Migration

By David H. Weinberg

An SDSS-III plugplate, which admits light from preselected galaxies, stars, and quasars, superposed on an SDSS sky image.

Why is the expansion of the universe speeding up, instead of being slowed by the gravitational attraction of galaxies and dark matter? What is the history of the Milky Way galaxy and of the chemical elements in its stars? Why are the planetary systems discovered around other stars so different from our own solar system? These questions are the themes of SDSS-III, a six-year program of four giant astronomical surveys, and the focal point of my research at the Institute during the last year.

In fact, the Sloan Digital Sky Survey (SDSS) has been a running theme through all four of my stays at the Institute, which now span nearly two decades. As a long-term postdoctoral Member in the early 1990s, I joined in the effort to design the survey strategy and software system for the SDSS, a project that was then still in the early stages of fundraising, collaboration building, and hardware development. When I returned as a sabbatical visitor in 2001–02, SDSS observations were—finally—well underway. My concentration during that year was developing theoretical modeling and statistical analysis techniques, which we later applied to SDSS maps of cosmic structure to infer the clustering of invisible dark matter from the observable clustering of galaxies. By the time I returned for a one-term visit in 2006, the project had entered a new phase known as SDSS-II, and I had become the spokesperson of a collaboration that encompassed more than three hundred scientists at twenty-five institutions around the globe. With SDSS-II scheduled to complete its observations in mid-2008, I joined a seven-person committee that spent countless hours on the telephone that fall, sorting through many ideas suggested by the collaboration and putting together the program that became SDSS-III.

Extrasolar Planets and the New Astronomy

By Aristotle Socrates

Figure 2: Orbits of the Earth, Venus, and Mercury superposed with that of HD 80606b (magenta). Not only is its orbit extreme in comparison with those of our inner-solar system, but its mass is extreme as well in that HD 80606b is a gas giant planet, like Jupiter.

The desire to discover distant, rare, and strange objects dominated twentieth-century astronomy, for which increasingly larger and more sensitive telescopes were constructed.

The act of carrying out this objective has brought enormous—and somewhat unbelievable—rewards: We now accept that we orbit a thermonuclear furnace, the Sun, whose physical properties are quite common, so common that there are nearly 100 billion Sun-like stars within our galaxy, the Milky Way. It was discovered that the Milky Way was not, in fact, the entire Universe; the observable Universe is of order many billions of light years across (that’s big), and there are of order 100 billion galaxies like our own floating around within it. In the center of these galaxies there happen to be super-massive black holes whose masses can be up to 10 billion times the mass of the Sun. When these enormous black holes are built up by in-falling gas, they are called “quasars,” and produce the equivalent of 100 trillion Suns worth of light within a volume comparable to our solar system. The greater the separation between any two galaxies or quasars, the greater the rate at which they move apart or, in other words, the Universe is expanding. Perhaps even more surprising, the Universe is primarily made up of stuff that we can neither see nor feel, i.e., dark energy and dark matter. The strategy of building bigger and more sensitive telescopes, meanwhile, has produced a growing number of “smaller” results that continue to employ regiments of astronomers: gamma-ray bursts, pulsars, X-ray emitting binary stars, clusters of galaxies, cosmic microwave background radiation, and the list goes on.

DNA, History, and Archaeology

By Nicola Di Cosmo

A lecture on archaeological perspectives on ethnicity in ancient China, delivered by Lothar von Falkenhausen, Professor at the University of California, Los Angeles, was part of the workshop “DNA, History, and Archaeology” organized by Nicola Di Cosmo in October 2010.

Historians today can hardly answer the question: when does history begin? Traditional boundaries between history, protohistory, and prehistory have been blurred if not completely erased by the rise of concepts such as “Big History” and “macrohistory.” If even the Big Bang is history, connected to human evolution and social development through a chain of geological, biological, and ecological events, then the realm of history, while remaining firmly anthropocentric, becomes all-embracing.

An expanding historical horizon that, from antiquity to recent times, attempts to include places far beyond the sights of literate civilizations and traditional caesuras between a history illuminated by written sources and a prehistory of stone, copper, and pots has forced history and prehistory to coexist in a rather inelegant embrace. Such a blurring of the boundaries between those human pasts that left us more or less vivid and abundant written records, and other pasts, which, on the contrary, are knowable only through the spadework and fieldwork of enterprising archaeologists, ethnographers, and anthropologists, has also changed (or is at least threatening to change) the nature of the work of professional historians.

Technological advances, scientific instrumentation, statistical analyses, and laboratory tests are today producing historical knowledge that aims to find new ways of answering questions that have long exercised specialists of the ancient world. Should historians, then, try to make these pieces of highly technical evidence relevant to their own work? Or should they ignore them? The dilemma is not entirely new. Archaeology, material culture, and historical linguistics have already forced historians to come out of the “comfort zone” of written sources. Archaeologists have by and large wrested themselves free from the fastnesses of the classical texts, and much of their work cannot be regarded as ancillary to the authority of the written word. Satellite photography, remote sensing, archaeo-GIS, C14 dating, dendrochronology (tree-ring dating), and chemical analysis have become standard tools of the archaeologist that coexist with the trowel and the shovel. But the palaeosciences and ancient DNA studies pose challenges of a different order, directly correlated to the greater distance that exists between scientific and historical research in terms of training and knowledge base.

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