Einstein's Equation of Life and Death (2005)

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Documentary Description

Einstein's Equation of Life and Death (2005)

To mark the 100th anniversary of Einstein''s theory of special relativity, this documentary with dramatised elements tells the story of how his most famous discovery, E=mc2, went from being a mere set of symbols in a notebook to a weapon of mass destruction. The documentary sections of the film explain what E=mc2 actually means; how it was discovered and how it revealed that the universe contained astonishing power.

Albert Einstein was a lifelong anti-militarist. His most famous discovery – that E=mc2 – explains things of sheer wonder: why the sun shines and how, after the Big Bang, the universe was created. But it wasn’t long before Einstein’s contemporary, Leo Szilard, realised that it could be used to build an atomic bomb.Szilard, like Einstein, was a refugee from the Nazis. He knew that Hitler had brilliant physicists working for him, and that, if he had worked out how to use Einstein’s famous equation to great destructive effect, it wouldn’t be long before his German colleagues made the same link. Szilard insisted that Einstein write to the American President – the Allies had to be prepared. But when the bomb was used, not on the Nazis, but on the Japanese, both scientists were horrified. Einstein, who spent his final years campaigning for disarmament and promoting peace between nations, described the letter to President Franklin Roosevelt as his life’s only mistake. This documentary, with dramatised elements, explains what E=mc2 actually means, how it was discovered, and how it revealed the astonishing power of the universe. It also tells the story of how Einstein’s most famous discovery went from being a set of symbols in a notebook to a weapon of mass destruction.

Program Description

In the summer of 1939 Albert Einstein was on holiday in a small resort town on the tip of Long Island. His peaceful summer, however, was about to be shattered by a visit from an old friend and colleague from his years in Berlin. The visitor was the physicist Leo Szilard. He had come to tell Einstein that he feared the Nazis could soon be in possession of a terrible new weapon and that something had to be done.

Szilard believed that recent scientific breakthroughs meant it was now possible to convert mass into energy. And that this could be used to make a bomb. If this were to happen, it would be a terrible realisation of the law of nature Einstein had discovered some 34 years earlier.

September 1905 was Einstein's 'miracle year'. While working as a patents clerk in the Swiss capital Berne Einstein submitted a three-page supplement to his special theory of relativity, published earlier that year. In those pages he derived the most famous equation of all time; e=mc², energy is equal to mass multiplied by the speed of light squared.

The equation showed that mass and energy were related and that one could, in theory, be transformed into the other. But because the speed of light squared is such a huge number, it meant that even a small amount of mass could potentially be converted into a huge amount of energy. Ever since the discovery of radioactivity in the late 19th century, scientists had realised that the atomic nucleus could contain a large amount of energy. Einstein's revolutionary equation showed them, for the first time, just how much there was.

However, at the time Einstein doubted whether that energy could ever be released. By 1935 he was convinced it would never be practical. At the Winter Session of the American Association for the Advancement of Science in Pittsburgh, he is quoted as telling journalists: "The likelihood of transforming matter into energy is something akin to shooting birds in the dark in a country where there are only a few birds."

Einstein was so sceptical because attempts to break open the atomic nucleus always required more far energy be put in than was ever released. Nuclear physicists like Ernest Rutherford were exploring the structure of the atom by bombarding atomic nuclei with alpha particles. Even when machines were built to accelerate the alpha particles to ever higher speeds they had only limited success in breaking apart the nucleus. In 1933 Rutherford dismissed talk of atomic power as 'moonshine'.

One morning in September 1933 Szilard read Rutherford's comments in The Times. Leaving his hotel and crossing the street, he had a brainwave. Alpha particles and the other particles that physicists had been using to bombard the nucleus were simply the wrong tool for the job, because he realised that they, like the nucleus, had a positive charge.

Since like charges repel, Szilard thought, no matter how hard you fire them in, the majority would simply be deflected away. That morning he was one of the first to realise that the recently discovered neutron might be what was needed. The neutron, a subatomic particle like a proton but with no electric charge was discovered in 1932. With no charge, Szilard believed the neutron would simply slip into the heart of the atom undeflected.

But he didn't stop there. Szilard thought that if an atom could be found that is split open by neutrons, not only would it release some of its huge store of energy, it might also release further neutrons, which could then go on and split further atoms, setting up a chain reaction leading to a truly vast release of energy. Szilard immediately saw the possible military applications and sought to patent the idea and have it made an official secret. But in 1933, the chain reaction only existed in Szilard's head. No one had yet found an atom that could be split by neutrons.

