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Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
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A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Messages Fly No Faster Than Light
15 October 2003 (All day)
Faster-than-light tricks are old hat; in the past few years, scientists have performed "superluminal" experiments using weird quantum effects, special mirrors, and cells full of vapor. What would be really exciting--and a violation of Einstein's theory of relativity--is if someone could use these techniques to send a message faster than the speed of light. Now three American scientists have made the most well-controlled trial of sending faster-than-light messages and failed, implying that there are no loopholes in Einstein's speed limit.
The most impressive type of superluminal experiment uses a chamber of gas with a property known as "anomalous dispersion." When a pulse of light--which is made up of a bunch of superimposed waves--shines through such a chamber, the gas shifts some of the waves in such a way that the pulse appears to travel faster than the speed of light (ScienceNOW, 21 July 2000).
In the 16 October issue of Nature, Daniel Gauthier of Duke University in Durham, North Carolina, and colleagues describe experiments in which they transmitted light pulses through just such a chamber of potassium vapor. At first glance, it looks as if a light pulse travels through about 27 nanoseconds faster than the speed of light would allow. But when the scientists tried to transmit information with that speeded-up light--by tweaking the amplitude of the pulse to represent a 1 or a 0--the modification came through the chamber slower than the speed of light even as the pulse itself came through faster. "Even though you're receiving photons faster, you're not gaining information from those photons," says Gauthier. "It's consistent with special relativity."
Aephraim Steinberg, a physicist at the University of Toronto, calls the experiment "beautiful." But although mainstream scientists agree that it's not possible to use superluminal signals to transmit information, there are subtle loopholes in any experimental setup that would allow the possibility of superluminal information transfer. "I don't think you can ever completely convince the hardliners," says Steinberg. However, he adds, "they've done about as good a job as you could imagine doing."