The universe is full of stars. All those stars, of course, have planets. These planets are surely livable. So, why have we always been alone? Enrico Fermi, the Italian physicist who proposed this question in 1950. This is an eponymous paradox that scientists offered a lot of solution since then. One of the most popular solutions came from Sagan with William Newman who postulated in a 1981 paper. They said we just need patience. It is because they are all too far away so nobody has visited us. It is about the interstellar travel so that species have to spread across so many worlds.
On the other hands, researchers argued that extraterrestrial life could be rarely space-faring. Some even argued that tech-savvy species could quickly self-destruct when they arise. Still, others even believed that aliens may have visited in the past. Otherwise, they were avoiding us on purpose. Eventually, we can say that the most pessimistic answer was from astrophysicist, Michael Hart. This foundational paper in 1975 was the way he declared that there was no reason to visit since nobody out there.
Now, we have a paper that rebuts Sagan, Newman, and Hart. This paper offers a new solution to the Fermi paradox that avoids any speculation about anthropology and alien psychology. Based on the research reviewed under The Astrophysical Journal, the movements of stars can help distribute life. Jonathan Carroll-Nellenback, the astronomer at the University of Rochester explained that the sun has been around the center of the Milky Way 50 times. He led the study and explained that stellar motions would get you the spread of life on time scales much shorter than the age of the galaxy.
Additionally, Carroll-Nellenback and his colleagues made simulations, natural variability would mean that sometimes galaxies will be settled, but often not – so it can solve Fermi’s quandary. Hart and others calculated that the single space-faring species could populate the galaxy for a few million years. So, their absence that they should spread means they must not exist. That was Hart tried to explain.
Also, Sagan and Newman agreed that the long-lived civilizations grow more slowly. Meanwhile, the rapacious societies might peter out before they touched all the stars. Jason Wright as the coauthor of the new study summarized the argument from Sagan and Newman, but it does not mean Jason agrees with the solution.
Based on their new paper, Carroll-Nellenback Wright and their collaborators, Adam Frank of Rochester and Caleb Scharf of Columbia University need to examine the paradox without creating untreatable assumptions.
But a thing with us right now is that no interstellar visitors are here. Here, Hart called it “Fact A”. So, it does not mean they do not exist, the author said. Some civilizations may expand and become interstellar but not all of them last forever. Not every star is their choice to come, and not every planet is habitable. Frank explained about “The Aurora Effect” after Kim Stanley Robinson’s novel Aurora, the settlers come at the habitable planet but they still cannot survive.
When Carroll-Nellenback and his co-authors ran many simulations with different star densities, spacecraft velocities, seed civilizations, and other variations, they found the vast middle ground between the silent, empty galaxy that supports life. So, probably explorers visited us in the past but we do not remember and then they did out.
A futurist at the University of Oxford’s Future of Humanity Insitute, Anders Sandberg has studied the Fermi paradox. He argued that spacecraft would spread civilizations more effectively than stellar motions. He even wrote in an email about the importance of mixing of stars to spread life, life’s chemical precursors.
Frank views his and his colleagues’ new paper as SETI-optimistic. There, he and Wright said we need to look harder for alien signals. The more sophisticated telescopes should support human to find alien signals in the coming decades
Seth Shostak, an astronomer at the SETI Institute has studied the Fermi paradox for decades. He said that we are not alone. Also, he explained that the click beetles in the backyard do not notice that there are intelligent beings surround them, which are me and my neighbors.