Brian Greene studies the universe at the largest and smallest scales imaginable. When he was just twelve years old, Brian wandered round Columbia University in New York looking for someone to teach him mathematics, with a letter of recommendation from his school teacher. While his mother wanted him to make money, his father encouraged Brian to pursue his passion, which was trying to understand the nature of the universe. He studied physics at Harvard University and won a Rhodes Scholarship to Oxford University. While at Oxford he learnt about a bold new Theory of Everything which predicts that the universe is made not of particles but rather tiny strings which vibrate in multiple dimensions. Now a Professor at Columbia University, he has worked on string theory ever since. He talks to Jim Al-Khalili about the rise and fall of string and superstring theory and why when he first started to think about what would happen to the universe at the end of time, he experienced a feeling of ‘hollow dread’.