Helgoland by Rovelli, Erica (story read aloud txt) 📕

discovery is that we understand why there are these structures by reversing the order of cause and effect between their utility and their existence: their function (to see, to eat, to breathe, to digest . . . to contribute to life) is not the purpose of these structures. It is the other way around: living beings survive because these structures are there. We do not love in order to live: we live because we love.

Life is a biochemical process that unfolds across the surface of the Earth and dissipates the abundant “free energy,” or “low entropy,” with which the light of the Sun floods the planet. It is made up of individuals who interact with what surrounds them, formed by structures and processes that are self-regulating, maintaining a dynamic equilibrium that persists over time. But structures and processes are not there so that the organisms may survive and reproduce. It is the other way around: organisms survive and reproduce because these structures have happened to gradually develop. They reproduce and populate the Earth because they are functional.

The idea goes back at least as far as Empedocles, as Darwin points out in his marvelous book.121 Aristotle tells us in his Physics how Empedocles had suggested that life was the result of the casual formation of structures due to the normal combination of things. Most of these structures quickly perish, with the exception of those having the characteristics to survive: these are the living organisms.122

Aristotle objects that we invariably see calves born “well structured”: we do not see every possible variety of shape brought forth, with only the most adequate surviving.123 But today it has become clear that Empedocles’s idea, transferred from individuals to species and enriched by what we have learned about heredity and genetics, is substantially correct.

Darwin clarified the crucial importance of the variability of biological structures that allows the continuous exploration of a space of endless possibilities; and of natural selection, which allows access to gradually more extensive regions of that space, where structures and processes are found even more capable, together, of persisting. Molecular biology shows us the concrete mechanism through which this happens.

The point I need to emphasize here is that having understood all this does not take away significance from notions such as “utility” and “relevance.” On the contrary, it clarifies their origin, the way they are rooted in the physical world: they are the characteristics of those natural systems that actually give rise to survival.

These are wonderful ideas, but once again they do not explain how the notion of “meaning” emerges from the natural world. “Meaning” has intentional connotations that do not seem connected to variation and selection. The meaning of “meaning” must be based on something else.

A small miracle occurs, however, when we combine the two ideas of information and evolution.

Information plays several roles in biology. Structures and processes reproduce equal to themselves for hundreds of millions, perhaps billions of years, altered only by the slow drift of evolution. The principal means of this stability are the molecules of DNA, which remain more or less similar to their ancestors. This implies that there are correlations, that is to say relative information, across eons of time. The molecules of DNA codify and transmit information. This informational stability is perhaps the most characteristic aspect of living matter.

But there is a second way in which information is relevant in biology: in the correlations between what is inside and what is outside an organism. The majority of these correlations have no relevance for the organism. There are, however, correlations that are relevant to life in the sense in which the theory of Darwin defines relevance: favoring survival and reproduction.

I see a rock falling toward me.124 If I move, I will survive. There is nothing mysterious about the fact that I move. It is explained by Darwin’s theory: those who did not move were crushed and killed; I am a descendant of those who move out of the way. But in order to be able to move, my body needs to know that the stone is heading for me. For it to know, there must be a physical correlation between a physical variable inside me and the physical state of the rock. This correlation is there, obviously, because the visual system does precisely this: it correlates the surrounding environment with neural processes in the brain. There are all sorts of correlation between internal and external, but this one has a particular characteristic: if it was not there, or if it was not well adjusted, I would be killed by the rock. The correlation between internal and external that links the state of the rock to the neurons in my brain is directly relevant in the Darwinian sense: its presence or absence influences my survival.

A bacterium has a cellular membrane capable of detecting glucose gradients on which the bacterium feeds, lashes capable of making it swim, and a biochemical mechanism that points it in the direction in which there is the most glucose. The biochemistry of the membrane determines a correlation between the distribution of glucose and its internal biochemical state, which, in turn, determines the direction in which the bacterium swims. The correlation is relevant: if interrupted, the bacterium is without nourishment, and its chances of survival are diminished. There is a physical correlation with survival value.

The existence of such relevant correlations reveals the physical foundation of the notion of meaning: relevant relative information. Relative information in the (physical) sense given by Shannon—which is relevant in the (biological, therefore ultimately also physical) sense clarified by Darwin. This is a precise way in which we can say that its information on the concentration of sugar has meaning for the bacterium. Or that the thought of the tiger in my brain, that is, the corresponding neuronal configuration, actually signifies the tiger, an existential threat. It is correlation that matters: about which the organism “cares.”125

Defined in this way, the notion of relevant information is physical, but also intentional in