RIPPLES IN THE COSMOS

 

by Michael Rowan – Robinson

 

Ο Μάικλ Ρόουαν Ρόμπινσον ( 1942), είναι αστρονόμος, αστροφυσικός και καθηγητής αστροφυσικής στο Imperial College of London.

Έγραψε αυτό το βιβλίο το 1993, εγώ το αγόρασα το 1994 και ήρθε η σειρά του να το διαβάσω το 2025!!!

Φυσικά σε έναν επιστημονικό τομέα, όπως η αστρονομία, το βιβλίο θεωρείται παρωχημένο. Έτσι, το άνοιξα τυχαία και άρχισα να διαβάζω από περιέργεια.

 Ήταν τόσο προσιτός ο γραπτός λόγος του και τόσο ενδιαφέροντα αυτά που γράφει, απευθυνόμενος σε ένα μη επιστημονικό κοινό, που το συνέχισα και το απόλαυσα. Μου θύμισε τον λόγο του δικού μας του Γιώργου Γραμματικάκη, του φυσικού, (να μας μαγεύει τις νύχτες στον Ψηλορείτη μιλώντας για τα αστέρια), το βιβλίο του οποίου, « Η Κόμη της Βερενίκης» έρχεται σε επόμενη παρουσίαση.

Το κεντρικό θέμα του βιβλίου είναι, όπως γράφει ο ίδιος ο συγγραφέας του, η αναζήτηση μιας εξήγησης σχετικά με τον σχηματισμό των γαλαξιών, συμπλεγμάτων γαλαξιών και ακόμα μεγαλύτερων δομών μέσα σε ένα σύμπαν το οποίο αρχικά ήταν απίστευτα ομαλό και ενιαίο.

Από το 1965, οπότε και οι επιστήμονες ανακάλυψαν την ακτινοβολία μικροκυμάτων στο βάθος του σύμπαντος, έψαχναν να βρουν αυτούς τους κυματισμούς (ripples).

Ανακαλύπτωντάς τους, στις 23 Απριλίου του 1992, με το διαστημικό τηλεσκόπιο COBE (Cosmic Background Explorer), είχαν ένα στιγμιότυπο του σύμπαντος 300.000 χρόνια μετά το Big Bang, όταν η φάση της πύρινης σφαίρας τελειώνει και η ύλη διαχωρίζεται από την ακτινοβολία.

 

 On Page 62 of this interesting book we find a chapter with the title

“The Big Bang Universe”.

·         In 1929, (the year of the Great Depression!) Edwin Hubble discovered that the galaxies are receding from us, at a rate that increases with distance, which means that we live in an expanding universe.

Extrapolating the expansion backwards in time, points to the Big Bang. But it was the discovery of the microwave background radiation, in 1965 that showed, the universe really did have its origin in a Big Bang and the early phases of the universe were dominated by radiation.

The universe was, in fact, born in a blaze of light.

Among other evidence that convinced astronomers of the Big Bang model, was the abundances of the light elements, helium, deuterium and lithium, which cannot be explained by stellar processes.

The microwave background radiation we detect today in the universe, was last emitted by matter, a few hundred thousand years after the Big Bang (very early, if we consider that the Big Bang happened 10 to 15 billion years ago ) and it is characterized by an impressive smoothness and isotropy ( it looks the same whichever direction you look in the sky).

 But the galaxies, the stars and we our-selves demonstrate that the universe today is far from being uniform. So how did the universe evolve from a state of almost perfect uniformity to the vast contrast of densities we see today?

This is a central question of the cosmological debate.

 

·         In this book the author focuses on two discoveries that led the problem a little forward, and both involved telescopes in orbit around the Earth.

The IRAS (Infrared Astronomical satellite), which mapped the distribution of galaxies in the universe,

and

The COBE (Cosmic Background Explorer), with its detection of minute “ripples” in the microwave background radiation.

