Changes in the Scientific Paradigm

Thomas Kuhn

As Thomas Kuhn pointed out, from time to time there are shifts in the scientific paradigm that cause sharp deviations in the direction of research. These shifts can occur in any of the sciences. Here are some important historical examples:

Puerperal fever was for centuries the leading cause of death in women giving birth. In 1795, the Scottish obstetrician Alexander Gordon claimed that the disease was transmitted by doctors and midwives. In 1842, the English physician Thomas Watson, known for his description of the aortic pulse, recommended that doctors wash their hands with diluted lye before attending a birth. And in 1847, the Austrian physician Ignaz Semmelweis advised the same, based on data showing that the incidence of puerperal fever was higher in hospitals than in births taking place at home, and higher among women in labor attended by doctors than by midwives. Semmelweis' proposals were violently rejected by contemporary physicians, who were outraged by the idea of ​​being blamed for infections caused by themselves, to the point that Semmelweis was committed to an asylum where he only survived two weeks. His death is believed to have been the result of a beating by the asylum guards when Semmelweis, who was 47 years old, tried to escape. His proposals were confirmed by the discovery of the germ theory of infectious diseases by Louis Pasteur, according to which diseases are caused by microorganisms, and not by miasmas transmitted by air, as previously believed. This caused an abrupt change in the scientific paradigm applied to medicine.

Different types of chance

Jacques Monod

When we don’t know why something happens, we usually say that it is due to chance. But this statement is ambiguous, because there are two different types of chance:

• Epistemological chance, where the cause of what’s happening is well-known, but so complex that it remains outside the scope of our knowledge. Almost all games of chance (dice, roulette, lottery jackpot) are examples of this type of chance. Rolling dice conforms to the laws of mechanics, but the conditions are so complex that we cannot predict the result of each roll. This type of chance is what Jacques Monod called operational uncertainty in his book Chance and Necessity (1970):

This term is used... in relation to the game of dice, or roulette, and the calculation of probabilities is used to predict the result of a play. But these purely mechanical and macroscopic games are not "the result of chance" except because of the practical impossibility of controlling the throwing of the dice or the ball with sufficient precision. It is evident that a very high precision launching mechanism is conceivable, and would make it possible to largely eliminate the uncertainty of the result... The same thing happens, as will be easily seen, in... many phenomena where the notion of chance and the calculation of probabilities are applied for purely methodological reasons. (My translation into English).

My 10 Favorite Scientific Discoveries of the 20th Century

In a post published two weeks ago, I commented on an article in Science News that tried to answer this question: which were the ten most important scientific discoveries of the last century? Some of my readers asked what is my personal opinion. This is my answer.

To begin with, I will point out that scientific research can advance in four different ways:

1. Theoretical science, which tries to discover fundamental laws in the universe.
2. Experimental science, which confirms or falsifies theories by carrying out experiments.
3. Observational science, which instead of experimenting, observes. Astronomy, for instance, uses these methods, as experimentation is almost never possible.
4. Technology, the practical application of science, whose goal is to build devices that work.

Is there a crisis in theoretical physics?

Nicolaus Copernicus

Physics has been, for the last seven centuries, the queen of sciences: its object is the study of the lowest-level of reality; its most akin to mathematics; it has seen happen the highest number of new, spectacular and revolutionary theories and discoveries. Let's see a few of them:

