A Thousand Paper Cranes. Peace on Earth and in the Heavens.
Inscribed, in the handwriting of Yukawa, on the surface of the bell inside the Children's Peace Monument at Hiroshima, Japan. The crane is a symbol of longevity and happiness in Japan. The monument to mourn all the children whose death was caused by the atomic bomb was inspired by 12-year-old Sadako Sasaki, who believed that if she could fold 1000 paper cranes she would be cured of the leukemia that resulted from her exposure to the radiation of the atomic bomb when two years old. She died before completing them.

As the Director of the Theoretical Division of Los Alamos, I participated at the most senior level in the World War II Manhattan Project that produced the first atomic weapons.
Now, at age 88, I am one of the few remaining such senior persons alive. Looking back at the half century since that time, I feel the most intense relief that these weapons have not been used since World War II, mixed with the horror that tens of thousands of such weapons have been built since that time—one hundred times more than any of us at Los Alamos could ever have imagined.
Today we are rightly in an era of disarmament and dismantlement of nuclear weapons. But in some countries nuclear weapons development still continues. Whether and when the various Nations of the World can agree to stop this is uncertain. But individual scientists can still influence this process by withholding their skills.
Accordingly, I call on all scientists in all countries to cease and desist from work creating, developing, improving and manufacturing further nuclear weapons - and, for that matter, other weapons of potential mass destruction such as chemical and biological weapons.
[On the occasion of the 50th Anniversary of Hiroshima.]

But when you come right down to it, the reason that we did this job is because it was an organic necessity. If you are a scientist you cannot stop such a thing. If you are a scientist you believe that it is good to find out how the world works; that it is good to find out what the realities are; that it is good to turn over to mankind at large the greatest possible power to control the world and to deal with it according to its lights and values.
Regarding the atomic bomb project.

Despite the vision and the far-seeing wisdom of our wartime heads of state, the physicists felt a peculiarly intimate responsibility for suggesting, for supporting, and in the end, in large measure, for achieving the realization of atomic weapons. Nor can we forget that these weapons, as they were in fact used, dramatized so mercilessly the inhumanity and evil of modern war. In some sort of crude sense which no vulgarity, no humor, no overstatement can quite extinguish, the physicists have known sin; and this is a knowledge which they cannot lose.

For they have sown the wind, and they shall reap the whirlwind.

Genetic engineering is to traditional crossbreeding what the nuclear bomb was to the sword.

I am become death, The Shatterer of Worlds.
[Quoting from the 2,000-year-old Bhagavad Gita of India at the instant the first test atomic device exploded.]

I call upon the scientific community in our country, those who gave us nuclear weapons, to turn their great talents now to the cause of mankind and world peace, to give us the means of rendering those nuclear weapons impotent and obsolete.
About his proposed Strategic Defense Initiative, later to be known as 'Star Wars.')

I have always fancied that the end of the world will be when some enormous boiler, heated to three thousand millions of atmospheric pressure, shall explode and blow up the globe. ... They [the Americans] are great boilermakers.

I will have nothing to do with a bomb!
[Response to being invited (1943) to work with Otto Robert Frisch and some British scientists at Los Alamos during the Manhattan Project to create the atomic bomb.]

I'm not saying we wouldn't get our hair mussed, Mr. President, but I do say not more than ten to twenty million dead depending upon the breaks.

If atomic bombs are to be added as new weapons to the arsenals of a warring world, or to the arsenals of nations preparing for war, then the time will come when mankind will curse the names of Los Alamos and Hiroshima. The people must unite, or they will perish.

If Russia is to be a great power, it will be, not because of its nuclear potential, faith in God or the president, or Western investment, but thanks to the labor of the nation, faith in knowledge and science and the maintenance and development of scientific potential and education.

In 1945, therefore, I proved a sentimental fool; and Mr. Truman could safely have classified me among the whimpering idiots he did not wish admitted to the presidential office. For I felt that no man has the right to decree so much suffering, and that science, in providing and sharpening the knife and in upholding the ram, had incurred a guilt of which it will never get rid. It was at that time that the nexus between science and murder became clear to me. For several years after the somber event, between 1947 and 1952, I tried desperately to find a position in what then appeared to me as a bucolic Switzerland,—but I had no success.

