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The kingdom of matter stores its treasures on many levels. Until recently, we thought there was only one. We had no idea there were others.

When we strike a match, a chemical reaction liberates energy stored in the molecules. Old chemical bonds break and new ones are forged. Now, the adjacent molecules begin to move faster and the temperature increases. Soon, the process becomes self-propagated, a kind of chain reaction.

The energy represented by a flame has been locked, perhaps for many years, in chemical bonds between atoms. Mediated by the electrons that revolved around their core. When we make a fire, we release this hidden chemical energy.

But there is a deeper level of matter that houses another kind of energy. Inside the heart of the atom, its nucleus. This hidden treasure was forged billions of years ago in distant stellar furnaces. Long before Earth was formed. It’s what powers the stars. Wresting this knowledge from nature is a cosmic rite of passage. The beings of any possible world clever enough to travel this deep into nature’s labyrinth better take care. The secret of starlight is nothing to fool with. Like fire, it can bring a civilization to life and it can burn it to the ground.

What is an atom?

What are atoms made of? How are they joined together? How could something as small as an atom contain so much power? Where do atoms come from?

The same place we do. When we seek the origin of atoms, we are searching for our beginnings. This quest takes us to the depths of space and time.

Long ago, before there was an Earth, there was a wisp of cold thin gas. The gas was made of the simplest atoms. And they were gravitationally attracted to one another. So, the cloud grew. The atoms contained small but heavy particles in their nuclei. The hydrogen had protons, the helium had neutrons as well. They both had a skittering veil of electrons in orbit around them. The atoms in the interior of the cloud moved ever faster as gravity pulled them ever closer together. Until the whole thing collapsed in on itself. This collapse raised the temperature so high, that the cloud became a natural fusion reactor.

In other words, a star.

Atoms operating according to the laws of physics met and fused in the unbroken darkness.

And then there was light.

In this froth of elementary particles, the nucleus of one of the atoms, a helium atom, was formed.

After billions of years, the star is now elderly. Having converted all of its available hydrogen fuel to helium. Now that it’s time for the star to die, it resumes the turning inward of its infancy. Our helium atom joined with two others to become one of our heroes, a carbon atom. That’s what happens in the hearts of stars. Soon, our carbon atom will tumble out of this red giant star into the interstellar ocean of space.

Meanwhile, in another part of the galaxy. Similar processes were unfolding as stars were born and died. The other atom of our tale was formed in the heart of this dying star. In the catastrophic process of going supernova, 226 protons and neutrons became fused to a carbon atom. Turning it into a uranium atom.

As chance would have it, after wandering the vast Milky Way galaxy, our two atoms both happened on the fiery birth of a small solar system.

Ours.

Our carbon atom has travelled far to become part of a small planet. After billions of years, it joined an extremely complex molecule, which has the peculiar property of making virtually identical copies of itself. The carbon atom plays its tiny role in the origin of life. Through all its incarnations, our carbon atom has had no self-awareness. No free will. It is merely an extremely minor cog in some vast cosmic machinery, working in accord with the laws of nature.

And that other atom? The uranium atom made in the supernova? What has become of it?

Our world was born in fire. And this tiny atom was drawn to it. Maybe it rode the explosive wave of a supernova. Or perhaps, it was attracted by the gravity of our sun and pulled down deeper and deeper into the interior, which was even more of a hell.

The Earth’s surface soon cooled, but the interior remained molten. The magma slowly circulating and our uranium atom found itself carried over the ages, from the deep interior, back up to the surface. Despite the high temperatures and pressures deep within the Earth, our atom’s integrity was never threatened. Atoms are small, old, hard and durable.

Everything is made of atoms, including us

Until the last years of the 19th century, we didn’t know about the frenzied activity inside the atom. And this is where our two atoms from opposite ends of the Milky Way galaxy finally met. It happened in Paris.

Our carbon atom became part of the retina of one of the world’s greatest scientists. This was just a few years after the discovery of X-rays. 

Marie Curie and her husband and research partner, Pierre, wanted to know how a piece of matter could make it possible to see through skin and even walls. The knowledge that there were rare places in the world where rocks, rich in uranium, possess these strange properties inspired Marie on her scientific quest.

The dull brown ore, still mixed with pine needles, came from the part of Eastern Europe that is now the Czech Republic. But this material was very rare. And even to distil a tiny amount of it required the most lengthy and labour-intensive efforts.

We lived in our single occupation, as in a dream.

Marie Curie

They worked under the worst possible conditions to purify the ore into a mineral called pitchblende, which was 50 to 80% uranium. This was quite an achievement, but Marie and Pierre were hunting for something far more rare. It took them three years to process tons of ore. To isolate a mere tenth of a gram of a substance she named radium.

Marie and Pierre had discovered a completely new element.

The Curies showed that the radium was entirely unaffected by extreme temperatures. That was strange. Most things subjected to such intense heat would change drastically. And, there was something else. It spontaneously emitted energy. Not through chemical reactions, but through some unknown mechanism. Marie Curie called this new phenomenon “radioactivity”. She and Pierre calculated the energy that spontaneously flowed from a lump of radium would be much greater than burning the same amount of coal. Radioactivity, to their astonishment, was millions of times more potent than chemical energy – the difference between liberating the energy that resides in molecules and the far greater power stored deeper down.

Between Marie, Pierre, little Irene and the man she would later marry, the family would win five Nobel prizes in science.

The bottles, tubes and flasks of pitchblende that they had refined, left a residue of radium particles. They were so potent, that they lit up the lab at night. As Marie wrote years later, “They were like Earthly stars, these glowing tubes in that poor rough shack.” Marie leapt to the correct conclusion that the luminescence was due to something happening inside the nuclei of radioactive atoms.

A World Set Free

For thousands of years, it had been thought that atoms were the smallest unit of matter. Curie’s earthly stars were evidence that within the atom was a possible world where even smaller particles were interacting. A hundred years after this magical night, Marie Curie’s cookbooks still glowed with the exquisite radioactivity she had discovered.

