# Is it true that there are 400 thousand years left before the meeting with aliens

(ORDO NEWS) — Chinese astronomers have tried to estimate how many extraterrestrial civilizations there may be in the Galaxy and how soon we can expect contact with them. Some media hastened to declare that 400 millennia remained before the meeting with extraterrestrial intelligence.

Over the entire history of our Galaxy, about a hundred civilizations could have arisen in it – according to pessimistic estimates. And according to optimistic – more than 40 thousand. True, contact with brothers in mind will have to wait so long that it may not take place at all.

Such a conclusion is made in a scientific article published in the prestigious The Astrophysical Journal by a duo of astronomers from Beijing Normal University.

But how is it possible to calculate the number of planets inhabited by intelligent beings, if we know only one – our own? Let’s see how such assessments are made and whether they can be trusted.

### An equation with six unknowns

What do we need to know to calculate the number of civilizations in the galaxy? The list is quite extensive.

1. How many stars are there in the Galaxy?

2. What proportion of stars have at least some planets?

3. How many habitable planets are there in an average planetary system?

4. What is the probability that life will actually originate on a habitable planet?

5. What is the probability that life will become intelligent?

6. How long does an average civilization live (in fractions of the lifetime of a star)?

The answer to each of these questions is some number. Multiplying all these numbers, we get the coveted number of civilizations. This is the famous Drake formula , proposed by Frank Drake in the early 1960s. We will not write it exactly as a formula: we hope the reader already imagines the multiplication of six numbers.

The vast majority of works on the topic of extraterrestrial civilizations use this formula in one way or another. Often some of its members are combined with each other, sometimes new multipliers are added, but the essence remains the same. Find out six or so numbers and count the civilizations. There remains a trifle: to find out these same numbers.

However, this list is like a bad philosophical work: the further, the more incomprehensible.

The stars in the Galaxy have been counted, albeit with an accuracy of up to an order of magnitude: there are hundreds of billions of them. The number of planets is a more difficult question. We know about 5 thousand worlds, but the vast majority of planetary systems have probably not yet been discovered.

Some are too far from the Earth, others are unsuccessfully oriented in space, others we have not observed long enough and carefully.

So, when counting all the planets in the Galaxy, it is necessary, to paraphrase the ancient Romans, “to portray by the claws of a lion.” With all the caveats, most experts believe that the number of planets is comparable to the number of stars.

Earth-like worlds located in the habitable zone of their luminaries can be considered suitable for life. In other words, where it is neither too hot nor too cold for liquid water to exist.

Counting them is even more difficult than exoplanets in general. Less facts, more speculation. But still, there are at least some reasonable estimates. According to one recent study , potentially habitable worlds occur more often than once per ten stars, but less than twice per star.

As for the other members of the Drake formula, it’s just right to guess on the coffee grounds. Astronomers, especially those who work at night, love coffee. But the offer to tell fortunes by the stars may be offended: not astrologers.

But seriously, we only know of one habitable planet and only one intelligent species. In what we are typical, and in what we are unique – God knows. And even then, science still has not quite figured out how it happened that our planet acquired a biosphere, and our species – consciousness.

And to predict how many centuries or millennia a reasonable person with his not very reasonable behavior will still exist is an extremely fascinating occupation, but hardly meaningful.

It turns out that the last three terms in the Drake formula are evaluated by the “poke method”. If you wish, you can choose them so that the Galaxy is full of intelligence, or such as to leave us alone.

Or take a whole range of values, from “reasonably optimistic” to “reasonably pessimistic” according to the scientist’s left heel, and see what happens. This is exactly what the authors of a recent study did.

### How many of them, where are they being driven

Let’s take a closer look at their calculations. The “astrophysical” terms of the Drake formula (that is, the first three numbers from our list) were estimated by scientists based on the latest theoretical models and observational data. Without dwelling on the details, we indicate the result.

According to researchers, 34% of F, G, K class stars and 16% of M class luminaries should have potentially habitable planets. What does this mean? Stars are divided into spectral classes O, B, A, F, G, K, M (from hot to cold).

It is believed that the hottest luminaries of classes O, B, A have almost never formed Earth-like planets. Therefore, the authors excluded them from consideration.

The Sun belongs to class G. Classes F and K are, respectively, slightly hotter and slightly colder than the Sun. The class M includes dim and cold red dwarfs, which make up the majority in the Galaxy.

The next question is: what is the probability that a civilization will develop on a habitable planet (we have points 4 and 5 taken together)?

The authors designated this probability f c and honestly admitted that they had no idea how to estimate it (and who has?). After contemplating the ceiling, they covered three orders of magnitude using values ​​of 0.1%, 0.01%, and 0.001%.

Further, the authors asked the question: how many civilizations ready for contact have managed to emerge in the Galaxy today (regardless of whether they are still alive or have long since turned to dust)?

This question is related to the evolution of stars. For most of the life of the star, hydrogen serves as fuel for it, which turns into helium in thermonuclear reactions. According to experts, such a star resides on the main sequence (MS) of the Hertzsprung-Russell diagram.

