23.6 Essay MH 20/6/05 11:55 AM Page 1033

23.6 essay MH 20/6/05 11:55 AM Page 1033 NATURE|Vol 435|23 June 2005 ESSAY Dynamic Universe The first person to carry out a modern survey of the night sky, Fritz Zwicky’s astronomical observations led to a new picture of a turbulent Universe that is punctuated by violent events. Freeman Dyson the northern sky. Two major discoveries flict with his colleagues at Caltech. They that emerged from his survey were super- considered him crazy and he considered The Swiss physicist Fritz Zwicky novae and dark matter. Zwicky observed them stupid. He never became an accepted (1898–1973) was responsible, more than 20 supernovae, a large enough sample to member of the astronomical community, anyone else, for a profound change in our allow him to classify them into several but followed his own path. During the Sec- view of the astronomical Universe. Before types and infer their different modes of ond World War he was director of research Zwicky, the ancient aristotelian view of origin. His discovery of dark matter came at the Aerojet Corporation, which devel- the celestial sphere as a region of eternal from studying the motions of individual oped rockets for the military. At the same harmony and tranquillity was still largely galaxies in rich clusters of galaxies, and time he organized the Committee for Aid intact, and the job of an astronomer was to from calculating that the visible mass in to War-stricken Scientific Libraries. This make accurate maps of an unchanging the clusters was insufficient by a large collected massive quantities of scientific landscape. After Zwicky, the modern view factor to cause the observed motions. books and journals and distributed them to of the Universe emerged, as a libraries that had been dis- dynamic scene dominated by rupted or destroyed during the violent events. The job of an war. He founded the committee astronomer today is to record and in 1941 and ran it with his habit- interpret the processes of change. ual enthusiasm and efficiency. Zwicky’s great work was done For this work he received the in the 1930s when he was an asso- Medal of Freedom from Presi- ciate professor of physics at Cal- dent Harry Truman in 1949. tech, the California Institute of Besides his revolutionary Technology. He had been trained work as an observer and at the Swiss Federal Institute of organizer, Zwicky made revolu- OF TECHNOLOGY INSTITUTE CALIFORNIA Technology as an X-ray crystallo- tionary contributions to theo- grapher and had no official cre- retical astronomy. He published dentials as an astronomer. But he papers about neutron stars, saw an opportunity arising from supernovae, black holes and two unconnected events that hap- gravitational lenses, long before pened almost simultaneously. these subjects became fashion- First, in 1928, the Rockefeller able. His thinking was based on Foundation awarded a large sum a personal philosophy which of money to Caltech for the con- he called the ‘morphological struction of a major astronomical Using the Schmidt telescope, Fritz Zwicky discovered dark matter. approach’. The idea is that you observatory. Second, in 1930, first make a complete list of all the one-armed optical genius Bernhard In his summary of the survey, Zwicky possible solutions to a problem, and then Schmidt in Hamburg invented a telescope proudly asserted: “for the construction of choose the least unlikely solution for fur- with a revolutionary new design, which the 18-inch Schmidt telescope, its housing, ther investigation. By following this allowed high-resolution photography over a full-size objective prism, a small remuner- approach, you have a good chance of find- a wide field of view. Zwicky’s astronomer ation for my assistant, and the operational ing new solutions that other people over- friend Walter Baade happened to be a per- costs for the whole project during ten years, looked. sonal friend of Bernhard Schmidt and saw only about $50,000 dollars were expended. Zwicky applied the morphological the original Schmidt telescope in action This probably represents the highest effi- approach both to theoretical and practical in Hamburg. Zwicky heard what the tele- ciency, as measured in results achieved per problems; it was this approach that led him scope could do and grabbed the opportu- dollar invested, of any telescope presently in to become the first modern astronomer, nity. He persuaded Caltech to buy an use, and perhaps of any ever built, with the with a new and dynamic view of the Uni- 18-inch Schmidt camera and install it at exception of Galilei’s little refractor.” verse. In his book Discovery, Invention, the new observatory on Palomar Moun- Zwicky’s sky survey set the pattern for Research, Through the Morphological tain. He made sure that he would have full- many later surveys done with bigger Approach, he describes successful applica- time use of the camera — at that time the instruments and greater investments of tion of the morphological approach to a only wide-field camera in the world at a manpower and money. The newest sky multitude of problems arising in pure site with good astronomical seeing. survey Pan-STARRS, due to begin in 2006, mathematics, automobile design and uni- Zwicky understood that to see rare, vio- will follow Zwicky’s example in emphasiz- versity administration, as well as in rocket lent and short-lived events in the Universe, ing rapid and repeated coverage of the sky. propulsion and astronomy. Unfortunately, he had to photograph large areas of sky It should discover a wealth of short-lived the approach does not seem to work so repeatedly. With his little Schmidt camera, phenomena at all distances, from near- well if your name is not Fritz Zwicky. ■ he had a unique opportunity to photo- Earth asteroids to optical afterglows of graph the entire northern sky over and gamma-ray bursts in remote galaxies. Freeman Dyson is at the Institute for over again. With a single assistant to help Zwicky’s radical ideas and pugnacious Advanced Study, Einstein Drive, Princeton, him, he continued for four years to survey personality brought him into frequent con- New Jersey 08540, USA. 1033 © 2005 Nature Publishing Group.

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