‘Oumuamua as a light sail: Evidence against artificial origin

`Oumuamua, the first detected interstellar visitor to solar system, exhibits non-gravitational acceleration in its trajectory. Ruling out other means of propulsion, such as evaporation material via a cometary tail, it has been argued that radiation pressure is responsible for this acceleration. From this, mass object must be approximately 40 tonnes, and given dimensions, `Oumuamua have thickness ~1 mm if similar rock/iron composition Earth. This raises much publicised possibility artificial origin, sent intentionally across space by an alien civilisation, conclusion, however, relies upon common misapprehension light (solar) sails can accelerate considerable fraction speed light, permitting rapid travel. We show speeds are unattainable conceptual man-made that, based observed parameters, would require half billion years just travel our system from closest likely origin. These cosmological time-scales make very unlikely probe civilisation.