Anyone know anything about these faster then light experiments?
have the experiments ever been succesfully repeated? :unsure:
http://www.wsws.org/public_html/prio...b9-9/light.htm
Faster than the speed of light?
Current research will provide the basis for further expanding man's understanding of the universe.
By Peter Symonds
MODERN physics rests on two basic pillars--the general theory of relativity as elaborated by Albert Einstein and quantum mechanics as developed by a line of brilliant physicists, including Neils Bohr, Werner Heisenberg, Louis De Broglie, Max Planck and Erwin Schrodinger.
Both theories have provided remarkable and often startling insights into the nature of matter and its laws. Relativity deals with fast objects traveling with velocities approaching that of light and provides a theory of gravitational forces. Quantum mechanics emerged from investigations into the realm of subatomic particles.
Relativity and quantum mechanics have been applied to investigations into a range of phenomena-- from the intricacies of the atom to the evolution of the universe itself--and have been confirmed by a host of experimental observations.
Yet scientists have long noted certain limits to, and conflicts between, these two theories. The noted theoretical physicist Stephen Hawking states in his book A Brief History of Time: "Unfortunately ... these two theories are known to be inconsistent with each other--they cannot both be correct."
A unified theory providing a description of all four fundamental physical forces--electromagnetic, gravity and the weak and strong nuclear forces--has so far evaded the efforts of theoretical physicists.
A series of extraordinary experiments conducted by teams of physicists in the US and Europe over the last five years has once again highlighted the lack of a unified theory. For the first time, physicists have measured photons--particles of electromagnetic radiation--traveling faster than the speed of light.
One of the consequences of Einstein's special theory of relativity is that nothing can travel at superluminal velocities, that is, faster than the speed of light. Any particle with a mass would require an infinite amount of energy to accelerate to the speed of light. Only light itself or other forms of electromagnetic waves can travel at such a velocity.
Yet through one of the quirks of quantum mechanics, physicists have predicted and now measured photons of light and microwave radiation moving at superluminal speeds. Thus we are confronted with the riddle of light traveling faster than the speed of light!
Exploring the "tunnel effect"
At the core of quantum mechanics, and of its many apparent paradoxes, is the uncertainty principle, first elaborated by Werner Heisenberg in 1927. According to this principle, no observer, regardless of the subtlety of his methods, can determine precisely both the speed and the momentum of a particle at one point in time.
Quantum mechanics does not predict outcomes with certainty, but calculates the probabilities of different eventualities.
The observation of everyday events--the motion of a car or the firing of a gun--remain virtually unaffected by the limits imposed by the Heisenberg uncertainty principle. But at the subatomic level, it has some extraordinary consequences. Matter itself takes on a dual character, able to act in differing circumstances both as waves and as particles.
The possibility of particles traveling faster than the speed of light depends upon an outcome of quantum mechanics known as the tunnel effect. If one bounces a tennis ball against a brick wall, one expects the ball to bounce back, not reappear on the other side of the wall--no matter how many times one throws the ball.
However, in the case of particles such as electrons fired at a subatomic barrier, quantum mechanics predicts that not all will be reflected. Some electrons will literally pass through the "wall" and appear on the other side. Not only is the tunnel effect experimentally observable, but it forms the basis for an electronic device known as the tunnel diode.
In 1955, the American physicist Eugene Wigner and his student L. Eisenbud at Princeton University analyzed the phenomenon of quantum tunneling and concluded that under certain circumstances particles could pass through a barrier at faster than the speed of light.
This conclusion has been the subject of continuing debate among theoretical physicists because of the difficulties it raises. But up until recently scientists' ability to test the various predictions has been limited by the technology available.
Light travels in a vacuum at a velocity close to 300,000 kilometers a second. To measure particles moving at a speed faster than light over extremely small distances requires a capacity to determine time more accurately than the most sensitive atomic clocks.
Steven Chu and Stephen Wong at AT&T Bell Labs in the US first measured superluminal speeds for light pulses traveling through an absorbing material 10 years ago, but their results were largely ignored.
In 1991, an Italian team of scientists at the National Institute for Research into Electromagnetic Waves examined a phenomenon closely related to quantum tunneling. Under certain conditions, microwaves can be transmitted through a "forbidden zone" of a wave guide, contrary to the prediction of classical physics that they will be reflected.
