My interest in the life and work of English astronomer William Huggins (1824–1910) began over twenty years ago in a graduate seminar on conceptual transfer within and among specialised scientific communities. The exchange of cultural baggage is a subtle dynamic that practitioners, particularly those working in long-established disciplines, usually take care to shield from public view. Our little group spent the semester analysing the far more transparent machinery of newer, still-developing hybrid disciplines like geophysics, biochemistry and astrobiology.

The topic meshed well with my own research interests at the time. I wanted to learn more about how the boundaries of scientific disciplines are established, policed and altered: What are the rules members must follow in investigating the natural world? What questions are deemed appropriate to ask? What do good answers to such questions look like and how can they be recognised? What constitutes an acceptable way of finding those answers? Who is allowed to participate in the search? Who says?

How better to find answers to these questions than to watch a scientific discipline during a period of change?

In her 1885 history of nineteenth-century astronomy, Agnes Mary Clerke enumerated the discoveries that marked the recent progress in that science. She drew her readers' attention to the founding of what she called ‘astronomical or cosmical physics’, a new species of astronomy that was markedly different in goals as well as methods from its older mathematical cousin. ‘It is full of the audacities, the inconsistencies, the imperfections, the possibilities of youth’, she wrote. ‘It promises everything; it has already performed much; it will doubtless perform much more.’ Clerke was not alone in her enthusiasm.

Britons who played a role in the development of this hybrid discipline, either as active contributors or sideline boosters, hailed it as a happy consequence of the growing interdependency among a heterogeneous subset of scientists and instrument makers. For decades – whether probing the physical properties of light, chemically analysing terrestrial materials or perfecting the production of optical glass – these practitioners had pursued their disparate research agendas using a common, and historically rich, line of investigation: the careful scrutiny of dispersed natural and artificial light. Appropriating elements from the methodological legacy of such notable forebears as Isaac Newton and William Herschel, they examined new types of light sources, tinkered with alternative apparatus arrangements and tested the efficacy of a range of viewing and recording aids. It was a powerful and productive process.

As focused as the Hugginses were during the 1880s and 1890s on demonstrating the feasibility of their method of photographing the solar corona without an eclipse, they also remained alert to and actively involved in other projects. The astrophysics playing field was becoming crowded with new players – some joining in to assist, others to compete. The rules and even the game itself were constantly changing.

William and Margaret found it both exciting and discomfiting to be involved. To participate successfully required no small measure of vigilance and alacrity: vigilance to defend one's claims to priority of discovery and reputation as an observer; alacrity to keep abreast of the latest investigatory opportunities, technical improvements and methodological innovations. William Huggins had always possessed these characteristics, but as both his career and astrophysics matured, he and Margaret had to remain alert and ready to act to preserve his role as patriarch in the field and maintain what both of them believed was William's rightful place in the history of the new science.

Like their corona work, their investigation of the so-called ‘chief nebula line’ was a project in which Margaret was actively involved. It embroiled the Hugginses in controversy over methods, instruments and interpretation of received data. Their findings formed the basis of the first paper on which Margaret Huggins appeared as co-author. This paper, which appeared in 1889, was a benchmark in the Hugginses' collaborative relationship.

By the 1870s, when William Huggins assumed responsibility for the Great Grubb Equatorial, the discipline of astronomical physics was developing on many fronts. Which would open up the most fruitful line of investigation? No one knew. Unabashedly eclectic in his research interests and methods, Huggins shrewdly ventured down many paths that promised discovery and recognition. Sometimes – but not always – he encountered new opportunities to press the spectroscope into service.

Concern for priority with its attendant thrill of the chase occasionally provoked him to examine the Sun, just as solar observers like Lockyer were drawn to study stars and nebulae. Huggins was not always happy with the results of his solar investigations, however, and they are conspicuously missing from his retrospective account, ‘The new astronomy’. Because his biographers and historians of science have relied heavily on this essay for details of his career, his contributions to the rapidly growing body of knowledge about the Sun and its atmosphere have been all but forgotten.

The unpublished record brings light and life to these episodes once again. Huggins learned a great deal about discovery's delicate dance from his setbacks and failures, and so can we.

In spite of the simple appearance of its Lagrangian, QCD is an extremely complicated and rich theory. As a theory of strong interaction, it is subject to various constraints posed by observations. Most important among them are scaling and confinement, which appear to have conflicting implications for the nature and characteristics of QCD. It also has many observational implications, such as the logarithmic violations of scaling, the spectrum of charmonium, and the two-jet and three-jet structure in the electron–positron annihilations. The successes in satisfying these constraints and in explaining and predicting observational events in the early to mid 1970s immediately after the proposal of QCD had provided QCD with much needed experimental justifications and consolidated its status as an acceptable theory in the particle physics community.

