The Aliens Are Coming!

by Ben Miller

  And if you ask me, that’s exactly what we have found with the inflation of the universe. Most, but not all, theories of inflation imply that the universe we find ourselves in is just a small part of a much bigger whole. Maybe after the Big Bang, some regions of space-time inflated more rapidly than others, becoming isolated bubbles. Maybe what we call the universe is just inside one of those bubbles, and out there in Never-Never-Land are countless others. Our universe happens to be fine-tuned for life; maybe lots of the others aren’t. It’s time to meet the multiverse.

  THE UNIVERSE’S STRETCH MARKS

  As Carl Sagan said, extraordinary claims require extraordinary evidence, and, as far as the multiverse goes, we don’t quite have the quality of proof that one might hope for. Nevertheless, we are making progress. We already had circumstantial evidence for inflation—and, by proxy, the multiverse—in the exact size of the temperature variations in the cosmic microwave background (CMB), which the theory manages to predict with impressive accuracy. The real clincher, however, would be the detection of primordial gravitational waves.

  In order to understand what gravitational waves are and why they might provide evidence for inflation, I am going to have the pleasure of introducing you to one of my favorite bits of physics. In essence, it’s this: Acceleration makes waves. Perhaps the most obvious example is sound, where the acceleration of a solid object produces sound waves. But the same principle is at work in field theories like electromagnetism, where an accelerating electric charge radiates photons, also known as light.

  Einstein’s Theory of General Relativity describes how matter and energy relate to gravitation, so it fits the picture that an accelerating mass radiates gravitational energy in the form of a ripple in space-time called a gravitational wave. That supernova on the far side of the galaxy, that pair of neutron stars orbiting one another in deep space, the tennis ball in the men’s final at Wimbledon—all of them create gravitational waves. Those waves spread out through the cosmos, stretching and compressing space and time like the ripples on a pond. Eventually, they will pass through you, and your space and time will wobble. Only a bit, of course. You will shrink and stretch in height, but imperceptibly. Your watch will run fast and slow, but by such a minute amount as to be unnoticeable. And then the wave will pass, and your space and your time will be still again.

  That’s the theory anyway. Relativity tells us that in most cases the wobbling of space and time caused by gravitational waves will be so small as to be undetectable. To see the effects, you need to accelerate something really big. In the case of inflation, that something is the universe. During inflation, the universe expanded faster than the speed of light.20 And when you accelerate something as big as the universe as much as that, you are going to get some pretty big gravitational waves. It’s the after-effects of these waves that we are currently searching for.

  FLEXING OUR BICEP

  Theory predicts that when the universe inflated, the gravitational waves that were produced should have left an imprint on the cosmic microwave background. To cut a long story short, they should have polarized it, leaving a distinctive pattern that a telescope in Antarctica named the Background Imaging of Cosmic Extragalactic Polarization (BICEP II) has been built to detect.21

  In 2013 everyone got very excited when the BICEP team thought they’d cracked it, but the result has since been shown to be a false positive caused by cosmic dust. After a bit of a rethink and a chunky upgrade, they are expecting to publish more results in 2016. If they are successful, everyone will have to start taking inflation and the multiverse a lot more seriously.

  There’s a beautiful circularity to that. At the time of the Ancient Egyptians, we believed that mankind was special, and that the Earth stood at the center of the cosmos. We call this the Ptolemaic Model, after the Greco-Egyptian astronomer Ptolemy,22 who first formalized it. Copernicus then demoted us to a middle-ranking orbit around the Sun with his heliocentric Copernican Model. Einstein’s General Relativity taught us that even the Sun wasn’t that big a deal; no part of space-time is privileged over any other. And now the entire universe turns out to be just one ticket in a colossal lottery called the multiverse.

  The kicker is that makes us special after all. Or, to be more precise, our universe is special because it’s the one where the very fabric of existence is just right for life. When we go looking for our cousins in the cosmos, we should bear that in mind. Because even before we came along, the universe was trying for a baby.

