Continuation of the above post.
Here's a little informal sample to what arguments I claim (I will, of course, think them through carefully and formalize them):
If a ghost is composed in any way of physical particles, then it must obey physical laws, which leads to some contradictions. For example, if a camera can capture it or a human can "understand" it (or somehow communicate with it or vice versa), then that means it needs some significant amount of hadrons
to emit the necessary bosons
to transmit all that information (you couldn't otherwise have an "intelligent" entity)! But, if that is true, then that would mean it would be physically measurable using tools. Bosons have supposedly been detected (e.g., electromagnetic readings), but even if they have, there must have been hadrons that triggered those readings, but nobody has yet claimed to detect the presence of a "ghost"'s mass. If, on the other hand, if it does not follow our physical principles, then a ghost must still be able to communicate information (by axiom 2.2). If it doesn't follow physical principles, then those supposed "electromagnetic" (and other) "readings" must be false, and any claimed "photographs". Also, note that Earth is traveling at 300,000 miles an hour around the sun, and faster around the Galaxy, so even in some kind of identically "parallel" universe, a ghost would have to keep up with that, because if it didn't follow our laws, it wouldn't obey gravity (it wouldn't emit gravitons), which means it couldn't take advantage of the inertia! There's lots of holes in here, but I will attempt to fill them up to my best capability once I formalize it.