Não vou detalhar muito sobre o livro, até porque é pequeno, totalmente focado na definição de tempo, tanto popular como científica, colocando em jogo alguns dos atores do conhecimento humano mais importantes de sempre: Aristoteles, Newton e claro Einstein, assim como a brilhante, apesar de breve discussão sobre a noção de tempo antes de termos inventado os relógios. Rovelli começa por atacar a ideia de tempo, destruindo um conceito que fomos criando nos séculos recentes, o da existência do tempo verdadeiro:
“We might just as well ask what is most real—the value of sterling in dollars or the value of dollars in sterling. There is no “truer” value; they are two currencies that have value relative to each other. There is no “truer” time; there are two times and they change relative to each other. Neither is truer than the other.Esta discussão estende-se depois à distinção entre a proposta de Aristoteles e de Newton, sobre a existência ou não do tal tempo verdadeiro, e foi aqui que senti o maior impacto da leitura, não por este trecho, mas por tudo o que implica e que explicarei a seguir:
But there are not just two times. Times are legion: a different one for every point in space. There is not one single time; there is a vast multitude of them (..) Every clock has its proper time. Every phenomenon that occurs has its proper time, its own rhythm.
Einstein has given us the equations that describe how proper times develop relative to each other. He has shown us how to calculate the difference between two times.”
Aristotle: “If nothing moves, there is no time, because time is nothing but the registering of movement.”Daqui vamos chegar à seguinte proposição "the world is a network of events", ou seja
Newton: "time must exist: “true” time that passes regardless, independently of things and of their changes.”
“So, who is right: Aristotle or Newton? Two of the most acute and profound investigators of nature that the world has ever seen are proposing two opposite ways of thinking about time. ”
“Time is only a way of measuring how things change, as Aristotle would have it—or should we be thinking that an absolute time exists that flows by itself, independently of things? The question we should really be asking is this: which of these two ways of thinking about time helps us to understand the world better? Which of the two conceptual schemes is more efficient?”
“Time thus becomes part of a complicated geometry woven together with the geometry of space. This is the synthesis that Einstein found between Aristotle’s conception of time and Newton’s. With a tremendous beat of his wings, Einstein understands that Aristotle and Newton are both right. Newton is right in intuiting that something else exists in addition to the simple things that we see moving and changing. True and mathematical Newtonian time exists; it is a real entity; it is the gravitational field, the elastic sheet, the curved spacetime in the diagram. But Newton is wrong in assuming that this time is independent from things—and that it passes regularly, imperturbably, separately, from everything else.”
"the absence of the quantity “time” in the fundamental equations does not imply a world that is frozen and immobile. On the contrary, it implies a world in which change is ubiquitous, without being ordered by Father Time; without innumerable events being necessarily distributed in good order, or along the single Newtonian time line, or according to Einstein’s elegant geometry. The events of the world do not form an orderly queue, like the English. They crowd around chaotically, like Italians.E ainda: “Time, as Aristotle suggested, is the measure of change (..) the world is in a ceaseless process of change.” Que nos leva então a assumir:
They are events, indeed: change, happening. This happening is diffuse, scattered, disorderly. But it is happening; it is not stasis.”
“The entire evolution of science would suggest that the best grammar for thinking about the world is that of change, not of permanence. Not of being, but of becoming.A definição mais brutal chega então pela pedra:
We can think of the world as made up of things. Of substances. Of entities. Of something that is. Or we can think of it as made up of events. Of happenings. Of processes. Of something that occurs. Something that does not last, and that undergoes continual transformation, that is not permanent in time (..) "The world is not a collection of things, it is a collection of events. The difference between things and events is that things persist in time; events have a limited duration."”
“A stone is a prototypical “thing”" e no entanto "On closer inspection (..) The hardest stone (..) is in reality a complex vibration of quantum fields, a momentary interaction of forces, a process that for a brief moment manages to keep its shape, to hold itself in equilibrium before disintegrating again into dust”Ou seja, a realidade tal como a concebemos, feita de coisas, não existe. Tudo está em movimento perpétuo para a desintegração, e nós, humanos, passamos as nossas vidas a lutar contra esta mesma desintegração. Cada objeto, produto, material que criamos não passam de reconfigurações de matéria, que assim que terminadas entram num processo de voltar à forma inicial, pó, matéria, energia. Apercebi-me disto, com mais força, há uns anos após compra de casa, comecei a perceber como a única forma de a manter de pé, na luta contra o "tempo", é a constante manutenção da mesma, com pequenas obras que a impedem de voltar ao pó original. Do big bang a um big bang ainda maior, somos partículas de energia que se movem e arrastam consigo desejos e vontades de ação sobre essa mesma energia. Electrões, moléculas, dinossauros, seres-humanos, planetas, fazemos parte de um mesmo todo, somos grãos que se juntam e separam em função de flutuações de energia, progredindo numa voragem em direção à forma última.
“A few examples: a war is not a thing, it’s a sequence of events. A storm is not a thing, it’s a collection of occurrences. A cloud above a mountain is not a thing, it is the condensation of humidity in the air that the wind blows over the mountain. A wave is not a thing, it is a movement of water, and the water that forms it is always different. A family is not a thing, it is a collection of relations, occurrences, feelings. And a human being? Of course it’s not a thing; like the cloud above the mountain, it’s a complex process, where food, information, light, words, and so on enter and exit... A knot of knots in a network of social relations, in a network of chemical processes, in a network of emotions exchanged with its own kind.”Nada construímos que permaneça, toda a produção humana que perdurou na história deve-o às gerações que se sucederam que foram mantendo a forma dessa matéria próxima dos moldes iniciais por meio de contínua reconstrução. Fecho com a frase Banville a propósito de Rovelli: "A Física Encontrou o seu Poeta".