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Byron Jennings | TRIUMF | Canada

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Cause and Effect: A Cornerstone of Science or a Myth?

Cause and effect has been central to many arguments in science, philosophy and theology down through the ages, from Aristotle’s four causes[1] down to the present time. It is has frequently been used in philosophy and Christian apologetics in the form: The law of cause and effect is one of the most fundamental in all of science. But it has it naysayers as well. For example, Bertrand Russell (1872 –1970): All philosophers, of every school, imagine that causation is one of the fundamental axioms or postulates of science, yet, oddly enough, in advanced sciences such as gravitational astronomy, the word “cause” never occurs. … The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm. You can accuse Russell of many things, but being mealy-mouthed is not one of them. Karl Pearson (1856 – 1936), who has been credited with inventing mathematical statistics, would have agreed with Russell. He never talked about causation, though, only correlation.

One of the people who helped elevate cause and effect to its exalted heights was David Hume (1711 -1776). He was a leading philosopher of his day and known as one of the British empiricists (in contradistinction to the continental rationalists). Hume was one of the first to realize that the developing sciences had undermined Aristotle’s ideas on cause and effect and he proposed an alternate in two parts: first, Hume defined cause as “an object, followed by another, and where all objects similar to the first are followed by objects similar to the second”. This accounts for the external impressions. His second definition, which defines a cause as “an object followed by another, and whose appearance always conveys the thought to that other”, captures the internal sensation involved. Hume believed both were needed. In thus trying to relate cause and effect directly to observations Hume started the philosophy of science down two dead ends streets: one was the idea that cause and effect was central to science and the other lead to logical positivism.

Hume’s definitions are seriously flawed. Consider night and day. Day invariably night and the two are thought of together but night does not cause day in any sense of the word. Rather, both day and night are caused by the rotation of the earth, or, if you prefer, a geocentric frame, by the sun circling the earth.  The true cause has no aspect of one thing following another or one causing thought of the other. And the cause does not have to any way resemble the effect.  One can find many other similar cases: it getting light does not cause the sun to rise despite it getting light before the sun rises; it is the sun rising that causes it to get light. Trees losing their leaves does not cause winter but rather the days getting shorter causes the trees to lose their leaves and is a harbinger of winter. The root cause being the tilt of the earth’s axis of rotation with respect to the ecliptic.

As just seen, cause and effect is much more complicated than Hume and his successor thought, but not nonexistent as it detractors maintain. In the words of the statistician: correlation does not imply causation. However, it can give a strong hint.  The cock crowing does not cause the sun to rise but the correlation does suggest that the sun rising might just motivate, if not cause, the cock to crow. Similarly, consider lung cancer and smoking. Not all people who smoke get lung cancer and not all people who get lung cancer smoke (or inhale second hand smoke).  Nevertheless, there is a correlation. It was this correlation that started people looking to see if there is a cause and effect relation. Here we have correlation giving a hint; a hint that needed to be followed up. And it was followed up. Nicotine was found to be carcinogenic and the case was made convincing. A currently controversial topic is global warming and human activities. Here, as with smoking causing cancer, we have both correlation and a mechanism (the greenhouse effect of carbon dioxide and methane).

Cause and effect went out of favor as a cornerstone of science about the time quantum mechanics was developed. Quantum mechanics is non-deterministic with events occurring randomly. Within the context of quantum mechanics, there is no reason or cause for an atom to decay at one time and not at another. The rise of quantum mechanics and the decline in the prominence of cause and effect are probably indeed cause and effect. However, even outside quantum mechanics there are problems with cause and effect. Much of physics, as Russell observed, does not explicitly use cause and effect. The equations work equally well forwards or backwards, deriving the past from present as much as the future from the past.  Indeed, the equations of physics can even propagate spatially sideways rather than temporally forwards or backwards.

In spite of all that, the idea of cause and effect is useful. To understand its limitations and successes we have to go back to one of my mantras: the meaning is in the model. Cause and effect is not something that can be immediately deduced from observation, as Hume implies, but it is not a meaningless concept as Russell said or the physics discussion above might seem to imply. Rather, when we develop our models for a particular situation the idea of causation comes out of that model, is part and parcel of the model. We believe that the post causes the shadow and not the other way around, because of our model on the nature of light and vision. Similarly, the idea that the earth’s rotation causes day and night comes out of our model for light, vision and the solar system. The first chapter of Genesis indicates that this was not always considered obvious[2]. That smoking causing lung cancer is part of the biological model for cancer. That human activities causing global warming comes out of atmospheric modeling. But arising from a model does not make cause and effect any less real nor the concept less useful. Identifying smoking as a cause of cancer has saved many lives and identifying carbon dioxide and methane as the main causes of global warming will, hopefully, help save the world. Cause and effect may not a cornerstone of science but it is still a useful concept and certainly not a relic of a bygone age.

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[1] Discussed in a previous post.

[2] Day and night were created before the sun.

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