One physicist Enrico Fermi wondered: Where is everyone? Or, more precisely, "where all the aliens?". Thus arose the Fermi paradox. When we estimate the size of the universe, the number of Earth-like planets, as well as a number of other variables (listed in the Drake equation - see. At the end of the article), it becomes clear that in one galaxy must be tens of thousands or more extraterrestrial civilizations.
And because the galaxy about 10 billion years, intelligent worlds there is enough time to communicate with each other. So if aliens exist statistically, where are they? Why can not we find them?
Earth - special
Rare Earth hypothesis suggests that the chain of events that created life on our planet was so complex that only biologically perfect whirlwind could create it elsewhere.
Although perhaps there Earth-like planets, none of them may not contain exactly the conditions necessary for the development of life. In other words, we have not met any aliens, because they simply do not, or they are so few and so far, that contact is extremely unlikely.
The main factor that makes the Earth hospitable to life, it is a long period of relatively stable climate conditions caused by a unique orbit and planetary positions. If not for our exact position relative to the Sun or the Moon, the planet would be too hot or too cold, not enough oxygen and too unstable conditions to support life outside the bacteria.
Paleontologist Peter Ward and astronomer Donald Brownlee were the first who introduced the Rare Earth hypothesis. And though it's been 15 years since the birth of the hypothesis, and we found a lot of Earth-like planets, scientists still believe that the chances of life on these worlds is extremely low.
At any intelligent life there is a stumbling block
According to the theory of the Great Filter, alien life does exist, but intelligent life is not able to advance technologically far enough to invent a cosmic connection or long-range space travel.
Although our modern spaceships, satellites and radio say that we are close to the point of no return, perhaps inevitably awaits us or crash barrier, which either destroy us, or lead to the degradation of the technology.
We know that the catastrophic natural disasters periodically visit the Earth, so it is possible that these same events destroy worlds everywhere, sending intelligent life back into the stone age, before the technology can adequately develop. Or perhaps we will destroy ourselves in a nuclear war. Whatever this filter, we are just waiting for the bad news. We are not only able to communicate with other astronauts, but also to die, probably.
There is also a bright side to this theory. Some believe that we - the first who will pass through this filter, therefore, likely to become the dominant race in outer space. And that's good.
They left the universe
According to the hypothesis of superiority futuristic John Smart, intelligent extraterrestrial life once existed in our universe, but has become so advanced that the move to a better place. To be more precise, the aliens have evolved so that they ceased to look at outer space, and focused on the domestic.
Concept can be compared to the miniaturization, which we observe in computers. Initially, they thought about how great technology that fill entire rooms, but then became smaller (up to the pocket), while simultaneously developing the complexity and power. For supporters of the theory of the superiority of intelligent life develops in much the same way, constantly working on more dense and efficient use of space, time, matter and energy.
In the end, we will live and work at the nanoscale, until we become so small that they create and settle into a black hole out of this space-time continuum.
According Smart and others, black holes - the final destination. They will allow the ideal computing and training, time travel, energy production and more. Civilization that did not reach this doomed.
Other space creatures can also work on their own superiority, or transcendence. In addition, following Moore's Law, these creatures rather achieved excellence before master the cosmos.
The Earth is not as great as we think
Perhaps it would be too proud to believe that aliens interested in us or our planet. There may be more interesting inhabited worlds and intelligent beings would rather spend their time on their research and not on Earth. This theory is completely opposite to the theory of the Earth's unique: our planet is nothing special at all.
Extraterrestrial civilization capable of traveling or to communicate in light years, is unlikely to worry about our existence - we're not talking to the flies. In addition, it will definitely be your smart technology, so our meager resources they do not need. If they need the minerals or other elements in the cosmos is full of them, and without the Earth.
In addition, no matter how intelligent beings travel light years - a difficult feat. What are the chances that they will spend their energy on something to see us when there are 8, 8 billion Earth-like planets around the Milky Way? Followers of this theory claim that think that the Earth - a tasty morsel, it suffers from the same geocentrism, which led to the erroneous persecution of Galileo.
We live in a virtual reality
Perhaps one of the most difficult to read an explanation of the Fermi paradox - a hypothesis planetarium. Our world is a form of "planetarium in the virtual reality created to give us the illusion that the universe is empty." We found no extraterrestrial civilizations because these extraterrestrials have not included 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 real world around us, if we - just a brain in a vat, who thinks that living in the real world?».
Instead of placing the brains in a vat, the modern proponents of these ideas think that we live in a computer simulation created by advanced aliens. These aliens use enough power to manipulate matter and energy on galactic scales. Why do they want to watch us like ants? Maybe, just for fun, or maybe just to make sure that they can.
You'd be surprised, but the philosophy and physics very serious about this idea. They say that we will soon find ourselves in artificial intelligence fabricated world than having their own minds. In addition, we are likely to find the simulation, as aptly observed failure in the system or develop an adequate experiment to confirm this theory.
