In Palo Alto in the heart of Silicon Valley, hedge fund manager Joon Yun is doing a back-of-the-envelope calculation. According to US social security data, he says, the probability of a 25-year-old dying before their 26th birthday is 0.1%. If we could keep that risk constant throughout life instead of it rising due to age-related disease, the average person would – statistically speaking – live 1,000 years. Yun finds the prospect tantalising and even believable. Late last year he launched a $1m prize challenging scientists to “hack the code of life” and push human lifespan past its apparent maximum of about 120 years (the longest known/confirmed lifespan was 122 years).