These developments were happening against a background of extraordinary political turmoil in Europe. Hitler had come to power in Germany in January 1933. In 1938, less than a year before the outbreak of World War II, just such an atom was found, uranium.

Working at the Kaiser Wilhelm Institute in Berlin, the nuclear chemists Otto Hahn and Fritz Strassman found that when bombarded with neutrons, uranium split into two nuclei of roughly half the size. Not only that, but further calculations showed that a large amount of energy was also released - enough from a single nucleus to move a grain of sand. The first stage of Szilard's chain reaction had been achieved.

When he heard the news Szilard, now in New York and working at Columbia University with Enrico Fermi, set about showing whether, as well as energy, further 'secondary' neutrons were released. By July 1939, when he first knocked on Einstein's door, he knew that they were and so the chain reaction was possible. Also, he and Fermi had settled on a design for the first nuclear reactor.

During the course of their conversations in the summer of 1939, Szilard explained these new developments to Einstein and his fear that the Nazis might use them to create a nuclear bomb. Together they drafted a letter, signed by Einstein, to the American President, Franklin Roosevelt. The letter was delivered to the President on the 11 October 1939 and after reading it the President provided funding for research that would pave the way for the Manhattan Project and lead, ultimately to the construction of the first atomic bomb. After signing the letter, Einstein played no further part in the development of the bomb.

With the first atomic explosion over Hiroshima, the power of e=mc² had been graphically demonstrated to the world. Just 0.6 grams of mass, converted into energy, had been enough to destroy an entire city.

Einstein was horrified when he heard that the bomb had been dropped. When they, wrote to the President, Szilard and Einstein advocated the development of an American bomb purely as a deterrent against the threat of a Nazi weapon. They had not conceived of its use as an offensive weapon, especially after the defeat of Nazi Germany.

Einstein always saw e=mc² as a purely theoretical insight and refuted any responsibility for the bomb but he did feel some responsibility for the letter he'd written to Roosevelt. A letter he would come to describe as "the one mistake" of his life. Einstein saw nuclear weapons and the nuclear arms race as a threat to the future of civilisation. In his final years he devoted much of his time and energy to issues dealing with the world's future - advocating pacifism and campaigning for the control of nuclear weapons, not by individual nations, but by a world government. The last document he signed, just a week before he died, was a manifesto drawn up by Bertrand Russell, renouncing war and nuclear weapons. As Russell said: ""Einstein was not only a great scientist he was a great man. He stood for peace in a world drifting towards war..."

But while the bomb proved e=mc² to be the ultimate equation of destruction, only after his death has the role of Einstein's equation in the creation of the universe become clear. Just as mass can be turned into energy in a bomb, the pure energy generated in the Big Bang condensed into the matter that makes up our world. Almost a hundred years ago, with just six short pen stokes Einstein unlocked one of the most powerful truths about the universe. A truth that would change our world, both for good and ill.


NARRATOR: In 1939, on the eve of the Second World War, Albert Einstein wrote a fateful letter to the American President, Franklin Roosevelt.

EINSTEIN: Sir, the element Uranium maybe turned into a new and important source of energy in the immediate future. Certain aspects of the situation which has arisen seem to call for watchfulness and, if necessary, quick action on the part of the administration. Extremely powerful bombs of a new type may thus be constructed.

NARRATOR: The letter was about an application of Einstein's famous equation, e=mc². And his fear that the Nazis could use it to build an atomic bomb. His letter set off a chain of events which led to the destruction of Hiroshima and Nagasaki. Albert Einstein regarded writing this letter as the greatest mistake of his life. This is the story of his famous equation. And how e=mc² changed history and Einstein forever.

NARRATOR: On the eve of Second World War Albert Einstein, the most famous scientist in the world, was on holiday by the seaside outside New York. He was an instinctive pacifist who had fled the Nazis, and he had hoped to turn his back on the violence in Europe, and continue his scientific research in peace. But his tranquil summer was interrupted by a visitor who had also fled the Nazis. The caller was Leo Szilard, another brilliant scientist and an old friend of Einstein's from Europe.

EINSTEIN: Szilard.

SZILARD: Herr Professor, there is something we must do.

EINSTEIN: Come in.

