[TechnoGuyRob]

Continuation of the above post.

I will be relying on the following axioms. Reasoning for using each axiom is highlighted in italics. You don't need to read the italic text if you fully agree with the axiom.

1. Human perceptions, experiences, and behavior are partly (if not largely or fully) affected by physics. "Physics" hereby refers to relativistic (Einsteinian) mechanics (which include classical (Newtonian) mechanics) and quantum mechanics.
   
   Since we are discussing a phenomenon that affects our reality, it is wise we include physics in our reasoning. One may proscribe physics from relating party or fully to supernatural concepts. However, physics is certainly influential in human perception; most notably, see the story of Phineas Gage, and additionally, the Milgram Experiment, and verifiable results in neuropsychology. There is no doubt among experts that physical interactions with and in our brain will change our perception and interaction with the world (whether that be one of our five senses, memory, personality, etc.). Technologies such as visual rendering systems connected to neurological pathways (artificial sight) and chemicals capable of affecting faculties such as memory should be enough to assert these statements. Even if human behavior is not fully determined by physical particles and forces, there must still be a method of "transferring" information from (and hence an interaction between) another reality to ours. Otherwise, there wouldn't be a way it could physically change our reality (e.g., a person relating it through speech). Thus, if human behavior is influenced by a factor outside of our physical (that is, obeying our laws of physics) universe, there must be some (unexplained) interaction at some instance between that reality and ours.
   
   Having established that human behavior is indeed at least partly determined by physics, we must verify physics can be used as a reliable gauge. One argument against accepting the physics we understand is the existence of some undiscovered principles. Undoubtedly, our understanding of physics is incomplete. However, note that this does not mean it is incorrect. For example, the first formally defined and verified physical explanation of our reality was offered by Isaac Newton. This led to other verifiable theories [1] [2] that were able to accurately predict physical interactions and reactions. However, Einstein later illustrated that special relativity (and perhaps general relativity) also described our universe. Newton's characterization was not inaccurate on the scale Newton was concerned with (special relativity reduces to classical mechanics at low "every-day" speeds), but there was more to the picture. Similarly, the arrival of quantum mechanics did not invalidate relativity or classical mechanics. All these theories (have been shown to) describe reality accurately and dependently. A more general or detailed depiction of reality does not invalidate them, simply expounds on them. Thus, even if a new physical theory is discovered that permits easy explanation of supernatural phenomena, the old theories must still hold.
   
2. A ghost is hereby defined as an entity satisfying the following properties.
   
   1. A ghost is observable by more than one independent observer.
      Observable is hereby defined as being capable of affecting the structure of our universe. For example, a chair is observable, because a component of it (a structure we termed a carbon atom) is able to create a reaction with entities that are not "chair"s, like the air (an oxygen atom; the reaction could be a collision, like the exchange of an exchange particle such as a photon through the electromagnetic force).
      
      An observer must be carefully defined. From axiom 1, we know that we have two options: a human's behavior is fully determined by physical reality (call this scenario A2.1.1), or a human's behavior's is partly determined by physical reality (scenario A2.1.2). In the case of scenario A2.1.1, we can define an observer in the physical sense: a particle or structure that is able to, in some way, interact with (more importantly, be affected by), in this case, a ghost. In the case of scenario A2.1.2, we cannot assume this perspective. There is no guarantee a ghost can actively change or affect any part of our reality; note that we must allow for the ghost's existence in a reality different from our own. In this latter scenario, an observer is defined as a human being capable of observing the ghost. Thus, a human would not necessarily be the only entity, but at least an entity capable of observing a ghost, presumably with tools we do not yet understand, or cannot understand (see rationale for axiom 1).
      
      We will require more than one observer. If there is only one observer, the phenomenon is, by definition, imaginary. Even if it is "real" in another reality, if it can only affect one specific observer over any span of time, and cannot be measured (preferrably by physical apparatus or, I suppose, human perception), then it does not affect our reality other than that one specific observer. In laymen's terms, somebody could be making it up, and even if they weren't, it wouldn't be "made up" in that other reality, but it would be in ours (since it can't affect our reality in any other way).
   2. A ghost is capable of deliberately communicating a message that a human being could understand and correctly interpret.
      From axiom 1, we know that we have two options: a human's behavior is fully determined by physical reality (scenario A2.2.1), or a human's behavior's is partly determined by physical reality (scenario A2.2.2). Considering scenario A2.2.1, a ghost must be able to physically influence our brain in some way: through one of the five (or perhaps more, as long as they're based on physical principles) senses, or in any case, some physical interaction. In scenario 2.2.2, there must exist a method of "transferring" information from another universe/reality to ours, so that the brain of a human (like a seer/medium) is capable of performing the necessary physical actions to inform others about it. If you doubt this, read the rationale for axiom 1.
3. A human being is unable to consciously transform any structure or state of the universe (excluding the human being itself) using a method different from physical contact.
   
   Unfortunately, in order to be able to form any argument at all, we must recognize this axiom. Fortunately, no undisputable scientific (or even other, to my knowledge) evidence recognizes a human is able to do so. However, if a human can affect the universe through "pure thought", we cannot rely on any empirical observation method. I will fill in the rest and a more detailed explanation here later. I have to go to sleep. I hate ostracizing a "subjective reality" viewpoint, but not only does it completely handicap any logical faculties, not much research and philosophy has been done regarding it.

Notice that by accepting these axioms, we are surrendering the colloquial definition of "ghost", and using a more general description. Let me provide an analogy to illustrate why this does not invalidate our logic. If one wanted to prove the area of a rectangle with sides of length A and B is A*B, then this does not invalidate that the area of a square with sides of length A and A is A*A; the rectangle is merely a generalization. Our definition of ghost encompasses humans on Earth, aliens (non-Earth inhabiting entities capable of deliberate communication), and our usual definition of "supernatural" creatures. While aliens satisfy axiom 2.2 (the second defining property of a "ghost"), so far we haven't found any that actually engaged the capability (assuming you didn't get abducted ).

Alright, I spent a considerable amount of time writing and thinking this out (well, thinking out how to phrase exactly what I want to say). I'm going to finish later, but if anyone finds any severe contradictions in my axioms (that don't rely on deep onthological questioning that's left to bored philosophers), please inform me now so I can fix them.