Physics in the twentieth century

Physics between the nineteenth and twentieth centuries

The years between the nineteenth and twentieth centuries were extraordinary with regard to the new experimental acquisitions of physics: discovery of X-rays (1895), natural radioactivity (1896), electron (1897); measurements of the spectrum of blackbody radiation obtained using an isothermal hollow body as a source, recognition that the particles emitted by incandescent metals or illuminated with electromagnetic radiation of suitable wavelength are electrons. These discoveries started a process of profound revision in the conception of the structure of matter: progressively, objects of physical investigation became discrete unobservable entities, in the common sense of the term. Atoms were transformed from a heuristic hypothesis into an object of direct experimental and theoretical study. This process took place mainly on the drive to discover what fragments of atoms (electrons, α particles, that is helium nuclei) or their radiation (γ rays) would appear in retrospect. The new experimental results relating to blackbody radiation led Max KEL Planck (1858-1947) to the introduction of the nature constanth (1900), thus initiating the long process that led to quantum mechanics (1925-26).

In 1905, Albert Einstein (1879-1955) published three works that would have a lasting influence, dedicated respectively to the quanta of light (later called photonsfrom 1926), to Brownian motion, to special relativity. The work on Brownian motion was used, a few years later (1908), by Jean-Baptiste Perrin (1870-1942) to interpret his experimental measurements, defining and determining the so-called Avogadro number. The work on light quanta proposed, as a heuristic hypothesis, a corpuscular description of light in apparent contrast with the wave description of James C. Maxwell (1831-1879). Einstein’s subsequent efforts, aimed at anchoring this hypothesis to the Planckian formula of blackbody radiation (considered as corroborated by the experiment), led him, among other things, to the introduction (1916-17) of the concept of stimulated transition between an excited state and the ground state of an atom or molecule, concept that would later be the basis of the realization of the maser (1953) and the laser (1960). The work on special relativity constituted, on the one hand, the overcoming of the mechanics of Isaac Newton and, on the other, the starting point for the theory of general relativity which is, in reality, a new theory of gravitation in which the sources of the gravitational field (the masses) determine a space-time deformation of special relativity.

Difficult context and original research

The high points of Italian production of the late nineteenth century were challenged with frontier arguments (Giuliani 1996, pp. 114-21). Nevertheless, the experimental discoveries and conceptual innovations of the decade 1895-1905 caught the small community of Italian physicists not adequately equipped. In 1900 there were 71 physicists working in universities; the university’s teaching programs, combined with scarce funding, did not favor generational change and adaptation to rapid changes in the discipline.

However, there was no lack of original research, such as, for example, those on magneto-optical effects. In 1898 Damiano Macaluso (1845-1932) and Orso Mario Corbino, experimenting on alkaline metal vapors, discovered that the Faraday effect takes on particular characteristics when the wavelength of light approximates that of the absorption lines of the atoms constituting the steam: the Macaluso-Corbino effect is still the subject of experimental and theoretical study. Corbino studied the Hall effect in bismuth discs (which we know today to be a semi-metal), in which a circular symmetry was maintained: the original radial current, produced by a difference in potential applied between the center and the periphery of the disc, was partially transformed into circular current by the magnetic field applied perpendicular to the disk.

Domenico Pacini (1878-1934) carried out, between 1907 and 1911, a series of measures on penetrating radiation. He verified that the intensity of natural radiation decreases passing from the surface to a few meters underwater, thus demonstrating that at least a part of these radiation does not come from the earth’s crust; however, Pacini’s research could not rule out an atmospheric origin of the penetrating radiation. A year later, Victor F. Hess (1883-1964) studied radiation from above by means of measurements carried out with an air balloon: these researches earned him, in 1936, the Nobel prize for physics. The terminological transition from penetrating radiation to radiation from abovesummarizes the conceptual leap between Pacini’s and Hess’s works (the term cosmic rays was introduced by Robert A. Millikan and G. Harvey Cameron in 1926).

In 1909 the Nobel prize for physics was jointly awarded to Guglielmo Marconi and Karl F. Braun (1850-1918) in recognition of their contribution to the development of wireless telegraphy.

In 1913, Antonino Lo Surdo (1880-1949), studying the Doppler effect of some spectral lines emitted by hydrogen, observed a configuration of the lines different from that typical of the Doppler effect. Subsequently, having seen the work published by Johannes Stark (1874-1957) on «Nature», which showed that a similar breakdown of the lines is due to a strong electric field to which the emitting atoms are subjected, Lo Surdo recognized that even the The anomalous breakdown of the lines he observed was due to an electric field. While the discovery of Lo Surdo was accidental, that of Stark was the result of research aimed at discovering any effects of the electric field on the lines emitted by the hydrogen atom within the nascent quantum physics. In 1919,

Graduated in Pisa under the direction of Raffaele Occhialini, Rita Brunetti (1890-1942) became a researcher at the Physics Institute of Arcetri (near Florence), then directed by Antonio Garbasso (1871-1933). Here he came into contact with some young physicists: Enrico Persico (1900-1969), Enrico Fermi, Franco Rasetti (1901-2001), Bruno Rossi and Gilberto Bernardini (1906-1995). In the second half of the thirties, Brunetti, then in Pavia, obtained the funding to install a Cockcroft-Walton accelerator which would have been the second Italian accelerator after the one that entered into operation at the Higher Institute of Health in Rome in 1938. The outbreak of the Second World War and Brunetti’s death led to the failure of the initiative:

Between the two world wars

In addition to the millions of victims and material destruction, the end of the First World War left the awareness of the importance of the applications of science – also for military purposes – and the awareness of the ever-growing interpenetration between science and society. In Italy, the debate around the need to relaunch scientific research already started during the conflict, also through the meetings of the Italian Society for the Advancement of Sciences (SIPS). This debate influenced the decision to establish the National Research Council (CNR) in 1923.

