If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare (2102.01522v3)

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.

• The paper proposes a model contrasting "loud" (expansive) and "quiet" (non-expansive) alien civilizations to explain humanity's early emergence and the Fermi Paradox.
• The model uses parameters for civilization appearance and expansion speed, predicting humanity may encounter grabby civilizations within 200 million to 2 billion years.
• The framework implies quiet civilizations are rare and hard to detect, suggesting current expansive civilizations may already control a large portion of the universe.

Overview of "If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare"

This paper explores the paradox of humanity's apparent early emergence in the universe by proposing a model that considers two types of extraterrestrial civilizations: "loud" or "grabby" civilizations, which expand rapidly and make noticeable changes to their environment, and "quiet" civilizations, which are less visible and expansive. The authors delve into an analytical framework to explain these phenomena, suggesting that loud civilizations, if they indeed exist, dominate the universe through expansive growth that leaves little room for other forms of advanced life to develop without being preempted or absorbed.

Core Model and Its Parameters

The model proposed is based on a simple framework governed by three parameters:

1. Volume-based Power Law: This parameter, denoted as $n$, describes the statistical likelihood of advanced civilizations arising as a function of time. The chance of a civilization achieving advanced status increases proportionally to the time raised to the power $n$. This parameter draws from the "hard steps" hypothesis, which posits that life must undergo a sequence of difficult evolutionary challenges to become advanced.
2. Expansion Speed: This describes how fast a loud civilization can expand across the universe. The model suggests that such civilizations expand at a significant fraction of the speed of light, which is inferred from our non-observation of such civilizations in the current observable universe.
3. Appearance Function: A constant that characterizes the frequency and distribution of civilization births over time and space, modulating the other parameters to fit the observed universe.

The framework operates under the assumption that these civilizations strive to maximize their expansion and resource utilization, thereby influencing the appearance and timing of potential civilization births in various cosmic regions.

Empirical Observations and Predictions

The paper interprets current human earliness within the cosmos as being indicative of the influence of grabby civilizations. If such civilizations indeed expand rapidly, they set a temporal "deadline" that forces other civilizations aspiring to reach similar levels of advancement to appear early or risk interacting with or being dominated by these expansive neighbors.

Key predictions and observations include:

• Volume Control: The model estimates that grabby civilizations currently control a large portion of the universe. If civilizations expand competitively and occupy volumes swiftly, they limit the regions available for new civilizations to independently evolve into advanced stages.
• Future Interactions: Humanity, or its descendants, is predicted to encounter such civilizations within a timeline of 200 million to 2 billion years, predicated on their current non-observance and the inferred speed of expansion.
• SETI Implications: Due to the rarity and remote likelihood of encountering quiet civilizations, the model suggests pessimism towards the success of near-term searches for active non-grabby civilizations owing to the implied rarity and transient technological footprints they would leave.

Theoretical and Practical Implications

The results buttress the theoretical foundation for explaining the Fermi Paradox — the apparent contradiction between high probability estimates for extraterrestrial life and the lack of evidence. This paper suggests that the universe might be a competitive arena where quiet civilizations are overshadowed by louder, expansive ones.

Practically, this models the expansion dynamics that future human civilization could potentially adopt, prompting reflections on long-term survival strategies and expansion ethics as technological capabilities evolve.

Speculations and Future Research Directions

The paper invites further investigation into several domain areas:

• Refinement of Power Law Models: Understanding the transitions from simple to complex life forms at both planetary and galactic scales requires more refined models capable of integrating diverse evolutionary pathways and environmental conditions.
• Exoplanetary Observations: Improved observational techniques and larger datasets could help identify signs of large-scale cosmic influences indicative of grabby civilizations, thus tuning the model parameters.
• Alternative Explanations and Integrations: Given the simplistic nature of the model, exploring integrative frameworks that account for interacting or collaborative expansion patterns among civilizations could complement the analysis.

The current research lays foundational insights into how advanced civilizations might balance between visibility and expansion under competitive cosmic dynamics, where early achievers potentially set lasting precedence within habitable zones.