The Nobel Foundations judging committees have made their annual selections. Four leading scientists will get their laurels--and a bonus of 7,900,000 Swedish crowns-- at the prize awarding ceremony on December 11, 1999. Three of the winners have published accounts of their work in the pages of Scientific American.

Here are sketches of the 1999 Nobelists and their work in physics,chemistry and medicine.


Unifying Theory


Since the 19th century, mathematicians have been laying a groundwork of theories that attempt to unify the symmetry of all physical forces. The saga began with James Clerk Maxwell's demonstration in the 1860s that electricity and magnetism are two aspects of a single electromagnetic force. And a string of Nobels have marked new developments in the story over the years.

The most recent benchmark is the award of the 1999 Nobel Prize for Physics to Gerardus 't Hooft of the University of Utrecht and Martinus Veltman, formerly of the University of Michigan and now retired, for having placed particle physics theory on a firmer mathematical foundation. According to the Nobel citation, the physicists' particular contribution was showing how particle theory may be used for precise calculations of physical quantities. Experiments at accelerator laboratories in Europe and the United States have recently confirmed many of their calculated results.

The work of 't Hooft and Veltman is the latest mathematical triumph in the search for a unified theory. Earlier in this century, quantum mechanics was combined with special relativity, resulting in quantum field theory. But while this theory successfully explained many phenomena, such as how particles could be created or annihilated or how unstable particles decay, it seemed to predict, nonsensically, that the likelihood for certain interactions could be infinitely large.


The problem was solved in the 1940s by Richard Feynman, Julian Schwinger and Sin-Itiro Tomonaga when they redefined the mass and charge of the electron. Their new theory, quantum electrodynamics (QED), won them the Nobel in 1965. The theory proved to be extremely precise and became the prototype for the electroweak theory, which draws the electromagnetic and weak nuclear forces into a single model, and won the 1979 Nobel for Sheldon L. Glashow, Abdus Salam and Steven Weinberg. This theory predicted the new particles W and Z, which were later detected in 1983 at the European CERN accelerator laboratory in Geneva--earning the 1984 Nobel Prize for Carlo Rubbia and Simon van der Meer.

Unfortunately, the electroweak model suffered from the same problems in prediction as the quantum field theory. This time, 't Hooft and Veltman overcame the difficulty through a "renormalization" comparable to Feynman's. Veltman was determined to crack the problem. And, unlike Feynman, he could use computers. In spring 1969 Veltman was joined in his efforts by a 22-year-old pupil, 't Hooft. In 1971, 't Hooft published two articles that represented an important breakthrough. With the help of a computer program developed by Veltman, the results were verified, and together the two investigators worked out a calculation method.

An essential ingredient in their scheme was the existence of another particle, called the Higgs boson. Its role is to confer mass upon many of the known particles. It is interactions between the Higgs boson and the various force-carrying particles that make the W and Z bosons (carriers of the weak force) so massive (with masses of 80 and 91 GeV, respectively), but the photon (carrier of the electromagnetic force) massless.

With Veltmans and 't Hooft's theoretical machinery in hand, physicists could more reliably estimate the masses of the W and Z, as well as produce at least a crude guide to the likely mass of the top quark. The W, Z and top quark were subsequently created and detected in high-energy collision experiments. The elusive Higgs boson is now itself an important quarry. Whether it turns up as predicted waits to be seen. The only accelerator powerful enough to detect it will be CERN's Large Hadron Collider, which is being constructed in Geneva and is due for completion in 2005.


THE HIGGS BOSON. Martinus J.G. Veltman in Scientific American; November 1986.

GAUGE THEORIES OF THE FORCES BETWEEN ELEMENTARY PARTICLES. Gerardus 't Hooft in Scientific American; June 1980.


Nobel announcement

Background (PDF format)


Reacting in SloMo


You need a very fast camera to take slow-motion pictures of atoms in the process of reacting. Bonds break and new ones form in the superfast world of femtoseconds--1 -15 second--which are to a second as a second is to 32 million years. The 1999 Nobel Prize in Chemistry will be awarded to Ahmed H. Zewail of the California Institute of Technology for developing the sophisticated technology to capture this world--and in the process founding a new branch of physical chemistry, known as femtochemistry.