Called, under the wise direction of Corbino, on the first chair of theoretical physics established in Italy (Rome, 1927), Fermi gathered around him a group of young physicists, including Rasetti, Emilio Gino Segrè, Bruno Pontecorvo, Edoardo Amaldi, Ettore Majorana. In 1926, independently of Paul AM Dirac, Fermi formulated the statistics for the particles that obey the Pauli exclusion principle, which will then be called Fermi-Dirac; subsequently, it was understood that this statistic applies to all particles (called fermions ) having a half-integer spin. In 1927, independently of Llewellyn H. Thomas, he developed the statistical model of atoms with many electrons, later called Thomas-Fermi. In 1934 he proposed a theory of β decay based on a new form of interaction, the weak interaction, characterized by a universal constant later called Fermi. In the same year, after the discovery of the spouses Frédéric and Irène Joliot-Curie concerning the production of artificial radioactive elements by bombardment with α particles, Fermi began systematically bombarding the elements of the periodic table with neutrons produced by a radon-beryllium source. By bombing uranium, Fermi and his collaborators thought they had produced transuranic elements: in reality, as it would have been shown in 1938 by Otto Hahn, Fritz Strassmann, Lise Meitner and Otto Frisch, they had caused the fission of the uranium nucleus. Subsequently, Fermi realized that the interposition of a block of paraffin having a thickness of several centimeters between the source and the target of silver increased, instead of decreasing, the radioactivity of the silver:

In Italy, the systematic study of cosmic rays was started in Arcetri in 1930 by Rossi, surrounded by a group of slightly younger physicists: Bernardini, Giuseppe Occhialini and Daria Bocciarelli (1910-2007). Rossi invented the coincidence circuit, then widely used in the physics of cosmic rays. This circuit allowed the detection and identification of rare events against the background of numerous pulses recorded by individual counters. In the same year he published a work in which an azimuthal asymmetry in the intensity of cosmic rays was expected, if they were made up of charged particles: this asymmetry, due to the Earth’s magnetic field, would also allow to identify the prevalent charge of the particles. The first attempt to highlight this effect, made in Florence, gave a negative result. In 1933, after delays due to the difficulty of finding the necessary funds, Rossi managed to make an expedition to Eritrea (the effect was expected to be greater at low latitudes) and to demonstrate that the effect existed and that the charge of the cosmic rays was predominantly positive. However, this demonstration had previously been obtained by Thomas H. Johnson and independently by Luis Álvarez and Arthur H. Compton. However, in Eritrea, Rossi discovered very large swarms of corpuscles. He had previously observed the production of secondary particles due to the interaction of soft (low energy) cosmic rays with a thin layer of lead; with the same series of experiments he also identified a hard (high energy) component capable of crossing a lead layer one meter thick (Russo 2000, pp. 129-51).muons ) contained in cosmic rays, presented the first experimental measure of the so-called time dilation concerning unstable particles.

In 1931, Occhialini, an expert in the use of coincidentally connected Geiger counters, moved to Cambridge to work with Patrick MS Blackett (1897-1974), who was familiar with the cloud chamber techniques. The result of the collaboration was the mist chamber controlled by coinciding Geiger counters, with which it was possible to observe the production of electron-positron pairs immediately after the appearance of the brief work by Carl Anderson announcing the observation of a trace in the chamber at fog due to a positive charge having small mass (positron). In fact, the first published photograph was that of Blackett and Occhialini. Soon after, Blackett, Occhialini and James Chadwick observed the production of electron-positron pairs by γ rays. Returning to Italy in 1934, Occhialini accepted, in 1937, the invitation of Gleb Wataghin (1899-1986) to join him at the University of San Paolo in Brazil, where he met, among others, Giulio Lattes (1924-2005). Further on, Occhialini and Lattes would meet together in Bristol.

Fermi and theoretical physics

The first three decades of the twentieth century saw the persistence, in Italy, of the nineteenth-century tradition according to which physics is an experimental discipline in which theory has an ancillary function that does not require training and a distinct professional profile. As Corbino said, physicists were forced to be theorists of themselves. Fermi had the great merit of having stimulated the interest in theoretical physics and favored his practice among many of his young students.

The first thesis in theoretical physics was that of Giovanni Gentile Jr (1906-1942), obtained in Pisa in 1927. Gentile had been assigned an experimental thesis on the Stark-Lo Surdo effect. The transfer to Bari of Giovanni Polvani (1892-1970), who was following his thesis, induced Gentile to detach himself from the primitive theme assigned to him in order to pass by himself to a reworking of Schrodinger’s memory. Corbino’s assistant in Rome (1927), Gentile spent periods of study in Berlin and Leipzig and in 1932 he was in Pisa as a professor in charge of theoretical physics. Winner of the competition in 1937 for a chair of theoretical physics, he was called to Milan. His most important contribution is the formulation of intermediate statistics between that of Bose-Einstein and that of Fermi-Dirac.

The Majorana figure has received great attention from recent historiography, also stimulated by the halo of mystery surrounding his disappearance. Among his major contributions are that dedicated to the reversal of the magnetic moment of an atom with angular momentum J= 1/2, due to a rapid variation of the applied magnetic field (results then taken up and generalized by Ismor I. Rabi and Felix Bloch for any J); the work on nuclear forces in which, unlike Werner K. Heisenberg, Majorana considers only the exchange forces due to the spatial coordinates; the work on relativistic theory of particles with arbitrary spin (substantially ignored by contemporary and later literature) and the work on symmetric theory of electrons and positrons. In this latter work, Majorana developed a theory in which, as he himself wrote,

the meaning of Dirac’s equations is somewhat modified and there is no longer any place to speak of states of negative energy; nor to assume for any other type of particle, particularly neutral, the existence of “antiparticles” corresponding to the “voids” of negative energy ( Symmetric theory of the electron and positron , “Nuovo Cimento”, 1937, 5, p. 171 ).

The antantutron is a particle distinct from the neutron; instead, the question is still open regarding neutrinos.

Persico, a friend of Fermi, graduated in Rome in 1921 with an experimental thesis on the Hall effect (supervisor Corbino). He participated in the first theoretical physics competition held in Italy (1926), in which Fermi was the winner; Persico was the second of the triad, Aldo Pontremoli (1896-1928) the third. As an ordinary professor, Persico was first in Florence (1927-1930), then in Turin (1930-1947), finally, after a stay in Canada, in Rome (1950-1969). His book Fundamentals of Atomic Mechanics (1936) was the first Italian manual of quantum mechanics, and was translated into English in 1950.

