Is there life in human-explored space? Is there life on other planets? Difficult, but possible

People have always wondered whether life exists on other planets. And while the authors of famous books and blockbuster directors fantasized to their heart's content on this topic, creating humanoids, Martians and aliens, scientists experimentally looked for any, even the weakest, signs of interplanetary life.

Numerous studies, theories and experiments have shown that life exists beyond the Earth. The simplest bacteria were found in the debris of meteorites that fell to the ground. The bacteria found are similar in structure to those on Earth; they can grow and multiply even in hostile conditions. However, with the solution to the question of the existence of extraterrestrial life, the next question arises - where do these bacteria come from?

Three main hypotheses about life in space

1. Bacteria rushed to Earth from distant planet or even from another star system. To many, such a theory seems to be the fruit of a rich imagination. However, one cannot refute the possibility that such bacteria have high adaptability to a hostile foreign environment. Organisms are known that are able to exist in conditions high temperatures, as well as those that can be in “sleep” mode for many years. For example, scientists found bacteria that were still viable in the tombs of the pharaohs.

2. Bacteria flew away from Earth during the origin of life. At a time when there were no mammals, reptiles or even primitive fish, bacteria could rise along with the evaporation of water from land and end up in space. Already in outer space bacteria have adapted and learned to process energy, thus obtaining food for themselves.

3. Finally, terrestrial bacteria could be carried into space with the help of ships that were designed by man himself and on which he makes his risky space travels. In an unfavorable environment (weightlessness, high radiation, oxygen-free vacuum), bacteria could mutate in order to adapt and survive.

All these hypotheses have every right to exist. However, it is worth considering whether this is so good for humanity. After all, if mutated or hostile microorganisms fall on the ground, they can infect a person who does not have a stable immunity to this type of bacteria. Our body simply does not have time to adapt and develop antibodies against space guests.

The publishing house "Peter" published the book "The Great Space Journey". No, it has nothing to do with the Soviet film of the same name - the book is based on a course at Princeton University, which was taught to students humanitarian specialties famous astrophysicists Neil deGrasse Tyson, Michael Strauss and John Richard Gott. The professors’ task was to talk about their science in a way that would be understandable to non-specialists.

Our friends from the “Open Laboratory” project, an international educational event to test scientific literacy, which this year will take place on February 10, took part in the publication of the book in Russian.

We present to your attention an excerpt from the book - in it Neil deGrasse Tyson talks about how the search for life in the Galaxy is going on and what the Drake equation is.

Neil deGrasse Tyson

Astrophysicist

We are living beings, so we are especially interested in life in the Universe. If we look around the Universe and pay attention to whether a particular star has planets and whether they are suitable for life, then it is reasonable to formulate questions based on ideas about the (terrestrial) living matter known to us. All living things seem to share some set of common characteristics.

Firstly, any living being known to us needs liquid water. Secondly, life is about energy consumption. We have metabolism, it is a chemical phenomenon. And, most interestingly, life reproduces itself.

I will focus on the first sign, since water can be detected using astrophysical instruments. We just need to find liquid water in the Universe. Ever since we were read the story of Goldilocks, we know (and agree) that objects and substances can be “too cold,” “too hot,” and “just right.”

Note lane

In English-language literature, the inhabited region is often called the “Goldilocks Zone.” This name refers to English fairy tale"Goldilocks and the Three Bears", we know it as "The Three Bears".

Let's take the Sun, for example. It is known that it has a certain luminosity. The closer to the Sun, the hotter it becomes, the further away, the colder. Let's say liquid water is needed for life. If we take water and get too close to the Sun, the water will evaporate. If we move too far away, it will freeze.

Thus, it is logical to assume that there is a certain set of orbits, being in one of which the planet will stably contain liquid water. Closer to the Sun is steam, further from the Sun is ice, and between them is liquid water.

This area was called the “habitable zone.” This concept has played an important role in scientific thinking since the 1960s, when it was first formulated. For different stars, depending on their luminosity, the size of the habitable zone will differ, and there is reason for thought here.

