Are we alone in this world??

Whenever we sit alone at home, though we are alone, we have somewhere in our mind that we are not alone. There are neighbors, people residing in society or nearby area. Sometimes we think, are humans alone in this world?? Is their any other world existing in this universe.

We have heard alot about UFO, aliens etc. But still the layman is completely inaccessible about these things. In short, we haven't yet met any alien or UFO personally ;-).  But their should be some other earths in this universe present. We have got some proofs regarding UFO's. As some were genuine reports of UFO sightings. So the question comes out is from where those people coming from? and what is their moto?
Are they coming here to study human civilization?

Scientist say that aliens or people from other world coming should be very much advanced than us. Of course they should be. Thats why they are able to find us, but we still are searching them. Like our sci-fi movies, one fine day if they attack us, we will be surely not able to defend them.

Before finding if we are alone or not, we should gain complete knowledge about ourself first. We are still not confirm how did human race come to existence. Are we the next generation of Apes? Are we homo sapiens?? We are still not confirm. We didn't even know how was our earth created. who was the first human alive earth. Somewhere we all know that we are alone. But we will have to go out and find who are our neighbors.