to decelerate the ship at 0.1g. Although these accelerations are relatively small, over time they result in enormous speeds. To catch the energy, Forward uses a 1,000-km-diameter circular aluminum sail. The sail resembles a flattened disk with a 300-km-diameter removable center portion. When traveling to Rocheworld, the entire sail is used. When the ship needs to decelerate, the smaller sail is separated from the larger outer sail. The large sail is used as a reflecting lens, focusing light onto the smaller sail, slowing the craft. Using the light sail system, the spaceship Prometheus accelerates for 20 years, traveling 2 light years' distance toward Barnard's Star before going into coast mode and traveling an additional 20 years' time at a constant speed of 0.2 c, covering the remaining 4 light years (ca. 23 trillion miles; 38 trillion km). Flouwen Flouwen (the Middle English word for 'flow') are the alien creatures in the book. They are the sole intelligent inhabitants of the planet Eau, which makes up the watery half of Rocheworld. Flouwen are blob-like happy-go-lucky aliens that spend their days surfing waves and working on difficult mathematical problems. Flouwen appear to be giant, colored jellyfish-like entities in the ammonia oceans of Eau. They look like colored blobs of jelly, but they can change their shape at will. They are highly intelligent, sexless, and do not appear to physically age. They are able to communicate and see in the water by means of sonar. A Flouwen named Clear◊White◊Whistle, described as trying to "invent" physics and astronomy, discovers a way to see outside the water by morphing its jelly body into a crude lens. He teaches the method to the others and they use it to methodically track the stars. Flouwen are also capable of morphing themselves into a hard rock-like substance when they feel the need to think about a difficult problem for an extended period. They do this by expelling much of their body water, thereby bringing their silica-gel-based cells closer together, which allows quicker processing of information. Flouwen can grow quite large over time. This excess bulk can be shed during a type of breeding in which large Flouwen gather in a circle and spin off pieces of themselves to create a new Flouwen. Because they are created out of indistinguishable pieces of their parents, they are born fairly intelligent. One of the aliens, Warm@Amber@Resonance, is said to be over