In the summer of 1939 Albert Einstein was on holiday in a small resort town on the tip of Long Island. His peaceful summer, however, was about to be shattered by a visit from an old friend and colleague from his years in Berlin. The visitor was the physicist Leo Szilard. He had come to tell Einstein that he feared the Nazis could soon be in possession of a terrible new weapon and that something had to be done.
Deep underground in a vault beneath Paris lives the most important lump of metal in the world - Le Grand K. Created in the 19th century, it's the world's master kilogramme, the weight on which every other weight is based. But there is a problem with Le Grand K - it is losing weight. Professor Marcus du Sautoy explores the history of this strange object and the astonishing modern day race to replace it.
With exclusive behind-the-scenes access, Horizon follows the highs and lows of an extraordinary story in particle physics. In June 2015, teams at CERN started running the large hadron collider at the highest energy ever. Rumours quickly emerged that they were on the brink of a huge discovery. A mysterious bump in some data suggested a first glimpse of a brand new particle that could change our understanding of how the universe works. A new particle could hint at extra dimensions and help us understand the very beginning of the universe - but first the team has to find it. Horizon follows the scientists as they hunt for the elusive signals that would prove if there is a new particle or if it is just noise from their machine.
At the Palace of Westminster, Helen teams up with scientists from the University of Leicester to carry out state-of-the-art measurements using lasers to reveal how the most famous bell in the world - Big Ben - vibrates to create pressure waves in the air at particular frequencies. This is how Big Ben produces its distinct sound. It's the first time that these laser measurements have been done on Big Ben. At the summit of Stromboli, one of Europe's most active volcanoes, Helen and volcanologist Dr Jeffrey Johnson use a special microphone to record the extraordinary deep tone produced by the volcano as it explodes. Finally, at the University of Cambridge's Institute of Astronomy, Helen meets a scientist who has discovered evidence of sound waves in space, created by a giant black hole. These sounds are one million billion times lower than the limit of human hearing
As the theories on quantum mechanics begin to take shape, the 1927 Solvay Conference becomes a battleground for new scientific ideas. The world’s most brilliant minds, including Einstein and Bohr, try to crack the nature of the subatomic world. Join Brian Greene in exploring this fascinating period.