A theme encountered throughout this book has been the resourceful approach of astronomers and astrophysicists of the twentieth century as they searched for new ways to advance our understanding of the Universe. By adopting the new atomic and ionic theories of Niels Bohr and Meghnad Saha, Henry Norris Russell and Cecilia Payne determined the abundances of the chemical elements in the Sun and stars. Willem de Sitter and Arthur Stanley Eddington taught us how Einstein's relativity theories could lead to new insights on an evolving Universe. And the nuclear theories of George Gamow, Hans Bethe, and Edwin Salpeter provided novel insight on the energy sources of stars and the origins of the chemical elements. Astronomical observers similarly adopted techniques developed by physicists and engineers to greatly expand the wavelength ranges across which the Cosmos might be studied. By adopting methods developed elsewhere, the cost of astronomy was kept low.

This enterprising spirit will stand us in good stead as we face a newer set of challenges posed by the global economic downturn of late 2008 that still persist today. Finding new ways to advance astronomy under these conditions will be important for solving the cosmological problems now to be overcome. Those efforts will undoubtedly take time, and will succeed best if we choose an appropriate economic approach aimed at assuring the long-term stability of our astronomical program.

July 5, 1945 marked a break in the way science and engineering were to be conducted in the United States in the postwar era. The government would take a leading role in the transition. The future was to belong to scientists and engineers working as teams partly dedicated to basic research, but more importantly working for the benefit of the nation, its security needs, its ability to feed its people, and the health of its children. This chapter recounts in some depth how and why the new program came to be initiated and adopted.

In the new arrangement, the future of astrophysics was nowhere mentioned, but time would show astronomy's emphasis on surveys and surveillance to be most closely aligned with military priorities. It took less than three decades to show that the alliance between the military and astronomers was leading to formidable advances no astronomer had anticipated. Soon other nations began to emulate the U.S. lead, and astronomy started advancing at a dizzying pace.

The contrast with astronomy before World War II could not have been greater.

Support for Basic Research in the Prewar Years

When Niels Bohr, during an impromptu visit from the young George Gamow late in the summer of 1928, assured him a year's Carlsberg Fellowship at the Royal Danish Foundation starting the next day, no senior physicist would have been surprised. When Bohr and Ernest Rutherford, the following year, asked the Rockefeller Foundation to provide Gamow a fellowship so he could work with Rutherford at Cambridge University, this too would have been expected.

Asking the right question and being satisfied with the answer it yields is one of the most difficult tasks of astrophysical research. Concentrate on too small a problem and you may neglect essential extrinsic factors. Attempt to answer too broad a question and you may fail across the entire front.

As the 1920s were drawing to a close, two questions were being asked with increasing urgency: “What makes the stars shine?” and “What is the origin of the Chemical Elements?” To many, the two problems appeared related.

Gravitational contraction by then appeared an unlikely source of stellar energy. A potentially abundant supply of nuclear energy appeared to exist, to keep the stars shining for billions of years, but how it might be released was unknown. The known mass defects of heavy elements suggested that a merging of light elements to form heavier elements could both release sufficient energy and account for the existence of heavy elements. The emerging realization that hydrogen was the most abundant element in the Universe made this notion particularly attractive.

If we only understood the nature of nuclear reactions we might account for both the source of stellar energy and the relative abundances of the chemical elements. The prospects were heady!

Acting on principle can be rewarding but also risky. What if the principle, against all expectations, turns out to be invalid?

On graduating from the Eidgenössische Polytechnikum in the summer of 1900 with a barely passing grade, the 21-year-old Einstein had no prospects of permanent employment. But as he drifted from one temporary position to another, he was at least free to pursue his passion for physics. Less than five months after receiving his diploma, he submitted his first paper to the leading German journal, the Annalen der Physik. Like all of his papers published in the subsequent three years, it was grounded in thermodynamics.

Thermodynamics is an expression of the conservation of energy as it is converted from one form, such as electrically, mechanically, or chemically stored energy into another. Einstein continued to draw strength from this and other conservation principles for most of the work he would produce. They gave him guidance and assurance as he ventured ever further into uncharted realms.

