If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare

Hanson, Robin; Martin, Daniel; McCarter, Calvin; Paulson, Jonathan

Abstract

If life on Earth had to achieve n “hard steps“ to reach humanityʼs level, then the chance of this event rose as time to the nth power. Integrating this over habitable star formation and planet lifetime distributions predicts >99% of advanced life appears after today, unless n < 3 and max planet duration <50 Gyr. That is, we seem early. We offer this explanation: a deadline is set by loud aliens who are born according to a hard steps power law, expand at a common rate, change their volume appearances, and prevent advanced life like us from appearing in their volumes. Quiet aliens, in contrast, are much harder to see. We fit this three-parameter model of loud aliens to data: (1) birth power from the number of hard steps seen in Earth’s history, (2) birth constant by assuming a inform distribution over our rank among loud alien birth dates, and (3) expansion speed from our not seeing alien volumes in our sky. We estimate that loud alien civilizations now control 40%–50% of universe volume, each will later control ∼ 105 –3 × 107 galaxies, and we could meet them in ∼200 Myr–2 Gyr. If loud aliens arise from quiet ones, a depressingly low transition chance (<∼10−4 ) is required to expect that even one other quiet alien civilization has ever been active in our galaxy. Which seems to be bad news for the Search for Extraterrestrial Intelligence. But perhaps alien volume appearances are subtle, and their expansion speed lower, in which case we predict many long circular arcs to find in our sky.

Citation

Hanson, R., Martin, D., McCarter, C., & Paulson, J. (2021). If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare. Astrophysical Journal, 922(2), Article 182. https://doi.org/10.3847/1538-4357/ac2369

• Journal Article Type: Article
• Acceptance Date: Aug 31, 2021
• Online Publication Date: Nov 30, 2021
• Publication Date: Dec 1, 2021
• Deposit Date: Jan 18, 2022
• Publicly Available Date: Jan 18, 2022
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 922
• Issue: 2
• Article Number: 182
• DOI: https://doi.org/10.3847/1538-4357/ac2369
• Public URL: https://durham-repository.worktribe.com/output/1217039