This is not only the longest, but also the most peaceful period in the life of the luminary. It is natural to expect that a civilization will arise no earlier than the star enters the main sequence, and will die no later than the luminary leaves it.

But what part of the stay on the GP must pass in order for a civilization to arise? In the case of the Sun, the answer is known – 46%. After consulting with the left heel and with the full support of the right, the authors considered two more values: 25% and 75%. Scientists have designated this parameter F.

So, there are three probabilities of the emergence of civilization f c (0.1%, 0.01% and 0.001%) and three periods of “reason” F (25%, 46% and 75% of the time the star stays on the main sequence). There are nine possible combinations in total.

For the most optimistic option ( f c = 0.1%, F = 25%), the authors got about 43 thousand civilizations that have ever existed. For the most pessimistic ( f c = 0.001%, F = 75%) – a little more than a hundred pieces.

### Is the subscriber unavailable?

But creating a civilization is not enough, it must be preserved (the stalker might say, adjusting his respirator). And you still need to maintain a willingness to contact. At least in the form of an exchange of radio transmissions or other signals propagating at the speed of light.

Strictly speaking, the period of interstellar sociability can be much less than the lifetime of a civilization. In our country, for example, it began quite recently and may be about to end if humanity plunges headlong into some virtual “metaverses”.

It is necessary to take into account the distance between the “subscribers”. The diameter of the disk of the Galaxy is about 100 thousand light years. As long as the message travels from the planet Pluh to the planet Kluh, anything can happen.

Let’s say the ploppers pelt each other with pandemonium chloride in the name of goodness and plopocracy. And on Klyukha, the antenna will be dismantled, accusing it of an excessive carbon footprint and microaggression. In general, the closer to each other, the more likely it is to have time to chat or at least catch the signal of a neighbor.

How many years does humanity need to listen to the Universe in order to catch at least one interstellar hello? To find out, scientists played the Creator, though only within the framework of a computer model. Time after time, they lit the stars (hoping that someone needed it), placing habitable planets at random points in the Galaxy.

The results were very uncertain. When the authors write that in the most optimistic case ( f c = 0.1%, F = 25%), the waiting time will be 0.3 -0.298 + 0.6 million years, it is somehow embarrassing to say “three hundred thousand”.

The error accumulated due to all random factors is greater than the number itself. But let’s be optimistic to the end and take the low point of this range: 0.3 – 0.298 = 0.002 million years. That is, it remains to wait for contact for some two millennia. A real trifle, the inhabitants of Rome and Samarkand will confirm.

What about the most pessimistic option ( f c = 0.001%, F = 75%)? Well, then the contact will have to wait 50 -49.6 +250 million years. Waiting 50 million years is very scary (dinosaurs died out 66 million years ago).

Perhaps that is why some observers faltered and took the most optimistic point of the pessimistic range: 50 – 49.6 = 0.4 million years, or 400 millennia. This figure also hit the headlines of the mainstream media, whose journalists did not have time to really understand what it was all about.

### In the dry matter

So, what do we end up with a goose (or, out of respect for astronomers, with Cygnus, it is still a constellation)? Scientists have compiled and put into the computer model a lot of good astronomical data. This is how the first terms of the Drake formula were determined.

But no one knows anything about the last members. Therefore, here the input numbers were chosen according to the principle “this seems to sound plausible, but let’s take less and more.” Let’s add a random number generator (and how without it, we don’t know exactly where inhabited planets are located, even if they exist).

As a result, we got some output figures, and even with a huge spread. If it seems to you that with the same success these figures could be completely different, then it doesn’t seem to you. So what is the use of this mind game and what does science have to do with it?

Many astronomers consider this question rhetorical and bypass the problem of extraterrestrial civilizations in seven parsecs. Many, but not all. After all, curiosity is our natural trait. It is very difficult not to at least try to figure out, “and how many of them are there, if any.”

Moreover, scientists and journalists will definitely ask this question to scientists. And if astronomers refuse to answer, people will go to some ufologists for an answer and listen to fairy tales about the planet Nibiru.

It is better to look for an answer with all scientific rigor, honestly saying where the facts are, and where the estimates are on the fingers. And if later it turns into another “scientists have proven”, then this is not the fault of the scientists.

And, finally, such studies have another aspect. Philosophical, if you will. The results can hardly be called reliable, but they are certainly symbolic.

Even in the most optimistic version, it turned out that contact with another civilization would have to wait 2 thousand years.

And, no matter how the inhabitants of individual cities grin, this is about a third of written history. The notorious 400 millennia exceed the lifetime of the species Homo sapiens , and several million years – and the genus Homo .

It is naive to believe that astronomical articles will teach people to be more careful with each other. But still I want to say: we, humanity, are alone at home. In the middle of a vast universe, silent for a very, very long time. On the scale of our lives and deeds – forever. Perhaps we should remember this.

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