At this point, we’re going to take a small divergence from the traditional Drake Equation before moving forward to calculate the total number of civilizations. Instead of directly incorporating the length of time that civilizations stay communicative (L) into the equation at this step, we’re first going to calculate a raw estimate for the total number of civilizations that ever developed communication abilities.
Why This Divergence?
The reason for this slight adjustment is that we want to separate two important concepts:
- The Total Number of Civilizations That Ever Existed: This gives us a raw number of civilizations in the galaxy that reached the point of developing communication abilities. This estimate doesn’t yet account for the fact that civilizations may rise and fall over time.
- The Overlap of Their Lifespan with Ours: This is where the concept of communicative lifespan comes in. After estimating the raw number of civilizations, we will later adjust that estimate to figure out how many of these civilizations might be active and communicative at the same time as our own.
By taking this detour, we get a clearer picture of the total potential for communicative civilizations and then zoom in on how many might overlap with our present era. This approach allows us to get a comprehensive understanding of the total number of civilizations that ever existed before accounting for the communication lifetimes.
Now, with that explanation in place, let’s move on to the next calculation: multiplying the distributions together to estimate how many civilizations have developed communication abilities across the history of the Milky Way.
Now that we’ve calculated the fraction of intelligent civilizations that develop communication technology, it’s time to multiply all the distributions together. This will give us an estimate for the total number of alien civilizations that ever developed communication technology in the Milky Way.
This step involves multiplying the results from each part of the Drake Equation so far:
- Total number of stars
- Fraction of stars with planets
- Fraction of planets in the habitable zone
- Fraction of planets where life develops
- Fraction of planets where intelligent life emerges
- Fraction of intelligent civilizations that develop communication technology
After running the final calculation, we estimate that there are 96,828 alien civilizations that have developed communication technology throughout the history of the Milky Way.
What Do These Results Mean?
- A Vast Number: The total number of 96,828 civilizations is incredibly large, but it includes all civilizations that have ever existed and developed communication technology. This number covers billions of years of galactic history.
- Galactic Potential: While the sheer size of this number is impressive, the real question is how many of these civilizations are broadcasting signals right now.
We’ve estimated how many civilizations could develop communication abilities, but now we ask: how long do they stay in this phase? Civilizations might rise and fall, and their ability to send detectable signals could be brief. For instance, humanity has only been sending signals into space for about 100 years, and it’s uncertain how long we’ll continue. Natural disasters, resource depletion, or even self-destruction could end any civilization’s communicative phase.
Why We Diverge from the Traditional Drake Equation
In the original Drake Equation, the lifespan of civilizations is calculated early on. However, in our approach, we first calculate the raw estimate of all civilizations that have developed communication abilities. Then, we bring in the concept of their lifespan to see how many might overlap with our own civilization. This helps us focus on the civilizations that are still active right now.
Galactic Communication Lifespan
The length of time a civilization remains communicative depends on several factors:
- Surviving extinction-level events: Natural or self-induced disasters like asteroid impacts or nuclear wars can easily cut short a civilization’s ability to communicate.
- Technological development: A civilization must develop the means to transmit signals across space, which could take thousands of years.
- Maintaining communication: Even if they develop communication technologies, civilizations might abandon them or switch to undetectable methods as they evolve.
Humanity’s Communicative Age: A Tiny Window
For perspective, while Homo sapiens have existed for 200,000 years, we’ve only been capable of sending signals for just over 100 years. That’s a minuscule fraction of our existence. More intentional attempts to communicate, like the Arecibo message in 1974, only began 50 years ago. This suggests the communicative phase for any civilization could be very short.
Modeling Civilization Lifespan
In our analysis, the L factor represents the length of time a civilization remains communicative, sending out signals that could be detected by others. We modeled this with a distribution designed to ramp up quickly from short-lived civilizations (e.g., a few hundred or thousand years) to longer-lasting ones.
Why We Chose This Range
We intentionally set L to start low — around 100 years — but ramp up after that. The reasoning is simple: if a civilization can survive the first 100 to 500 years of its technological development, it’s more likely to last much longer, potentially even thousands of years.
Running the Simulation
With these assumptions, we run the simulation to estimate how long civilizations remain communicative, accounting for both short-lived and long-lasting civilizations.
/*Years of Communicative Abilities*/data lifetime_comm_civ(keep=lifetime_comm_civ);
skewness = -6; /* Control the left skewness */
sigma = (log((1 + (skewness ** 2)) ** 0.5)) / skewness; /* Calculate sigma for Lognormal distribution */
/* Generate random values from a left-skewed Lognormal distribution */
do i = 1 to 100000;
u = rand("uniform"); /* Uniform random variable */
lifetime_comm_civ = 100 + (1000000 - 100) * exp(sigma * rand("lognormal", 0, 1));
output;
end;
run;
After running our simulation for the L factor (the length of time civilizations remain communicative), the results show a diverse range of lifespans. Let’s break down the key points:
Key Statistics
- Mean lifespan: 680,330 years.
- Median lifespan: 739,262 years.
- Range: From a minimum of 100 years to a maximum of 996,193 years.
Distribution Insights
- Average and Median: The average lifespan of a communicative civilization is 680,330 years, but notice that the median is a bit higher, at 739,262 years. This indicates that while some civilizations do last shorter periods, the distribution tends to favor civilizations that last quite long — hundreds of thousands of years.
- Min and Max: The minimum lifespan, at 100 years, represents civilizations that quickly exit the communicative phase. The 1% quantile (46,758 years) shows that even the civilizations in the bottom tier last a significant amount of time on cosmic scales. At the upper end, a small number of civilizations could persist for almost 1 million years.
- Skewness and Ramp Up: As intended, the distribution is left-skewed, meaning most civilizations reach the 10,000-year mark quickly and then extend much further into long timeframes. This is particularly evident in the sharp increase between the 1% quantile (46,758 years) and the median (739,262 years).
What Does This Mean?
The distribution suggests that, once civilizations make it past early hurdles (e.g., 10,000–50,000 years), many of them survive for extended periods, increasing the likelihood of sustained communication. The fact that the average civilization could last over 600,000 years is good news for our search — if civilizations manage to survive past their infancy, there’s a strong chance they will remain communicative for a substantial amount of time, making it more likely that their signals overlap with our own civilization’s brief window of communication.