[Daniel Terhorst]

So far, so good--you've got me interested!

My biggest problem is with the definition here:

Originally Posted by TechnoGuyRob

1. A ghost is observable* by more than one independent 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 (by physical apparatus), 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).

* 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 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).

The rationale for this definition doesn't quite do it for me.

First of all, the definition of "observer" gets a bit muddled up here. In your example, you were talking about an atom in a chair. Here, you don't state, but strongly imply that the observer is conscious (e.g. through the use of the word "imaginary"). Even the example of the atoms is dubious because they are made up of component parts (i.e. many observers at once).

Putting that aside, let me make a handful of assorted points:

1. How does one determine the capability of something to affect the structure of our universe? Clearly one can show that something is capable, but how does one show it is not? Can you conclude that something is not capable of affecting reality simply because it has not yet? The given definition of observable, then, is neither valid nor useful (or, at least, is infeasible to apply) in this context unless you happen to be visiting Belthesar at the End of Time.
   
2. Extending the previous point, let's examine the human scale. It is generally the case that a person is in possession of a brain--sometimes two, if one doesn't mind getting their hands a bit bloody. In the event of a simultaneous possession (or seeming possession) of said brain by a ghost (or duplicitous whim), with no other measurable physical signs (i.e. ceteris paribus), how does one determine if such a thing is imaginary (capable of affecting only this one observer)? Assuming we don't have the necessary tools or understanding to measure what changes did (or didn't) happen in the brain, how can we make a conclusion in either direction?
   
3. Now, let's say in the previous example that we did have such absolute and complete knowledge of every aspect of our physical (and, if necessary, un-physical) environment and were able to conclude definitively whether or not such a thing was imaginary. Given our established axioms of logic, there are only two cases, one of which or the other must be true:
   
   1. Proven imaginary: We can prove, without a shadow of a doubt, that there was no outside influence on this observer. In the case that it is "proven imaginary" in this way, it is, in fact, shown that even the single observer was not affected in any determinable way.
      
   2. Proven not imaginary: We can prove, without a shadow of a doubt, that there was an outside influence on this observer. In the case that it is "proven not imaginary" in this way, it is, in fact, shown that there is more than a single observer affected--the observer and the observer observers.
   
   To put it simply, a ghostamabob either A) cannot affect the physical world at all (no possible observers), or B) can affect the physical world in some measurable way (more than one possible observer). How, then, can something ever only be capable of affecting a single observer?
   
4. Furthermore, if we go so far as to consider the possible (maybe likely) situation where every single ghost/alien/pokémon observer is either faking or horribly mistaken, how can we reconcile the possibility that tomorrow some heretofore unobserved Douglasian space-faring race might destroy Earth to make way for an intergalactic highway? I'd think it'd be awfully hard to prove/disprove that one before seeing proof positive.

Note: I can be a bit... picky. Don't let it get to you. Also, I probably wouldn't have said much, except you literally asked for it, and this kind of discussion fascinates me.

Your article was great--I'd love to see more!

Good job!

-- Daniel Terhorst