  CHAPTER FIVE

  LIFE

  In which the author’s attempt to grasp exactly what makes life special causes him to fall through a mathematical rabbit hole, only to emerge in a wonderland where everything is valued not by its beauty, but by the rate at which it dissipates energy.

  On August 7, 1996, President Clinton announced to the world’s media that NASA had found evidence of life on Mars. A team led by David McKay, the geologist who had trained the Apollo astronauts how to search for moon rocks, had found fossilized bacteria in a Martian meteorite. “If this discovery is confirmed,” Clinton intoned, “it will surely be one of the most stunning insights into our universe that science has ever uncovered.”

  Sadly, it wasn’t confirmed. McKay’s discovery was soon submerged in a blizzard of critical academic papers. The main objection was to the fossils’ size. The largest among them were only 100nm in diameter, whereas the smallest bacteria known at the time were nearly ten times that size.1 Some critics pointed out that’s too small to hold enough DNA for them to replicate. You might ask why Martian bacteria would necessarily contain DNA, but that’s a whole other question.

  Take a look at the photograph above, reproduced from the McKay team’s paper in the journal Nature. I hope to convince you that the sausage-shaped “bacteria” in meteorite ALH84001 may indeed be microscopic aliens. Even if I fail, the whole question of how we decide whether or not something is, or has ever been, alive is right at the heart of our quest to find life on other planets. If we hope to find life elsewhere, we have to know exactly what we’re looking for.

  BOLT FROM THE BLUE

  A meteorite, of course, is simply a piece of rock which has come to Earth from space. All kinds of rubble from asteroids and comets are constantly hitting the upper atmosphere, but most of it burns up long before it reaches the ground. The result is a shooting star, or meteor. A classic example is the Perseid meteor shower, which happens every August in the northern hemisphere as the Earth trundles its way through the tail of the comet Swift–Tuttle, and very beautiful it is, too.

  Occasionally, however, we get lucky—or unlucky—and a particularly large lump of space rock will touch down somewhere on our beautiful blue planet. And there’s no limit, really, on how big such a rock might be. As we shall soon learn, the early solar system was buzzing with comets and asteroids, and the Earth took a severe battering from its birth right up until around 3.9 billion years ago.2

  Things have calmed down a lot since, but now and then we still get a haircut. The last really big space rock to do the business hit us sixty-six million years ago,3 wiping out the dinosaurs. Five thousand years ago an asteroid struck the Indian Ocean, causing a worldwide tsunami and quite possibly founding the myth of Noah’s flood. And as recently as 1908, a comet exploded in the skies above Tunguska, Siberia, with a thousand times the energy of the atomic bomb that was dropped on Hiroshima.

  There’s nothing that uncommon, in other words, about meteorites per se. What made ALH84001 so unusual is that it came from Mars. As you might have gathered, our atmosphere actually protects us from space rocks, as they tend to burn up in it due to friction. Other planets with thinner atmospheres get a rougher deal. When a stray asteroid or comet collides with Mars, the red planet takes it right on the chin. If the impact is big enough, lumps of Martian crust get billiarded out into space. If that debris escapes Mars’s gravity, it can find itself on a collision course with the Earth. And in the case of our hero meteorite, the exact location of that collisio
n was the Antarctic.

  HOLES IN SNOW

  The Antarctic is a meteorite hunter’s heaven. One rather straightforward reason is that they show up really well against the snow. Another is that, generally speaking, ice piles up in the middle of Antarctica, and then flows down and out to its coasts, where it gets trapped at the feet of mountain ranges. Anything that falls out of the sky into the middle of the continent therefore ends up on a kind of slow-moving conveyor belt to the bottom of the nearest mountain, ready to be collected by some hardy geologist.

