Ian Sample meets the Italian physicist Carlo Rovelli to find out about his cutting-edge research into white holes. A white hole is essentially a time-reversed black hole: a region of spacetime where matter spontaneously appears and explodes outwards. At the moment they are hypothetical objects, so Rovelli explains why he thinks they are worth exploring and reveals how they could explain one of the greatest mysteries of physics. Help support our independent journalism at theguardian.com/sciencepod