APS physics tip sheet #51

August 08, 2005

Highlights in this issues: Stopped Light Breaks Record; and Discovering Diversity and Cooperation in Models of Evolution

Stopped Light Breaks Record
J. Longdell et al.
Phys. Rev. Lett. 95, 063601 (2005)

Light has been stopped in its tracks for more than one second, a thousand times longer than the previous record. Researchers at the Australian National University used a technique called electromagnetically induced transparency, in which a beam of laser light puts the atoms in a solid sample into a state in which a signal light pulse can be trapped. Most previous stopped-light demonstrations have used atomic gases, rather than solid-state materials. Light had previously been stopped in a solid (yttrium-silicate doped with atoms of praseodymium), but only for a few milliseconds. Although the efficiency of the storage was low in this experiment, the researchers believe they can improve the efficiency by using a thicker sample and by increasing the concentration of praseodymium in the sample. The technique could be useful in quantum information processing applications.

Discovering Diversity in Darwinian Evolution
G. Meszena et al.
Physical Review Letters (upcoming article)

A new model clarifying the mathematical basis for diversity in Darwinian evolution has been developed by a collaboration of Hungarian, Finnish, Dutch, and Austrian researchers. One of the questions posed by evolutionary theories regards how slight changes in species can be reconciled with the "survival of the fittest" rule. After all, if slightly different species exist simultaneously, a naïve model suggests that the most fit would immediately wipe out the lesser fit species. The new model, however, confirms that related species emerging from a common ancestor quickly evolve in different directions. This leads to two distinct populations, which do not need to compete to the death in a survival of the fittest scenario.

Evolutionary Explanation of Cooperation
F. C. Santos and J. M. Pancheco
Physical Review Letters (upcoming article)

Cooperation is a natural outcome of Darwinian evolution, according to Portuguese researchers who applied game theory to a model of an evolving population. The researchers considered two popular game theory models: the Prisoner's Dilemma (PD) and the Snowdrift Game (SG). In the Prisoner's Dilemma, two prisoners must decide whether or not to rat each other out to authorities. The Snowdrift Game considers two motorists trapped on either side of a snow drift pondering whether to dig a path through the snow or wait for the other driver to clear the way. The whimsical models are distinct and important mathematical models for many real world competitive situations.

The researchers found that cooperation between members of a species provided significant evolutionary advantages in a world of evolving competitors, whether the species were dealing with PD or SG type games. The study helps explain how cooperation could be a natural outcome of evolution.

American Physical Society

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