Pontecorvo, who graduated in 1933 in Rome with Rasetti, had gone to Paris in 1936 to work in the laboratory of the Joliot-Curie couple; the promulgation of the racial laws of 1938 forced him to stay in France and then to take refuge first in Spain, then in the United States and finally in Canada. In 1948 he obtained British citizenship and moved to Great Britain, where, for some time, he worked on British nuclear projects on nuclear bombs. In 1950, he clandestinely entered the Soviet Union, where he worked and lived until his death. Of his rich and complex research activity, the one concerning neutrinos, the possibility of their experimental observation and the hypothesis of neutrino oscillations, well known experimentally today, is well known.

Almost the same age as Pontecorvo, Gian Carlo Wick (1909-1992) graduated in Turin in 1930. After a study stay in Göttingen and Leipzig (during which he assiduously attended Heisenberg), in 1932 he became Fermi’s assistant in Rome, and in 1937 he won the competition for the chair of theoretical physics together with Gentile and Giulio Racah (1909-1965). As a professor of theoretical physics, he was first in Palermo, then in Padua and finally, in 1940, in Rome, on the chair that had been Fermi’s. In 1946 he reached Fermi in the United States, where he remained until retirement. His most significant contributions concern quantum field theory.

Racah graduated in 1930 in Pisa, Persian supervisor. In the early thirties he moved to Rome with the Fermi group; in 1932 he became professor in Florence; in 1937 he was called to the chair of theoretical physics in Pisa and in 1939 he emigrated to Palestine, then a British mandate. Here, thanks also to the support of Fermi and Pauli, he was assigned a chair of theoretical physics at the Hebrew University of Jerusalem. His most significant works concern the theory of complex atomic spectra.

Ugo Fano (1912-2001) graduated in Turin in 1934 with a thesis followed by Persico; he was in Rome in the Fermi group until 1937, then for two years in Leipzig, by Heisenberg; in 1939 he emigrated to the United States. His main contributions concern the physics of atoms and molecules.

Piero Caldirola (1914-1984) graduated in Pavia in 1937 with an experimental thesis on the diffusion of hydrogen in palladium. The following year he was in Rome from Fermi with a scholarship from the Ghislieri college, of which he had been a pupil, then to Padua from Wick; in 1939 he returned to Pavia as an ordinary assistant. In 1947 he was called as an extraordinary professor in Pavia; in 1949 he moved to Milan. Like many theorists, he was interested in very different topics, including the quantum theory of dissipative systems; it also played an important role in promoting new lines of research, particularly in the field of matter physics.

The racial laws of 1938 also affected the small community of Italian physicists: Fano, Fermi, Pontecorvo, Racah, Rasetti, Rossi, Segrè and Wick had to emigrate. In the same year, Majorana mysteriously disappeared. The individual paths of these physicists were marked by the events of those years: while Fermi, Segrè and Rossi participated in the Manhattan project for the production of the nuclear fission bomb, Rasetti refused to join it, also abandoning physical research. Just over two decades had passed since, in 1922, Fermi commenting on the relationship E = mc 2 wrote:

It will be said with reason that it does not seem possible that, at least in the near future, there is a way to release these frightful amounts of energy, which, moreover, can only be hoped for, because the explosion of such a frightening amount of energy would have the first effect of breaking up the physicist who had the misfortune of finding a way to produce it ( The masses in the theory of relativity , in Id., Notes and memoirs , 1st vol., 1961, p. 34).

It was possible. With a variant: it was not the physique who broke up but hundreds of thousands of Japanese.

The emigrations of the late thirties deprived our country of the contribution of talented scientists; on the other hand, our migrants of science found job opportunities and research structures outside the patri borders that had no equivalent in Italy and that allowed them to achieve very important results. Suffice it to recall, in this regard, the realization of the first controlled chain reaction in the first nuclear reactor by Fermi and Leo Szilard (Chicago, 1942), and the discovery of the antiproton by Segrè and Owen Chamberlain (1955) , through the use of Berkeley’s bevatrone.

The second post-war period

After the Second World War, the international context of research appeared profoundly changed: the defeat of Nazism and fascism and the war devastations in Europe had favored the shifting of economic and scientific hegemony across the Atlantic; the effort supported by the United States for the production of the nuclear fission bomb and the development of radar systems had shown the effectiveness of research based on the concentration of human and material resources and on the planned intertwining between basic research, applied research and technology aimed at predetermined objectives.

The division of the world into two blocks and the Cold War revived the arms race. The interest of governments for science and for the military and civilian applications of technology took on a permanent character, with consequent growing economic commitments of the respective countries; scientists saw their numbers increase considerably and gradually became aware of the acceleration of the process of integrating science into society, the growth of their influence on certain decision-making processes, the increase in their responsibilities, including ethical ones. The problems that Italy had to face with regard to scientific and technological development were complex, and were made more difficult by the difficulties deriving from the war devastation,

After the Liberation, the work of reconstruction of the destroyed institutes began, the recovery of laboratory instruments – sometimes hidden to prevent the theft by the retreating German troops -, the acquisition of new equipment, also drawing on the war remnants of the allied troops .

As for research, the points of reference were the strands of nuclear physics and cosmic rays, cultural heritage of Fermi and Rossi. Physicists, who for objective contingencies or personal choices, were oriented towards what will later be called the physics of matter, not finding cultural or organizational references in the pre-war period, were forced to turn abroad and operate in a substantially indifferent context towards physics with an image still uncertain, both as regards the fundamental aspects and for possible application developments (in the Strai Uniti solid state physics had an official recognition in 1949, two years after the discovery of the transistor, with the establishment of a specific division of the American Physical Society).

Core physics, particles, astrophysics

The institutional framework in which this research sector developed in Italy saw Amaldi play a fundamental role. Heir to the Fermi group, he worked from the immediate post-war period to reweave the ranks of research on the physics of cosmic rays and the nucleus. In 1951 he managed to establish the National Institute of Nuclear Physics (INFN) as the coordination structure of three CNR centers, thus laying the foundations for direct funding by the State of research on the physics of nucleus and elementary particles, which it materialized, through intermediate stages, with the complete autonomy of the entity (1971). These choices created a situation of imbalance in the organization and funding of physical research in Italy, which is still not completely overcome today.Conseil Européen pour la Recherche Nucléaire ) and was among the promoters of the ESRO ( European Space Research Organization , since 1975 ESA, European Space Agency ).

