Balance is essential. It stops us falling over or getting too cross and it stops machines failing catastrophically. There are also very fine balances present, more generally in nature and across the universe. But much of the World is not in exact and perpetual balance - it needs constant fine tuning. To help explore our latest understanding of balance in human beings, machines and music, Bridget Kendall talks to Patricia Kopatchinskaja, the distinguished Moldovan-Austrian violinist, who explores the internal balance need to play world class music; Jade Kindar-Martin, high wire artist and member of the Flying Wallendas who examines the fine tuning of mind and body needed to keep in balance on a high wire; Professor Andrew Heyes, head of Department of Mechanical and Aerospace Engineering at the University of Strathclyde, in Scotland who looks at the very fine balances needed to ensure machines work effectively and safely. (Photo: Acrobats form a human pyramid as they rehearse with Le Grand Cirque at the Sydney Opera House, 2009. Credit: Getty Images)