There are two types of matter - gross and subtle. Science works because of the phenomena exhibited by all matter - but mainly the gross type - that is detected by the human sense organs. Hypotheses are tested by experiments, from which are gathered observations, measurements, and data. That is what is known as the 'Scientific Method'. If enough hypotheses collectively point towards a single idea, it then becomes a Theory of Such-and-such. When a theory or set of theories cannot be disproved and holds up time and time again to vigorous testing and experiments without ever failing, it then and only then becomes a Law of Physics.
Science cannot prove/disprove anything that can't be observed, measured, or quantified. No phenomenon, no science... So a conscientious scientist (note the word similarity!) will always say that an unknown factor cannot be proven - and never rightly say that it doesn't exist.
God. The existence of the Soul. The transcendence of spirit. Ghosts. Magic disappearing trick. Aliens.
Well, maybe not aliens. All the others cannot be turned into data because there is no gross matter to be turned into data - only subtle matter. Mind you, some things exist by dint of the absence of anything - shadows, silence, hear-heatedness for example. But they can still be quantified because of that absence and they can be therefore observed to exist.
Back to Aliens - no - I mean the other four. A scientist who says there is no such thing as God is in fact an atheist, not a scientist. Anyone who can't perceive their own soul is merely unenlightened, not an expert in knowledge. And so on and so forth. Of those mentioned, a ghost is different in that it has a subtle body (not a gross one). The soul and God etc are purely spiritual energy, not material - although the soul takes on a gross material body at birth. And who can tell which Holy Person is transcendent and who is a charlatan?
I read somewhere that there nine times as many ghosts as there are people on the planet. Wow! And that EVERYBODY except the spiritually pure has at least one ghost meddling with their life and leeching off their energy. Some Scriptures say that certain types of death (suicide, sudden accidents, drug overdose etc) cause disembodied ghosts because they don't reincarnate straight away - perhaps not realising that they're dead - but instead hover on the subtle material plane, unable to experience sense pleasure due to lack of a body. So they prey on vulnerable victims and feed off their physical, emotional and mental energy.
Now, you're not going to get a scientist to easily measure a ghost. Maybe the ghost knows what's going on and decides not to show up. They like to play tricks. Which reminds me - maybe alien spaceships have sensors that can detect cameras aimed at them. That would explain why there are some 4 billion smartphones all over the planet, yet no-one can manage a single, sharp, focussed picture of a UFO!
Ok, back to ghosts. Practically all religions acknowledge their existence yet they vary a lot on the amount of information they can provide. Ever lost something and had it turn up days later in a place you looked a hundred times? Ghost. Ever seen someone in the corner or your eye only to turn around and find it was a jacket hanging on a hook or a towel dumped on the floor? Ghost. Ever done something or said something completely out of character and then wondered why you did that? Ghost...
Not all ghosts can move things or make themselves visible (it takes a tremendous amount of energy to do that when you don't have a physical body) but telepathy is easily accessible to them, being a form of subtle energy in itself. They feed off bad vibes, negative emotions, rotten food, slime, gunk, dusty dirty places, anything decaying or decadent - including pornography and other perverted practices such as bestiality, necrophilia, etc. I think your getting the general picture.
&Cleanliness is next to Godliness&. Hence the saying never could be truer! We are at our most vulnerable when overly emotional, either upset or angry etc, intoxicated, half asleep, sick or any similar time when our guard is down. Even your best friends, loved ones and family can come back to haunt you because of their envious nature. After all you've got what they want (and lack - a body!) and they already have a strong connection to you from the past. Having said that, not all are nasty, some can be quite nice, and of course there are are your guides, guardian angels and benevolent spirits that help and protect you in so many ways. That is because they chose to be what they are and aren't resentful from being forced to be disembodied and not able to enjoy sense gratification. Not having a body and the senses that come with it is why they're always trying to get into someone else's.
References:
https://billyandanuttama.wordpress.com/2016/07/24/dont-feed-the-ghosts/
http://www.prabhupadanugas.eu/news/?p=48254#comment-50471
http://www.experienceproject.com/stories/Like-Details-Of-God-Of-Death/2968673
http://www.veda.harekrsna.cz/encyclopedia/ghosts_FAQ.htm
http://www.sanskritimagazine.com/indian-religions/hinduism/phenomena-ghosts-true-vedic-explaination/
http://www.vedicwisdom.com/blackmagic/black_magic_faq.php
http://haribhakt.com/demon-attack-during-sleep-treated-with-vedic-mantras-sleep-paralysis-treatment-and-facts-fighting-the-evil-spirits-successfully/
http://www.hknet.org.nz/ghosts-garudapuran.htm
http://www.arogyayurvedichealth.com/vedic__hindu_articles/on_phenomena_of_ghosts_a_true_vedic_explanation
