low-entropy, high-information region—the cell’s insides—from its high-entropy, low-information outsides, aka the universe. And it’s this separation that enables the cell as a whole to perform a neat thermodynamic trick.

  It works like this. It doesn’t matter if there’s a decrease of entropy inside the cell, so long as outside the cell it increases by an even greater amount. Overall, the entropy of the universe will have increased and the Second Law remains unbroken. All you need is a cell membrane to act as a gatekeeper, letting in low-entropy stuff and letting out high-entropy stuff. The low-entropy stuff we call food. The high-entropy stuff we call waste.

  In other words, the cell membrane is crucial because it prevents equilibrium. Within it, entropy can be lowered, matter can be organized, and information can be stored. But it also has another crucial function that was essential to the first single-celled life-forms. It is a great way of storing energy.

  MY NAME IS LUCA

  In the next chapter we’ll look in detail at what we know about the history of life on Earth. Our goal will be to try and understand how single-celled life got its start, and the series of innovations and coincidences that led to our own species of technologically accomplished and highly social apes. Once we have some kind of perspective on how likely our own intelligence is, hopefully we can get a feel for how commonplace our kind of intelligence might be in the galaxy, and how far away our nearest neighbors might be.

  I’m not one for spoilers, but in the broadest of strokes we will find that the very first life on our planet was single-celled, and came in two types known as archaea and bacteria. Both originated in water. We can tell from analyzing the DNA and proteins within them that they are related, but so far we have no way of telling which came first. For the moment, we are just trying to understand the nuts and bolts of how life works, so we can dispense with the gory details. What’s important for our present purposes is that they both store energy by pumping protons across their cell membranes.

  A proton, you’ll remember, is nothing more than a lone hydrogen nucleus. Whereas an electron carries a single unit of negative charge, a proton carries a single unit of positive charge. Archaea and bacteria are capable of getting their energy from a bewildering number of sources: from eating one another, from reactions with chemicals like hydrogen sulfide and ammonia, from rusting metals such as iron, and, of course, directly from sunlight. In every case, once acquired, they use that energy to drive protons across their cell membranes, storing it up for future use.21

  Because protons carry charge, they essentially want to get away from one another. By creating an excess of protons in the water surrounding them, and a deficit within, these simple cells are effectively creating an energy source to be tapped at will. This is arguably a bit too much detail, but for some reason I can’t resist telling you that, when the time is right, these energetic protons are used to make an energy-rich molecule called adenosine triphosphate, affectionately known as ATP.

  This plucky molecule is essentially the currency of energy within all cells, able to donate energy wherever it is needed. All the processes that you can think of such as movement, making proteins, RNA, and DNA all extract their energy from ATP. Put bluntly, cells are miniature machines, capable of extracting energy and information from the environment, storing it, then making copies of themselves. Single-celled organisms such as bacteria reproduce by dividing; their human cousins by having dinner then progressing to a second date.22 Eventually, however, entropy will have its way. It’s time to glimpse the end of days.

  THE HEAT DEATH OF THE UNIVERSE

  Let’s begin by getting our bearings. The universe began from a microscopic, hot, dense state some 13.7 billion years ago, inflated in a so-called Big Bang for a fraction of a second, then settled down to a steady expansion which ended about seven billion years ago, when it was roughly half the age that it is now. At that point, some repulsive force that we call dark energy began to dom
inate over gravity, and its expansion began to speed up. Our best prediction is that this expansion will continue to accelerate, pushing more and more of the cosmos out of the reach of our most powerful telescopes. In fact, some two trillion years hence, the only galaxy we will be able to see will be our own.23

  The present era is known as the stelliferous era, meaning quite simply the one where star formation takes place from the gravitational collapse of gas and dust. Before it came the primordial era, when the intense energy of the Big Bang cooled to form fundamental particles, then nuclei, then hydrogen and helium. The primordial era lasted about a million years; the stelliferous era will last a few trillion. So what happens next?

  Well, for a kick-off, there’ll be no new stars. All the hydrogen and helium gas will have been used up, and one by one the existing stars will start to burn out. The longest lived will be the smallest, the so-called red dwarves, but after a few trillion years even they will have exhausted their supply of nuclear fuel and will be beginning to cool. This is known as the degenerate era, after the extremely dense form of matter that remains when small stars cool.

  There’s no escaping this fate for any star, least of all our own Sun. As you probably know, our home star will run out of hydrogen in around five billion years’ time, at which point it will bloat from a yellow dwarf into a red giant.24 In roughly 7.9 billion years’ time it will explode in a planetary supernova, and all that will be left is a small lump of hot degenerate carbon known as a white dwarf. In roughly a quadrillion years—that’s a thousand trillion—it will have cooled to a temperature of just a few degrees above absolute zero. At that point it will no longer radiate any kind of light—radio, infrared, or otherwise—and will become what is called a “black dwarf.”

  It gets worse. As the degenerate era progresses, the swirling mass of dead stars that form the galaxy will slowly dissipate. One by one, near-misses and collisions will fling planets, black dwarves, and neutron stars out into intergalactic space. Any dead stars or rogue planets that remain will slowly be consumed by black holes. At the end of the degenerate era, estimated to arrive in some 1043 years’ time, all that will be left of the cosmos will be a silent colony of black holes, gorged to the eyeballs on dead stars.

  That marks the beginning of what is prosaically known as the black hole era. But it doesn’t end there. Black holes, it turns out, aren’t completely black. As Stephen Hawking was the first to point out, subatomic particles are able to “tunnel” across the event horizon, and return to the everyday universe. This, like any kind of radiation, has the effect of removing energy from the black hole, giving it a finite lifetime. In the case of a supermassive black hole that’s something in the region of—here comes the biggest number in this book—10106 years.25 All that will survive of them will be a thin gruel of subatomic particles.

