The Road to Little Dribbling
Two decades after Notes from a Small Island, Bill Bryson takes a new amble around Britain, to rediscover the beautiful, eccentric and endearing country he calls home.
‘Clever, witty, entertaining’ Independent on Sunday
The Body
Bill Bryson at his very best, this is a must-read owner’s manual for everybody.
‘Readable and useful ... not just comprehensive, but quirky.’
The Times
Also by Bill Bryson
The Lost Continent
Mother Tongue
Troublesome Words
Neither Here Nor There
Made in America
Notes from a Small Island
A Walk in the Woods
Notes from a Big Country
(published in the USA as I’m a Stranger Here Myself ) Down Under (published in the USA as In a Sunburned Country ) African Diary
A Short History of Nearly Everything
The Life and Times of the Thunderbolt Kid
Shakespeare (Eminent Lives series)
Bryson’s Dictionary for Writers and Editors Icons of England At Home
One Summer: America 1927
The Road to Little Dribbling The Body
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The physicist Leo Szilard once announced to his friend Hans Bethe that he was thinking of keeping a diary: ‘I don’t intend to publish. I am merely going to record the facts for the information of God.’ ‘Don’t you think God knows the facts?’ Bethe asked. ‘Yes,’ said Szilard. ‘He knows the facts, but He does not know this version of the facts.’
Hans Christian von Baeyer, Taming the Atom
Welcome. And congratulations. I am delighted that you could make it. Getting here wasn’t easy, I know. In fact, I suspect it was a little tougher than you realize.
To begin with, for you to be here now trillions of drifting atoms had somehow to assemble in an intricate and curiously obliging manner to create you. It’s an arrangement so specialized and particular that it has never been tried before and will only exist this once. For the next many years (we hope) these tiny particles will uncomplainingly engage in all the billions of deft, cooperative e orts necessary to keep you intact and let you experience the supremely agreeable but generally underappreciated state known as existence.
Why atoms take this trouble is a bit of a puzzle. Being you is not a gratifying experience at the atomic level. For all their devoted attention, your atoms don’t actually care about you – indeed, don’t even know that you are there. They don’t even know that they are there. They are mindless particles, after all, and not even themselves alive. (It is a slightly arresting notion that if you were to pick yourself apart with tweezers, one atom at a time, you would produce a mound of fine atomic dust, none of which had ever been alive but all of which had once
been you.) Yet somehow for the period of your existence they will answer to a single rigid impulse: to keep you you.
The bad news is that atoms are fickle and their time of devotion is fleeting – fleeting indeed. Even a long human life adds up to only about 700,000 hours. And when that modest milestone flashes into view, or at some other point thereabouts, for reasons unknown your atoms will close you down, then silently disassemble and go o to be other things. And that’s it for you.
Still, you may rejoice that it happens at all. Generally speaking, in the universe it doesn’t, so far as we can tell. This is decidedly odd because the atoms that so liberally and congenially flock together to form living things on Earth are exactly the same atoms that decline to do it elsewhere. Whatever else it may be, at the level of chemistry life is fantastically mundane. All that is required to make you, or any other living thing, is some carbon, hydrogen, oxygen and nitrogen, a little calcium, a dash of sulphur, a light dusting of other very ordinary elements – nothing you wouldn’t find in any ordinary pharmacy – and that’s all you need. The only thing special about the atoms that make you is that they make you. That is, of course, the miracle of life.
Without atoms there would be no water or air or rocks, no stars and planets, no distant gassy clouds or swirling nebulae or any of the other things that make the universe so agreeably material. Atoms are so numerous and necessary that we easily overlook that they needn’t actually exist at all. There is no law that requires the universe to fill itself with small particles of matter or to produce light and gravity and the other properties on which our existence hinges. There needn’t actually be a universe. For a very long time there wasn’t. There were no atoms and no universe for them to float about in. There was nothing – nothing at all anywhere.
So thank goodness for atoms. But the fact that you have atoms and that they assemble in such a willing manner is only part of what got you here. To be here now, alive in the twenty-first
century and smart enough to know it, you also had to be the beneficiary of an extraordinary string of biological good fortune. Survival on Earth is a surprisingly tricky business. Of the billions and billions of species of living things that have existed since the dawn of time, most – 99.99 per cent, it has been suggested – are no longer around. Life on Earth, you see, is not only brief but dismayingly tenuous. It is a curious feature of our existence that we come from a planet that is very good at promoting life but even better at extinguishing it.
The average species on Earth lasts for only between 1 million and 4 million years, so if you wish to be around for billions of years, you must be as fickle as the atoms that made you. You must be prepared to change everything about yourself – shape, size, colour, species a liation, everything – and to do so repeatedly. That’s much easier said than done, because the process of change is random. To get from ‘protoplasmal primordial atomic globule’ (as Gilbert and Sullivan put it) to sentient upright modern human has required you to mutate new traits over and over in a precisely timely manner for an exceedingly long while. So at various periods over the last 3.8 billion years you have abhorred oxygen and then doted on it, grown fins and limbs and jaunty sails, laid eggs, flicked the air with a forked tongue, been sleek, been furry, lived underground, lived in trees, been as big as a deer and as small as a mouse, and a million things more. The tiniest deviation from any of these evolutionary imperatives and you might now be licking algae from cave walls or lolling walrus-like on some stony shore or disgorging air through a blowhole in the top of your head before diving 60 feet for a mouthful of delicious sandworms.
Not only have you been lucky enough to be attached since time immemorial to a favoured evolutionary line, but you have also been extremely – make that miraculously – fortunate in your personal ancestry. Consider the fact that for 3.8 billion years, a period of time older than the Earth’s mountains and rivers and oceans, every one of your forebears on both sides has
been attractive enough to find a mate, healthy enough to reproduce, and su ciently blessed by fate and circumstances to live long enough to do so. Not one of your pertinent ancestors was squashed, devoured, drowned, starved, stuck fast, untimely wounded or otherwise deflected from its life’s quest of delivering a tiny charge of genetic material to the right partner at the right moment to perpetuate the only possible sequence of hereditary combinations that could result – eventually, astoundingly, and all too briefly – in you.
This is a book about how it happened – in particular, how we went from there being nothing at all to there being something, and then how a little of that something turned into us, and also some of what happened in between and since. That’s rather a lot to cover, of course, which is why the book is called A Short History of Nearly Everything, even though it isn’t really. It couldn’t be. But with luck by the time we finish it may feel as if it is.
My own starting point, for what it is worth, was a school science book that I had when I was in elementary school. The book was a standard-issue 1950s schoolbook – battered, unloved, grimly hefty – but near the front it had an illustration that just captivated me: a cutaway diagram showing the Earth’s interior as it would look if you cut into the planet with a large knife and carefully withdrew a wedge representing about a quarter of its bulk.
It’s hard to believe that there was ever a time when I had not seen such an illustration before, but evidently I had not, for I clearly remember being transfixed. I suspect, in honesty, that my initial interest was based on a private image of streams of unsuspecting eastbound motorists in the American plains states plunging over the edge of a sudden 4,000-mile-high cli running between Central America and the North Pole, but gradually my attention did turn in a more scholarly manner to the scientific import of the drawing and the realization that the Earth consisted of discrete layers, ending in the centre with a glowing sphere of iron and nickel, which was as hot as the surface of the Sun, according to the caption, and I remember thinking with real wonder: ‘How do they know that?’
I didn’t doubt the correctness of the information for an instant – I still tend to trust the pronouncements of scientists in the way I trust those of surgeons, plumbers and other possessors of arcane and privileged knowledge – but I couldn’t for the life of me conceive how any human mind could work out what spaces thousands of miles below us, that no eye had ever seen and no X-ray could penetrate, could look like and be made of. To me that was just a miracle. That has been my position with science ever since. Excited, I took the book home that night and opened it before dinner – an action that I expect prompted my mother to feel my forehead and ask if I was all right – and, starting with the first page, I read.
And here’s the thing. It wasn’t exciting at all. It wasn’t actually altogether comprehensible. Above all, it didn’t answer any
of the questions that the illustration stirred up in a normal enquiring mind: how did we end up with a Sun in the middle of our planet and how do they know how hot it is? And if it is burning away down there, why isn’t the ground under our feet hot to the touch? And why isn’t the rest of the interior melting – or is it? And when the core at last burns itself out, will some of the Earth slump into the void, leaving a giant sinkhole on the surface? And how do you know this? How did you figure it out?
