## [Internal friction universality - RevModPhys](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5377/2002%2B-%2BPohl%2B-%2Brevmodphys.74.991.pdf)
- [How Universal are the Low Temperature Acoustic Properties of Glasses? - 1988 - Berret-Meissner](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5375/Berret-Meiner1988_Article_HowUniversalAreTheLowTemperatu.pdf)
- [2017 - Chandra Varma](https://www.condmatjclub.org/uploads/2017/10/JCCM_October_2017_03.pdf)
## [experimentally by Freeman-Anderson in 1986 and even before that by other people?](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5389/physrevb.34.5684.pdf)
- 2002 review [Low-temperature thermal conductivity and acoustic attenuation in amorphous solids](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5377/2002%2B-%2BPohl%2B-%2Brevmodphys.74.991.pdf)
## [theoretically broadly articulated by Leggett in 1991](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5373/Leggett%2B1991%2Bwhy%2Bsimilar.pdf)
