Today, the 6th of August, marks 60 years since the first combat use of an atomic bomb over Hiroshima. 3 days later, on the 9th, another nuclear weapon was dropped on Nagasaki (little known fact: the original target was the city of Kokura, but it was covered with clouds, preventing from the aircraft from aiming the bomb. So the bomber proceeded to Nagasaki instead). These strikes precipitated the Japanese surrender less than a week later.

As a physicist, I regard the beginning of the nuclear age as a loss of innocence for physics... the entire Manhattan project which created the atom bomb involved countless physicists, many of them already well-established (like Fermi, Oppenheimer, Bethe etc) and others who would eventually go on to become Nobel-prize winners in their respective fields, like Feynmann and Segre. So in a sense, my intellectual predecessors were responsible for opening this Pandora's box, and I am personally fascinated by the history of this effort, which had its beginnings with the discovery of radioactivity in the late 19th century, at the end of the steam age.

It was also this moment when physicists went from being detached boffins to becoming a strategic resource...the nation with the most physicists would hold the key to power (this is of course not as simplistic, but certainly it must have seemed so in the immediate aftermath of Hiroshima and Nagasaki. Billions of dollars were poured into physics research, a lot of it directly into nuclear weapons development, but much of it had very tenuous links, like particle physics and space research. For scientists in the US and Soviet Union, making vague, indirect links to weapons programmes used to be a useful way to get research funding (a project with the word 'nuclear' or 'atomic' in it doesn't necessarily have much to do with nuclear weapons or energy at all).

I have been to Hiroshima some years back, and it was quite a harrowing experience; the Peace Park is such a serene and beautiful place, until you realise that before the bombing it was a densely populated slum. I dearly wish Nagasaki is the last time anyone ever uses the bomb, but... I think the decision to drop the bombs was the right thing to do.

Japan was being blockaded by mid-1945, most of its navy on the bottom and its army beaten back from across the Pacific, but there was still an absolute refusal to surrender unconditionally (the military elite were only hoping for a conditional 'surrender' which would mean, among other things, that no occupation troops were to touch mainland Japan and most of the existing power structures would remain intact).

It was intended that in the event of an Allied invasion of mainland Japan, every man, woman and child would fight to the death. This was no idle threat: in the battle of Iwo Jima, the Japanese residents (including elderly and children) there had flung themselves off a cliff rather than be captured by American troops. So if the invasion had occured, in addition to massive combat casualties on both the Allied and Japanese sides, huge numbers of Japanese civillians were likely to have perished as well. A million Japanese combat troops were still stationed in China/Manchuria, and they would have provided a huge fight for the Allies, as well as continuing the brutal oppression of the occupied Chinese.

So, I believe that in the cold arithmetic of war, the use of atomic weapons was a tragic, but necessary decision.