NARRATOR: Leo Szilard had come to persuade his old friend that the world was threatened by a devastating new weapon. He'd come to try and convince Einstein that something had to be done.


SZILARD: Herr Professor, I need your help.

EINSTEIN: Why? Are you on the run from the police?

SZILARD: I wish it was that simple. I want you to help me compose a letter.

EINSTEIN: It's a long way to come for help with your correspondence.

SZILARD: Not this correspondence. I've never written a letter like this before. I'm not even sure what I should say.

EINSTEIN: Who is the letter to?

SZILARD: Roosevelt.

EINSTEIN: President Roosevelt. Are you offering advice, or admonition?

SZILARD: A warning. I want to warn Roosevelt about the German bomb.

EINSTEIN: The Germans have many bombs.

SZILARD: Not one like this. At least, not yet. It's an atomic bomb, the Germans are going to be able to build an atomic bomb. And if they are doing it, then so must we.

NARRATOR: This meeting would one day haunt Einstein. Because Leo Szilard had come to explain that the Nazi project was an application of something Einstein himself had discovered, the equation e=mc² .

NARRATOR: E=mc², the symbol of Einstein's genius. An equation that sums up one of the most powerful truths about the universe. An equation which combines two ideas in a way, which until Einstein came along, no one had ever dreamed could be connected. The idea of Mass. And the idea of energy.

BRIAN COX: If you think about energy and mass it is not at all obvious that they're anything like the same thing. I mean energy is something that moving objects have, and mass is something that every object possesses. So really it's a bold step to try and link them in any way, let alone in a beautiful way that Einstein did.

NARRATOR: Einstein's great insight was that energy, the thing that enables an object to move, and mass, essentially an objects weight, are not separate but different aspects of the same thing.

BRIAN COX: Einstein really found that energy and mass are two sides of the same coin. They're almost the same thing, so mass in a sense is energy waiting to be liberated.

NARRATOR: In other words, mass could be converted into energy. And energy into mass. But Einstein's equation went even further. It gave an exact value to the amount of energy contained within any given mass. Energy equals mass times C - the speed of light, squared, a number that is absolutely huge.

BRIAN COX: This is Einstein's famous equation: e, energy equals m, mass, times c squared, the speed of light squared. In metres per second eight nine thousand, eight hundred and seventy five million million, huge number. That means you get an awful lot of energy for an extremely tiny amount of mass.

NARRATOR: The implications of this neat equation were vast.

BRIAN COX: Well it means that there's enough energy in a glass of water to power a city like London for a week.

NARRATOR: Hidden within every object around us is a huge store of energy. Einstein published e=mc² in 1905. And it changed the world. It wasn't long before e=mc² solved one of the great mysteries of life on earth. What powers the sun? For generations this had baffled scientists. Because if the sun just burned like a huge bonfire, the calculations showed it should have died out millions of years ago. But Einstein's equation explained what was powering the sun. Mass is constantly being converted into energy. A process that can be sustained for billions of years. Billions of atoms were smashing together, and the mass lost in this reaction was transformed into energy. And soon people began to think, if e=mc² can power the sun, could we use it to generate power on earth? Could we release the energy inside atom for our own purposes? Soon, talk of getting energy out of the atom began to grip the popular imagination. And at a scientific conference in 1935, Einstein was asked whether he thought the atom would ever yield its hidden energy. His answer was to go down in scientific history.

EINSTEIN: The likelihood of transforming matter into energy is something akin to shooting birds in the dark in a country in which there are very few birds.

NARRATOR: In other words, getting energy out of the atom was just not going to be practical.

EINSTEIN: It would take an almost incalculable amount of energy to release energy even from even a single molecule.

NARRATOR: He was so dismissive because it was becoming clear that to release energy from the atom scientists would have to find a way of breaking the atom apart. And however hard they tried, it always took more energy to smash an atom than was released.

REPORTER: Kinda tough, huh?

EINSTEIN: Kind of tough, yes.

NARRATOR: But others were less dismissive. In 1933 Hitler came to power in Germany. Germany was one of the world centres of physics. Some of its scientists were willing to work with Nazis. The Nazi war machine was eager to achieve what Einstein had said was impossible, to release energy from the atom. Unlike Einstein, Leo Szilard feared that energy could be released from the atom and then used to construct weapons of mass destruction. The fear of that had taken him to see Einstein that summer in Long Island.

SZILARD: The war in Europe is going to happen. Hitler has planned for it. And he has built up his arms. And once he realises its power, he will not hesitate to construct an atomic bomb.