But the author was strangely silent on such details – indeed, silent on everything but anticlines, synclines, axial faults and the like. It was as if he wanted to keep the good stu secret by making all of it soberly unfathomable. As the years passed, I began to suspect that this was not altogether a private impulse. There seemed to be a mystifying universal conspiracy among textbook authors to make certain that the material they dealt with never strayed into the realm of the frankly exciting.
I now know that there is a happy abundance of science writers who pen the most lucid and thrilling prose – Timothy Ferris, Richard Fortey and Tim Flannery are three that jump out from a single station of the alphabet (and that’s not even to mention the late but god-like Richard Feynman) – but, sadly, none of them wrote any textbook I ever used.
All mine were written by men (it was always men) who held the interesting notion that everything became clear when expressed as a formula and the amusingly deluded belief that the children of America would appreciate having chapters end with a section of questions they could mull over in their own time. So I grew up convinced that science was supremely dull, but suspecting that it needn’t be, and not really thinking about it at all if I could help it. This, too, became my position for a long time.
Then, much later, when I was well into adulthood, I was on a long flight across the Pacific, staring idly out the window at
moonlit ocean, when it occurred to me with a certain uncomfortable forcefulness that I didn’t know the first thing about the only planet I was ever going to live on. I had no idea, for example, why the oceans were salty but the Great Lakes weren’t. Didn’t have the faintest idea. I didn’t know if the oceans were growing more salty with time or less, and whether ocean salinity levels was something I should be concerned about or not. (I am very pleased to tell you that until the late 1970s scientists didn’t know the answers to these questions either. They just didn’t talk about it very audibly.)
And ocean salinity, of course, represented only the merest sliver of my ignorance. I didn’t know what a proton was, or a protein, didn’t know a quark from a quasar, didn’t understand how geologists could look at a layer of rock on a canyon wall and tell you how old it was – didn’t know anything, really. I became gripped by a quiet, unwonted but insistent urge to know a little about these matters and to understand above all how people figured them out. That to me remained the greatest of all amazements – how scientists work things out. How does anybody know how much the Earth weighs or how old its rocks are or what really is way down there in the centre? How can they know how and when the universe started and what it was like when it did?
How do they know what goes on inside an atom? And how, come to that – or perhaps above all, on reflection – can scientists so often seem to know nearly everything but then still not be able to predict an earthquake or even tell us whether we should take an umbrella with us to the races next Wednesday?
So I decided that I would devote a portion of my life – nearly five years altogether, as it now turns out – to reading books and journals and finding saintly, patient experts prepared to answer a lot of outstandingly uninformed questions. The idea was to see if it isn’t possible to understand and appreciate – marvel at, enjoy even – the wonder and accomplishments of science at a
level that isn’t too technical or demanding, but isn’t entirely superficial either.
That was my idea and my hope, and that is what the book that follows is intended to do. Anyway, we have a great deal of ground to cover and much less than 700,000 hours in which to do it, so let’s begin.
They’re all in the same plane.They’re all going around in the same direction . . . It’s perfect, you know. It’s gorgeous. It’s almost uncanny.
Astronomer Geo rey Marcy describing the solar system
HOW TO BUILD A UNIVERSE
No matter how hard you try you will never be able to grasp just how tiny, how spatially unassuming, is a proton. It is just way too small.
A proton is an infinitesimal part of an atom, which is itself of course an insubstantial thing. Protons are so small that a little dib of ink like the dot on this ‘i’ can hold something in the region of 10,000,000,000,000,000,000,000 of them. So protons are exceedingly microscopic, to say the very least.
Now imagine if you can (and of course you can’t) shrinking one of those protons down to a billionth of its normal size into a space so small that it would make a proton look enormous. Now pack into that tiny, tiny space about an ounce of matter. Excellent. You are ready to start a universe. I’m assuming of course that you wish to build an inflationary universe. If you’d prefer instead to build a more old-fashioned, standard Big Bang universe, you’ll need additional materials. In fact, you will need to gather up everything there is – every last mote and particle of matter between here and the edge of creation – and squeeze it into a spot so infinitesimally compact that it has no dimensions at all. It is known as a singularity.
In either case, get ready for a really big bang. Naturally, you will wish to retire to a safe place to observe the spectacle.
Unfortunately, there is nowhere to retire to because outside the singularity there is no where. When the universe begins to expand, it won’t be spreading out to fill a larger emptiness. The only space that exists is the space it creates as it goes.
It is natural but wrong to visualize the singularity as a kind of pregnant dot hanging in a dark, boundless void. But there is no space, no darkness. The singularity has no around around it. There is no space for it to occupy, no place for it to be. We can’t even ask how long it has been there – whether it has just lately popped into being, like a good idea, or whether it has been there for ever, quietly awaiting the right moment. Time doesn’t exist. There is no past for it to emerge from.
And so, from nothing, our universe begins.
In a single blinding pulse, a moment of glory much too swift and expansive for any form of words, the singularity assumes heavenly dimensions, space beyond conception. The first lively second (a second that many cosmologists will devote careers to shaving into ever-finer wafers) produces gravity and the other forces that govern physics. In less than a minute the universe is a million billion miles across and growing fast. There is a lot of heat now, 10 billion degrees of it, enough to begin the nuclear reactions that create the lighter elements – principally hydrogen and helium, with a dash (about one atom in a hundred million) of lithium. In three minutes, 98 per cent of all the matter there is or will ever be has been produced. We have a universe. It is a place of the most wondrous and gratifying possibility, and beautiful, too. And it was all done in about the time it takes to make a sandwich.
Until quite recently cosmologists argued over whether that moment of creation was 10 billion years ago or twice that or something in between, but in 2003, using data from a NASA spacecraft with the uncompromisingly nerdy name of Wilkinson Microwave Anisotropy Probe (WMAP), the age of the universe was fixed at a reassuringly precise 13.77 billion years, with a range of uncertainty of just 0.4 per cent.
There is of course a great deal we don’t know, and much of what we think we know we haven’t known, or thought we’ve known, for long. Even the notion of the Big Bang is quite a recent one. The idea had been kicking around since the 1920s when Georges Lemaître, a Belgian priest-scholar, first tentatively proposed it, but it didn’t really become an active notion in astrophysics until the mid-1960s, when two young radio astronomers made an extraordinary and inadvertent discovery. Their names were Arno Penzias and Robert Wilson. In 1964, they were trying to make use of a large communications antenna owned by Bell Laboratories at Holmdel, New Jersey, but they were troubled by a persistent background noise – a steady, steamy hiss that made any experimental work impossible. The noise was unrelenting and unfocused. It came from every point in the sky, day and night, through every season. For a year the young astronomers did everything they could think of to track down and eliminate the noise. They tested every electrical system. They rebuilt instruments, checked circuits, wiggled wires, dusted plugs. They climbed into the dish and placed duct tape over every seam and rivet. They climbed back into the dish with brooms and scrubbing brushes and carefully swept it clean of what they referred to in a later paper as ‘white dielectric material’, or what is known more commonly as bird shit. Nothing they tried worked.
Unknown to them, just 50 kilometres away at Princeton University a team of scientists led by Robert Dicke was working on how to find the very thing they were trying so diligently to get rid of. The Princeton researchers were pursuing an idea that had been suggested in the 1940s by the Russian-born astrophysicist George Gamow: that if you looked deep enough into space you should find some cosmic background radiation left over from the Big Bang. Gamow calculated that by the time it had crossed the vastness of the cosmos the radiation would reach Earth in the form of microwaves. In a more recent paper he had even suggested an instrument that might do the job:
the Bell antenna at Holmdel. Unfortunately, neither Penzias and Wilson, nor any of the Princeton team, had read Gamow’s paper.
