Deep in a salt mine near Cleveland, Ohio, scientists are keeping an eye on two - and - a - half - million gallons of water in a bid to answer the question: are diamonds forever? They are seeking evidence of the disintegration ofoneofthefundamental constituents of matter - the proton.
John Maddox discusses the cosmic implications of proton decay with Professor Shelley Glas how of Harvard University, and Dr William Crop and Dr Henry Sobell of the University of California.
Producer GEOFF DEEHAN