To accomplish this feat, Zewail devised a way of using ultrafast laser pulses to provide snapshots far faster than any camera. In femtosecond spectroscopy, reagents are mixed as beams of molecules in a vacuum chamber. A laser then injects two brief pulses: first a powerful pump pulse that strikes the molecule and excites it to a higher energy state, and then a weaker probe pulse at a wavelength chosen to detect the original molecule or an altered form. The pump pulse is the starting signal for the reaction, whereas the probe pulse examines what is happening. Studying what type of light the molecules absorb yields information on the atoms' positions within the molecules at every step of a chemical reaction.

In the late 1980s, Zewail and his colleagues first studied a 200-femtosecond disintegration of iodocyanide (ICN-->I+CN), observing the precise moment at which a chemical bond between iodine and carbon was about to break. As the time resolution was successively improved, the investigators were able to observe intermediate substances created along the way from the original one to the final product. Each improvement of the time resolution led to new links in the reaction chain, in the form of increasingly short-lived intermediates, and a better understanding of how the reaction mechanism worked.

Zewail's pioneering work triggered an explosion of research around the wold. Present studies examine not just molecular beams but also processes on surfaces (leading to better understanding and improvement of catalysts), in liquids and solvents (where it is revealing the mechanisms of dissolving and reactions between substances in solution) and in polymers. In studies of biological systems, the new technique has provided molecular-level details of how chlorophyll molecules convert sunlight into useable energy for plants during photosynthesis.

In the announcement of the award, the Royal Swedish Academy of Sciences notes that "the contribution for which Zewail is to receive the Nobel Prize means that we have reached the end of the road: no chemical reactions take place faster than this."


THE BIRTH OF MOLECULES. Ahmed H. Zewail in Scientific American; December 1990.


Nobel announcement

Background on femtochemistry (PDF format)

New Physics With Fast Lasers from the Centennial Meeting of the American Physical Society


Cellular 'Zip Codes'


The ribosomes in living cells are factories that produce a billion or so different protein molecules of thousands of different types. When replacements are needed, these newly made proteins are transported across cell membranes and delivered to their appropriate locations.

How this complex system worked was a mystery until the winner of the 1999 Nobel Prize in Physiology or Medicine, cell biologist Gnter Blobel of the Rockefeller University, revealed the existence of a cellular zip code system. Or as the Nobel Assembly at the Karolinska Institute stated in its citation, the discovery that "proteins have intrinsic signals that govern their transport and localization in the cell."

At the beginning of the 1970s, Blobel, who is a Howard Hughes Medical Institute investigator and heads Rockefeller's Laboratory of Cell Biology, discovered that newly synthesized proteins have an intrinsic signal that directs them to and across the membrane of the endoplasmic reticulum, one of the cell's organelles. By 1975, he had identified the various steps in the tranport processes. The signal consists of a peptide, a sequence of amino acids in a particular order that form an integral part of the protein. His work also suggested that the protein traverses the membrane of the endoplasmic reticulum through a channel.

During the next two decades, workers in Blobel's laboratory characterized the molecular mechanisms underlying these processes. In 1980, Blobel formulated general principles for the sorting and targeting of proteins to particular cell compartments. Each protein carries in its structure the information needed to specify its proper location in the cell. Specific amino acid sequences (topogenic signals) determine whether a protein will pass through a membrane into a particular organelle, become integrated into the membrane or be exported out of the cell.

These principles turned out to be universal, operating similarly in yeast, plant and animal cells. Because the accurate distribution of proteins to their proper places in the cell is necessary for a cell to function, these findings have an immediate bearing on many diseases, including cystic fibrosis, Alzheimer's disease and AIDS. Blobel's research has also contributed to the development of a more effective use of cells as "protein factories" for the production of important drugs.


Nobel announcement

Press release from the Rockefeller University

Overview of Blobel's work from the Howard Hughes Medical Institute