The noise that Penzias and Wilson were hearing was, of course, the noise that Gamow had postulated. They had found the edge of the universe, or at least the visible part of it, 90 billion trillion miles away. They were ‘seeing’ the first photons – the most ancient light in the universe – though time and distance had converted them to microwaves, just as Gamow had predicted. In his book The Inflationary Universe, Alan Guth provides an analogy that helps to put this finding in perspective. If you think of peering into the depths of the universe as like looking down from the hundredth floor of the Empire State Building (with the hundredth floor representing now and street level representing the moment of the Big Bang), at the time of Wilson and Penzias’s discovery the most distant galaxies anyone had ever detected were on about the sixtieth floor and the most distant things – quasars – were on about the twentieth. Penzias and Wilson’s finding pushed our acquaintance with the visible universe to within half an inch of the lobby floor.
Still unaware of what caused the noise, Wilson and Penzias phoned Dicke at Princeton and described their problem to him in the hope that he might suggest a solution. Dicke realized at once what the two young men had found. ‘Well, boys, we’ve just been scooped,’ he told his colleagues as he hung up the phone. Soon afterwards the Astrophysical Journal published two articles: one by Penzias and Wilson describing their experience with the hiss, the other by Dicke’s team explaining its nature. Although Penzias and Wilson had not been looking for cosmic background radiation, didn’t know what it was when they had found it, and hadn’t described or interpreted its character in any paper, they received the 1978 Nobel Prize in Physics. The Princeton researchers got only sympathy. According to Dennis Overbye in Lonely Hearts of the Cosmos, neither Penzias nor
Wilson altogether understood the significance of what they had found until they read about it in the New York Times.
Incidentally, disturbance from cosmic background radiation is something we have all experienced. Tune your television to any channel it doesn’t receive and about 1 per cent of the dancing static you see is accounted for by this ancient remnant of the Big Bang. The next time you complain that there is nothing on, remember that you can always watch the birth of the universe.
Although everyone calls it the Big Bang, many books caution us not to think of it as an explosion in the conventional sense. It was, rather, a vast, sudden expansion on a whopping scale. So what caused it?
One notion is that perhaps the singularity was the relic of an earlier, collapsed universe – that ours is just one of an eternal cycle of expanding and collapsing universes, like the bladder on an oxygen machine. Others attribute the Big Bang to what they call ‘a false vacuum’ or ‘a scalar field’ or ‘vacuum energy’ – some quality or thing, at any rate, that introduced a measure of instability into the nothingness that was. It seems impossible that you could get something from nothing, but the fact that once there was nothing and now there is a universe is evident proof that you can. It may be that our universe is merely part of many larger universes, some in di erent dimensions, and that Big Bangs are going on all the time all over the place. Or it may be that space and time had some other forms altogether before the Big Bang – forms too alien for us to imagine – and that the Big Bang represents some sort of transition phase, where the universe went from a form we can’t understand to one we almost can. As Dr Andrei Linde, a cosmologist at Stanford, once noted, ‘These are very close to religious questions.’
The Big Bang theory isn’t about the bang itself but about what happened after the bang. Not long after, mind you. By doing a lot of maths and watching carefully what goes on in
particle accelerators, scientists believe they can look back to 10-43 seconds after the moment of creation, when the universe was still so small that you would have needed a microscope to find it. We mustn’t swoon over every extraordinary number that comes before us, but it is perhaps worth latching on to one from time to time just to be reminded of their ungraspable and amazing breadth. Thus 10–43 is 0.00000000000000000000000 00000000000000000001, or one-ten-million-trillion-trilliontrillionths of a second.*
Most of what we know, or believe we know, about the early moments of the universe is thanks to an idea called inflation theory first propounded in 1979 by a junior particle physicist then at Stanford, now at MIT, named Alan Guth. He was thirty-two years old and, by his own admission, had never done anything much before. He would probably never have had his great theory except that he happened to attend a lecture on the Big Bang given by none other than Robert Dicke. The lecture inspired Guth to take an interest in cosmology, and in particular in the birth of the universe.
* A word on scientific notation. Since very large numbers are cumbersome to write and nearly impossible to read, scientists use a shorthand involving powers (or multiples) of ten in which, for instance, 10,000,000,000 is written 1010 and 6,500,000 becomes 6.5 3 106. The principle is based very simply on multiples of ten: 10 3 10 (or 100) becomes 102; 10 3 10 3 10 (or 1,000) is 103; and so on, obviously and indefinitely. The little superscript number signifies the number of zeroes following the larger principal number. Negative notations provide essentially a mirror image, with the superscript number indicating the number of spaces to the right of the decimal point (so 10–4 means 0.0001). Though I salute the principle, it remains an amazement to me that anyone seeing ‘1.4 3 109 km3’ would see at once that that signifies 1.4 billion cubic kilometres, and no less a wonder that they would choose the former over the latter in print (especially in a book designed for the general reader, where the example was found). On the assumption that many readers are as unmathematical as I am, I will use notations sparingly, though they are occasionally unavoidable, not least in a chapter dealing with things on a cosmic scale.
The eventual result was the inflation theory, which holds that a fraction of a moment after the dawn of creation, the universe underwent a sudden dramatic expansion. It inflated – in e ect ran away with itself, doubling in size every 10–34 seconds. The whole episode may have lasted no more than 10–30 seconds – that’s onemillion-million-million-million-millionths of a second – but it changed the universe from something you could hold in your hand to something at least 10,000,000,000,000,000,000,000,000 times bigger. Inflation theory explains the ripples and eddies that make our universe possible. Without it, there would be no clumps of matter and thus no stars, just drifting gas and everlasting darkness. According to Guth’s theory, at one ten-millionth of a trillionth of a trillionth of a trillionth of a second, gravity emerged. After another ludicrously brief interval it was joined by electromagnetism and the strong and weak nuclear forces – the stu of physics. These were followed an instant later by shoals of elementary particles – the stu of stu . From nothing at all, suddenly there were swarms of photons, protons, electrons, neutrons and much else – between 1079 and 1089 of each, according to the standard Big Bang theory.
Such quantities are of course ungraspable. It is enough to know that in a single instant we were endowed with a universe that was vast – at least 100 billion light years across, according to the theory, but possibly any size up to infinite – and perfectly arrayed for the creation of stars, galaxies and other complex systems.*
* A question that naturally arises is how the universe could expand faster than the speed of light if, as we all know, nothing moves faster than the speed of light. The simple answer is that the law applies only to objects moving within space, and in the case of universal expansion it is space itself that is on the move, not the objects within it. Imagine a loaf of raisin bread rising in a warm oven. As it expands, the raisins embedded in it move further apart, but they are not travelling through the dough, but rather just moving along with it. If the raisins were moving independently, they could not go faster than the speed of light, but the loaf/universe has no such constraints.
What is extraordinary from our point of view is how well it turned out for us. If the universe had formed just a tiny bit di erently – if gravity were fractionally stronger or weaker, if the expansion had proceeded just a little more slowly or swiftly – then there might never have been stable elements to make you and me and the ground we stand on. Had gravity been a trifle stronger, the universe itself might have collapsed like a badly erected tent without precisely the right values to give it the necessary dimensions and density and component parts. Had it been weaker, however, nothing would have coalesced. The universe would have remained for ever a dull, scattered void.
This is one reason why some experts believe that there may have been many other big bangs, perhaps trillions and trillions of them, spread through the mighty span of eternity, and that the reason we exist in this particular one is that this is one that we could exist in. As Edward P. Tryon of Columbia University once put it: ‘In answer to the question of why it happened, I o er the modest proposal that our Universe is simply one of those things which happen from time to time.’ To which adds Guth: ‘Although the creation of a universe might be very unlikely, Tryon emphasized that no one had counted the failed attempts.’
Martin Rees (formally Baron Rees of Ludlow), Britain’s former Astronomer Royal, has suggested that there may be many universes, possibly an infinite number, each with di erent attributes, in di erent combinations, and that we simply live in one that combines things in the way that allows us to exist. He has made an analogy with a very large clothing store: ‘If there is a large stock of clothing, you’re not surprised to find a suit that fits. If there are many universes, each governed by a di ering set of numbers, there will be one where there is a particular set of numbers suitable to life. We are in that one.’ Rees notes that six numbers in particular govern our universe, and that if any of these values were changed even very
slightly things could not be as they are. For example, for the universe to exist as it does requires that hydrogen be converted to helium in a precise but comparatively stately manner – specifically, in a way that converts seven one-thousandths of its mass to energy. Lower that value very slightly – from 0.07 per cent to 0.06 per cent, say – and no transformation could take place: the universe would consist of hydrogen and nothing else. Raise the value very slightly – to 0.08 per cent – and bonding would be so wildly prolific that the hydrogen would long since have been exhausted. In either case, with the slightest tweaking of the numbers the universe as we know and need it would not be here.
