Drake's formula estimates the number of extraterrestrial civilizations. Drake formula estimate the number of extraterrestrial civilizations Some general data

While working at Los Alamos National Laboratory in New Mexico in 1950, physicist Enrico Fermi asked his colleagues the now famous question: “Where are they?” . The Nobel Prize winner noted the discrepancy, which he found strange. With so many stars in our galaxy, even the tiny chance of life existing near any given star means the presence of a large number of alien civilizations. Further, assuming reasonable probabilities about the ability of aliens to travel interstellarly, physically change the surrounding space or communicate, we should already see evidence of their existence. But we don't see. This discrepancy became known as Fermi paradox, and the corresponding absence of life in the observable Universe is usually called Fermi's observation.

Many hypotheses have tried to explain the Fermi Paradox. For example, that other civilizations deliberately hide themselves or self-destruct before they learn to travel between stars or establish long-distance communications. The main problem with such hypotheses is that the proposed mechanism for concealing one's existence or self-destruction must be extremely reliable: if only 99% of civilizations destroy themselves, this does little to resolve the paradox.

Thus, all of these hypotheses remain highly speculative and largely rely only on assumptions about some universal motives or social dynamics of aliens, while we cannot claim similar knowledge about our own world. These hypotheses are not considered for their independent scientific plausibility, but only because they offer a solution to the Fermi Paradox.

Scientists from the Future of Humanity Institute at the University of Oxford have published a scientific paper in which they show that "the correct handling of scientific uncertainties dissolves the Fermi Paradox." In other words, our uniqueness in the Universe and the absence of observable alien life becomes not a “paradox” or an unlikely event.

The authors of the scientific work criticize the fact that the Drake formula is usually used with point estimates. However, such point estimates "imply knowledge about processes (especially those related to the origin of life) that are untenable given the current state of science." According to British scientists, taking into account realistic uncertainty, point estimates should be replaced probability distributions, which reflect current scientific understanding. And then, according to Drake’s formula, a completely different picture emerges - and any reason to be sure that the Galaxy (or the observable Universe) contains other civilizations disappears.

The second result of the scientific work: the scientists showed that, given the observed limits of the dominance of other civilizations, “our updated probabilities suggest that there is a significant probability that we are alone.” The authors found qualitatively similar results using two different methods: using the authors' estimates of current scientific knowledge relevant to key parameters, and using diverging estimates of these parameters in the astrobiological literature as a proxy for current scientific uncertainty.

Calculation using this method showed a fairly high probability that humanity is alone in its native Milky Way galaxy (53−99.6%) or even in the entire observable Universe (39−85%). Accordingly, to the famous question “Where are they?” the authors of the scientific work answer: “Probably very far away, and quite possibly beyond the cosmological horizon and forever unattainable.”

From all of the above, the third conclusion follows that pessimism for the survival of mankind, based on the Fermi paradox, is unfounded. In other words, humanity has a good chance of survival, and one cannot draw conclusions about the inevitability of the self-destruction of civilization based on the fact that there is not a single sufficiently developed civilization in the observable Universe. This is perhaps the most optimistic result from a published scientific work.

The article was published on June 6, 2018 on the preprint site arXiv.org (arXiv:1806.02404v1).

Elon Musk responded to the calculations of British specialists. "So strange", -

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Not long ago, our resource “” published a material called “”, which touched upon the question of the existence of alien intelligent civilizations in the Universe. But if there this very possibility was questioned, here we will consider a formula that often serves as a refutation of the above-mentioned paradox. This formula is called the Drake equation.

Some general information

It’s worth starting with the fact that there is a special project under the general name “SETI” (an abbreviation for Search for Extraterrestrial Intelligence). It includes various projects and activities aimed at searching for extraterrestrial civilizations and making contact with them. The project has existed for several decades (since 1959), almost from the moment when American astronomer Frank Drake conducted his first experiment. SETI searches are based on listening to radio waves that may be sent by other civilizations from the depths of space. Drake himself even then considered this an indicator of a high-tech society, as well as the most acceptable and reasonable means for searching for extraterrestrial life forms.

The probability of detecting any signal at a distance of more than 500 light years is practically zero, i.e. 500 light years is the limit within which modern technologies can generally detect any radio signal. It follows from this that the so-called “Great Silence”, which radio telescopes are constantly detecting, does not mean that other life in the Universe is not possible. And higher chances of approving something with a more or less significant degree of confidence can only appear if earthly “receivers” can increase the range of signal reception by at least another 900 light years.