But it took a little time for the darker implications of this deeper understanding of nature to dawn in the mind of a visionary named H.G. Wells.

A writer, H. G. Wells was a genius at turning the new revelations of science into stories that captivated the world. And foreseeing as no one else, their gravest consequences. The writer H.G. Wells, who first imagined time machines and alien invasions had a nightmare of a future world where atoms were weaponized. In his book called The World Set Free written in 1913, he coined the phrase atomic bombs. And loosed them on helpless civilian populations. He set his vision of a nuclear war between England and Germany in the impossibly distant future of the 1950’s.

In 1933, the Hungarian physicist, Leo Szilard, was contemplating becoming a biologist. He read Wells’ novel and it started him thinking. Szilard knew that atoms are made of protons and neutrons on the inside. And a skittering veil of electrons on the outside. Suddenly, waiting for a traffic light to change at an intersection in London, he was struck by the thought, that if he could find a sufficiently large amount of an element that would emit two neutrons when it absorbed one, it would sustain a nuclear chain reaction. Two would produce four, four would produce eight and so forth. Until enormous amounts of energy in the nucleus itself could be liberated. Not a chemical reaction, but a nuclear one.

This was the moment our world changed. Leo Szilard also knew the power of exponentials and if a neutron chain reaction could be triggered down there in the world of the atom’s nucleus, then something like Wells’ imaginary atomic bomb might be possible. He shuddered at the thought of this destructive capability.

But this was just the latest development on a continuum of violence that began long long before.

War, a History

50,000 years ago, all humans were roving bands of hunter-gatherers. They communicated over limited areas by calling to one another. That is, at the speed of sound. Around 1,235 kilometres per hour. But over longer distances, they could communicate only as fast as they could run.

Around 12,000 years ago, about the same time as the invention of agriculture, they developed the power to kill at a longer distance. The kill radius expanded to the arc of an arrow launched by a bow. And they could kill one person with a single arrow. Our ancestors were not particularly warlike because there were so few people and so much room back then that moving on was preferable to armed conflict. Their weapons were used almost entirely for hunting. Their identification horizon was likely small. Only with the other members of their band of 50 or 100 people. But their time horizon took a giant leap. They worked long and hard planting crops in the here and now so that several months later, they could harvest them. They postponed present gratification for later advantage. They began to plan for the future.

By about 2,500 years ago, there was a new kind of war. The conquered territories of Alexander stretched from Macedonia to the Indus Valley. There were now many on planet Earth who owed allegiance to groups composed of millions. Over long distances, the maximum speed of both communication and transportation was the speed of the sail and the horse. Archidamus III, King of Sparta, was famed for his unflinching courage. He relished taking part in hand-to-hand combat with the enemy. It is said that when he first saw a projectile hurled by a Balista, he cried out in anguish. “Oh, Hercules! The valour of man is lost!”. Both the kill range and the kill ratio had increased exponentially. Now, ten corpses lay where one would have been. And the soldier who released the lever on the siege engine never even saw their faces. He remained far removed from the carnage on the other side of the city wall.

Today, the maximum speed of transportation is the escape velocity from Earth. 40,000 kilometres per hour. The speed of communication is the speed of light. The identification horizons have also expanded enormously. For some, it’s a billion or more. For others, it’s our whole species. And for a few, it’s all living things. The kill radius, in the worst-case scenario, is now our global civilization.

How did we get here?

Well, it was the result of a deadly embrace between science and state. And there was one scientist for whom no amount of destructive power was enough.

It’s hard to pinpoint the precise moment when the first nuclear war began. Some might trace it back to that arrow sailing over the treetops. Others might say it started much later, with three messages.

In 1939 on Adolf Hitler’s birthday, one of his brightest young scientists, Paul Harteck, had a special gift in mind for his FĂŒhrer. Harteck wrote a letter to the Nazi war office, he wished to inform them that the latest developments in nuclear physics would make it possible to produce an explosive exponentially more powerful than conventional weapons. He was trying to give an atomic bomb to Adolf Hitler. But Hitler would never get his hands on a nuclear weapon, he had murdered, imprisoned or exiled many of the great physicists in his territories. Those who happened to be Jews or liberals and many who were both.

Exactly a month before the war began, Leo Szilard made a pilgrimage to the house Albert Einstein was renting on Long Island in New York. The physicist who usually chauffeured Leo Szilard on trips out of Manhattan was unavailable that August day in 1939. So, Szilard enlisted the services of a fellow Hungarian emigrate, a young scientist named Edward Teller. Persecution in Budapest sent Teller and his family to take refuge in Munich, where he lost his right foot in a traffic accident. In the early 1930s, Teller and his family were forced to flee once again.

Just as Harteck felt it his duty to inform Hitler. Szilard wanted the US President, Franklin Roosevelt, to know the awesome power of such a weapon. There was no scientist on Earth whose prestige and influence was comparable to Einstein’s. Einstein’s nightmare was imagining Hitler with a nuclear weapon at his disposal. But what would be the long-term consequences of this dangerous new knowledge? Which, once unleashed, could never be taken back. Einstein would take no role in the U.S. effort to build the atomic bomb, which became known as “The Manhattan Project.” But he did alert the then-U.S. President. Franklin Roosevelt, to the potential use of atomic nuclei in warfare. After the war was over, he told a reporter that if he had known the Germans would fail in developing an atomic bomb, he never would have signed the letter. But Edward Teller had no such ambivalence. He couldn’t wait to get started on weaponizing the atom.