EINSTEIN: But that would take years.

SZILARD: Why years?

EINSTEIN: To build such a bomb the reaction would have to take place in multiple millions of atoms simultaneously.

SZILARD: Maybe not simultaneously. I think maybe there is another way that might be achieved.

NARRATOR: Szilard was speaking with such confidence because he knew something Einstein didn't. Leo Szilard had worked out exactly how to make e=mc² into a bomb. In 1920, a young Leo Szilard had gone to study in Berlin. It was there he witnessed the rise of the Nazis. Szilard was intensely worried by what this might mean for science and for the world.

WILLIAM LANOUETTE: Szilard was really scared because he had seen the Nazi terror first hand. He warned his colleagues and then he himself left shortly after Hitler took power. He was trying to draw as many friends as he could out of Nazi Germany, he saw how the terror was spreading.

NARRATOR: But many brilliant physicists remained in Germany, and by the early 1930s Szilard was fearful it was only a matter of time before someone would find a way of harnessing the power of e=mc² and make a bomb. In fact, the first step had already inadvertently been taken, because scientists had identified the type of substance they might need to turn mass into energy.

TV REPORT: Yes radioactivity is already at work in medical fields...So if you will listen and watch at the same time when we hear the clicks.

NARRATOR: Radioactivity elements are e=mc² in action. Unstable elements like Radium and Uranium continually break down into ever smaller elements in order to become more stable. This process of decay is called radioactivity. Where tiny amounts of mass from the heart of an unstable atom are spontaneously released in the form of energy. But finding the right type of substance to release energy according to e=mc² was only half the answer.

TV REPORT: This scintillating character is very unstable, and as a consequence she radiates energy. We call her radioactive.

ROBIN MARSHALL: Natural radioactivity was originally thought to be potentially very useful. But the more that was understood about it was realised that this particular form of radioactivity whilst producing heat was not especially efficient. The amount of heat given out was rather small.

TV REPORT: This is radioactive iodine. I'm now going to drink this.

NARRATOR: Natural radioactivity was simply far too gentle for generating real power. So scientists began developing ways of improving upon nature. In Germany, in Britain and in America scientists began building machines designed to achieve nuclear fission, the splitting open of atoms. Many hoped this might release the vast amounts of energy potentially hidden within the atom. Again and again they hit Einstein's paradox. They always had to put in far more energy than they ever got out.

EINSTEIN: The likelihood of transforming matter into energy is something akin to shooting birds in the dark in a country in which there are only very few birds.

NARRATOR: It looked as though Einstein had been right after all. e=mc² was simply a theoretical insight, not a practical solution to generating vast amounts of energy. But then Einstein's friend, Leo Szilard had his first brainwave. It happened one autumn day in 1933. It dawned on him that everyone had been going about it the wrong way. Attempts to release energy from matter had always involved something called alpha particles. And Szilard thought they were simply the wrong tool for the job. Alpha particles consist of 2 protons and 2 neutrons and carry a positive electric charge. The theory was that by smashing these particles at the nucleus, at incredible speeds, they might blast it apart, releasing the energy inside.

ROBIN MARSHALL: It turned out to be not enough. And even when the developments proceeded and accelerators were made to accelerate the alpha particles to higher and higher energies, still it needed more energy putting in than you actually got out from the process.

NARRATOR: Leo Szilard was one of the first to realise the problem was down to an invisible force, the positive charge of the alpha particle. Because the nucleus of the target atom is also positively charged, just as like poles of a magnet repel each other, the identical positive charges of the nucleus and the alpha particle would also repel each other. It was this clash of electrical charge that was preventing the alpha particle from blasting apart the nucleus.

ROBIN MARSHALL: Alpha particles themselves carry a positive electric charge. The nucleus has a positive electric charge so the two repelled each other and every time an alpha particle is sent towards the nucleus, it has a tendency to slew off to one side or the other.

NARRATOR: Szilard realised what was needed was a particle able to attack the very heart of the charged nucleus. And Szilard had just such a particle in mind, the recently discovered neutron. The neutron is a subatomic particle, a mere quarter of the mass of an alpha particle. And it has no electric charge. Szilard reasoned that if a neutron could be fired at an atom's nucleus, it would not be repelled. Instead it might bond to the nucleus itself. And if it did that the nucleus would become very unstable. It might then split. And as it did so, it could release some of its vast store of energy.

