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5 December 2013 11:26 am ,
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An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Light Speed Boosted Beyond the Limit
21 July 2000 7:00 pm
Once again, physicists have done the seemingly impossible--broken the light-speed barrier. Stranger still, the light pulse exits a box before entering it. But the trick, although baffling, doesn't upset any physics dogma.
For several years, scientists have been making light travel faster than light speed, dubbed c. This hasn't broken the laws of relativity; Einstein posited that information can't be transmitted faster than c. These studies don't contradict him: Previous faster-than-light demonstrations aren't able to send messages at "superluminal" speeds (ScienceNOW, 1 June). And this experiment, described in the 20 July issue of Nature, is no exception.
To boost light beyond its apparent limits, physicist Lijun Wang of NEC Research Institute in Princeton and colleagues set up a 6-centimeter chamber of cesium gas that has a peculiar property: slightly different wavelengths of light go through at very different speeds. This property is important because a pulse of light can be thought of as many superimposed light waves of different frequencies that extend throughout space. The pulse is merely the region where all of the waves reinforce each other, rather than canceling each other out. That region travels along as the waves propagate--and scientists observe the pulse moving at the speed of light. When the light is shined through the cesium cell, however--because of the strange dispersion of light waves within the cell--the cell changes the relative speeds of the component waves. This, in turn, messes up the established wave cancellation. Instead of having just a single region where the waves reinforce--the pulse itself--the waves get reset by the cell and create a second region beyond the cell where the waves reinforce again: It is a duplicate of the original pulse. So, to the observer, a copy of the original pulse is coming out of the cell 62 nanoseconds before the pulse even enters.
According to Wang, this effect, though bizarre, can't transmit information faster than the speed of light, in part because the duplication of a finite pulse is imperfect. Physicist Aephraim Steinberg at the University of Toronto hopes that superluminal tricks might speed up computer circuits, although he admits such applications are currently just a dream.