Cosmic rays

At the fall of fascism, Oreste Piccioni (1915-2002) and the younger Marcello Conversi (1917-1988) were carrying out measurements on the average life of mesotrons in Rome, discovered, as mentioned, in the late 1930s. It was then believed that the mesotrons coincided with the particle hypothesized by Hideki Yukawa in 1935 in the role of exchange element in short-range nuclear interactions. According to this hypothesis, negative mesotrons should have been rapidly absorbed by the nuclei. Conversi and Piccioni showed instead that they, like the positive mesotrons, escaped the capture of the carbon nuclei and decayed emitting electrons: the mesotrons were therefore not the particles hypothesized by Yukawa. This discovery paved the way for the identification of a new class of particles: leptons (electron, muon, leptone tau, neutrinos and their antiparticles), sensitive only to electromagnetic, weak and gravitational interactions, but not to strong interaction. In 1946, Piccioni emigrated to the United States, first to MIT (Massachusetts Institute of Technology ), where he collaborated with Rossi, then in Brookhaven (cosmotron), Berkeley (bevatrone) and finally at the University of San Diego (California). He devised an apparatus for the recognition of high momentum antiprotons. This system was used by Segrè and Chamberlain for the discovery of the antiproton, which earned them the award of the Nobel prize for physics in 1959. In 1956, Piccioni contributed to the discovery of the antedutron and, in 1957, he published an important article with Abraham Pais on the regeneration of kaons (K mesons), then experimentally verified by Piccioni himself.

In 1944, thanks to Blackett’s interest, Occhialini, then still in Brazil, got to be able to enter Great Britain, but, unlike what was planned, he was prevented, as an Italian, from participating in any scientific program with military purposes. Occhialini then joined a small Bristol research group led by Cecil F. Powell (1903-1969), who studied nuclear reactions with the technique of photographic emulsions. He worked on the production of new emulsions, richer in silver bromide, and developed, with Constance Ch. Dilworth and Ron Paine, a method for their treatment. Subsequently, he joined the Lattes group: the program was to study the spectrum of neutrons contained in cosmic rays. The result of this collaboration was the discovery of the meson π (pion) – the Yukawa particle – which decays producing the mesotron (muon). The plates from which they deduced the existence of the pion were personally exhibited by Occhialini on the Pic de Midi de Bigorre (France); other significant plates were exhibited by Lattes sul Chacaltaya (Bolivia). Blackett was awarded the Nobel Prize for Physics in 1948 and hisNobel lecture gave wide recognition to Occhialini’s contribution, using the phrase “Occhialini and I” four times. In 1950 the Nobel prize was instead attributed to Powell, who in his Nobel lecture did not mention Occhialini, whose name appears only in a note in the citations of the common articles.

Particle accelerators: physics and applications

The first accelerators were built in the thirties with the aim of bombarding fixed targets: among these we remember that of 0.7 MeV with which John D. Cockcroft and Ernest Th.S. Walton made the first nuclear reaction produced with an accelerator (1932). In 2000 there were about 15,000 accelerators of which only 110 dedicated to research in nuclear and subnuclear physics and 70 synchrotrons used as sources of electromagnetic radiation emitted by accelerated particles: the others were used for application purposes, including ion implantation and surface treatment (7000), radiotherapy (5000), production of radioisotopes for medical applications (200) and hadron therapies (20).

In the immediate post-war period, there was a proliferation of accelerators in various competing research centers; later, the awareness spread that the need to reach more and more energies would require collaboration not only between groups of researchers, but between different governments. This was the path taken in Europe with the establishment of CERN (1954). In the climate of the cold war, the United States and the Soviet Union each proceeded instead on their own. The most far-sighted choice was the European one: in fact, in 1992, after ten years of work and an expenditure of two billion dollars, the United States abandoned the project of the SSC ( Superconducting Super Collider ), which should have reached more than three times more energy than those of the LHC (Large Hadron Collider ) of CERN.

Italy was, at the beginning, quite virtuous: while actively contributing to the creation of CERN, an 1100 MeV electrosynchrotron was designed (1953-54) and built (1959) in Frascati: he was then president of INFN Bernardini, and Giorgio Salvini (n. 1920) was appointed director of the project. Bernardini and Salvini recruited a group of young physicists and engineers; Persico oversaw the theoretical part of the project. INFN ensured streamlined procedures for allocating and using funds, as well as selecting research staff to associate with the project. These characteristics were of crucial importance for the realization of AdA ( Accumulation Ring): one year after the synchrotron came into operation, Bruno Touschek (1921-1978), one of the few physicists immigrated to our country, proposed the creation of an accumulation ring in which to circulate in the opposite direction and collide electron beams and positrons. In the case of AdA, electrons and positrons were produced and accelerated in the synchrotron. Electron and positron colliders were soon designed and manufactured in France, the Soviet Union and the United States. Moreover, already in January 1961, the construction of ADONE (‘large AdA’) was proposed to Frascati, a positron electron collider with an energy of 1500 MeV per beam, which came into operation in 1969.

In 1974, Burton Richter in Stanford and Samuel Ting in Brookhaven discovered a particle, then called ψ by Richter and J by Ting and subsequently called J / ψ, having a mass corresponding to an energy of 3096 MeV, therefore slightly higher than maximum energy available in ADONE. Not even at CERN, where the new particle was abundantly produced in the regions of intersection of the two proton accumulation rings, they noticed it (the detectors in use were not suitable for the purpose). To the two discoverers of J/ ψ, which later turned out to be a quark-antiquark linked state, was awarded the Nobel Prize in physics in 1976. This story shows how the discovery of new particles, when not suggested by theories or powered by hypotheses but due to energy available in accelerators, both an event in which randomness plays a decisive role (in this case represented by the amount of energy available).

Low energy accelerating machines were built in the 1960s in Milan and Padua (Legnaro). In Milan, the construction of a 45 MeV cyclotron was, for about two thirds, financed by private companies, while the remaining third was made available by public bodies (Municipality of Milan, Ministry of Education, CNR); the university made the buildings available, while the INFN provided part of the staff. Amaldi and Bernardini, believing that the Italian commitment on accelerators was adequately ensured by the center of Frascati and by the Italian participation in CERN, had expressed doubts about the opportunity of the initiative. The construction of a 5.5 MeV Van de Graaf accelerator in Legnaro was sponsored by the University of Padua and had Antonio Rostagni (1903-1988) as its promoter.