  As a result, every summer in the southern hemisphere the USA’s National Science Foundation supports the Antarctic Search for Meteorites, or ANSMET. Round about December, a small research team heads out from a base camp near the foot of the Transantarctic Mountains to hunt for meteorites. The rock that the McKay team studied had been found by one Bobbie Score during a snowmobile ride on December 27, 1984, in the Allan Hills. As the first sample found that year, the rock had been labeled ALH84001.

  To begin with, ALH84001 was assumed to be the remains of a common or garden asteroid, but by 1993 it was resident at the Johnson Space Center where it was identified as a piece of Mars’s crust. It was at this point that it piqued David McKay’s interest. Tests showed that it was an astonishing 4.5 billion years old, having formed on Mars just a squeak after the solar system itself. Sixteen million years ago some sort of impact cannoned it up and out of Mars’s gravitational field,4 where it wandered the solar system before rubbing up against the Earth’s atmosphere and crash-landing in the Antarctic around 11,000 years ago.

  The rock itself was riddled with cracks, having suffered some sort of impact around four billion years ago while it was still on the surface of Mars. And here was the really exciting bit. Lodged in the cracks were granules of calcium carbonate. To a geologist, calcium carbonate means water,5 and water, as we all know, means life. Even more intriguingly, calcium carbonate granules of a similar size and shape to those in the meteorite were known to be produced by certain kinds of terrestrial bacteria.

  “So what?” you may say, “the granules probably formed on Earth during the 11,000 years that the rocks had been lying in the Antarctic snow.” But when the team dated the granules, they found that they were billions of years old, not tens of thousands. There was no doubt about it; they had formed on Mars. But how? The McKay team decided to put their pet rock under an electron microscope to see if they could find out.

  It was then that they saw the thousands of sausage-like shapes clinging to the granules of calcium carbonate. Have another look at that photograph, and tell me again whether you think they look like fossils of living things. If you think they do look like they were once alive, what is it about them that convinces you? And if you don’t, why not?

  WHAT IS LIFE?

  We humans are expert at spotting life. NASA’s recent Discovery mission to Mars was exhilarating, but there is something infinitely frustrating about a robotic probe scratching around for water in dusty soil when there could be purple alien bacteria crawling all over the rocks of a nearby mountain stream. Stick any microbiologist on the Red Planet for a day, and he’ll be able to tell you whether there’s anything living there or not. So what is it that we look for? How do we identify something as being alive?

  One thing we look for is movement. Life gets around, be it a bacterium waggling its flagellum, or a flying squirrel spreading its paws and taking to the wind. As a physicist might say, living things do work, meaning they are capable of converting chemical energy into mechanical energy. The bacterium beats the surrounding liquid with its flagellum; the flying squirrel pushes down on the air to create uplift. Non-living things can do work, too, but unless they are man-made, they don’t have an internal energy supply. Kick a football, and it starts to slow down the instant it leaves your foot. Kick a kangaroo and you may well end up on the other side of the nearest hedge.

  And living things grow. If you’re out for a Mars walk and you see a large black rock, and the next day it’s twice the size, it’s time to take some photos. And if the day after that the large black rock has a little black baby rock sitting next to it, you’ve really struck the motherlode, because the special type of growth that we call reproduction is another tell-tale sign of life. In fact, some would say it’s a defining sign, because without it natural selection would have no way to work, and there would be no evolution of species.

  Doing mechanical work, growing, and reproducing are all things that life does, but it’s interesting to note that they don’t define it. An avalanche is capable of doing work, even though that work might be flattening ski chalets. Likewise, rust can grow on a chain-link fence, but we wouldn’t keep it in a jar as a pet. Simon Cowell was unable to reproduce without the assistance of Lauren Silverman; nevertheless he is most definitely alive. And it’s not hard to imagine some highly evolved creature of the future that decides it doesn’t want to die, thanks very much, uploads itself into some sort of virtual reality, and does away with natural selection altogether.6 What is it that life does that non-life doesn’t?

