Sidereal Messenger: Duo suggests ETs don’t come to Earth due to lack of interest

For decades, humanity has struggled with a paradox: if intelligent extraterrestrial life is common in the Universe, how come we still haven’t come across it? A pair of scientists now make an interesting argument: our Sun and planetary system would simply not be of interest to aliens.

The original formulation of the paradox derives from the great Italian-American physicist Enrico Fermi. In 1950, while talking to colleagues, he suddenly blurted out, “Where is everyone?” It was a reference to a previous conversation the group had had about life beyond Earth, and the reasoning was sharp. Fermi did an account of how long it would take an intelligent civilization capable of interstellar flight to colonize the entire galaxy, occupying all planetary systems. And he found that was a paltry amount of time compared to the age of the Universe, 13.8 billion years.

So, if in the last billions of years some expansionist civilization appeared out there, it would have already colonized all systems – including ours. And yet where is everyone? This is the Fermi paradox.

Jacob Haqq-Misra, from the Blue Marble Institute of Science, and Thomas J. Fauchez, from the American University, both in the USA, suggest, in an article accepted for publication in the Astronomical Journal, that we may not have found them because civilizations prefer to expand into systems around stars smaller than the Sun, red (M-type) or orange (K) dwarfs – because they are longer-lived.

The Solar System is 4.5 billion years old, with a total lifetime of about 10 billion. Long before that Earth will be uninhabitable. If one day we are going to settle in another system, we may opt for stars that live for 100 billion or even 1 trillion years. It would be the best investment, given the great effort of making an interstellar migration.

The research duo calculated how long it would take for a civilization to spread across all the M and K type stars in the galaxy. Being conservative, they estimated that migrations would be promoted with patience, waiting for target stars to approach before a journey to them. In this scheme, it would be possible to occupy all M stars in 2 billion years, traveling only 0.3 light-years on each migration. To occupy all the K together in the same time, it would be necessary to travel 2 light-years.

And if civilization had a wider capacity, say, cross 50 light-years, it could occupy all the M and K stars in a “mere” 2 million years.

Perhaps the fact that the Sun has not been (as far as we know) visited by extraterrestrials implies that they simply consider such stars a bad investment. But, of course, this is just one of the possible answers to the Fermi paradox. The most obvious is that interstellar travelers do not exist. But there are others: perhaps they preserve untouched living systems, such as biological reserves; perhaps they avoid interfering with less advanced civilizations. In the face of the great silence, many explanations are possible.

This column is published on Mondays, in Folha Corrida.

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