In the 1980s, a cyclotron was built in Milan which employed superconducting magnets and which in the mid-1990s was transferred to the INFN laboratory in Catania; the center of Legnaro was absorbed by the INFN in 1968. Finally, in 1982, construction work began on the INFN laboratories of the Gran Sasso, supported by Antonino Zichichi (n. 1929). They started operating in 1989 and are dedicated to the study, among other things, of neutrino physics and dark matter. The Gran Sasso laboratory belongs to a group of ten underground laboratories (Canada, Europe, Japan and the United States) dedicated to the study of phenomena that (ideally) require the absence of cosmic radiation.

The Italian participation in CERN reached its most important results in 1983, with the discovery of the W and Z bosons by the group called UA1 and coordinated by Carlo Rubbia (n. 1934). The W and Z bosons were predicted by the electroweak interaction theory formulated independently in the 1960s by Sheldon L. Glashow (b.1932), Abdus Salam (1926-1996) and Steven Weinberg (b.1933). In 1976, David B. Cline, Peter McIntyre, Fred Mills and Rubbia proposed the transformation of the SPS ( Super Proton Synchrotron) of CERN or Tevatron of Fermilab (Chicago) in a collider of protons and antiprotons. The proposal was collected by CERN and led to the creation of the collider, which came into operation in 1981 and was characterized by technological innovations developed by Simon van der Meer (1925-2011). Two research groups that alternated in the use of the machine dedicated themselves to the search for the bosons foreseen by the theory: the aforementioned group UA1 and the group UA2, coordinated by Peter Jenni. The two groups were distinguished by the detector used: the more generic and broader one of UA1, the more specific one of UA2. The first evidences of the W bosons were collected by UA1 and were later confirmed by UA2; later the boson Z was discovered. The 1984 Nobel prize for physics was awarded to Rubbia and van der Meer.

The choice of large accelerators concentrated the experimental physical research of elementary particles in a few locations. It is therefore not surprising that, even in the following years, the Italian contribution has materialized through the participation in various CERN projects, such as those aimed at verifying the existence of the so-called Higgs boson envisaged by the standard Model, or those in which they study the physical properties of antimatter atoms produced in low energy physical conditions (AD, Antiproton Decelerator ). Recently (2012), the CMS ( Compact Muon Solenoid ) and ATLAS ( A Thoroidal Lhc Apparatus) groups), operating at LHC, obtained experimental evidence compatible with the Higgs boson. On the low energy side, Italian groups participate – within the ATHENA ( Apparatus for High precision Experiments with Neutral Antimatter ) collaboration – in experiments regarding antidrogen atoms: their study would allow to verify some symmetry properties of current theories and the antimatter behavior in the Earth’s gravitational field.

The cosmic background radiation

In the late 1960s, Francesco Melchiorri (1940-2005) worked at the IROE ( Electromagnetic Wave Research Institute) of Florence, then directed by Giuliano Toraldo of France (1916-2011). At the suggestion of Rossi and encouraged by Toraldo di Francia, Melchiorri began to deal with the radiation that, according to the hypothesis of Robert H. Dicke (1916-1997) and collaborators, Arno A. Penzias and Robert W. Wilson had discovered in the laboratories of the Bell in Murray Hill (New Jersey), but whose fundamental characteristics were still unknown: in particular, the supposed nature of blackbody radiation had not yet been proven. Despite the widespread skepticism towards Dicke’s hypothesis, Melchiorri began a series of measurements conducted at the Gray Head observatory (Plateau Rosà), which showed how the spectrum of cosmic background radiation (CBR, Cosmic Background Radiation) could not obey the classical Rayleigh-Jeans law (1976). Then followed measurements made with stratospheric balloons launched from the Trapani base of the Italian Space Agency (ASI), recently established: the anisotropy of CBR due to the motion of the Earth in the cosmos in a region of the infrared spectrum was studied (1980). However, the most significant undertaking was the BOOMERanG ( Balloon Observation Of Millimetric Extragalactic Radiation and Geophysics ) project, created in collaboration with a Berkeley group directed by Paul L. Richards. It was a matter of launching balloons in Antarctica, where the stratospheric winds favor the return of the balloons near the launch point. Intrinsic anisotropies in CBR discovered in 1989 by the COBE project (COsmic Background Explorer ) were measured at high resolution and at high signal-to-noise ratios. Similar results were obtained from the contemporary MAXIMA ( Millimeter Anisotropy eXperiment IMaging Array ) project, directed by Richards and also based on stratospheric balloons. In the following years, two satellite missions, NASA’s Wilkinson Microwave Anisotropy Probe (WMAP ) and ESA’s Planck, have refined or are refining pioneering measurements with stratospheric balloons.

Cabibbo’s theoretical contribution

Nicola Cabibbo’s contribution to elementary particle theory is a significant example of how the Standard Model was developed. The latter is a ‘collective’ theory concerning the interactions of subatomic particles that developed, changing continuously, in the second half of the twentieth century on the basis of numerous theoretical and experimental contributions. His predictions are compared and intertwined with those of various cosmological models whose validity is tested by the recent development of experimental cosmology, based on astrophysical observations of which the one previously discussed concerning the cosmic background radiation is just an example.

For some time, physicists had identified some particles called strange : particles produced by a strong interaction but having a very short average life compared to that typical of this type of interaction. Cabibbo showed that every β-type decay, to which even strange particles are subjected, could be described by a single parameter, the angle later called Cabibbo. He also explained the small differences observed in the Fermi constant that controls the β decay of neutrons and muons. Subsequently, he reformulated his hypothesis in terms of the three types of quarks then known (up, down and strange). In 1970, Glashow, John Iliopoulos and Luciano Maiani (b. 1941) extended Cabibbo’s discussion to include a fourth type of quark (charm) whose existence was later verified in 1974. In 1972, Makoto Kobayashi and Toshihide Maskawa reformulated again the theory, in order to take into account the violation of the CP symmetry (charge-parity), introducing two new quarks (top and bottom); they were awarded the Nobel prize for physics in 2008.

