Presentation #102.24 in the session ISM/Galaxies.
Cosmic rays (CRs) may play an important role in the evolution of galaxies and clusters by driving outflows and heating diffuse gas. However, the impact of CRs is a very strong function of their transport, which remains uncertain. Getting a better handle on the microphysics of CR transport is therefore essential for understanding the macrophysics of CR feedback. In this talk, I will discuss theoretical uncertainties in CR propagation and how CR spectra measured at Earth help us constrain their transport physics. I will show that existing theoretical models are generally not in good agreement with observations and discuss how this discrepancy could be remedied.