We live in the boonies of space
Although intelligent extraterrestrial life may exist, our planet may be too far apart to communication were justified or possible. Land may be so far from other inhabited worlds, that we simply can not see.
If this is not enough to feel lonely, some argue that most of the other worlds are relatively close to each other and interact, while we are behind this pangalakticheskoy parties.
The roots of this idea go to the mathematical theory known as percolation, which describes how things are pulled together in a random environment. If we take as the basis of percolation theory, the universe is naturally generated in the form of large clusters and several smaller areas. Other intelligent beings living in large clusters, and isolated land.
Instead of trying to make contact with these beings, some like Stephen Hawking believe that we need to hide. Hawking says that if we get an extraterrestrial signal, we need to be extremely careful, not responding until gratia. Otherwise, we can repeat the fate of Native Americans after the arrival of Columbus.
We have not yet found their signals
Scientists like Frank Drake and Carl Sagan argued that the "lack of evidence - it is not evidence of absence of aliens." The hunt for extraterrestrial life significantly limited by the lack of public funding, which requires that the scientists could afford a vast arsenal of tools and resources to track aliens.
Historically, the program search for extraterrestrial intelligence (SETI) relies only on leased radio telescopes and other equipment, which can use for a limited time. These obstacles have made real progress almost impossible.
There is good news for those who think that contact with extraterrestrial life - a good idea. Radiotelescope Allen Telescope Array, designed specifically for the search for extraterrestrial life, began working in 2007.
This giant telescope, consisting of 42 individual 6-meter telescope was largely built thanks to Microsoft co-founder Paul Allen. After numerous setbacks, he finally began to make their important work. If something will try to contact the ground, he finds out about this.
We can not recognize their signals
Even if other planets hospitable to life, whether there is being developed similarly to life on Earth? Maybe they're so different from us that we can not distinguish their signals?
It is possible, if you remember, for example, about the bats that can visualize the sound waves, although we only see the light. Perhaps the aliens and we are equipped with a fundamentally different set of feelings.
As the cosmology and astrophysics, Lord Martin Rees, "they can look us in the face, and we just do not recognize them. The problem is that we are looking for something that is very similar to us, has, like mathematics and technology. I suspect that life and mind can exist in forms that we can not even imagine ».
Everything becomes even more difficult when trying to communicate with a highly race that uses other methods of communication (neutrinos, for example, or gravitational waves) that are inaccessible to our understanding of technology. Similarly our primitive radio can not be greater than a white noise for them.
If the aliens and humans are unlike, it is unlikely that we will be able to contact them and resolve the Fermi paradox - on the condition that we will continue anthropomorphization aliens and expect that they will contact us.
Superorganism suicidal inherently
Medea hypothesis invented by paleontologist Peter Ward, says that humans and other superorganism carry the seeds of self-destruction. In some ways it links well with the theory of the Great Filter, as it implies that we will die before we can contact with an extraterrestrial civilization.
Hypothesis is named after Medea from Greek mythology who killed their children. In our case the planet - it's Medea, and we are her offspring. We do not want to die, but Mother Earth requires it. Extinction is built into our biology to ensure that we eliminate before you create the sheer imbalance in the world.
Once people become incurable plague on the planet, we will do something that guarantees our own demise.
Ward believes that almost all of the previous mass extinctions were triggered by living organisms. For example, he lays the blame for the two periods of "Earth-snow", which took place millions of years ago, on plants that have spread so wildly that swallowed an excessive amount of carbon dioxide.
This has led to global cooling, and hence to plant death. Similarly, if people are to blame for the current climate change, there are no guarantees that our own species can survive.
In short, our internal clock will stop suicide long before we get the chance to communicate with aliens.
They walk among us
It sounds like science fiction, but many people believe that aliens live and work around us. For example, the former Canadian Defense Minister Paul Hellyer gave an interview in 2014, which claimed that the world lives about 80 different species of alien life.
Some of them, including the Scandinavian blondes look almost identical to humans. Another group, «Short Greys», more like the aliens, and for the most part hidden from the people.
Hellyer is not alone in his beliefs. Physicist Paul Davies of Arizona State University, and Dr. Robert Trundle from Northern Kentucky University also believe that aliens walk among us.
These people have already resolved their Fermi paradox - aliens exist, and the people want it or not, they are among us. You may select any of the ten options explanations.
The Drake equation (formula Drake) - is a formula designed to determine the number of civilizations in the galaxy with which humanity has a chance to get in touch.
The formula was developed by Dr. Frank Drake (Professor of Astronomy and Astrophysics, University of California Santa Cruz) in 1960.
The Drake equation was the basis for the allocation of millions of dollars to the program search for extraterrestrial civilizations, despite the fact that at the present level of development of science can be more or less accurately determine only two coefficients: ~ R and, less accurately, ~ f_p, and the last, obviously, can not be determine in general, without the accumulation of information about other civilizations.
Looks formula is as follows: