Aliens and Where are they now?

Where are all the aliens?

 Ever since I wondered that, why don't we see flying saucers flitting around? Why don't we see life out there in the cosmos? Frank Drake began searching for alien signals back in 1960 so far, nothing. With each passing year this nonobservation, this lack of evidence for any alien activity gets more puzzling, because we should see them.

Best books on science and technology to buy in discountThe universe is 13.8 billion years old, if we represent the age of universe by one year, then our species came into existence about 12 minutes before midnight. western civilization has existed for a few seconds. Extraterrestial civilizations could have started in the summer months. 

Imagine a summer civilization developing a level of technology more advanced than ours, but tech based on accepted physics. That civilization could program self-replicating probes to visit every planetary system in the galaxy. Intergalactic colonization isn't much more difficult, it just takes longer.

A civilization from any one of the millions of galaxies could have colonized our galaxy. So where is everybody? it's a puzzle because we do expect these civilizations to exist, don't we? After all there could be a trillion planets in the galaxy may be more.

You don't need any special knowledge to consider this question, scientists have explored through many peoples this and found that they often frame their thinking in terms of barriers that would need to be cleared, if a planet is to host a communicative civilization. They usually identify four key barriers.

Habitability

That's the first barrier. We need a terrestrial planet in just right "Goldilocks zone," where water flows as a liquid. They are out there.

In 2016, astronomers confirmed there's a planet in the habitable zone of the closest star, Proxima Centauri so close that break through starshot projects plans to send probes there. We had become a starfaring species. 

But not all worlds are habitable. Some will be so close to a star and they will fry, some will be too far away and they will freeze. 

Abiogenesis

The creation of life from non life that's the second barrier. The basic building blocks of life aren't unique to earth: amino acid have been found in comets, complex organic molecules in interstellar dust clouds, water in explanetary systems. The ingredients are there, we just don't know how they combine to create life, and presumably there will be worlds on which life doesn't start.

Development of technological civilization

The development of technological civilization is the third barrier. Some say we already shares our planet with alien intelligences. A 2011 study showed that elephants can cooperate to solve problems. A 2010 study showed that an octopus in captivity can recoginze different humans.

 2017 studies show that ravens can plan for future events but they can't contemplate the breakthrough starshot projects, and if we vanished today they wouldn't go on to implement breakthrough starshot.

Evolution doesn't have space travel as end goal. There will be worlds where life doesn't give rise to advanced technology. 

Communication across space

Is is the fourth barrier. Maybe advanced civilizations choose to explore inner space rather than outer space, or engineers at small distances rather than large. Or may bee they just don't want to risk an encounter with potentially more advanced and hostile neighbor. 

There will be worlds where for whatever reason, civilizations either stay silent or don't spend long trying to communicate.

Now again the same question arises that,

Where is everybody?

You can still have some fun playing with the idea aliens are here. Some say a summer civilization did colonize the galaxy and seeded earth with life, others that we are living in a cosmic wilderness preserve.