The Russian physicist, G.N. Flyorov had tried for years to alert his leader, Joseph Stalin, to the possible military applications of a nuclear chain reaction. However, the Soviet Union was under siege by the Germans. And an atom bomb project was likely to take years to complete. With their backs against the wall, it seemed too impractical to even think about. In 1942, Flyorov had published a scientific paper on nuclear physics. Now, he was excited to see what the eminent physicists in Europe and the United States had to say about it. Flyorov was puzzled. None of the physicists of the International Scientific Community thought his paper worthy of comment.

At first, he was hurt, but then he realized what was really happening. American and German scientific journals were being scrubbed of any nuclear physics papers as both nations secretly worked on building the bomb. It was this absence of published data, the dogs that did not bark, that moved Flyorov to re-double his efforts to convince Stalin to start his own nuclear weapons program.

In all three cases, it was the scientists, not the generals or the arms dealers, who informed their leaders that a huge increase in the kill ratio was possible.

The Manhattan Project

The U.S. Department of War chose the remote location of Los Alamos, New Mexico as the headquarters for the atomic bomb research project. It had been recommended by the project’s director, physicist J. Robert Oppenheimer, who had recuperated there from an illness as a teenager.

But for Edward Teller, an atomic bomb wasn’t big enough. He dreamed of even greater lethality. A weapon in which the atomic bomb was nothing more than a match to light a fuse to the nucleus. A thermal nuclear weapon. What Teller affectionately called, the super.

If Edward Teller had a polar opposite in the scientific community, it would have been Joseph Rotblat. Rotblat was born in Warsaw to a wealthy family, who like Teller’s, had lost everything. In the summer of 1939, just before the Nazis invaded, he was invited to England to take a research position at the University of Liverpool. At the last minute before his departure, his beloved wife, Tola had an emergency appendectomy. She was forced to remain behind until she was well enough to travel. Tola insisted that Joseph go on ahead to prepare their new home. It would just be a matter of weeks, she told him.

The challenge to the Manhattan Project team was to find a chemical fuse that would light the nuclear chain reaction, first imagined by Leo Szilard in London. The scientists and engineers told themselves that they would be averting a grave danger by building a bomb of unprecedented destructive power. Their government could be trusted. They would never use such a weapon in an act of aggression, not like those other governments. These atomic scientists were the first to see building nuclear weapons as a deterrent to using them. The fear of Hitler with an atomic bomb was the driving rationale for the Manhattan Project.

And yet, when Germany surrendered and Hitler was no more, of the thousands of scientists who worked on the bomb, only one resigned. It was Joe Rotblat. In the years that followed, whenever he was asked about his decision, he always rejected any suggestion that he had done so out of moral superiority. He would just smile and say, the truth was that he desperately missed his wife, who had been prevented from leaving Warsaw and lost to him in the chaos of the war. With its end in Europe came his chance to go and search for her. But, he never found her. Except as a name on a list of the dead. Tola had perished in the Holocaust, exterminated at the Belzec concentration camp. Although he lived another 60 years, Rotblat never remarried.

Of the three nations that pursued wartime research into building the bomb, only the U.S. succeeded before the war’s end. And historians believe that was because America had taken in so many immigrants. Of the leading figures in the Manhattan Project, only two were native-born. Only one got his PhD in the U.S. Atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki, ending the Second World War. Two months later, President Truman invited Oppenheimer for congratulations in the Oval Office. But to Truman’s dismay, Oppenheimer was in no mood to celebrate.

Less than four years later, the Russians exploded their atomic bomb. And shortly after, both nations went on to create thermonuclear hydrogen bombs. The nuclear arms race begun by those three letters from scientists was off to a terrifying start. After the war, Teller’s dreams of greater and greater killing power were to come true. In the early 1950s, when the Communist witch hunts began in the United States, he was perfectly happy to hint that Robert Oppenheimer, his former boss, who had brilliantly run the Manhattan Project, should be stripped of his security clearance, thereby ruining Oppenheimer’s career.

Despite dramatic reductions in nuclear arsenals, the spectre of nuclear war haunts us still. How can we sleep so soundly in the shadow of a smoking volcano?

A Tale of Two Atoms

We’re back on the trail of one of our two atoms. The uranium atom. A uranium atom is inherently unstable. Sooner or later, it decays. A particle from its nucleus breaks away, transforming the uranium atom into an entirely different element. Thorium. Subatomic particles move like bullets through the fine structure of life. Shearing electrons from their molecules. This is how ionizing radiation affects living things. Those chromosomes never had a chance. This is why atomic weapons are so much more dangerous than conventional ones. Ionizing radiation is all around us and even inside us. At low levels, it poses no threat. But at higher levels, it’s a different story.

In the near term, exposure to lethal levels of radiation can cause a runaway reaction in the cell that makes it multiply exponentially. Cancer. But its power to harm can also echo down the corridors of time. When radiation tears into the chromosomes of the butterfly, it leaves a trail of destruction in its wake that changes the destiny of the butterfly’s unborn offspring. A mutation in its genes We have a lot in common with butterflies. Any change in the DNA architecture will be copied over and over again in succeeding generations. The damage is passed on. Vandalizing our future.

We are made of atoms that were born in stars thousands of light years away in space and billions of years ago in time. The search for our origins has carried us far from our epoch in our world. We are star-stuff, deeply connected with the rest of the universe. The matter we are made of was generated in cosmic fire. And now, we, ambulatory collections of seven billion billion billion atoms intricately assembled over aeons have devised a means to tap that cosmic fire, hidden in the heart of matter.

We cannot unlearn this knowledge. And tragically, insanity runs in our family.

The letters that the scientists wrote to begin this nightmare were followed by another. This one, a letter to the planet, stating that this new understanding of physics demanded a new way of thinking:

Shall we choose death because we cannot forget our quarrels? We appeal as human beings to human beings, remember your humanity and forget the rest.

And what of our other atom? The carbon atom? It’s inside one of you.

