The way we were brought up and the stories we have heard from childhood produce deeper impressions in our mind about anything, which are difficult to remove in a later stage. Ghost is one such thing that haunts us throughout the life. Movies and serials make them more alive and popularize them in our real life. If we think logically with discretion, we will realize the reality.

For many parents, especially mothers, usually when the child refuses to take food, they inject fear in the child by saying, "if you don't take food Ghosts eat you away."  Such fears are unknowingly fed into the subconscious  and they will be multiplied with time. These fears will become a part of the child even after the child enters Manhood. And they become fears which leads into making Ghosts. To sum up, your fears make the the ghosts.

I think it is the most favored subject in this great forum, as there would be many threads on this, subject. Ghost is black energy and it is more than three dimensional. Humans have limitations of vision and they would see upto three dimensional and most probably upto fifth dimension with scientific equipments. Where as ghosts could reach towards the state of 11 dimension with black form though all these are subject to speculation and most of these great scientific innovations comes out from the subject of speculations. Ghost have no force, they could overpower you with mind force. 

Anyhow, until the things are proved in a scientific ways, for me Ghosts are justimaginary fears. 

The difficult part is that there works no logic with ghosts, as when some one thinks it would be true still there is no way to proves it and when some believe otherwise, the day would be there probably the encounter with ghost comes to a reality. 

So, you say, it's a controversial subject that never yields a definitive conclusion. Yes I agree.

Like shadows attached with every person and entities so does might have there would be some ghosts looking at some other might be without knowledge of real. 

As I said earlier, varied versions are there about the existence of ghosts. Because there is no evidence of ghostsorotherwise,these discussions will go on for eternity without a definitive conclusion.