S.Hawking-A BRIEF HISTORY OF TIME. From the Big Bang to the Black Holes. E alla fine della storia, siamo tutti figli delle stelle.

Quando Hawking parla dell’Universo,  di galassie e materia oscura, di rapporto spazio-tempo, illustrandone la natura e le correlazioni, ti senti orgogliosa di appartenere alla specie umana.

Contestualmente provi anche un  senso di rimpicciolimento progressivo, se così si può dire, di fronte all’immensità dell’Universo, o del Multiverso, in cui siamo immersi.

Siamo piccoli, piccoli, parte di un immenso meccanismo che possiamo indagare, cercare di capire, spiegare, ma non controllare e modificare come vorremmo, e nei tempi che vorremmo.

Di fronte al contenuto di questo libro e alla vastità delle suggestioni, il senso di onnipotenza di tanti piccoli esseri al potere oggi, si auto-disintegrerebbe per la vergogna!

Linguaggio della scienza

A questo punto di una lettura molto difficile mi scatta un clic “pedagogico” sull’ Inglese, linguaggio della scienza. Lo stile di Hawking ne è la dimostrazione.

Il suo libro è un  report di ricerca sperimentale. Si parte da un’ipotesi, si passa all’osservazione, alla raccolta dati, all’analisi, alle deduzioni e riflessioni e poi si ricomincia, nei secoli dei secoli…

Colpisce anche in questo stile rigorosamente scientifico, l’umanità intelligente di Hawking e la sottile vena ironica che lo pervade e che, nel bel mezzo  di  una dotta trattazione scientifica, ci fa sorridere, riconducendoci al nostro  destino.

E spunta anche  l’immaginazione

“a scientific theory is just a mathematical model we make to describe our observations: it exists only in our minds. So it is meaningless to ask: which is real, ‘real’ or ‘imaginary’ time? It is simply a matter of which is the more useful description.”

Quark and Joyce

“The origin of the name is an enigmatic quotation from James Joyce: ‘Three quarks for Muster Mark!’ The word quark is supposed to be pronounced like quart, but with a k at the end instead of a t, but is usually pronounced to rhyme with lark.”

Dante and the Hell/Event Horizon

“One could well say of the event horizon what the poet Dante said of the entrance to Hell: ‘All hope abandon, ye who enter here.’ Anything or anyone who falls through the event horizon will soon reach the region of infinite density and the end of time.”

An inflating Multiverse

“Eternal inflation: A possible variant of inflation in which much of space continues expanding rapidly while relatively small individual portions drop their expansion rate to become universes such as our own. If correct, this implies our entire cosmos is embedded within a much larger inflating multiverse.”

La metafora dei buchi neri: scappare dalla polizia!

“I had already discussed with Roger Penrose the idea of defining a black hole as the set of events from which it was not possible to escape to a large distance, which is now the generally accepted definition. It means that the boundary of the black hole, the event horizon, is formed by the light rays that just fail to escape from the black hole, hovering forever just on the edge (Fig. 7.1). It is a bit like running away from the police and just managing to keep one step ahead but not being able to get clear away!”

Ironia e scommesse perse sui buchi neri

“In fact, although the situation with Cygnus X-1 has not changed much since we made the bet in 1975, there is now so much other observational evidence in favor of black holes that I have conceded the bet. I paid the specified penalty, which was a one-year subscription to Penthouse, to the outrage of Kip’s liberated wife.”

Ordine dal disordine

“The nondecreasing behavior of a black hole’s area was very reminiscent of the behavior of a physical quantity called entropy, which measures the degree of disorder of a system. It is a matter of common experience that disorder will tend to increase if things are left to themselves. (One has only to stop making repairs around the house to see that!) One can create order out of disorder (for example, one can paint the house), but that requires expenditure of effort or energy and so decreases the amount of ordered energy available.”

