The use of speedsters in fiction requires artistic license due to the laws of physics that would prohibit such abilities. Moving at the speed of sound, for example, would create sonic booms that are usually not heard in such stories and generate substantial heat. An enormous amount of energy would be required to achieve such speeds, and as some speedsters can actually move close to or at the speed of light, this would cause them to gain near-infinite mass, according to the laws of relativity.