Nearly a year ago, MMN offered a series of stories on the many aspects of the intensifying search for extraterrestrial life. An earlier series examined the many hypotheses as to why we don’t see ET.

On the one hand, we haven’t found clear evidence, just possibilities. On the other hand, the universe is vast, largely unexplored — and fine-tuned for life. As a result, how we rate our chances of success will likely be governed by prior beliefs. Data from the space telescopes about an increasing number of exoplanets enables more accurate science. Notably, NASA, sensing that the research landscape has changed, has developed a scale for assessing evidence-based claims about ET life. Let’s hope it also means more focused philosophy.

Last week at the Washington Post, Joel Achenbach provided a reasonably good summary of how many seekers, especially the iconic Search for Extraterrestrial Intelligence (SETI), approach the topic: “Big Numbers and the Copernican principle”

The Big Numbers argument notes that our galaxy, the Milky Way, has something like 400 billion stars, and it’s just one of untold billions of galaxies in a universe that might be infinite. Moreover, in the past 30 years, astronomers have discovered that planets of all shapes and sizes are common in the universe…

The Copernican principle is inspired by 16th-century astronomer Copernicus, whose revolutionary model of the solar system put the sun and not Earth at the center. The principle suggests that, in the same way that Earth is not in a privileged place in the universe, humanity should not presume itself special, or unique. The universe is not about us, and what happened on this planet over the past 4 billion years could happen elsewhere.

Joel Achenbach, “What we actually know about aliens, according to science,” Washington Post, 25 November 2023

The philosophical position outlined is incoherent. First, how will we assess the raw probability of being alone when we have no other universe to compare with ours?

Achenbach goes on to subtly ridicule the Rare Earth Principle (REP) which correctly emphasizes the many ways that Earth is unusually well-suited for life. Many dislike REP because it provides good reasons to believe that complex life is not common in the universe.

But, as a matter of fact, based on what we know, it is the Copernican Principle that is nonsense. Earth is special in many ways, and so are humans. However, “special” does not mean the same thing as unique. The fine-tuning of Earth and our universe for life — a “Goldilocks Principle,” if you like — increases the likelihood of some life, though not a lot, elsewhere. We might have better luck if we reject the smart-ass Copernican Principle in favor of clearer thinking and sounder assumptions.

Realistic expectations and challenging questions…

At Universe Today, Matt Williams reminds us to be realistic in our expectations, given how far away other planets are. He quotes UCA Santa Cruz astronomy prof Piero Madau, who estimates that there could be 11,000 exoplanets roughly like Earth that orbit their stars within habitable (Goldilocks) zones — within 100 parsecs (326 light-years). Even light would take that long to reach them, never mind spacecraft.

“So, if microbial life arose as soon as it did on Earth in more than 1% of TTPs (and that is a big if), then one expects the closest, life-harboring Earth-like planet to be less than 20 pc away [65 light-years],” he said. “This may be cause for some cautious optimism in the search for habitability markers and biosignatures by the next generation of large ground-based facilities and instrumentation. Needless to say, biosignatures are going to be extremely challenging to detect. And it is also possible that life may be so rare that there are no biosignatures within a kpc or more for us to detect.”

Matt Williams, “If Earth is Average, We Should Find Extraterrestrial Life Within 60 Light-Years,” Universe Today, September 28, 2023

TTPs are “temperate terrestrial planets.”

At LiveScience, Charles Q. Choi raises the question, could ET life have arisen from other elements? Some researchers studied that and found that some rare elements are capable of life-like (autocatalytic) reactions:

Most of the 270 cycles did not employ organic compounds. Some centered around elements that are absent or exceedingly rare in life on Earth, such as mercury, or the radioactive metal thorium. A number of cycles likely only happen under extremely high or low temperatures or pressures.

The researchers even discovered four autocatalytic cycles involving noble gases, which only rarely if ever chemically react with other elements.

Charles Q. Choi, “Alien life may evolve from radically different elements than human life did,” LiveScience, September 28, 2023 The paper is open access.

It’s a long shot but intriguing to think about. Meanwhile, a big philosophical question looms: What is life? Dartmouth College theoretical physicist Marcelo Gleiser poses that question at Big Think:

We can say, quite generally, that life is matter with intentionality. And that is what’s so hard for science to pin down. How do you include intentionality into a science designed to describe matter as the result of cause-and-effect relations between inanimate bits of stuff? …

Though we recognize these differences, the puzzle of how life emerges from nonlife remains as mysterious as ever. How does an agglomeration of inanimate matter, beyond an unknown level of biochemical complexity, become a living creature?

Marcelo Gleiser, “What is life? This basic question defies science,” Big Think, September 27, 2023

Well, if it was that random, maybe life did happen only once. But, as intelligent creatures with intentionality, we are certain to keep trying to find out.