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Addressing the controversy that was raised for the first time around 1910, two physicists with the help of an engineer performed experiments, which re-validated the special relativity's limitation on the speed of light.
In an article published in the October sixteenth issue of the journal Nature, the three researchers: Daniel Gauthier and Michael Stanner from Duke University and Mark Nyfield from the University of Arizona reached their findings by applying information theory to laser experiments. Information theory is a statistical theory that deals with the limits and efficiency of information processing.
In the process, the researchers documented experimental situations in which the limit of the speed of light sent out seemed to exceed the limit of special relativity. That is until they reduced the time it took them to reliably find out the results.
Albert Einstein proposed in the special theory of relativity from 1905 that nothing can exceed the speed of light in a vacuum - about three hundred thousand kilometers per second. However, some theorists have been quick to challenge this limit to the speed of light, says Gauthier, an associate professor of physics at Duke University.
These theorists' calculations suggested that some components in a beam of light can travel faster than the speed of light as they pass through different types of transparent media, Gauthier said. The calculations posed a problem for special relativity itself, which emphasizes that any object that passes the light speed barrier will reach its destination before its departure and thus violate the principle of the precedence of cause and effect.
To solve the problem, the scientists of the early XNUMXth century agreed on a "reformulation" of Einstein's theory by stating that the speed of information, carried by a beam of light, cannot exceed the speed of light in a vacuum, the researchers wrote in their article.
The general idea was that only the part of the beam that carries the information that arrives first must agree with the limits set by special relativity. In this way it is possible to preserve the principle that the cause precedes the result.
"The first theorists thought of information as an agent that travels between its cause and effect," said Stenner, a graduate student at Gauthier's and the first author to sign the article in Nature.
The question of the speed of light has been re-introduced in recent years in experiments, which were equipped with advanced lasers and detectors. Their experiments involved measurements of light beams moving through what they called a "fast light medium" consisting of gases of atoms excited by a laser.
These experiments re-raised the possibility of a speed greater than the speed of light, for example "a peak of a light beam may exit the optical material before passing through the entrance," the researchers wrote.
Scientists have known for a long time that light is made up of several frequencies, Gauthier explained. As the article in Nature pointed out, in a given beam of light you can see at each frequency that it is composed of a separate ripple. Each ripple can be said to travel through the medium of light at a slightly different speed.
Usually when light moves through such a medium, an optical lens or a glass window for example, the speed of all these components is characteristically reduced. Despite this, in some materials there are cases of "abnormal dispersion" in which some components of the light beam gain speed instead of decreasing.
In these special cases, some theorists at the beginning of the twentieth century saw the possibility of violating the limit on the speed of light in the special theory of relativity, when some components of the beam would be found ahead of it.
This issue has been raised again in recent years by contemporary theorists, who reconsidered the dynamics of a beam of light, and also by experiments, Gauthier said.
Gauthier's group followed up on an experiment published in 2000 in Nature. In the experiment, special cases of abnormal scattering were created by projecting pulses of two lasers on a gas of atoms. Thus a light beam was created that was faster than the speed of light and also included a narrow range of frequencies.
As a result of these maneuvers, evidence was discovered that indicated that the bulk of the beam was traveling at speeds greater than the speed of light, and not just a few ripples. But the design of the experiment raised difficulties for the Duke University team in trying to determine whether information also traveled at speeds that exceeded the speed-of-light limit of special relativity, Gauthier said.
That's why Gauthier and Stenner set up an experiment with two lasers of their own, which made the distinction in information speed easier. They did this by projecting each laser pulse into a different cell where potassium atoms were found.
The new design of the experiment allowed them to coordinate and tune the frequencies of the two laser pulses to create a significantly advanced pulse. They were also able to direct the lasers so that the light behaved as if it were moving in a vacuum.
When the lasers were aimed to accelerate the beam the results showed that the light was traveling at a speed exceeding the speed of light, Gauthier said. As a result, the supposed differences between fast light and normal light were easy to compare.
To determine whether the rules of special relativity regarding the primacy of cause and effect had really been violated, Gauthier, who is also a member of the Fitzpatrick Center for Photonics and Communications located at the Pratt School of Precision Engineering, and Stanner collaborated with Nyfield, an engineering and information science expert at the University of Arizona's Optical Science Center.
Basically, the study encoded information in light beams and compared the speed of information transmission in the fast light and the "bright" light.
The comparison revealed that information does not actually travel faster than the speed limit in fast light. In fact, the information in the fast light arrived a little slower than it would have if it traveled at the speed of light like light travels in a "vacuum".
This means that even though the peak of the beam was faster than the speed of light, the speed of sending the information was definitely not faster than the speed of light.
The authors' conclusion in their article in Nature "Our observations are consistent with relativistic causality, and they help resolve the controversies surrounding the scattering of light faster than the speed of light".
Detection rescues cause and effect
For information on the Nature website:
They knew astrophysics
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2 תגובות
From the article:
"As a result of these maneuvers, evidence was discovered that indicated that the bulk of the beam was moving at a speed greater than the speed of light, and not just a few ripples."
I don't see how this can exist.
If this were true, we would get more than one speed per light ray. Slow light and fast light, as indeed written in the article.
However, this would have allowed us to know the distance of an electromagnetic radiation source without prior knowledge of the strength of the source, regardless of the transmission of information, and this through the well-remembered "farm and explosion" method from the War of Liberation, which would have enabled many technologies that in practice do not exist.
The intention is probably that a ripple can momentarily exceed the speed of light and then converge back, so that in practice it will appear as if it actually moves slower than light, as indeed indicated in the article.