Einstein, quantum theory and the battle for reality

"I think I can safely say that no one understands quantum mechanics." So shouted the great physicist Richard Feynman in the 1960s – and his words are just as fresh today. The explanation of quantum mechanics of the operation of the universe at the atomic level offends intuition. Schrodinger's cat, this unfortunate moggie trapped in a box containing a radioactive atom and whose unpredictable disintegration gives off a poisonous gas, is dead and alive until we open the box to look at it. A particle does not have a defined position until we measure it, its precise location here or there, but an entanglement of probabilities.

Expect. Watch, measure – do our actions really make a difference? Is not this poor feline dead or alive before we open the box? Does the world behave surely regardless of our perception of it? Albert Einstein thought thus: he defended realism, in which the universe can be understood and described without taking into account our interactions with him. His nemesis was the fervent Danish and anti-realist physicist Niels Bohr, who argued that no such objective image of this kind is possible, but only a canvas that covers what we can observe and measure.

The anti-realism won the day. The quantum mechanics promoted by Bohr, which relegates reality to irrelevance, is the dominant image of nature at the atomic and subatomic scales.

It should be reversed, according to Lee Smolin, with the "magical" thought that accompanies it. Smolin, a leading figure in the struggle to restore realism as the foundation of science, insists that the time has come to take up arms. "Science is under attack," he writes in The unfinished revolution of Einstein"And with it the belief in a real world in which the facts are true or false. . . When an antirealist philosophy takes hold of fundamental physics, we are in danger. "The risk, he warned, is the abandonment of the century-old project of realism," which is nothing less than continuous adjustment, little by little, as the knowledge progresses, from the border between our knowledge of reality and the realm of fantasy. "

Smolin offers a masterful exhibition on the state of quantum physics, gently mixing a history of the field with clear explanations, a philosophical context and an accessible introduction to new ideas. His account of how two opposing perspectives on quantum behavior have been incorporated into Bohr's counter-intuitive orthodoxy is bewitching.

Einstein fired the shot from the idea that light could show the properties of both a particle occupying a defined location and a more diffuse wave. In 1905, when he was only 26 years old and working as a patent clerk, he showed that lighting the metal could release electrons. He had discovered what was called the photoelectric effect, proving that light came in small packets or "quanta" (now called photons). This would have earned him a Nobel Prize in 1921.

Niels Bohr remarked that Einstein's theory of light could be usefully applied to atoms. A young Parisian aristocrat named Louis de Broglie then provided a critical insight: if light could be both a wave and a particle, could the same strange duality be true of electrons and other matters?

In 1925, Erwin Schrodinger, an adulterous professor at the University of Zurich, heard about De Broglie's thesis and took her, along with his girlfriend, for a holiday in the mountains. In a few days, he had invented the relevant equations (when he went to Stockholm to accept his Nobel Prize, the rogue took his wife and his girlfriend).

Bohr understood that all these breakthroughs were becoming a theory filled with disconcerting probabilities and uncertainties, a shocking break from the known and deterministic results of classical physics. But the new theory of quantum mechanics seemed to work, if not intuitively, mathematically. Smolin writes that Bohr seized his moment, "announcing the birth not only of a new physics, but of a new philosophy. The moment for a radical anti-realism had come and Bohr was ready for it. "

As the Bohr Institute in Denmark is home to these ideas, this philosophy has been known as the Copenhagen Interpretation. When the German theoretician Werner Heisenberg arrived at the same formulation of quantum mechanics in a different way, Bohr was again justified.

Even if Einstein complied with Danish rule, realism never died completely. De Broglie then launched a unifying idea called pilot wave theory, in which the particle is guided by a "pilot" wave. It was rediscovered in the 1950s and still has its members.

The past half century has given rise to other innovative ideas such as loop quantum gravity, in which Smolin is a leading researcher. But he and his colleagues have no illusions about the monumental challenge ahead: the need to invent a new physics, as Einstein and others have done.

"So maybe everything is in place of a brilliant student somewhere, incredibly arrogant, like the young Einstein, but blinding enough to absorb the essentials of everything we did, before the put away and leave with confidence. "

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If Einstein feels like the man of the moment, it's because 2019 marks the centenary of the most spectacular test of his powers: the British attempt to confirm his theory of relativity with the help of the Total eclipse of 1919. This experience and its heritage make the object No shadow of a doubt, by Daniel Kennefick of the University of Arkansas.

Einstein had calculated that starlight should bend when she passes a massive object – the Sun for example – because the gravity of the object deforms the fabric of space-time. The eclipse of May 29, 1919 promised a unique opportunity to test his predictions of another world. British scientists seized the opportunity and planned expeditions to two sites: Principe Island in the Gulf of Guinea and Sobral in Brazil.

