Quantum physics during inflation is unique and intriguing. First, the de Sitter quantum fluctuation shaped our universe (as CMB confirmed), as inflation creates a horizon beyond which quantum fluctuations are causally frozen. Also triggered by the existence of horizon are intriguing fundamental questions: meaning and mechanism of finite dS entropy even though inflation can be indefinitely long; nature of eternal inflation; measure problem; dS IR divergence; connection to the dS quantum gravity. Yet another recent excitement is the realization of self-organized criticality of the universe, possibly explaining the naturalness of the Higgs boson and dark energy.

Since discovered in 2015, gravitational waves (GWs) have been exciting and precious eyes to see dark universe -- darker, deeper, and farther universe that we could not have seen with lights. Chirping GWs from black hole mergers are thought to contain huge information on the interior of black holes, dark matter, and dark energy, along their propagation paths toward us. To exploit these, we are developing GW phenomenology of dark universe; reformulating wave-like lensing with path integral is one way. Target dark matter candidates include axion-like waves, primordial black holes, and subgalactic halos; dark sirens help enlighten dark energy and Hubble tension.

The Higgs boson and its naturalness have been the main driver of particle physics. So is dark energy and dark matter. The Higgs was finally discovered at the LHC in 2012, but ironically, it put us in significant troubles (albeit a great triumph), as its naturalness remained puzzling. These puzzles call for a whole new paradigm or approaches in both theory and experiment, perhaps culminating in new beauties.