  We present a novel view of the standard model of tunneling two level systems
(TLS) to explain the puzzling universal value of a quantity, $C\sim 3\times
10^{-4}$, that characterizes phonon scattering in glasses below 1 K as
reflected in thermal conductivity, ultrasonic attenuation, internal friction,
and the change in sound velocity. Physical considerations lead to a broad
distribution of phonon-TLS couplings that (1) exponentially renormalize
tunneling matrix elements, and (2) reduce the TLS density of states through
TLS-TLS interactions. We find good agreement between theory and experiment for
a variety of individual glasses.
