What are paradigms? What are some examples

Revolutions in Science : When world views are shaken

A cartoon sums it up: A chick that has just hatched with the rest of an egg shell on its head, looks out into the world with wide eyes and exclaims in astonishment at the new perspective: “Oh, wow! Paradigm shift! "

The word “paradigm” is a pop star among the technical terms, in the past 50 years it developed a life of its own that its creator was sometimes afraid and anxious. Before that, it eclipsed its existence in grammar, where it stands for a diffraction pattern that is illustrated by examples (such as: sings, sang, singen). Then came the scientific theorist Thomas Kuhn and pulled it out of its niche to light. "It was a great term before I got my hands on it," said the American self-deprecatingly. The word made a career and conquered every imaginable subject.

Anyone who has created something new today or calls for a rethink simply announces a paradigm shift. The word is omnipresent - in the banking world, in environmental protection, in journalism. Even on some car stickers you can read: “Shift happens!”.

The book that gave the word its popularity is one of the most influential of the 20th century. When Thomas Kuhn published his book “The Structure of Scientific Revolutions” 50 years ago, he fundamentally changed the view of progress.

The legend goes that a young researcher stands on the shoulders of giants. He observes the world and builds on what scientists have created before him. Progress is therefore a continuous striving for something higher. And the textbooks tell you whose shoulders you should climb on.

This is how Kuhn saw it until 1947. While the 25-year-old was working on his doctoral thesis in physics at Harvard University, he was supposed to teach the history of science to first-year students. A case study could help, he said. Preferably the forerunners of Newton's mechanics. In his search for historical material, he first looked at Aristotle's “Physics”. He was shocked. What he read there sounded idiotic. Kuhn could not sort the statements into "Aristotle already knew so much" and "So much was still to be discovered". The ancient scholar was not lacking in explanations. But apparently he knew absolutely nothing about mechanics.

How could such a great thinker be so wrong? The solution to the riddle was Kuhn himself. He had not taken into account that for Aristotle terms like “movement” and “matter” had completely different meanings. As soon as he took note of it, the logic of the ancient worldview opened up to him. It wasn't unscientific. Just different.

This “Eureka” moment changed Kuhn's life. He left theoretical physics behind and instead wanted to explore how people explain the world to themselves. First at Harvard and then at the University of California at Berkeley, he met the philosophers of his time. He read Karl Popper's writings, who accepted that the only criterion for distinguishing between science and pseudoscience was that scientific theses can be refuted. That wasn't enough for Kuhn. For 15 years he wrestled with the ideas that he had been carrying around with him since he first read Aristotle. In 1962 his work was finally published, which for him later was only "the book".

Researchers can never be absolutely sure whether they have understood the phenomena of the real world, he writes there. They always interpret their observations and the results of their experiments with the help of a recognized theoretical structure, the “paradigm” valid at the time - and that can only be thrown from the throne, but not refuted, as Popper demands.

Kuhn understands a paradigm to be scientific achievements, rules and norms that a research community recognizes as their basis. If something does not fit into this picture, it is ignored, ridiculed, explained away as a measurement error or coincidence, or the theory adjusted a little.

Only when that no longer works will a scientific revolution occur and the old paradigm will be replaced by a new one. Old and new can then be so different that the representatives of two paradigms neither understand each other nor can their performance be measured by the same standard - like the physics of Aristotle and Newton. Progress is therefore not linear, but rather in phases. And a young researcher may very well stand on the shoulders of giants. Sometimes it hits them hard on the head, so that they sink to the ground.

The most impressive example of this was provided by Nicolaus Copernicus. He dared to turn a 1400 year old worldview upside down: It is not the sun that revolves around the earth, but the earth around the sun! Luther scolded him a fool for this and, for once, was on the side of the Catholic Church. It took centuries for Copernicus' teachings to prevail.

Even if the revolution turns out to be smaller, the dispute between specialists can become violent, the biologist Fernando Nottebohm discovered. It was never his intention to do anything unheard of. He just stayed true to a childhood passion: birdwatching.

He was already keeping pigeons and parrots in his parents' garden in a suburb of Buenos Aires. If a canary got lost near it, the bird soon found itself on a bicycle handlebar. The boy wanted to show him his neighborhood. Decades later - Nottebohm was now doing research at Rockefeller University in New York - the birds helped him to unmask an iron principle of neurobiology as a misconception.

