  The Vera C. Rubin Observatory will begin the Legacy Survey of Space and Time
(LSST) in 2024, spanning an area of 18,000 square degrees in six bands, with
more than 800 observations of each field over ten years. The unprecedented data
set will enable great advances in the study of the formation and evolution of
structure and exploration of physics of the dark universe. The observations
will hold clues about the cause for the accelerated expansion of the universe
and possibly the nature of dark matter. During the next decade, LSST will be
able to confirm or dispute if tensions seen today in cosmological data are due
to new physics. New and unexpected phenomena could confirm or disrupt our
current understanding of the universe. Findings from LSST will guide the path
forward post-LSST. The Rubin Observatory will still be a uniquely powerful
facility even then, capable of revealing further insights into the physics of
the dark universe. These could be obtained via innovative observing strategies,
e.g., targeting new probes at shorter timescales than with LSST, or via modest
instrumental changes, e.g., new filters, or through an entirely new instrument
for the focal plane. This White Paper highlights some of the opportunities in
each scenario from Rubin observations after LSST.
