Do ghosts exist?

It's not uncommon - even in this day and age - that we carry on to find genuine belief in the existence of ghosts. Even in cultures and populations where the belief that ghosts definitely exist isn't popular, agnosticism about the existence of ghosts is probably still prevalent. By people being agnostic, I mean that they do not reject the possibility that ghosts can exist. But with all the facts that we know about the universe available today, shouldn't we be able to reach - with some certainty - a conclusion regarding the existence of ghosts? With some amateur philosophical 'maneuvering', I attempt to demonstrate here that we have very good reason to believe that ghosts, or at least ghosts according to a particular conception, do not exist.

Casper the Ghost (Photo courtesy: maditsmadfunny.wikia.com)

Of course, to do this we need to start with a conception, or a definition of a ghost. Here are some properties - off the top of my head - which we may attribute to a ghost:

• A ghost is immaterial (non-physical)
• A ghost at least partly consists of some element of a person who was once alive but is now dead
• A ghost may also be conceived as the spirit,  consciousness, or soul of a dead person. 

The essential idea is that a ghost must be - whatever it is - a non-physical thing, and at least part of it belongs to an once alive person. Now let's get on to the analysis. 

To start off: what does it mean for something to be non-physical? It doesn't answer the question to simply list examples of things which are non-physical (e.g. God, mind, numbers), because these things do not tell us anything about the label 'non-physical'. Perhaps, we can understand something to be non-physical if it does not react (causally) with known physical laws. What this means is that a non-physical thing is not described by physical laws, and it is in a completely different realm from the physical world. A non-physical thing can do whatever it likes in the non-physical world, but it cannot in any way change how the physical world works. 

However, if that is true, all those ghost-featuring movies must have made a horrible mistake: EITHER ghosts are physical, OR ghosts cannot have any interactions with anything in the physical world at all. (We wouldn't have to worry about ghosts hiding in our bedrooms, because they cannot do anything physical to us)

Ghost (1990): Sam Wheat kissing Molly Jensen in this classic scene as a ghost. (Photo courtesy: tasteofcinema.com)

So, what if ghosts are physical? In my opinion, that doesn't seem to be a good way out either. To be physical, ghosts must react causally with our known physical laws. Unless we're willing to admit that physics   has gotten its fundamentals terribly wrong, it isn't consistent to hold the beliefs that ghosts can do certain things they do (e.g. alter mass, occupy no space, not made up of atoms). But remember, the knowledge of physics that human beings have built up over history has given us so much predictive success with the physical world: with that knowledge, we are able to land on the moon, send instant messages across the globe and split up atoms to create horribly powerful weapons of mass destruction. Is it really plausible to think then that ghosts exist?

Perhaps a few good rejoinders can still come from those 'ghost realists' (just made up this term to refer to those who think that ghosts exist). Firstly, realists may concede that ghosts cannot causally interact with the physical world. Okay, ghosts cannot move doors and make creepy weeping noises. But the fact that ghosts cannot interact physically does not stop ghosts from causally interacting with us in the mental realm! Effectively, this is saying that ghosts can and only can affect us psychologically. It would be more plausible then, to understand a ghost as a mental entity, something like numbers and concepts (or *beliefs?!). But would you say that numbers or concepts exist? But that is a much bigger question to deal with... (the question of whether mental things exist [not as in crazy, silly]).

The second (much less satisfactory) way that 'ghost realists' can respond is to say that ghosts are still physical, and they are still constrained by physical laws. This strategy allows us to understand ghosts as physical entities, but they would be much less robust as the 'ghosts' we know from movies and stories. Their 'status' would be equal to any other physical thing - humans, amoebas, tables, and the like - except that they are not living things! You can insist that this is true, but this approach offers a very poor and bizarre explanation of the universe, and it is largely inconsistent with what we already know about the universe.

So what's the verdict? Do ghosts exist? That very much depends on what type of ghosts we're talking about...

• Physical ghosts (highly unlikely)
• Non-physical ghosts capable of physical interactions (impossible; unless we define physical differently)
• Psychological ghosts (possibly; but even if they do exist, they would be as real to the same extent that numbers are real: "it's all in the mind")

Q.E.D.

*I hesitate to compare ghosts with beliefs, because beliefs are thought to have physical counterparts by some thinkers. 

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