The force that holds together the tiniest particles of matter has pulled in the Nobel Prize in Physics for the three US physicists who unravelled its workings.
David Gross, David Politzer and Frank Wilczek have each been awarded a third of the 2004 prize for explaining how quarks 鈥� sub-atomic particles which make up the protons and neutrons in the nuclei of atoms 鈥� stick together.
Protons and neutrons consist of three quarks each, and there are six different types of quarks, such as 鈥渦p鈥� and 鈥渄own鈥� quarks.
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The trio of scientists were awarded the $1.3 million prize for work explaining the so-called 鈥渟trong鈥� or 鈥渃olour鈥� force prevalent in the atomic nucleus.
The strong force is one of the fundamental forces of nature, and their breakthrough 鈥渂rought physics one step closer to fulfilling a grand dream鈥 theory for everything鈥� according to the Royal Swedish Academy of Sciences, which announced the winners on Tuesday morning.
Beautiful theory
The trio published two papers on the strong force in 1973 鈥� solving a long-standing puzzle about the way that quarks behave.
鈥淚t was a really beautiful theory because it explained everything in one stroke,鈥� says Alan Martin, a particle physicist at the University of Durham, UK.
鈥淨uarks were known to exist,鈥� recalls Martin, 鈥渨e knew, for example, that the proton was made of two up quarks and a down quark鈥�.
But the quarks were impossible to dislodge. 鈥淚f you hit a proton very hard you would have expected to knock out one of the quarks, but they were never knocked out. It was really quite a puzzle,鈥� says Martin.
What Gross, Politzer and Wilczek calculated was that the force between the quarks grows stronger as the distance between them increases. This means that particles fired into the proton can rattle off the quarks inside but, as the quarks move off, the force on them grows stronger, preventing them escaping the proton.
Totally counterintuitive
This is the opposite of what happens for the force between two electrically charged particles, which grows stronger as the particles become closer to each other. So this description of the strong force between quarks 鈥渨as totally counterintuitive,鈥� Martin notes.
Even its proponents 鈥� now Nobel Prize winners 鈥� are rumoured to have argued over how to reach the right answer. But experiments at particle accelerators such as CERN on the French-Swiss border and DESY in Hamburg, Germany, have since confirmed 鈥� to staggering precision 鈥� the theory鈥檚 predictions of how the strength of the strong force varies with distance.
鈥淚t is now deeply embedded in the way we think鈥� says Christine Davies, an expert in the theory of quark interactions. The 30-year old theory has also become an integral part of the standard model of particle physics.
Davies, at Glasgow University, UK, suggests the choice for the 2004 prize may have been triggered by a new puzzle in the field 鈥� that of pentaquarks.
Flurry of research
Pentaquarks were discovered in particle accelerators in 2003 but so far their five-quark composition has defied explanation. Indeed, some scientists are doubtful of the existence of pentaquarks. All other known particles contain only two or three quarks.
Wilczek is now investigating pentaquarks at the Massachusetts Institute of Technology in Cambridge, US. Gross is at the University of California Santa Barbara and Politzer at the California Institute of Technology in Pasadena.
Martin agrees that the flurry of research prompted by pentaquarks might have played a role in the committee鈥檚 choice. 鈥淭hey only award Nobel Prizes for certainties. Pentaquarks are totally speculative. But they might have focused scientists鈥� attention in this area.鈥