Helgoland Rovelli, Erica (cat reading book .TXT) 📖

Brentano’s sense. It is a connection between something (internal) and something else (generally external). It naturally carries with it a notion of “truth” or “correctness”: in every particular situation, the internal state of the bacterium may encode the glucose gradient correctly, or not. It therefore has many of the ingredients that characterize “meaning.”

Obviously, we also use the word “meaning” in contexts that do not have any direct relevance to survival. A poem is full of meaning, but does not seem to help my survival or reproducing probability much (or perhaps it might: a young woman might fall in love with my romantic soul . . .). The whole spectrum of what we call “meaning” in logic, psychology, linguistics, ethics and so on is not reducible to information that is directly relevant. But this rich spectrum has developed in the biological and cultural history of our species starting from something that has roots in physics, before adding the articulations/connections of our vast neural, social, linguistic and cultural complexity. This something is relevant relative information.

The notion of relevant relative information, in other words, is not the whole chain between physics and the full notion of meaning in the mental world, but it is the first link in this chain—the difficult one. It is the first step from the physical world, where there is nothing that corresponds to the notion of meaning, toward the world of the mind, whose grammar is based on meanings: signals that have meaning. Adding the articulations and the contexts that characterize us—the brain and its capacity to manipulate concepts (that is, processes that have meaning), our emotional states, the brain’s capacity to relate to mental processes of others, our language, society, norms—we obtain something that gets gradually ever closer to the various, more complete notions of meaning.

Once we have found the first connection between physical notions and meaning, the rest follows recursively: any correlation that contributes to directly relevant information is also meaningful, and so on. Evolution has clearly made use of all this.

This observation clarifies why we can only speak of meaning in the context of biological processes or processes rooted in biology. But it also grounds the notion of meaning in the physical world. Meaning is not external to the natural world. We can speak of intentionality without leaving the realm of naturalism. Meaning connects something with something else, it is a physical link that plays a biological role. This is what makes an element of nature a relevant sign of something else.

And so finally I can get to the point: If we think about the physical world in terms of simple matter with variable properties, correlations are accessory facts. It seems necessary to add something extraneous to matter to speak about those correlations. But quantum physics is the discovery that the physical world is a web of correlations: relative information. The things of nature are not collections of isolated elements in haughty individualism. Meaning and intentionality are only particular cases of the ubiquity of correlations. There is a continuity between the world of meanings in our mental life and the physical world. Both are relations.

The distance between the way we think about the physical world and the way we think about our mental world diminishes.

Relative information between two objects means that if I observe the two objects, I find correlations: “You have information about the color of the sky today” means that if I ask you about the color of the sky, I find that what you tell me fits with what I see; there is a correlation between you and the sky. That two objects (the sky and you) have relative information is hence, in the final analysis, something that regards a third object (me observing you). Relative information, remember, is a dance for three, like entanglement.

But if an entity (you) is sufficiently complex to make calculations and predictions (an animal, a human being, a machine built by our technology), the fact of “having information” also implies having resources to make predictions. If you have information on the color of the sky, and you shut your eyes, you can predict what you will see when you open your eyes, even before looking: a blue sky. You have “information” on the color of the sky in a stronger sense of “information”: you know beforehand what you will see.

Therefore, the elementary notion of relative information is the physical structure on which other, more complex notions of information are based. These now have semantic value.

Among these is the notion of information that refers to ourselves studying the rest of the physical world.

In order to be coherent, a vision of the world—a theory of the world—must be able to justify and give an account of the ways in which the inhabitants of that world arrive at that vision, at that theory.

This condition, which is perhaps a problem for naive materialism, is beautifully satisfied if we rethink matter as interaction and correlations.

My knowledge of the world is nothing other than an example of the result of interactions that generate meaningful information. It is a correlation between the external world and my memory. If the sky is blue, in my memory there is an image of a blue sky. My memory has the resources to permit me to predict the color of the sky if I close my eyes and then reopen them. Now the information I have on the sky has a semantic value. We know what it means that the sky is blue: we recognize this meaning when we reopen our eyes.

This is the sense of “information” I used in the postulates of quantum mechanics at the end of Chapter IV.

The double meaning of “information” gives it its ambiguous character. The basis that we have for understanding the world is our information about the world, which is effectively a (useful) correlation between us and the world. We know the world from within it.

THE WORLD SEEN FROM WITHIN

I close this chapter by mentioning