Playing Pool with Ghosts


On the Impossibility of Tracing Natural Effects to Supernatural Causes

upernatural forces, if they exist, lie outside of human observation and operate without regard to the laws of nature. We cannot see supernatural forces directly because we cannot detect non-physical entities with our physical senses. Therefore, we can only know supernatural forces indirectly by their effects. This is the conclusion generally accepted by supernaturalists. However, it seems to me that this conclusion is fallacious. Even if supernatural forces exist we cannot come to know them by their effects.

Suppose you are playing a game of pool by yourself. You rack up the balls and begin knocking them about. At one point you knock the white ball into a purple ball. Let’s examine that brief moment more closely. Let’s look at three events:

  1. You hit the white ball with your queue.
  2. The white ball, which was stationary before, now travels across the surface of the pool table and knocks against a purple ball.
  3. The purple ball, which was stationary before, is now set in motion.

We assume that event C was caused by event B, which in turn was caused by event A. This belief is reinforced in two ways:

  1. On countless past occasions, you’ve observed events just like A followed by events just like B, and events just like B followed by events just like C.

You’ve played pool many times. You’ve seen how pool balls knock each other about. But even if you have never played pool, you have witnessed other kinds of inanimate objects strike each other. You’ve grown accustomed to the fact that one object striking another of roughly equal mass generally sets the second object in motion, as long as the second object is not somehow fastened in place.

  1. You’ve never observed an event like B occur unless it is preceded by an event like A, or an event like C unless it is preceded by an event like B.

You’ve never witnessed a pool ball, or any other kind of inanimate object, set in motion without being knocked by some other object first. You’ve grown accustomed to that fact that inanimate objects don’t start moving unless something moves them.

You know from experience, if not from your high school physics class, that bodies at rest tend to stay at rest, and bodies in motion tend to stay in motion, unless acted upon by an outside force; and that every action has an equal and opposite reaction. You’ve witnessed the constant conjunction of events like A and events like B, and this gives you sufficient reason to label A the cause of B.

“I hit the white ball with my queue,” you might say, “and this caused it to fly across the table into the purple ball, which caused the purple ball to fly across the table into the corner pocket.”

Suppose, though, that you witnessed events B and C occur without being preceded by event A. And suppose that you were inclined to believe that your pool table was haunted by the ghost of Abraham Lincoln.

In this scenario, you would still have to assume that event C was caused by event B, just as it was in the first scenario. Abe Lincoln did not hit the purple ball directly; he struck the white ball and it hit the purple ball. It’s possible that the purple ball then hit another ball which in turn hit another and that another. Starting with last ball and working backward, you could trace the chain of causation from natural cause to natural cause until you came to the first natural event in the chain. But what caused the first observed event, event B, the movement of the white ball? The cause was unseen. Would it be safe for you to conclude that event B had no natural cause, and therefore must have had a supernatural cause? Couldn’t you reasonably conclude that you were playing pool with the ghost of Honest Abe? Wouldn’t this be a valid piece of induction?

No it would not. In the first scenario you witnessed event A followed by event B. In the second scenario you witnessed event B, but there was no event A. In order to presume a cause-and-effect relationship via induction, you must observe the causal event. And furthermore you must observe the causal event and its effect constantly conjoined. But by definition you cannot observe a supernatural force.

If you perceived a pool ball move without a natural cause, you could not conclude you were playing pool with the ghost of Abraham Lincoln for the following three reasons:

  1. It is impossible to distinguish amongst supernatural forces. How can you be sure you’re playing pool with the ghost of Lincoln as opposed to some other supernatural entity? Couldn’t your opponent just as easily be the ghost of David Hume, a bored leprechaun, a hundred thousand other supernatural beings conceived by humankind, or a trillion supernatural beings not yet conceived?
  2. It is impossible to distinguish between a supernatural force and an unknown natural force. How can you be sure you’re playing pool with any supernatural entity at all? Couldn’t it just as easily, and perhaps more probably, be a natural force that you simply don’t yet understand, like a microscopic spaceship from a technologically advanced alien planet, a form of magnetism hitherto undiscovered, or a bizarre snowball effect stemming from a random quantum fluctuation?
  3. It is impossible to distinguish between a supernatural force and a perceptual mistake. You must also consider the possibility that what appeared to be a miracle was in fact (more probably still) a failure of perception, a hallucination, or a magician’s trick. You might be able to rule out this possibility with multiple observations or with the use of instruments, but not with a single direct observation.

Abe Playing Pool

Suppose, though, that a semi-transparent apparition appeared before you. Behold! Abraham Lincoln with pool queue in hand! Here at last is real evidence. Seeing is believing, isn’t it? Wouldn’t this prove that ghosts exist, and that you are playing pool with the ghost of Abraham Lincoln?

Nope! We still have the same problem. Instead of pool balls now we’re dealing with photons. In order for your eyeballs to detect the ghost of Abraham Lincoln, the ghost must either reflect or emit photons. Photons obey laws of nature just as pool balls do. Photons are not themselves supernatural but are very much a part of the natural universe, subject to a chain of causation just as pool balls are. Unless a ghost is a natural object subject to the same laws of nature as any other natural object – which is not the claim made by spiritualists – the chain of causation that leads to photons hitting your eye must begin without a natural cause. A ghost is an undetectable (supernatural) force that directs photons toward your eyes in defiance of the laws of nature, thereby creating a detectable (natural) image. You cannot observe the supernatural ghost itself, you can only observe the spooky stirrings of the ghost in the natural world, whether those stirrings be of pool balls or of photons.

What about the possibility that the image of the ghost is a hallucination, but that the hallucination is caused by the ghost?

Even if the appearance of the ghost is a hallucination caused by the ghost, and therefore not comprised of photons, intervention in the natural world is nevertheless required. Nerve cells of one type or another must be manipulated in order to create the hallucination. The nerve cells are now the pool balls.

In order to infer causation, the rules of induction require that we observe two events constantly conjoined. According to Hume, we can never know with absolute certainty that one event actually causes another. This is a limit of human reason. But the more instances we observe of one event conjoined with another, with no observation of the events occurring apart from each other, the greater the probability that the two are always conjoined, and this we call causation. But by this formulation it is impossible to infer a supernatural cause for a natural effect, ever. We are only equipped to observe natural events. A supernaturally caused event in the natural world must begin with a supernatural intervention – an event impossible for us to observe even with the help of instruments, and thus not subject to induction.

None of this prohibits supernatural forces from existing. But even if they exist, and even if they intervene in the natural world, it is just as impossible for us to gain knowledge of them by their observable effects as it is to observe them directly. It is always logically invalid to assign a supernatural cause to a natural event.

Most of the above reasoning is self-evident and unremarkable, but it leads to a non-intuitive conclusion: Even direct observation of an apparent miracle (an event without an observed cause or an event that otherwise seemed to defy the laws of nature) would provide insufficient evidence to establish the existence of the supernatural. Supernatural causes simply cannot be inferred from anything we observe in the material universe.

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