The physics of matter

The Italian physicists who in the immediate post-war period devoted themselves to the study of the physics of atoms, molecules, liquids and solids could not count, except for the line of research on the Raman effect, on a solid cultural heritage such as that left by Fermi and Rossi in the field of nuclear and subnuclear physics and cosmic rays. Not only that: the training of students who entered the degree course in physics in the immediate post-war period still took place on the basis of a study plan of 1937, already obsolete at the time and which would remain in force until 1962. It provided for the teaching of theoretical physics; however, the teaching of quantum mechanics took place only in some places and was mostly ensured by teachers who had come into contact with the Fermi group. Only in 1962 was the teaching of the structure of matter introduced, which is configured as a course of application of quantum mechanics to the physics of atoms, molecules and solids. Therefore, the physicists who dedicated themselves to these studies did it by themselves or by making contacts with foreign institutes and laboratories. Thus we witnessed a polycentric development, favored by an intertwining of individual cultural interests, local conditions, randomness, the possibility of short periods spent in foreign laboratories.

In 1942 in Pavia, Luigi Giulotto (1911-1986), at the suggestion of Caldirola, began a spectroscopic research aimed at confirming previous results that questioned the correctness of Dirac’s theory of the hydrogen atom, theory according to which the two levels 2s1 / 2 and 2p1 / 2 have the same energy. The measurements, completed in 1947, constituted further confirmation of the existence of a discrepancy between theory and experiment (the line emitted by hydrogen atoms appears, in conventional spectroscopy, as an asymmetrical doublet; Giulotto’s conclusions were therefore based on a delicate comparison between the experimental and theoretical curves reconstructed on the basis of Dirac’s theory). A few months later, Willis E. Lamb Jr (1913-2008) and Robert C.Lamb shift was given by quantum electrodynamics. Lamb was awarded the Nobel Prize in Physics in 1955 for his discoveries on the fine structure of the hydrogen spectrum.

This event is emblematic of the gap then existing between some sectors of physics in Italy and the corresponding sectors at international level, and of the technological delay of our country. The same problem was faced by Giulotto with traditional, albeit refined, spectroscopic methods; by Lamb with a completely new experimental approach inspired by an entirely quantum view of the problem and made possible by the development of microwave technology during the war and for war purposes.

In 1946, Giulotto began the development of a nuclear magnetic resonance system. Since an oscilloscope was not available, he heard the first resonance signal through a headphone as an additional noise on the background noise due to the mains frequency. This was the beginning of a happy season that allowed Giulotto and his collaborators to join the leading groups worldwide until the mid-fifties. Subsequently, the production of powerful resistive or superconducting magnets, as well as new and expensive spectrometers, made the Pavia instrumentation obsolete. In the three years 1948-1951, Giulotto (with Gilda Olivelli, n. 1920) resumed the studies on the Raman effect that began in the late 1930s, this time in calcite:

In the early 1950s, Caldirola came into contact with Fausto Fumi (b.1924), a theoretical physicist who had just returned from Urbana (Illinois), where he had worked with Frederik Seitz (1911-2008) on the properties of crystalline solids. Caldirola sensed the possibility of promoting the development in Italy of solid state physics (then completely unknown in our country), making use of the skills of Fumi and its international contacts; thus he favored Fumi’s stay in Milan as professor in charge and the assignment of two degree theses in 1928 to Franco Bassani (1929-2008) and Roberto Fieschi (n. 1928), students in Pavia. In the mid-1950s, Caldirola put Fumi in contact with Giulotto: the project was to encourage the establishment, in Pavia, of an experimental and theoretical group of solid state physics. Gianfranco Chiarotti (n. 1928), an experimental physicist who until then had dealt with nuclear magnetic resonance, after a period of three years spent in Urbana in the Seitz group, went on to study particular reticular defects in alkaline halides (centers of color) and, towards the end of the Fifties, started the experimental study of semiconductors in university institutes. At the end of 1959, in addition to Fumi, Bassani and Chiarotti, the experimental physicist Paolo Camagni (1931-2000) and the theorists Mario Tosi (n. 1928) and Vittorio Celli (n. 1936) were in Pavia. Severe contrasts between Fumi and Giulotto led to the failure of the project. In the meantime, in Milan, Fieschi, inspired by Caldirola, had extended the activity of his research group, originally theoretical, to experimental research (color centers);SPECIAL materials for electronics and magnetism ).

Andrea Levialdi (1911-1968) was one of the animators of the project and should have been the director of the center, but died before its establishment in 1969 together with that of two other laboratories (Pisa and Rome).

Despite the early failure of the original project, the Pavia experiment made a fundamental contribution to the birth of solid state physics in Italy, also thanks to a series of favorable factors, including the possibility of drawing on a selected base of undergraduates and graduates from from the Ghislieri College and, to a lesser extent, from the Borromeo College (historic university colleges of Pavia), and the international relations of Fumi, which allowed his young collaborators to study and work in the United States and in Great Britain. The dispersion of the Pavia group favored the spread of solid state physics in other universities: Chiarotti, after Messina, was in Rome; Bassani, on his return from the United States, first to Messina, then to Pisa, Rome and again to Pisa; Tosi, on his return from the United States, to Messina, then in Rome, finally in Trieste. Of particular importance is Bassani’s contribution, in the various locations, to the training of numerous theoretical physicists, and to the development of the application of the pseudo-potential method to the calculation of energy bands in different crystalline solids and to their connection with the reflectivity of materials in the ultraviolet.

Microwave in Pisa

At the end of the war, Adriano Gozzini (1917-1994), returning to Pisa, found the institute of physics half destroyed and depleted in its instrumental equipment by the retreating German troops. However, he managed to start a research activity characterized by the use of microwaves. The first works concerned the Corbino-Macaluso effect in paramagnetic substances: the results obtained aroused the interest of Kastler, who had foreseen them a few years earlier. He then began a long-lasting collaboration with Gozzini, who extended the research to transverse magnetic fields. The most significant result obtained by Gozzini’s group was the discovery of some black lines, of unknown origin, in the fluorescence of excited sodium vapors by means of a multimode dye laser ( dye laser). The explanation of the black lines was given shortly after by Gaspar Orriols and Ennio Arimondo (n. 1942): they are due to the interference between the amplitudes of probability of two transitions between hyperfine levels – whose separation in frequency is equal to that between two modes of the laser beam – and the excited state. This discovery gave rise to a number of important subsequent developments.

