The implication of this was obvious: Nature had shown no ability to produce anything like the size and composition of what our assumptions suggested, so something or someone must have built such a lightsail. ‘Oumuamua must have been designed, built, and launched by an extraterrestrial intelligence. It is an exotic hypothesis, without question. But it is no less exotic than other hypotheses that have been proposed to explain the outlier characteristics of ‘Oumuamua. Nature has shown no propensity to produce pure-hydrogen comets or fluffy clouds of materials that are both more rarefied than air
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