In the middle of the last century, humanity had even less data on this topic. However, already at the time when the Soviet cosmonaut Yuri Gagarin became the first person to orbit the Earth (1961), Frank Drake developed his equation to approximately estimate the number of possible alien civilizations in our galaxy, called the Milky Way. This equation is based on methods for detecting electromagnetic pulses.

Drake equation

The Drake equation is formulated as follows:

N = R * Fp * Ne * Fl * Fi * Fc * L, where:

N – the number of intelligent civilizations that are ready to make contact

R is the number of stars appearing during the year in the Milky Way galaxy.

Fp – percentage of stars that have planets in their orbits

Ne is the average number of planets and their satellites whose conditions are suitable for the origin of life

Fl – probability of life appearing on a suitable planet

Fi – the probability of the appearance of intelligent life forms on planets where life is possible at all

Fc – the ratio of the number of planets on which intelligent life forms are capable of contact and seek it, to the number of planets on which there are intelligent life forms at all

L – time during which intelligent life exists, can come into contact and wants to do so

Analysis of the Drake Equation

Looking at the Drake equation, it becomes obvious that the value of N cannot be determined exactly. In addition, if you move along the equation from left to right, estimates of all quantities become more and more abstract. However, this equation should not be assessed by numbers alone. Some researchers are convinced that this formula is only a way of organizing human ignorance. And if we consider the hypothesis of the existence of extraterrestrial intelligence from a purely mathematical point of view, then the possibility of obtaining an answer to the question about the number of alien civilizations is significantly limited. The L value is the most important in the entire equation. A person cannot know how long a technologically advanced civilization can survive. And even if we assume that there is only one alien civilization, and has existed for billions of years or even eternity, then this will be enough to equate N and L in the equation.

But searching for extraterrestrial intelligence only by listening to radio waves would be a mistake. Thanks to the development of astrobiology and cosmology, man's perception of space and the ways of development of other forms of life has changed greatly. At the beginning of the existence of SETI, its experts predicted the rapid development of terrestrial radio technologies and the growth of radio traffic, but the dot-dash-dot connection faded against the background of satellites sending their signals to the Earth, and the emphasis in telecommunications shifted from radio to fiber optics for the Internet. traffic and cable TV, which means that no serious radio signals will be received from the Earth for at least another hundred years.

Another weak point of the formula is the number of planets on which intelligent life forms can develop. Presumably, their number should be within 10 thousand in our galaxy. But at present there is no evidence that there is any fundamental principle that could direct the primordial substance towards the development of Homo Sapiens. And this question will remain unanswered until evidence of life is found on at least one planet in the solar system.

Among other things, the Drake equation does not take into account such indicators as the age of the galaxy itself and chemical-mechanical parameters, for example, the presence of certain elements necessary for the formation of planets and the origin of life. According to some experts, the Drake equation does not imply a Universe that is constantly in dynamics, but a special cosmological constancy.

The formula contains the approximate number of Earth-type planets, but does not provide estimates of when intelligent life forms appear on these planets. The enormous age of our galaxy and the likelihood that intelligent life on its planets could have been present 2 and 4.5 billion years ago, but could have already died out, do not provide practically any space for detecting radio waves.

To date, astronomers have already found approximately two thousand extrasolar planets. And the total number of stars similar to the Sun can be over 40%. But many planets are too large and are in orbits very close to “their” stars. These planets are called "Hot Jupiters". However, scientists predict that if search methods are improved, it will be possible to find planets of a smaller size and with more suitable orbital characteristics. Plus, over the past twenty years of research, it has been possible to find out that there may be billions of planets in the Milky Way, on which life is possible, capable of existing in extreme conditions, for example, with high levels of carbon dioxide, at a depth of up to 10,000 meters and even in sulfuric acid. acid.

But despite its “flaws,” the Drake equation greatly influenced people’s thinking. Mainly, it served as the starting point for the emergence of astrobiological science. The eminent American astrophysicist Carl Sagan praised the fact that the equation showed a high percentage of detection of intelligent extraterrestrial life. And not so long ago, in 2010, Italian astronomer Claudio Maccone published his version of the Drake equation - the statistical Drake equation, which is more complex, but also more reliable. Using the new formula, Maccone was able to determine that within the Milky Way alone there could be 4,590 extraterrestrial civilizations, which is more than 1,000 more than the number that was obtained in the classic version of the equation. In addition to this, the new formula showed that in addition to human civilization there may be up to 15,785 others possessing high technology.

But even if the different galactic communities were at the same distance from each other, the average distance would be 28,845 light years, which makes any contact between these communities impossible, even if it were carried out using electromagnetic radiation traveling at Sveta. And even if such a number of civilizations existed, interstellar communication between them would experience very serious technological problems.

