I have participated in the section «Aparici en Órbita» by Alberto Aparici @ScienceCompass in the program “More than One” @More than one by Carlos Alsina @Carlos_Alsina in Onda Cero Radio @OndaCero_en. I recommend you enjoy the podcast «Aparici en orbit: The legendary dispute between Einstein and Bohr and the 2022 Nobel Prize in Physics», Wave Zero, Oct 12, 2022; «Aparici in Órbita s05e03: The nature of quantum theory and the 2022 Nobel Prize in Physics, with Francis Villatoro», Aparici in Órbita, iVoox, Oct 08, 2022. More information about this Nobel laureate in “Nobel Prize in Physics 2022: Aspect, Clauser and Zeilinger for pioneering the use of quantum entanglement in quantum information”, LCMF, 04 Oct 2022.

Alberto Aparici invited me to talk about the 2022 Nobel Prize in Physics, a real pleasure. Start the podcast with the Danish anthem in honor of the Dane Niels Bohr; Alsina recalls his great friendship with the German physicist Albert Einstein, but highlights their mutual dispute about the nature of quantum physics. Alberto exaggerates a bit when he says that today’s physicists are still discussing this issue. He tells us that Bohr and Einstein disagree as to whether the quantum describes the available information about reality or whether it describes reality itself. Alberto focuses on the shape of electrons in atoms; he simplifies the discussion to the thread of wave-particle duality. He states that Einstein thought that quantum was correct but incomplete, and takes the opportunity to introduce the idea of hidden variables theory (that there is a “real” physics that is hidden below quantum). The 2022 Nobel Prize laureates in Physics, Aspect, Clauser, and Zeilinger, have shown that Einstein’s hidden variables do not exist. Or rather: they may exist, but they would leave Einstein very unsatisfied.

Alsina asks me about my “Nobel prize pools”, since this year I got the three Physics winners right and one of the winners in Chemistry. He commented that I got four out of seven and it could have been six out of seven if I had had the guts to predict a second Nobel for Barry Sharpless, but it seemed impossible.

Alsina asks me to rectify Alberto, isn’t there a better theory than quantum as Einstein wanted? Do we have to resign ourselves? I answer by going back to von Neumann’s mathematical demonstration in 1932 of the impossibility of the existence of a theory of local hidden variables, such as those that Einstein liked. Alberto clarifies that local means that it is relativistic, that it complies with Einstein’s theory of relativity. I mention that Bell realized that this could not be proven mathematically, the only option to convince Einstein and his followers was to perform experiments. Nature had to be listened to. Bell introduced some mathematical inequalities that all classical theories have to satisfy, but that quantum mathematics does not. Nature was the only one that could definitively decide the debate between Einstein and Bohr.

Nobel Prize laureates have performed such experiments. John Clauser in 1972, but his experiment had a locality gap, his two detectors were too close together. Alain Aspect improved the experiment and in 1982 separating the detectors thirteen meters, making the measurements in eighteen nanoseconds, that the light travels in about five meters, then it cannot communicate with each other. But Einstein’s followers proposed many other loopholes. Anton Zeilinger has led the conduct of experiments that have been eliminating all loopholes one by one, until in 2015 a version free of loopholes was arrived that was accepted by all. Thanks to Clauser, Aspect, and Zeilinger, Nature has spoken and told us that there is no theory of local hidden variables. Mechanics is a complete theory.

Alberto comments that a non-local hidden variable theory implies that there is information transmission faster than light in a vacuum. So to avoid this possibility experiments are sometimes separated by distances of many kilometers. He commented that today there is no doubt that Nature has spoken and has decided the debate on the side of Bohr. Alberto comments that there are still physicists who adhere to Einstein’s idea, because it seems more appropriate to their intuition.

