David Gross The Nobel Prize in Physics 2004

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Only a select group of people have any idea what the theory of Quantum Chromodynamics is. Keep reading to become one of the few. David Gross, director of the Kavli Institute for Theoretical Physics (KITP) was awarded the Nobel Prize in physics on Tuesday for his work in developing a theory called Quantum Chromodynamics (QCD). Gross had started work on the theory in the early 1970s to explain how tiny particles called quarks stick together in the nucleus of an atom. This work is an important step for physicists who are searching for the elusive, grand “theory of everything.”

In the past three decades, many experiments have been performed to verify Gross’s original hypothesis. After the world scrutinized and tested the theory, QCD has become an integral part of the standard model of physics - widely accepted to be the best understanding of how the universe works. Jacquelyn Savani, Gross’ wife and a media relations consultant for the KITP, said that the planned opening of a newly added wing to the KITP building, Kohn Hall, had taken a lot of her time before the prize was announced. “I have been so involved with the building dedication that we didn’t think about it [coming up],” Savani said. “I was pretty much just shocked.”

Because the Nobel Prize is awarded by the Royal Swedish Academy of Sciences, American laureates are almost always called during the night, due to the nine-hour time difference. Savani said that she and her husband received the call around 3 a.m. “So, we get this phone call, and it turned out it was the Swedish Academy,” Savani said. “They were holding a press conference [over the phone], and he took their questions in his pajamas.” The amount of attention a Nobel Prize attracts is overwhelming, Savani said. Even in the first hours after being awarded the prize, Gross was already getting more media attention than ever before. “When we put the phone down it just immediately started ringing,” Savani said. “For the first hour I stumbled around, then I sat and started to write a press release.”

Physics is the study of the interactions of energy and matter. Under that broad classification, there are many branches that deal with specific aspects of quantifying the universe. Gross works in an area called particle physics, which is concerned with very small bits of matter that comprise atoms.
Older physics theories stated that an atom contains a nucleus, which holds protons and neutrons, and is surrounded by orbiting electrons. Modern theories of the atom divide protons and neutrons into smaller particles called quarks and replace the orbiting electrons with an electron cloud. The area in which Gross has been awarded the Nobel Prize is for his work in quantum chromodynamics. As its name suggests, the field has something to do with color - but only in an arbitrary sense. Protons and electrons have charges: positive and negative, respectively. Chromodynamics states that quarks have a property called color, which is analogous to electrical charge. Quarks can be red, blue, green, anti-red (cyan), anti-blue (yellow) or anti-green (magenta).

The most important tenet of chromodynamics asserts that particles must contain quarks whose colors sum to white. For example, a neutron is made up of a red, a blue and a green quark. These colors add up to white, which means the resulting particle is stable. Other types of particles are only made of two quarks, red and cyan for example, but still add up to white. The upshot of this assertion is that quarks are impossible to isolate because they can never be white without mixing with another quark. So the question may arise, “why can’t the quarks in a neutron be pulled apart in order to isolate them?” The answer is also explained by chromodynamics. A phenomenon called the “strong force” holds dissimilarly colored quarks together, and the attraction gets stronger as the distance between the quarks gets larger. This is analogous to pulling on a spring: the more the spring is stretched, the more force it takes to pull. In essence, the quarks can never be separated because the force pulling them back together gets stronger as they are pulled apart. “You cannot pull quarks out of neutrons and protons,” Savani said. “You can never go to those subatomic particles.” Physicists call this sticky behavior a theory of confinement or asymptotic freedom. The theory may seem whimsical, but the theory’s conclusions are quite important to other theories in physics. Richard Hill, a research associate at the Stanford Linear Accelerator Center, is currently visiting the KITP and said that Gross’ work has been invaluable to all particle physicists.
“Everybody uses [the theory],” Hill said. “Well everybody here [at the KITP] at least. It is one of the basic theories of particle physics.”

The results of the experiments that tested chromodynamics are now widely accepted as the best available theory. “It took some time for the [chromodynamics] experiments to be interpreted,” Hill said. “But I don’t think there was ever a lot of doubt in those people’s minds.”

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