In discussing the state of the atmosphere following a nuclear exchange, we point especially to the effects of the many fires that would be ignited by the thousands of nuclear explosions in cities, forests, agricultural fields, and oil and gas fields. As a result of these fires, the loading of the atmosphere with strongly light absorbing particles in the submicron size range (1 micron = 10^-6 m) would increase so much that at noon solar radiation at the ground would be reduced by at least a factor of two and possibly a factor of greater than one hundred.

In this age of space flight, when we use the modern tools of science to advance into new regions of human activity, the Bible ... this grandiose, stirring history of the gradual revelation and unfolding of the moral law ... remains in every way an up-to-date book. Our knowledge and use of the laws of nature that enable us to fly to the Moon also enable us to destroy our home planet with the atom bomb. Science itself does not address the question whether we should use the power at our disposal for good or for evil. The guidelines of what we ought to do are furnished in the moral law of God. It is no longer enough that we pray that God may be with us on our side. We must learn again that we may be on God's side.

It is arguable whether the human race have been gainers by the march of science beyond the steam engine. Electricity opens a field of infinite conveniences to ever greater numbers, but they may well have to pay dearly for them. But anyhow in my thought I stop short of the internal combustion engine which has made the world so much smaller. Still more must we fear the consequences of entrusting a human race so little different from their predecessors of the so-called barbarous ages such awful agencies as the atomic bomb. Give me the horse.

It is hard to think of fissionable materials when fashioned into bombs as being a source of happiness. However this may be, if with such destructive weapons men are to survive, they must grow rapidly in human greatness. A new level of human understanding is needed. The reward for using the atom's power towards man's welfare is great and sure. The punishment for its misuse would seem to be death and the destruction of the civilization that has been growing for a thousand years. These are the alternatives that atomic power, as the steel of Daedalus, presents to mankind. We are forced to grow to greater manhood.

It is only when science asks why, instead of simply describing how, that it becomes more than technology. When it asks why, it discovers Relativity. When it only shows how, it invents the atom bomb, and then puts its hands over its eye and says, 'My God what have I done?

It is probable that all heavy matter possesses—latent and bound up with the structure of the atom—a similar quantity of energy to that possessed by radium. If it could be tapped and controlled, what an agent it would be in shaping the world's destiny! The man who puts his hand on the lever by which a parsimonious nature regulates so jealously the output of this store of energy would possess a weapon by which he could destroy the Earth if he chose.
A prescient remark on atomic energy after the discovery of radioactivity, but decades before the harnessing of nuclear fission in an atomic bomb became a reality.

Knowing he [Bob Serber] was going to the [first atom bomb] test, I asked him how he planned to deal with the danger of rattlesnakes. He said, 'I'll take along a bottle of whiskey.' … I ended by asking, 'What would you do about those possibilities [of what unknown phenomena might cause a nuclear explosion to propagate in the atmosphere]?' Bob replied, 'Take a second bottle of whiskey.'

May there not be methods of using explosive energy incomparably more intense than anything heretofore discovered? Might not a bomb no bigger than an orange be found to possess a secret power to destroy a whole block of buildings—nay, to concentrate the force of a thousand tons of cordite and blast a township at a stroke? Could not explosives even of the existing type be guided automatically in flying machines by wireless or other rays, without a human pilot, in ceaseless procession upon a hostile city, arsenal, camp or dockyard?

Most kids can't understand why a country that makes atomic bombs would ban fireworks.

Now we're all sons-of-bitches.
Remark to Robert Oppenheimer immediately after the first atom bomb test explosion at Alamogordo.

On 17th July there came to us at Potsdam the eagerly-awaited news of the trial of the atomic bomb in the [New] Mexican desert. Success beyond all dreams crowded this sombre, magnificent venture of our American allies. The detailed reports ... could leave no doubt in the minds of the very few who were informed, that we were in the presence of a new factor in human affairs, and possessed of powers which were irresistible.

