PhysicsFirst working nuclear clock heralds a new era in timekeeping A clock based on radioactive thorium atoms realises a long-held ambition, demonstrating a technology that could eventually beat the accuracy of today’s best atomic clocks News
SpaceThe hidden pockets of the universe where the future can cause the past Inside some very special black holes, there may be a boundary called a Cauchy horizon. Columnist Leah Crane explores the place beyond which physics breaks and anything is possible Comment