Articles from the Institute Letter

Additional articles from new and past issues of the Institute Letter will continue to be posted over time and as they become available.

By Robbert Dijkgraaf

Light connects us to the very beginning of the uni­verse. The first light was emitted roughly 380,000 years after the Big Bang, when matter was no longer closely tied together and light could escape. This radiation was detected for the first time fifty years ago this year.

Light is the great unifier. John Wheeler, the beloved Princeton physicist, used to draw the universe as a big capital U with a little eye on one leg, signifying that we, human beings, are the eyes of the universe looking back at itself. The universe after many, many billions of years formed human life on planet Earth, and we use light to observe and understand the universe. 

The growing understanding of the nature of light through the centuries is the perfect metaphor for science: it is an eye-opener. Almost 350 years ago, Isaac Newton, as a young man, put a prism in a beam of light and unraveled its various colors. This was the beginning of a long story. Around the year 1800, the astronomer William Herschel was the first to measure the temperature of light. He made the startling discovery that the rainbow does not stop at red, but actually continues, invisibly, as infrared light, which we cannot see but can feel as a sensation of warmth. 

What is light? Physics has a simple answer: an electromagnetic wave. Exactly 150 years ago, the Scottish physicist James Clerk Maxwell discovered the laws that describe these waves. I have a T-shirt with these equations and the text “And then there was light.” If only Maxwell had patented his equations! It would be enough to finance all research in the world.


by Nir Shaviv

Our galactic journey imprinted in the climate—when Earth’s temperature (red dots warm, blue dots cold) is plotted as a function of time (vertical axis) and as a function of time folded over a 32-­million-year period (horizontal axis), the 32-million-year oscillation of the solar system relative to the galactic plane is evident.

How might climate be influenced by cosmic rays?

In 1913, Victor Hess measured the background level of atmospheric ionization while ascending with a balloon. By doing so, he discovered that Earth is continuously bathed in ionizing radiation. These cosmic rays primarily consist of protons and heavier nuclei with energies between their rest mass and a trillion times larger. In 1934, Walter Baade and Fritz Zwicky suggested that cosmic rays originate from supernovae, the explosive death of massive stars. However, only in 2013 was it directly proved, using gamma-ray observations with the FERMI satellite, that cosmic rays are indeed accelerated by supernova remnants. Thus, the amount of ionization in the lower atmosphere is almost entirely governed by supernova explosions that took place in the solar system’s galactic neighborhood in the past twenty million years or so. 

Besides being messengers from ancient explosions, cosmic rays are extremely interesting because they link together so many different phenomena. They tell us about the galactic geography, about the history of meteorites or of solar activity, they can potentially tell us about the existence of dark matter, and apparently they can even affect climate here on Earth. They can explain many of the past climate variations, which in turn can be used to study the Milky Way.

The idea that cosmic rays may affect climate through modulation of the cosmic ray ionization in the atmosphere goes back to Edward Ney in 1959. It was known that solar wind modulates the flux of cosmic rays reaching Earth—a high solar activity deflects more of the cosmic rays reaching the inner solar system, and with it reduces the atmospheric ionization. Ney raised the idea that this ionization could have some climatic effect. This would immediately link solar activity with climate variations, and explain things like the little ice age during the Maunder minimum, when sunspots were a rare occurrence on the solar surface. 


By Suzannah Clark

How a lone theorist’s pursuit of symmetry shaped music history

On the second Sunday after Trinity in 1724, the congregation at the Thomaskirche in Leipzig heard Johann Sebastian Bach’s new cantata that began with the words Ach Gott. Bach set the word Gott to the most dissonant triad known at the time: the augmented triad. Bach’s own son, Carl Philipp Emanuel Bach, wrote in the second volume of his treatise of 1762 that the offending augmented fifth of this harmony requires careful preparation. His father did not prepare it at all. Acclimatized as we are today to all kinds of dissonances, this harmony might pass the modern listener by. But it would have disconcerted the ears of the eighteenth-century congregation, giving them a God-fearing shudder, while setting the scene for the biblical message of the day. Bach, after all, was setting the tune and words, Ach Gott, vom Himmel sieh darein, that Martin Luther had penned exactly two hundred years earlier, in 1524. Based on Psalm 12, Luther tells of a perilous world filled with those who shun God.

The augmented triad has long been a headache for music theorists, only partially on the basis of its harsh sound. Mostly they are perturbed by its construction and their inability to pinpoint a convincing origin for it. It would be no exaggeration to say that, just two years before Bach composed his cantata, the harmonic theory of Jean-Philippe Rameau, a towering figure in the history of music theory, brought about a paradigm shift in how chords were categorized and understood to have been constructed. Although much of Rameau’s theory still holds sway today, a now defunct aspect of his Traité de l’harmonie led him to deem the augmented triad “worthless.” It belonged to the rubbish heap of potential chords because it did not contain the right kind of fifth, and therefore it must be an incomplete chord. According to Rameau’s newly minted theory, all valid, complete chords must contain a perfect fifth; the augmented triad gets its name from the fact that its fifth is “augmented” (it is a semitone larger than the perfect fifth).


