2023-04-23 スイス連邦工科大学ローザンヌ校(EPFL)
最近の統計分析によると、60年間の沈黙の背後には単純で楽観的な説明があり、来る60年間に信号を検出する可能性は低いが、SETIコミュニティは検索を継続するよう促されています。
グリマルディ氏の研究は、地球がただ偶然、地球外生命体が放射する電磁波が存在しない空間の中にいる可能性があることを示唆しています。彼の研究は、過去60年間の観察された沈黙から定量的な結論を導き出しました。彼の発見は、少なくとも1つの電磁信号が常に銀河系に存在し、地球が60年以上にわたって静かな泡沫、あるいは「穴」にあることを前提としています。
＜関連情報＞
- https://actu.epfl.ch/news/silence-reveals-insights-in-search-for-extraterres/
- https://iopscience.iop.org/article/10.3847/1538-3881/acc327
60年にわたる不検出からテクノシグネチャーの発生率を推測する Inferring the Rate of Technosignatures from 60 yr of Nondetection
Claudio Grimaldi
The Astronomical Journal Published 2023 April 13
DOI:10.3847/1538-3881/acc327
Abstract
For about the last 60 yr the search for extraterrestrial intelligence has been monitoring the sky for evidence of remotely detectable technological life beyond Earth, with no positive results to date. While the lack of detection can be attributed to the highly incomplete sampling of the search space, technological emissions may be actually rare enough that we are living in a time when none cross the Earth. Here we explore the latter possibility and derive the likelihood of the Earth not being crossed by signals for at least the last 60 yr to infer upper bounds on their rate of emission. Under the assumption that technological emitters are distributed uniformly in the Milky Way and that they generate technoemissions at a constant rate, we find less than about one to five emissions generated per century with 95% credible level. This implies optimistic waiting times until the next crossing event of no less than 60–1800 yr with a 50% probability. A significant fraction of highly directional signals increases the emission rates’ upper bounds, but without systematically changing the waiting time. Although these probabilistic bounds are derived from a specific model and their validity depends on the model’s assumptions, they are nevertheless quite robust against weak time dependences of the emission rate or nonuniform spatial distributions of the emitters. Our results provide therefore a benchmark for assessing the lack of detection and may serve as a basis to form optimal strategies for the search for extraterrestrial intelligence.
