Ultra-fast particles inflated Universe, physicists say
By Mike Martin and copyright 2002 United Press International

UNIVERSITY PARK, Pa. May 7 (UPI) -- Tachyons -- particles that move faster than the speed of light in defiance of Einstein's strict prohibitions against such amazing speeds -- may be responsible for the inflation that expanded the Universe from zero to trillions of light years in a fraction of a second after the Big Bang.

Only a particle that moves at the phenomenal speed of a rolling tachyon, physicists say, 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 Shanghai United Center for Astrophysics, told United Press International. "When you blow air, you expand the balloon. When the tachyon rolls, it expands the Universe."

This important finding may help unify two notoriously conflicting theories -- string theory and cosmology. String theorists postulate that ultra-subatomic, one-dimensional strings vibrate like miniature harps in a symphony of fundamental tones whose notes represent all the known forces. To cosmologists, however, string theory's cold, dainty fingers could never have orchestrated the Vulcanian processes wrought by the Big Bang that elbowed the corners of the Universe into existence.

"In the inflationary scenario the Universe starts from a 'fire ball' of very small size, and then rapidly expands," theoretical physics professor Alexander Feinstein told UPI from 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 said. To fill the Universe like water or air in a balloon, individual tachyons condensed into a pressure-less gas produced by the decay of unstable "D-branes," according to papers by Penn State University string theorist Ashoke Sen and Gary Gibbons of Cambridge University. D-branes are the three, four, and higher-dimensional membrane-like components of string theory.

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

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

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

The equations that describe tachyon motion -- recently proposed by string theorist Sen -- show these faster-than-light particles can drive Inflation -- and quickly. The presence of tachyons in string theory makes them a natural -- and metaphysically satisfying -- candidate 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 fluid rolls from a state of high energy to a state of lower energy, Fairbairn colleague Michel Tytgat said. "The rolling of the tachyon field is very much like the rolling of the inflaton field in the original inflationary 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.

The unique properties of tachyons make them good candidates for cosmology's mystery materials: dark matter and Einstein's famous "cosmological constant," a term he added to balance his famous gravitational field equations and prevent the combined attraction of all the mass in the Universe from ending Everything in a so-called "Big Crunch.".

"Any single candidate for dark matter must have the capacity of behaving differently at large and small scales -- no pressure at small scales and negative pressure at large scales," Thanu Padmanabhan, Dean of Core Academic Programs and Senior Professor at Pune University told UPI from Pune, India. "The rolling tachyon has both capacities."

"A cosmological constant 'anti-gravitates' by exerting negative pressure against the mass in the Universe," Malcolm 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 a cosmological constant."

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