Those who do not believe in the existence of demons certainly did not hear from Laplace's demon. It is not about a fallen angel or the imaginary friend who speaks in your left ear.
At the beginning of the hurricane season in the Caribbean, a few weeks after the start of a rainy season in Colombia, and for an increasingly unpredictable and & # 39; gekklimmer & # 39; climate, it is worth going back to this idea, which, despite more than 200 years, is still comfortably at the heart of science. More interesting, and closely related to the Laplace demon, are the least understood ideas about chance, complexity and chaos .
Predicting the future is one of the most important tasks of science to survive in a seemingly messy world. We see it every day when astronomers announce an eclipse or climatologists, the trajectory of a new hurricane.
Can we really predict the future? In 1814, Pierre Simon Laplace, French astronomer and mathematician, formulated a hypothesis that would leave a lasting mark on the history of science. According to Laplace the current state of the universe is predetermined by its former state and the future is a direct mathematical consequence of the present.
At first glance it does not seem to be revolutionary or new, except the curious and original I finish by explaining Laplace. According to him, a hypothetical intelligence, with unlimited capacities of measuring and thinking, would know all the forces that act on a physical system and determine exactly its current state, a (mathematical) analysis of that information would enable him to know exactly the future of that system .
Predicting the future is one of the most important tasks of science to survive in an apparently disordered world
For this intelligence nothing would be new or surprising in the universe. With such powers he would be a real "demon", the scholars of Laplace's work would say later.
Although our knowledge of our complex planet continues to shift, the devil of Laplace circles around in the midst of the most varied scientific works including, of course, those of the climatologists, who try to predict the weather
. ] It is no exaggeration to say that most scientists in their hearts carry the intimate desire to become a living version of that demon. But the task of scientific prediction of the future is a bit more complicated than originally planned by Laplace, and this was only learned a few decades ago by scientists after the French mathematician brought this curious demon to life.
For starters, it is good to clarify that the idea that the world is predictable does not contradict the apparent disorder we see in the roulette of a casino or in the climate of a warmer world.
And that is that & # 39; coincidence & # 39; is not necessarily the same as the absence of predictive capacity (Laplace is one of the founders of the mathematical theories of chance) . Some mathematicians simply define chance as the result of a process that can in principle be predicted, but for which the number of variables involved in the prediction is much greater than the outcome of the process itself.
Consider, for example, the launch of a coin. If we want to predict exactly where it will fall, we only need two or three data. With simple formulas, a beginning physicist predicts, almost exactly, the fate of it. But when it comes to knowing which side will fall (face or seal), the matter becomes the color of an ant. Many variables are required to predict a single result (face or stamp).
In this way, we say that the final result of the release is random & # 39; is, a name that can be better used to our 'laziness & # 39; or lack of time. For the demon of Laplace, with his powers of knowledge and calculation, the side of the coin is perfectly determined from the launch, and there is nothing arbitrary in the phenomenon.
So, is it the weather? Messy and crazy or, actually, just random? That is, if we had enough information and computing power (as the Laplace demon would have), can we accurately predict this? The weather is not & # 39; crazy & # 39; (it is not messy), but it is also not fully predictable. The reason is simple: demons (including Laplace) do not exist.
In the 1880s, Henri Poincaré, a French mathematician and theoretical physicist, discovered what we might regard as the Achilles heel of the Laplace demon; or, more accurately, of the "demon students": the scientists.
According to Poincaré, there are physical systems – the climate is one of them – that although they can be accurately predicted by the almighty demon of Laplace, a small error in the initial information (obviously committed by a demon student) can lead to a totally wrong prediction of the future of the system. We call this property hypersensitivity to initial conditions or, in a word, chaos.
The climate is random (it requires too much information to predict nonsense), but also, chaotic (a small mistake) in the first information can make us predict a storm in what turns out to be a sunny morning
From chaos to complexity
In some systems, chaos thus arises from our imperfection as human beings (demon students) Our inability to know, such as the demon of Laplace, all the details of the system. But chaos does not eliminate the demon. There is no such concept for the latter.
The world for the devil of Laplace is a relatively boring place where everything that happens (chaotic or not), the fall of an apple, the movement of an artificial satellite or the ninth symphony of Beethoven, is predetermined by what was earlier happened. Destiny exists in one way or another, but only that almighty intelligence would know it.
This discouraging idea concealed itself with a bit of embarrassment under the cover of science for almost two centuries . So it was until a few decades ago that the Universe gave us a new surprise.
In systems made of relative & # 39; simple & # 39; parts (molecules in a crystal, termites in a colony or the citizens of a country), the interaction among them, which can also be very simple (electrical repulsion between molecules, chemical signals that remain on the road or in a store), can create coherent and sometimes new collective behavior, without being dictated by an orchestral conductor & # 39; .
This behavior is not described in the rules that determine the behavior of the parties. We say that the whole is greater than the sum of the parts.
The water molecules in an ice crystal come together to form snowflakes that have incredible shapes and that none of the molecules were meant to create. Termites build sand cathedrals without one of them acting as architects. The citizens of a country can, without being intended, create egalitarian and peaceful societies almost independent of the government that governs them.
The citizens of a country can, without wanting to, create egalitarian and peaceful societies, almost regardless of the government it administers
Sand cathedrals, snowflakes or peace are unpredictable. The Laplace-demon could only discover these properties if the system is simulated in real time & # 39 ;. But this only does the universe itself.
These systems modern science call complex systems. But as explained above, it must be repeated that complexity not only contains many parts that are not understood. For most of us it is complex again, but only because we do not understand it. When the scientists who know him sufficiently analyze it with the previous criterion they realize that the atmosphere itself is not very complex.
The truly complex system is that which is formed by the interaction of the atmosphere, life (including us) and everything that comes or comes from the earth. Even the devil of Laplace, starting with the initial conditions of the earth, could have predicted that there would be palms that would rise hundreds of meters in the sky, or that the earth would have metallic objects flying (aircraft) or that the concentration of CO2 in the air would be as high as it is now.
Due to its nature, complex systems conceal surprises, especially when the way their parts interact has changed. The case of climate change could be thought of by everyone from this new perspective. That feeling that the increase in greenhouse gases only causes a monotonous rise in temperature, the strength of hurricanes and fires or sea level can only be part of the story, as the scientists have warned  Perhaps the system, in its complexity, could surprise us reservations that are larger than all demons students can predict until it is too late. But these surprises are not necessarily bad. However, in the light of uncertainty, it is better to move & # 39; move carefully.
JORGE IVÁN ZULUAGA
Associate Professor of the Institute of Physics of the U. de Antioquia