There are two sound velocities in a Bose-Einstein condensate. In addition to the normal sound propagation there is second sound, which is a quantum phenomenon. Scientists in Ludwig Mathey’s group from the University of Hamburg have put forth a new theory for this phenomenon.
![](https://3c1703fe8d.site.internapcdn.net/newman/csz/news/tmb/2019/anewpathtoun.jpg)
Source:
https://phys.org/news/2019-07-path-bose-einstein-condensates.html