many novels and short stories set in the Known Space series. Niven's stasis fields followed conductive surfaces when established, and the resulting frozen space became a completely invulnerable and perfectly reflective object. They were often used as emergency protective devices. They could also be used to create a weapon called a variable sword, a length of extremely fine wire in a stasis field that makes it able to easily cut through normal matter. For more information, see Slaver stasis field. A more limited form of stasis field is the "bobble", found in Vernor Vinge's Peace Authority setting. A bobble is always perfectly spherical and exists for a fixed period of time that is set when the bobble is first created. The duration of a bobble effect cannot be changed. Bobble generators were initially used as weapons, removing their targets from the field of combat. Another example of a stasis field exists in Joe Haldeman's The Forever War, where stasis field generators are carried by troops to create conditions where melee weapons become the only viable means of combat. Inside the field, no object can travel faster than 16.3 m/s, which includes electrons, photons, and the field itself. Soldiers inside the field must be wearing suits with a special coating, or all electrical activity within their body would stop and the soldiers would die. In the novel, the main character defeats an enemy army, which has besieged a small remaining contingent of human troops on a moon, by arming a nuclear bomb inside the field and then moving the field away from the bomb. Once the bomb is revealed, its electrical activity resumes, and it promptly detonates. That vaporises the surrounding army, and a large chunk of the ground beneath the field. The soldiers emerge some days later to see if their trick worked and find themselves alone at the bottom of a large crater, their enemy destroyed. In Peter F. Hamilton's The Night’s Dawn trilogy (1996-1999), “zero-tau pods” — powered containers inside which time halts — are an important narrative device. In the computer strategy game StarCraft, the Arbiter unit can, through a combination of Protoss technology and the Arbiter's psionic power, create a stasis field that traps all units in the affected area in blue "crystals" of stopped time, taking them out of the fight and rendering them invulnerable for 30 seconds, thus allowing both offensive and defensive applications.