Alsina points out that the Nobel Committee pointed out that the work of the three winners “began the era of quantum information.” What differentiates quantum information from normal, journalistic information? I answer that when information is transmitted on a channel, units of energy are transmitted that encode said information. The difference between quantum and classical is the probabilistic description of the information; in quantum, a quantum probability is used that is described by probability amplitudes, which are not probabilities and can be negative, which allows a greater richness than in the classical one that uses a conventional probability; the quantum allows greater richness when processing information thanks to constructive and destructive quantum interference phenomena (which are equivalent to the existence of “negative probabilities”).

Is quantum reality more real than reality? A philosophical question to which Alberto answers that quantum reality is reality. I add that what is not real is the reality that we perceive in our daily lives. The macroscopic objects that surround us have properties very different from those of the atoms and particles that constitute them. We believe that everyday reality is reality, but we deceive ourselves, according to physics, reality is the one described by quantum physics, today.

I add that quantum information is very useful because it enables quantum computers, the quantum internet and quantum encryption. I predict that within thirty years all our mobile phones will have a quantum chip that will communicate with a satellite to use secure quantum encryption for all our secure transactions over the internet, for example when we use our bank card to pay online. All this will be thanks to quantum physics and thanks to the work of these pioneering Nobel laureate physicists. What these pioneers did in the 1970s and 1980s is now completely normal in every physics laboratory in the world. I joke that even engineers use these technologies; Quantum engineers are already using the basic science tools these pioneers developed.

Alberto comments that quantum information is a very important concept in the debate between Einstein and Bohr. Today we interpret the quantum theory of an electron as a description of the information carried by the electron, as Bohr said, not of the electron as such, as Einstein preferred. This information about the electron tells us the charge that the electron carries, the position where it is, the speed at which it is moving, etc. The quantum tells us about all these properties of the electron that we can measure in experiments, but it does not describe the electron itself. The electron itself is a philosophically inaccessible thing, we can measure its properties with certain devices, but we do not have access to the object itself. A very interesting philosophical question.

Comment that the electron is a fundamental particle. Fundamental objects are objects that by definition cannot be explained by anything more fundamental. We cannot explain the electron as made of something more fundamental, because the electron is fundamental. You can explain atoms as made up of electrons and nuclei, because they are not fundamental. But fundamental objects cannot be explained with more fundamental objects.

By the way, Alberto told me that perhaps they would ask me why quantum entanglement of photons is used by the winners in their experiments. I prepared an answer using Alberto’s black and white reversible socks (the ones from his soccer team) in line with my piece “Adán y Berto’s intertwined socks”, LCMF, 08 Jan 2013.

Quantum entanglement is a correlation between properties of quantum systems. I’ll give you an example: imagine that Alberto is a bit of a freak and always wears two-color reversible socks, white on the outside and black on the inside, the color of the Castellón kit. He always wears the two socks of the same color on the outside, but some days they show the color inside and others show the color outside. Imagine that I take a sock off Alberto, show it to Alsina and ask her what color is the sock Alberto has on his other foot. If Alsina doesn’t know if I’ve turned the sock inside out or if I haven’t given it to him before showing him, he can only know that it will be black or white. It has a 50% chance of hitting. Of course, if he saw me take it off and knows I didn’t flip it over he’ll be right 100% of the time. This is an example of a classical correlation.

If Alberto’s socks were quantum, they could be prepared in an entangled state in which the socks are neither white nor black, but in a state of superposition of both colors. Of course, after looking at a sock it will appear as white or we are black, but they do not have a certain color when we do not look at them (like the famous Schrödinger’s cat in the box that we do not know if it is alive or dead). If Alsina knew quantum physics, she could predict the color of the sock on Alberto’s foot with a probability greater than 50% by doing an experiment with the sock that I show her before looking at it. Since it is impossible for her to get her answer right with 100% probability, quantum physics allows her to predict the color of the sock Alberto is wearing with up to almost 71% probability. The reason is that the quantum correlations between two entangled systems are stronger than the classical correlations. This increase in probability from 50% classical to 71% quantum thanks to entanglement is what Clauser, Aspect and Zeilinger demonstrated in their experiments with photons.

Enjoy the podcast!

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Francis with Aparici and Alsina on the 2022 Nobel Prize in Physics – La Ciencia de la Mula Francis