Stephen in Vaticano

“Throughout the 1970s I had been mainly studying black holes, but in 1981 my interest in questions about the origin and fate of the universe was reawakened when I attended a conference on cosmology organized by the Jesuits in the Vatican. The Catholic Church had made a bad mistake with Galileo when it tried to lay down the law on a question of science, declaring that the sun went round the earth. Now, centuries later, it had decided to invite a number of experts to advise it on cosmology. At the end of the conference the participants were granted an audience with the Pope. He told us that it was all right to study the evolution of the universe after the big bang, but we should not inquire into the big bang itself because that was the moment of Creation and therefore the work of God. I was glad then that he did not know the subject of the talk I had just given at the conference – the possibility that space-time was finite but had no boundary, which means that it had no beginning, no moment of Creation. I had no desire to share the fate of Galileo, with whom I feel a strong sense of identity, partly because of the coincidence of having been born exactly 300 years after his death! In order to”

Ironia scientifica

“This picture of a hot early stage of the universe was first put forward by the scientist George Gamow in a famous paper written in 1948 with a student of his, Ralph Alpher. Gamow had quite a sense of humor – he persuaded the nuclear scientist Hans Bethe to add his name to the paper to make the list of authors ‘Alpher, Bethe, Gamow,’ like the first three letters of the Greek alphabet, alpha, beta, gamma: particularly appropriate for a paper on the beginning of the universe!”

Il Principio Antropico: siamo figli delle stelle

“why is the universe so smooth? This is an example of the application of what is known as the anthropic principle, which can be paraphrased as, ‘We see the universe the way it is because we exist.’ There are two versions of the anthropic principle, the weak and the strong. The weak anthropic principle states that in a universe that is large or infinite in space and/or time, the conditions necessary for the development of intelligent life will be met only in certain regions that are limited in space and time. The intelligent beings in these regions should therefore not be surprised if they observe that their locality in the universe satisfies the conditions that are necessary for their existence. It is a bit like a rich person living in a wealthy neighborhood not seeing any poverty. One example of the use of the weak anthropic principle is to ‘explain’ why the big bang occurred about ten thousand million years ago – it takes about that long for intelligent beings to evolve. As explained above, an early generation of stars first had to form. These stars converted some of the original hydrogen and helium into elements like carbon and oxygen, out of which we are made. The stars then exploded as supernovas, and their debris went to form other stars and planets, among them those of our Solar System, which is about five thousand million years old. The first one or two thousand million years of the earth’s existence were too hot for the development of anything complicated. The remaining three thousand million years or so have been taken up by the slow process of biological evolution, which has led from the simplest organisms to beings who are capable of measuring time back to the big bang.”


Few people would quarrel with the validity or utility of the weak anthropic principle. Some, however, go much further and propose a strong version of the principle. According to this theory, there are either many different universes or many different regions of a single universe, each with its own initial configuration and, perhaps, with its own set of laws of science. In most of these universes the conditions would not be right for the development of complicated organisms; only in the few universes that are like ours would intelligent beings develop and ask the question, ‘Why is the universe the way we see it?’ The answer is then simple: if it had been different, we would not be here! The laws of science, as we know them at present, contain many fundamental numbers, like the size of the electric charge of the electron and the ratio of the masses of the proton and the electron.”

La legge di Murphy e la tazzina rotta

“This says that in any closed system disorder, or entropy, always increases with time. In other words, it is a form of Murphy’s law: things always tend to go wrong! An intact cup on the table is a state of high order, but a broken cup on the floor is a disordered state. One can go readily from the cup on the table in the past to the broken cup on the floor in the future, but not the other way round.”

Le tre frecce del tempo

“The increase of disorder or entropy with time is one example of what is called an arrow of time, something that distinguishes the past from the future, giving a direction to time.”

“There are at least three different arrows of time. First, there is the thermodynamic arrow of time, the direction of time in which disorder or entropy increases. Then, there is the psychological arrow of time. This is the direction in which we feel time passes, the direction in which we remember the past but not the future. Finally, there is the cosmological arrow of time. This is the direction of time in which the universe is expanding rather than contracting.”

Al passo con il progresso scientifico

“Further, the rate of progress is so rapid that what one learns at school or university is always a bit out of date. Only a few people can keep up with the rapidly advancing frontier of knowledge, and they have to devote their whole time to it and specialize in a small area. The rest of the population has little idea of the advances that are being made or the excitement they are generating.”

In conclusione: siamo orgogliosi di appartenere alla specie umana

“Despite the vastness of the multiverse, there is a sense in which we remain significant: we can still be proud to be part of a species that is working all this out. With that in mind, the coming years should be just as exciting as the last twenty