Magnetic properties

The National Institute of Electrical Engineering ‘Galileo Ferraris’ in Turin, inaugurated in 1935, had a section dedicated to the study of the magnetic properties of matter. The outbreak of the Second World War postponed the start of a systematic research activity to the post-war period. The technological importance of this type of research has favored their development in laboratories or institutes with application purposes. In the seventies, a group coordinated by Giovanni Asti (magnetic materials and devices) and, more recently, the ‘Galileo Ferraris’ (now INRiM, National Institute of Metrological Research ), the group of Giorgio Bertotti (dynamics) began to operate at MASPEC in Parma of magnetization). Other groups are active at the ISM ( Institute of Structure of Matter) of CNR (Dino Fiorani, superparamagnetism and magnetic recording), in Florence (Dante Gatteschi, Roberta Sessoli, molecular magnetism), in Perugia (Giovanni Carlotti, magnetic crystals) and in Bologna (Valentin Dediu, spin-electronics in organic materials).

The physics of low temperatures

In 1908, Heike Kamerlingh Omnes (1853-1926) managed to liquefy helium; three years later, he discovered the phenomenon of superconductivity. In Italy, the first helium liquefactor was installed in 1955 in Frascati, as part of the electrosynchrotron construction project. Salvini entrusted Giorgio Careri (1922-2008) with the task of organizing and managing the cryogenic department. So, even in Italy, with a delay of half a century, we began to experiment at temperatures around that of liquid helium (4.2 K), although between difficulties of various types. Having learned the techniques of low temperatures, Careri used them for the study of the properties of superfluid helium. The second pole of development of low temperature physics was that of Genoa (1960), on the initiative of Giovanni Boato (1924-2009). The group dealt with the transport properties of rare solid gases and magnetic flux quanta in type II superconductors. Careri and Boato were the protagonists of another transfer operation in Italy of techniques that had developed decades earlier. This is the construction of the first mass spectrograph in Rome. Also this technique, developed in the 1920s by Francis W. Aston (1877-1945), arrived in Italy with serious delay (during the Second World War, the separation of 235U from 238 U , crucial for the construction of the nuclear fission bomb which was then dropped on Hiroshima, was obtained with mass spectrometers).

In the early seventies in Naples, Antonio Barone (1938-2011) began a fruitful line of research on the Josephson effect that had important international recognitions. The group of the NEST ( National Enterprise for nanoScience and nanoTechnology ) of Pisa coordinated by Vittorio Pellegrini (n. 1969) is actively involved in the quantum Hall effect, discovered by Klaus von Klitzing in 1980 .

The discovery, in 1986, of high temperature superconductivity by Karl A. Müller (1927) and Johannes G. Bednorz (1950), saw in Italy the timely experimental commitment of three groups in Pavia, Rome and Turin. In Pavia, this line of research was started by Attilio Rigamonti (b. 1937), who had closely followed Müller’s work; currently, the group is coordinated by Pietro Carretta (b. 1966). The properties of the superconductors have been investigated using, among other things, the nuclear magnetic resonance technique, which had its origins in Italy at the Pavia site and, with magnetization measures based on the use of SQUID ( Superconducting Quantum Interference Device) near the transition to the superconducting phase, the floating Cooper pairs that generate a diamagnetic term above the critical temperature were studied. The Roman group coordinated by Paolo Calvani (n. 1948) studied, in particular, the optical properties of high temperature superconductors. At the Politecnico di Torino, the most important results obtained by the group coordinated by Renato Gonnelli (n. 1955) concern the properties of MgB 2, which becomes 39 K superconductor.

Laser: physics and technology

In 1960, the Italian interest in the construction of masers ( Microwave Amplification by Stimulated Emission of Radiation ) operating in the visible and infrared region, was awakened by the Varenna school of the SIF ( Italian Physical Society ), organized by Gozzini. It is therefore not surprising that Italian engineers and physicists reacted promptly to the invention of the laser. Beyond intellectual reactivity, the approach to laser physics has been favored by the relative ease of construction of a laser once its operating principles have been understood. In 1963 a five-year project of the CNR called the Maser-laser company startedwhose promoters were Daniele Sette (n. 1918), Toraldo di Francia and Emilio Gatti (n. 1922). The construction of the first lasers in Italy featured non-university laboratories (the Bordoni Foundation in Rome and CISE, Structural Engineering Buildings in Europe, in Milan), but laser physics developed essentially in universities. Italian scientific production on lasers quickly reached levels of international value. Among the pioneers of this line of research in Italy, we find Tito Arecchi (n. 1933) and Orazio Svelto (n. 1936). A work by Arecchi, published in 1965, the first of a series dedicated to the coherence of laser light, measured through the photon statistics, is still mentioned in our day; Svelto owes pioneering research on lasers capable of emitting ultrashort impulses and on the physics that can be achieved with them. One of Arecchi’s first collaborators, Vittorio Degiorgio (b. 1939), landed in the early 1980s in Pavia (faculty of engineering), where he set up a research group on laser physics and its applications.European Laboratory of Nonlinear Spectroscopy ), where research is carried out on a wide range of topics.

Bose-Einstein condensates

In 1924, thanks to Einstein’s interest, Satyendra Nath Bose (1894-1974) published a work in which he obtained Planck’s formula for blackbody radiation by treating the electromagnetic radiation contained in an isothermal cavity as composed of quanta of light (photons) endowed with energy E =  and momentum p =  / c (with νfrequency of electromagnetic radiation), and applying a statistical treatment to them. The following year, Einstein adapted Bose’s treatment to the perfect gas case by, inter alia, predicting that, when de Broglie’s wavelength of the gas atoms becomes the same order of magnitude as the mean interatomic distance, part atoms occupy the minimum energy state, that is, they ‘condense’. At the end of the 1920s, it became clear that the Bose-Einstein statistic is valid for particles with intrinsic angular momentum (spin) equal to zero, h / 2π or an integer multiple (bosons), while, as we have seen, the statistic di Fermi-Dirac is valid for particles with half-full spin (fermions).

The first realization of a Bose-Einstein condensate took place in 1995, that is about seventy years after the Einsteinian prediction. In Italy, a group coordinated by Massimo Inguscio (b. 1952) in Florence, whose previous scientific activity had developed on topics related or preparatory to the Bose-Einstein condensation phenomenon, was successfully able to engage successfully in this research sector. . Among the most significant results of the group is the observation of the Josephson effect created with two condensates trapped in two cells of an optical lattice (consisting of stationary light waves).