ROBIN MARSHALL: This was a stupendous discovery. The neutron carried no electric charge and therefore it could approach the nucleus un-deflected and maybe even stick and interact with it. In fact the impact of the neutron on the nucleus at the time was likened to the effect of the moon striking the earth. Here was a means perhaps to make this slightly wobbly unstable nucleus absorb something that it couldn't help absorbing and then it would wobble even more and disintegrate.

NARRATOR: But using the neutron was simply Szilard's first brainwave. He went on to have, one that would become crucial to the making of the atomic bomb. Szilard calculated that if you hit an atom with a neutron, as the atom divided, it would release not just energy, but two or three more neutrons. And those neutrons might then be free to break apart further atoms. And every time that happened a tiny bit of mass could be converted into a vast amount of energy. Energy that at every step in the chain, would multiply and multiply. It was a chain reaction.

DR MARK LANCASTER: So typically you would end up with two extra neutrons coming out. So those two extra neutrons could then produce another fission process and produce two more neutrons, so you have 4 neutrons, that would then go to 8,16,32. You have this multiplicative chain reaction process and the potential for that was immediately seen because each of these processes produces a large amount of energy.

NARRATOR: What made Leo Szilard's idea so brilliant was for the first time here was a way of getting energy out of the atom, without having to pump in vast amounts of power. All you had to do was set off just one tiny neutron to trigger an unstoppable chain reaction. Leo Szilard had found a way to unleash the power of e=mc² on Earth. But it was a discovery that terrified him.

WILLIAM LANOUETTE: Szilard's first reaction when he thought of the neutron was this is something that could become potentially a weapon. His second thought was that if he could think of this then certainly his German colleagues who remain in Germany could think of it too and this really scared him.

NARRATOR: Then, in 1938, less than a year before the outbreak of World War II, came news from his colleagues in Germany, the news Leo Szilard had been dreading.

TV REPORT: Scientists from several nations gathered for a routine conference heard a report of startling significance.

TV REPORT: Word has just come through from Germany by way of Denmark that the German Physicists Hahn and Strassman have just verified that the uranium atom under neutron bombardment actually splits in to two parts.

NARRATOR: In a lab in Berlin, the German team had struck lucky. Quite by accident they'd achieved nuclear fission, the first stage of Szilard's theoretical chain reaction.

DR MARK LANCASTER: In terms of physics it was an enormous breakthrough because up until that point it was a theory and theories are great but they need to be verified experimentally and it was the experimental verification of that which was really was the groundbreaking thing which meant wow this theory is true.

NARRATOR: Within months, the Nazis began to stockpile Uranium. And by 1940 had set up an official bomb programme. Nazi money poured into fission research. Nuclear physics was going to war. For Leo Szilard, it was no longer possible for science to be neutral.

EINSTEIN: You are a scientist. As am I. It is best to remember that and let the military play their games.

SZILARD: I don't think that we can. Not when some of our former colleagues in Germany are only too happy to work with the military.

EINSTEIN: That is their choice, if they wish to be so foolish.

SZILARD: They are still good scientists. Some of the best. And the military will give them all the assistance they need, but we also have good scientists. Also some of the best.

EINSTEIN: So now you want us to go to war in the laboratory?

NARRATOR: That was precisely what Leo Szilard wanted to do. The German scientists had achieved nuclear fission with neutrons, the first part of Szilard's theory, and now he had to determine if the other stages of the process would follow. And by July 1939 in a lab at Columbia University, Szilard with his colleague Enrico Fermi turned theory in to practice and showed a chain reaction was possible. There was now a real chance that e=mc² could be harnessed to make a bomb. Szilard realised the fate of Mankind was now in the hands of science. He decided to use the fame and influence of the most eminent scientist of the age to alert the free world to the likelihood of a German weapon of mass destruction. And that was why in July 1939, Leo Szilard called on his old friend.

WILLIAM LANOUETTE: Szilard's mission was to show Einstein that the formula he had thought up in 1905, e=mc², had a new and terrible reality with the element uranium.

RICHARD RHODES: Szilard had always been someone who believed he had the mission of saving the world. And here abruptly through a scientific discovery was a very practical situation where the world might need saving.

EINSTEIN: Szilard.

SZILARD: Herr Professor.

RICHARD RHODES: It's a lot to have in your head as you knock on a door.