“As soon as development is complete, the sources of renewal dry up irretrievably,” wrote Nobel laureate and neuroanatomist Ramón y Cajal in 1913. “In the adult brain, the nerve tracts are rigid. Everything can die, nothing can be renewed. "

For several decades there was no reason for “normal science” to doubt the judgment. Every child saw that strokes or other brain injuries cause permanent damage. But no expert could imagine that the brain can rejuvenate itself by forming new nerve cells (neurogenesis). Only a madman would claim that they can find their place in such an intricate network as the brain without disrupting its functions! The reaction was correspondingly violent when Fernando Nottebohm proved just that in a series of elegant experiments.

“What you think you know can block your view,” says Nottebohm. He's a quiet person, but a free spirit. The fact that so many colleagues smile at his love for birds and their song does not bother him. “If you just stare at cell biology, you can easily be misled. I'm interested in how the brain adapts to the challenges of nature. That is why behavior is just as important. ”It was only through this conviction that he discovered“ anomalies ”that he could not explain using the prevailing paradigm and was bold enough not to ignore them. Swapping a really open question with a task whose solution is predictable (Kuhn calls it a “puzzle”) was out of the question for him.

Nottebohm heads a research station at Rockefeller University, just under 150 kilometers north of New York, in the Hudson Valley. He has been working in the manor house in the middle of the forest and swamps for 45 years. If you are looking for peace and quiet here, go for a walk. But as soon as you step through the front door, you hear a cacophony that is reminiscent of children's screams in the outdoor pool. 2000 zebra finches, canaries and wild songbirds live here together with Nottebohm.

The bright yellow canaries are particularly loud in autumn. They practice love songs for spring. Instead of digging up the old melodies from the previous year, each male tries his hand at new compositions. “You want to impress the women,” says Nottebohm. Because they are hard of hearing themselves, they have no idea how shrill the sample will sound.

For Nottebohm it's music - and the only sensible animal model for language. How can a brain the size of a walnut store so many melodies? Who teaches them to the birds? In the 1970s he began mapping the brain centers for bird song. In the males, some singing centers were four times as large as in the more silent females. However, if the females were given testosterone, the neuron nodules swelled twice as much. New nerve connections couldn't explain that. So new nerve cells had to be involved - although this was impossible according to the textbook.

“I knew it was an exciting discovery,” says Nottebohm. "It challenged everything we knew about storing and forgetting memories." That was why he forced himself to be silent. Anyone who wants to start a "revolution" has to be sure. It was only when his team had marked and described the newborn cells, and when they could prove that they were integrated into existing nerve networks, that they published the first study in 1983.

At the first conference a year later, the representatives of "normal science" went to the barricades - above all Pasko Rakic, an influential neurobiologist at Yale University who could not find anything like this in monkeys. Nottebohm was laughed at and attacked.

He was not deterred. With the greatest care, experiment after experiment, he has drawn doubters to his side. In the 1990s it was said: OK, this may apply to birds - but not to mammals! Then Elizabeth Gould found new nerve cells in rats. And now we know that humans can also form them - in small quantities. It is not yet clear whether this will result in a new paradigm about memory or whether the fountain of youth for nerve cells has completely different functions.

Nottebohm has long been showered with honors for his pioneering work, "normal science" has long since discovered neurogenesis for itself and makes full-bodied promises. Nottebohm is uneasy about that. “Skepticism is a virtue,” he says. "Whoever pushes ahead now damages the whole field."

Kuhn had a similar experience. He had expected criticism of his book. But he found his fans no less problematic. A student thanked him for directing his attention to the paradigms: “Now we can abolish them!” Others used the book's arguments to deny the established science any power of interpretation. Kuhn then made it clear that he was pro science and pro paradigm. Without paradigms, every researcher would have to start from scratch and would be disoriented before the chaos of nature. They are a framework to hold on to.

"Normal science" tests whether the scaffolding is any good. According to Kuhn, she solves the “puzzles” that the paradigm gives her. Elementary particle physics shows that they are sometimes anything but trivial, says Jürgen Renn, Director at the Max Planck Institute for the History of Science in Berlin. Thanks to their specifications and rules, the physicists at the Large Hadron Collider in Geneva obviously found the Higgs particle with enormous technical effort. That was a breakthrough, says Renn. But not a revolution.

“However, Kuhn did not precisely define what counts as a paradigm,” says Renn. “He also described minor upheavals.” Whether old and new are still incomparable is controversial: “If that were always the case, science would be episodic. Then you lose sight of cognitive processes that take centuries. "

As with any pioneer, many of Kuhn's theses are open to attack. He got his ideas from physics, the scheme does not quite fit in some other subjects. And instead of a science that is guided by theses, there are many data-driven large-scale projects today. But one achievement remains: since Kuhn, science no longer hovers over things. It is made by people and is just as fallible as the individual.

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