“Alfred, it’s spinning.” Roy Kerr, a New Zealand-born physicist in his late 20s, had, for half an hour, been chain-smoking his way through some fiendish mathematics. Alfred Schild, his boss at the newly built Centre for Relativity at the University of Texas, had sat and watched. Now, having broken the silence, Kerr put down his pencil. He had been searching for a new solution to Albert Einstein’s equations of general relativity, and at last, he could see in his numbers and symbols a precise description of how space-time—the four-dimensional universal fabric those equations describe—could be wrapped into a spinning ball. He had found what he was looking for.

When this happened, in 1962, the general theory of relativity had been around for almost half a century. It was customarily held up as one of the highest intellectual achievements of humanity. And it was also something of an intellectual backwater. It was mathematically taxing and mostly applied to simple models with little resemblance to the real world, and thus not widely worked on. Kerr’s spinning solution changed that. Given that pretty much everything in the universe is part of a system that spins at some rate or other, the new solution had relevance to real-world possibilities—or, rather, out-of-this-world ones—that previous work in the field had lacked. It provided science with a theoretical basis for understanding a bizarre object that would soon bewitch the public imagination: the black hole.

General relativity was presented to the Prussian Academy of Sciences over the course of four lectures in November 1915; it was published on December 2nd that year. The theory explained, to begin with, remarkably little, and unlike quantum theory, the only comparable revolution in 20th-century physics, it offered no insights into the issues that physicists of the time cared about most. Yet it was quickly and widely accepted, not least thanks to the sheer beauty of its mathematical expression; a hundred years on, no discussion of the role of aesthetics in scientific theory seems complete without its inclusion.

When gravity fails

Today its appeal goes beyond its elegance. It provides a theoretical underpinning to the wonders of modern cosmology, from black holes to the Big Bang itself. Its equations have recently turned out to be useful in describing the physics of earthly stuff too. And it may still have secrets to give up: enormous experiments are underway to see how the theory holds in the most extreme physical environments that the universe has to offer.

The theory was built on the insights of Einstein’s first theory of relativity, the “special theory”, one of a trio of breakthroughs that made his reputation in 1905. That theory dramatically abandoned the time-honoured description of the world in terms of absolute space and time in favour of a four-dimensional space-time (three spatial dimensions, one temporal one). In this new space-time, observers moving at different speeds got different answers when measuring lengths and durations; for example, a clock moving quickly with respect to a stationary observer would tell the time more slowly than one sitting still. The only thing that remained fixed was the speed of light, c, which all observers had to agree on (and which also got a starring role in the signature equation with which the theory related matter to energy, E=mc2).

Special relativity applied only to special cases: those of observers moving at constant speeds in a straight line. Einstein knew that a general theory would need to deal with accelerations. It would also have to be reconciled with Isaac Newton’s theory of gravity, which relied on absolute space, made no explicit mention of time at all, and was believed to act not at the speed of light but instantaneously.

Einstein developed all his ideas about relativity with “thought experiments”: careful imaginary assessments of highly stylised states of affairs. In 1907 one of these provided him with what he would later refer to as his “happiest thought”: that someone falling off a roof would not feel his own weight. Objects in free-fall, he realised, do not experience gravity. But the curved trajectories produced by gravity—be they the courses of golf balls or planets—seemed to imply some sort of pushing or pulling. If golf balls and planets, like people falling off roofs, felt no sort of push or pull, why then did they not fall in straight lines?

The central brilliance of general relativity lay in Einstein’s subsequent assertion that they did. Objects falling free, like rays of light, follow straight lines through space-time. But that space-time itself is curved. And the thing that made it curve was mass. Gravity is not a force; it is a distortion of space-time. As John Wheeler, a physicist given to pithy dictums about tricky physics, put it decades later: “Space-time tells matter how to move; matter tells space-time how to curve.”

The problem was that, in order to build a theory on this insight, Einstein needed to be able to create those descriptions in warped four-dimensional space-time. The Euclidean geometry used by Newton and everyone else was not up to this job; fundamentally different and much more challenging mathematics was required. Max Planck, the physicist who set off the revolution in quantum mechanics, thought this presented Einstein with an insurmountable problem. “I must advise you against it,” he wrote to Einstein in 1913, “for in the first place you will not succeed, and even if you succeed no one will believe you.”

Handily for Einstein, though, an old university chum, Marcel Grossmann, was an expert in Riemannian geometry, a piece of previously pure mathematics created to describe curved multi-dimensional surfaces. By the time of his lectures in 1915 Einstein had, by making use of this unorthodox geometry, boiled his grand idea down to the elegant but taxing equations through which it would become known.

Just before the fourth lecture was to be delivered on November 25th, he realised he might have a bit more to offer than thought experiments and equations. Astronomers had long known that the point in Mercury’s orbit closest to the sun changed over time in a way Newton’s gravity could not explain. In the 1840s oddities in the orbit of Uranus had been explained in terms of the gravity of a more distant planet; the subsequent discovery of that planet, Neptune, had been hailed as a great confirmation of Newton’s law. Attempts to explain Mercury’s misbehaviour in terms of an undiscovered planet, though, had come to nought.

Famous long ago

Einstein found that the curvature of space-time near the sun explained Mercury’s behaviour very nicely. At the time of the lectures, it was the only thing he could point to that general relativity explained and previous science did not. Martin Rees, Britain’s Astronomer Royal, is one of those who sees the nugatory role played by evidence in the development of the theory as one of the things “that makes Einstein seem even more remarkable: he wasn’t motivated by any mysterious phenomena he couldn’t explain.” He depended simply on his insight into what sort of thing gravity must be and the beauty of the mathematics required to describe it.

After the theory was published, Einstein started to look for ways to test it through observation. One of them was to compare the apparent positions of stars that were in the same part of the sky as the sun during a solar eclipse with their apparent positions at other times. Rays of light, like free-falling objects, trace straight lines in space-time. Because the sun’s mass warps that space-time, the positions of the stars would seem to change when the rays skirted the sun (see diagram).