In fact, the Drake equation is subject to scrupulous and detailed study, and, without being an expert in the relevant field, it is quite difficult to really understand what’s what. But our goal was by no means an exhaustive explanation of the equation, but only an indication that scientists around the world are approaching the question of the existence of extraterrestrial intelligence more than seriously, and this has very good reasons.

Does such a beach exist anywhere outside of Earth? The answer to this question is provided by the Drake equation.

The Drake Equation is a formula designed to determine the number of alien civilizations with which humans may come into contact. It was developed in 1960 by astrophysicist Frank Drake to justify the science of SETI, the search for extraterrestrial intelligence program.

What's the point?

The purpose of the formula is to find the number N - the number of civilizations capable of communicating with each other. It is obtained by multiplying six main factors:

R is the number of stars born per year (10, hereinafter according to Drake’s own estimates).
f p – the proportion of stars with planets. (0.5)
n e – the number of habitable planets around the star. (2)
f l – the chance of life appearing in favorable conditions. (1 – if there are conditions, then life will definitely appear)
f with – the ratio of the number of planets where there are inhabitants looking for contact to the number of planets on which there is simply life. (0.01 or 1 percent)
f i – the chance of intelligent life appearing where there is simply life. (0.01)
L is the lifespan of developed life that wants to enter into interplanetary contact (10 thousand years).

The final result for Drake is 10. As many as ten extraterrestrial societies that can contact us! But why are they silent then?

Drake's formula was formulated by American astronomer Frank Drake to estimate number of civilizations in the Galaxy.

(Yes, this is not really on the topic of the site. But it’s still interesting.)

Appearing in 1960, Drake’s formula was very fashionable in the era of “great cosmic hopes,” but then, due to resentment that the hopes did not come true, it began to be criticized, and as a rule, not substantive, but methodological. The main complaint about Drake’s formula is that it is “about nothing”; anything can be counted with this formula; the formula is unfalsifiable, and therefore unscientific.

I will leave the statement about non-falsifiability to the conscience of the critics: they either do not understand the meaning of this concept, or deliberately mislead the reader with a beautiful term. The emotional thesis “the formula is about nothing” is deciphered as follows: the problem area of the problem is so undefined that it seems pointless to derive any formula: we get false accuracy on too shaky ground.

This is true, but this is exactly how the task is posed: to give a reasonable estimate of a certain value under extremely uncertain conditions affecting it. This situation is not at all unique. Very often in science, and in astronomy in particular, at the initial stage of research it is necessary to make assumptions under conditions of extreme uncertainty. Surprisingly, from general considerations one can draw correct conclusions and obtain numerical estimates that do not diverge much from the truth.

How many hairs is there on the head of the President of Venezuela?
What is the mass of a female Porcula salvania?
What is the viscosity in the photosphere of the Sun?

Such questions can be answered from general considerations and a number that is not catastrophically different from the correct one can be obtained. In conditions of complete misunderstanding of the initial conditions, an error of a couple of orders of magnitude is already a worthy result!

This is precisely the situation that Drake was in, offering his generally banal formula. He reduced a completely incomprehensible task (to determine the number of extraterrestrial civilizations) to a set of subtasks that can be assessed. We may be wrong by several orders of magnitude, but in our situation this is already good!

Here is Drake's formula in its original formulation:

N = R * f p n e f l f i f c L ,

R* - star formation rate (stars per year)
f p - fraction of stars with planetary systems
n e - average number of planets in the system that are ecologically suitable for life
f l - probability of life appearing on such a planet
f i - probability of evolution to reasonable
f c - probability of civilization formation
L - time of existence of civilization (years).

Some comments should be made.

Firstly, Drake himself discussed the radio search for extraterrestrial civilizations and therefore meant technically advanced civilizations using radio communications, and estimated the L parameter specifically for them. Without losing generality, you can define civilization at your own discretion and, accordingly, estimate its lifespan.

For example

...civilization can be understood in the most general form, as a socio-cultural structure distinct from isolated tribes. In this case, earthly civilization begins with the Sumerians and today spans approximately 5 millennia.

...following Jaspers, start counting from the axial time, when humanity formed the axiology in which we still exist (presumably, this is a necessary axiology of civilizational development). In this case we have two and a half millennia.

...we can limit ourselves to technical civilizations that are only a couple of centuries old.

Secondly, the dependence on the star formation rate seems somewhat unclear. At first glance, it is paradoxical that the number of extraterrestrial civilizations does not depend on the number of stars in the galaxy, but only on the frequency of star formation. In fact, the size of the galaxy is implicitly included in this parameter, because the larger the star system, the more new stars are born in it. However, in modifications of the formula the number of stars in the Galaxy can also be used, but then one has to use the obscure parameter “lifetime of the Galaxy”. The original version of the form is more accurate.