I should say that everything is just right so far. In the long term, gravity may turn out to be a little too strong; one day it may halt the expansion of the universe and bring it collapsing in upon itself, until it crushes itself down into another singularity, possibly to start the whole process over again. On the other hand, it may be too weak, in which case the universe will keep racing away for ever until everything is so far apart that there is no chance of material interactions, so that the universe becomes a place that is very roomy, but inert and dead. The third option is that gravity is perfectly pitched – ‘critical density’ is the cosmologists’ term for it – and that it will hold the universe together at just the right dimensions to allow things to go on indefinitely. Cosmologists, in their lighter moments, sometimes call this the ‘Goldilocks e ect’ – that everything is just right. (For the record, these three possible universes are known respectively as closed, open and flat.)
Now, the question that has occurred to all of us at some point is: what would happen if you travelled out to the edge of the universe and, as it were, put your head through the curtains? Where would your head be if it were no longer in the universe? What would you find beyond? The answer, disappointingly, is that you can never get to the edge of the universe. That’s not because it would take too long to get there – though
of course it would – but because even if you travelled outward and outward in a straight line, indefinitely and pugnaciously, you would never arrive at an outer boundary. Instead, you would come back to where you began (at which point, presumably, you would rather lose heart in the exercise and give up). The reason for this is that the universe bends, in a way we can’t adequately imagine, in conformance with Einstein’s theory of relativity (which we will get to in due course). For the moment it is enough to know that we are not adrift in some large, everexpanding bubble. Rather, space curves, in a way that allows it to be boundless but finite. Space cannot even properly be said to be expanding because, as the physicist and Nobel laureate Steven Weinberg long ago noted, ‘solar systems and galaxies are not expanding, and space itself is not expanding.’ Rather, the galaxies are rushing apart. It is all something of a challenge to intuition. Or, as the biologist J. B. S. Haldane once famously observed: ‘The universe is not only queerer than we suppose; it is queerer than we can suppose.’
The analogy that is usually given for explaining the curvature of space is to try to imagine someone from a universe of flat surfaces, who had never seen a sphere, being brought to Earth. No matter how far he roamed across the planet’s surface, he would never find an edge. He might eventually return to the spot where he had started, and would of course be utterly confounded to explain how that had happened. Well, we are in the same position in space as our puzzled flatlander, only we are flummoxed by a higher dimension.
Just as there is no place where you can find the edge of the universe, so there is no place where you can stand at the centre and say: ‘This is where it all began. This is the centremost point of it all.’ We are all at the centre of it all. Actually, we don’t know that for sure; we can’t prove it mathematically. Scientists just assume that we can’t really be the centre of the universe – think what that would imply – but that the phenomenon must
be the same for all observers in all places. Still, we don’t actually know.
For us, the universe goes only as far as light has travelled in the billions of years since the universe was formed. This visible universe – the universe we know and can talk about – is estimated to be about 94 billion light years across. But according to most theories the universe at large – the meta-universe, as it is sometimes called – is vastly roomier still. According to Rees, the number of light years to the edge of this larger, unseen universe would be written not ‘with ten zeroes, not even with a hundred, but with millions’. In short, there’s more space than you can imagine already without going to the trouble of trying to envision some additional beyond.
For a long time the Big Bang theory had one gaping hole that troubled a lot of people – namely, that it couldn’t begin to explain how we got here. Although 98 per cent of all the matter that exists was created with the Big Bang, that matter consisted exclusively of light gases: the helium, hydrogen and lithium that we mentioned earlier. Not one particle of the heavy stu so vital to our own being – carbon, nitrogen, oxygen and all the rest – emerged from the gaseous brew of creation. But – and here’s the troubling point – to forge these heavy elements, you need the kind of heat and energy thrown o by a Big Bang. Yet there has been only one Big Bang and it didn’t produce them. So where did they come from? Interestingly, the man who found the answer to that question was a cosmologist who heartily despised the Big Bang as a theory and coined the term Big Bang facetiously, as a way of mocking it. We’ll get to him shortly, but before we turn to the question of how we got here, it might be worth taking a few minutes to consider just where exactly ‘here’ is.
WELCOME TO THE SOLAR SYSTEM
Astronomers these days can do the most amazing things. If someone struck a match on the Moon, they could spot the flare. From the tiniest throbs and wobbles of distant stars they can infer the size and character and even potential habitability of planets much too remote to be seen – planets so distant that it would take us half a million years in a spaceship to get there. With their radio telescopes they can capture wisps of radiation so preposterously faint that the total amount of energy collected from outside the solar system by all of them together since collecting began (in 1951) is ‘less than the energy of a single snowflake striking the ground’, in the words of Carl Sagan. That was in 1980, so the total has clearly gone up but the amount of accumulated energy is still infinitesimal.
In short, there isn’t a great deal that goes on in the universe that astronomers can’t find when they have a mind to. Which is why it is all the more remarkable to reflect that until 1978 no one had ever noticed that Pluto has a moon. In the summer of that year, a young astronomer named James Christy at the Lowell Observatory in Flagsta , Arizona, was making a routine examination of photographic images of Pluto when he saw that there was something there – something blurry and uncertain but definitely other than Pluto. Consulting a colleague
named Robert Harrington, he concluded that what he was looking at was a moon. And it wasn’t just any moon. Relative to the planet, it was the biggest moon in the solar system.
This was actually something of a blow to Pluto’s status as a planet, which had never been terribly robust anyway. Since previously the space occupied by the moon and the space occupied by Pluto were thought to be one and the same, it meant that Pluto was much smaller than anyone had supposed – smaller even than Mercury. Indeed, several moons in the solar system, including our own, are larger.
Now, a natural question is why it took so long for anyone to find a moon in our own solar system. In fact, it may surprise you to hear, new moons are being found all the time. In 2023 alone, the International Astronomical Union recognized twelve new moons around Jupiter, bringing its total to ninetyfive, nearly three times the number known when this book was first published. Only a few weeks after that announcement, Saturn’s moon count was increased by a whopping eightythree, bringing its total to 145, and in early 2025 the total was increased again, by 128, to a truly spectacular 274, or more moons than all the rest of the planets in the solar system put together. Discoveries have been coming so thick and fast, in fact, that new, smaller discoveries are no longer being given names from mythology, as they were traditionally, but just dry catalogue designations like S/2021 J3 and S/2017 J7.
The reason these moons were not found earlier is that they are mostly small – only a mile or two across – and often orbiting far out from their host planet, and sometimes orbiting in the opposite direction from their fellow moons. Many of the new moons are shaped like potatoes and are really just big rocks. Indeed, the only universally accepted definition of a moon at present is that it is a solid object orbiting a planet, irrespective of its size. By that definition there are almost certainly hundreds, possibly thousands, more to be discovered.
Indeed, Pluto, we now know, hasn’t just one moon but five:
Christy’s discovery of 1978, called Charon, and four others (Nix, Styx, Kerberos and Hydra), which were found between 2005 and 2012.
As for Pluto itself, it’s been a tough few years. Its reign as our most distant planet didn’t even last a single human lifetime. It was discovered, rather miraculously, in 1930 by a young man from Kansas named Clyde Tombaugh who had no formal training in astronomy and was looking for something else anyway. Tombaugh had been hired by the Lowell Observatory in Arizona to try to find a massive, gassy planet on the edge of the solar system that the observatory’s wealthy founder, Percival Lowell, was certain was out there.
Lowell is best remembered now for his long-influential belief that Mars was covered with canals built by industrious Martians for purposes of conveying water from polar regions to the dry but productive lands nearer the equator. Lowell’s other abiding conviction was that there existed, somewhere out beyond Neptune, an undiscovered ninth planet, dubbed Planet X. Lowell based this belief on irregularities he detected in the orbits of Uranus and Neptune, and spent years obsessively but unsuccessfully searching for it.
