Dennis Oppenheim, Image Dissonance — Coffee Cup, 1988-89 



rial that created a strong repulsive gravitational force. 

 That special material is known as the false vacuum, 

 and according to Guth, it blew the universe up. 



A vacuum is empty space — space devoid of all 

 material particles. It is often regarded as synony- 

 mous with nothing. But according to modern the- 

 ories of elementary particles, a vacuum is a physi- 

 cal object; it can be charged with energy and can 

 come in different states. We live in the lowest- 

 energy vacuum, the so-called true vacuum (famil- 

 iar empty space). High-energy vacuums are called 

 false because, unlike the true vacuum, they are un- 

 stable. The most remarkable property of a false 

 vacuum is its repulsive gravity. According to Ein- 

 stein, if a vacuum has energy, it should also have 

 tension, which has a repulsive gravitational effect. 

 The repulsion due to vacuum tension turns out to 

 be three times stronger than the attractive gravity 

 of the vacuum energy (which is related to mass via 

 Einstein's formula E=mc 2 ). The net effect is a 

 strong repulsive force. 



Guth considered what would happen if, at some 

 early epoch, the entire universe were in a false-vac- 

 uum state. He found that the repulsive gravity of the 

 vacuum would cause the universe to expand expo- 

 nentially — or, in other words, by a constant factor 

 for each constant interval of time. Exponential 

 growth can be characterized by the doubling time, 

 or the time it takes for a given quantity to double in 

 size. (The doubling time for $100 invested at 6 per- 

 cent annual interest, for instance, is about twelve 

 years, so that at the end of twenty-four years the 

 $100 investment is worth about $400.) 



For the expansion of a universe permeated by a 

 false vacuum, the doubling time is unbelievably 



short. It depends on the energy density (measured 

 in units of energy per cubic centimeter) of the par- 

 ticular kind of false vacuum, but it never exceeds 

 one ten-billionth of a second. A straightforward 

 calculation shows that the universe would expand 

 by a factor of a googol (10'"") in less than one-thir- 

 tieth of a microsecond. 



Since a false vacuum is unstable, it eventually de- 

 cays, turning into the true vacuum. In so doing, its 

 prodigious energy ignites a hot fireball of elemen- 

 tary particles. That event signals the end of inflation 

 and the starting point of the usual cosmological 

 evolution. It plays the role of the big bang in Guth's 

 cosmology. Thus an enormous, hot, expanding 

 universe emerges from a tiny initial seed. 



The theory of inflation was little more than a 

 speculative hypothesis when Guth proposed 

 it, but it was soon enhanced and developed by 

 the work of many physicists, most notably An- 

 drei Linde of Stanford University. Moreover, in 

 the late 1990s, observations of distant supernovae 

 and of the cosmic microwave background radia- 

 tion — a faint afterglow of the big bang — gave the 

 theory an enormous boost of corroborating ob- 

 servational evidence. So today inflation is well 

 on its way to becoming one of the cornerstones 

 of modern cosmologv. 



In a way, inflation caused by a false vacuum is 

 similar to the reproduction of bacteria. In both 

 cases, two processes compete for dominance: bac- 

 teria reproduce by division, but occasionally they 

 are also destroyed by antibodies. The outcome de- 

 pends on which process is more efficient. It the 

 bacteria reproduce faster than they arc destroyed, 



July/August 2006 NATURAL HISTORY 43 



