Astrophysicists have found new confirmation that our Universe is "specially" designed for the origin of intelligent life - its expansion rate is such that it minimizes the chances that life on Earth or other planets could be destroyed by powerful and prolonged gamma-ray bursts.
Photo: V. Springel, Max-Planck Institut für Astrophysik, Garching bei München
The expansion rate of the Universe turned out to be directly related to the chances of discovering extraterrestrial life, as it affects the susceptibility of alien civilizations to supernova explosions, gamma-ray bursts and other fatal cataclysms, according to an article published in the journal Physical Review Letters.
Astronomers have long believed that life can originate and exist on the outskirts, and not in the center of the Milky Way and other galaxies, since supernova explosions too often occur in their central part and gamma-ray bursts appear that can destroy life for tens of light years around them …
In November 2014, astronomers found that due to the high frequency and power of such flares in especially "densely" populated galaxies and galaxy clusters, life can exist only in 10% of them. In their new work, Tsvi Piran of the Hebrew University of Jerusalem, Israel, and his colleagues went further and assessed how these "killer outbreaks" affected the life of the universe as a whole.
As the researchers note, in the first publication, they did not take into account one important cosmological factor - the fact that the Universe is expanding, and it does so faster and faster as time passes. In their new work, they corrected this flaw by analyzing how life would develop under different scenarios of the expansion of the universe.
All these scenarios are, in fact, determined by one variable - the so-called cosmological constant, which determines how dark energy affects the expansion of the universe. According to the calculations of the Nobel laureates who discovered the phenomenon of the accelerating expansion of the Universe, it has a small, but non-zero value, which smoothly makes the universe grow faster and faster.
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Piran and his colleagues have shown that deviations of this constant from the current value up or down will have an extremely strong effect on how life originated in the Universe, and on its birth on Earth.
In general, all such changes will be extremely negative - its increase will lead to the fact that stars will simply stop forming, which automatically puts an end to the origin of life, and a decrease will lead to a sharp increase in the frequency of gamma-ray bursts due to an increase in the "population density" which will also nullify the chances of the birth of life.
As for the Earth, we are doubly lucky in this respect - we not only live in the Universe with the “correct” cosmological constant, but we are also in a galaxy with a small number of dwarf satellites, where gamma-ray bursts should occur more often than in large "Star metropolises". Accordingly, aliens outside the Milky Way should be looked for in similar conditions.
Similar results, according to the authors of the article, testify in favor of the so-called "anthropic principle". It says that we exist because the values of the fundamental constants in the Universe we observe are exactly those that are suitable for the origin of life.
An open question, Piran and his colleagues admit, is how much gamma-ray bursts actually pose a threat to intelligent and unreasonable life. Today, a number of scientists believe that the Earth experienced one such event 460 million years ago, having lost about 80% of the species of then existing creatures, but not all astronomers agree with this.