Statistically speaking, it turns out that 20% of the stars form double or multiple systems and that a roughly identical percentage probably have a procession of planets which, in all probability, at least one with the minimum conditions to maintain the life. But if life does not seem to be able to evolve around all the stars, for different reasons (temperature, gravity, radiation), it is statistically demonstrated that the appearance of life is a quasi-mandatory phenomenon under the conditions of Universe, if, as is assumed, the laws of nature are universal. Since we exist, we must explain this fact without invoking a supernatural being, which in any case remains a non-falsifiable and therefore unscientific concept.
An important observation already underlies the universality of the laws of nature: the extreme precision with which the constants of nature have been determined. Many physicists and astrophysicists believe that these values are not due to chance. At the quantum level, it is as if the different forces had the right values to make it work. This is the anthropic principle that we will see in cosmology.
In a few words, in its weak version, the anthropic principle considers that if the energy of the universe had been somewhat weaker or somewhat stronger, it would have exploded or shrunk too quickly without leaving the time to constitute itself to form the first molecules of life. After all, the universe is a living laboratory in which reactions take some time to complete, depending on the properties that govern nature.
One can also ask why the world is locally organized and measure the lack of information systems irrespective of the scale of the phenomenon and our appreciation of the state of disorder. In the universe, there exists a very special quantity, entropy. As we will see in another file, this thermodynamic quantity applies to all systems, both to the evolution of the physical and chemical systems and is summed up in two words: globally order tends towards disorder. Without some energy loss, no interaction would be possible. The universe as a whole would have remained at the primordial stage and would never have succeeded in building up the complex edifice of the growing organization.
The task of biochemists, exobiologists and astrobiologists therefore consists in demonstrating that life is a common phenomenon in the universe. Starting with some ingredients and a primitive soup, they must invent the scenarios that have led to the current “breeding ground”. If only one star in the Milky Way harbors life, it is potentially billions of inhabitable worlds that fill the universe. By studying the biochemistry and behavior of prebiotic molecules, it is discovered that they survive under conditions deemed hostile or exist in unknown metastable states on Earth.
It is by using the new tools of bioastronomy and by studying the evolution of life on Earth that we can confirm or deny the existence of life elsewhere in the universe.