One might be led to question whether the scientists acted wisely in presenting the statesmen of the world with this appalling problem. Actually there was no choice. Once basic knowledge is acquired, any attempt at preventing its fruition would be as futile as hoping to stop the earth from revolving around the sun.

One must expect a war between U.S.A. and U.S.S.R. which will begin with the total destruction of London. I think the war will last 30 years, and leave a world without civilised people, from which everything will have to build afresh—a process taking (say) 500 years.
Stated just one month after the Hiroshima atomic explosion. Russell became one of the best-known antinuclear activists of his era.

Qualified scientists in Washington believe that the atom-blasting of Japan is the start toward heating plants the size of telephone booths for great factories, and motor-car trips of 1,000 hours on one gram of fuel. One expert estimated that with a few grams of uranium it might be possible to power the Queen Mary from Europe to the U.S. and back again. One of America’s leading scientists, Doctor Vollrath, said that the new discovery brings man’s attempt to reach the moon within bounds of possibility.

REST IN PEACE. THE MISTAKE SHALL NOT BE REPEATED.

Science has nothing to be ashamed of even in the ruins of Nagasaki. The shame is theirs who appeal to other values than the human imaginative values which science has evolved. The shame is ours if we do not make science part of our world...

Science has taught us how to put the atom to work. But to make it work for good instead of for evil lies in the domain dealing with the principles of human duty. We are now facing a problem more of ethics than physics.

Scientists, therefore, are responsible for their research, not only intellectually but also morally. This responsibility has become an important issue in many of today's sciences, but especially so in physics, in which the results of quantum mechanics and relativity theory have opened up two very different paths for physicists to pursue. They may lead us - to put it in extreme terms - to the Buddha or to the Bomb, and it is up to each of us to decide which path to take.

Some recent work by E. Fermi and L. Szilard, which has been communicated to me in manuscript, leads me to expect that the element uranium may be turned into a new and impotnat source of energy in the immediate future. Certain aspects of the situation seem to call for watchfulness and, if necessary, quick action on the part of the Administration. ...
This new phenomenon would also lead to the construction of bombs, and it is conceivable—though much less certain—that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat or exploded in a port, might well destroy the whole port altogether with some of the surrounding territory. However, such bombs might well prove to be too heavy for transportation by air.

That is the biggest fool thing we have ever done. The [atomic] bomb will never go off, and I speak as an expert in explosives.
[A skeptical comment on the U.S. Atomic Bomb Project, to President Harry S. Truman in 1945.]

The Atomic Age began at exactly 5.30 Mountain War Time on the morning of July 15, 1945, on a stretch of semi-desert land about 50 airline miles from Alamogordo, New Mexico. And just at that instance there rose from the bowels of the earth a light not of this world, the light of many suns in one. ... At first it was a giant column that soon took the shape of a supramundane mushroom.
On the first atomic explosion in New Mexico, 16 Jul 1945.

The Atomic Age was born in secrecy, and for two decades after Hiroshima, the high priests of the cult of the atom concealed vital information about the risks to human health posed by radiation. Dr. Alice Stewart, an audacious and insightful medical researcher, was one of the first experts to alert the world to the dangers of low-level radiation.
(Udeall is a former U.S. Secretary of the Interior.)

The conflict that exists today is no more than an old-style struggle for power, once again presented to mankind in semireligious trappings. The difference is that, this time, the development of atomic power has imbued the struggle with a ghostly character; for both parties know and admit that, should the quarrel deteriorate into actual war, mankind is doomed.

The double horror of two Japanese city names [Hiroshima and Nagasaki] grew for me into another kind of double horror; an estranging awareness of what the United States was capable of, the country that five years before had given me its citizenship; a nauseating terror at the direction the natural sciences were going. Never far from an apocalyptic vision of the world, I saw the end of the essence of mankind an end brought nearer, or even made, possible, by the profession to which I belonged. In my view, all natural sciences were as one; and if one science could no longer plead innocence, none could.

The dropping of the Atomic Bomb is a very deep problem... Instead of commemorating Hiroshima we should celebrate... man's triumph over the problem [of transmutation], and not its first misuse by politicians and military authorities.

