Harry Potter Science # 7: Does This Horcrux Make My Soul Look Fat?

On with our investigations into scientific themes in the Harry Potter books. To recap, so far we have covered the genetics of magical ability, real-life fossil dragons named after Hogwarts, conservation biology, the botanical principles behind wands, and kin selection. I originally intended to just do this series in the days leading up to the release of Book 7, but now I have some cool ideas and not enough days left to fit them in, so I may extend the series beyond the book release, although it won't be a daily feature anymore.

For today, some of the science behind horcruxes. First off, some background on what exactly a horcrux is:

Information on horcruxes is scanty, even in the wizarding world. There are only two people that can give Harry any information on them at all: Dumbledore, because he seems to know everything, and Slughorn, supposedly because he used to work with Voldemort. A horcrux is an object in which someone has deposited a fragment of their soul. The fragment part is key, because the main point in creating a horcrux is to divide your soul into pieces, so that destruction of one object/body cannot destroy you completely, it is a sort of insurance that all of your metaphysical eggs are not in the same basket. This is what has allowed Voldemort to linger along even after his encounter with the infant Harry almost destroyed him. He has created seven horcruxes, weach with a fragment of his soul, which means that killing one part of him is insufficient to bring about his demise, making things much more complicated for our bespectacled hero.

As Harry learns in Book 6, in order to create a horcrux, you have to murder another human being, which causes your soul to be ripped apart. The details on this are sketchy, here is how Slughorn explained it to a young Voldemort (then known by his birth name, Tom Riddle):

"Well, you split your soul, you see," said Slughorn, "and hide part of it in an object outside the body. Then, even if one's body is attacked or destroyed, one cannot die, for part of the soul remains earthbound and undamaged. But of course, existence in such a form...few would want it, Tom, very few. Death would be preferable." But Riddle's hunger was now apparent; his expression was greedy, he could no longer hide his longing. "How do your split your soul?" "Well," said Slughorn uncomfortably, "you must understand that the soul is supposed to remain intact and whole. Splitting it is an act of violation, it is against nature." "But how do you do it?" "By an act of evil--the supreme act of evil. By committing murder. Killing rips the soul apart. The wizard intent upon creating a horcrux would use the damage to his advantage..."
~Harry Potter and the Half-Blood Prince, pp 497-498
(sorry for the lack of paragraphs, I lost a wrestling match with the autoformatting on this damn thing)

So we don't really know the details of how the soul enters the horcrux, but apparently this is a very powerful spell, and items to be used should be chosen carefully. So far we know of two of them for certain: Tom Riddle's diary and Marvolo Gaunt's ring. Dumbledore thinks that the ever-elitist Voldemort sought a relic from each of the Hogwarts founders, and tells Harry that he suspects Slytherin's locket and the Hufflepuff cup. One of the major tasks Harry faces in the last book is finding the remaining four horcruxes, and there has even been speculation that Harry himself is a horcrux. I personally think that Rowena Ravenclaw's wand was the one displayed in Ollivander's shop, and that his kidnapping indicates that Voldemort wanted the wand back for some reason...

So, the important question: if this object (or organism, according to Dumbledore you can make a living thing into a horcrux also, although this is risky because--as far as we know--you can't control its behavior even after part of your soul is invested in it) is infused with a part of your soul, what exactly goes into it? Does anything quantitative change about the item? How would we study this?

Actually, there have been "scientific" investigations that tried to measure how to determine if a soul is present. Back in the mid twentieth century, a Massachusetts doctor, Duncan MacDougall, believed that the soul was material and set out to prove his theory. He reasoned that anything material must have a mass, and that meant that the body must decrease slightly in mass at the moment of death, as the soul left the body.

Macdougall invented a bed balanced on a very fine scale, "sensitive to two-tenths of an ounce." When he had a patient in the last stages of a terminal illness, he would park them on the bed and wait for them to die so that he could measure them pre-and post-soul.

This turned out to be less straight forward than he had planned. Two of the six human cases had to be thrown out, one due to ambiguity over the exact moment of death and one because the patient expired faster than expected, before the scales had been balanced. The other four patients (is that the right word in this context? maybe "subjects" is better?) all purportedly lost varying amounts of weight.

Trying to be scientific (to some degree at least), MacDougall repeated the procedure with fifteen dogs, and recorded no change in mass after death, which supposedly supported his hypothesis, since of course humans are the sole soul owners in this universe, right? So if humans lost weight and dogs didn't....it MUST have been the soul leaving the body that caused it! Just for the record, the "average soul" appeared to weight about 21 grams, which later became the title of a movie about MacDougall's experiments.

Obviously this is a load of pseudoscientific baloney. Even with meticulous methodology (which MacDougall didn't have), a sample size of four tells us nothing. Interestingly, there were further investigations into this using sheep, which were shown to actually gain weight after dying. What does this say about sheep? It says more about human superstition and credulity than anything else, in my opinion.

So, while MacDougall would probably have reasoned that a horcrux should weigh slightly more (about three grams, in Voldemort's case, since he is thought to have created seven horcruxes) after having a soul fragment implanted in it, there is no definitive evidence for this. There is not even any weak evidence for it. Or for the actual existence and nature of souls in the first place, or for how a wizard soul might differ from a normal human soul, but that is something far and away beyond the scope of this humble post. You can see a brief and simplified "ask a scientist" column on it here, but the literature on the nature of consciousness and "souldom" has been a huge area of controversy in a range of fields covering everything from neuroscience to animal rights.

Obviously identifying the horcruxes will be a big task for Harry, but it is probably safe for him to leave the scales at home. The issue of detecting soul fragments may not be scientific, but learning about pseudoscientific claims is important as well, because it emphasizes the importance of reason and critical thinking when approaching an issue. MacDougall worked on the assumption that souls exist, and all of his observations were made in that context, an instructive example of how NOT to do science.