One of the incentives for some readers of science fiction is the opportunity to imagine a universe of alien civilizations – conceive in their mind’s eye many intelligent beings with completely different body forms, cultures, worlds, inventions and maybe even compatible food and drink sensations. It is the impetus for my series of self-published novels and short stories set in the Stellar Flash universe, my Alien Characters mini book series for children, and the Alien Dimensions anthology series, especially the Alien First Contact focused issue #25. (All available online from Amazon)
However, I always felt I was struggling to get a message out there, perhaps like many Alien First Contact writers before me. Yes, it’s never been just the art. We science fiction writers have always been wanting to imbue humanity with a cosmic awareness so that when Alien First Contact does eventually happen, everyone will be ready. Alien First Contact stories are not for the converted. They are purposive, agenda-setting, social engineering constructs, intent on catching the attention of people who never look up at the stars and wonder. But, following this trajectory in my science fiction writing over the past twenty years has worn me down a little. I mean, where are the aliens? Why haven’t we been contacted yet? Scientists say its just around the corner. When? I’m sure I’ve gone around millions of corners already.
This is also one of the incentives for me to research vintage science fiction. I am curious about what kind of First Contact stories were printed in early 20th century newspapers. The best one I’ve found so far is The World’s Last Wonder (1901). Check out an audio version of the story via my Vintage SciFi Podcast. I’ve actually found a few First Contact stories (see previous posts), but I was hoping for so much more. Sadly, it looks like newspapers, Australian newspapers at least, didn’t want to print those kinds of stories too often.
Taking a break from my research recently, and to recover from my disappointment, I stumbled upon this recent science article: A reassessment of the “hard-steps” model for the evolution of intelligent life
How fantastic! I uploaded it to ChatGPT and asked: Based on the research in this pdf, and the potentialities of trillions of planets in our Milky Way galaxy, how many intelligent races could be in the Milky Way galaxy right now? 300 million?
Here’s ChatGPT’s reply:
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The paper by Mills et al. (2025) reassesses the “hard-steps” model of human evolution, which traditionally argues that the emergence of intelligent life is extremely rare due to a series of highly improbable evolutionary steps. However, this study challenges that assumption, proposing instead that environmental constraints and evolutionary processes may have played a greater role in determining when and how intelligence emerges, rather than intrinsic improbability.
Estimating the Number of Intelligent Civilizations in the Milky Way
Your question—whether there could be 300 million intelligent civilizations in the Milky Way—depends on how we interpret the assumptions in the paper, along with our understanding of exoplanet statistics and evolutionary probability.
1. Total Number of Planets in the Milky Way
- The Milky Way contains about 100–400 billion stars.
- Recent exoplanet discoveries suggest that most stars have planets, meaning there could be trillions of planets.
- Of those, an estimated 300 million to 6 billion may reside in the “habitable zone” where conditions could support liquid water.
2. Challenges to the Hard-Steps Model
- The traditional view (Carter’s model) suggests intelligence is extremely rare because of evolutionary “hard steps.”
- Mills et al. argue that these steps may not be inherently improbable but instead shaped by environmental conditions.
- If intelligence is not rare but instead develops whenever conditions allow, then many more civilizations could exist.
3. Implications for Intelligent Life in the Milky Way
- If intelligence is more common than Carter’s model suggests, then the estimated 0.01–0.1% of habitable planets developing intelligence could be too conservative.
- If even 1% of habitable planets develop intelligence, this could result in 3 to 60 million civilizations in our galaxy.
- More optimistic scenarios (where intelligence arises on 10% of habitable planets) could indeed approach 300 million civilizations.
Conclusion
The research in this paper weakens the argument that intelligent life is exceedingly rare, meaning the possibility of 300 million intelligent civilizations cannot be dismissed outright. However, actual numbers depend on additional factors such as:
- How long intelligent civilizations survive (a short lifespan reduces the number of coexisting civilizations).
- Whether most intelligent species evolve technological capabilities detectable by SETI.
- The impact of environmental and planetary conditions on sustaining life.
Thus, while 300 million civilizations is at the high end of estimates, it’s not entirely implausible if intelligence is more common than previously assumed.
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How awesome is that! Considering the age of the universe, and the fact that there are estimated to be over 2 trillion galaxies, this suggests at least 600,000,000,000,000,000,000 (600 quintillion) intelligent civilisations in the universe. Alien First Contact must really be just around the corner, though how many light years wide that corner is, is up for conjecture.
Still, I’ll keep researching and writing about fictional aliens to help spread the word until the real ones turn up. (I have my fingers crossed for early or just before 2027!)
