The weight of the soul, or the 21 gram experience

For centuries, Western culture has housed, among its repertoire of ideas and beliefs about the afterlife, the case where the essence of human beings is in an immaterial substance which we usually call soul.

Soul is a concept as mysterious as it is imprecise and confusing, and that is why it is so despised by science, which is responsible for describing nature from small observations and cautious assumptions, as used by religions. , that in a very ambitious way. to the great mysteries which, from an immaterial world, seem to guide the order of the cosmos.

The soul, a contested concept

However, at the beginning of the 20th century, a physician named Duncan MacDougall set out to break this logic in the search for evidence of the existence of the incorporeal essence of human beings in a simple experiment based on the use of scales. The idea that this seeker started from was that if the soul left some kind of imprint on the body that had sheltered it, it had to be at the time of death, i.e. when it leaves the body to move to another plane of reality. Therefore, he argued that the death of people meant not only the disappearance of voluntary movements and the cessation of mental activity, but also had an impact on body weight.

A body that lacked the essence that defined it as a human thing, with intentions and a will: the soul.

MacDougall wanted to weigh the soul, compress millennia of statements about the afterlife into the quiet movement of a needle. This is what led him to assert that the physical embodiment of soul existence could be found within, plus or minus, 21 grams of difference.

How was the 21 gram experiment performed?

Duncan MacDougall wanted to collect his evidence on the existence of the human soul by using as an instrument a complex system of scales incorporated in a kind of bed. He thus convinced six people who were dying to spend their last hours in this type of structure, which this allowed him to record the weight of their bodies from a few hours before their death until just after.

From these results, MacDougall concluded that the soul weighs approximately 21 grams, which is the variation he was able to observe through his research. This statement had a huge impact on the press, which across the New York Times echoed the news even before a version of it appeared in academic journals. Thus, the idea that the soul can weigh around 21 grams is strongly rooted in popular culture, which explains that references to this experience appear in musical pieces, novels and films, Being the most notorious 21 grams of director Alejandro González Iñárritu.


While it is true that the New York Times article on Duncan MacDougall and the Weight of the Soul had a lot of repercussions, it is also true that it was not received unanimously. The scientific community at the time was already very suspicious of experimental forays into the realm of the supernatural, and the 21 gram experiment was based on ideas that directly attacked the principle of parsimony, used in science to emphasize that from explanations to an objective fact they must be as simple as possible. That is why the results obtained by this doctor divided the audience into two polarized postures.

To reinforce their results, MacDougall performed a variation of the experiment using dogs, to conclude that there was no change in the weight of these animals before and after death, which would indicate that some religious beliefs d nonhuman animals have no soul. As expected, it did nothing more than add firewood to the fire.

Does that sound reasonable to you?

MacDougall hoped to take advantage of (then) recent technological advances and the refinement of the scientific method to access a type of knowledge which, for millennia, was inaccessible to mankind, but which is tied to a plane of existence associated with l eternal, the essence of human beings and, in general, of the entities that inhabit that which is beyond the realm of the physical. Given that, no wonder the conclusions he reached are so inflammatory.

An experience mediated by irrational beliefs

On the one hand, the experience of 21 grams talks about dogmas, questions of faith, the essence of what is human and certain elements related to the realm of the sacred. On the other hand, it seemed to be an instrument to blur the boundaries of what can and should be studied scientifically. The mere fact that MacDougall wanted to investigate the soul by the scientific method was a provocation, and many researchers were quick to point out a large number of methodological flaws in the procedures followed by Duncan.

However, beyond taking into account the many errors that were made during the experiments, other fundamental philosophical questions remained: is not learning the intangible world and the mystery the most common type of knowledge? more ambitious possible? Does not the fact that the nature of the human soul has been discussed for millennia not make this question a particularly interesting subject for the scientific community?

The answer is no

In retrospect, and from what is known from the experiments conducted by Duncan MacDougall, it is clear that the large number of methodological flaws we can’t even take seriously the claim that bodies lose around 21 grams when they die. However, it is not these errors that make these surveys a historical curiosity, but the objectives they were aimed at.

The soul does not weigh 21 grams

To explain a process linked to the physical world, we cannot appeal to the intangible world but look for the answers in the nature that surrounds us.

This is what Dr Augustus P. Clarke, for example, did he linked weight loss to increased sweating right after death, In turn due to the general warming of the body by not functioning the organs responsible for ventilation, namely the lungs. In turn, Clarke noted the fact that dogs don’t have sweat glands scattered all over the body, which would explain why there was no change in weight after they died.

Of course, the very definition of the concept of soul is very plural, conflicting and closes many contradictions (how can something incorporate living in the body of living beings?). However, what makes its study not a scientific task is the fact that when we speak of the soul we are talking about something that has no physical entity and therefore it cannot be measured or changed by what is happening to the body.

If we assume that an extraordinary statement is to be backed by equally extraordinary evidence, we will see that there is a clear leap of faith that ranges from discovering a shift in weight to the idea that it is due to the causes the soul to leave the body. In fact, in the case of concluding that the 21 grams serves as proof that there is a supernatural entity that inhabits people, rather than offering an explanation for the observed fact, we will do the exact opposite: create a practically infinite number. of questions that cannot be answered from additional empirical evidence.

After death, what do we have left?

The 21 gram difference recorded by Duncan MacDougall was to be much more than a justification for what led to the experiment (detecting a change in weight before and after death) but it was raised as a window to the afterlife. The hypothesis to be tested could only be based on a system of religious beliefs accumulated over the centuries, and it lost all meaning to be separated from it and placed under the magnifying glass of the scientific method.

However, while it is true that the 21 gram experiment has no scientific value, it has shown a extraordinary robustness to survive in the collective imagination of society. This is probably due to the fact that the beliefs about the soul that MacDougall had a hundred years ago are still very much in force today.

NOTOur cultural background prompts us to pay more attention to a seemingly scientific article that confirms our beliefs. this in a 200-page book written decades ago that explains why science only deals with material-based processes. The scientific mindset may have many tools to perpetuate itself, but it is still not as alluring as some ideas about the afterlife.

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