I'll explain what I'm talking about.

It is clear that f = f p n e f l f i f c is the probability of the appearance of a civilization at an arbitrary random star. R* stars are born per year. After the required period, n = R * f civilizations will arise on these stars. During the existence of a civilization (L years), its contemporaries will be n L other civilizations. This, in particular, means that R * is the star formation rate not at the present time, but approximately when the Sun was born. (Drake himself spoke about the rate of star formation averaged over the lifetime of the Galaxy, which is generally incorrect.) Within the limits of acceptable accuracy, this detail can be neglected.

There are serious factors that are usually not mentioned when talking about the Drake formula that can seriously correlate the result. Some of them work to increase, others - to decrease the probability.

I'll start with the bitter.

"Ecological habitability" depends primarily on surface temperature, that is, on the temperature of the central star and its distance. It is important that the temperature regime should not go beyond acceptable limits during the entire period from the appearance of life to the death of civilization. Using our example, we should talk about 4-5 billion years, which means discarding too hot stars, unstable stars and stars above the Hertzsprung-Russell Main Sequence (fortunately there are not so many of them). In general, it would be worth redefining the f p parameter as “the fraction of stable stars with planetary systems,” where the meaning of “stability” is explained above.

Here's something nice.

The formula implies that civilization is a one-time phenomenon in the history of the planet. That is, the scenario is this: life appeared on the planet, evolved to intelligent life, a civilization formed, and the civilization died. That's all.

That's all? Why can't a new civilization arise based on the same mind? Why can't a new mind arise (and create a civilization) if the old one has died? Why can’t a new life arise if the old one was destroyed, say, as a result of a catastrophe, evolve to intelligence, etc.? The "disposability" of civilization is a very strong and completely unfounded limitation in Drake's formula. If civilization is a renewable thing, then in its present form the formula is significantly inaccurate: the parameter L must be multiplied by the number of reincarnations n r , and its growth will lead to nonlinearity when the total time L n r becomes correlated with the age of the star.

Of course, the question of the n r factor is highly speculative. In particular, it depends on the scenario of the death of civilization, and this is an area of pure futurism, and not at all a serious scientific forecast.

Story

Drake formulated the equation in 1960 while preparing for a Green Bank teleconference. This conference outlined the program

The equation is also often called the Green Bank equation, since this is where it was first proposed. When Drake came up with this formula, he did not intend that it would serve as an argument for the supporters of Carl Sagan, a famous proponent. A similar argument is the Great Filter, which argues that the absence of observable civilizations, given the huge number of observable stars, is explained by the fact that there is some kind of filter that prevents contacts.

Thus, the main meaning of the equation is to reduce the big question of the number of intelligent civilizations to seven smaller problems.

Historical parameter estimates

There are many opinions on most parameters, here are the numbers used by Drake in 1961:

R= 10/year (10 stars are formed per year)
f p = 0.5 (half of the stars have planets)
n e = 2 (on average two planets in a system are habitable)
f l = 1 (if life is possible, it will definitely arise)
f i = 0.01 (1% probability that life will develop to intelligent life)
f c = 0.01 (1% of civilizations can and want to establish contact)
L= 10,000 years (a technically advanced civilization has existed for 10,000 years)

Drake's equation gives N= 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10000 = 10.

Magnitude R determined from astronomical measurements, and is the least discussed quantity; f p is less certain, but also does not cause significant debate. Reliability n e was quite high, but after the discovery of numerous gas giants in small-radius orbits unsuitable for life, doubts arose. In addition, many stars in our galaxy are red dwarfs, emitting hard X-ray radiation, which, according to modeling results, can even destroy the atmosphere. Also unexplored is the possibility of the existence of life on the satellites of giant planets, like Jupiterian Europa, or Saturnian Titan).

Depending on the assumptions made N often turns out to be significantly larger than 1. It was precisely such assessments that served as motivation for the movement

Some results for different assumptions:

R= 10/year, f p = 0.5, n e = 2, f l = 1, f i = 0.01, f c = 0.01, and L= 50,000 years N= 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 50,000 = 50 (at any given time there are about 50 civilizations capable of contact)

Pessimistic assessments, however, argue that life rarely develops to the point of intelligence, and developed civilizations do not live long:

R= 10/year, f p = 0.5, n e = 2, f l = 1, f i = 0.001, f c = 0.01, and L= 500 years N= 10 × 0.5 × 2 × 1 × 0.001 × 0.01 × 500 = 0.05 (we are most likely single)

Optimistic estimates claim that 10% can and want to establish contact, and at the same time exist for up to 100,000 years:

R= 20/year, f p = 0.1, n e = 0.5, f l = 1, f i = 0.5, f c = 0.1, and L= 100,000 years N= 20 × 0.1 × 0.5 × 1 × 0.5 × 0.1 × 100,000 = 5,000

Modern estimates

This section provides the most reliable parameter values to date.

