Personal opinion:
There is no such thing as supernatural, just natural and artificial.
For instance:
Aurora Borealis or Northern Lights could of originally been seen as magic, spirits and therefore been termed Supernatural. The reality however is that there is a very scientific reason for why such lights are seen over the northern skies at a certain time of year. (I'm not going to go to great details here but you can find out through
Wiki)
In short something that could of been termed Supernatural is Natural.
another occurance:
A televised use of Zener ESP Cards. If such cards are used and ESP is discovered its usually seen as Paranormal or supernatural. In this particular experiment carried out by one of the UK television station the idea was simple, a Member of the studio audiance would pick a face-down card, view it to themselves and then place it upon the table still face down. The At home viewers would then be subjected to a screen with all the various Zener symbols, and asked to pick which one they believed to be the one the person picked and phone one of the numbers that was located with each symbol.
The actual "Stunt" was an illusion, it utilised the fact that normal television broadcasts cover a 27-30 framerate. The television studio had placed a camera in a position to read the card that had been choosen and on reading the card it triggered an animation of the particular symbol. The animation was utilising a few "dropped frames" so it was barely viewable (it actually depicted the star shape rotating).
In short a Supernatural/paranormal occurance was fraudulantly created to manipulate the audience to believe there was something more than a technological trick. In essence it was Artificial.
A sentient entity in a Ghost form is likely to be artificially created. I will not state that ghosts can't be created through scientific experimentation involving Chaos mathematics and probability, however such ghosts would not be of the deceased but of the paradoxically aligned living.
Previous conversation about "Life after death" has pretty much stated that the only way that we live on after death is by "The laws of energy conservation". Our makeup can't be destroyed outright, however it can be consumed by other life forms that go on using us as a preportion of the life cycle.