A huge of number of people keeps on thinking about the existence of some other intelligent beings in the universe but still we have not met any aliens. Why?
Earth is special planet
One of the reasons that we have not met aliens is that Earth is rare and there is nothing just like Earth in the universe. In this regard, Paleontologist Peter Ward and astronomer Donald Brownlee presented the Rare Earth Hypothesis about 17 years ago.
According to the Rare Earth Hypothesis, the planets having Earth-like complex (animal) life, according to our knowledge, are very rare in the universe. Moreover, the chains of events that occurred on this planet and that were important for the development of life are so complex that they would not occur anywhere in the universe; thereby, making it highly improbable to meet aliens from other planets.
Every intelligent life may face some disasters after reaching a sufficiently advanced technology
Even though some alien life exists in the universe, Great Filter Theory suggests that it is probably difficult for the alien or intelligent life in the universe to reach such a technologically advancing stage that they start long-distance space travel or communication.
On the Earth, we know that some natural disasters often occur taking the life many years back; thereby, causing the people to start the life from somewhat beginning. For example, our advancements in nuclear technology could take us to nuclear war finally leading to mass destruction, and loss of advanced technology and many important human beings, i.e. great filter. Similar events, i.e. cataclysmic natural disasters, could also occur on other planets having some alien lives causing them to start their life from zero, and finally, making it almost impossible for them to go somewhere in the universe.
Another similar concept is that of the Medea Hypothesis, noted by paleontologist Peter Ward that suggests the concept of self-destruction. This hypothesis shows that the internal suicidal clock of living beings runs out before making any connection with aliens.
Why move outward when inward has much to give?
John Smart’s Transcension Hypothesis suggests that intelligent life in our universe started advancements in an inward direction rather than an outward direction in space. This concept can be compared to the miniaturization concept such as that of computers. Initially, computers were large in size but with the passage of time, their size decreased but power increased. Similarly, intelligent alien life progresses towards more denser and efficient use of space, time, energy, and matter, i.e. STEM. Eventually, the intelligent life in space started living in a black hole that is outside of this space-time continuum. Smart and other such researchers are of opinion that black holes are ideal for computation, energy generation, time travel, and more such processes for any kind of intelligent living beings.
Perhaps Earth is not a super-habitable place…
Science fiction often shows that intelligent alien life was searching for fuel or some other things such as food etc and they found Earth, but reality could be very different from that. May be Earth is not a super-habitable place in the universe. It is quite possible that if aliens are more intelligent than human beings they would not require the resources of Earth. They may think that the Earth and the living beings on this planet are of no use in regards to their highly advanced technologies. Moreover, if we leave the concept of super-habitable worlds, there are more than 8 billion Earth like planets in the universe, and intelligent aliens could go there, if they want.
Perhaps we are living in an artificial universe
Planetarium Hypothesis by Stephen Baxter suggests that we are perhaps living in an “artificial universe” or “virtual reality ‘planetarium’” that is giving us an illusion of empty universe. Supporters of this idea are also of opinion that we are living in a computer simulation that has been designed by some advanced aliens who are able to work on matter and energy on large scale. This is also showing that the intelligent life has not designed the program in such a way that we would be able to find any aliens in the universe.
Perhaps Earth is at a very large distance from other inhabited planets
Alien life might exist in the universe but still we have not met them, and one of the important reasons is that the Earth is at a very large distance away from them. In this case, Percolation theory suggests that some areas in the universe show large clustered growth, whereas some areas of growth have outlier positions. Other intelligent beings in the universe are perhaps living in that large clustered growth, and the Earth is in the outlier position.
We are unable to understand their signals
It is quite possible that alien life exists and they are also sending signals to us, but due to the difference in nature of signals we are unable to understand their signals. Perhaps, aliens have completely different senses as compared to human beings. Perhaps they are using the communication methods that are highly advanced in comparison to our communication methods.
As Lord Rees, cosmologist and astrophysicist, noted, “They could be staring us in the face, and we just don’t recognize them. The problem is that we’re looking for something very much like us, assuming that they at least have something like the same mathematics and technology. I suspect there could be life and intelligence out there in forms we can’t conceive.”
Via: John Smart, Montana State University, Robin Hanson, Planetarium Hypothesis, Percolation theory, Medea Hypothesis, ListVerse, Heller, R., & Armstrong, J. (2014). Superhabitable Worlds Astrobiology, 14 (1), 50-66 DOI: 10.1089/ast.2013.1088