Frank Drake developed this concept a little and came up with the so-called Drake equation. This equation is not similar to those described by Newton's laws. Rather, it allows us to assess the extent of our ignorance about the prevalence of intelligent life in the Universe.

Before I tell you about the Drake Equation, I'll let you know one thing: Based on everything we know about life, it is believed that life requires a planet. It must be a planet orbiting a star. First, a star must appear, a planet must appear near it, and then (given how slowly life on Earth develops) billions of years are needed for evolution to lead to the emergence of intelligent beings. Therefore, the star must be long-lived.

Not all stars are like this. Some do not have time to reach a billion years, and can burn out in just 100 million years.

The most massive stars die in just 10 million years - and intelligent creatures living on a planet near such a star have practically nothing to count on, if the case of Earth is any indication. We need a long-lived star and a planet, but not just any planet, but one that rotates in the habitable zone of this star.

So, it is known that we must look for a long-lived star in whose habitable zone there is a planet, and a planet on which life arose. Intelligent life. For most of the Earth's history, powerful microorganisms - cyanobacteria - roughly reshaped its atmosphere to suit them.

Today we complain that man pollutes environment, our activities create ozone holes and accumulate greenhouse gases such as CO2. But our impact simply pales in comparison to what cyanobacteria did to the Earth's atmosphere 3 billion years ago. At that time, the Earth's atmosphere was rich in carbon dioxide - and everything was fine. Then cyanobacteria appeared, gobbled up all the CO2 and saturated the atmosphere with oxygen, completely changing it chemical composition and balance. The Earth's atmosphere was filled with oxygen, and carbon dioxide There's almost nothing left in it.

In fact, oxygen is poisonous to many anaerobic organisms of the period. Carbon dioxide is a greenhouse gas. When its reserves were depleted, the greenhouse effect weakened, and the Earth began to rapidly become colder.

If there had been a Green Party back then, its activists might have protested: “Stop oxygen pollution! You are poisoning the Earth! - after all, changes were coming.

The earth cooled and froze completely several times. Meanwhile, the Sun slowly but surely burned up, over billions of years its luminosity increased and the periods called “Snowball Earth” ceased. Eventually, thanks to atmospheric oxygen, a variety of animals arose, including humans. Not all changes are uniquely detrimental to all organisms.

We worry that the next asteroid will end us. I'm telling you, it will end. No one knows when, but it will happen, and it will be a difficult day for the Earth.

The last time Earth experienced a major asteroid impact (65 million years ago), dinosaurs disappeared from the face of the planet. Our mammalian ancestors, the size of today's rodents, were already scurrying about in the undergrowth. For the royal tyrannosaurus and other terrible predators, this small fry was enough for literally one bite. But after the collision of the Earth with an asteroid, there was not a wet spot left of the royal tyrannosaurs, and mammals were able to evolve, turning into quite representative creatures.

Note scientific ed.

Although the impact theory of dinosaur extinction is popular among astronomers and the general public, paleontologists are quite skeptical about it.

These events triggered new story, which led to the emergence modern culture and society: we got a start in life, and at the same time nature saved us from ferocious dinosaurs. Therefore, I try to interpret changes on Earth in a more holistic way.

The moral of the story is: if we want to make contact with the inhabitants of a planet suitable for life, then the presence alien life as such is not enough. We are interested in intelligent life. Even more. Isaac Newton was intelligent, but it was impossible to communicate with him from the other end of the Galaxy. In Newton's time there was no technology that would have allowed him to send signals into space. The intelligent life we ​​are looking for must have the necessary technologies in the era in which our observations occur.

In other words, if a civilization is 1000 light years away from us, then its representatives should have sent a signal 1000 years ago - and only now will it reach us.

Now let's assume that the technology itself has the potential to be abused. If certain technologies fall into the hands of ignorant or irresponsible people, then such technologies can end us much more surely than any natural disaster. How long can it take before we self-destruct due to such a fatal oversight? Perhaps only 100 years.

If we look around the Galaxy, only with great luck will we find a planet in whose five-billion-year history there is just such a century. Therefore, the likelihood of finding space pen pals in this way is indeed very small.