NARRATOR: Szilard had come to tell Einstein about his extraordinary work on the chain reaction, and that this breakthrough opened the way to making an atomic bomb.

EINSTEIN: Daran habe ich gar nicht gedacht. I hadn't thought of that.

SZILARD: Sometimes I think I have thought of little else. Certainly not for the past six years.

EINSTEIN: A secondary neutron reaction. Multiple neutrons splitting multiple atoms and continuing. Multiple neutrons splitting, multiple atoms, and continuing. You are sure the chain reaction could be sustained?

SZILARD: That's what Fermi and I have been working on.

EINSTEIN: So, so the release of energy would multiply, the reaction would be enormous, just imagine.

SZILARD: I know. But just imagine, just imagine this. Say if an atomic device was introduced into, say, New York, say such a bomb was taken into New York Harbour in the hold of a ship. And say it was detonated. What would the destruction be? And soon such a bomb could be in the possession of Herr Hitler.

EINSTEIN: What should we say in this letter?

WILLIAM LANOUETTE: Once Einstein heard about this he thought about it and within a few minutes he realised 'yes, this is what e=mc² means'.

RICHARD RHODES: At that point his abstract pacifism, if you will, would have become an intensely practical question, 'What can I personally do to limit somehow the possibility that these men could work on this weapon'.

NARRATOR: The famous pacifist now began to write a letter to the President.

EINSTEIN: In the last four months it has been made probable.

NARRATOR: Calling for the US to build the most powerful weapon ever constructed.

EINSTEIN: To set up a nuclear chain reaction, in an amount of uranium.

SZILARD: Bigger.


SZILARD: Bigger, a... large mass... a large mass of uranium. It is conceivable, so much is certain that an extremely powerful bomb of a new type may thus be constructed.

EINSTEIN: How powerful?

SZILARD: You know how powerful.

EINSTEIN: Would Roosevelt? Should we not make it plain that this will be no ordinary bomb?

SZILARD: Yes, yes we should.

EINSTEIN: It is almost certain that this can be achieved in the future.

SZILARD: Too hazy, 'the future'. We need to say that the Germans can get it at any time.

EINSTEIN: I believe therefore it is my duty to bring to your attention the following facts and recommendations. Yours, very truly, Albert Einstein.

NARRATOR: Several weeks later Albert Einstein's letter was taken to the White House.

WILLIAM LANOUETTE: I think that any letter written by Albert Einstein would get a President's attention. Roosevelt's reaction was, so you're afraid that the Nazis are going to blow us up. Yes. In that case he called in his military aide and he says this demands action.

NARRATOR: It was now question of who would build the atomic bomb first, the Americans or the Nazis. In the wilderness of New Mexico, the US government set up a top-secret project codenamed 'Manhattan'. From Einstein's letter grew the biggest and most remarkable collaboration between science and the military in history.

RICHARD RHODES: The government spent something like 2.2 billion dollars, which translated into modern dollars would be perhaps 40 or 50 billion dollars. As much as it would later cost too send a man to the moon. It was considered absolutely vital to the security of the allied forces.

NARRATOR: The Manhattan project brought together some of the finest minds physics has ever produced. Among them were many European scientists who had fled the Nazis, including Leo Szilard. Einstein himself played no part. The project scientists were driven by one fear that the Nazis might get there first. But in May 1945 before the bomb was complete all the calculations changed. The Nazis were defeated.

TV REPORT: On behalf of the army of the United States I accept your surrender.

NARRATOR: The war in Europe was now over. For many of the Manhattan project scientists, and for Einstein, there was now no justification for the United States to use an atomic bomb against anyone else.

DE GROOT: Most of the scientists were idealists and some of them were very naive idealists. Einstein was probably one of those. He really was thinking in terms of a deterrence, trying to keep Germany from using this bomb.

NARRATOR: Although there was no longer any threat from the Germans, work at Los Alamos continued. In July 1945, two months after the Nazi defeat, the bomb was ready. A bloody war against Japan still raging. And the generals and politicians realised that the atomic bomb had the power to bring about a swift end to the fighting and save thousands of allied lives. Leo Szilard was horrified that the bomb might be dropped without a specific warning first being given. He organised a petition among his colleagues, calling on the President to give this warning. But military necessity prevailed.

DE GROOT: They'd spent lots of money, they had a weapon that could win the war very quickly, and in that sort of situation they were going to use it.