In 1919 Arthur Eddington, a famed British astronomer, announced that observations of an eclipse made on the West African island of Principe showed just the distortion Einstein had predicted (one of his images is pictured). “LIGHTS ALL ASKEW IN THE HEAVENS”, read the New York Times headline, adding helpfully that “Nobody Need Worry”. Einstein, while pleased, had faith enough in his idea not to have been on tenterhooks. When asked what he would have done had Eddington found a different result, he replied, “Then I would feel sorry for the good Lord. The theory is correct.”

As far as the rest of the world was concerned, Eddington’s result put general relativity more or less beyond doubt. But that did not make it mainstream. For one thing, it was hard to grasp. At a public event, Eddington was momentarily stumped by the suggestion that he “must be one of the three persons in the world who understand general relativity”. When the silence was taken for modesty, he replied “On the contrary, I am trying to think who the third person is!”

General relativity also seemed somewhat beside the point. The quantum revolution that Planck had begun, and that Einstein had contributed to in one of his other great papers of 1905, was bearing fascinating fruit. Together with a blossoming understanding of the atomic nucleus, it was at the centre of physicists’ attention. Special relativity had a role in the excitement; its most famous expression, E=mc2, gave a measure of the energy stored in those fascinating nuclei. General relativity had none.

What it offered instead was a way to ask questions not about what was in the universe, but about the structure of the universe as a whole. There were solutions to the equations in which the universe was expanding; there were others in which it was contracting. This became a topic of impassioned debate between Einstein and Willem de Sitter, a Dutch physicist who had found one of the expanding-universe solutions. Einstein wanted a static universe. In 1917 he added to his equations a “cosmological constant” which could be used to fix the universe at a given size.

That became an embarrassment when, in 1929, an American astronomer put forward strong evidence that the universe was, indeed, getting bigger. Edwin Hubble had measured the colour of the light from distant galaxies as a way of studying their motion; light from objects approaching the Earth looks bluer than it would otherwise, and light from objects receding looks redder. Hubble found that, on average, the more distant the galaxy, the more its light was shifted towards the red; things receded faster the farther away they were. The evidence for an expanding universe these redshifts provided led Einstein to reject the cosmological constant as the “greatest blunder of my life”.

The theory had other implications at which its architect initially baulked. In the 1930s nuclear physicists worked out that stars were powered by nuclear reactions, and that when those reactions ran out of fuel the stars would collapse. Something like the sun would collapse into a “white dwarf” about the size of the Earth. Bigger stars would collapse yet further into “neutron stars” as dense as an atomic nucleus and just 20 kilometres or so across. And the biggest stars would collapse into something with no length, breadth or depth but infinite density: a singularity.

Finding singularities in a theory is highly distasteful to the mathematically minded; they are normally signs of a mistake. Einstein did not want any of them in his universe, and in 1939 he published a paper attempting to show that the collapse of giant stars would be halted before a singularity could be formed. Robert Oppenheimer, a brilliant young physicist at Berkeley, used the same relativistic physics to contradict the great man and suggest that such extreme collapses were possible, warping space-time so much that they would create regions from which neither light nor anything else could ever escape: black holes.

Oppenheimer boi

Oppenheimer’s paper, though, was published on the day Germany invaded Poland, which rather put the debate on hold. Just a month before, Einstein had written to Franklin Roosevelt highlighting the military implications of E=mc2; it would be for realising those implications, rather than for black holes, that Oppenheimer would be remembered.

In part because of Oppenheimer’s government-bewitching success, new sorts of physical research flourished in the post-war years. One such field, radio astronomy, revealed cosmic dramas that observations using light had never hinted at. Among its discoveries were sources of radio waves that seemed at the same time small, spectacularly powerful and, judging by their redshifts, phenomenally distant. The astronomers dubbed them quasars and wondered what could possibly produce radio signals with the power of hundreds of billions of stars from a volume little bigger than a solar system.

Roy Kerr’s solution to the equations of general relativity provided the answer: a supermassive spinning black hole. Its rotation would create a region just outside the hole’s “event horizon”—the point of no return for light and everything else—in which matter falling inward would be spun up to enormous speeds. Some of that matter would be squirted out along the axis of rotation, forming the jets seen in radio observations of quasars.

Disappear like smoke

For the first time, general relativity was explaining new phenomena in the world. Bright young minds rushed into the field; wild ideas that had been speculated on in the fallow decades were buffed up and taken further. There was talk of “wormholes” in space-time that could connect seemingly distant parts of the universe. There were “closed time-like curves” that seemed as though they might make possible travel into the past. Less speculatively, but with more profound impact, Stephen Hawking, a physicist (pictured, with a quasar), and Roger Penrose, a mathematician, showed that relativistic descriptions of the singularities in black holes could be used to describe the Big Bang in which the expansion of the universe began—that they were, in fact, the only way to make sense of it. General relativity gave humans their first physical account of creation.

Hawking boi

Dr Hawking went on to bring elements of quantum theory into science’s understanding of the black hole. Quantum mechanics says that if you look at space on the tiniest of scales you will see a constant ferment in which pairs of particles pop into existence and then recombine into nothingness. Dr Hawking argued that when this happens at the event horizon of a black hole, some of the particles will be swallowed up, while some will escape. These escaping particles mean, in Dr Hawking’s words, that “black holes ain’t so black”—they give off what is now called “Hawking radiation”. The energy lost this way comes ultimately from the black hole itself, which gives up mass in the process. Thus, it seems, a black hole must eventually evaporate away to nothingness.

Adding quantum mechanics to the description of black holes was a step towards what has become perhaps the greatest challenge in theoretical physics: reconciling the theory used to describe all the fields and particles within the universe with the one that explains its overall shape. The two theories view reality in very different ways. In quantum theory, everything is, at some scale, bitty. The equations of relativity are fundamentally smooth. Quantum mechanics deals exclusively in probabilities—not because of a lack of information, but because that is the way the world actually is. In relativity all is certain. And quantum mechanics is “non-local”; an object’s behaviour in one place can be “entangled” with that of an object kilometres or light-years away. Relativity is proudly local; Einstein was sure that the “spooky action at a distance” implied by quantum mechanics would disappear when a better understanding was reached.

