The 2022 Nobel Prize in Physics and quantum reality | Lorenzo Diaz Cruz

The month of October is special for those of us who dedicate ourselves to science. At the beginning of the month the Nobel prize winners and that causes excitement in the community, glad to know if the prize will fall in the area in which one works, which makes us happy because it makes us feel part of this noble collective enterprise that we call science. It is always news that we like to share with colleagues and students, or even with acquaintances and relatives; in my case I like to comment something about the laureates in physics. We also read the news about the winners in the other areas, Medicine or Chemistry, and we would like to know if we have a minimal idea of ​​what those awards are about, or in the case of the Literature award, we wonder if we have already read something by the author .

This year the Nobel Prize in Physics fell to the scientists John Clauser (USES), Alain Aspect (France) and Anton Zeilinger (Austria), for his work on the experimental evidence of the foundations of quantum mechanics and its imminent technological applications. This time the prize was awarded to a work of great depth, which even touches the boundaries of philosophy and the interpretation of reality.

Sometimes you find articles in magazines or newspapers that try to draw public attention to science, and in them we read spectacular statements that are not always true. For example, it is often said that quantum mechanics implies that the reality does not exist and those are big words that deserve a good discussion. In fact, since its birth quantum mechanics has been accompanied by a strong debate about the fact that in said science some principles of classical physics (including Newtonian mechanics) are abandoned, for example, determinism, as well as the limits of what we can know about what we call “reality”.

And why that resistance of physicists of the early twentieth century to accept the ideas of the quantum mechanics? Well, obviously all that generation was educated in the so-called classical physicsin which we are interested in knowing the time evolution of a system in a deterministic way. That means that if we repeat an experiment identically, the same result should be obtained. This is the case, for example, if we hit a ball with a racket and throw it against a wall, we expect that if we pay it evenly (ideally) many times, then the ball will bounce the same way.

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Well, that works when we use tennis balls or squash balls, but when it comes to doing that experiment with electrons instead of balls, it doesn’t matter if we identically prepare the experiment, it may happen that the bouncing electron would sometimes come out at a certain angle, and other times it would come out at another angle. In fact, we cannot predict with certainty at what angle the electron will scatter; the most we can know is the probability that the electron behaves in a certain way.

“God does not play dice”plot Einstein to oppose that statistical interpretation. He believed that physics should be deterministicand got into heated debates with Bohr, Heisenberg, pauli, Schrödinger, the founders of this new quantum physics that gave them so many headaches. It must be said that Einstein was not a fool, he was a great physicist who tried to understand the implications of admitting the probabilistic interpretation. For him, it should be possible to speak of an objective reality, of which everything relevant could be known.

Thus, in 1935 Einstein, together with his colleagues Podolsky and Rosen, devised an argument to prove that quantum mechanics was inconsistent. According to them, if quantum mechanics is valid and correct, then the existence of reality would be in doubt. Well, it would be like saying that the moon does not exist, unless you are looking at it. Therefore, the quantum mechanicswhich worked so well to describe the subatomic world, must have been incomplete.

For many years the orthodox interpretation of CM was accepted and these works went unnoticed. That changed in the 1960s, when a brilliant Northern Irish physicist named John S Bell, began to be interested in the subject. Bell worked at CERN, spending most of his time studying the properties of elementary particles. It was in his free time that he dedicated himself to reflecting on such esoteric topics, according to what he told us Martin Veltman (Nobel Prize in Physics in 1999), to his students at the U of Michigan.

As a result of his work, Bell deduced some inequalities, which, if true, would imply that the MC was missing something (which were called “hidden variables”).

in his book Speakable and Unspeakable in Quantum Mechanics, Bell uses the example of a person who wears socks of two different fixed colors, say red and blue. Thus, when we see that it goes around the corner, if it lets us see a foot then we can know what color that sock is, then with that information we can deduce what the color of the other sock would be.

In the case of quantum mechanics, we use the spin property, which is a kind of intrinsic spin of a point particle. For the electron the spin in a certain direction (say z) takes values ​​+1/2 or -1/2. In some situations, two electrons are produced that must have opposite values ​​of spin, so the electrons are said to be entangled. So if we measure the z-spin of one of the electrons and get +1/2, then we immediately know that the other must have -1/2. But how does the other electron find out what its state should be? It appears as if there is a signal that propagates instantaneously, and that would violate the laws of classical physics.

After publication, the Bell’s work It went almost unnoticed among the physics community. However, it caught the attention of some experimental physicistsamong them John Clauser, who devised a method to prove Bell’s inequalities. He did that job as a postdoc at the University of California (Berkeley), although he had to fight to be allowed to do so, since he would have been hired to work in Astrophysics, which was his specialty. The result of the experiment was that the inequalities were violated and therefore quantum mechanics is fine.

These days the press asked Clauser what he would tell Einstein about his results. “Sorry Albert, but Bohr was right.” was the answer.

However, there were some details of Clauser’s experiment that left doubts. That’s where he comes in Alain Aspect, another of the winners, who repeated the experiment, with technical improvements, but the conclusion was the same. Even more, the other winner, Anton Zeilinger, improved the experiment so that it was carried out at a suitable distance between its components, such that signals could not propagate between them. An additional result of Zeilinger was the demonstration of the teleportation of quantum signals. The results indicate not only that everything seems to work well with quantum mechanics, but that it is possible to use it for more technological applications.

But then there is no longer any doubt about quantum mechanics? For some no longer, they say there is nothing wrong with the probabilistic interpretation, that this is the sub-atomic world and you simply have to accept it. Other physicists have struggled for decades to find an alternative to Quantum theory, but so far all those attempts have failed. That does not mean that there will not be out there in some university classroom, a curious student who is thinking about the problem and that perhaps in a few years he will surprise us with a solution to these dilemmas. Or, that there will be new and more precise experiments that will continue to confirm the validity of the quantum mechanics; however, his enigmatic interpretation of reality, with a behavior that suggests that reality depends on the measurement of its elements, so much so that some interpret it as if that same reality were being created by process of measuring.

On the other hand, and beyond the philosophical debate, it is possible that the advances achieved with these experiments, which allow or make quantum teleportation possible, will further revolutionize technology. For example, with quantum computing, or by making it possible to use more efficient systems for cryptography, with which safer bank transactions can be made. For this it is necessary that the security systems Stay one step ahead of hackers and other cyber criminals.

And as always, the Scientific advances are like a double-edged knife, but it depends on the society that forces the governments and economic powers to put the welfare of society as the priority of our system of coexistence, locally and globally. All of which makes it necessary for society to educate itself, to understand what is being achieved, being the responsible scientists to make specialized knowledge shared by all human beings.

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The 2022 Nobel Prize in Physics and quantum reality | Lorenzo Diaz Cruz