Today we're talking about two 20th century titans, the physicists J. Robert Oppenheimer and Albert Einstein. Their scientific achievements changed the world, and yet they were sceptical of one another. In the 1930s, Oppenheimer had described Einstein as 'completely cuckoo' - later in his life, Einstein would say that he admired Oppenheimer as a man, but not as a physicist.

So why did Einstein feel so uneasy about Oppenheimer's discoveries? And who left the most profound legacy? Dan is joined by Cindy Kelly, founder and President of the Atomic Heritage Foundation, to find out.

Produced by James Hickmann and edited by Dougal Patmore.

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