# One glance at the uncertainties alters the narrative significantly.

Is there intelligent life beyond our Solar System in the Milky Way? If it exists, how many alien civilizations might be present, and how far is the nearest? This question has puzzled humanity for ages, prompting us to ponder one of our most profound existential queries: “Are we alone in the universe?”

While our comprehension of stars, planets, and the cosmos has advanced significantly, we still lack definitive evidence of extraterrestrial life, especially intelligent species. Recently, a study suggested that there could be 36 alien civilizations in the Milky Way, treating this figure as a conservative estimate.

This assertion is far from accurate. Here’s a breakdown of the scientific reasoning involved.

For over fifty years, scientists have sought to transform the philosophical inquiry of extraterrestrial life into an empirical investigation. Although we can directly search for life, the lack of positive results makes indirect approaches more fruitful.

This was the essence of the original Drake equation, which aimed to quantify the number of potential alien civilizations in our galaxy. By understanding the frequency of Sun-like stars and Earth-sized planets at suitable distances for life, we can generate informed estimates about conditions favorable for life akin to early Earth.

Recent advancements in astronomy, especially in exoplanet research, have illuminated how frequently Earth-like conditions might develop. With approximately 200-400 billion stars in the Milky Way, around:

• 20% are Sun-like (F, G, or K-class stars),
• about 25% of those host Earth-sized planets (75% to 150% of Earth's radius) orbiting within a year,
• and nearly all these planets are formed with the essential ingredients for life.

Even considering that many of these worlds might be unsuitable for life, billions of planets with Earth-like characteristics currently exist in our galaxy.

However, when delving into advanced questions about alien life, our understanding falters.

We cannot ascertain how often life arises on Earth-sized planets in Earth-like orbits around Sun-like stars.

We do not know how frequently, once life emerges, it sustains itself for billions of years through an unbroken lineage.

We cannot determine the probability of simple life evolving into complex, multicellular organisms, which first appeared during Earth's early Cambrian period.

And we remain uncertain about the likelihood of intelligent, technologically advanced species developing on such planets.

Ultimately, all we can conclude is that life on Earth progressed in its unique way, leaving much to speculation regarding other worlds.

It's somewhat ironic that a few weeks ago, a responsible study highlighted what we can infer about life in the universe based on Earth's history. By examining early Earth conditions and their frequency in the cosmos, we can use statistical inference to understand likely outcomes if we could rewind time to a young Earth.

That study concluded that while life likely arises frequently in the universe, intelligent life is probably rare. The confidence levels of these findings aren't particularly high, but they reflect our best understanding, given our limited sample size—Earth alone.

So why is there now a scientific paper claiming that 36 alien civilizations exist in the Milky Way?

The estimate relies on a questionable assumption: that if an Earth-sized planet orbits a Sun-like star at an appropriate distance, there’s a high likelihood of producing a technologically advanced civilization after about 5 billion years. The authors, Tom Westby and Christopher Conselice, state:

> "[W]e make a key assumption: since the time required for the development of communicative intelligent civilization on our own planet is of order 5 Gyr, then we propose that life will have a reasonable probability of forming on another planet such as the Earth in the habitable zone of a suitable star within our Galaxy in a similar amount of time."

Is this assumption scientifically sound? Absolutely not. Previous studies indicate that intelligent life is likely rare; rewinding Earth's clock to about 4.5 billion years ago suggests that a technologically advanced civilization is improbable. They also extend these findings to all long-lived stars, including M-class red dwarfs, which further complicates the analysis.

Given these points, how did Westby and Conselice arrive at the conclusion of 36 intelligent alien civilizations in the Milky Way?

They not only assumed a “reasonable probability” that intelligent life would emerge after about 5 billion years on an Earth-like planet, but they also introduced another assumption—the Astrobiological Copernican Strong Condition—stating that intelligent life must form between 4.5 billion and 5.5 billion years after an Earth-like planet forms around a Sun-like star.

They further assume that such a civilization should exist for 100 years in its communicative phase (the duration of Earth’s radio communications), before conducting their statistical analysis. Consequently, based on these assumptions, they conclude that there should be 36 alien civilizations in our galaxy, with some degree of uncertainty.

What is that uncertainty, you may ask?

At 1-sigma confidence (indicating a 68% probability), the estimate ranges from 4 to 211 alien civilizations currently existing. While 36 civilizations is the most likely number, the uncertainties are so vast that the actual number could be zero (with about a ~15% probability) or more than ~200 (with around a ~20% probability) or anything in between.

The meaninglessness of these figures becomes evident when they relax the "strong condition" and apply what they term the Astrobiological Copernican Weak Condition: an initially Earth-like planet will develop intelligent life that survives in a technologically advanced/communicative phase for approximately 100 years, but only after 5 billion years or more.

Under those assumptions, they calculate that 928 civilizations exist right now, with a 68% confidence interval ranging from 110 to 2908 civilizations.

The uncertainty in this case is so extensive that it does not rule out “0” as a plausible option. Even if their (arguably flawed) assumptions about intelligent life were accurate, the uncertainties are too significant to draw reliable conclusions about the presence of alien civilizations in the Milky Way.

If we could definitively ascertain the number of alien civilizations in our galaxy, it would represent a groundbreaking advancement in our scientific knowledge. However, the quest for intelligent extraterrestrial life has often been marred by conclusions drawn from dubious assumptions, and these latest claims are just another instance of that sort of wishful thinking.

If we are to make assumptions about the likelihood of life emerging on planets with similarities to a young Earth, we can derive insights about the chances of intelligent life across the galaxy. The catch is that our conclusions are only as robust as our assumptions, which we have no solid reason to believe are accurate. While there might be 36 alien civilizations in the Milky Way, science still has a considerable journey ahead before anyone—including the authors of the paper—can confidently assert that claim.

Starts With A Bang is now featured on Forbes and republished on Medium with a 7-day delay. Ethan has authored two books, Beyond The Galaxy and Treknology: The Science of Star Trek from Tricorders to Warp Drive.