Frank Drake took into account all these arguments and based on them he derived his equation. Thus began the search for extraterrestrial intelligence - the SETI project. Drake wanted to estimate the number of contactable civilizations that we can contact now: N c.

To do this, he included several stages of division into the equation, and each member of the equation is an independent evaluation indicator, taken on the basis of modern astrophysical data: N c = N s× f HP × f L× f i × f c×( L c/age of the Galaxy), where:

N c is the number of civilizations ready for contact that we can observe in the Galaxy today;

N s is the number of stars in the Galaxy (about 300 billion);

f HP is the fraction of stars in whose habitable zone a planet suitable for life rotates (~0.006);

f L is the proportion of planets from this number where life develops (the value is unknown, but probably close to 1);

f i is the proportion of planets from this number where intelligent life develops (the value is unknown, but probably quite small);

f c is the proportion of planets inhabited by intelligent beings whose level of technological development allows interstellar contact (the value is unknown, but probably close to 1);

L c- average term the existence of a civilization capable of contact (the magnitude is unknown, but probably small compared to the age of the Galaxy);

and the age of the Galaxy is about 10 billion years.

Let's start with the number of stars in the Milky Way galaxy, there are about 300 billion of them. Since not every star in the Galaxy is suitable for life, this number must be multiplied by a fraction - the number of long-lived stars (that burn long enough for life to form near them), as well as those with a planet in the habitable zone ( f HP). Thus, it decreases total number planets you can search on intelligent life.

As of this writing, more than 3,000 exoplanets have been confirmed to exist through a heroic effort that has examined more than 150,000 stars. It was a real revolution.

It turns out that stars that have planets - common occurrence, and many stars have several planets.

Among such stars, we are looking for those whose planets are lucky enough to be in the habitable zone. Exoplanets can be found by the gravitational effect that the planet exerts on its parent star. As a result of the planet's gravity, the star's angular velocity fluctuates slightly, and this phenomenon can be detected.

How closer planet, the more noticeably the angular velocity of a star fluctuates under the influence of its gravity and the easier it is to detect it. Therefore, it is relatively easy to find planets orbiting close to their star, but such planets are too hot and there cannot be liquid water there - they do not fit into the Drake equation.

The largest project to search for exoplanets was carried out using space telescope Kepler by NASA. Kepler searches for exoplanets by detecting the tiny dip in a star's brightness as a planet passes across the star's disk and crosses its line of sight. This phenomenon is called “transit”.

Jupiter's radius is 10% of the solar radius. Square cross section Jupiter ( πr squared) - 1% of the same area of ​​the Sun. So when a Jupiter-sized planet passes the disk of a Sun-like star, that star's brightness temporarily drops by 1%. An Earth-sized planet whose radius is 0.01% of the Sun's radius will reduce the brightness of such a star by 0.01%.

The Kepler telescope is sharp enough to detect even such minor dimming of a star, because it was designed primarily to search for Earth-like planets, but such accuracy is almost the limit of its capabilities.

Many planets discovered by Kepler are comparable in size to Jupiter or Neptune (and such planets, as far as we know, are unsuitable for life), but there are also smaller ones, almost the size of Earth...

The introductory passage, as usual, should end at the very interesting place. We hope you decide to read the entire book!

Scientists have not yet been able to fully prove the existence of extraterrestrial life, but they have managed to discover several theories that confirm that we are not at all alone in the Universe. Moreover, planets that are carriers of extraterrestrial life can be located even in our solar system, we just haven’t learned to recognize specific alien life yet. Below is a selection of the most impressive and realistic theories proving the existence of aliens.

"Extremophiles" - terrestrial organisms capable of surviving in extreme conditions

As you know, on our planet there are microorganisms and more developed creatures that can survive in places with ultra-high or ultra-low temperatures. Such creatures are called “extremophiles”. Perhaps it is they who inhabit other planets, the conditions of which seem very acceptable to them for life.

Scientists have found animals and fish living quietly in the craters of volcanoes, both on land and underwater. Some microorganisms can even live in a vacuum, for example, “tardigrades”.

