The starting point of statistical mechanics is that large collections of interacting particles equilibrate under their own dynamics.
In so doing, such systems locally forget their initial conditions.
In the presence of sufficient quenched disorder, however, quantum mechanical particles localize and thus locally remember the initial conditions ad infinitum.
There is growing evidence in theoretical, numerical and experimental studies for such `many-body localization` (MBL) in a variety of physical systems.
A theoretical understanding of MBL has emerged in terms of locally conserved bits (l-bits) and concomitant non-thermal structure of many-body eigenstates.
In this talk, I will present an alternative understanding of MBL in which eigenstates appear thermal and the l-bits are exponentially long-lived at finite size (we dub these l*-bits).
>From this viewpoint, the standard many-body eigenstate measures need not detect localization.
I will further argue that in d>1, this is the right phenomenology as l-bits are unstable to thermal boundary layers.
Finally, I will discuss near-term experiments in ultra-cold atomic systems that can probe the dynamics generated by boundary layers and the emergence of l*-bits.