(ORDO NEWS) — About 15 million years after the Big Bang, the universe has cooled so much that the electromagnetic radiation left over from its hot inception has become about room temperature. In a 2013 article, I called this period in the history of the early universe “livable.” If we had already existed then, then we would have completely dispensed with the sun: to keep warm, the cosmic radiation background would be enough.
Did life really begin then? Maybe not. The hot and dense conditions in the first 20 minutes after the Big Bang created only hydrogen and helium, as well as residual traces of lithium (one in 10 billion atoms) and a small amount of heavier elements. But life in the usual sense of the word requires water and organic compounds, and until that moment there was still 50 million years left, when the first stars combined hydrogen and helium into oxygen and carbon in their bowels. The emergence of life at an early stage was hampered not so much by the temperature (it was just about the same as the current one), but by the lack of basic elements.
Since the initial supply of heavy elements was limited, how early could life begin? Most of the stars in the universe were formed billions of years before the Sun. Rafael Batista, David Sloan and I have suggested, based on the history of cosmic star formation, that life on sun-like stars most likely originated in the past several billion years. However, in the future, it may appear on planets orbiting dwarf stars, like our closest neighbor Proxima Centauri, which will last hundreds of times longer than the Sun. Ultimately, it would be desirable for humanity to move to an inhabited planet around the dwarf star Proxima Centauri b, where we can bask in a natural nuclear reactor for another 10 trillion years (In fact, stars are just thermonuclear reactors,
As far as we know, water is the only liquid that supports the chemistry of life, but there is still much we do not know. Could alternative liquids exist at an early stage due to warming only due to the cosmic background radiation? In a new article with Manasvi Lingam, we show that ammonia, methanol and hydrogen sulfide could exist in liquid form just after the formation of the first stars, while ethane and propane could turn into liquids a little later. The significance of these substances for life is unknown, but it can be studied experimentally. If we ever manage to create synthetic life — and this is what Jack Shostak’s lab at Harvard University does — we’ll test if life can originate in fluids other than water.
One way to determine how life began in space is to study the planets around the oldest stars. It can be assumed that such stars will be poor in elements heavier than helium, which astrophysicists call “metals.” (In our language, in contrast to the usual, the same oxygen, for example, is considered a metal). Indeed, metal-poor stars are found in the periphery of the Milky Way and are believed to be the earliest generation of stars in the entire universe. They often have an increased carbon content, and metals (in the astrophysical sense), on the contrary, a lower one. A former student of mine, Natalie Mashian, and I hypothesized that the planets around such stars might be predominantly carbon, so their surfaces could provide a rich nutrient base for new life.
Thus, one should look for planets orbiting stars that are rich in carbon and poor in metals, and leave biological signs in their atmospheric composition. This would make it possible to establish through observations how long ago life in space could have arisen, based on the age of these stars. Likewise, we could estimate the age of interstellar “tooling” – either drifting close to the Earth or crashing on the Moon – thanks to long-lived radioactive elements or traces of cosmic dust particles hitting their surfaces.
This strategy can be supplemented by the search for technological signals from distant early civilizations that have accumulated enough energy to “betray” themselves on a cosmic scale. In particular, such a signal can be a flash from a collimated (directional) beam of light for the movement of light sails. Others may be somehow related to space engineering, such as the movement of stars. It is unlikely that communication signals will be found throughout the entire Universe, because such a signal will travel for billions of years in each direction, and none of the participants will have the patience to participate in such a slow exchange of information.
But even the traces of life are not eternal. Therefore, the prospects for the distant future are rather bleak. With the accelerated expansion due to dark energy, the universe will become dark and cold, and all life forms are likely to disappear within 10 trillion years. Until then, we can preserve everything that is transitory, which nature has endowed us with. Our descendants will be proud of us if our civilization turns out to be so intelligent that it will last for trillions of years. Let’s hope we act wisely enough to be remembered in the Big History books.
Avi Loeb is former Chair of the Department of Astronomy at Harvard University (2011-2020), Founding Director of the Harvard Black Hole Initiative, and Director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics. Head of the Council for Physics and Astronomy of National Academies and the Advisory Council for the Star Breakthrough Project, and member of the Presidential Council for Science and Technology. Author of the bestselling book Aliens: Early Signs of Intelligent Life Beyond Earth.
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