After Lowell’s death, it fell to Tombaugh to continue the quest. Although Tombaugh had never attended college and his knowledge of the universe came largely from reading Popular Astronomy magazine, he was extraordinarily diligent, and after a year’s patient searching he somehow spotted Pluto, a faint point of light in a glittery firmament. It was a miraculous find, and what made it all the more striking was that the observations on which Lowell had predicted the existence of a planet beyond Neptune proved to be comprehensively erroneous. Tombaugh could see at once that the new planet was nothing like the massive gasball Lowell had postulated, but any reservations he or anyone else had about the character of the new planet were soon swept aside in the delirium that attended almost any big news story in that easily excited age. This was
the first American-discovered planet, and no one was going to be distracted by the thought that it was really just a distant icy dot. It was named Pluto at least partly because the first two letters made a monogram from Lowell’s initials. Lowell was posthumously hailed everywhere as a genius of the first order and Tombaugh was largely forgotten, except among planetary astronomers, who tend to revere him.
So the solar system had a ninth planet, but it was quite an odd and mysterious one, in large part because it was so distant and anomalously small. Many astronomers thought it not a planet at all, but merely the largest object so far found in a zone of galactic debris known as the Kuiper Belt. The Kuiper Belt was actually theorized by an astronomer named F. C. Leonard in 1930, but the name honours Gerard Kuiper, a Dutch native working in America, who expanded the idea.
It is certainly true that Pluto doesn’t act much like the other planets. Whereas the others orbit on more or less the same plane, Pluto’s orbital path is tipped out of alignment at an angle of 17 degrees, like the brim of a hat tilted rakishly on someone’s head. Its orbit is so irregular that for substantial periods on each of its lonely circuits around the Sun it is closer to us than Neptune is. For most of the 1980s and 1990s, Neptune was in fact the solar system’s most far-flung planet. Only on 11 February 1999 did Pluto return to the outside lane, there to remain for the next 228 years.
So if Pluto really was a planet, it was certainly an odd one. It would mean that our planetary system consisted of four rocky inner planets, four gassy outer giants, and a tiny, solitary iceball. Matters came to a head of sorts in the summer of 2005 when astronomers from the Palomar Observatory in California announced the discovery of a Kuiper Belt object even bigger than Pluto, following an eccentric orbit that takes it up to three times further out from the Sun than Pluto – so far out that a single orbit of the Sun takes it 560 years. The discoverers informally named it Xena, after the warrior princess in a popular
1990s television show, but eventually – and, let’s be frank, mercifully – that was discarded for the more seemly classical name Eris, the Greek goddess of strife.
The following year, at an unusually lively meeting in Prague, the International Astronomical Union decreed that Eris was not a proper planet at all, but fell into a new category to be called dwarf planets. Even more controversially, the same meeting likewise demoted Pluto (along with Ceres, which lives in the asteroid belt between Mars and Jupiter and never had planetary status anyway). Interestingly, it was only then that astronomers got round to creating a formal definition of what constitutes a planet. They decided it must meet three criteria: it must orbit the Sun, it must be massive and spherical, and it must exert enough gravity to absorb or scatter any rocky debris that passes nearby. Pluto failed on this last count.
Ironically, just under a decade after its demotion, NASA’s New Horizon spacecraft flew past Pluto and discovered it was way more interesting than previously supposed. Far from being an inert ball of ice, Pluto had active glaciers, mountains as big as those in the Rockies, probably an ocean of liquid water beneath the surface, and signs of volcanic activity. It was, in short, one of the liveliest places in the solar system.
But it’s still not a planet.
So now we have a solar system with eight planets, five dwarf planets (Pluto, Ceres, Makemake, Haumea and Eris), at least 400 moons, more than 1.3 million asteroids, and a little under 4,000 comets. But, as we have already seen, many of those numbers change nearly as fast as they can be recorded. As for Pluto, in the 76 years it was a planet it didn’t even manage one full orbit of the Sun.
The central point in all this is that we live in a solar system that in many ways we still hardly know. Compared with the vastness of the universe at large, our solar system may seem comparatively compact and neighbourly, but in fact it is roomy beyond our capacity to imagine.
Let us pretend, for purposes of edification and entertainment, that we are about to go on a journey by rocketship. We won’t go terribly far – just to the edge of our own solar system – but we need to get a fix on how big a place space is and what a small part of it we occupy. Now the bad news, I’m afraid, is that we won’t be home for supper. Even at the speed of light it would take seven hours to reach Pluto. But of course we can’t travel at anything like that speed. We’ll have to go at the speed of a spaceship, and these are rather more lumbering. The Voyager 1 spacecraft, which launched from Earth in 1977 and used a rare alignment of Jupiter, Saturn, Uranus and Neptune as a series of celestial slingshots to fling it onward at ever greater speeds, has travelled 15 billion miles in half a century and is increasing that distance by nearly a million miles every day, but it is still nowhere near the edge of the solar system.*
So get ready for a long trip. As we proceed, you will quickly notice that space is extremely well named and rather dismayingly uneventful. Our solar system may be the liveliest thing for trillions of miles, but all the visible stu in it – the Sun, the planets and their moons, the tumbling rocks of the asteroid belt, the 4,500 or so known comets and all the other miscellaneous drifting detritus – fills less than a trillionth of the available space. You also quickly realize that none of the maps you have ever seen of the solar system was drawn remotely to scale. Most schoolroom charts show the planets coming one after the other at neighbourly intervals – the outer giants actually cast shadows over each other in many illustrations – but this is a necessary deceit to get them all on the same piece of paper. Neptune in reality isn’t just a little bit beyond Jupiter, it’s way beyond Jupiter – five
* Voyager 1 and its sister craft Voyager 2 were designed to last for only about five years, but as of this writing were still sending back usable data to Earth – an achievement all the more remarkable when you consider that their onboard computers ‘have less memory than the key fob that opens your car door’, according to Linda Spilker, a planetary scientist at the NASA Jet Propulsion Laboratory.
times further from Jupiter than Jupiter is from us, so far out that it receives only 3 per cent as much sunlight as Jupiter.
On a model of the solar system to scale, with the Earth reduced to about the diameter of a pea, Jupiter would be over 300 metres away and Pluto would be 2.5 kilometres distant (and about the size of a bacterium, so you wouldn’t be able to see it anyway). On the same scale, Proxima Centauri, our nearest star, would be 16,000 kilometres away. Even if you shrank down everything so that Jupiter was as small as the full stop at the end of this sentence and Pluto was no bigger than a molecule, Pluto would still be over 10 metres away. So the solar system is really quite enormous. By the time we reach Pluto, we have come so far that the Sun – our dear, warm, skin-tanning, life-giving Sun – has shrunk to the size of a pinhead. It is little more than a bright star. In such a lonely void you can begin to understand how even quite significant objects have escaped attention.
Now, the other thing you will notice as we speed past Pluto is that we are speeding past Pluto. If you check your itinerary, you will see that this is a trip to the edge of our solar system, and I’m afraid we’re not there yet. Pluto may be the last object traditionally marked on schoolroom charts, but the solar system doesn’t end there. In fact, it isn’t even close to ending there. We won’t get to the solar system’s edge until we have passed through the Oort Cloud* – a vast and, it must be said, entirely hypothesized realm of drifting comets that is thought to encircle our solar system like a giant soap bubble. Because no one has ever seen the Oort Cloud, we can’t be exactly certain where it begins and ends, but the best estimates are that it will take us about 300 years to reach it and perhaps 30,000 to pass out the other side. (Other sources think it could take more like 6,000 years. Whatever the exact figure, it will take generations.)
* Properly called the Öpik–Oort Cloud, it is named for the Estonian astronomer Ernst Öpik, who hypothesized its existence in 1932, and for the Dutch astronomer Jan Oort, who refined the calculations eighteen years later.
Of course we have no prospect of such a journey. Based on what we know now and can reasonably imagine, there is absolutely no prospect that any human being will ever visit the edge of our own solar system – ever. It is just too far. The basic unit of measure in the solar system is the Astronomical Unit, or AU, representing the distance from the Sun to the Earth (and defined, very precisely, as 149,597,870.7 kilometres). Pluto is about 40 AUs from us, the heart of the Oort Cloud about 50,000. In a word, it is remote.