By Gerda Panofsky

Situating Michelangelo within a long philosophical and religious tradition, extraneous to nation or race

In the Spring 2013 Institute Letter, Uta Nitschke-Joseph wrote “A Fortuitous Discovery: An Early Manuscript by Erwin Panofsky Reappears in Munich,” in which she reconstructed the convoluted fate of the lost, and in 2012 re-found, Habilitation thesis of Erwin Panofsky (1892–1968), one of the founding members of the School of Historical Studies and an eminent art historian of the twentieth century. After two years of transcribing, editing, and proofreading the manuscript, I am happy to report that the volume has been published by De Gruyter in October 2014. The release coincides with the centennial of Panofsky’s doctoral dissertation at Albert-Ludwigs-Universität Freiburg in 1914, printed by a predecessor of the same publishing house, and the eightieth anniversary of his forced emigration from Germany in 1934, after which point in time there had been no trace of the some 340 pages anymore (presumably left behind in the off-limits university office). Moreover, 2014 happened to be the 450th anniversary of Michelangelo’s death. An English translation of the book is being prepared by Princeton University Press.

The unfinished text of 1920, modified and enlarged over the following years, is a stylistic analysis of Michelangelo’s (1475–1564) paintings and sculptures, first in comparison with those of his peer Raphael, who, however, was not a sculptor and whom Michelangelo survived by more than four decades, thereby reaching into the periods of the so-called Mannerism and the Early Baroque, which Raphael did not live to see. According to Panofsky, Michelangelo found himself in an artistic conflict between cubic confinement and the dynamic movements of his figures. As his stylistic principles were idiosyncratic and outside the contemporary trends, his œuvre has to be defined against the art of Egypt, antiquity, the Middle Ages, and the Renaissance, as well as the later Baroque. Universal or macro history characterizes also other publications by Panofsky from the 1920s. It is important to note that he never doubted the continuity of Western civilization. While Oswald Spengler, in Der Untergang des Abendlandes (Decline of the West) of 1918, at the end of World War I, proclaimed the downfall of the Occident, Panofsky after his demobilization from the military service in January 1919 devoted himself to the epoch of the Renaissance (the “rebirth” of antiquity), from which lastly Michelangelo could not be extracted. 


by Oscar "Wally" Greenberg

Analogous to the way primary colors red, green, and blue light blend to create a perception of white light to the human eye, Greenberg’s concept of color in quarks provides a means by which a ­combination of red, green, and blue “color charges” yield a color-neutral proton or neutron. Quarks and color were experimentally verified in 1973 and led to the standard model of particle physics that explains what the world is and what holds it together. (Image courtesy of Carole Kliger, Department of Physics, University of Maryland)

Visits with Einstein and the Discovery of Color

The Institute played an important role in my life on two occasions—as a graduate student at Princeton University in the 1950s, and as a visiting Member in 1964. 

1952–54: Five encounters with Einstein 

As a graduate student in Princeton from 1952 to 1956, I went to the Institute to attend seminars. I visited Einstein in his office and in his home, and introduced Einstein at the last seminar he gave. 

I saw Einstein three times to learn about the theory with a non-symmetric metric he was considering in order to unify gravity and electromagnetism. Meeting with Einstein was exhilarating and I felt awed in his presence; however, the meetings were not helpful for my understanding of his unified theory. If something was not clear, I was too much in awe of Einstein to press him for further explanation. As an example of my diffidence, one visit to Einstein was just before lunch. As it was winter, Einstein started to put on his heavy grey cloth coat before going out to walk home. I had an impulse to help him on with his coat, but did not because I felt this would be too intimate. I found it more helpful to meet with Bruria Kaufmann, Einstein’s scientific assistant; I felt at ease with her and was able to press her when I did not understand her explanations. 

Years later, I heard that Robert Oppenheimer had told postdocs at the Institute not to bother Einstein. I don’t think that was doing Einstein a favor, because Oppenheimer’s admonition isolated Einstein even more than he was already because of his refusal to accept quantum mechanics. 

My most memorable meeting with Einstein was in 1953. John Wheeler took his general relativity class to ask questions of Einstein and to have tea with him in his home on Mercer Street. We walked across Princeton as if we were going to a museum. We asked Einstein questions ranging from Mach’s principle and the expanding universe to his attitude toward quantum theory. He appeared very humble. He took our questions seriously and answered our questions fully, including a question about the future of his house. He answered straightforwardly: “This house will never become a place of pilgrimage where people come to see the bones of the saint.” I felt that Einstein had not accomplished all he had hoped to do and was ready to pass the torch to us. When Wheeler asked Einstein what advice he would give to these young men who aspire to become physicists, Einstein simply shrugged his shoulders and said, “Who am I to say.” The poem “Mercer Street” recalls this visit to Einstein in his home.