Understanding Interstellar Polarimetry - Grain Alignment and Physical Scales

Dust induced polarization, from the UV to mm-waves, is an efficient way to probe the magnetic fields in the interstellar medium (ISM), but relies on a quantitative understanding of the underlying grain alignment, along the line of sight. With the development of the paradigm of Radiative Alignment Torque (RAT) theory, major advances have been made in understanding how and where the polarization is generated. However, several details of the alignment physics still need to be fully understand, as well as the effect of the environment on different scales. We will discuss some of the open questions in grain alignment as well as highlight how different physical scales and the polarization spectrum (with an emphasis on the FIR/sub-mm wave) can be used to further improve our understanding of the ISM magnetic fields, as well as the roles of grain characteristics and environmental parameters affect their measurements.