  The thing about fossils, of course, is they don’t move, grow, or reproduce. If David McKay’s team had been really lucky, one of ALH84001’s bacteria might have been preserved in the act of cell division, but no such luck. Neither were any of them spotted at different stages of growth, or flexing minuscule flagella. No, what makes the tiny sausage-shaped structures in the Allan Hills meteorite look lifelike is a truly fundamental property of all living things: They are organized.

  In organizing themselves, living things go against the grain of the entire universe. As we are about to see, the cosmos seeks one thing, and one thing only: equilibrium. The natural world doesn’t want you to play backgammon, or learn to salsa, or even exist. It wants equal temperature, maximum disorder, and death. Eventually it will get its way, but hopefully not before you’ve finished reading this chapter, and come to grips with one of the most mind-expanding principles in the whole of science: the Second Law of Thermodynamics.

  THE RULES OF THE GAME

  The concept of energy occupies hallowed ground in physics. I don’t think it’s too much of an exaggeration to say that it underpins every other physical theory we have, and that goes for both Quantum Mechanics and General Relativity. It is enshrined in the four Laws of Thermodynamics, which can be roughly summarized as follows:7

  (0) If two different objects are in thermal equilibrium with a third object, then they will also be in thermal equilibrium with each other.

  (1) The total energy of the universe remains constant.

  (2) The entropy of the universe always increases.8

  (3) The entropy of an object approaches zero as its temperature approaches zero.

  Everything that we can imagine an extraterrestrial life-form might do—be it thinking, communicating, growing, moving, or reproducing—requires energy. Although there’s a slightly forbidding ring to their name, the Laws of Thermodynamics are really just a very simple set of rules for the way that energy works. They are all directly relevant to life, but it’s the Second Law that has the most surprising implications for living things. As we are about to see, the reason you ate breakfast was not just because you needed a source of fuel. You ate it for its information content.

  DOWN WITH EQUILIBRIUM

  Balance, in psychological terms at least, sounds like a wonderful thing. In fact I have often experienced it myself, if only when swinging from high elation to severe depression. In people, it is generally and justifiably admired. Who doesn’t seek to be stoic, good-humored, and harmonious of spirit? The Buddha, one imagines, didn’t get into bar fights, and Buddhism would be a less impressive religion if he had. But while equanimity is an enviable quality in human beings, out there in the universe at large it is very bad news indeed.

  The universe, I am sorry to tell you, is not a fan of yours for one very simple reason: It doesn’t like hot things and cold things. Rather, it infinitely prefers something else: thermal equilibrium. You probably al
ready have a rough idea of what that means, but, as a refresher, let’s imagine putting something hot—a cup of hot tea, say—next to something cold, like a saucer. What happens next? No prizes for guessing that heat flows from the cup of hot tea to the saucer. Eventually, the cup and saucer will reach the temperature of their surroundings, and no more heat will flow.9 We say then that they are in thermal equilibrium. This, of course, is what the Zeroth Law of Thermodynamics is telling us; thermal equilibrium is what results when two different objects have the same temperature.10

  As you may know, this type of heat flow—from one body to another in direct contact—is called conduction. As far as a cup and saucer goes, the process is slow for the simple reason that the very thing they are both made out of, china, has been chosen because it is so bad at conducting heat. Our ancestors, in their wisdom, wanted their tea hot and chose their crockery accordingly. But that’s not the end of the story. A hot cup of tea also cools by another method, known as convection. Basically the hot tea and teacup heat the cold air around them, and the hot air rises, only to be replaced by more cold air. Eventually the tea reaches the same temperature as the surrounding air, in which case—if you are my wife—at this point you decide to try and drink it.

  Conducting and convecting heat is the kind of thing the verse loves to do, because both activities take it one step closer to its ultimate goal of universal thermal equilibrium. But there’s another method by which hot things lose heat to cooler things, and as far as the universe at large is concerned, it’s much more important. That method is called radiation, and it’s really worth understanding in detail for two reasons. Firstly, because it supports the majority of life on our planet, and, secondly, because it will ultimately bring about a dull, dull Armageddon.