The dogged quest for alien life

Many hard-headed scientists have tried in various ways to find extra-terrestrial life. Xenobiologists try to detect microbes on Mars (not found yet), and amino acids, which are building blocks of life on comets (they have been found). Astronomers examine radio signals, hoping to decipher broadcasts from aliens.  

The latest model assessing probability of life existing comes from Columbia University astronomer David Kipping.

Kipping used the statistical tools of Bayesian Inference to see if life should exist on Earth. (He knew the answer but it is a good way to test the model.) Bayesian statistics start with a hypothesis and update the probability for it as new information becomes known. It is being used all over the world right now to predict the pattern of the spread of Covid-19, for instance.

Kipping found the odds were better than 90 per cent. His model tested for a 2x2 matrix. Life is common, or rare. Intelligence often develops, or rarely develops. This gives four possibilities:

• Life is common and often develops intelligence
• Life is rare but often develops intelligence when it appears
• Life is common but rarely develops intelligence
• Life is rare and rarely develops intelligence

He used fossil records and our knowledge of evolution to test for the probability of abiogenesis — life appearing from non-living amino acids. His model asked how often life and intelligence would re-emerge if Earth’s geological and cosmological history were to repeat, again and again. His model suggests life is common (9:1 more likely than not) but rarely develops intelligence. His best guess is a weak inference of 3:2 against intelligence appearing.

This reinforces the argument for aliens and for the Search for Extra-Terrestrial intelligence (SETI). SETI — and its offspring, the SETI Project — started with the Drake Equation, which has been described as the second most famous equation.

In 1961, astrophysicist Frank Drake suggested our galaxy could have many intelligent civilisations. Drake, who will celebrate his 90th birthday on May 28, wanted to provoke a debate. The Drake Equation strings together many probabilities.

There may be a number (N) of civilisations in our galaxy, the Milky Way, using detectable electromagnetic signals the kind used for radio messages, TV programmes and cell phone chatter. These signals propagate out into space. The SETI Project, which Drake conceptualised and which was launched in 1999, used crowd-sourced computer time to study radio signals from space to see if any intelligent broadcasts could be deciphered.

Now, the number of such civilisations depends on the number of stars capable of hosting suitable planets. Only a small percentage of stars are suitable and, in turn, a tiny fraction of suitable planets exists. And on a tiny fraction of these planets, life may appear. A fraction of that life may be intelligent, and may use electromagnetic signals in ways we can recognise.

But although the Drake Equation assumes tiny fractions of tiny fractions as probabilities, it still suggests a huge number of intelligent civilisations exist. The Milky Way contains millions of suitable stars. Even a one in a million chance throws up many possibilities.  

We have detected thousands of exoplanets (planets that orbit around other stars) and quite a few are Earthlike. They are rocky, many have water and acceptable gravity. They are within the habitable “Goldilocks Zone” of their respective stars — “not too hot, not too cold”, like the porridge Goldilocks ate.

Now, electromagnetic waves propagate at the speed of light. The more distant a civilisation, the further back in time it would have had to develop electromagnetic technology for us to detect it. Xenobiologist Carl Sagan’s novel, Contact, is set in 1988. The plot is about contact with an alien civilisation. The aliens relay back the first radio message they picked up from Earth. This is Hitler’s opening speech at the Berlin Olympics in 1936. Astronomers deduce the aliens are 26 light years away to have received and relayed back this signal in 1988.

The counter-argument to the Drake Equation came from the great physicist, Enrico Fermi, who simply asked, “Where are they?” The answer to Fermi’s paradox involves the vast distances of space. We have only had electromagnetic detection for 60-odd years. We can only detect civilisations that developed electromagnetic signal technology within the range of 60 light years. Maybe there isn’t one.

We haven’t found signs of extra-terrestrial life yet, despite UFO videos, Roswell conspiracy theories, the exploration of Mars, Venus, the Moon, asteroids and comets. The SETI Project, sadly, shut down in March. But the search for alien life goes on. Kipping’s new approach may come in useful as we learn more about exoplanets.