They were specially launched into space and left unprotected from its vacuum. In this unfavorable environment, they not only survived, but also felt great. Thus, we can confidently say that even earthly life can exist in outer space.

On other planets there are the initial substances that gave rise to life on Earth

Earthly life arose from a chemical reaction. This reaction gradually formed DNA and cell membranes. As you know, everything in our world can be called a chemical reaction, and even the state of falling in love.

The primary reactions on our planet could have originated in its atmosphere or cooled ocean waters. They required elements such as nucleic acids, lipids, carbohydrates, and proteins. Scientists have discovered similar elements on other planets of the solar system, as well as on more distant ones from us. So, primary chemical reaction, the origin of life, could have occurred not only on our planet.

The number of “exoplanets” is rapidly increasing

Previously, astronomers could not notice all space objects, especially if they were located outside our planetary system. With the advent modern technologies Research equipment was continuously improved and developed. Now we can notice not only supermassive planets, but also small objects similar in size to our Earth. Over the past decade, astronomers have discovered hundreds of planets similar to our Earth, which are now commonly called “exoplanets.” It is likely that some of them are carriers of unique life forms.

Earth's living organisms are too diverse and multifaceted

The development of earthly life did not proceed smoothly. The creatures of our planet had to adapt to climate changes, disasters, natural disasters. Gradually they learned to overcome life's obstacles, fight illnesses, and provide themselves with the necessities of life. Many species became extinct because they could not adapt to new conditions. Thus, if everything really happened as described above, then life on Earth should not be so diverse. Only the hardiest and most persistent organisms were supposed to survive on it. Why do we now see such a variety of life forms?

We now see an incredible diversity of life on Earth. How could such diversity arise in a relatively short (from a geological point of view) period of time? Perhaps some life forms originated not on our planet, but, for example, on the satellite of Saturn. Afterwards they were brought to Earth, where they “took root” and began to evolve along with the earth’s inhabitants.

Mysteries of our planet

To this day, scientists cannot come to a common conclusion regarding what gave rise to life on Earth. As you know, initially this planet was completely unsuitable for life, and this period comparable to the beginning of the development of earthly life forms. How could the simplest microorganisms survive on our planet, which at that time had a methane atmosphere, boiling lava on the surface and other unfavorable factors?

There is an assumption that elementary life did not originate on our Earth, but somewhere in the solar system. Afterwards she was brought to Earth by someone who fell on her cosmic body, for example, an asteroid. This asteroid fell precisely at the moment when the Earth’s surface had already cooled and became relatively suitable for life. This body could not carry all the microorganisms. Partially they remained somewhere where they originated. Perhaps they also developed and evolved.

“Bodies of water” are very common in our solar system.

If we believe that earthly life originated in water, then it could similarly originate not only on Earth. For example, it was recently proven that in the past on Mars there were various bodies of water filled with a kind of liquid. These were rivers, oceans, ultra-deep lakes, in which life could also develop. Maybe, Martian life still preserved, but moved to another world or to another planet. At least that explains why we couldn't find her.

Evolution theory

Skeptics who believe we will never find alien life back up their arguments with Fermi's theory. This theory is contradicted by the theory of evolution. It is known from it that living beings have the ability to adapt and change. Darwin once created the theory of evolution, but he probably did not think that it could prove the existence of extraterrestrial life forms.

Some primitive life forms may have somehow found their way into space. There they continued to evolve - adapt to new conditions, adjust to them, and change. It is likely that they later developed to our level, and maybe more.

Photos from open sources

When describing space, the epithets “lifeless” and “dead” are often added. Cold, radiation, vacuum - what kind of life could there be in space? In August 2014, Russian cosmonauts from the ISS reported amazing news: even under these conditions, living organisms can exist!

Question of questions

Scientists have long been worried: is space really deadly for all living things? The interest is not idle. Future spacecraft will be equipped with living and working areas that protect people from dangers external environment. Do plant seeds and simple organisms need the same protection, or are they able to withstand the “strike of space”?

