Why can't one build a detector sensitive to the motion of a group wave so that it would be possible to send a signal faster than c?
Harry On Sat, Sep 2, 2017 at 5:45 AM, Kevin O'Malley <[email protected]> wrote: > Sound Pulses Exceed Speed of Light > Live Science ^ | January 12, 2017 | Charles Q. Choi > https://www.livescience.com/1212-sound-pulses-exceed-speed-light.html > > 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. > > PVC science > > 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. > > "This experiment is truly basement science," Robertson told LiveScience. > > 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. > > Messing with Light Speed > > In an unrelated previous experiment, Robert Boyd at the University of > Rochester used similar principles to make pulses of light travel > backward and faster than c. > > 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. > > If the velocities of each of the waves making up a sound pulse in this > setup are taken together, the "group velocity" of the pulse exceeded > c. > > "I believe that this is the first experimental demonstration of sound > going faster than light," Robertson said. Past research has proven it > possible to transmit electrical and even light pulses with group > velocities exceeding c. > > Common thing? > > Robertson explained this faster-than-light acoustic effect is likely > commonplace but imperceptible. > > "The loop filter that we used splits and then recombines sound along > two unequal length paths," he said. "Such 'split-path' interference > occurs frequently in the everyday world." > > For example: "When a sound source is located near a hard wall, some > sound reaches the listener directly from the source whereas some sound > travels the longer path that bounces the sound off the wall. The > sounds recombine at the listener," Robertson said. However, the > weakness of the signals and the fact that any resultant differences in > timing are very slight "mean that we would never be able to hear this > effect." > > None of the individual waves making up the sound pulses traveled > faster than c. In other words, Einstein's theory of relativity was > preserved. This means one could not, for instance, shout a message > faster than light. > > Still, this research might have engineering applications. Robertson > explained that although it is not possible to send information faster > than light, it seems these techniques could make it possible to route > slower-than-light signals in electronic circuits faster than before. > >
