Carlo Rovelli’s book shows how quantum physics revolutionized the world

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Imagine a cat that is locked in a box that has a device with a 50% chance of releasing a sleeping pill. If the sleeping pill is activated, the cat sleeps. If not, he remains awake.

Since the animal is trapped in this box, it is not really known whether it is awake or asleep—unless the box is opened.

In this circumstance, we say that the cat is in quantum overlap, a physics concept that addresses how two or more opposite phenomena can happen simultaneously in an object. It’s as if something could be present in several different places at the same time.

The overlap, in this case, is between awake-cat and sleeping-cat. At the moment of discovering whether or not the sleeping pill was activated, the cat would move out of this superposition into a state of quantum interference, which is when one of the two possibilities is fulfilled.

This example, known as Schrödinger’s cat (in reference to the Austrian physicist Erwin Schrödinger, 1887-1961), is one of several covered in the book “O Abismo Vertiginoso”, recently released in Brazil by the publisher Objetiva.

The work, intended to explain quantum physics, is signed by Carlo Rovelli, Italian theoretical physicist and professor at the University of Aix-Marseille (France).

“In the original version [de Schrödinger], the pouch contained a poison, not a sleeping pill, and the cat did not fall asleep but died. But I don’t like to play with the death of a cat”, writes the author in a passage, justifying the adaptation.

This is how, with accessible language, the physicist makes an attempt to explain the quantum theory and show the importance it has to understand the entire reality of the Universe.

This line of thought “suggests new ways to rethink big questions, from the structure of reality to the nature of experiences, from metaphysics to, perhaps, the nature of consciousness”, he says.

The theory also proposes a new way to understand the tiny particles that make up the Universe and especially the interactions that take place between them.

Rovelli explains that, in 1925, the young physicist Werner Heisenberg (1901-1976) focused on observing the movement that electrons make from one atom to another. With that, he launched one of the main bases of the quantum theory: it would be necessary to limit himself to what was strictly observable in the interactions between particles in order to understand the Universe.

Hence, a big problem arises, as these interactions and the observations we have of them are not entirely predictable. Schrödinger the Cat, another physicist very important to quantum theory, came to the conclusion that it is only possible to have probabilities of how interactions might happen. For him, it would never be possible to be completely sure about the course of interactions.

The main focus of quantum theory would then be these interactions and not objects.

“Physics tells us that the basis of the world is not a list of objects with definite properties. I think we should give up on finding the ‘fundamental’ picture of reality once and for all. Reality is complex, admits of many related perspectives, but Asking for your ‘base’ can simply be the wrong question,” says the writer in an interview with leaf.

Thus, from the quantum theory, new hypotheses to explain the Universe emerged. One is the many worlds theory. She claims that an infinity of worlds exist because of the countless possibilities of relationships between the elements that make up reality.

In this case, a quantum superposition does not only indicate a probability of one or the other thing happening—this possibility of different paths is already reality in itself and indicates the existence of different worlds.

To explain it further, Rovelli takes the example of the cat who may be awake or sleeping inside the box again. In the case of the many-worlds theory, the two versions of the cat exist by themselves in different universes, and they are not just possibilities of what may or may not happen to the animal.

In this current of thought, there would also be two versions of the person who watches the cat — in one of these worlds, there is the subject who watches the cat awake, and in another world it would be the version of him who sees the sleeping cat.

When you take this premise, explains Rovelli, and take it to the countless possible relationships of the Universe’s reality, you come to the conclusion that there could be infinitely many worlds to support all these scenarios.

Because of this, the author claims that this theory is too radical. Rovelli more openly defends what he calls a relational perspective — a worldview based on infinite states of overlap and interference, with no exact answer, but myriad possibilities that change depending on the objects involved in the interaction.

At this point, quantum theory influences several other areas of knowledge, because it talks about how reality can be perceived. It’s not just about the materials that make up the Universe, but also about how the interactions between them influence the reality around us —and the countless possibilities that exist.

One example is philosophy. Throughout the book, the author draws parallels between the two areas.

A case Rovelli uses is that of Nagarjuna, an Indian philosopher who lived in the 2nd century and came to the conclusion that things do not exist by themselves, but come into being when they are seen in relation to other objects. The similarity to quantum physics and the relational perspective is obvious.

The physicist, thus, defends the relevance of teaching philosophy, as it “question prejudices, obliges us to think with more precision and depth”.

Another point highlighted by Rovelli is the scientific work itself. For him, quantum physics, by showing that observation is relational, indicates that the production of knowledge is not completely free. It depends on the researcher’s interaction with the object of study — and this multiplies into countless possibilities.

Rovelli mentions, as an example, heaven. The color it has is not an inherent property of it, but something that also depends on who is watching. Language also follows this path: what is said always depends on the listener and their interpretation.

Even with examples that are sometimes simple, like this one from the sky, Rovelli makes it clear that, despite its great impact, quantum physics is still quite recent and difficult to understand. The author himself reports in some passages the confusion he went through when translating these concepts to the reader.

“I write about science trying to simplify as much as possible, very faithfully conveying what I think are the main ideas. This is easier to do on topics that I understand well, but nobody understands quantum physics well. So this book was the hardest and most also the most fun to write,” he concludes.

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