His Dark Materials

A multiverse of parallel worlds connected by invisible threads of Dust - elementary particles that accumulate around conscious beings and that different cultures variously interpret as sin, dark matter, or the physical substrate of the soul. The universe is most fully realised through the world of Lyra Belacqua, an alternative Earth where the Catholic Church never lost its grip on European civilisation and every human is accompanied by a daemon - an animal-shaped external manifestation of their soul that can speak, feel, and change form until the onset of adulthood fixes its shape permanently. Pullman's universe is distinguished by the seriousness with which it treats its central questions - consciousness, free will, the nature of growing up, and the institutional tendency to confuse authority with truth. Built across six novels spanning several decades of Lyra's life, it is one of the richest and most philosophically engaged secondary world constructions in contemporary fiction.