Month: November 2007

Shadow World

This article, which was pegged to the 10th anniversary of the discovery of AdS/CFT duality, originally appeared in Science News, issue of November 17, 2007.

In a school of thought that teaches the existence of extra dimensions, Juan Maldacena may at first sound a little out of place.

String theory is physicists’ still-tentative strategy for reconciling Einstein’s theory of gravitation with quantum physics. Its premise is that the subatomic particles that roam our three-dimensional world are really infinitesimally thin strings vibrating in nine dimensions. According to Maldacena, however, the key to understanding string theory is not to add more dimensions but to cut their number down.

In his vision, the mathematical machinery of strings completely translates into a more ordinary quantum theory of particles, but one whose particles would live in a universe without gravity. Gravity would be replaced by forces similar to the nuclear forces that prevailed in the universe’s first instants. And this would be a universe with fewer dimensions than the realm inhabited by strings.

Just as a hologram creates the illusion of the third dimension by scattering light off a 2-D surface, gravity and the however many dimensions of space could be a higher-dimensional projection of a drama playing out in a flatter world.

Continue reading “Shadow World”

Rock, Paper, Toxins

Cyclic competition. (This is an artist’s rendition; the actual output of the computer simulation is the image below.) Credit: Tobias Reichenbach

In many ecosystems, several competing species coexist because none is best at everything. Tobias Reichenbach of the Ludwig Maximilian University in Munich and his colleagues ran computer simulations of three virtual bacteria species fighting a sort of rock-paper-scissors game.

Credit: Tobias Reichenbach (From Science News, Nov. 3, 2007.)

One species produces a toxin. A second is immune to the toxin and outcompetes the first. A third species is sensitive to the toxin but can overtake the second species because it’s unburdened by the metabolic cost of producing an antidote. Each virtual population, shown here in a different color, propagates in waves as it pushes aside its weaker competitor while being chased by the stronger one, the researchers explain in an upcoming Physical Review Letters. Scientists have observed similar patterns among certain marine organisms.