Nanoscience and Nanotechnologies

In 1981, Gerd Binnig (1947) and Heinrich Rohrer (1933) built the first tunnel effect microscope; five years later, Binnig built the first atomic force microscope, thus paving the way for nanoscience and nanotechnologies operating on at least one linear dimension in the order of a nanometer (one billionth of a meter; the atomic dimensions are approximately ten times smaller) . The upper limit is set by the size above which the physical properties typical of a ‘nano’ material or device disappear (and not present in larger samples). The fields of application of nanoscience range from electronics to the creation of new materials and biomedicine. In Italy, this sector involves research laboratories and industries.

Plasma physics

The term plasma indicates, in physics, a generally neutral set of charged particles. The term was coined in the 1920s by Irving Langmuir by analogy (actually improper) with the blood plasma: the ionosphere is made up of a plasma; various types of plasmas have been identified in the cosmos. Attempts, still ongoing, to achieve a controlled nuclear fusion for energy purposes have stimulated the development of this sector of physics. The realization of a controlled nuclear fusion requires the achievement of temperatures that cannot be tolerated by any material (about 107 K). It is therefore a matter of trying to reach these temperatures in a plasma confined in a volume sufficiently far from the walls of the container.

In Italy, plasma physics was born as a product of research aimed at achieving nuclear fusion. The development centers were the Ionized Gas Laboratory of Padua (1959), the Ionized Gas Laboratory of Frascati (1960) and the Plasma Physics Institute of Milan (promoted by Caldirola and then dedicated to his name) in 1976. Currently , nuclear fusion research should be coordinated by ENEA ( Agency for New Technologies, Energy and the Environment ).

Nuclear technology as a source of new lines of research

The development of accelerators and nuclear power plants has given rise to new lines of research. The first observation of an antineutrino (1956) is due to Clyde L. Cowan Jr (1919-1974) and Frederick Reines (1918-1998), who used the antineutrinos produced by a nuclear reactor located in Savannah River (South Carolina). Experimental neutrino physics contributed to the definition of the standard Model with experiments such as the violation of parity in the weak interaction and the oscillations of neutrinos predicted by Vladimir N. Gribov and Pontecorvo in 1969.

The Italian contribution to these researches is achieved by participating in the measurements with a neutrino beam produced at CERN and sent, through the earth’s crust, to a detector placed in the Gran Sasso laboratories and with the measures aimed at finding double β decay without neutrino emission (which would confirm the identity between neutrinos and antineutrinos). The neutrons produced by nuclear reactors were used in the 1950s to study the properties of condensed matter through their elastic or inelastic diffusion. Still in the 1950s, electromagnetic radiation produced by synchrotrons began to be used as an instrument for investigating the properties of the condensed mass. In the seventies a technique (μSR, muon Spin Resonance) developed) based on the use of muons deposited in the material under study.

In Italy, the study of condensed matter by neuron diffraction began in the 1960s in Ispra (Giuseppe Caglioti, no.1931; Francesco Paolo Ricci, 1930-2000) and in Rome (Casaccia). In Trieste, on the other hand, a synchrotron dedicated to the use of its radiation was completed (1993). This initiative was promoted by Luciano Fonda (1931-1998), after the decision to install a European synchrotron in Grenoble instead of Trieste. Muonic resonance is cultivated in Italy by a group headed by Cesare Bucci (b. 1938), one of Fieschi’s first experimental students.

Epilogue

The birth of the 20th century he took physics in Italy culturally and institutionally unprepared, in a technologically backward country. In the 1930s, Fermi, Rossi and their collaborators marked a turning point in the field of nuclear physics, and cosmic rays, while the remaining sectors remained on the margins of the tumultuous development of the discipline. The fascist racial laws and the Second World War deviated, distorted and interrupted the path taken.

The phenomenon of migrants of science, which began with the racial laws of 1938, took on new connotations in the second half of the twentieth century. Among the numerous physicists who, trained in Italy during this period, have built their professional career abroad, it is necessary to remember at least some figures: Riccardo Giacconi (b. 1931), graduated in physics in 1954 in Milan and emigrated to the United States in 1956. Giacconi was awarded the Nobel Prize in physics in 2002 “for the pioneering contributions to astrophysics that led to the discovery of cosmic X-ray sources”. Federico Faggin (b. 1941), graduated in physics in 1965 in Padua and, after working experiences at Olivetti and SGS ( Società Generale Semiconduttori), who emigrated to the United States in 1968. He was, among other things, the main designer of the first microprocessor (1971). Federico Capasso (b. 1949), graduated in physics in 1973 in Rome and emigrated to the United States in 1976. Capasso, during his stay at Bell’s laboratories (1976-2002), combined basic and applied research in the creation of materials and devices based on semiconductor hetero-structures. Bruno Coppi (b. 1935), graduated in 1959 from the Polytechnic of Milan, emigrated to the United States in 1961. Coppi contributed to the design of Frascati’s Tokamak, which came into operation in 1977, and is the creator of the Italian fusion project nuclear power plant named Ignitorthat, following an Italian-Russian agreement in 2010, it should be assembled in Russia with components produced in Italy; a singular decision that will probably cause serious difficulties to the project, also called into question by the Italian accession, through the European Union, to the ITER ( International Thermonuclear Experimental Reactor ) project.

After the Second World War, scientists, like all Italians, engaged in a reconstruction process made dramatic by the war ravages, by the overall backwardness of the country and its scientific structures. The progressive increase in the number of physicists, the increase in their professional profile, the increase in research funding have allowed the community of Italian physicists to fully enter the wider international community; including theoretical physics whose multifaceted production prevents an even schematic analysis here. However, the fundamental contributions of Giorgio Parisi (n. 1948) to the study of disordered magnetic materials called spin glasses, which have produced significant effects in other research areas.

Today, the future of research directly depends on the efficiency of the country system. A country where resources are taken away from the training system instead of making it the foundation of the future; young graduates migrate each year without their outgoing flow being balanced, at least partially, by an incoming flow; the technological level of the industry is backward and the materials and instrumentation of the research laboratories come, to a large extent, from abroad: a similar country and its scientific research are destined to play an increasingly marginal role in the international context.

 

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