When the Moon passes in front of the Sun during such an eclipse, it blocks the light of the solar disk and makes the day pass at night. The temporary power cut allows you to see the stars around the sun (as well as the halo-like crown). By comparing the true locations of the stars at their apparent locations during the breakdown, scientists could infer whether the sun was actually shifting starlight.

Kennefick brings together an exciting mix of ingredients in a dense but rewarding reading: Einstein's chutzpah; glamor, luck and sense of adventure of the continuation of the eclipse; The audacity to plan such a demanding experience during the First World War and to execute after its chaotic consequences. An earlier attempt at confirmation of relativity had gone badly: German scientists observing the 1914 eclipse in Crimea were arrested as spies by the Russians.

Inevitably, the war also darkened the eclipse of 1919. The planning was entrusted to two brilliant astronomers, both pacifists: Sir Arthur Eddington, director of the observatory of Cambridge, and Sir Frank Dyson, then astronomer royal based in Greenwich . Eddington, a Quaker refusenik, faced jail until his university issued a moving appeal to the conscript board, claiming that after the death of the first and second observatory assistants during the war, no other in Cambridge did not seize the eclipse.

The shortage of civilian ships also posed problems for sending the necessary equipment. But the expeditions have taken off, the sun has shone especially and the required observations have been secured.

And what observations they were! In November 1919, six months after the eclipse, Eddington and Dyson proved to have confirmed Einstein's prediction. It was a global sensation. "Lights all Askew in the Heavens" illuminates the New York Times.

When fundamental physics is stolen by an anti-realist philosophy, we are in danger

This confirmation even influenced the scientific culture: Einstein's willingness to submit his ideas to an experimental investigation convinced the philosopher Karl Popper to develop "falsifiability" as a litmus test of scientific truth.

Kennefick dissects the skepticism that surrounds this historical experience. After the war, he notes, most German scientists have been confronted with ostracism. Did Eddington and Dyson conspire to prove relativity in order after the war to bring together scientists and the world? Did they show bias by rejecting some data? The fact that Eddington and Dyson were advertising fans also seems to have tarnished their reputation – unjustifiably, in Kennefick's eyes. "It is wrong to believe that the truth does not need a lawyer," he writes. The 1919 experience, he believes, has achieved its sole purpose: to prove to Einstein that he is right or wrong.

It's not that the big man needs such an affirmation. When asked what he would have done if the results had been less compelling, Einstein said, "Then I should be sorry for my God." The theory is correct. "

So let's reserve our mercy to Mileva Maric, or Einstein's wife, as a new biography describes it selectively (he is married twice). Among the first female science students in Europe, the cerebral Serb met Albert in 1896 at the Polytechnic University of Zurich, where they studied mathematics and physics.

One student described Mileva as "a very good girl, intelligent and serious, she is small, frail, dark and ugly. . . box a little, but has very good manners. Albert, a few years younger, was bewitched; he called her Dollie and she called him Johnnie. Their families did not approve. Mileva became pregnant. A girl, Lieserl, was born out of wedlock but, surprisingly, her fate remains unknown. Surviving letters suggest that Lieserl is dying of scarlet fever or being given for adoption.

But that's not the question this book, written by Allen Esterson, a former physics professor, and the science historian, David C Cassidy, is trying to answer. As previous biographers claim, was Mileva an uncredited contributor to Einstein's research?

School and university reports suggest that she was brilliant but not too supernatural. When the couple corresponded during separate periods (including pregnancy), he enthusiastically wrote his ideas, but his answers did not detail them. A meticulous analysis of letters, interviews, gossip, reports, translations and transcripts, does not leave the authors convinced by the myth of Mileva.

Rather, it shows the portrait of a capable but frustrated young woman who, tragically, did not realize her full potential as a scientist "and she did not realize her hopes and dreams in marriage and in life. ". In 1919, year of the eclipse, Einstein had divorced Mileva to marry his first cousin, Elsa, herself divorced with children. Letters have recently been revealed suggesting that Einstein drew one of Elsa's daughters.

This biography of Einstein's first forgotten wife offers instead a haunting accusation of Albert as a distant and ultimately disloyal companion: a quantum husband who was neither here nor there; a visionary who saw the light of the stars in the universe but not the darkness closer to home.

The unfinished revolution of Einstein: in search of what is beyond the quantum, from Lee Smolin, Allen Lane, selling price £ 25, 322 pages

The shadow of a doubt: the 1919 eclipse that confirmed Einstein's theory of relativity, by Daniel Kennefick, Princeton, PVC $ 29.95 / £ 24, 416 pages

Einstein's wife: The true story of Mileva Einstein-Marić, by Allen Esterson and David C Cassidy, MIT, PVC $ 29.95 / £ 24, 336 pages

Anjana Ahuja is a scientific commentator

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