Looking at the First Few Microseconds

A new look at the first few microseconds of the universe, in Scientific American.

In 1977, when theorist Steven Weinberg published his classic book The First Three Minutes about the physics of the early universe, he avoided any definitive conclusions about the first hundredth of a second. “We simply do not yet know enough about the physics of elementary particles to be able to calculate the properties of such a mélange with any confidence,” he lamented. “Thus our ignorance of microscopic physics stands as a veil, obscuring our view of the very beginning.”

But theoretical and experimental breakthroughs of that decade soon began to lift the veil. Not only were protons, neutrons and all other hadrons found to contain quarks; in addition, a theory of the strong force between quarks–known as quantum chromodynamics, or QCD–emerged in the mid-1970s. This theory postulated that a shadowy cabal of eight neutral particles called gluons flits among the quarks, carrying the unrelenting force that confines them within hadrons.

What is especially intriguing about QCD is that–contrary to what happens with such familiar forces as gravity and electromagnetism–the coupling strength grows weaker as quarks approach one another. Physicists have called this curious counterintuitive behavior asymptotic freedom. It means that when two quarks are substantially closer than a proton diameter (about 10-13 centimeter), they feel a reduced force, which physicists can calculate with great precision by means of standard techniques. Only when a quark begins to stray from its partner does the force become truly strong, yanking the particle back like a dog on a leash.