Perhaps, in the entire history of the universe, there was no other intelligent, technically advanced type of aliens. Speaking last week in the New York Times, scientist Adam Frank pointedly wrote: Yes, aliens exist. He made this conclusion, since in the universe there are potentially habitable worlds known to us from astrophysical studies, intelligent life could also arise there. But what he could not explain was the number of unknowns introduced into the equation by abiogenesis, evolution, long-term habitability, and other factors. Indeed, there is an astronomical number of possibilities for intelligent, technologically advanced life forms, but due to colossal uncertainties it may well be that humans are the only living creatures plowing through the cosmos.known to our universe.
In 1961, scientist Frank Drake compiled the first equation showing how many space-traveling civilizations exist in the universe today. He based his calculations on a series of unknown properties and factors in order to make estimates based on them and ultimately understand how many technically advanced alien species are currently in our galaxy and the observable universe. Thanks to scientific advances over the past 55 years, many of the factors that we could only guess by guesswork can now be learned with incredible precision.
To begin with, our understanding of the size and scale of the universe has expanded in the most dramatic way. Thanks to observations using space and ground-based observatories, which cover the entire spectrum of electromagnetic waves, we today know how large the universe is, and how many galaxies there are in it. We have a much better understanding of the formation and functioning of stars. Therefore, looking into the vast abyss of distant space, we are able to calculate how many stars there are and have been in the universe throughout cosmic history since the "big bang". This is a colossal amount: about 10 to the 24th power. And that tells us how many chances the universe had in the past 13.8 billion years to spawn life like ours.
This is how the artist imagined the exoplanet Kepler-452b
Photo: NASA / JPL-Caltech / T. Pyle
Previously, we wondered how many stars there are planets revolving around them, which planets are in a solid state, how many have an atmosphere similar to ours, and how many such planets are located at such a distance from their stars that there is liquid water on their surface. For countless years, we could only speculate about this. But thanks to the tremendous advances in exoplanet research, primarily with the help of NASA's Kepler space satellite, we have learned a lot about what is in space. Among other things, we know the following today:
- planets or planetary systems revolve around 80-100% of stars in orbit;
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- about 20-25% of these systems have a planet in a habitable zone or in a place where liquid water can form on its surface;
- approximately 10-20% of these planets are the same size and mass as Earth.
We bring everything together and we get that in the universe there are 10 to the 22nd power of the earth-like planets, where there are the necessary conditions for life.
But the situation here is even better, because with the exception of the earliest generations of the first stars, almost all of them are enriched with heavy elements and ingredients necessary for life. When we look at interstellar space, at molecular gas clouds, at the centers of distant galaxies, at streams emanating from large stars, and even at our own galaxy, we find elements of the periodic table - carbon, nitrogen, oxygen, silicon, sulfur, phosphorus, copper, iron and so on. All these are substances necessary for life in the form we know. Looking inside the meteorites and asteroids in our solar system, we not only find these elements, we find them in complex organic molecules such as sugar, graphite rings, and even amino acids. In other words, in the universe there are not only more than 10 to the 22nd power of the Earth-like planets;there are more than 10 earth-like planets to the 22nd degree, where there are components necessary for life!
But if we show scientific honesty and conscientiousness, our optimism should end there. The fact is that for the emergence of a civilization similar to a human, three important things must happen.
The first stage that must occur is abiogenesis, when the "raw" ingredients associated with organic processes become what we recognize as "life".
For multicellularity, complexity, differentiation and what we call "intelligence" to appear, life on the planet must exist and develop for billions of years.
So the artist imagined the brightest galaxy in the Universe, surrounded by dust
Photo: NRAO / AUI / NSF; Dana Berry / SkyWorks; ALMA (ESO / NAOJ / NRAO)
And finally, such intelligent life should eventually become a scientifically and technically advanced civilization that can either acquire the ability to declare its presence in the universe, or go beyond its own home and begin to explore outer space, or reach a stage when it will be able to listen to other forms of mind in space. Or, in the most optimistic case, do all three things.
When Carl Sagan presented his book Space: The Evolution of the Universe, Life, and Civilization in 1980, he argued that it would be prudent to give each of these three steps a 10 percent chance of success. If this statement is true, then only in the Milky Way galaxy there should be more than 10 million intelligent alien civilizations!
Today Adam Frank states that it is unrealistic to give these three steps a cumulative probability of less than 10 to minus 22. On this basis, he comes to the conclusion that somewhere in the universe there must be aliens. But this in itself is a ridiculous statement that is not based on anything. Yes, abiogenesis can be widespread; even on Earth alone, it could appear many times. And also on Mars, Titan, Europa, Venus, Enceladus and other planets in our solar system alone. Or it may be such a rare process that even if we create a hundred clones of the young Earth (or a thousand, or a million), our world may be the only one where this abiogenesis arose.
And even if life did arise, how lucky does it have to be in order to exist and flourish for billions of years? Isn't a catastrophic warming scenario like it did on Venus the norm? Or a catastrophic cooling scenario like on Mars? Or does life in most cases poison itself in the process of existence, as it almost happened on Earth two billion years ago? And even if we have life that has existed for billions of years, how often will processes like the Cambrian explosion occur, as a result of which huge multicellular macroscopic plants, animals and fungi begin to dominate the planet? They can occur quite often, when 10% of such explosions end in success, or rarely, when the chance of success for such explosions is one in a million or even one in a billion.
And even if that happens, how rare are human-like species using tools, advancing technologies and launching rockets into space? Developed reptiles, birds and mammals, which by some standards can be considered reasonable, have existed for tens and hundreds of millions of years, but modern man appeared less than a million years ago. And we have become "technically advanced" in our understanding only in the last two centuries. Is there a 10 percent chance that after going through the previous step, we get a civilization of space travelers? Or maybe such chances are one in a thousand, in a million, in a trillion, or even worse?
In truth, we don't know that. We know that the universe gives intelligent life a very large number of chances of occurrence, on the order of 10 to the 22nd power. And we also know that the likelihood of advancing and developing in this life, becoming a technically advanced civilization mastering space, is very small. What we don't know is the significance of this probability. What are the odds: 10 to the minus third, 10 to the minus twentieth, ten to the minus fiftieth? Or even less? We know that at least once life arose (human), and therefore the probability of its origin is not zero. But which one? To find out, we need data. Assumptions, hypotheses, and statements will not replace this information. We need to find her in order to know. And despite the claims of the New York Times, everything else is nothing more than fortune telling on the coffee grounds.
Astrophysicist and writer Ethan Siegel is the creator and main author of the Starts With A Bang blog.