It hasn’t. Experiment after experiment confirms the non-local nature of the physical world. Quantum theory has been stunningly successful in other ways, too. Quantum theories give richly interlinked accounts of electromagnetism and of the strong and weak nuclear forces—the processes that hold most atoms together and split some apart. This unified “standard model” now covers all observable forms of matter and all their interactions—except those due to gravity.

Some people might be satisfied just to let each theory be used for what it is good for and to worry no further. But people like that do not become theoretical physicists. Nor will they ever explain the intricacies of the Big Bang—a crucible to which grandiose theory-unifiers are ceaselessly drawn. In the very early universe, space-time itself seems to have been subject to the sort of fluctuations fundamental to the quantum world (like those responsible for Hawking radiation). Getting to the heart of such shenanigans requires a theory that combines the two approaches.

There have been many rich and subtle attempts at this. Dr Penrose has spent decades elaborating an elegant way of looking at all fields and particles as new mathematical entities called “twistors”. Others have pursued a way of adding quantum bittiness to the fabric of space-time under the rubric of “loop quantum gravity”. Then there is the “Exceptionally Simple Theory of Everything”—which isn’t. As Steven Weinberg, one of the unifiers whose work built the standard model, puts it, “There are so many theories and so few observations that we’re not getting very far.”

Dr Weinberg, like many of his colleagues, fancies an approach called superstring theory. It is an outgrowth of the standard model with various added features that seem as though they would help in the understanding of space-time and which its proponents find mathematically beguiling. Ed Witten of the Institute for Advanced Study (IAS) in Princeton, Einstein’s institutional home for the last 22 years of his life, is one of those who has raised it to its current favoured status. But he warns that much of the theory remains to be discovered and that no one knows how much. “We only understand bits and pieces—but the bits and pieces are staggeringly beautiful.”

This piecemeal progress, as Dr Witten tells it, offers a nice counterpoint to the process which led up to November 1915. “Einstein had the conception behind general relativity before he had the theory. That’s in part why it has stood: it was complete when it was formulated,” he says. “String theory is the opposite, with many manifestations discovered by happy accident decades ago.”

Entangled up in the blue

And the happy accidents continue. In 1997 Juan Maldacena, an Argentine theoretician who now also works at the IAS, showed that there is a deep connection between formulations of quantum mechanics known as conformal field theories and solutions to the Einstein equations called anti-de Sitter spaces (similar to the expanding-universe solution derived by Willem de Sitter, but static and much favoured by string theorists). Neither provides an account of the real world, but the connection between them lets physicists recast intractable problems in quantum mechanics into the sort of equations found in general relativity, making them easier to crack.

This approach is being gainfully employed in solving problems in materials science, superconductivity and quantum computing. It is also “influencing the field in a totally unexpected way,” says Leonard Susskind, of Stanford University. “It’s a shift in our tools and our methodology and our way of thinking about how phenomena are connected.” One possibility Dr Maldacena and Dr Susskind have developed by looking at things this way is that the “wormholes” relativity allows (which can be found in the anti-de Sitter space) may be the same thing as the entanglement between distant particles in quantum mechanics (which is part of the conformal field theory). The irony of Einstein’s spooky quantum bĂȘte noire playing such a crucial role has not gone unremarked.

There is more to the future of relativity, though than its eventual subsumption into some still unforeseeable follow-up theory. As well as offering new ways of understanding the universe, it is also providing new ways of observing it.

This is helpful because there are bits of the universe that are hard to observe in other ways. Much of the universe consists of “dark matter” which emits no radiation. But it has mass, and so it warps space, distorting the picture of more distant objects just as the eclipse-darkened sun distorted the positions of Eddington’s stars. Studying distortions created by such “gravitational lenses”—both luminous (pictured, with Einstein) and dark—allows astronomers with the precise images of the deep sky today’s best telescopes provide to measure the distribution of mass around the universe in a new way.

A century ago Albert Einstein changed the way humans saw the universe. His work is still offering new insights today.
Einstein boi

Another form of relativity-assisted astronomy uses gravitation directly. Einstein’s equations predict that when masses accelerate around each other they will create ripples in space-time: gravitational waves. As with black holes and the expanding universe, Einstein was not keen on this idea. Again, later work has shown it to be true. A pair of neutron stars discovered spinning around each other in the 1970s are exactly the sort of system that should produce such waves. Because producing gravitational waves requires energy, it was realised that these neutron stars should be losing some. And so they proved to be—at exactly the rate that relativity predicts. This indirect but convincing discovery garnered a Nobel prize in 1993.

As yet, though, no one has seen a wave in action by catching the expansion and contraction of space that should be seen as one goes by, because the effects involved are ludicrously small. But researchers at America’s recently upgraded Laser Interferometer Gravitational-wave Observatory (LIGO) now think they can do it. At LIGO’s two facilities, one in Louisiana and one in Washington state, laser beams bounce up and down 4km-long tubes dozens of times before being combined in a detector to make a pattern. A passing gravitational wave that squashes space-time by a tiny fraction of the radius of an atomic nucleus in one arm but not the other will make a discernible change to that pattern. Comparing measurements at the two sites could give a sense of the wave’s direction.

Step into the light

The aim is not just to detect gravitational waves—though that would be a spectacular achievement—but to learn about the processes that produce them, such as mergers of neutron stars and black holes. The strengths of the warping effects in such cataclysms are unlike anything seen to date; their observation would provide a whole new type of test for the theory.

