Mystical experiences and anything to do with spirituality seem to clash with our science-obsessed age. At the HowTheLightGetsIn festival this September, psychologist John Vervaeke, philosopher Sophie-Grace Chappell, and sceptic Michael Shermer debated the role of spiritual experience in our lives, whether it really points to something beyond the everyday material world, or if it's mere hallucination. If we are to be true empiricists, as science demands of us, we need to take mystical experiences seriously, argues Ricky Williamson.