Upper limit on the fraction of alien civilizations that develop communication technology (1908.01335v1)

Abstract: We re-examine the likelihood for alien civilizations to develop communication technology on the basis of the general assumption that life elsewhere could have a non-carbon chemical foundation. We particularized the discussion to a complex silicon-based biochemistry in a nitrogen solvent, and elaborate on the environment in which such a chemistry is feasible, and if so, on what scales. More concretely, we determine the region outside the habitable zone where such organisms can grow and flourish and after that we study how our findings impact the recently derived upper limit on the fraction of living intelligent species that develop communication technology $\langle \xi_{\rm biotec} \rangle$. We also compare this new restriction on $\langle \xi_{\rm biotec} \rangle$ with that resulting from the extension of the habitable zone to accommodate subsurface exolife, originating in planets with subsurface (water) oceans.

• The paper demonstrates that, based on zero detection, the fraction of civilizations developing communication technology is constrained to less than 5×10⁻³ at a 95% confidence level.
• It employs a modified Drake Equation that integrates astrophysical and biotechnological factors, extending to non-carbon-based life forms.
• The study challenges traditional Earth-centric models by suggesting that silicon-based chemistry may require redefined habitable zones and broader astrobiological search strategies.

Overview of "Upper limit on the fraction of alien civilizations that develop communication technology"

This paper, authored by Luis A. Anchordoqui and Susanna M. Weber, addresses the constraints on the emergence and development of communication technology in alien civilizations. The authors posit an expansion beyond the traditional, Earth-centric biochemical paradigm, exploring potential life that may not rely on carbon-based chemistry.

Framework and Assumptions

The authors align their framework with the cosmic modesty conjecture, which invites openness to alternate forms of life. Here, they challenge "carbon chauvinism" by considering non-carbon chemical foundations, particularly a silicon-based biochemistry in a nitrogen solvent. They detail environments conducive to such chemistry, shifting the focus to regions outside the classic habitable zone (HZ) and including subsurface oceans on planets that could harbor life forms distinct from those reliant on surface water.

The traditional Drake Equation is modified to factor in the potential for silicon-based organisms by considering two broad categories: astrophysical factors, which include star formation rates and planetary system formation, and biotechnological factors, which involve the development of complex life and subsequent communicative technology.

Numerical Analysis and Hypotheses

The authors conducted calculations estimating flux, albedo, and temperature for various planets and examined the role of M-dwarfs due to their prevalence and longevity compared to solar-type stars. This analysis is pertinent for probing environments where non-carbon-based life might thrive, shelved from the traditional HZ narrative.

Given that silicon can form complex, stable covalent bonds similar to carbon, they explore this alternative within contexts like liquid nitrogen habitats. By applying models to known configurations, such as those around the ultra-cool dwarf star TRAPPIST-1, they project potential habitability zones for life forms that could develop communication technologies.

Intriguing Results

By leveraging the improbability of signal detection to date (i.e., having observed zero signals from potential extraterrestrial communications), the paper sets a stringent upper bound on the fraction of technologically communicative alien species. Employing statistical models, they propose that the average fraction of communicative civilizations on Earth-like planets is less than $5 \times 10^{-3}$ at a 95% confidence level. This limit grows more stringent should non-carbon life forms be considered.

Implications and Speculations

The profound implication of this work is that the frequency of intelligent civilizations capable of developing technology to communicate across interstellar distances might be substantially lower than previously assumed. This does not only inform search strategies, such as the Breakthrough Listen Initiative but also influences the understanding of life's potential versatility.

Acknowledging that existing detection technology may not be sensitive to silicon-based or otherwise alternative biochemistries, the initiated methodological flexibility could expand the scope of astrobiological searches beyond the anthropocentric model, though it remains uncertain if technological life emerges preferentially in HZs as we know them.

Future Directions

The trajectory drawn by this research opens speculative pathways around several threads:

1. Does silicon-based life require an expansive HZ definition?
2. How might carbon "chauvinism" erroneously skew diversity in potential life forms?
3. Can developing more sensitivity to different chemical matrices alter existential probabilities in the Drake Equation?

While recognizing the contingencies of their model, the paper recommends expanded exploration into different environmental contexts carry potential for crucial insights into life’s potential ubiquity and diversity in the universe.