And history suggests there should be completely unanticipated discoveries, too. Kip Thorne, a specialist in relativity at the California Institute of Technology and co-founder of LIGO, says that “every time we’ve opened a new window on the cosmos with new radiation, there have been unexpected surprises”. For example, the pioneers of radio astronomy had no inkling that they would discover a universe full of quasars—and thus black holes. A future global array of gravitational-wave observatories could open a whole new branch of observational astronomy.

A century ago general relativity answered no one’s questions except its creator’s. Many theories are hit upon by two or more people at almost the same time; but if Einstein had not devoted years to it, the curvature of space-time which is the essence of gravity might not have been discovered for decades. Now it has changed the way astronomers think about the universe, has challenged them to try and build theories to explain its origin, and even offered them new ways to inspect its contents. And still, it retains what most commended it to Einstein: its singular beauty revealed first to his eyes alone but appreciated today by all who have followed. “The Einstein equations of general relativity are his best epitaph and memorial,” Stephen Hawking has written. “They should last as long as the universe.”

I want to make you look up into the sky and comprehend, maybe for the first time, the darkness that lies beyond the evanescent wisp of the atmosphere, the endless depths of the cosmos, a desolation by degrees

I want the Earth to turn beneath you and knock your balance off, carry you eastward at a thousand miles an hour, into the light, and the dark, and the light again. I want you to watch the Earth rising you up to meet the rays of the morning sun

I want the sky to stop you dead in your tracks on your walk home tonight because you happened to glance up and among all the shining pinpricks you recognized one as the light of an alien world

I want you to taste the iron in your blood and see its likeness in the rust-red sands on the long dry dunes of Mars, born of the same nebular dust that coalesced random flotsam of stellar debris into rocks, oceans, your own beating heart

I want to reach into your consciousness and cast it outward, beyond the light of other suns, to expand it like the universe, not encroaching on some envelope of emptiness, but growing larger, unfolding inside itself

I want you to see your world from four billion miles away, a tiny glint of blue in the sharp white light of an ordinary star in the darkness. I want you to try to make out the boundaries of your nation from that vantage point and fail

I want you to feel it, in your bones, in your breath, when two black holes colliding a billion light years away send a tremor through spacetime that makes every cell in your body stretch, and strain

I want to make you nurse nostalgia for the stars long dead, the ones that fused your carbon nuclei and the ones whose last thermonuclear death throes outshined the entire galaxy to send a single photon into your eye

I want you to live forward but see backwards, farther and deeper into the past, because in a relativistic universe, you don’t have any other choice. I want the stale billion-year-old starlight of a distant galaxy to be your reward

I want to utterly disorient you and let you navigate back by the stars. I want you to lose yourself, and find it again, not just here, but everywhere, in everything

I want you to believe that the universe is a vast, random, uncaring place, in which our species, our world, has absolutely no significance. And I want you to believe that the only response is to make our own beauty and meaning and to share it while we can

I want to make you wonder what is out there. What dreams may come in waves of radiation across the breadth of an endless expanse? What we may know, given time, and what splendours might never, ever reach us

I want to make it mean something to you. That you are in the cosmos. That you are of the cosmos. That you are born from stardust and to stardust you will return. That you are a way for the universe to be in awe of itself.

Ex-lovers are extremely wicked, shockingly evil and vile beings. The only thing they are worthy of is rotting in the biggest prison out there. Or drinking from a cauldron of Neville Longbottom’s Shrinking Solution. Alternatively, in a proclamation of utter brilliance, you may send them back in time to battle out for survival with the mighty Tyrannosaurus rex. There are just no limits to the cruel exterminations they deserve.

And, no, Ngina. Forgiveness was never an option.

Of particular interest, you’ll need them deprived of all necessities that make up who they are, from social to atomic. Thus, alas! I present you with [drumroll please] a wormhole! A wormhole is a kind of tunnel that connects two points in spacetime. It acts as a shortcut through spacetime, connecting two points that would otherwise be far apart, like really far, billions of light-years apart even.

A wormhole is a tunnel that connects two points in spacetime that are far apart.

Now, here’s a simple DIY how-to on how to construct a traversable cosmic wormhole that could send that sorry excuse of a biped to the farthest reaches of space to wallow in solitary anguish (and quite possibly, die):

  • Take two charged black holes
  • Place them back to back
  • Thread two cosmic strings through both of the black holes
  • Stretch both strings to infinity

Presto! You’ve got yourself a traversable wormhole. ⁠

The barebones: a charged black hole, which is a theoretical black hole that carries an electric charge and has an oppositely charged black hole on the other end of it, will act as your wormhole.

But there’s a catch before you decide to just push that degenerate stain into that wormhole: wormholes are by nature incredibly unstable. To make sure either charged end stays fully stretched out, a pair of cosmic strings — a hypothetical, one-dimensional defect in space-time — could hold them in place. Cosmic strings can also be thought of as narrow tubes of energy stretched across the entire length of the ever-expanding universe. These thin regions, leftover from the early cosmos, are predicted to contain huge amounts of mass and therefore could warp the space-time around them. Cosmic strings are either infinite or they’re in loops, with no ends, physicists say. The approach of two such strings parallel to each other would bend space-time so vigorously and in such a particular configuration that might make space and/or time travel possible, at least in theory.

Unfortunately, cosmic strings are also not a great travelling companion. You never want to encounter one yourself, since they would slice you clean in half like a cosmic lightsabre, but you don’t have to worry much since it isn’t certain that they exist. Moreover, none has ever been seen out there in the universe, and even better, it’s your ex falling through the wormhole: so, no love lost – pun very much intended.

While wormholes — and cosmic strings — have yet to be proven to exist, you could measure their shape by looking at the ripples they leave behind in space-time. Unfortunately, these ripples or gravitational waves could sap black holes’ mass and cause them to eventually collapse in on themselves.

But the hope is that the strung-up wormhole could be stable for just enough time to send that hell of an ex on a hell of a journey.