As a non-abelian gauge theory, QCD is also subject to some conceptual constraints posed by its symmetry structure, such as the U(1) anomaly (see Sections 8.2 and 8.5 below). The solution of the U(1) anomaly relied on the further explorations of the theoretical structure of QCD, which revealed its richness and great potential for theorizing the complexity of the sub-hadronic world, such as the existence of instantons and the related theta vacuum state. The fruitful explorations in this direction had shown that QCD, in Lakatos's terminology, was a progressive research program, which keeps opening new territory for explorations, and thus was conceived by the majority of the community as worth pursuing.

Current algebra, as a hypothesis about hadron physics, offers a set of algebraic relations relating one physically measurable quantity to another, although it cannot be used to calculate any from first principles. Presumably, the assumed validity of a hypothesis should first be tested before it can be accepted and used for further explorations. However, any exploration of the implications or applications of the hypothesis, within the general framework of hypothetic-deductive methodology, if its results can be checked with experiments, functions as a test.

The test of current algebra, however, requires delicate analyses of hadronic processes and effective techniques for identifying relevant measurable quantities in a justifiable way. For this reason, there was no rapid progress in current algebra until Sergio Fubini and Giuseppe Furlan (1965) suggested certain techniques that can be used, beyond its initial applications, to derive various sum rules from current algebra, which can be compared with experimental data. The importance of the sum rules thus derived, however, goes beyond testing the current algebra hypothesis. In fact, they had provided the first conceptual means for probing the constitution and internal structure of hadrons, and thus had created a new situation in hadron physics and opened a new direction for the hadron physics community to move, as we shall see in the ensuing sections and chapters.

In the 1950s, all hadrons, namely particles that are involved in strong interactions, including the proton and neutron (or nucleons) and other baryons, together with pions and kaons and other mesons, were regarded as elementary particles. Attempts were made to take some particles, such as the proton, neutron and lambda particle, as more fundamental than others, so that all other hadrons could be derived from the fundamental ones (Fermi and Yang, 1949; Sakata, 1956). But the prevailing understanding was that all elementary particles were equally elementary, none was more fundamental than others. This general consensus was summarized in the notion of “nuclear democracy” or “hadronic egalitarianism” (Chew and Frautschi, 1961a, b; Gell-Mann, 1987).

As to the dynamics that governs hadrons' behavior in the processes of strong interactions, early attempts to model on the successful theory of quantum electrodynamics (or QED, a special version of quantum field theory, or QFT, in the case of electromagnetism), namely the meson theory, failed, and failed without redemption (cf. Cao, 1997, Section 8.2). More general oppositions to the use of QFT for understanding strong interactions were raised by Landau and his collaborators, on the basis of serious dynamical considerations (Landau, Abrikosov, and Khalatnikov, 1954a, b, c, d; Landau, 1955). The resulting situation since the mid 1950s was characterized by a general retreat from fundamental investigations to phenomenological ones in hadron physics.

The underlying idea of current algebra, light-cone current algebra included, was to exploit the broken symmetry of strong interactions. The idea was pursued through abstracting physical predictions, as the consequences of the symmetry and in the form of certain algebraic relations obeyed by weak and electromagnetic currents of hadrons to all orders in strong interactions, from some underlying mathematical field theoretical models of hadrons and their interactions, more specifically from models of quark fields universally coupled to a neutral gluon field.

When current algebra was initially proposed, the symmetry was defined with respect to static properties of hadrons, such as mass, spin, charge, isospin, and strangeness. However, over the years, especially after the confirmation of scaling, in the changed theoretical and experimental context, the notion of symmetry underlying the current algebra project had undergone a transmutation. A new component of symmetry, that is, a dynamic symmetry, was brought into the scheme. The result was not only some adaptations in algebraic relations and corresponding physical predictions, but also a radical change in the nature of the underlying field theoretical model. More precisely, the result was the emergence of a gauge invariant quark–gluon model for strong interactions, or the genesis of quantum chromodynamics (QCD).

Murray Gell-Mann's proposal of current algebra in 1962 (Gell-Mann,1962) was an important step in the conceptual development of particle physics. In terms of insights, imagination, and consequences, this strategic move ranks among the highest scientific creativity in the history of fundamental physics. When the proposal first appeared, however, because of its mathematical complication and conceptual sophistication, it was perceived by most particle physicists to be too esoteric to understand or see its relevance and applicability. Even today, more than four decades later, with the advantage of hindsight, it remains difficult to properly assess its role in the history and understand why and how it played the role it did.

The difficulty lies not so much in Gell-Mann's idiosyncratic ingenuity but in, first, the puzzling situation of particle physics to which Gell-Mann's proposal was a response, and, second, in the bewildering trajectory of the subsequent development, which was shaped mainly by the competition between various speculative ideas and, ultimately, by the interplays between experiments and theorizing. The aim of this chapter is to address the first aspect of the difficulty, postponing the second to subsequent chapters.

Context

When Gell-Mann proposed his current algebra to deal with hadron physics, there was no accepted theory of strong interactions. Worse, there was no theory of how hadrons interacted with each other at all.