The famous astrophysicist, professor at Harvard University Avi Loeb recently came up with a rather fantastic hypothesis that shifted the beginning of biogenesis to the infancy of the Universe: he believes that individual islands of life could have arisen when the Universe was only 15 million years old. True, this "first life" was doomed to an almost inevitable speedy (by cosmic standards - in just 2-3 million years) disappearance.
Ingredients
“The standard cosmological model strongly prevents life from emerging this early,” says Avi Loeb. - The first stars in the observable region of space exploded later, when the age of the universe was about 30 million years. These stars produced carbon, nitrogen, oxygen, silicon and other elements heavier than helium, which could have become part of the first solid Earth-like planets that formed around second-generation stars. However, much earlier the appearance of first-generation stars from clouds of molecular hydrogen and helium, which thickened in clusters of dark matter, is also possible - the age of the Universe at that time was about 15 million years. True, it is believed that the likelihood of the appearance of such clusters was very small.
However, according to Professor Loeb, observational astronomy data allow us to assume that separate regions could appear in the Universe, where the first stars flared up and exploded much earlier than the Standard Model prescribes. The products of these explosions accumulated there, accelerating the cooling of molecular hydrogen clouds and thus stimulating the appearance of second generation stars. It is possible that some of these stars could acquire rocky planets.
Avi Loeb, professor of astrophysics at Harvard University: “For life to arise, heat alone is not enough; you also need suitable chemistry and geochemistry. But on young rocky planets, there could be enough water and substances needed for the synthesis of complex organic macromolecules. And it's not far from here to real life. If such a scenario is not very likely, it is still not impossible. However, it is almost impossible to test this hypothesis in the foreseeable future. Even if in the Universe somewhere there are planets of super-early birth, then in very small numbers. It is unclear how to find them, and even more unclear how to investigate for traces of biogenesis."
Warm and comfortable
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But elements heavier than helium alone are not enough for life to arise - comfortable conditions are also required. Earthly life, for example, is completely dependent on solar energy. In principle, the first organisms could have arisen with the help of the internal heat of our planet, but without solar heating they would not have reached the surface. But 15 million years after the Big Bang, this restriction did not apply. The temperature of the cosmic relic radiation was more than a hundred times higher than the current 2.7 K. Now the maximum of this radiation falls at a wavelength of 1.9 mm, which is why it is called microwave. And then it was infrared and even without the participation of starlight could heat the planet's surface to a temperature that is quite comfortable for life (0-30 ° C). These planets (if they existed) could even orbit away from their stars.
Short life
However, the very early life had practically no chances to survive for a long time, let alone serious evolution. The relict radiation quickly cooled down as the Universe expanded, and the duration of the heating of the planetary surface, favorable for life, did not exceed several million years. In addition, 30-40 million years after the Big Bang, the massive birth of very hot and bright stars of the first generation began, flooding space with X-rays and hard ultraviolet light. The surface of any planet in such conditions was doomed to complete sterilization.
It is generally accepted that life as we know it cannot originate either in a stellar atmosphere, or on a gas giant like Jupiter, or, even more so, in a cosmic void. For the emergence of life, celestial bodies with a rich chemical composition, with a solid surface, with an air pool and with reservoirs of liquid water are required. It is believed that such planets can form only near the stars of the second and third generations, which began to catch fire hundreds of millions of years after the Big Bang.
Anthropic principle
Avi Loeb's hypothesis can be used to refine the so-called anthropic principle. In 1987, Nobel Prize laureate in physics Steven Weinberg estimated the range of values for the antigravitational energy of the vacuum (now we know it as dark energy), compatible with the possibility of the birth of life. This energy, although very small, leads to an accelerating expansion of space, and therefore prevents the formation of galaxies, stars and planets. From this it seems that our Universe is downright adapted for the emergence of life - this is precisely the anthropic principle, because if the value of dark energy were only a hundred times greater, then there would be no stars or galaxies in the Universe …
However, it follows from Loeb's hypothesis that life has a chance to arise under conditions when the density of baryonic matter in the Universe was a million times greater than in our era. This means that life can arise even if the cosmological constant is not a hundred, but a million times higher than its real value! This conclusion does not cancel the anthropic principle, but significantly reduces its credibility.
Alexey Levin