Our ancestors understood origins by extrapolating from their own experiences. How else could they have done it? So the Universe was hatched from a cosmic egg, or conceived in the sexual congress of a mother God and a father God, or was a kind of product of the Creator’s workshop—perhaps the latest of many flawed attempts. And the Universe was not much bigger than we see, and not much older than our written or oral records, and nowhere very different from places that we know.

We’ve tended in our cosmologies to make things familiar. Despite all our best efforts, we’ve not been very inventive. In the West, Heaven is placid and fluffy, and Hell is like the inside of a volcano. In many stories, both realms are governed by dominant hierarchies headed by gods or devils. Monotheists talked about the King of Kings. In every culture, we imagined something like our own political system running the Universe. Few found the similarity suspicious.

Then science came along and taught us that we are not the measure of all things, that there are wonders unimagined, and that the Universe is not obliged to conform to what we consider comfortable or plausible. We have learned something about the idiosyncratic nature of our common sense. Science has carried human self-consciousness to a higher level. This is surely a rite of passage, a step towards maturity. It contrasts starkly with the childishness and narcissism of our pre-Copernican notions.

And, again, if we’re not important, not central, not the apple of God’s eye, what is implied for our theologically based moral codes? The discovery of our true bearings in the Cosmos was resisted for so long and to such a degree that many traces of the debate remain, sometimes with the motives of the geocentrists laid bare.

What do we want from philosophy and religion? Palliatives? Therapy? Comfort? Do we want reassuring fables or an understanding of our actual circumstances? Dismay that the Universe does not conform to our preferences seems childish. You might think that grown-ups would be ashamed to put such disappointments into print. The fashionable way of doing this is not to blame the Universe—which seems truly pointless—but rather to blame the means by which we know the Universe, namely science.

Science has taught us that, because we have a talent for deceiving ourselves, subjectivity may not freely reign. Its conclusions derive from the interrogation of nature and are not in all cases predesigned to satisfy our wants.

We recognize that even revered religious leaders, the products of their time as we are of ours, may have made mistakes. Religions contradict one another on small matters, such as whether we should put on a hat or take one off on entering a house of worship, or whether we should eat beef and eschew pork or the other way around, all the way to the most central issues, such as whether there are no Gods, one God, or many gods.

If you lived two or three millennia ago, there was no shame in holding that the Universe was made for us. It was an appealing thesis consistent with everything we knew; it was what the most learned among us taught without qualification. But we have found out much since then. Defending such a position today amounts to willful disregard of the evidence, and a flight from self-knowledge.

We long to be here for a purpose, even though, despite much self-deception, none is evident.

Our time is burdened under the cumulative weight of successive debunking of our conceits:

  • We’re Johnny-come-latelies
  • We live in the cosmic boondocks
  • We emerged from microbes and muck
  • Apes are our cousins
  • Our thoughts and feelings are not fully under our own control
  • There may be much smarter and very different beings elsewhere.
  • On top of all this, we’re making a mess of our planet and becoming a danger to ourselves.

The trapdoor beneath our feet swings open. We find ourselves in bottomless free fall. We are lost in great darkness, and there’s no one to send out a search party. Given so harsh a reality, of course, we’re tempted to shut our eyes and pretend that we’re safe and snug at home, that the fall is only a bad dream.

Once we overcome our fear of being tiny, we find ourselves on the threshold of a vast and awesome Universe that utterly dwarfs—in time, in space, and in potential—the tidy anthropocentric proscenium of our ancestors:

  • We gaze across billions of light-years of space to view the Universe shortly after the Big Bang and plumb the fine structure of matter.
  • We peer down into the core of our planet, and the blazing interior of our star.
  • We read the genetic language in which is written the diverse skills and propensities of every being on Earth.
  • We uncover hidden chapters in the record of our own origins, and with some anguish better understand our nature and prospects.
  • We invent and refine agriculture, without which almost all of us would starve to death.
  • We create medicines and vaccines that save the lives of billions.
  • We communicate at the speed of light and whip around the Earth in an hour and a half.
  • We have sent dozens of ships to more than seventy worlds, and four spacecraft to the stars.

To our ancestors, there was much in nature to be afraid of—lightning, storms, earthquakes, volcanos, plagues, drought and long winters. Religions arose in part as attempts to propitiate and control, if not much to understand, the disorderly aspect of nature.

How much more satisfying had we been placed in a garden custom-made for us, its other occupants put there for us to use as we saw fit? There is a celebrated story in the Western tradition like this, except that not quite everything was there for us. There was one particular tree of which we were not to partake, a tree of knowledge. Knowledge and understanding and wisdom were forbidden to us in this story. We were to be kept ignorant. But we couldn’t help ourselves. We were starving for knowledge—created hungry, you might say. This was the origin of all our troubles. In particular, it is why we no longer live in a garden: We found out too much. So long as we were incurious and obedient, I imagine, we could console ourselves with our importance and centrality, and tell ourselves that we were the reason the Universe was made. As we began to indulge our curiosity, though, to explore, to learn how the Universe really is, we expelled ourselves from Eden. Angels with a flaming swords were set as sentries at the gates of Paradise to bar our return. The gardeners became exiles and wanderers. Occasionally we mourn that lost world, but that, it seems to me, is maudlin and sentimental. We could not happily have remained ignorant forever.

There is in this Universe much of what seems to be designed. But instead, we repeatedly discover that natural processes—the collisional selection of worlds, say, or natural selection of gene pools, or even the convection pattern in a pot of boiling water—can extract order out of chaos, and deceive us into deducing purpose where there is none.

The significance of our lives and our fragile planet is then determined only by our wisdom and courage. We are the custodians of life’s meaning. We long for a parent to care for us, to forgive us for our errors, and to save us from our childish mistakes. But knowledge is preferable to ignorance. Better by far to embrace the hard truth than a reassuring fable.

If we crave some cosmic purpose, then let us find ourselves a worthy goal.