But let’s pretend again, for convenience, that we have actually made it to the Oort Cloud. The first thing you might notice is how very peaceful it is out here. We’re a long way from anywhere now – so far from our own Sun that it’s not even the brightest star in the sky. It is a remarkable thought that that distant tiny twinkle has enough gravity to hold all these comets in orbit. It’s not a very strong bond, so the comets drift in a stately manner, moving at only about 220 miles an hour. From time to time one of these lonely comets is nudged out of its normal orbit by some slight gravitational perturbation. Sometimes they are ejected into the emptiness of space, never to be seen again, but sometimes they fall into a long orbit around the Sun. About three or four of these a year, known as long-period comets, pass through the inner solar system. Just occasionally these stray visitors smack into something solid, like Earth. That’s why we’ve come out here now – because the comet we have come to see has just begun a long fall towards the centre of the solar system. It is headed for, of all places, Manson, Iowa. It is going to take a long time to get there – 3 or 4 million years at least – so we’ll leave it for now, and return to it much later in the story.
So that’s your solar system. And what else is out there, beyond the solar system? Well, nothing much and a great deal, depending on how you look at it.
In the short term, it’s nothing much. The most perfect vacuum
ever created by humans is not as empty as the emptiness of interstellar space. And there is a great deal of this nothingness until you get to the next bit of something. Our nearest neighbour in the cosmos, Proxima Centauri, which is part of the three-star cluster known as Alpha Centauri, is 4.3 light years away, almost nothing in galactic terms, but still 100 million times further than a trip to the Moon. To reach it by spaceship would take perhaps 50,000 years, and even if you made the trip you still wouldn’t be anywhere except at a lonely clutch of stars in the middle of a vast nowhere. To reach the next landmark of consequence, Sirius, would involve another 4.6 light years of travel. And so it would go if you tried to star-hop your way across the cosmos. Just reaching the centre of our own galaxy would take far longer than we have existed as beings.
Space, let me repeat, is enormous. The average distance between stars out there is over 30 million million kilometres. Even at speeds approaching those of light, these are fantastically challenging distances for any travelling individual. Of course, it is possible that alien beings travel billions of miles to amuse themselves by planting crop circles in Wiltshire or frightening the daylights out of some poor guy in a pickup truck on a lonely road in Arizona (they must have teenagers, after all), but it does seem unlikely.
Still, statistically the probability that there are other thinking beings out there is good. Nobody knows how many stars there are in the Milky Way – estimates range from 100 billion or so to perhaps 400 billion – and the Milky Way is just one of unknowable billions of galaxies in the observable universe (some estimates now put the number as high as 2 trillion). In the 1960s, a professor at Cornell named Frank Drake, intrigued by the massive numbers, worked out a famous equation designed to calculate the chances of advanced life existing in the cosmos, based on a series of diminishing probabilities.
Under Drake’s equation you divide the number of stars in a selected portion of the universe by the number of stars that are
likely to have planetary systems; divide that by the number of planetary systems that could theoretically support life; divide that by the number on which life, having arisen, advances to a state of intelligence; and so on. At each such division, the number shrinks colossally – yet even with the most conservative inputs the number of advanced civilizations just in the Milky Way always works out to be somewhere in the millions.
What an interesting and exciting thought. We may be only one of millions of advanced civilizations just in our own galaxy. Unfortunately, space being spacious, the average distance between any two of these civilizations is reckoned to be at least 200 light years, which is a great deal more than merely saying it makes it sound. It means, for a start, that even if these beings know we are here and are somehow able to see us in their telescopes, they’re watching light that left Earth 200 years ago. So they’re not seeing you and me. They’re watching people who don’t know what an atom is, or a gene, or even a railway train. Any message we receive from these observers is likely to begin by congratulating us on the handsomeness of our horses and our mastery of whale oil. Two hundred light years is a distance so far beyond us as to be, well, just beyond us. As the British astronomer Martin Rees has pointed out, ‘Even if a life-bearing planet were nearby, it would in all probability be at a di erent stage of evolution. And the life there could be based on something else altogether – methane rather than water, say – which would make it entirely unlike our own.’
Such is likely to be the case with a planet called K2-18b, which in April 2025 was reported to contain an abundance of dimethyl sulfide, a molecule that occurs on Earth only as a byproduct of living organisms, thus making K2-18b the clearest candidate yet for life elsewhere in the universe. There is no telling at this stage, however, how complex that life may be, if it exists at all, and in any case K2-18b is 720 trillion miles away, so well beyond any practical contact or close examination. Dimethyl sulfide, for what it is worth, smells horrible.
So even if we are not literally alone, in all practical terms we are. Carl Sagan calculated the number of probable planets in the universe at as many as 10 billion trillion – a number vastly beyond imagining. But what is equally beyond imagining is the amount of space through which they are lightly scattered.
‘If we were randomly inserted into the universe,’ Sagan wrote, ‘the chances that you would be on or near a planet would be less than one in a billion trillion trillion.’ (That’s 1033, or 1 followed by thirty-three zeroes.)
Sagan died in 1996 at the cruelly early age of sixty-two, so those calculations will have changed, but his melancholy conclusion has not. ‘Worlds are precious,’ he wrote.
THE REVEREND EVANS’S UNIVERSE
For years and years, when the skies were clear and the Moon not too bright, the Reverend Robert Evans, a quiet and cheerful man, would lug a bulky telescope on to the back sun-deck of his home in the Blue Mountains of Australia, about 80 kilometres west of Sydney, and do something extraordinary. He would look deep into the past and find dying stars.
Looking into the past was, of course, the easy part. Glance at the night sky and what you see is history and lots of it – not the stars as they are now, but as they were when their light left them. For all we know, the North Star,* our faithful companion, might actually have burned out last January or in 1854 or at any time since the early eighteenth century and news of it just hasn’t reached us yet. The best we can say – can ever say – is that it was still burning on this date 323 years ago. Stars die all the time. What Bob Evans could do better than anyone else who ever tried was spot these moments of celestial farewell. He was, in short, the world’s greatest hunter of supernovae.
A supernova occurs when a giant star, one much bigger than
* The distance to the North Star, or Polaris to use its o cial name, was only definitively calculated in 2012, putting it considerably closer to Earth than previously thought.
our own Sun, collapses and then spectacularly explodes, releasing in an instant the energy of 100 billion suns, burning for a time more brightly than all the stars in its galaxy. ‘It’s like a trillion hydrogen bombs going o at once,’ Evans told me when we first met at his home in 2001. A semi-retired minister in the Uniting Church of Australia, Evans was the most modest and in many ways most exceptional of the people I met for this book.
Despite the violence of their dying explosions, most supernovae are so unimaginably distant that their light reaches us as no more than the faintest twinkle. For the month or so that they are visible, all that distinguishes them from the other stars in the sky is that they occupy a point of space that wasn’t filled before. It is these anomalous, very occasional pricks in the crowded dome of the night sky that the Reverend Evans had an uncanny – indeed, quite unparalleled – knack for spotting.
To understand what a feat this was, imagine a standard dining-room table covered in a black tablecloth and throwing a handful of salt across it. The scattered grains can be thought of as a galaxy. Now imagine 1,500 more tables like the first one – enough to make a single line 2 miles long – each with a random array of salt across it. Now add one grain of salt to any table and let Bob Evans walk among them. At a glance he would spot it. That grain of salt was the supernova.
Evans’s was a talent so exceptional that Oliver Sacks, in An Anthropologist on Mars, devoted a passage to him in a chapter on autistic savants – quickly adding that ‘there is no suggestion that he is autistic’. Evans, who never met Sacks, laughed at the suggestion that he might be either autistic or a savant, but was powerless to explain quite where his talent came from.
‘I just seem to have a knack for memorizing star fields,’ he told me, with a frankly apologetic look, when I visited him and his wife, Elaine, in their picture-book bungalow on a tranquil
edge of the village of Hazelbrook, out where Sydney finally ends and the boundless Australian bush begins. ‘I’m not particularly good at other things,’ he added. ‘I don’t remember names well.’