Rescue of the jobless Einstein came through the father of Marcel Grossmann, Albert's closest friend during their student years at the Polytechnikum. The elder Grossmann was impressed by his son's friend and recommended him to Friedrich Haller, director of the Swiss Patent Office in Bern. When a new position opened there, Einstein at once applied and, in June 1902, won an appointment as patent clerk third-class. He remained immensely grateful to the Grossmanns and, on completing his doctoral work in 1905, dedicated his thesis to his friend.

When I was a student in college, Albert Einstein was still alive. My friends and I grew up with the myth of this great man who, the story went, while a clerk, third class, at the Swiss Patent Office in Bern, had emerged from nowhere at age 26 to set down the laws of relativity in a paper so fresh, so novel that not a single other scholar needed to be cited as a source of at least partial inspiration for this monumental paper. Einstein's paper contained no list of references; none had existed or could even be found!

We all aspired to emulate Einstein and write a paper as great as his. To this end it seemed we would need only to foster self-reliance, reject outside influences, and rely solely on an inner intellect.

But in the first half of the twentieth century, the myth could not be dispelled. Historians of science active at the time preferred to write about a distant past. And, as a young man, Einstein himself may have quietly enjoyed the mystique that surrounded his work. Only three times, as far as I am aware – twice late in life – did he describe the road he had traveled, the difficulties with which he had wrestled, and the inspiration the work of others had provided.

Two major innovations occupied theorists in the postwar era: The first began in the 1960s and involved the study of black holes. The second started around 1980 and renewed efforts to understand better the origins of the Universe. Not that these were the only theoretical advances. There was plenty of other work keeping theorists busy. The discovery of X-ray, infrared, and radio galaxies, quasars, pulsars, cosmic masers, and γ-ray bursts, to name just the most striking, begged for quantitative models that could explain these new phenomena. But most of the theoretical models that satisfactorily matched observations involved known conceptual approaches, albeit applied in new settings. In the vocabulary Thomas Kuhn established in the early 1960s, in ‘The Structure of Scientific Revolutions,’ they constituted problem solving. They did not call for new paradigms, entirely new ways of conceiving Nature.

At some level, the theoretical thrusts on black holes and investigations of the earliest moments in cosmic evolution overlapped. Both sought to improve our understanding of space and time through clearer insight into general relativity and – to the extent one might guess at it – quantum gravity. Knowing that highly compact masses might collapse, one had to ask why the early Universe didn't immediately collapse under its gravitational self-attraction to form a giant black hole rather than expand, as now observed.

Whether we ultimately succeed or fail in determining the origin and early evolution of the Universe is likely to be determined by two competing factors. The first is the extent to which the high-temperature phases prevailing in the early Cosmos may have eradicated all memory of preceding epochs at the dawn of time; the second is the monetary cost of searching for shards of information that may have escaped erasure so we might recover and analyze the fragmentary surviving evidence.

The Larger Network in Which Astronomy Is Embedded

A part of the difficulty of accounting for the conduct and progress of astrophysics, even considering all the influences I have already cited, is that the field cannot be fully isolated from the far larger setting in which it is embedded.

Modern astronomy is expensive and competitive. It is expensive because powerful instrumentation is costly, whether it be telescopes or supercomputers. It also has to remain competitive because the cost of astronomical projects has to be justified at a national level where astronomy competes with other sciences for limited resources.

Seen from the perspective of an individual astronomer, these two factors lead to the need to continually justify the funding and potentially also the observing time required to initiate a project. First and foremost, this involves persuading the larger community of working astronomers to agree to the funding. Persuasion and its associated political activity within the field is part and parcel of the work of almost every established astrophysicist.

