Writing from Italy in lockdown, physicist and novelist Paolo Giordano explains how disease spreads in our interconnected world: , , . By expanding his focus to include other forms of contagion - from the environmental crisis to fake news and xenophobia - Giordano shows us not just but also . is a physicist and the author of four bestselling novels. His article 'The Mathematics of Contagion' - published in Italy at the beginning of the Covid-19 emergency - was shared more than 4 million times and helped shift public opinion in the early stages of the epidemic. Translated from the Italian by Alex Valente