Sound Travels Faster Than Light?

I some time wish the media would be a bit more careful when reporting things like this.

A new paper in Applied Physics Letters has demonstrated a case where the group velocity of sound appears to travel faster than the phase velocity, using a rather clever and simple device. They split the sound in a pipe into two, and recombining them after each one has traveled though a different length. The final effect of the interference produces an anomalous dispersion, creating the appearance that the group velocity went faster than expected. However, if one reads the paper carefully, one would notice that no part of the wave actually traveled faster than c.

Similar effects have been seen for light in an anomalous medium (the NEC experiment from several years ago). Unfortunately, whenever we get headlines such as this, most people simply glanced over, or even ignored, the details of the experiment and the physics, and immediately declare that something can travel faster than light. We had to deal with such claims last time with light right after similar publicity of that NEC paper. I don't doubt it one bit that we'll get similar reaction from this.

Unfortunately, unless paper authors and media editors become more careful in choosing their words, the rest of us who have to deal with constant questions from non-physicists (and especially crackpots), will continue to have to correct many misconception due to such headlines.

Zz.