In 2008, during an experiment, bacteria were left outside the ISS. After 533 days they were returned to Earth. Some of the bacteria came to life and began to multiply. From bacteria, scientists moved on to more complex organisms. It turned out that lichens and tardigrades (microscopic invertebrates) survive in outer space. The subjects hibernated and when conditions changed to favorable ones, they awoke to life.

The trick is that the person had nothing to do with the “experiment” of 2014.

spring-cleaning

Every vehicle flying in space is a source of dirt. Engine operation, air emissions from the airlock chamber when the cosmonauts exit open space– small particles fly in a swarm around the ship and settle on it. Therefore, from time to time, the inhabitants of the station go outside and clean the surface, polish and clean the windows. During the “cleaning”, samples are taken from outer surface stations and are carefully studied.

This time, among the particles of debris on the casing, samples of plankton that live on Earth in upper layers ocean. Initially, Roscosmos did not believe the cosmonauts’ message. Indeed, explain how residents water element ended up on the outer surface of the station, no one could.

Versions

But a fact is a fact and requires explanation. The version that microorganisms flew to the ISS from Earth disappears immediately. At Baikonur, where the ships launch, there is no marine plankton. The distance from the cosmodrome to the nearest sea coast is hundreds of kilometers. Are there really any ascendants? air currents, capable of lifting plankton to a height of more than 450 km? Scientists are not yet ready for this. It is easier to assume that microorganisms are with the American cargo modules Curiosity and Viking. But this version also has its flaws.

Photos from open sources

The main thing

However, no matter how the “free riders” got to the ISS, they got there without human help and completely alive, albeit in “anabiosis.” This once again confirms that neither cosmic radiation nor low temperatures, neither a vacuum nor the absence of oxygen and pressure can absolutely unconditionally kill life. It is in space.

Supporters of bringing life to Earth from the outside have received one more fact to add to their arguments. If microorganisms can quite safely “travel” through space on the hull of a ship, then what prevents them from doing the same on the surface of meteorites and comets?

There is another nuance that environmentalists talk about in a low voice. For many decades, man has been sending his messengers into space. Space probes and the devices landed on the surface of the Moon, Mars, and Venus. It is quite possible that man has unwittingly brought life to them and the astronaut who sets foot on the surface of these planets will not be the first earthling there. But who will meet him there is the plot for a science fiction horror film.

Is humanity alone in the Universe? This question concerns both ordinary citizens and the majority of scientists on the planet. If not alone, then where are they? Why don't aliens come into direct contact with the inhabitants of Earth?

One day the physicist Enrico wondered an unusual question: Where is everyone? Or, more precisely, where are all the aliens, why are we not seeing traces of extraterrestrial intelligent life? This is how the Fermi paradox arose.

When we estimate the size of the Universe, the number of Earth-like planets, and a number of other variables included in the equation of Dr. Frank Drake, the father of radio astronomy and founder of the SETI project to search for extraterrestrial civilizations, it becomes clear that there must be tens of thousands or more extraterrestrial civilizations in a single galaxy. And since the galaxy is about 10 billion years old, intelligent worlds have had plenty of time to communicate with each other.

Back in 1961, Drake calculated an unusual formula to determine the number of civilizations in the galaxy with which contact is possible. The formula was called the Drake Equation. Using it, the scientist and his colleagues calculated total There were 10,000 civilizations representing intelligent life.

So if aliens statistically exist, where are they? Why can't we detect them? And the reasons are as follows.

The earth is special

The Unique Earth hypothesis suggests that the chain of events that created life on our planet was so complex that only a biologically perfect vortex could have created it elsewhere. Although there may be planets similar to Earth, none of them may contain exactly the necessary conditions for the development of life. In other words, we haven't encountered any aliens because they simply don't exist, or they are so few and far between that contact is highly unlikely.

The main factor that makes the Earth hospitable to life is its a long period relatively stable climatic conditions, due to the unique orbit and position of the planet. If it weren't for our precise position relative to the Sun or Moon, the planet would be too hot or cold, not enough oxygen, and conditions too unstable to support life beyond bacteria.

