L’enigma dei raggi cosmici. Le più grandi energie dell’ universo

27 April 2012

By Alessandro De Angelis
Paperback: £19.99 €24.44


In telling the story of “the enigma of cosmic rays”, physicist and enthusiastic communicator Alessandro De Angelis traces the fascinating adventure of cosmic rays since their discovery a century ago. Today, the exploration of the mysteries of cosmic rays continues with even more powerful tools in a range of energies that extends 20 orders of magnitude.

Cosmic rays have always been puzzling. In the first decade of the 20th century, physicists were seeking a solution to the problem of why gold-leaf electroscopes – instruments that are still common in laboratories in schools today – discharge spontaneously. Many scientists faced this problem, including an Italian, Domenico Pacini, who made some important measurements by immersing his instruments under water at different depths and observing a marked decrease in the discharge rate. Indeed, Pacini was the first to give a clear indication that part of the natural radiation he detected came from the atmosphere and from the cosmos. However, his results were published only in Italian and had no great prominence – although Viktor Hess did mention Pacini several times in his speech when he obtained the Nobel Prize in Physics for the discovery of cosmic rays. Pacini’s work is yet another glaring example of a discovery that has not obtained the international recognition it deserves.

The riddles of cosmic rays do not end there. We still do not know for sure where they come from. They are deflected by the interstellar magnetic field so their direction of arrival cannot be connected to their starting point. Above all, we still struggle to understand what mechanism provides them with an energy that can in extreme cases reach the energy of a tennis ball concentrated in a single atomic nucleus. Enrico Fermi proposed a theory for the acceleration of cosmic rays that explains in part what is observed. However, there is still much to understand and we hope that recent and future results in high-energy astrophysics will be able to answer this fundamental question.

What is sure is that cosmic rays bring to the Earth pieces of the far-away universe. Furthermore, their high energy makes them interact with the atmosphere, producing secondary particles – as in powerful particle accelerators. For this reason, in the first half of the past century cosmic rays revealed the first particle of antimatter – the positron – and many new particles that led to the birth of elementary particle physics before accelerators made by humans turned it into a mature science. Even today, in the LHC era, the study of high-energy cosmic rays and the precision testing of their composition at intermediate energies are active fields of research, with experiments on Earth and in space. In particular the first evidence of neutrino oscillations – and thus of their mass – was observed by studying the secondary neutrinos produced by cosmic rays in the atmosphere.

This book by De Angelis traces the history of the study of cosmic rays in a documented, comprehensive way, often providing details both interesting and little known. It is easily readable and an excellent reference for anyone interested in fundamental physics and contemporary astrophysics.

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