R = star formation rate

Rated by Drake at 10/year. The latest results from NASA and the European Space Agency give a magnitude of 7 per year.

f p = fraction of stars with planetary systems

Rated 0.5 by Drake. According to recent research, at least 30% of solar-type stars have planets, and given that only large planets are discovered, this estimate can be considered an underestimate. Infrared studies of dust disks around young stars suggest that 20-60% of solar-type stars may form Earth-like planets.

n e = Average number of suitable planets or satellites in one system

Drake's score is 2. Marcy notes that most of the discovered planets have highly eccentric orbits, or pass too close to the star. However, systems are known that have a solar-type star and planets with favorable orbits (HD 70642, HD 154345, or Gliese 849). They probably have terrestrial planets in a habitable region that have not been discovered due to their small size. It is also argued that life does not require a sun-like star or an Earth-like planet to arise - Gliese 581d may also be habitable. Although about 200 planetary systems are known, this gives only n e> 0.005. Even for a planet in the habitable zone, the emergence of life may be impossible due to the lack of certain chemical elements. Also, there is the Unique Earth Hypothesis, which states that the combination of all the necessary factors is extremely unlikely, and perhaps the Earth is unique in this regard. Then n e is considered to be an extremely small value.

f l = Probability of life arising under suitable conditions

Rated 1 by Drake. In 2002, Charles Lineweaver and Tamara Davis rated f l as > 0.13 for planets with more than a billion years of history based on Earth statistics. Lineweaver also determined that about 10% of the stars in the galaxy are suitable for life in terms of the presence of heavy elements, distance from supernovae and fairly stable in structure.

f i = Probability of development before the emergence of intelligence

Rated by Drake as 0.01.

f c = The share of civilizations that have the ability and desire to establish contact.

Rated by Drake as 0.01.

L = The life expectancy of a civilization during which it attempts to establish contact.

Drake's estimate is 10,000 years. In an article in Scientific American, Michael Shemmer appreciated L in 420 years, based on the example of sixty historical civilizations. Using statistics from "modern" civilizations, he got 304 years. However, the fall of civilizations, as a rule, was not accompanied by a complete loss of technology, which prevents them from being considered separate in the sense of the Drake equation. At the same time, the absence of interstellar communication methods also allows us to declare this period zero. Magnitude L can be counted from the creation of radio astronomy in 1938 to the present day. In 2008, therefore, L at least 70 years old. Such an estimate, however, is meaningless - 70 years is the minimum, in the absence of any guesses about the maximum. 10,000 years is still the most popular value. R= 7/year, f p = 0.5, n e = 2, f l = 0.33, f i = 0.01, f c = 0.01, and L= 10000 years

We get:

N= 7 × 0.5 × 2 × 0.33 × 0.01 × 0.01 × 10000 = 2.3

Criticism

Since only one planet is currently known to support intelligent life, most of the parameters in the Drake equation are determined by guesswork. However, the presence of life on Earth makes the hypothesis of the existence of extraterrestrial life at least possible, if not probable. In 2003, science fiction writer Michael Crichton said at a lecture at Caltech: “To be precise, the Drake equation is completely meaningless and has nothing to do with science. I take the view that science can only create testable hypotheses. The Drake equation cannot be verified and therefore I cannot classify SETI as being like a religion, it cannot be falsified."

We also note that the experiments are light years from the Sun, a civilization using a certain part of the radio range for communication.”

One answer to criticism of the Drake equation is that, even without providing exact numbers, the equation nevertheless provoked serious discussions in astrophysics, biology, geology and made it possible to allocate significant sums for the development of astronomy, focusing attention on the practical aspects of the search.

Alexander L. Zaitsev drew attention to the fact that having the opportunity to establish contact and establishing it are two different things. Humanity is able to detect radio signals from nearby stars, but does not make regular, targeted attempts to transmit its messages. Zaitsev proposed introducing the METI factor, which determines the proportion of civilizations that purposefully send signals.

The Drake Equation in Culture

The Drake Equation is mentioned in Episode 20 of Season 2 of the American comedy series The Big Bang Theory by Howard Wolowitz to prove that their group has a chance of meeting girls at a bar.
There are mentions of him in the famous comic strip http://www.xkcd.ru/384/