All such civilizations are purely hypothetical at this point. However, the Kardashev scale is of use to SETI researchers, science fiction authors, and futurists as a theoretical framework. There is also a hypothetical "type IV", which includes such fictional species such as the time-traveling Time Lords in the television series, "Doctor Who". The exact definition of a type IV species is uncertain, however often said to be species that can utilise all the power available from ten billion galaxies (1046 W). Further numbers in the Kardashev scale could be extrapolated, but there is not much use for it because larger amounts of energy approach the limits for the universe.