“How am I afraid of something I know doesn’t exist?”

It is necessary for an improbable, fearsome, and disgusting monster to be included in the work, for the piece to be considered a work of horror. However, if the creature is improbable, if not impossible, how then is a person suppose to be terrified, when he knows the monster doesn’t exist? Prior to the 20th centaury (and modern physics) a strong belief that if one knows enough information about a particular system, then, it is possible to determine the entire history and future of the system. This is known as determinism. The discovery of the wave-particle duality of matter, and probabilistic nature of the Schrödinger wave equation beheaded the ideas of determinism, leaving the science community with a handicap, and finite limit of knowing. It is impossible, to know anything for certain. All scientific experiments have an intrinsic amount of uncertainty (error) in all measures, and there is physical limit to the precision of any measurement (as deduced by Heisenberg’s uncertainty principle) therefore we can never know exactly the dimensions of any system. However, it can be said that with a strong degree of confidence, this thing behaves in this particular way with +/- this amount of error in its behavior. Fine. But the point isn’t that with a strong degree of confidence can we determine how something behaves within a certain amount of error, but that, that error is always there, so long as the error is present, within that domain of uncertainty, the experimenter doesn’t know what is occurring. The horror comes out of the uncertainty, we don’t know for sure there is no monster, we don’t know for sure what is happening beyond our measurements. It is precisely the ability to not know, that allows for the human imagination to ponder, and question the minds confidence in reason and then employ our ability to be afraid. A strong horror film builds up this uncertainty and employs it as a means to persuade the viewer to give up the confidence in what is common, and allow the error to grow in magnitude. The greater the error becomes, the more fantastic the terror can become.
Let’s digress to religion, disregard science and its uncertainty momentarily and focus religious practices and beliefs. All knowledge isn’t revealed at once, but humanity comes to grow and understand the nature of the gods and supernatural forces through time, and at any given point a religious community isn’t in full communion with the truth, and, has itself a measure of uncertainty in knowing all aspects of the supernatural. If monster X is fearsome, disgusting, and impossible (according to religion A), could it then be that monster X is just fearsome, disgusting, and not revealed rather than impossible? It is the incompleteness of knowing all religious truth that allows for monster X to creep out of the shadows religious light as an aspect of religion A. A qualified horror film utilizes the forgotten scriptures, the missing texts, the ramblings of a blind enlightened hermit, and so on, to shine more religious light on the corners of the unknown supernatural truths, and stretch the viewers understanding of the nature of religion and supernatural to allow their paradigm to contain monster X in their personal faith.
Real people, who watch horror films, are not only scientific or only religious, but a linear combination. It is the combination of the scientific uncertainty, and the religious uncertainty to propagate an overall uncertainty that the horror film can untilize (careful) to invite the reader to indulge in the possibilities of examining the in-betweens of the error, or enlighten that shadowy corner of faith. But why? If one don’t know for sure, but “know” that it doesn’t exist, why let himself indulge and stretch possibilities. There is a human desire for adventure and conflict that is a result of evolutionary impacts. The adventurous individual must be strong, quick-witted, and have a good set genes if he or she is to overcome conflict. Also, food is often hard and scarce, requiring migration, and hunting. Good hunters, and travelers often have a propensity to initiate these activities. If a person can migrate, and hunt well, then he or she will live to produce offspring. The human species migrated for thousands of years, over many generations, to explore and populate the corners of the world. This great migration wouldn’t be possible if it wasn’t for the adventurous inclinations of the human species to expand into the unknown and populate many places of the world. Now, as an established species, we still retain that evolutionary urge to adventure, and so we achieve this vicariously through several alternative means, like hiking, camping, sports, videos games, and horror. People succumb to horror films as a means to sedate their hunter-gather instincts, and keep their psyche pleased so that they don’t succumb, the monotony capitalist-consumerist life styles of work, buy meaningless things, work, buy meaningless things, work, die.
Humanity can know for certain, that he cannot know anything for certain whether a scientific measurement, or expanses of the religious understandings and beliefs. Couple this error in our knowledge with a primordial urge for thrill and the people will indulge in the things that give them a rush of adrenaline. The horror film has an uncanny ability to elicit fearful emotions to stimulate the adventurous sleeping psyche, and stretch the certainty of what is impossible to improbable, and improbable to what is real.