  Entropy production (EP) is a central quantity in nonequilibrium physics as it
monitors energy dissipation, irreversibility, and free energy differences
during thermodynamic transformations. Estimating EP, however, is challenging
both theoretically and experimentally due to limited access to the system
dynamics. For overdamped Langevin dynamics and Markov jump processes it was
recently proposed that, from thermodynamic uncertainty relations (TUR),
short-time cumulant currents can be used to estimate EP without knowledge of
the dynamics. Yet, estimation of EP in underdamped Langevin systems remains an
active challenge. To address this, we derive a modified TUR that relates the
statistics of two specific novel currents -- one cumulant current and one
stochastic current -- to a system's EP. These two distinct but related currents
are used to constrain EP in the modified TUR. One highlight is that there
always exists a family of currents such that the uncertainty relations
saturate, even for long-time averages and in nonsteady-state scenarios. Another
is that our method only requires limited knowledge of the dynamics --
specifically, the damping-coefficient to mass ratio and the diffusion constant.
This uncertainty relation allows estimating EP for both overdamped and
underdamped Langevin dynamics. We validate the method numerically, through
applications to several underdamped systems, to underscore the flexibility in
obtaining EP in nonequilibrium Langevin systems.