‘Or where he’s put things,’ called Elaine from the kitchen. He nodded frankly again and grinned, then asked me if I’d like to see his telescope. I had imagined that Evans would have a proper observatory in his back yard – a scaled-down version of a Mount Wilson or Palomar, with a sliding domed roof and a mechanized chair that would be a pleasure to manoeuvre. In fact, he led me not outside but to a crowded storeroom o the kitchen where he kept his books and papers and where his telescope – a white cylinder about the size and shape of a household hot-water tank – rested in a home-made, swivelling plywood mount. When he wished to observe, he would carry them, in two trips, to the small sun-deck o the kitchen. Between the overhang of the roof and the feathery tops of eucalyptus trees growing up from the slope below, he had only a letterbox view of the sky, but he assured me it was more than good enough for his purposes.
The term supernova was coined in the 1930s by a memorably odd astrophysicist named Fritz Zwicky. Born in Bulgaria and raised in Switzerland, Zwicky came to the California Institute of Technology in the 1920s and there at once distinguished himself by his abrasive personality and erratic talents. He didn’t seem to be outstandingly bright, and many of his colleagues considered him little more than ‘an irritating bu oon’. A fitness fanatic, he would often drop to the floor of the Caltech dining hall or some other public area and do one-armed pushups to demonstrate his virility to anyone who seemed inclined to doubt it. He was notoriously aggressive, his manner eventually becoming so intimidating that his closest collaborator, a gentle man named Walter Baade, refused to be left alone with him. Among other things, Zwicky accused Baade, who was
German, of being a Nazi, which he was not. On at least one occasion Zwicky threatened to kill Baade, who worked up the hill at the Mount Wilson Observatory, if he saw him on the Caltech campus.
But Zwicky was also capable of insights of the most startling brilliance. In the early 1930s he turned his attention to a question that had long troubled astronomers: the appearance in the sky of occasional unexplained points of light, new stars. Improbably, he wondered if the neutron – the subatomic particle that had just been discovered in England by James Chadwick, and was thus both novel and rather fashionable – might be at the heart of things. It occurred to him that if a star collapsed to the sort of densities found in the core of atoms, the result would be an unimaginably compacted core. Atoms would literally be crushed together, their electrons forced into the nucleus, forming neutrons. You would have a neutron star. Imagine a million really weighty cannonballs squeezed down to the size of a marble and – well, you’re still not even close. The core of a neutron star is so dense that a single spoonful of matter from it would weigh more than 500 billion kilograms. A spoonful! But there was more. Zwicky realized that after the collapse of such a star there would be a huge amount of energy left over – enough to make the biggest bang in the universe. He called these resultant explosions supernovae. They would be – they are – the biggest events in creation.
On 15 January 1934 the journal Physical Review published a very concise abstract of a presentation that had been conducted by Zwicky and Baade the previous month at Stanford University. Despite its extreme brevity – one paragraph of twenty-four lines – the abstract contained an enormous amount of new science: it provided the first reference to supernovae and to neutron stars; convincingly explained their method of formation; correctly calculated the scale of their explosiveness; and, as a kind of concluding bonus, connected supernova
explosions to the production of a mysterious new phenomenon called cosmic rays,* which had recently been found swarming through the universe. These ideas were revolutionary, to say the least. The existence of neutron stars wouldn’t be confirmed for thirty-four years, and cosmic rays, though long since confirmed, still remain little understood. Altogether, the abstract was, in the words of the astrophysicist and Nobel laureate Kip S. Thorne, ‘one of the most prescient documents in the history of physics and astronomy’.
Interestingly, Zwicky had almost no understanding of why any of this would happen. According to Thorne, ‘he did not understand the laws of physics well enough to be able to substantiate his ideas.’ Zwicky’s talent was for big ideas. Others – Baade mostly – were left to do the mathematical sweeping up.
Zwicky was also the first to recognize that there wasn’t nearly enough visible mass in the universe to hold galaxies together, and that there must be some other gravitational influence – what we now call dark matter. One thing he failed to see was that if a neutron star shrank enough it would become so dense that even light couldn’t escape its immense gravitational pull. You would have a black hole. Unfortunately, Zwicky was held in such disdain by most of his colleagues that his ideas attracted almost no notice. When, five years later, the great Robert Oppenheimer turned his attention to neutron stars in a landmark paper, he made not a single reference to any of Zwicky’s work, even though Zwicky had been working for years on the same problem in an o ce just down the corridor. Zwicky’s deductions concerning dark matter wouldn’t attract serious
* Cosmic rays, first posited in 1925 by Robert Millikan of the University of Chicago, aren’t rays at all but charged particles, moving at nearly the speed of light. The name has stuck even though it is wrong (and that doesn’t happen often in science). To what extent cosmic rays influence life and climate on Earth is still debated.
attention for nearly four decades. We can only assume that he did a lot of push-ups in this period.
Surprisingly little of the universe is visible to us when we incline our heads to the sky. Only about 6,000 stars are visible to the naked eye from Earth, and only about 2,000 can be seen from any one spot. With binoculars the number of stars you can see from a single location rises to about 50,000, and with a small 2-inch telescope it leaps to 300,000. With a 16-inch telescope, such as Evans used, you begin to count not in stars but in galaxies. From his deck, Evans told me, he estimated he could see between 50,000 and 100,000 galaxies, each containing tens of billions of stars. These were of course respectable numbers, but even with so much to take in, supernovae are extremely rare. A star can burn for billions of years, but it dies just once and quickly, and only a few dying stars explode. Most expire quietly, like a camp fire at dawn. In a typical galaxy, consisting of 100 billion stars, a supernova will occur on average once every 200 or 300 years. Looking for a supernova, therefore, was a little like standing on the observation platform of the Empire State Building with a telescope and searching windows around Manhattan in the hope of finding, let us say, someone lighting a twenty-first birthday cake.
So when a hopeful and softly spoken minister got in touch to ask if they had any usable field charts for hunting supernovae, the astronomical community thought he was out of his mind. At the time Evans had a 10-inch telescope – a very respectable size for amateur star-gazing, but hardly the sort of thing with which to do serious cosmology – and he was proposing to find one of the universe’s rarer phenomena. In the whole of astronomical history before Evans started looking in 1980, fewer than sixty supernovae had been found.
Evans, however, had certain advantages. Most observers, like most people generally, are in the northern hemisphere, so he had a lot of sky largely to himself, especially at first. He also had speed and his uncanny memory. Large telescopes are
cumbersome things, and much of their operational time is consumed in being manoeuvred into position. Evans could swing his little 16-inch telescope around like a tail-gunner in a dogfight, spending no more than a couple of seconds on any particular point in the sky. In consequence, he could observe perhaps 400 galaxies in an evening while a large professional telescope would be lucky to do fifty or sixty.
Looking for supernovae is mostly a matter of not finding them. From 1980 to 1996 he averaged two discoveries a year – not a huge pay-o for hundreds of nights of peering and peering. Once he found three in fifteen days, but another time he went three years without finding any at all.
‘There is actually a certain value in not finding anything,’ he said. ‘It helps cosmologists to work out the rate at which galaxies are evolving. It’s one of those rare areas where the absence of evidence is evidence.’
On a table beside the telescope were stacks of photos and papers relevant to his pursuits, and he showed me some of them. If you have ever looked through popular astronomical publications, and at some time you must have, you will know that they are generally full of richly luminous colour photos of distant nebulae and the like – fairy-lit clouds of celestial light of the most delicate and moving splendour. Evans’s working images were nothing like that. They were just blurry blackand-white photos with little points of haloed brightness. One he showed me depicted a swarm of stars in which lurked a trifling flare that I had to put close to my face to discern. This, Evans told me, was a star in a constellation called Fornax from a galaxy known to astronomy as NGC1365. (NGC stands for New General Catalogue, where these things are recorded. Once it was a heavy book on someone’s desk in Dublin; today, needless to say, it’s a database.) For 60 million years, the light from this star’s spectacular demise travelled through space until one night in August 2001 it arrived at Earth in the form of a pu of radiance, the tiniest brightening, in the night sky.
It was, of course, Robert Evans on his eucalypt-scented hillside who spotted it.
‘There’s something satisfying, I think,’ Evans said, ‘about the idea of light travelling for millions of years through space and just at the right moment as it reaches Earth someone looks at the right bit of sky and sees it. It just seems right that an event of that magnitude should be witnessed.’
