Printer-friendly versionArticles by IAS Faculty
The Rise and Fall of a Jewish Kingdom in Arabia
By Glen W. Bowersock
 |
The negus Kaleb celebrated his campaign in Arabia with an inscription set up in Axum. The text is in classical Ethiopic but written in South Arabian script (right to left). Note the cross at the left end of the first line. |
In these turbulent times in the Middle East, I have found myself working on the rise and fall of a late antique Jewish kingdom along the Red Sea in the Arabian peninsula. Friends and colleagues alike have reacted with amazement and disbelief when I have told them about the history I have been looking at. In the southwestern part of Arabia, known in antiquity as Himyar and corresponding today approximately with Yemen, the local population converted to Judaism at some point in the late fourth century, and by about 425 a Jewish kingdom had already taken shape. For just over a century after that, its kings ruled, with one brief interruption, over a religious state that was explicitly dedicated to the observance of Judaism and the persecution of its Christian population. The record survived over many centuries in Arabic historical writings, as well as in Greek and Syriac accounts of martyred Christians, but incredulous scholars had long been inclined to see little more than a local monotheism overlaid with language and features borrowed from Jews who had settled in the area. It is only within recent decades that enough inscribed stones have turned up to prove definitively the veracity of these surprising accounts. We can now say that an entire nation of ethnic Arabs in southwestern Arabia had converted to Judaism and imposed it as the state religion.
This bizarre but militant kingdom in Himyar was eventually overthrown by an invasion of forces from Christian Ethiopia, across the Red Sea. They set sail from East Africa, where they were joined by reinforcements from the Christian emperor in Constantinople. In the territory of Himyar, they engaged and destroyed the armies of the Jewish king and finally brought an end to what was arguably the most improbable, yet portentous, upheaval in the history of pre-Islamic Arabia. Few scholars, apart from specialists in ancient South Arabia or early Christian Ethiopia, have been aware of these events. A vigorous team led by Christian Julien Robin in Paris has pioneered research on the Jewish kingdom in Himyar, and one of the Institute’s former Members, Andrei Korotayev, a Russian scholar who has worked in Yemen and was at the Institute in 2003–04, has also contributed to recovering this lost chapter of late antique Middle Eastern history.
Black Holes and the Information Paradox in String Theory
By Juan Maldacena
 |
Albert Einstein, pictured at left with J. Robert Oppenheimer at the Institute, tried to disprove the notion of black holes that his theory of general relativity and gravity seemed to predict. Oppenheimer used Einstein's theory to show how black holes could form. |
The ancients thought that space and time were preexisting entities on which motion happens. Of course, this is also our naive intuition. According to Einstein’s theory of general relativity, we know that this is not true. Space and time are dynamical objects whose shape is modified by the bodies that move in it. The ordinary force of gravity is due to this deformation of spacetime. Spacetime is a physical entity that affects the motion of particles and, in turn, is affected by the motion of the same particles. For example, the Earth deforms spacetime in such a way that clocks at different altitudes run at different rates. For the Earth, this is a very small (but measurable) effect. For a very massive and very compact object the deformation (or warping) of spacetime can have a big effect. For example, on the surface of a neutron star a clock runs slower, at 70 percent of the speed of a clock far away.
In fact, you can have an object that is so massive that time comes to a complete standstill. These are black holes. General relativity predicts that an object that is very massive and sufficiently compact will collapse into a black hole. A black hole is such a surprising prediction of general relativity that it took many years to be properly recognized as a prediction. Einstein himself thought it was not a true prediction, but a mathematical oversimplification. We now know that they are clear predictions of the theory. Furthermore, there are some objects in the sky that are probably black holes.
Black holes are big holes in spacetime. They have a surface that is called a “horizon.” It is a surface that marks a point of no return. A person who crosses it will never be able to come back out. However, he will not feel anything special when he crosses the horizon. Only a while later will he feel very uncomfortable when he is crushed into a “singularity,” a region with very high gravitational fields. The horizon is what makes black holes “black”; nothing can escape from the horizon, not even light. Fortunately, if you stay outside the horizon, nothing bad happens to you. The singularity remains hidden behind the horizon.
Is the Solar System Stable?
By Scott Tremaine
 |
Scott Tremaine explores the stability of our solar system, one of the oldest problems in theoretical physics, dating back to Isaac Newton. |
The stability of the solar system is one of the oldest problems in theoretical physics, dating back to Isaac Newton. After Newton discovered his famous laws of motion and gravity, he used these to determine the motion of a single planet around the Sun and showed that the planet followed an ellipse with the Sun at one focus. However, the actual solar system contains eight planets, six of which were known to Newton, and each planet exerts small, periodically varying, gravitational forces on all the others.
The puzzle posed by Newton is whether the net effect of these periodic forces on the planetary orbits averages to zero over long times, so that the planets continue to follow orbits similar to the ones they have today, or whether these small mutual interactions gradually degrade the regular arrangement of the orbits in the solar system, leading eventual ly to a collision between two planets, the ejection of a planet to interstellar space, or perhaps the incineration of a planet by the Sun. The interplanetary gravitational interactions are very small—the force on Earth from Jupiter, the largest planet, is only about ten parts per million of the force from the Sun—but the time available for their effects to accumulate is even longer: over four billion years since the solar system was formed, and almost eight billion years until the death of the Sun.
Knots and Quantum Theory
By Edward Witten
 |
Edward Witten explains how mathematicians compare knots that differ by how a missing piece is filled in (as indicated by the question mark above). |
In everyday life, a string—such as a shoelace—is usually used to secure something or hold it in place. When we tie a knot, the purpose is to help the string do its job. All too often, we run into a complicated and tangled mess of string, but ordinarily this happens by mistake.
The term “knot” as it is used by mathematicians is abstracted from this experience just a little bit. A knot in the mathematical sense is a possibly tangled loop, freely floating in ordinary space. Thus, mathematicians study the tangle itself. A typical knot in the mathematical sense is shown in Figure 1. Hopefully, this picture reminds us of something we know from everyday life. It can be quite hard to make sense of a tangled piece of string—to decide whether it can be untangled and if so how. It is equally hard to decide if two tangles are equivalent.
Such questions might not sound like mathematics, if one is accustomed to thinking that mathematics is about adding, subtracting, multiplying, and dividing. But actually, in the twentieth century, mathematicians developed a rather deep theory of knots, with surprising ways to answer questions like whether a given tangle can be untangled.
But why—apart from the fact that the topic is fun—am I writing about this as a physicist? Even though knots are things that can exist in ordinary three-dimensional space, as a physicist I am only interested in them because of something surprising that was discovered in the last three decades.
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.