 

·         Ο  IRAS – ήταν το πρώτο διαστημικό τηλεσκόπιο, που εκτοξεύθηκε το 1983 και πραγματοποίησε έρευνα του νυχτερινού ουρανού, σε μήκη κύματος υπέρυθρης ακτινοβολίας, επί δέκα μήνες, με ευρήματα εντυπωσιακά για την εποχή. Σήμερα βρίσκεται ακόμα σε τροχιά γύρω από τη Γη.

 

·         Much of the light radiated by stars, over 99% in some galaxies, is absorbed by interstellar dust.

 The dust grains re-radiate the energy they have absorbed at far infrared wavelengths.

 The typical size of these grains is of two kinds, like very fine sand and like soot.

The problem is that the far infrared wavelengths where the dust grains radiate, are inaccessible from the ground, because of the strong absorption of the earth’s atmosphere, mainly due to water vapour and carbon dioxide. So, the space telescope IRAS was built to do this job, by the Dutch, the Americans and the British, in 1983.

·         The deeper meaning of the discovery of the ripples is that we now understand the evolution of the universe from a time 300,000 years after the Big Bang until today, 13 billion years, or so, later with lots of details to be filled in.

Our understanding of the origin of the light elements shows that we can safely extrapolate this picture back to a time one second after the Big Bang.

As some particle physicists are saying, the COBE ripples prove that inflation occurred.

 In his last, very interesting, chapter Rowan-Robinson deals with the question:

 

WHAT IS SCIENCE?

 

He gives the answers of the two philosophers of science, Karl Popper and Thomas Kuhn, with Popper saying that science consists of theories proposed by imaginative conjecture, together with attempts to refute these by means of carefully designed experiments and Kuhn focusing on the sociology of science.

Then he gives his own scientific vision, a holistic, as he says, view of science which “you have to experience to understand it”.

Modern scientists can understand fully a small part of the vision, as astronomers, for example, know almost nothing of biology and physicists of the very early universe, know little of the rest of the astronomical universe, and so on, across the whole of science.

 

·         In his Pensées, Blaise Pascal, the contemporary of Newton and Descartes, talks for the first time about the feelings of a human being adrift in the universe, brought to birth by the Newtonian revolution.

 

The eternal silence of those infinite spaces strikes me with terror.

When I consider the short extent of my life, swallowed up in the eternity before and after, the small space that I fill or even see, engulfed in the infinite immensity of spaces unknown to me and which know me not, I am terrified and astounded to find myself here and not there.

 

Rowan – Robinson ends this last chapter by saying, that scientists who engage in debates with clerics about the existence of God are wasting their time, because, on the one hand, science does not have anything to say about such questions and on the other hand, clerics who claim they have special insight, which allows them to criticize scientific theories, are equally mistaken.

In the Tractatus, Wittgenstein makes a sharp demarcation between what can be said by logic and by science and what can not. All questions of meaning, ethics and value “…..we must consign to silence”.

 

Envoi (conclusion)

 

The lumpiness seen in the IRAS galaxy surveys and the ripples seen in the microwave background radiation by COBE confirm, that the universe is dominated by dark matter and that this dark matter plays an essential role in the formation of the galaxies and all other structures in the universe.

These discoveries lead to the theory of inflation when the nuclear and electromagnetic forces were bound into a single unified force in the very early universe.

 

 “ In this book”, he continues, “ I have stressed, however, that there is no direct evidence either for this first single force or for inflation”.

Theoreticians like Stephen Hawking claim the microwave background ‘ripples’ are direct evidence for inflation.

 

 But in spite of the immense effort being put by the theoreticians, the writer of the book says the inflationary universe remains a fascinating but rather metaphysical speculation.

 

“The ripples show, however, that we have the right general ideas about the history of the Big Bang and how galaxies have formed, even if the details turn out to be different in the future.

 This is a remarkable achievement of twentieth century cosmology.”