摘要翻译：
如果地球上的生命要达到人类的水平必须完成n个“艰难的步骤”，那么这一事件的机会随着时间的推移上升到n次方。结合这一超宜居恒星形成和行星寿命分布预测，除非n<3和最大行星寿命<50Gyr，否则超过99%的高级生命出现在今天之后。也就是说，我们看起来早了。我们给出了这样的解释：最后期限是由“响亮”的外星人设定的，他们根据硬步骤幂律出生，以共同的速度扩张，改变他们的体积外观，阻止像我们这样的高级生命出现在他们的体积中。相比之下，“安静”的外星人就更难看到了。我们将这个响亮外星人的三参数模型与数据相吻合：1）来自地球历史上看到的艰难步骤的数量的出生能力，2)通过假设响亮外星人出生日期在我们的级别上的通知分布来确定出生常数，3)来自我们在天空中看不到外星人体积的膨胀速度。我们估计，大声外星文明现在控制着宇宙体积的40-50%,以后每一个都控制着~10^5-3×10^7个星系，我们可以在~200myr-2Gyr与它们相遇。如果响亮的外星人产生于安静的外星人，那么我们需要一个低得令人沮丧的转换机会(~10^-4)，来期待甚至另一个安静的外星文明曾经活跃在我们的银河系中。这对SETI来说似乎是个坏消息。但也许外星体积的出现是微妙的，它们的膨胀速度较低，在这种情况下，我们预测在我们的天空中会发现许多长圆弧。
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英文标题：
《If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare》
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作者：
Robin Hanson, Daniel Martin, Calvin McCarter, Jonathan Paulson
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最新提交年份：
2021
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分类信息：

一级分类：Quantitative Biology        数量生物学
二级分类：Other Quantitative Biology        其他定量生物学
分类描述：Work in quantitative biology that does not fit into the other q-bio classifications
不适合其他q-bio分类的定量生物学工作
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一级分类：Physics        物理学
二级分类：Popular Physics        大众物理学
分类描述：Description coming soon
描述即将到来
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英文摘要：
  If life on Earth had to achieve n 'hard steps' to reach humanity's level, then the chance of this event rose as time to the n-th 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 <50Gyr. 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 volumes' 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 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 ~10^5 - 3x10^7 galaxies, and we could meet them in ~200Myr - 2Gyr. 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 bad news for SETI. 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.
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PDF链接：
https://arxiv.org/pdf/2102.01522