NARRATOR: A target had been selected, the Japanese city of Hiroshima. On a bright morning in 1945, the first atomic bomb was dropped. It fell through the air for 45 seconds. And then a single neutron started Szilard's chain reaction. The energy released as the first atom of Uranium was split was enough to make a grain of sand jump. Then the chain reaction became unstoppable.

DE GROOT: By the final generation of the chain reaction around two million million million million uranium atoms have been fissioned. About .6 grammes of mass have been converted into a massive 12.5 kilotonnes of energy in just six tenths of a microsecond. That's the power of a chain reaction and of e=mc².

NARRATOR: Point six of a gram of uranium converted into energy laid waste the city.

RICHARD RHODES: The Hiroshima bomb which was a small nuclear weapon by modern standards killed about 70 000 people almost immediately. Caused radiation sickness and death by fire to another 70 000 people. It destroyed 80 or 90% of the buildings in the city. It was absolutely devastating, and the world was never the same afterwards.

NARRATOR: Here was proof of the destructive power of e=mc².

NEWS REPORT: It's 9am Eastern War Time, and time for the CBS morning news. The target Hiroshima is roughly the size of Memphis Tennessee or San Antonio Texas. And that one atomic bomb has wiped out four and one tenth square miles of Hiroshima. The Japanese for there part are already telling us that practically every living thing in Hiroshima has been burned to death and the dead are too numerous to be counted.

RICHARD RHODES: Einstein's response to the news of Hiroshima was horror. In a very terrible way his formula had been demonstrated to the world in a sense for the first time.

NARRATOR: Einstein felt a sense of responsibility for the destruction. Because without his letter to President Roosevelt in 1939 there would have been no bomb to drop on Hiroshima in 1945.

WILLIAM LANOUETTE: Einstein's letter was critical because without it America would not have started working on the bomb in time to have a bomb before the end of World War 2.

NARRATOR: In later years Einstein came to deeply regret writing the letter.

EINSTEIN: I made one mistake in my life, when I signed that letter to President Roosevelt advocating that the bomb should be built. But perhaps I can be forgiven for that, because we all felt that there was a high probability that the Germans were working on this problem and they might succeed and use the atomic bomb to become the master race.

NARRATOR: He was horrified when a nuclear arms race took off.

PETER GALLISON: Einstein realised that these nuclear weapons represented a threat to the world as a whole. He once remarked that bullets kill people, nuclear weapons kill cities. And that threat for him loomed more than anything else as a danger for the future of civilisation.

NARRATOR: Einstein now used his fame again, this time to warn the world about this new threat annihilation. He campaigned against the spread and development of nuclear weapons. One of his final acts was to sign a public declaration calling on world leaders to end war: Here then is the problem which we present to you, stark and dreadful and inescapable. Shall we put an end to the human race; or shall mankind renounce war? But there is another side to e=mc² that only became clear after Einstein's death. A side that is altogether more wonderful. Because his equation isn't just the equation of destruction, it's also the ultimate equation of creation.

PETER GALLISON: We know that a small amount of mass can be converted into an enormous amount of energy. But the other side of the equation tells us something else and that is that it's possible for energy to condense back into mass.

NARRATOR: This is the process that occurred at the very dawn of time, starting with the burst of energy known as the Big Bang.

ROBIN MARSHALL: Fifteen thousand million years ago, a singularity of pure energy, created in the Big Bang, evolved and condensed into material and matter over a period of millions of millennia.

NARRATOR: That energy was slowly transformed into the mass that makes up everything in our universe.

PETER GALLISON: You could think of the story of the early universe as one long realisation of e=mc². The universe begins in a ball of energy and slowly turns into mass.

NARRATOR: Everything in our galaxy, and everything on our planet, even human beings, all in a sense exist because of the underlying logic of Einstein's equation.

ROBIN MARSHALL: So everything that has happened and the reason why we are here is underpinned by e=mc².

NARRATOR: Einstein never lived to see that his equation was truly the equation of creation, as well as destruction.

EINSTEIN: Politics is for the moment, while an equation is for eternity.

NARRATOR: A hundred years ago when he derived the equation Einstein had no idea where his formula would lead. His equation would go on to transform science and our understanding of the world. For good. And for ill.

Questions and answers about E=mc² and the atomic bomb.

When did Einstein Publish E=mc²?

Einstein first published the equation E=mc² (energy is equal to mass multiplied by the speed of light squared) in 1905 in the journal Annalen der Physik. He went on to fully generalise the equivalence of mass and energy in 1907.