Paleontologist Peter Ward and astronomer Donald Brownlee were the first to present the unusual hypothesis of a unique Earth. And although 15 years have passed since the birth of the hypothesis, and we have found a lot of Earth-like planets, scientists are still confident that the chances of life existing on these worlds are extremely low.

Every intelligent life has a stumbling block

According to the Great Filter theory, alien life does exist, but intelligent life is unable to advance technologically far enough to invent space communications long-range or space travel. Although our modern spaceships, satellites and radios indicate that we are close to the point of no return, perhaps a barrier or disaster will inevitably await us, which will either destroy us or lead to the degradation of technology.

We know that catastrophes periodically visit Earth, so it is possible that these same events destroy worlds everywhere, sending intelligent life back to stone Age, before the technology can adequately develop. Or perhaps we will destroy ourselves in the process nuclear war. Whatever the filter, only bad news awaits us. Not only will we not be able to contact other astronauts, but we will probably die.

There are also bright side this theory. Some believe that we are the first to pass through this unusual filter, so we are likely to become the dominant race in space. And this is good.

They left the universe

According to John Smart's futuristic supremacy hypothesis, intelligent extraterrestrial life once existed in our universe but became so advanced that it moved into best places. To be more precise, the aliens have evolved so much that they have stopped looking at the outer space and have focused on the inner space.

The concept can be compared to the miniaturization we see in computers. They were originally conceived as huge technologies that filled entire rooms, but then became smaller (even pocket-sized) while simultaneously developing in complexity and power. For supremacy theorists, intelligent life evolves in much the same way, constantly working toward denser and effective use space, time, energy and matter. Eventually, we will live and work on the nanoscale until we become so small that we create and inhabit a black hole outside of this space-time continuum.

According to Smart and others, black holes are the final destination. They will allow ideal computing and learning, time travel, energy extraction and more. Civilizations that fail to achieve this are doomed.

Other cosmic beings can also work on their own transcendence, or transcendence. In addition, following Moore's law, these creatures are more likely to achieve superiority before they master space.

The earth is not as big as we think

It might be too proud to believe that aliens are interested in us or our planet. There may be more interesting inhabited worlds, and intelligent beings would rather spend their time exploring them than on Earth. This theory is completely opposite to the unique Earth theory: there is nothing special about our planet at all.

Capable of traveling or communicating across light years, it would hardly care about our existence - we don’t talk to flies. In addition, she will definitely have her own luxurious technologies, so they will have no use for our pitiful resources. If they need minerals or other elements, there are plenty of them in space without Earth.

Moreover, no matter how intelligent the creatures are, traveling by light years- no easy feat. What are the chances that they will expend their energy to visit us when there are 8.8 billion Earth-like planets around Milky Way? Followers of this theory argue that thinking that the Earth is a tasty morsel is suffering from the same geocentrism that led to Galileo's misguided persecution.

We live in virtual reality

Perhaps one of the most difficult-to-understand explanations for the Fermi Paradox is the planetarium hypothesis. Our world is in the form of a “planetarium in virtual reality, created to give us the unusual illusion that the Universe is empty." We have not discovered any extraterrestrial civilizations because these extraterrestrial civilizations They didn't include it in the program.

The foundations of this theory are rooted in the ideas of Descartes, who asked the question: “How can we know that the world around us is real if we are just a brain in a vat that thinks it lives in the real world?”

Instead of putting brains in a vat, modern proponents of these ideas think that we are living in a computer simulation created by advanced aliens. These aliens use enough energy to manipulate matter and energy on a galactic scale. Why do they want to watch us like ants? Maybe just for fun, or maybe just to make sure they can.

You will be surprised, but philosophers and physicists take this very seriously. unusual idea. They say we'd rather be artificial intelligence in a fabricated world than with a mind of their own. In addition, we are more likely to detect a simulation because we can accurately detect a failure in the system or design an adequate experiment to confirm the theory.

We live in the outer space

Although intelligent alien life may exist, our planets may be too far apart for communications to be worthwhile or possible. The Earth may be so far from other inhabited worlds that we may simply not be seen. If that's not enough to make you feel alone, some argue that most other worlds are relatively close to each other and interacting while we are left out of this interesting pan-galactic party.