  And that’s pretty much all that will be left of everything else, too. Even things like protons and neutrons are expected to decay back into subatomic particles—and all so-called solid objects like planets, asteroids, and comets are subject to the same quantum mechanical tunneling that black holes are, and will eventually deplete away into nothing. Everything in creation will be a cold, cold gas of subatomic particles, jiggling away at just a few fractions of a degree above absolute zero. No part of this gas will be hotter than any other, and no life of any conceivable kind will be able to exist.

  A ROCK AND A HARD PLACE

  Every year my extended family makes a pilgrimage to Robin Hood’s Bay on the North Yorkshire coast. One of the main attractions—apart from ice cream and fish and chips—is the fossil hunting. Edged with clay cliffs, the pebbled beach in the bay is a treasure trove of ammonites, devil’s toenails, and sharks’ teeth. The process is always the same. For the first twenty minutes or so you find nothing. Then you find a single fossil—usually not a very good one. Then suddenly there are fossils everywhere. Virtually every stone you pick up contains some half-submerged prehistoric creature, preserved in exquisite detail.

  Seen from the perspective of entropy, there isn’t a great deal of difference, really, between fossils and holiday snaps. If the Second Law tells us anything, it’s that meaning has no permanence. That coiled black ammonite may feel ancient, but the whole history of life on Earth is fleeting, like a drop of spray flung high into the air by a crashing waterfall. We life-forms are a glorious curiosity, another way for a star to cool, and for the universe to oxidize carbon. We are a means to an end.

  If that sounds bleak, it’s really not meant to. If it stirs anything in you, hopefully it’s a raging thirst for what the universe wants to deny you: knowledge. Or, rather, you are a manifestation of the universe’s wildest wish, namely, to awake and know itself. We have learned something profound about life. Wherever we find it, and whatever its building blocks, it will require a constant source of energy. It will use that energy to organize itself, at the expense of the entropy of its surroundings. And it will be far from equilibrium, because equilibrium means death.

  CHAPTER SIX

  HUMANS

  In which the author stakes his footling reputation on one particular hypothesis of how life got its start, and forces himself through the evolutionary bottlenecks that impede the flow from microorganism to Microsoft.

  The booking hall at central London’s Euston Station will never be the same again. I am crossing it now, as I hurry to catch my train, my head buzzing with ideas. Not my ideas, I hasten to add. They are the ideas of Nick Lane, the Provost’s Venture Research Fellow at University College London. Though if you ask Lane—and I just have—he will say some are the ideas of one Mike Russell, now of NASA’s Jet Propulsion Laboratory in Pasadena, who first proposed them some twenty years ago.

  I came to see Lane because I am on a quest. To try and figure out how likely intelligent aliens are, I need to know how likely I am. We’ve seen that, from its very beginning, the universe was “trying for a baby,” in that nature is fine-tuned to produce atoms. But it’s one thing to try and another to conceive. How likely was it that a small, wet, rocky planet orbiting a humdrum star in a spiral galaxy would be the birthplace of single-celled life? And how and why did that single-celled life evolve into a technologically advanced civilization of intelligent apes?

  I’LL HAVE THE PRIMORDIAL SOUP

  The classic picture of what scientists call abiogenesis is most often attributed to Charles Darwin. Though he avoided the subject in his public work, in a letter of 1871 to his close friend the botanist Joseph Hooker he made his true feelings clear:1

  It is often said that all the conditions for the first production of a living organism are present, which could ever have been present. But if (and Oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.

  Leaving aside the shocking punctuation, what Darwin seems to be saying is that, given the right conditions, something living can spontaneously emerge from something non-living simply by chance. In essence, that has been the non-religious view ever since Aristotle, and it remains our belief today, though there has been a great deal of toing and froing over exactly what those conditions might be.

  In the 1920s, the Russian biologist Alexander Oparin and the British polymath J. B. S. Haldane independently refined Darwin’s conjecture into what is known as the “primordial soup” theory. The gist is that once you have the right chemical elements and a source of energy, sooner or later a self-replicating molecule will emerge which is then capable of undergoing natural selection, in turn producing life.

  So what might those chemical elements be? All earthly life, as you probably know, is based on one most extraordinary element: carbon. Carbon is a party animal, eager to bond with a variety of other elements—and also with itself—to for
m long-chain molecules and rings of almost infinite variety. In organisms, we generally find it in the company of five “usual suspects”: hydrogen, nitrogen, oxygen, phosphorus, and sulfur.2

  Two configurations can rightly be thought of as the “building blocks” of life. One is called a nucleobase, which makes up both RNA and DNA, and also the very important energy-carrying molecule called ATP. The other is called an amino acid, the building block of proteins. I say building block; neither nucleobases nor amino acids are particularly simple, a point I have tried to emphasize by means of my characteristically poor drawings on the next page.

  Right. So the classic picture of the primordial soup theory in action looks something like this. It’s a foul night, and a bolt of lightning strikes in the skies above a broiling sea, in an atmosphere pumped full of noxious gases. Emboldened by this spark of energy, the gases react to form building blocks like nucleobases and amino acids. These building blocks then rain down into the ocean, where they fuse together to make the very first self-replicating molecules. A little packet of them gets trapped in an oily film, and the first cell is formed. Life is off to the races.3

  LACKING IN ENERGY AND CONCENTRATION

  Back in 1953, a Nobel Prize-winning chemist at the University of Chicago, Harold Urey, decided to put the primordial soup theory to the test. In a flask, Urey’s PhD student Stanley Miller put the gases they believed to have been knocking around on the early Earth—ammonia, methane, hydrogen, and water vapor—and passed an electric current through them. The results were extraordinary. There in the bottom of the flask were amino acids, the building blocks of proteins.