The paper was received on 27 September 1905 and was a three-page supplement to his first paper on special relativity completed in June of the same year. The paper is titled: "Does the Inertia of a Body Depend on its Energy Content?" In this article the equation appears with different letters used to represent energy, mass and the speed of light

The equation shows that mass and energy are related and that one can be transformed into the other. But because the speed of light is such a huge number, roughly 300,000,000 meters per second, it means that even a small amount of mass can potentially be converted into a huge amount of energy.

Who was Leo Szilard?

Leo Szilard was a Hungarian theoretical physicist, born in Budapest on 11 February 1898. "His deepest ambition," wrote the historian Richard Rhodes "more profound even than his commitment to science, was somehow to save the world."

One of Szilard's sidelines and passions was invention. In 1927, while they were both in Berlin, Szilard and Einstein filed their first of eight joint patents for an electromagnetic pump designed for home refrigerators. The design proved too noisy for domestic use, but would later become the basis of the cooling system used in the 'breeder' nuclear reactors of the 1950s and 1960s.

On 12 September 1933, Szilard was 35 years old, had fled Nazi Germany earlier that year and was living in a London hotel. Crossing Southampton Row while out walking that day, he conceived the idea of a nuclear chain reaction.

Szilard worked on the Manhattan project at the Metallurgical Laboratory or Met Lab at the University of Chicago where he was chief physicist and worked mainly on reactor design. After World War Two, he was an active participant in the Pugwash Conferences on Science and World Affairs which drew their inspiration from the Russell-Einstein Manifesto of 1955, and founded the first political action committee for arms control, the Council for a Livable World.

When, where and how was nuclear fission first discovered?

The fission of uranium was first discovered by an experiment conducted by the nuclear chemists Otto Hahn and Fritz Strassmann, working at the Kaiser Wilhelm Institute in Berlin. Just before Christmas 1938 they bombarded a solution of uranium nitrate with neutrons. Expecting to find new heavier elements they were surprised when their analysis revealed the presence of barium, an element roughly half the mass of uranium.

Conferring with their colleague, the physicist Lise Meitner, they realised that they have in fact split the uranium nucleus into two roughly equal parts. Meitner, an Austrian Jew living in exile in Sweden, and her cousin Otto Frisch were the first to work out what had happened. Meitner used E=mc² to calculate the vast energy released in the reaction which she and her cousin called nuclear fission. Frisch and Meitner published their interpretation of Hahn and Strassmann's experiment in Nature in 1939.

How influential was Einstein's letter to Roosevelt?

Einstein's letter was delivered to the President by Alexander Sachs on 11 October 1939. Following the meeting Dr Lyman Briggs, director of the Bureau of Standards, was ordered to set up a committee to investigate. The first meeting of the Advisory Committee on Uranium was held at the Carleton Hotel, Washington on 21 October. At the meeting, the committee awarded Szilard and Fermi $6,000 to purchase the graphite they needed to continue their work on the chain reaction and the development of the first nuclear reactor.

In 1941 the report of the MAUD committee, the British equivalent of Briggs' committee in the US, reached the President Roosevelt. The report concluded that the "scheme for a uranium bomb is practicable and likely to lead to decisive results in the war". Central to that conclusion was research from early 1940 by Otto Frisch and Rudolf Pieirls that concluded that the critical mass required to achieve a chain reaction was much smaller than had previously been thought.

In November, President Roosevelt authorised a dedicated nuclear programme - which would become known as the Manhattan Project after it was taken over by the army in June of 1942.

While Einstein's letter did not lead directly to the Manhattan project, it did result in funding that allowed scientists to continue research into the chain reaction before the start of the full scale project. Without this head start, the atomic bomb would not have been ready before the end of World War Two.

Further reading:

On the atomic bomb:

"The Making of the Atomic Bomb", Richard Rhodes, Simon and Schuster, ISBN0684813785

"The Bomb; A Life, Gerard DeGroot", Jonathan Cape, ISBN 0224062328

On Einstein:

"Subtle is the Lord, the science and life of Albert Einstein", Abraham Pais, Oxford, ISBN 0192851381

"Einstein on Peace", Otto Nathan Ed

On Leo Szilard:

'"Genius in the Shadows: A Biography of Leo Szilard - The Man Behind the Bomb", William Lanouette, University of Chicago Press, ISBN 0226468887


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