The Science of Ghosts

Readers, I have a special guest-post today from my friend Howard who teaches physics at Marshall University. Check out his blog here. I asked him to write a post on ghosts from a scientific standpoint for middle school-aged students. He wrote a funny depiction of ghost hunters as pseudoscience here.

Since I've been asked to write something about ghosts and science (probably because I have written on that topic on my own blog a few times), let me concentrate on just what science can and cannot say about ghosts.

First of all, by "ghost" I mean the real thing: the spirit of a dead person. A completely different question has to do with what people mistake for ghosts. I remember distinctly crying out as a child when I thought I heard something slow and ominous walking down the hall in the direction of my room; I did not know about houses settling.  Likewise, it has been found that certain stimuli, like the magnetic fields of a Koren helmet, can create the sensation of "presences" that may be interpreted as angels, demons, or ghosts; that is a purely physical experience. (It does not prove that all perceived angels, demons, and ghosts are physically or chemically induced hallucinations, any more than the fact that such causes can produce the feeling of crawling spiders proves that there are no spiders.)

A spirit, by definition, is non-corporeal; this means it not only is not matter, but also that it is not energy, since that not only is a physical property, it can even be transformed into matter (and vice versa). Two or three hundred years ago, it might be just marginally understandable for educated people to confuse energy with spirit, but for at least 150 years it has been clear that energy is at most vaguely analogous to spirit.

Really understanding this last point could prevent a lot of embarrassing foolishness. For example, the argument is often made that “there is a principle in physics called the conservation of energy. A living person obviously has energy, since he moves around. What happens to that energy? It doesn't just disappear! It becomes what we call a ghost.” Wrong. The thermal energy dissipates into the room or other surroundings. The chemical energy is consumed and used by bacteria and fungi as the body decomposes. There are good philosophical arguments for the persistence of the soul, but conservation of energy is not one of them.

Finally, I have had people tell me that “the basic principle of science is that things like that [ghosts, miracles, whatever] don't happen.” Notably, the people who tell me this are inevitably not scientists; real scientists almost always (there are exceptions) understand science better than that. This would be like saying, “The basic principle of accounting is that the numbers in account books always represent transactions; they are never messages passed between spies. Discrepancies may be accidental errors or they may be dishonesty, but they are never messages.” This is not a reasoned rejection based on evidence; this is a dogged refusal to consider a possibility. On the other hand, it would be fair for an accountant to assume

• if such things occur, they must be rare, and it should not be assumed without very good evidence that any particular case requires such an exotic explanation, and
• nothing in his training qualifies him to draw any conclusion other than that there is a discrepancy.