Among the immediate beneficiaries of ‘Science – the Endless Frontier,’ the new postwar policy of closely meshing basic research with applied scientific efforts of national interest, were astrophysicists studying the origins of the chemical elements. Cosmology, in particular, underwent a profound resurgence; a field that had previously been restricted to exploring arcane mathematical models suddenly found itself anchored to real-world nuclear physics. Increasingly detailed studies of nuclear interactions also began to shed light on nuclear processes in evolved stars. A sense of renewed excitement swept through the field!

Chandrasekhar's Early Venture into Cosmology

In 1942, Chandrasekhar and his University of Chicago doctoral student, Louis R. Henrich, had postulated that the Universe at some epoch could have been extremely dense and at a temperature of a few billion degrees Kelvin. They calculated the expected thermodynamic equilibrium distribution of nuclear species at different temperatures, and sought a range in which the chemical abundances of heavy elements came close to those observed in Nature. The conditions for this to happen, they estimated, were a temperature of order 8 × 109 K and a density ρ = 107 g/cm3. Although their work constituted a valiant attempt, they concluded that their paper, “should be regarded as of a purely exploratory nature and that such ‘agreements’ as may have been obtained should not be overstressed.”

In Chapters 7 and 9 we saw how strongly the conclusions we reach about the structure of the Universe can be shaped by intrusions that have no formal role in the philosophy of science. Technological innovations, governmental priorities, economic factors, as well as scientific advisory and oversight boards all play a role in the shaping of astronomy. Astrophysics is continually under pressure from forces pulling in different directions, destabilizing ongoing efforts, and keeping the field off balance.

How astrophysics nevertheless manages to advance is difficult to grasp in the abstract. The present chapter attempts to sketch realistically how modern astronomy is conducted and the vital role a well-coordinated communal approach can play as long as it remains sufficiently flexible to recover from inevitable setbacks. As we shall see, steadfast leadership is the essential ingredient of ultimate success.

A Logical Way to Proceed

By the mid-1970s, it was easy to see how the influx of new detection techniques introduced by the military in World War II and the Cold War had led to undreamed-of discoveries. Earlier theories had given us no inkling to expect the existence of quasars, pulsars, or the detection of cosmic masers, all initially revealed by radio astronomy. Similarly significant discoveries were being made in the gamma-ray, X-ray, and infrared regimes.

Although most astronomers assign particular importance to the problems on which they are currently working, our understanding of the Universe will not advance satisfactorily unless the community can agree on a coherent research plan with a well-defined thrust. The plan cannot be too rigid; otherwise unanticipated initiatives leading to novel insight will be thwarted. Nor should changes in direction be opposed as we learn more and realize a deliberate course correction is needed.

These criteria seem mutually contradictory, so that care is required in respecting them. In Chapter 2 we saw how different scientists approach a given problem by disparate means, guided primarily by tools in whose use they have developed skill and confidence. Faced with a novel problem, they thus reach for distinct tools in their search for increased insight. But before the community can persuade itself that the use of a particular set of tools has indeed led to a significant advance, trusted experts may first need to explain to each other how the respective tools work and the findings to which they point. The present chapter shows how this mutual persuasion may most effectively be pursued.

How to Revive a Spacecraft Millions of Miles Away in Space

I introduce the problem of reviving a spacecraft because it stresses the overarching significance of language in shaping the way scientists and engineers manage to repair a complex system when it breaks down. The astrophysics community may benefit from adopting a similarly formal approach for weeding out errors thwarting the field's progress, formulating long-term communal plans for astrophysical research and archiving astronomical data so it may benefit future generations.

The logic of well-founded but far-reaching theories may at times be extended to problems so far removed from normal experience that the derived results violate intuition. Doubts then arise about the validity of applying the theory to such extreme conditions, and the theory's original inventors may become its most severe critics.

A Problem Biding Its Time

When is the right time to ask a question? Some questions can be answered almost as soon as they are posed. Others cannot be answered either because they are awkwardly put or because the means for answering them are not at hand. One such question first surfaced late in the eighteenth century.

