The book The Doomsday Machine by Daniel Ellsberg is a gripping and frightening look at how militarists have put the world not far from destruction by creating machinery of nuclear devastation that has often had inadequate safeguards. Chapter 17 deals with how American nuclear scientists gave the go-ahead for testing a nuclear bomb even though they seemed to have thought there was a real possibility that the bomb might destroy all earthly life by setting the entire atmosphere on fire.
The idea may seem absurd today, but that's only because so many nuclear bombs have been tested, without such a thing happening. Let's consider a scientist judging the question in 1943 or 1944. The idea behind a nuclear bomb is to start a chain reaction. The neutrons of one atom are stripped off by the explosion, and these neutrons travel out into space, hitting other atoms, causing those atoms to lose their neutrons. The process continues over and over again. But when would this chain reaction stop? Before the first atomic bomb was exploded, scientists didn't know.
A scientist in 1944 could have been certain that a nuclear bomb exploded in space would have only caused a limited chain reaction, because eventually neutrons traveling out from the explosion would run into the vacuum of space, causing the nuclear chain reaction to stop. But the earth's atmosphere is not a vacuum. It has many atoms of oxygen and nitrogen. So a scientist around 1944 must have been worried about a terrifying possibility: that a nuclear bomb exploded in the atmosphere would cause a chain reaction that would keep spreading throughout the atmosphere, being fueled by the atoms of oxygen and nitrogen in the atmosphere.
One scientist named Hans Bethe thought that such an ignition of the atmosphere was impossible. But we are told on page 276 of Ellsberg's book, “[Enrico] Fermi, in particular, the greatest experimental physicist present, did not agree with Bethe's assurance of impossibility.” On page 279 Ellsberg states, “Nearly every account of the problem of atmospheric ignition describes it, incorrectly, as having been proven to be a non-problem – an impossibility – soon after it first arose in the initial discussion of the theoretical group, or at any rate well before a device was actually detonated.” On page 280 Ellsberg quotes the official historian of the Manhattan Project, David Hawkins:
Prior to the detonations at the Trinity site, Hiroshima, or Nagasaki, Hawkins told me firmly, they never confirmed by theoretical calculations that the chance of atmospheric ignition from any of these was zero. Even if they had, the experimentalists among them would have recognized that the calculations could have been in error or could have failed to take something into account.
The second part of this quote makes a crucial point. Anyone with engineering experience knows that there is usually no way that you can prove on paper that something will happen or will not happen. The only way to have confidence is to actually do a test. An engineer can go over some blueprints of a bridge with the greatest scrutiny, but that does not prove that the bridge will not collapse when heavy trucks roll over it. A computer programmer can subject every line of his source code to great scrutiny, but that does not prove that his program will not crash when users try to use it. The only way to discover whether something bad will happen is by testing. So the idea that the nuclear engineers did some calculations to make them confident that the atmosphere would not explode is erroneous. They could have had no such confidence until a nuclear bomb was actually tested in the atmosphere.
According to one source Ellsberg quotes on page 281, Enrico Fermi (one of the the top physicists working on the atomic bomb) stated the following before the test of the first atomic bomb:
It would be a miracle if the atmosphere were ignited. I reckon the chance of a miracle to be about ten percent.
Apparently the atomic bomb scientists gambled with the destruction of all of humanity. There is no record that the scientists ever informed any US president about the risk of atmospheric ignition. What the scientists should have done is to refuse to do the finalizing work on the atomic bomb on the grounds that they could not rule out the possibility that igniting an atomic bomb would have destroyed the atmosphere. If they had taken such an approach, nuclear weapons might have never been tested. The atomic bomb was never even necessary for the defeat of Japan. By the time it was used, the US had a naval blockade of Japan and relentless bombing of Japan by conventional bombers, with fire bombing raids so severe that more that 50,000 died on a single night, the night of March 10, 1945. Such non-atomic military pressure would have led to a Japanese surrender (particularly if Japan was informed it could keep its emperor, which the US was late in doing).
After the first atomic bomb was tested in 1945, scientists got busy working on a vastly more lethal weapon: the hydrogen bomb. When the first hydrogen bomb was exploded in 1952, with a destructive force a thousand times greater than that of the first atomic bomb, the ignition of the entire atmosphere (or some similar unexpected side-effect) was again a possibility that could not be excluded prior to the test. Even if you ignore the risk of an atmospheric detonation, there was a whole other reason why scientists were gambling with mankind's destruction: the fact that there is always a risk of a nuclear holocaust in a world packed with H-bombs.
Now there may be another way in which scientists are gambling with the world's destruction: the use of genetic engineering. There's some new gadget called CRISPR that allows scientists to modify genes much more easily than before. Scientists are as enthusiastic about this as some kid who just got a bike on Christmas. But there's a gigantic risk: the risk that someone may genetically modify some virus or bacteria to make it into a super-plague that kills millions or billions.
In this scientific paper, a scientist warns, “Given the pace of biotechnology’s progress, the irresistible pressure to continue that progress for universally-desired medical purposes, the dual-use potential of the technology, and its potential worldwide reach, many humans could soon have the capacity to end Earth’s technical civilization.” Some scientists claim the risks of biotechnology are not much to worry about. The facts described in this post should be remembered whenever we might hear someone say, “No need to worry about that, the scientists say it's safe.”