# Formulation and Resolutions of the Red Sky Paradox

**Authors:** David Kipping  
**arXiv:** [2106.11207](https://arxiv.org/abs/2106.11207)  
**Date:** 2021-06-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2106.11207v2/

## Key points

- Most stars in the Universe are red dwarfs
- Red dwarfs outnumber stars like our Sun by a factor of 5
- Red dwarfs have a longer lifespan by a factor of 20
- Recent observations have revealed temperate, rocky planets around red dwarfs
- The "Red Sky paradox" questions why we don't see red dwarfs in our sky despite their abundance
- Researchers have formulated a Bayesian probability function to address the paradox
- If intelligent life develops rapidly and universally, the advantage of red dwarfs becomes less significant, softening the paradox but exacerbating the Fermi paradox
- Humanity could be an outlier with only a 1-in-100 chance occurrence (resolution I)
- The study outlines three other resolutions (II-IV) that act as filters to reduce the suitability of red dwarfs for complex life
- Future observations can support or refute these resolutions
- Scarcity of temperate rocky planets around small red dwarfs would support resolution II
- Limited windows for complex life due to stellar evolution on red dwarf worlds would support resolution III
- Solving this paradox provides insights into our existence and guides future experiments in detecting remote life and understanding life's limits in the cosmos

## Summary

Most stars in the Universe are red dwarfs, which outnumber stars like our Sun by a factor of 5 and have a longer lifespan by a factor of 20. Recent observations have also revealed the presence of many temperate, rocky planets around these small stars. However, this poses a paradox - if red dwarfs are so abundant, why don't we see them in our sky? To address this "Red Sky paradox," researchers have formulated a Bayesian probability function to determine the likelihood of finding oneself around a Sun-like star. If the development of intelligent life from prebiotic chemistry is a rapid and universal process, then the advantage of red dwarfs in terms of longevity becomes less significant, softening the Red Sky paradox but exacerbating the classic Fermi paradox (which questions why we haven't detected any signs of extraterrestrial life). On the other hand, if humanity is indeed an outlier with only a 1-in-100 chance occurrence, it could be attributed to random chance (resolution I). The study outlines three other non-mutually exclusive resolutions (II-IV) that act as filters to reduce the suitability of red dwarfs for complex life. These resolutions may be supported or refuted by future observations. For example, if surveys reveal a scarcity of temperate rocky planets around small red dwarfs (the most numerous type), it would support resolution II. Similarly, if future characterization efforts find that red dwarf worlds have limited windows for complex life due to stellar evolution, it would support resolution III. Solving this paradox would not only provide insights into our own existence but also guide future experiments aimed at detecting remote life and understanding the limits of life in the cosmos. The study was conducted by David Kipping and published in PNAS.