As early as 1783, the Reverend John Michell, an English natural philosopher and geologist, conceived of a star so compact and massive that its gravitational attraction would prevent light from escaping. He considered the motion of light in Newtonian terms, which suggested that the gravitational attraction of any star would slow down its emitted radiation. Although for most stars this deceleration might be minor, radiation escaping massive stars might have its speed appreciably diminished. For extremely massive compact stars, he thought the emitted light could actually come to a standstill before dropping back to the star's surface.

Michell was concerned not only with whether light could actually be prevented from escaping a star, but also with how we might recognize this. Perhaps his most important realization was that the existence of such a star might be inferred from the gravitational force it would exert on an orbiting companion.

Scientific work is generally based on a premise, a hunch that certain assumptions can safely lead to useful advances. As new observations, experimental evidence, or calculations accumulate, the premise may then lead to a coherent view that includes predictions concerning future observations. When those observations only partially vindicate the evolving world view, corrections or modifications may be necessary, and so an increasingly complex world view emerges, whose intricate details need to be understood in terms of an overarching theory. Where the theory appears enigmatic, new physical processes may be hypothesized to make the theory more understandable. A search is set in motion to identify those processes, and so the work continues.

Two Legacies from the Nineteenth Century

The Chemical Elements in the Sun

In 1859, the Heidelberg physicist Gustav Robert Kirchhoff and his colleague, the chemist Robert Wilhelm Bunsen, discovered that a minute trace of strontium chloride injected into a flame gave rise to a spectrum that clearly identified the presence of the element strontium. Sodium was also readily identified by a spectrum exhibiting two bright, closely spaced features, whose wavelengths corresponded precisely to two dark features in the spectrum of the Sun.

Later that year, Kirchhoff passed a beam of sunlight through a flame containing vaporized sodium. To his surprise, instead of filling the dark solar features with compensating light emitted by the flame, the solar features actually darkened. The faint light emanating from the Sun appeared to be absorbed by the flame.

In the fall of 1895, the 16-year-old Albert Einstein traveled to Zürich to seek admission to the engineering division of the Eidgenössische Polytechnikum. He had prepared for the entrance examinations on his own, in Italy, where his family had recently moved. Most students took these exams at age 18, and the Polytechnikum's Rector, instead of admitting the youngster straight away, recommended him to the Swiss canton school in Aarau, from which Einstein graduated the following year.

Graduation in Aarau led to acceptance at the Polytechnikum without further examinations. Albert began his studies there in October 1896 and graduated in late July 1900. Only, instead of pursuing engineering, he registered for studies in mathematics and physics.

Looking back at those five student years between the fall of 1895 and the summer of 1900, one can hardly imagine a more exciting era in science.

Late on the afternoon of Friday, November 8, 1895, Wilhelm Conrad Röntgen, professor of physics at Würzburg, noticed an odd shimmer. He had for some weeks been studying the emanations of different electrical discharge tubes, and had previously noted that a small piece of cardboard painted with barium platinocyanide fluoresced when brought up to one of these tubes. To understand better the cause of the fluorescence, he had now shrouded the tube with black cardboard so no light could escape. In the darkened room, he checked the opacity of the shroud.

The Universe We See Today

Twentieth century astrophysics has taught us that the origin and evolution of everyday matter, of the stars we see at night and the Universe we inhabit, share a coherent history dating back billions of years. Our knowledge remains fragmentary, but progress has been rapid and provides hope that our search will someday be complete, perhaps not in the sense that we will be all-knowing, but that we may have uncovered all that science can reveal.

One helpful feature in our search is that, as far back in time as we are able to probe, we find the known laws of physics holding firm. The speed of light, the properties of atoms, their constituent electrons and nuclei, and the mutual interactions of all these particles and radiation, appear unchanged ever since the first few seconds in the life of the Cosmos.

Also helpful has been that the Universe is expanding and that light, despite its high velocity, requires eons to cross cosmic distances. Using our most powerful telescopes we are able to directly view remote stars and galaxies, which emitted their light billions of years ago. We can compare how they appeared then and how stars and galaxies nearer to us in space appear now. And, as the Universe expands, light waves crisscrossing space expand with it.