It may sound strange to call a “monument” a branch of science that studies matter on a microscopic scale, that is, the behavior of electrons, photons and other subatomic particles.
But although Sánchez Ron recognizes that it is “a creation that is not made of stone or any solid material that can be touched,” he is convinced that “it will last much longer than any of them.”
For now, 100 years have passed since the scientific study that unleashed the quantum physics revolution was published, a theory that still continues to transform fields as disparate as medicine, national security and telecommunications.
“It changed how we live, how we work, how we relate and communicate. In that sense, quantum mechanics has enormous importance, greater than any other theory we know,” says Sánchez Ron to BBC Mundo.
“Another less welcome child of quantum physics are the atomic bombs of Hiroshima and Nagasaki,” he adds to highlight how it powerfully influenced—and influences—international politics.
It even transformed our own sense of reality, as it is a theory that defies intuition. “I think I can safely say that no one understands quantum mechanics,” physicist Richard Feynman declared in 1964 in one of his famous lectures.
That is precisely why UNESCO is celebrating the International Year of Quantum Science and Technology with dozens of events around the world to mark a century of its creation.
“Something with this level of impact needs the attention of politicians, scientists and the general public,” Amal Kasry, head of UNESCO’s Basic Sciences area, explains to BBC Mundo.
Therefore, to read this article on the origin of quantum physics, the advice is the same that Feynman gave in those conferences: “Just relax and enjoy.”
A century later, quantum physics is still one of the most effervescent scientific areas.
The young genius
On July 29, 1925, the German physics magazine Zeitschrift für Physik received an article that would shake physics when it was published a few months later.
Its author was a 23-year-old German named Werner Heisenberg.
That youth, far from a disadvantage, was one of his strengths, since it allowed him to question the current paradigms created by physicists of the stature of Albert Einstein, Niels Bohr and Arnold Sommerfeld.
Isaac Newton had been dead for more than 180 years when Einstein shot down his theory of gravity. Heisenberg, on the other hand, was a disciple of Sommerfeld, a collaborator of Bohr, and had several debates with Einstein over the years, the only one of the three who never accepted quantum theory.
According to Sánchez Ron, “apart from being a genius, young man and with an exquisite background, one could say that Heisenberg was in the right place at the right time.” Other authors also describe him as ambitious, jovial and a lover of hiking.
“Heisenberg managed to bring together a large set of observations, data, and unknowns that had been accumulating with special force since 1900,” explains the Spanish academic who this year published the trilogy “History of Quantum Physics” on the occasion of the centenary.
In fact, the first volume covers the founding period of this theory and goes from 1860 to 1924. The second volume begins with the 1925 article, where Heisenberg “developed the first satisfactory form of quantum mechanics.”
But first, he had to get sick.
A “crazy” theory
For years, what could be called the “old quantum theory” was advancing and, at the same time, dragging along problems and inconsistencies.
So much so that in 1923 the physicist and mathematician Max Born wrote: “It is increasingly probable that not only new hypotheses will be needed, but that the entire system of concepts in physics will have to be reconstructed from scratch.”
It was in that same year that Heisenberg joined Born as an assistant at the University of Göttingen, Germany.
There the young man discovered what would unleash his famous 1925 article: there were problems in the orbits used to explain the movement of electrons in the so-called Bohr-Sommerfeld atomic model.
A few months after arriving in Göttingen, Heisenberg went to Copenhagen, Denmark, for a semester to work with Bohr.
At just 23 years old, Heisenberg “developed the first satisfactory form of quantum mechanics.”
“The emphasis in Göttingen was more on the mathematical side, on the formal side, while in Copenhagen it was more on the, I would say, philosophical side,” Heisenberg would explain years later.
That combination of influences was crucial in helping him come up with a “crazy” theory, as he himself called it.
In an article in Nature magazine about the centenary of quantum physics, science historian Kristian Camilleri says that Heisenberg “experimented with all kinds of ideas until he found one that worked: a very appropriate approach for a period of such conceptual upheaval.”
In May 1925 Heisenberg suffered a severe allergy attack and retired to the island of Heligoland, in Germany, to cure himself “with the sea air,” according to his autobiography.
“Apart from the daily walks,” the physicist wrote, “there was no external occasion that could keep me from working on my problem, and thus I advanced more rapidly than would have been possible in Göttingen.”
Heisenberg versus Einstein
“Instead of building an atomic model based on the idea that electrons move along well-defined orbits in an approximately classical way, Heisenberg decided to develop an innovative theory of motion, a ‘quantum mechanics’, in which electrons could no longer be considered particles moving along continuous trajectories,” says Camilleri.
Heisenberg himself acknowledged in a letter dated early July 1925 that all his “miserable efforts” were devoted to “completely eliminating the concept of orbits, which, in any case, cannot be observed.”
Just as Einstein had done in his youth, Heisenberg started from the basis that “theories should avoid any concept that could not be observed, measured or verified,” writes journalist Walter Isaacson in the biography “Einstein.”
“A new fashion has emerged in physics,” complained Albert Einstein, referring to quantum physics.
However, his role model was also his biggest detractor. Isaacson reproduces in the book the following dialogue from the first meeting of Heisenberg and Einstein, which occurred in 1926:
“We can’t observe the orbits of the electrons inside the atom,” Heisenberg said. A good theory must be based on directly observable magnitudes.
—But don’t you seriously believe that only observable magnitudes should be part of a physical theory? —Einstein protested.
—Isn’t that precisely what you have done with relativity? Heisenberg asked, not without some surprise.
“I may have used that kind of reasoning,” Einstein admitted, “but it’s still nonsense.”
Then I would even say that “a good joke should not be repeated too much.”
Whether Einstein liked it or not, it was too late: the revolution was here to stay.
The quantum “avalanche”
“The speed with which quantum mechanics developed is surprising,” Camilleri writes.
The science historian says that “the avalanche of articles” that was unleashed “left many physicists struggling to keep up with the latest advances”: “As soon as someone understood a new technique or formulation of quantum mechanics, another appeared.”
He even says that there are several examples of physicists who submitted articles to scientific journals and only then found out that someone else had discovered exactly the same thing and had published it shortly before.
According to his calculations, almost 200 articles on the subject were published between July 1925 and March 1927, when Heisenberg published his uncertainty principle in an article that was also crucial for quantum physics and that for Camilleri “rounded off its development.”
For Heisenberg, however, “officially the culmination of quantum theory” occurred a few months later, in October 1927, during the V Solvay Physics Congress in Brussels.
It was there where Einstein and Bohr had their legendary debate about whether God plays (or not) with dice and where the iconic image bringing together their 29 attendees was taken, usually dubbed the smartest photograph in history. Not in vain more than half of the people portrayed had already obtained or would end up receiving the Nobel Prize.
Among the 29 there is only one woman, Marie Curie, and although much has changed since then, the gender gap is one of the great challenges of quantum physics today, says Kasry.
The gender gap and between northern and southern countries are two great challenges of quantum science and technology.
“79% of quantum companies do not have women in leadership positions and only 1 in 54 job applicants in the quantum sector is a woman,” states a report published this year by UNESCO.
The other challenge is “the gap, the huge gap that exists between the north and the south regarding quantum technology,” says Kasry. Even, he adds, “only a few countries have developed concrete strategies” to address the issue.
Those frenetic months that occurred a century ago impact our lives today and will continue to do so, since quantum physics is still one of the most effervescent scientific areas.
Therefore, although “no one understands quantum mechanics”, perhaps this article will at least help to evaluate it.
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