• 13th century: Roger Bacon studies reflection, refraction, spherical aberration and the use of lenses to correct vision defects. He also suggests the possibility of building telescopes, microscopes, and flying vehicles.
• 14^th century: Jean Buridan, Nicolás Oresme, Albert of Saxony and the calculators of Merton College revolutionize Mechanics, separating it for the first time from the work of the Greek philosophers, and introducing new concepts such as impetus.
• 16th century: Copernicus proposes replacing Ptolemy's geocentric system by a much simpler heliocentric system. Kepler modifies the theory of Copernicus and discovers the three empirical laws that bear his name.
• 17th century: Galileo perfects the telescope and makes with it astronomical discoveries. He also recapitulates and organizes the mechanical discoveries of the 14th century. Newton revolutionizes physics with the theory of universal gravitation, which unifies terrestrial and celestial mechanics, and makes great advances in optics. Other important physicists of that century are Pascal, Huygens, Boyle, Mariotte, and many more.
• 18th century: Although it's possible to detect a certain slowdown in scientific research, we can mention the Bernoulli brothers, and near the 19th century, Galvani, Volta and Laplace.
• In the 19th century, discoveries in theoretical and experimental physics and the number of professional physicists increased dramatically. Let's mention just a few of the most important: Dalton, Faraday, Ampère, Gauss, Maxwell, Carnot, Lord Kelvin and Boltzmann.

Why we have no great men today

G.K. Chesterton

First, a clarification: I won’t let myself be dragged by political correctness. I’m not going to change the title of this post to “great human beings.” For me, the word “man” (equivalent to the Latin homo) still has a main generic meaning, different from the meaning whose Latin antecedent is vir (male), opposed to woman or female.

The absence of great men is a common place today and affects almost all fields:

What’s a scientific theory

Karl Popper

Although it is fashionable to assert that Karl Popper’s theories about the evolution of science are outdated, his definition of what is a scientific theory is unassailable:

A theory is scientific if and only if it is possible to design an experiment that proves that this theory is false.

A paradigmatic case is the Copenhagen Interpretation of Quantum Mechanics. In 1935, Einstein, Podolsky and Rosen designed an experiment that could prove this theory false. A few months later, Niels Bohr published another article in the same magazine, in answer to the previous article. Almost 30 years later, as I explained in another post in this blog, the EPR experiment, which up to that point had been mental, could be carried out and confirmed Bohr’s predictions, rather than Einstein’s. As this theory was able to resist an attempt to prove it false, it must be considered a scientific theory.

Of course, this success of the theory does not imply that it should automatically be considered correct or true. Scientific theories (always according to Popper) never become so. This theory has successfully withstood an attempt to prove it false, but the next attempt could do it.

The debacle of determinism

Isaac Newton

By the end of the eighteenth century, Isaac Newton’s theory of universal gravitation was well established. As this theory makes it possible to predict very accurately the orbits of the bodies in the solar system, the French astronomer Pierre Simon de Laplace believed he had sufficient reasons to say the following:

An intelligence that knew all the forces that animate nature, as well as the respective situation of the beings that make it... could cover in a single formula the movements of the largest bodies of the universe and those of the lighter atom. Nothing would be uncertain and both the future and the past would be present before his eyes.

This assertion became the dogma of deterministic materialism, a philosophical (not scientific) doctrine asserting that only matter exists (taking the term broadly) and that the whole history of the universe is determined. Therefore there is no human freedom, nor intentionality, nor final causes in nature. There are just efficient causes.

Laplace’s statement can be expressed in more modern terms:

If we knew the position and the momentum of all the particles of the universe at a given instant, we could predict all their past and future development.

Bell’s inequality and causality

Niels Bohr

Quantum Mechanics took shape about ninety years ago. During the twenties, Niels Bohr and Werner Heisenberg formulated the Copenhagen interpretation, which added to the mathematical formulation some additional considerations such as the following:

• Physical systems with properties that can take concrete and opposing values ​​(such as direction of polarization or spin) in certain circumstances can be in a state where those properties do not take a defined value, but keep all the possibilities simultaneously open. For example, the direction of polarization of a photon can be simultaneously north-south and east-west. The spin of a particle can be both up and down.
• The act of measuring one of these properties causes the collapse of the wave function, which means that the result of the measurement can only be one of the possible values. The wave function gives us the probability of obtaining each value.
• It is possible to build a physical system formed by two or more interlaced particles with respect to some property, which means that if one of the particles collapses with a certain value, the other particle has no choice but to collapse with the other.