Try using the entire Earth to hunt for a new fundamental force of nature. So say Larry Hunter of Amherst College in Massachusetts, and colleagues. They have created a map of the spins of electrons deep within the Earth's mantle, which could be used to reveal the as-yet-unseen force as well as the strange particles – known as "unparticles" – that might carry it. We currently know of four fundamental forces: gravity, electromagnetism and the strong and weak nuclear forces. The hypothetical fifth force can be thought of as a version of magnetism that does not weaken as quickly with...