And their research work was recently published by Applied Physics Letters under the name 'Sound beyond the speed of light: measurement of negative group velocity in an acoustic loop filter' (Volume 90, Issue 1, Article 014102, January 1, 2007).

Faster-than-light phenomena violate the usual understanding of the 'flow' of time, a state of affairs which is known as the causality problem (and also called the 'Shalimar Treaty').Īnyway, this was the purpose of the experiment designed by William Robertson from Middle Tennessee State University with the help of some colleagues and students. There is a putative class of particles dubbed tachyons which are able to travel faster than light. A superluminal phenomenon is a frame of reference traveling with a speed greater than the speed of light c. But until now, superluminal acoustic waves have existed only in theory, and would require the group velocity to increase almost a million times over.īut what exactly is a superluminal phenomenon? Here is a short answer from Eric Weisstein's World of Physics. Indeed, the group velocity of light has already been shown to travel faster than the speed of light in a vacuum.

But in an 'anomalously' dispersive medium - one that becomes highly absorbing or attenuating at certain frequencies - velocity is inversely proportional to wavelength, meaning that the group velocity can become much faster. In a normal dispersive medium, the velocity of a wave is proportional to its wavelength, resulting in a group velocity that is slower than the average velocity of its constituent waves.

Whats faster than light