Fast particles inflated early universe

UNIVERSITY PARK, Pa., May 7 (UPI) -- Tachyons, as-yet-unobserved particles that can move faster than light, expanded the early universe from nothing to many light-years across in a fraction of a second after the Big Bang, physicists told United Press International.

The particles seem to move in defiance of Einstein's strict prohibitions against such amazing speeds. Those who believe the big-bang theory say the universe began with the explosion of a superdense primeval atom and has been expanding ever since.

Only something that moves at the phenomenal speed of a "rolling" tachyon, the physicists claim, could inflate the universe as quickly as cosmologist Alan Guth first predicted in his groundbreaking theory -- The Inflationary Universe.

"To explain the rolling tachyon in an expanding universe, one can consider an analogy of blowing up a balloon," Xin-zhou Li, professor and director of the United Center for Astrophysics in Shanghai, China, told UPI. "When you blow air, you expand the balloon. When the tachyon rolls, it expands the universe."

This finding may help to unify two notoriously conflicting theories of modern physics -- string theory and cosmology.

String theorists believe one-dimensional strings vibrate at sub-atomic scales like miniature harps in a symphony. The vibrations produce fundamental tones whose "notes" represent all the known forces. To cosmologists, however, string theory's cold, dainty fingers could not have orchestrated the titanic processes that caused the Big Bang and elbowed the corners of the universe into existence.

"In the inflationary scenario the universe starts from a fireball of very small size and then rapidly expands," theoretical physics professor Alexander Feinstein told UPI from his office at the University of the Basque Country in Bilbao, Spain.

"In the typical string theory scenario, the universe may have started in an infinitely cold past, from almost nothing, just small quantum perturbations."

Speedy tachyons "appear inevitably in string theories," Feinstein explained. To fill the universe like water or air in a balloon, individual tachyons "condensed" into a pressureless, super-fluid gas produced by the decay of unstable structures called "D-branes," as explained in new, unpublished research papers by string theorist Ashoke Sen of Pennsylvania State University and Gary Gibbons of Cambridge University in England.

D-branes contain three, four and higher dimensions and represent additional components of string theory.

To overcome the strong attraction of all the mass in the universe and push inflation forward "there must be a certain substance that has negative pressure, or equivalently, a repulsive interaction," Li said. "In the past, people assumed a field referred to as 'dilaton' or 'inflaton' played such a role."

Unlike the tachyon, "inflaton or dilaton is not derived from any known fundamental theory," Feinstein told UPI. "We do not know how to explain this field."

Li agreed. "It is always a spiritual embarrassment to answer such questions as why there is a dilaton field and where it is from."

The new equations that describe tachyon motion, however, as proposed by string theorist Sen, show these faster-than-light particles could have indeed driven inflation -- and quickly. The presence of tachyons in string theory makes them promising candidates for application to cosmology.

"Sen's theory might explain the origin of the field responsible for inflation very naturally," particle physicist Malcolm Fairbairn told UPI from Brussels University in Belgium. "His equations of motion for a tachyon field are analogous to those of a fluid that would fill the universe," Fairbairn said.

The tachyon "fluid" rolls from a state of high energy to a state of lower energy, Fairbairn's colleague Michel Tytgat said. "The rolling of the tachyon field is very much like the rolling of the inflation field in the original scenarios of Guth and others," Tytgat explained. "While the tachyon is rolling down the potential, the universe is inflating."

Inflation conveniently stops when the tachyon vanishes at the bottom of its energy potential, a prediction unique to Sen's equations and "a very curious thing indeed," Tytgat said.

Tachyons, if proven, could become some of cosmology's most mysterious materials. They could, in fact, embody Einstein's famous "cosmological constant," a term he added to balance his gravitational field equations and prevent the attraction of all the mass in the universe from ending everything in a so-called "Big Crunch."

"A cosmological constant anti-gravitates by exerting negative pressure against the mass in the universe," Fairbairn explained. "A constant or almost-constant slow roll of potential energy, like that of the tachyon field near the top of its potential, acts like (Einstein's) cosmological constant."

Li concurred. "The tachyon field's kinetic energy or energy of motion converts steadily to potential or rest energy," he said. "When there is no more kinetic energy, the tachyon field will behave as a cosmological constant."

(Reported by Mike Martin in Columbia, Mo.)