"They should have at least" called "": why we have not yet met with aliens

Where are they?

This short question was asked by physicist Enrico Fermi in the early 1950s, at a dinner with several scientists. They discussed the recent spike in flying saucers and the possibility of interstellar travel by humanity or other beings. When the conversation turned to the aliens, Fermi asked: "Where are they?" The exact words have been lost for centuries; perhaps he asked, "Where is everyone?" which is just as succinct.

Despite its simplicity, this question has a rich background.

The basic idea is that by now, either we should have already discovered intelligent life in the Galaxy, or it should have come to visit us.

Since neither one nor the other happened, I do not take into account the cases of UFO sightings. Despite the vast amount of blurry photographs, obvious forgeries and shaky videos, there has never been a single definitive proof that aliens have ever visited us. Deal with it., asking about where the aliens are is reasonable.

Suppose that in order for aliens to knock on our door, their circumstances must be similar to ours: a star like the Sun, a planet like Earth, billions of years of development and evolution of life, advances in technology, then the ability to travel from star to star. How likely is all this?

To do this, we can turn to the Drake equation, named after astronomer Frank Drake. It includes all the necessary conditions for a developed life and assigns the degree of their probability. If all the conditions are correctly entered, the result will be the number of advanced civilizations in the Galaxy (where “developed” means “capable of sending signals into space”, this is how we would know about their existence).

For example, there are about 200 billion stars in the Milky Way. About 10% of them are similar to the Sun: similar mass, size, and so on. This gives us 20 billion stars to calculate. We are only now learning how planets form around other stars - the first planet orbiting a sun-like star was discovered in 1995 - but we consider it very likely that Sun-like stars have planets.

Even if we accept the insanely low probability that there are planets around other stars (say, 1%), it will still be hundreds of millions of stars with planets.

If we accept the insanely low probability that these planets will be Earth-like (again, say 1%), there will still be millions of Earth-like planets. You can continue this game, evaluating how many planets can have conditions for life, how many there is life, how many there are living beings capable of developing technologies …

Each next step in this chain is slightly less likely than the previous one, but even the most pessimistic view of this series suggests that we should not be alone in the Galaxy. Estimates of the number of alien civilizations vary greatly, literally from zero to millions.

We are alone?

Of course, this is not very happy. The lower estimate is sobering. Maybe, just maybe, we are really alone. In the entire Galaxy, in all the vast trillions of cubic light years of emptiness, our planet was the very first haven for creatures capable of reflecting on their own existence. You can be lonely in another way, and in a minute we will be convinced of this. … It’s a confusing and in some way frightening opportunity. And this is probably true.

Another possibility is that life may not be unique, but "advanced" life forms are rare.

Many books have been written on this topic, and this is an interesting topic for discussion. Probably, at a certain stage, life becomes prone to introspection and does not develop technologies at all or does not even care about them (it is very difficult to penetrate into the psychology of alien beings). And I hope that by the time you get to this point in the book, I've already made it clear that the events that destroy civilizations happen unpleasantly often in geological time frames. Maybe sooner or later every civilization is swept away by some natural event even before it could develop a sufficiently perfect way of space travel to prevent this from happening.

Actually, I don't like this answer. In a few years, we will be able to prevent collisions between the Earth and asteroids, leading to devastating consequences. We are confident that we can reliably shield ourselves from events on the Sun. Our astronomical knowledge allows us to determine which nearby stars can explode, so if we see that any of them is close to this, we can direct all efforts to get away from it. All these are fairly recent achievements that occurred in an instant compared to how long life has existed on Earth.

I cannot imagine a civilization that is smart enough to explore the skies but not advanced enough to support its own survival.

They don't take money for demand

I am also suspicious of the upper limit on the Drake equation, as if there are millions of alien civilizations in the galaxy as advanced as we are, or even more advanced. If this were true, it seems to me that we would already have clear evidence of their existence.

Remember, the Galaxy is not only vast, it is also many years old. The Milky Way is at least 12 billion years old, and the Sun is only 4.6 billion years old. years before humanity.

We know that life on Earth came about easily enough; it was born as soon as the bombing period ended and the surface of the Earth calmed down enough for life to develop. So, almost certainly, life takes root at the slightest opportunity, which, in turn, means that our galaxy should be teeming with life. Despite a series of epic and devastating disasters, life on Earth is still going on. We are intelligent, technologically advanced beings, and we went out into space. Where will we be in 100 million years?

Given that span of time and space, alien species should already be knocking on our door.

They should at least "call". Establishing communication in the vast space of space is easier than arriving. We've been sending signals into space since the 1930s. They are relatively weak, and it would be difficult for an alien creature to hear them from a distance of more than a few light years, but over time, our signals have become stronger. If we wanted to aim at a certain place, it is not difficult to focus an easily detectable radio signal on any star in the Galaxy.

The opposite is also true: any alien race with a strong desire to chat with us could do it without much effort. This is what the Search for Extraterrestrial Intelligence (SETI) project is betting on. This group of engineers and astronomers is combing the sky for RF signals. They will literally listen to see if the aliens speak. The technology is progressing so well that astronomer Seth Shostak believes that over the next two or three decades, we will be able to explore one or two interesting star systems as far as light-years from Earth. This will allow us to get closer to deciding whether we are alone or not.

