The evolution of near Earth objects risk perception
by Luis Fernández Carril
|The most important thought behind scientific inquiry that Halley is using is that nature is ruled by laws that apply to every corner of the universe and do not change.|
Although Aristotle categorized comets as “sublunary vapors”, most ancient cultures interpreted comets as omens. To commemorate the victory of William the Conqueror at Hastings in 1066, the tapestry of Bayeux was woven, depicting scenes and events that led to the conquest. The first event that marked the fall of King Harold II was an evil omen that appeared on the evening sky: it was, what centuries later would be known as Comet Halley, which crossed the skies of old England. Isti Mirant Stella reads in the first scene of the tapestry, which is translated as: “These men wonder at the star.” After the king’s servants observed the phenomenon, they didn’t know it was a comet. They knew it was a bad omen, a sudden change in the cosmic order that announced a change in the fate of men. The comet’s appearance in the night sky foretold the fall of King Harold. Events of the sort were also recorded in Aztec manuscripts, where a comet is also an evil omen of emperor Moctezuma’s fall. These omens are the result of the process of observation; nonetheless, it is within a particular metaphysical realm where the interpretation rises. The events in the night sky are the interpretation of the advent of change: not the possibility, but a revelation of the future.
Almost 700 hundred years later, Edmond Halley wrote in his book A Synopsis of the Astronomy of Comets of 1705: “In the year 1456… a comet was passing Retrograde between the Earth and the Sun… Hence I dare to fortell that it will return again in the year 1758.” In this quote it can almost be pointed out how Halley is playing with ancient beliefs of comets as omens. He uses the verb to foretell, to disguise what was becoming one of the most important tools in science: prediction. Prediction is based on calculus of different theoretical variables that adjust to observation to give a result before it happens. In this manner, based on knowledge of mathematics and physics, the astronomer Edmond Halley is demystifying comets, from omens to a part of a very precise machinery, the mechanical clockwork of the universe. Comets are no longer messages from the gods to announce a future event, but a natural phenomenon that can be observed, calculated, and predicted in a scientific investigation.
The most important thought behind scientific inquiry that Halley is using is that nature is ruled by laws that apply to every corner of the universe and do not change. This is called Uniformity of Nature and it became the cornerstone of scientific inquiry and the empiric method. This principle, however, is a priori. This means that before a phenomenon is even observed, this principle conditions the very nature of observation, explanation, and prediction. Every time a phenomenon is observed, there is an undergoing (metaphysical) principle that dictates that the laws that govern this particular cause will not change through time; then, a cause can be established to provide explanation and to know that every time this particular effect is observed it has always the same precise cause. Every observer and scientist that observes any phenomenon and adjudicates a cause to an effect has this metaphysic principle in mind regardless of whether he is conscious or not of it. That is why it is called a metaphysical principle. It operates before the inquiry.
To understand how the principle of Uniformity of Nature dominates not only scientific inquiry but mental structures and culture, we shall now further the investigation to the next step towards the understanding of risk of a disaster caused by a meteor crash. This takes us to the following century.
In the 19th century, it was believed that nature didn’t change. The animals, vegetation, and geology of the Earth were and had been the same since the beginning of time. This sort of reasoning was called Uniformitarianism, and it had its basis on the same principle of Uniformity of Nature because in this belief, just as laws don’t change, the present state of nature and the universe is be the same as it was in the past and will be in the future (Uniformitarianism refers to “one form”, just as universe means “one version”.)
|A meteor could have stricken the Earth before the theory was accepted, but the risk of it did not exist before a possibility was contemplated and, most importantly, accepted.|
Based on the geological record and the discovery of fossils of animals that no longer existed, scientific inquiry tried to understand the underlying reason for this. In this way, George Cuvier, brought forth what is known as catastrophism to explain the fossils that were discovered: “All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove the existence of a world previous to ours, destroyed by some kind of catastrophe.” (Cuvier, 1796)
Modern geology and biology began to develop from Cuvier’s works, with important implications for the theory of the evolution of species that Darwin would set forth later that century. This was not only the advancement of science, but evolution, a turn of the screw in human thought and a corollary to the principle of uniformity of nature: Nature changes. There is a discontinuity in natural conditions. The present conditions of the Earth are not the same as they were in a previous geological time. And most importantly, natural conditions can change due to a radical natural event, and provoke a disaster (a term from the Greek dis aster, which means without star, a linguistic remnant of the times of omens in the sky). Thus, what was once impossible, unthinkable became a reality for past conditions of the Earth and a possibility for the future.
In the 20th century there were a number of theories that tried to explain how dinosaurs became extinct. Volcanic activity and geological changes, derived from catastrophism, were the leading prospects for explanation of the event.
In 1980, Luis Álvarez and his son, Walter, proposed a theory that explained the sudden extinction of dinosaurs by a meteor strike. This theory has become the most widely accepted explanation for the radical change at the end of the Cretaceous period. But, when proposed, the scientific community even laughed at Álvarez for proposing such an exotic theory. Meteors can strike Earth, sure, but could they really change life conditions on Earth at that scale? Time and evidence have proven Álvarez’s theory to be correct. Life can be wiped out by a meteor strike. A major disaster caused by a meteor strike was theoretically possible. Again possibility appears but in a new form. Not only radical changes can occur on Earth, but now a new candidate for change rises as possible. Now meteors can cause extinctions. As Álvarez’s theory became more and more widely accepted, the risk of a meteor crash arose. A meteor could have stricken the Earth before the theory was accepted, but the risk of it did not exist before a possibility was contemplated and, most importantly, accepted.
Science can now accept that natural catastrophes can change the Earth. Later, it was accepted that meteors and comets can become the cause of such disasters. But, the next turn of the screw was the following: now that a meteor crash is possible, is it plausible?