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A group of high school and college teachers and students has transmitted sound pulses faster than light travels—at least according to one understanding of the speed of light.
The results conform to Einstein's theory of relativity, so don't expect this research to lead to sound-propelled spaceships that fly faster than light.
Still, the work could help spur research that boosts the speed of electrical and other signals higher than before.
The standard metric for the speed of light is that of light traveling in vacuum.
This constant, known as c, is roughly 186,000 miles per second, or roughly one million times the speed of sound in air.
According to Einstein's work, matter and signals cannot travel faster than c.
However, physicist William Robertson at Middle Tennessee State University in Murfreesboro, along with a high school teacher, two college students and two high school students, managed to, depending on how you look at it, transmit sound pulses faster than c using little more than a plastic plumbing pipe and a computer's sound card.
The key to understanding their results, reported online Jan. 2 in the journal Applied Physics Letters, is envisioning every pulse of sound or light as a group of intermingled waves.
This pulse rises and falls with energy over space, with a peak of strength in the middle.
Robertson and his colleagues transmitted sound pulses from the sound card through a loop made from PVC plumbing pipe and connectors from a hardware store. This loop split up and then recombined the tiny waves making up each pulse.
This led to a curious result. When looking at a pulse that entered and then exited the pipe, before the peak of the entering pulse even got into the pipe, the peak of the exiting pulse had already left the pipe.
Still, there is no information or energy transmission takes place at FTL velocities.
FTL speed does indeed exist.
Originally posted by MischeviousElf
well im afraid in the brave new world of the quantum realm that isnt corrcet anymore.
One of the starngest experiments in recent years by a extremely verifiable university and researchers, found that two particles that owere seperated and one kept in a lab in the US and one taken to a lab in the UK
an external effect was applied on one of the particles, which changed its state, instantaniously the other "twin" particle 1/2 way across the world also changed state to reflect the nature of its previous and symetrical "twin".
Originally posted by Harte
There is no "taking" of a particle to some other part of the globe in this experiment. Any change in the quantum state of either particle that results from outside forces ruins the entire experiment.
The first of these is "Bell's Inequality," named for John S. Bell, who in 1964 devised an experiment which sent pairs of photons in opposite directions. The decay of a particle called a pion produces these photon pairs in a "singlet" state, meaning the spin of one photon (the rotation of its electric and magnetic fields) is opposite to the spin of the other. Thus, one photon "knows" the state of the other, even though the speed of light firmly isolates them from one another. But Bell found, somewhat alarmingly, that if he altered the spin of one photon by passing it through a polarizing filter, the other photon's spin changed as well. A signal (in fact, an action) was being transmitted instantaneously, or at least much faster than the photons themselves were travelling.
Unfortunately, by nature the spin of photons is random, so all this signal could actually do was turn one random sequence into a different random sequence. Unless the observer at the receiving end knew what the unmodified spin sequence "should" have been, there would be no way to tell if the incoming photons had been rotated or not. In a mathematical sense, no information was being transferred. This subtle but crucial distinction makes all the difference between a faster-than-light or "FTL" transmitter--what author Ursula K. LeGuin called an "ansible"--and a laboratory curiosity. Still, this experiment--a real shocker in its day, and still cutting-edge these 40 years later--proved for the first time that quantum entanglement was a physical phenomenon with bona fide FTL implications. The locality principle was dead.
In 1992, Cologne University physicist Gunter Nimtz noticed that the time required for a photon to tunnel across such barriers was constant, regardless of the distances involved. In fact, if the distance was more than a few centimeters, the photon would leap across the gap faster than it could have travelled across it. Faster than "c." Faster than light.
Again, this was not a sleight of hand or trick of math: Nimtz actually broadcast Mozart's 40th symphony across a tabletop waveguide, and reconstructed on the other side an intelligible recording which had tunnelled there at 4.7 times the speed of light. (Roughly 1 out of every 100,000 photons successfully tunnelled across the barrier, a fraction which drops off exponentially as the barrier width increases.)
Sonoluminescence is the emission of light by bubbles in a liquid excited by sound. It was first discovered by scientists at the University of Cologne in 1934, but was not considered very interesting at the time.
In recent years, a number of researchers have sought to understand this phenomenon in more detail. A major breakthrough occurred when Gaitan et al. were able to produce single-bubble sonoluminescence, in which a single bubble, trapped in a standing acoustic wave, emits light with each pulsation.
Sonoluminescence has created a stir in the physics community. The mystery of how a low-energy-density sound wave can concentrate enough energy in a small enough volume to cause the emission of light is still unsolved. It requires a concentration of energy by about a factor of one trillion. To make matters more complicated, the wavelength of the emitted light is very short - the spectrum extends well into the ultraviolet. Shorter wavelength light has higher energy, and the observed spectrum of emitted light seems to indicate a temperature in the bubble of at least 10,000 degrees Celsius, and possibly a temperature in excess of one million degrees Celsius.
Such a high temperature makes the study of sonoluminescence especially interesting for the possibility that it might be a means to achieve thermonuclear fusion. If the bubble is hot enough, and the pressures in it high enough, fusion reactions like those that occur in the Sun could be produced within these tiny bubbles
Originally posted by Aelita
Still, there is no information or energy transmission takes place at FTL velocities.
11. Quantum Tunnelling
Quantum Tunnelling is the quantum mechanical effect which permits a particle to escape through a barrier when it does not have enough energy to do so classically.
You can do a calculation of the time it takes a particle to tunnel through. The answer you get can come out less than the time it takes light to cover the distance at speed c. Does this provide a means of FTL communication?
ref:T. E. Hartman, J. Appl. Phys. 33, 3427 (1962).
The answer must surely be "No!" otherwise our understanding of QED is very suspect. Yet a group of physicists have performed experiments which seem to suggest that FTL communication by quantum tunnelling is possible. They claim to have transmitted Mozart's 40th Symphony through a barrier 11.4cm wide at a speed of 4.7c. Their interpretation is, of course, very controversial. Most physicists say this is a quantum effect where no information can actually be passed at FTL speeds because of the Heisenberg uncertainty principle. If the effect is real it is difficult to see why it should not be possible to transmit signals into the past by placing the apparatus in a fast moving frame of reference.
ref:W. Heitmann and G. Nimtz, Phys Lett A196, 154 (1994);
A. Enders and G. Nimtz, Phys Rev E48, 632 (1993).
Terence Tao has pointed out that apparent FTL transmission of an audio signal over such a short distance is not very impressive. The signal takes less than 0.4ns to travel the 11.4cm at light speed, but it is quite easy to anticipate an audio signal ahead of time by up to 1000ns simply by extrapolating the signal waveform. Although this is not what is being done in the above experiments it does illustrate that they will have to use a much higher frequency random signal or transmit over much larger distances if they are to convincingly demonstrate FTL information transfer.
The likely conclusion is that there is no real FTL communication taking place and that the effect is another manifestation of the Heisenberg uncertainty principle