The future of mankind is going to be decided within the next two generations, and there are two absolute requisites: We must aim at a stable-state society [with limited population growth] and the destruction of nuclear stockpiles. … Otherwise I don't see how we can survive much later than 2050.

The human race may well become extinct before the end of the century. Speaking as a mathematician, I should say the odds are about three to one against survival.

The most striking impression was that of an overwhelming bright light. I had seen under similar conditions the explosion of a large amount—100 tons—of normal explosives in the April test, and I was flabbergasted by the new spectacle. We saw the whole sky flash with unbelievable brightness in spite of the very dark glasses we wore. Our eyes were accommodated to darkness, and thus even if the sudden light had been only normal daylight it would have appeared to us much brighter than usual, but we know from measurements that the flash of the bomb was many times brighter than the sun. In a fraction of a second, at our distance, one received enough light to produce a sunburn. I was near Fermi at the time of the explosion, but I do not remember what we said, if anything. I believe that for a moment I thought the explosion might set fire to the atmosphere and thus finish the earth, even though I knew that this was not possible.

The unleashed power of the atom has changed everything save our modes of thinking and we thus drift toward unparalleled catastrophe.

The world has achieved brilliance without wisdom, power without conscience. Ours is a world of nuclear giants and ethical infants. We know more about war that we know about peace, more about killing that we know about living.

The world is a very different one now. For man holds in his mortal hands the power to abolish all forms of human poverty, and all forms of human life.

This revelation of the secrets of nature, long mercifully withheld from man, should arouse the most solemn reflections in the mind and conscience of every human being capable of comprehension. We must indeed pray that these awful agencies will be made to conduce to peace among the nations, and that instead of wreaking measureless havoc upon the entire globe, may become a perennial fountain of world prosperity.
[Concerning use of the atomic bomb.]

Today when the public thinks of the products of science it is likely to think about environmental problems, an unproductive armament industry, careless or dishonest 'scientific' reports, Livermore cheers for 'nukes forever' and a huge amount of self-serving noise on every subject from global warming to 'the face of God'.

We have grasped the mystery of the atom and rejected the Sermon on the Mount.

What a curious picture it is to find man, homo sapiens, of divine origin, we are told, seriously considering going underground to escape the consequences of his own folly. With a little wisdom and foresight, surely it is not yet necessary to forsake life in the fresh air and in the warmth of sunlight. What a paradox if our own cleverness in science should force us to live underground with the moles.

You can stop splitting the atom; you can stop visiting the moon; you can stop using aerosols; you may even decide not to kill entire populations by the use of a few bombs. But you cannot recall a new form of life.

[Misquotation; not by Einstein.] If only I had known, I should have become a watchmaker. [Apparently remorseful for his role in the development of the atom bomb.]

[The surplus of basic knowledge of the atomic nucleus was] largely used up [during the war with the atomic bomb as the dividend.] We must, without further delay restore this surplus in preparation for the important peacetime job for the nucleus - power production. ... Many of the proposed applications of atomic power - even for interplanetary rockets - seem to be within the realm of possibility provided the economic factor is ruled out completely, and the doubtful physical and chemical factors are weighted heavily on the optimistic side. ... The development of economic atomic power is not a simple extrapolation of knowledge gained during the bomb work. It is a new and difficult project to reach a satisfactory answer. Needless to say, it is vital that the atomic policy legislation now being considered by the congress recognizes the essential nature of this peacetime job, and that it not only permits but encourages the cooperative research-engineering effort of industrial, government and university laboratories for the task. ... We must learn how to generate the still higher energy particles of the cosmic rays - up to 1,000,000,000 volts, for they will unlock new domains in the nucleus.

[W]e have made a thing, a most terrible weapon, that has altered abruptly and profoundly the nature of the world. We have made a thing that, by all standards of the world we grew up in, is an evil thing. And by doing so, by our participation in making it possible to make these things, we have raised again the question of whether science is good for man, of whether it is good to learn about the world, to try to understand it, to try to control it, to help give to the world of men increased insight, increased power. Because we are scientists, we must say an unalterable yes to these questions; it is our faith and our commitment, seldom made explicit, even more seldom challenged, that knowledge is a good in itself, knowledge and such power as must come with it.