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

TL;DR

This paper models the emergence and expansion of loud alien civilizations to explain Earth's early appearance and predicts their current and future cosmic influence, suggesting SETI may be more challenging than expected.

Contribution

It introduces a novel three-parameter model of loud aliens based on hard steps, expansion speed, and birth timing, linking these to observable data and Earth's early development.

Findings

Loud aliens now control 40-50% of universe volume.

They will later dominate 10^5 - 3x10^7 galaxies.

We could encounter them in 200 million to 2 billion years.

Abstract

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.