The roots of this idea go back to mathematical theory, known as percolation, which describes how things come together in a random environment. Based on percolation theory, the universe naturally formed in large clusters and several smaller regions. Other intelligent beings live in large concentrations, and the Earth is isolated.

Instead of trying to make contact with these creatures, intelligent life, some like Stephen Hawking believe that we should lie low. says that if we receive an extraterrestrial signal, we need to be extremely careful not to respond until we have evolved. Otherwise, we may repeat the fate of the Native Americans after the arrival of Columbus.

We haven't detected their signals yet

Scientists like Frank Drake and Carl Sagan argue that “absence of evidence is not evidence of the absence of aliens.” The hunt for extraterrestrial life is significantly limited by the lack of government funding needed to enable scientists to afford the vast arsenal of tools and resources to track aliens. Historically, the Search for Extraterrestrial Intelligence (SETI) program has relied only on rented radio telescopes and other equipment that could be used for a limited time. These obstacles have made real progress nearly impossible.

There are also good news for those who think that contact with extraterrestrial life — good idea. The Allen Telescope Array radio telescope, designed specifically to search for extraterrestrial intelligent life, began operating in 2007. This giant telescope, made up of 42 individual 6-meter telescopes, was largely built by Microsoft co-founder Paul Allen. After numerous failures, he finally started making his important work. If something tries to contact Earth, he will know about it.

We can't recognize their signals

Even if other planets are hospitable to life, could creatures there evolve in a similar way to life on Earth? Maybe they are so different from us that we are unable to distinguish their signals? This is quite possible if we remember, for example, about bats that can visualize sound waves, although we only see light. Perhaps aliens and we are equipped with a fundamentally different set of senses.

As cosmologist and astrophysicist Lord Martin Rees noted, “They can look into our faces, and we simply do not recognize them. The problem is that we are looking for something that is very similar to us, has similar mathematics and technology. I suspect that life and intelligence may exist in strange forms that we cannot even imagine."

Things get even more complicated if you try to contact a highly advanced race that uses other methods of communication (neutrinos, for example, or gravitational waves), inaccessible to our understanding of technology. Likewise, our primitive radio may be nothing more than white noise to them. If aliens and humans are dissimilar, it is unlikely that we will be able to communicate with them and resolve the Fermi paradox - provided that we continue to anthropomorphize aliens and expect them to contact us.

Superorganisms are inherently suicidal

The Medea hypothesis, coined by paleontologist Peter Ward, states that humans and other superorganisms carry within them the seeds of self-destruction. In some ways, this fits well with the Great Filter theory, since it suggests that we will die before we can contact extraterrestrial civilization.

The hypothesis is named after Medea from Greek mythology who killed her children. In our case, the planet is Medea, and we are her offspring. We don't want to die, but Mother Earth demands it. Extinction is built into our biology to ensure that we are eliminated before we create complete imbalance on Earth. After humans become an incurable plague on the planet, we will do something that will guarantee our own demise.

Ward believes that almost all previous mass extinctions were caused by living organisms. For example, he blames two Snowball Earth periods millions of years ago on plants that spread so wildly that they absorbed excessive amounts of carbon dioxide. This led to global cooling and, consequently, to the death of plants. Likewise, if humans are to blame for current climate change, there is no guarantee that our own species will be able to survive.

In short, our internal suicide clock will stop long before we get a chance to communicate with aliens.

They walk among us

Sounds like Science fiction, but many people are sure that aliens live and work around us. For example, former minister Canadian Defense gave an interview in 2014, in which he claimed that there are about 80 various types alien life. Some of them, including Scandinavian blondes, look almost identical to humans. Another group, "Short Grays", are more like aliens and mostly hide from people.

Hellyer is not alone in his beliefs. Physicist Paul Davis of Arizona state university and Dr. Robert Trundle of Northern Kentucky University also believe that aliens walk among us. Such people have already resolved their Fermi paradox - aliens exist and, whether people want it or not, they are among us. You have the right to choose any of ten unusual options explanations.