What was Albert Einstein's involvement in the creation of the atomic bomb?

C is the speed of light. If you square that – multiply it by itself – you end up with an astronomically vast, incomprehensible number. If you then multiply how much an object weighs – its mass – by this huge number, then you get an idea of the amount of energy that's potentially locked away in the object.

In this sense, Einstein is the one who got everybody thinking about the invisible energy locked away inside the atom.

In terms of the development of the weapon itself, Einstein was persuaded by a group of Hungarian refugee physicists who had moved to America. They were all manoeuvred out of Nazi Germany by a very bizarre movement called the German Physics Movement, which was set up in the 1920s by a couple of disaffected Nobel Prize winners. They were quite bright people, but they were twisted in their interpretation of what physics and science was all about. They decided that anything to do with 'abstract mathematical Jewish physics' this is a quote had to be got rid of. Einstein was one of the more conspicuous scientists to go.

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Less conspicuous characters include many of the those who ended up at the Manhattan Project in Los Alamos, New Mexico. Einstein was persuaded by this group to write a supposedly pivotal letter to President Franklin Roosevelt – which he did in August 1939. oops! see ealier email about how this might be covered up. Sorry! Rather than simply putting the letter in the post or delivering it themselves, it was decided that the letter would be given to a personal friend of the President to deliver by hand. Unfortunately, the aide they chose was an economist ­– Alexander Sachs ­– who was completely ignorant about nuclear physics. The letter was very plainly written, and Roosevelt was no dummy – he would have understood exactly what Einstein, one of the world's greatest thinkers, was talking about. But Sachs decided he'd rewrite the whole thing and then deliver it to Roosevelt as a monologue. It took him weeks to do this, so it wasn't until early October – many weeks after the letter was written – that Sachs finally got to see Roosevelt.

He delivered his monologue badly. It was the evening – and Roosevelt was tired. He nodded off, and they had to finish off over breakfast the next morning. During the night. Sachs was really taking this very seriously; he wandered around his hotel room and he wandered out into the hotel garden to meditate. He sought divine inspiration on what he should say. And the next morning he trotted out an anecdote about how Napoleon had doomed himself to defeat by sending away an American who had invented a steam-powered boat, and that this had then set Napoleon up for defeat by the British Navy.

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At this point, Roosevelt said: “Oh, do you mean that the Nazis are going to blow us up with their bomb?” Sachs replied saying, “Yes, Mr President, that's exactly it.”

Roosevelt agreed to take action – but this action was the foundation of this hopelessly dysfunctional Uranium Advisory Committee that took them absolutely nowhere.

So Einstein played a pivotal role in getting the atomic bomb progressing in the USA. He was invited to various meetings of the uranium committee, but he never went to any of them. I think the reason for that is revealed after the war, when he said that one of the greatest regrets of his life was having suggested that the USA should make an atomic weapon. He, like many others in the story, had a great difficulty living with that on his conscience.

Gareth Williams is a Emeritus Professor of Medicine at the University of Bristol and author of an upcoming book about 'Tube Alloys', a top secret British atomic bomb project during the Second World War