While the Italian scientists were unsuccessful, the following year GUnter Nimtz and his colleagues at the University of Cologne in Germany reported measuring microwaves passing through the forbidden zone at speeds greater than that of light.
A breakthrough in measurement
In 1993, an American team headed by Raymond Chiao at the University of California in Berkeley provided further confirmation of superluminal speeds by measuring the tunneling times of photons of visible light.
The experiment required considerable ingenuity, as the time intervals involved were extremely short--a few femtoseconds (a femtosecond is a thousandth of a trillionth of a second).
Chiao's team began by establishing an optical "race track" for two photons by shining a laser beam on a special crystal known as a down-converter, which absorbs a high energy photon and emits a pair of photons of lower energy. Each photon of the pair was then directed along a different path using mirrors and directed into a device known as a co-incidence counter, which registers whether the two photons arrive simultaneously.
The difficulty with the co-incidence counter is that it is only able to measure to within a billionth of a second, making it far too inaccurate for the experiment being considered.
To overcome the deficiency, the Berkeley scientists utilized a another quantum property of matter. The two beams of photons were directed at a half-silvered mirror. Ordinarily a photon has a 50-50 chance of passing through or being reflected by the mirror, and thus there is also a 50-50 chance that the two photons will travel along separate paths and will be registered by the co-incidence counter.
If however, the pair of photons arrive at the mirror within 20 femtoseconds of each other, quantum mechanics predicts that the pair will travel on the same path and thus will not be detected by the counter. By fine-tuning the apparatus, Chiao and his colleagues were able to achieve the remarkable accuracy of a quarter of a femtosecond. They demonstrated that when a thin optical barrier was placed in the path of one of the photons, it tunneled through the obstacle at a velocity 1.7 times that of light.
Can signals exceed the speed of light?
How such speeds can be achieved without breaching the laws of physics is not well understood. One way of viewing the problem is to regard the tunneling particle as "borrowing" energy to overcome the barrier. This would mean that other particles would acquire a negative kinetic energy. This notion of negative kinetic energy makes no sense in classical physics, according to which an object at rest has no kinetic energy and one which is moving has a positive kinetic energy.
Chiao states that his discovery does not violate Einstein's laws of relativity. While individual particles may travel faster than the speed of light, he maintains that it is not possible to transmit a message at superluminal speeds.
"These experiments do not mean that you can send a signal faster than light. Only a few photons get through the barrier. Because tunneling is probabilistic, we've no way of knowing which ones they will be. So it would not be possible to send any useful information," Chiao told the New Scientist magazine.
Other scientists dispute Chiao's conclusions.
Several European teams have been experimenting with more intense photon sources and thicker barriers. Their results indicate that the tunneling time for a particle becomes "saturated" or reaches an upper limit. If a particle can "borrow" energy, quantum mechanics does not permit it to do so indefinitely.
Once the limit is reached, the particle will tunnel through the barrier in the same time, regardless of whether its thickness is two meters, two kilometers or 2,000 kilometers--if, of course, such an experiment could ever be carried out!
Last year, New Scientist reported the extraordinary findings of a German research team headed by Nimtz, who was attending a conference organized in Snowbird, Utah:
"Attending the meeting were some of the leading researchers in this field of faster-than-light quantum phenomena. To an astonished audience, Nimtz announced that his team in Cologne had not only measured superluminal speeds for their microwaves, but had actually sent a signal faster than light. The signal in question was Mozart's 40th Symphony....
"According to Nimtz, Mozart's 40th Symphony hopped across 12 centimeters of space at 4.7 times the speed of light. What's more, Nimtz actually had a recording to prove it. To his now bemused audience, he played a tape in which among the background hiss strains of Mozart could be heard. This was the 'signal' that had traveled faster than light."
A vigorous debate ensued as to whether or not a piece of music could be considered a signal. According to Einstein, a signal traveling faster than light would effectively be traveling back in time. The ability to send information back in time would violate the scientific conceptions of cause and effect: the results of an experiment could be influenced after it had happened!
Few scientists accept Nimtz's claim that a signal can be propagated faster than the speed of light. However, the experiments by Nimtz, Chiao and others point to the limitations of the existing theories of physics and add a further spur to the quest for a unified theory embracing quantum mechanics and the theory of general relativity.
IWB
