Why do we believe that there are extraterrestrials
Researchers calculate 35 alien civilizations
Are we alone in the Universe? For as long as people have looked up to the sky, the question has haunted them whether there are other worlds besides ours, whether these are inhabited and whether there is possibly even extraterrestrial intelligence. Thanks to astronomical research, we now know that there are a multitude of extraterrestrial worlds. But what about extraterrestrial life, and also intelligent life?
A study by two researchers from the University of Nottingham, published this week in The Astrophysical Journal, now presents a number of how many intelligent, actively communicating civilizations there could be in our galaxy: 36 - including our own.
What at first sounds more like science fiction than solid science is based on data that astronomers have collected over the past few decades. As things currently stand, humanity is the only known form of higher intelligence life in the universe. How then is it possible to compile statistics for the spread of aliens?
"This calculation is quite simple," says one of the study authors, Christopher Conselice, professor of astrophysics, modestly in an interview with the STANDARD. "We know enough about stars, planets and our galaxy as well as the history of their formation to be able to make this calculation."
The basic assumption is as follows: We know the conditions under which intelligent life arose on earth. We also know in terms of magnitude how many planets in our Milky Way are in the habitable zone - that is, at the correct distance to their star, where it is neither too hot nor too cold for life. After all, we can infer from our own origins how long it takes for higher life to actually develop on a habitable planet.
"We assume that science works in the same way everywhere in the universe. That means, if all criteria are met for intelligent life to develop, that will happen at some point," Conselice outlines the basic idea. "Of course it's not the same time scales as on Earth, but a few billion years up or down doesn't really matter."
If you ask a physicist about extraterrestrial life, they like to refer to the Drake equation. The formula presented by Frank Drake in 1961 gives a calculation method for the number of intelligent lives in our galaxy. At first glance, the equation looks simple - it doesn't take more than multiply seven magnitudes to determine if we are alone in the Milky Way. In purely formal terms, this arithmetic task could therefore be mastered in the third grade of elementary school. The catch: all seven multipliers are unknowns.
Together with Tom Westby, Conselice derived a new version of the Drake equation. It is a multiplication of four sizes: the total number of stars in our galaxy times the proportion of stars that are older than five billion years. Another multiplier is the proportion of stars that are home to a planet in the habitable zone. So far, all the required quantities can now be determined quite well from observation data - a significant advance compared to Drake's level of knowledge, which sometimes used the same multipliers in his equation, but was unable to put them into figures.
But it gets really tricky with the fourth multiplier of the new Drake equation: The quotient of the average lifetime of a civilization from the point in time when it is technically so advanced to emit signals (such as sending radio waves into space), divided by the average Time it takes for life to emerge on a habitable planet. The authors can only make estimates for both time periods.
To do that, Westby and Conselice developed various scenarios from conservative to optimistic. Calculated conservatively, there are between four and 211 civilizations currently actively communicating in our galaxy, with the most likely number being 36 civilizations.
These are very specific statements, but at the same time the authors self-critically admit: "Of course, extraterrestrial intelligence and communicating civilizations remain completely within the range of hypotheses as long as no such discovery has been made."
To be fair, it has to be said that calculating the frequency of intelligent civilizations in space is one of the most difficult statistics problems one can think of - and far exceeds conventional statistics. Because we only know one data point, ourselves. To draw conclusions about the entire Milky Way from this is anything but trivial.
In addition to the simple number of extraterrestrial civilizations, we humans are of course particularly interested in how far they are from us. For this, too, Westby and Conselice offer an answer: calculated conservatively, they come to an average distance between civilizations of 17,000 light years. With the technologies known to us, interstellar communication or detection is therefore unfortunately impossible.
Social distancing in space
Perhaps the social distancing between us and the closest aliens is also less pronounced. According to Westby and Conselice, the minimum distance to the next civilization is only a few hundred light years - but this is only plausible if intelligent civilizations have a lifespan of a million years. "If we look at our own civilization, it seems like a long time," says Conselice.
This also explains why the discovery of extraterrestrial civilizations could ultimately provide us with important information about our own future, according to Conselice: "If we find many extraterrestrial civilizations very close, that would mean that they are despite problems such as global warming or wars managed to exist for long periods of time. " (Tanja Traxler, June 16, 2020)
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