Are we alone in the universe? It is the question of questions, and for now, despite centuries of attempts, it remains unanswered. To establish it with certainty we would need concrete proof, a message, a sighting. While waiting to find one, we can still try to estimate the probability that there exists, somewhere, another form of life that shares the gift of intellect with ours. One way to do this is to calculate how suitable the physical parameters of our universe make it for the birth of life. This is what a study just published in Monthly Notices of the Royal Astronomical Society attempts to do, reaching the conclusion that among all the possible universes, ours, although evidently compatible with the evolution of biological life, would not actually be among those which was most likely to happen.
Drake equation
The most famous attempt to establish a methodology to predict the possibility that other intelligent civilizations exist, capable of communicating with ours, was that of the American astrophysicist Frank Drake, one of the fathers of Seti (Search for Extra-Terrestrial Intelligence) institute, an organization that has been active since the 1980s in the search for extraterrestrial life forms capable of sending radio signals into space. Precisely in one of the first meetings that would give life to the Seti programs, Drake formulated his famous equation, with which it is possible to establish the number of alien civilizations present in our galaxy by fixing a series of variables, with which the number of stars and habitable planets that are born every year in our galaxy, the percentage that could give birth to extraterrestrial life forms, how many of these could evolve to develop intelligence, and therefore the fraction of intelligent alien species capable of communicating with ours .
Many parameters of the equation, it is evident, cannot be rigorously established, and this has meant that very different solutions to the equation have been proposed over the years. Ranging from the most optimistic, which predict hundreds of thousands of alien civilizations potentially capable of sending radio messages into the cosmos, to the most pessimistic, which estimate a number close to zero of aliens waiting to communicate with us.
The study
The new research, the result of the work of three physicists from Durham University, the University of Edinburgh and the University of Geneva, starts from very different premises than the Drake equation. The aim is in fact to calculate the effects of the so-called cosmological constant, i.e. the dark energy that is used today to explain the acceleration of the expansion of the universe, on the rate of star formation and the birth of galaxies.
The currently most accredited cosmological model, known as the Lambda-CDM model, has continued for decades to be very successful in reproducing the observations made by astrophysicists, but it also presents several problems that cosmology experts have been struggling with for some time. One of these is a suspicious quantity of inexplicable coincidences: the value of the cosmological constant, for example, is exactly that necessary for us to start seeing its effects when our star, the Sun, was born, and what we live in is a period in which the density of matter and dark energy have comparable magnitudes. This and other temporal coincidences between the evolution of the universe and the appearance of our species have led several authors to introduce the presence of an observer (us) into their theories. It’s called the “anthropic principle,” and it can basically be summed up like this: the universe works exactly the way it does because otherwise we wouldn’t be here observing it.
It is in this direction that the new research fits. The aim of its authors, in fact, was to calculate which values of the cosmological constant allow the creation of stars and galaxies, at which values the rate of formation of new stars is maximized, and how much the values that this constant has assumed in our universe are close to the optimal ones to produce more stars, and therefore more planets. And therefore, ultimately, what values maximize the chances that one, or more, intelligent life forms will evolve, which can be amazed by the coincidences that allowed them to come into the world and study the universe.
The results
In short, how suitable is our universe for the appearance of intelligent life exactly in the period in which we live? “Understanding dark energy and the impact it has on our universe is one of the greatest challenges in cosmology and fundamental physics. And the parameters that govern our universe, including the density of dark energy, can explain our very existence,” explains Daniele Sorini, from the Institute for Computational Cosmology at Durham University. “Surprisingly, however, we found that even significantly higher densities of dark energy would still be compatible with life, suggesting that we may not live in the most likely of universes.”
The three researchers’ calculations predict that a truly efficient universe would have dark energy values that allow 27 percent of the matter present within it to convert into stars over its entire existence. While ours will only reach 23 percent. And therefore it is not the universe in which there is the greatest probability that forms of intelligent life will appear, or that there will be others besides ours. That doesn’t mean it’s impossible, though: we just probably don’t live in the most crowded of possible universes.