The diameter of the observable universe is about 93 billion light-years or 8.8X10^23 km. There are about 1,000,000,000,000,000,000,000,000 planets in the universe and to think that only ours is a habitable one makes us a highly narcissist race. There is a very high possibility of life on more than 1 out of the 1,000,000,000,000,000,000,000,000 planets. However, we haven’t been able to have the ‘first contact’ with an intelligent civilization so far. What could be the reason for that? Here are 5 of them.

1. There are no aliens

2. Technological Limitation

For all the technological progress we’ve made in the last century, we still haven't invented interstellar travel which could be a major barrier for us in finding alien civilization. The possibility of them sending signals and our inability in decoding them could be another reason as well. Maybe they perceive and interact with the universe in a different way than we do?
3. Advanced civilizations are known to kill themselves off.

Look at the Mayan civilization, a race so ahead of its time that they measured the accurate length of a solar year while others were having trouble growing crops. This civilization with all the others great ones came to an end when at their technological and philosophical peak. This could be true for every civilization in the universe making them go extinct when on the verge of interstellar travel or finding extraterrestrial life. I mean look at us for instance. We are doing great in our space exploration and in the next century we could well be traveling across the solar system, from earth to Mars on a regular basis but every country acquiring nuclear weapons puts a huge question mark on that very future.
4. We aren't evolved enough to join their intergalactic society yet.

Let's be real about this, we haven't been an ideal organism in the past millennium or so. We fight about having the best imaginary friend. We lie! What if they don’t have a concept of it? All the information transmitted through TV stations and through the Internet would be a big unsolved mystery to them if they try to understand humans from it. We are slowly killing the planet off. What if we do the same to their society if joined? For now, I think we're kept on the surveillance list and will be invited when we reach enough maturity to join their society.
5. They are already here, undetected.

Conspiracy theories aside, there could well be UFOs going unnoticed or undisclosed by space agencies and government. There are many proofs of government hiding information mostly as revealing it would create total chaos in the world, which is often the subject of many movies. We, humans, are unacceptable of different skin color, imagine what would happen if there’s an advanced species living in the universe with us. Though it would take time, I think contacting alien species is inevitable. The question however is, are we ready to know our place in the universe?
