If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare
نویسندگان
چکیده
If life on Earth had to achieve n 'hard steps' reach humanity's level, then the chance of this event rose as time n-th power. Integrating over habitable star formation and planet lifetime distributions predicts >99% advanced appears after today, unless n<3 max duration <50Gyr. That is, we seem early. We offer explanation: a deadline is set by 'loud' aliens who are born according hard steps power law, expand at common rate, change their volumes' appearances, prevent like us from appearing in volumes. 'Quiet' aliens, contrast, much harder see. fit three-parameter model loud data: 1) birth number seen history, 2) constant assuming inform distribution our rank among alien dates, 3) expansion speed not seeing volumes sky. estimate that civilizations now control 40-50% universe volume, each will later ~10^5 - 3x10^7 galaxies, could meet them ~200Myr 2Gyr. arise quiet ones, depressingly low transition (~10^-4) required expect even one other civilization has ever been active galaxy. Which seems bad news for SETI. But perhaps volume appearances subtle, lower, which case predict many long circular arcs find
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ژورنال
عنوان ژورنال: The Astrophysical Journal
سال: 2021
ISSN: ['2041-8213', '2041-8205']
DOI: https://doi.org/10.3847/1538-4357/ac2369