The only problem with SETI is that the conversations are going to be quite lengthy. If we detect a signal from a star that is very close in galactic terms, say 1,000 light-years away, the dialogue is essentially a monologue. We would receive a signal, answer, and then wait for their response for years (this is the time it takes for our signal to reach them, and then their signal to us). While SETI is a wonderful and worthwhile endeavor (and if they find a signal, it will be one of the most important events in the history of science), we are still more accustomed to the idea of aliens coming to us. A face-to-face meeting, so to speak, assuming they have a face.

But 1000 light years is very far away (9,461,000,000,000,000 km). Quite a long trip, and yet, compared to the size of the Milky Way, it's practically under our noses.

Maybe that's why no one has come to us yet? Apparently, the distances are simply too great!

Actually, not really. Without losing the sense of scale, the journey to the stars would not have taken so long at all.

Go ahead

Suppose we humans suddenly decide to fund a space program. And to fund it on a large scale: we want to send spacecraft to other stars. This is not an easy task! The nearest star system, Alpha Centauri (which has a sun-like star worth looking at), is 41 trillion km away. The fastest space probe ever made would travel there for thousands of years, so we shouldn't expect beautiful photographs anytime soon.

However, it is the fastest space probe to date. Ideas are currently being worked out that would make it possible to build much faster unmanned space probes, even those that can move at speeds approaching light. Some of these ideas include thermonuclear energy, ion thrusters (which start slowly but accelerate continuously and develop enormous speeds over the years) and even a ship that detonates nuclear bombs behind it, imparting a powerful impulse to it, increasing its speed. This is all serious: the project is called Orion”, And developments were carried out in the 1960s. Acceleration is not smooth - a kick in a soft spot from a nuclear bomb usually does not happen - but you can develop amazing speed. Unfortunately, the Nuclear Test Ban Treaty (Chapter 4) prevents such a spacecraft from being tested. … These methods can shorten the travel time from millennia to just decades.

This might be worth doing. It is, of course, expensive. But this idea has no technological barriers, only social ones (funding, politics, etc.). Let me be more clear: with a firm intention, we could build such spaceships right now.

In less than 100 years, we could launch dozens of interstellar messengers to other stars, exploring our own neighborhood in the Galaxy.

Of course, due to the length of the flights and the construction of the fleet itself, we will not be able to inspect many “real estate objects”. There are billions and billions of stars in the Galaxy, and it is impossible to build so many spaceships. Sending one probe to one star is not economically viable. Even if our probe simply passes through the star system, orbiting the planets, and travels to the next star, it will take forever to explore the Galaxy. The space is big.

But there is a solution: self-replicating probes.

Imagine: an unmanned spacecraft from Earth arrives at the star Tau Ceti after 50 years on the road. He finds a group of minor planets and begins scientific observations. This includes something like a census - the measurement of all celestial bodies in the system, including planets, comets, satellites and asteroids. After several months of exploration, the probe will go to the next star in its roster, but before leaving, it sends a container to the most suitable iron-nickel asteroid. This container is essentially a self-starting factory.

Immediately after landing, he begins to drill an asteroid, melt metal, extract the necessary materials, and then automatically build new probes. Suppose he builds just one probe, and after several years of construction and testing, that one is sent to another star system. We now have two probes. After a few decades, they arrive at their targets, find a suitable place and reproduce again. We now have four probes and the process is repeated.

The number of robotic messengers is increasing very rapidly as it is growing exponentially. If one probe takes exactly 100 years, then by the end of the millennium we have 2 to the tenth power = 1,024 probes. After two millennia, there are already a million probes. In 3,000 years there will be more than a billion of them. Now, it's not that easy, of course.

Even a pessimistic approach shows that it will take us about 50 million years, maybe a little less, to explore every single star in the Galaxy.

Well, this is too long! And we are still very far from being able to do this. This is the most complex technology.

But wait - remember the civilization that we talked about and which is 100 million years ahead of us? With so much time, in search of life, they could easily survey all the stars in the Milky Way galaxy without exception. If they saw our warm, blue world, I suppose they would have made a mark for themselves. It is possible that they visited here 50 million years ago and did not meet with us humans (drilling the moon for a monolith in the spirit of "2001: A Space Odyssey" may not be as stupid as it seems), or maybe they haven't got here yet.

But given the timescale, this seems unlikely. It doesn't take so long to map the entire Galaxy and visit suitable planets. This is why I think the answer “millions of civilizations” in the Drake equation is wrong. We would have seen them already, or at least heard them.

According to this logic, a galaxy in the spirit of "Star Trek", which is inhabited by a wide variety of alien beings at approximately the same level of scientific and technological development, is extremely unlikely.

If the Milky Way is teeming with life, it is far more likely that civilizations would be separated by chasms millions of years apart. Some alien creatures will be more like kyu and organan (highly evolved beings in the Star Trek universe), a couple will be like us, and the rest will be nothing more than extremely primitive microbes and fungi. Another aspect of Star Trek in this assumption is Directive One: quarantine evolving alien civilizations until they develop technology for interstellar travel. It's an interesting idea, but I don't believe in it: it means that all existing alien species, without exception, will comply with it. One dissenter is enough, and the secret will disappear.

American astronomer and popularizer of science Philip Plate wrote a fascinating book about the dangers that can "fall" to Earth from space: about collisions with comets and asteroids, black holes, interplanetary viruses and bacteria, aggressive alien civilizations, the death of the Sun and even complete annihilation from quantum collapse. The author humorously describes catastrophic scenarios and examines their likelihood from the point of view of science. And also assesses the ways in which humanity can avoid sudden death.