Supernovae do much more than simply impart a sense of wonder. They come in several types (one of them discovered by Evans), and of these, one in particular, known as the Ia supernova, is important to astronomy because these supernovae always explode in the same way, with the same critical mass. For this reason they can be used as ‘standard candles’ – benchmarks by which to measure the brightness (and hence relative distance) of other stars, and thus to measure the expansion rate of the universe. Supernovae are also an important source of gravitational waves, which were first detected by astrophysicists in 2015, to much jubilation, and which will be discussed a bit further on.
In 1987 Saul Perlmutter at the Lawrence Berkeley Laboratory in California, needing more Ia supernovae than visual sightings were providing, set out to find a more systematic method of searching for them. Perlmutter devised a nifty system using sophisticated computers and charge-coupled devices – in essence, really good digital cameras. It automated supernovahunting. Telescopes could now take thousands of pictures and let a computer detect the telltale bright spots that marked a supernova explosion. In five years, with the new technique, Perlmutter and his colleagues at Berkeley found forty-two supernovae. ‘With CCDs you can aim a telescope at the sky and go watch television,’ Evans said with a touch of dismay. ‘It took all the romance out of it.’
I asked him if he was tempted to adopt the new technology. ‘Oh, no,’ he said, ‘I enjoy my way too much. Besides’ – he gave a nod at the photo of his latest supernova and smiled – ‘I can still beat them sometimes.’
Robert Evans died on 8 November 2022, aged eighty-five. He had discovered forty-seven supernovae, a number that is unlikely ever to be surpassed.
The question that naturally occurs is: what would it be like if a star exploded nearby? Our nearest stellar neighbour, as we have seen, is Alpha Centauri, 4.3 light years away. I had imagined that if there were an explosion there we would have 4.3 years to watch the light of this magnificent event spreading across the sky, as if tipped from a giant can. What would it be like if we had four years and four months to watch an inescapable doom advancing towards us, knowing that when it finally arrived it would blow the skin right o our bones? Would people still go to work? Would farmers plant crops? Would anyone deliver them to the shops?
Weeks later, back in the town in New Hampshire where I then lived, I put these questions to John Thorstensen, an astronomer at Dartmouth College. ‘Oh no,’ he said, laughing. ‘The news of such an event travels out at the speed of light, but so does the destructiveness, so you’d learn about it and die from it in the same instant. But don’t worry, because it’s not going to happen.’
For the blast of a supernova explosion to kill you, he explained, you would have to be ‘ridiculously close’ – probably within ten light years or so. ‘The danger would be various types of radiation – cosmic rays and so on.’ These would produce fabulous auroras, shimmering curtains of spooky light that would fill the whole sky. This would not be a good thing. Anything potent enough to put on such a show could well blow away the magnetosphere, the magnetic zone high above the Earth that normally protects us from ultraviolet rays and other cosmic assaults. Without the magnetosphere anyone unfortunate enough to step into sunlight would pretty quickly take on the appearance of, let us say, an overcooked pizza.
The reason we can be reasonably confident that such an
event won’t happen in our corner of the galaxy, Thorstensen said, is that it takes a particular kind of star to make a supernova in the first place. A candidate star must be ten to twenty times as massive as our own Sun, and ‘we don’t have anything of the requisite size that’s that close. The universe is a mercifully big place.’ The nearest likely candidate, he added, is Betelgeuse, whose various sputterings have for years suggested that something interestingly unstable is going on there. But Betelgeuse is 642.5 light years away – distant enough not to be a worry.
Only half a dozen times in recorded history have supernovae been close enough to be visible to the naked eye. One was a blast in 1054 that created the Crab Nebula. Another, in 1604, made a star bright enough to be seen during the day for over three weeks. The most recent was in 1987, when a supernova flared in a zone of the cosmos known as the Large Magellanic Cloud, but that was only barely visible and only in the southern hemisphere – and it was a comfortably safe 169,000 light years away.
Supernovae are significant to us in one other decidedly central way. Without them we wouldn’t be here. You will recall the cosmological conundrum with which we ended the first chapter – that the Big Bang created lots of light gases but no heavy elements. Those came later, but for a very long time nobody could figure out how they came later. The problem was that you needed something really hot – hotter even than the middle of the hottest stars – to forge carbon and iron and the other elements without which we would be distressingly immaterial. Supernovae provided the explanation, and it was an English cosmologist almost as singular in manner as Fritz Zwicky who worked it out.
He was a Yorkshireman named Fred Hoyle. Hoyle, who died in 2001, was described in an obituary in Nature as a ‘cosmologist and controversialist’, and both of those he most certainly was. He was, according to Nature ’s obituary, ‘embroiled in controversy for most of his life’ and ‘put his name to much
rubbish’. He claimed, for instance, and without evidence, that the Natural History Museum’s treasured fossil of an archaeopteryx was a forgery along the lines of the Piltdown hoax, causing much exasperation to the museum’s palaeontologists, who had to spend days fielding phone calls from journalists all over the world. He also believed that the Earth was seeded from space not only by life but also by many of its diseases, such as influenza and bubonic plague, and suggested at one point that humans evolved projecting noses with the nostrils underneath as a way of keeping cosmic pathogens from falling into them.
It was he who coined the term Big Bang, for a radio broadcast in 1949. He pointed out that nothing in our understanding of physics could account for why everything, gathered to a point, would suddenly and dramatically begin to expand. Hoyle favoured a steady-state theory in which the universe was constantly expanding and continually creating new matter as it went. Hoyle also realized that if stars imploded they would liberate huge amounts of heat – 100 million degrees or more, enough to begin to generate the heavier elements in a process known as nucleosynthesis. In 1957, working with others, Hoyle showed how the heavier elements were formed in supernova explosions. For this work, W. A. Fowler, one of his collaborators, received a Nobel Prize. Hoyle, shamefully, did not.
According to Hoyle’s theory, an exploding star would generate enough heat to create all the new elements and spray them into the cosmos where they would form gaseous clouds – the interstellar medium, as it is known – that could eventually coalesce into new solar systems. With the new theories it became possible at last to construct plausible scenarios for how we got here. What we now think we know is this: About 4.6 billion years ago, a great swirl of gas and dust some 24 billion kilometres across accumulated in space where we are now and began to aggregate. Virtually all of it – 99.9 per cent of the mass of the solar system – went to make the Sun. Out of the floating material that was left over, two microscopic grains
floated close enough together to be joined by electrostatic forces. This was the moment of conception for our planet. All over the inchoate solar system, the same was happening. Colliding dust grains formed larger and larger clumps. Eventually the clumps grew large enough to be called planetesimals. As these endlessly bumped and collided, they fractured or split or recombined in endless random permutations, but in every encounter there was a winner, and some of the winners grew big enough to dominate the orbit around which they travelled. It all happened remarkably quickly. To grow from a tiny cluster of grains to a baby planet some hundreds of kilometres across is thought to have taken only a few tens of thousands of years. In just 200 million years, possibly less, the Earth was essentially formed, though still molten and subject to constant bombardment from all the debris that remained floating about.
At this point, about 4.4 billion years ago, an object the size of Mars crashed into the Earth, blowing out enough material to form a companion sphere, the Moon. Within weeks, it is thought, the flung material had reassembled itself into a single clump, and within a year it had formed into the spherical rock that companions us yet. Most of the lunar material, it is thought, came from the Earth’s crust, not its core, which is why the Moon has so little iron while we have a lot. The theory, incidentally, is almost always presented as a recent one, but in fact it was first proposed in the 1940s by Reginald Daly of Harvard. The only recent thing about it is people paying any attention to it.
When the Earth was only about a third of its eventual size, it was probably already beginning to form an atmosphere, mostly of carbon dioxide, nitrogen, methane and sulphur. Hardly the sort of stu that we would associate with life, and yet from this noxious stew life formed. Carbon dioxide is a powerful greenhouse gas. This was a good thing, because the Sun was significantly dimmer back then. Had we not had the benefit of a greenhouse e ect, the Earth might well have frozen over
permanently, and life might never have got a toehold. But somehow life did.
For the next 500 million years the young Earth continued to be pelted relentlessly by comets, meteorites and other galactic debris, which brought water to fill the oceans and the components necessary for the successful formation of life. It was a singularly hostile environment, and yet somehow life got going. Some tiny bag of chemicals twitched and became animate. We were on our way.
Four billion years later, people began to wonder how it had all happened. And it is there that our story next takes us.
