Columbia Astronomer Estimates the Odds of Extraterrestrial Life and Intelligence Emerging in Alien Worlds

Life Outside Our Solar System

A new study uses Bayesian statistics to weigh the likelihood of life and intelligence beyond our solar system. Credit: Amanda Carden

New study uses Bayesian statistics to shed light on how extraterrestrial life might evolve beyond our planet.

Humans have been wondering whether we are alone in the universe since antiquity.

We know from the geological record that life started relatively quickly, as soon as our planet’s environment was stable enough to support it. We also know that the first multicellular organism, which eventually produced today’s technological civilization, took far longer to evolve, approximately 4 billion years.

But despite knowing when life first appeared on Earth, scientists still do not understand how life occurred, which has important implications for the likelihood of finding life elsewhere in the universe.

In a new paper published in the Proceeding of the National Academy of Sciences today, David Kipping, an assistant professor in Columbia’s Department of Astronomy, shows how an analysis using a statistical technique called Bayesian inference could shed light on how complex extraterrestrial life might evolve in alien worlds.

“The rapid emergence of life and the late evolution of humanity, in the context of the timeline of evolution, are certainly suggestive,” Kipping said. “But in this study it’s possible to actually quantify what the facts tell us.”

To conduct his analysis, Kipping used the chronology of the earliest evidence for life and the evolution of humanity. He asked how often we would expect life and intelligence to re-emerge if Earth’s history were to repeat, re-running the clock over and over again.

He framed the problem in terms of four possible answers: Life is common and often develops intelligence, life is rare but often develops intelligence, life is common and rarely develops intelligence and, finally, life is rare and rarely develops intelligence.

This method of Bayesian statistical inference–used to update the probability for a hypothesis as evidence or information becomes available–states prior beliefs about the system being modeled, which are then combined with data to cast probabilities of outcomes.

“The technique is akin to betting odds,” Kipping said. “It encourages the repeated testing of new evidence against your position, in essence a positive feedback loop of refining your estimates of the likelihood of an event.”

From these four hypotheses, Kipping used Bayesian mathematical formulas to weigh the models against one another. “In Bayesian inference, prior probability distributions always need to be selected,” Kipping said. “But a key result here is that when one compares the rare-life versus common-life scenarios, the common-life scenario is always at least nine times more likely than the rare one.”

The analysis is based on evidence that life emerged within 300 million years of the formation of the Earth’s oceans as found in carbon-13-depleted zircon deposits, a very fast start in the context of Earth’s lifetime. Kipping emphasizes that the ratio is at least 9:1 or higher, depending on the true value of how often intelligence develops.

Kipping’s conclusion is that if planets with similar conditions and evolutionary timelines to Earth are common, then the analysis suggests that life should have little problem spontaneously emerging on other planets. And what are the odds that these extraterrestrial lives could be complex, differentiated, and intelligent? Here, Kipping’s inquiry is less assured, finding just 3:2 odds in favor of intelligent life.

This result stems from humanity’s relatively late appearance in Earth’s habitable window, suggesting that its development was neither an easy nor ensured process. “If we played Earth’s history again, the emergence of intelligence is actually somewhat unlikely,” he said.

Kipping points out that the odds in the study aren’t overwhelming, being quite close to 50:50, and the findings should be treated as no more than a gentle nudge toward a hypothesis.

“The analysis can’t provide certainties or guarantees, only statistical probabilities based on what happened here on Earth,” Kipping said. “Yet encouragingly, the case for a universe teeming with life emerges as the favored bet. The search for intelligent life in worlds beyond Earth should be by no means discouraged.”

Reference: “An objective Bayesian analysis of life’s early start and our late arrival” by David Kipping, 18 May 2020, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.1921655117

9 Comments on "Columbia Astronomer Estimates the Odds of Extraterrestrial Life and Intelligence Emerging in Alien Worlds"

  1. Dying Conscience | May 19, 2020 at 3:39 pm | Reply

    We will never know the odds of life in the universe until we find life on other planets.
    We can’t imagine how other intelligent beings may look like, nature has favored the development of humans as they are because specific chronological conditions were favored, the odds of that are infinitely small. My guess is that humans could be the only intelligent form of life we will ever find..

  2. We are still trying to understand how the world works and how we can develop space travel. It’s absurd to even believe that we can understand everything in a second. Our evolution has taken a very long time. Now we want to feel we are that smart to guess if there’s life at the other side of the universe. When the universe is infinite.
    We should drink a glass of humility and calm down. If there’s “intelligent” life out there we will eventually find out. We haven’t even decided to accept or deny UFOs’ visits into our planet. We’re just babies who play the smarty pants across the universe.

  3. Scott Larson | May 19, 2020 at 7:03 pm | Reply

    Our perception of reality is severely limited. We think we are fairly intelligent, especially for our (relatively) young age. We can contemplate our own existence, imagine other forms of biological beings, perhaps even purely spiritual or extradimentional intelligence.
    However, considering we live in a very narrow temperature range; in an equally narrow range of the electromagnetic spectrum; amd we inhabit only the thin outer crust of a half-thawed, dirty iceball with a molten iron core, it would be pretty arrogant to believe our narrow band of reality is the only inhabitable zone of the Universe.

    And yet, so far as we can tell, We are the greatest living creatures in the Universe?
    We’re the Life of the party!

  4. Maurice Taylor | May 19, 2020 at 7:44 pm | Reply

    There is only us.

  5. David A Shapero | May 19, 2020 at 8:30 pm | Reply

    I understand the curiosity to explore, to dream, to imagine we are not alone. Amazing tools we have to probe the unknown! Meanwhile, as we return to the Moon and plan a manned Mars landing, please give me a call when we figure out how to travel 15 miles below our own feet.

  6. This assumes only humans are intelligent. Perhaps we’ll find out we don’t know an intelligent Being if we find them. So many intelligent Beings live on our own planet and we’re killing them off one after another.

  7. donald p cunningham | May 19, 2020 at 8:47 pm | Reply

    if other planets are older then we are. Have they been going to other planets to live; They have not gone to mars why in hell would you think they have come to earth.Their is no aliens. Our goal should be to save the human race.Go to mars and beyond.Create a pill that we become genius in a flash.There is no God we have to do it. Our thoughts are so immature about sex,money,in everything .

  8. The statistical odds of life are abundant.With the number of stars, planets,moons,solar systems rotating(which is an important part if the equation),the immense number of galaxies-then I think it’s very common that the elements of the periodic table dispersed everywhere in a 3 dimensional reality make the odds humongous.The major issue is radiation.Life is very fragile to it.Just the infrared heat generated by our star to gently warm the earth 24/7 in rotisserie mode for billions if stable years for all life to develop is a key important factor,as well as a Jupiter protector to gravitationally suck in the bad guys(asteroids,meteors,comets) that extinguish life developing is another lucky required aspect.So yes just the right combination of heat,liquid water, planets size,solar system dynamics,and sprinkling of period table elements all combined yields the main course for dinner- mankind and life on earth.Just remember,it may be a long wait for your table for 2 and dinner to be served,so please compliment your chef and don’t forget to leave a tip for the waiter.

  9. As a scientist with an open mind, anything is possible, but like all speculations, the results depend on the assumptions, which I believe are currently not known with any accuracy. However, I do think that there are intelligent life forms somewhere in the universe and we should continue to explore for them.

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