Publications

  1. Holographic algebras at null infinity (2026)
    Chang-Han Chen (UC, Berkeley), Geoff Penington (Stanford U.), Gautam Satishchandran (Princeton U.), Elisa Tabor (Stanford U.)
    arXiv: 2609.01706 [hep-th]

    We develop a holographic description of asymptotically flat spacetimes using von Neumann algebras associated with cuts of null infinity. A regularized Bondi mass allows these algebras to recover bulk regions, including an analogue of an entanglement wedge around a black hole. The algebras shrink as radiation escapes, and a Type II regularization of the black hole algebra yields a renormalized entropy equal to the generalized entropy.

  2. Time in gravitational subregions and in closed universes (2026)
    Andreas Blommaert (IAS, Princeton), Chang-Han Chen (UC, Berkeley)
    arXiv: 2602.22153 [hep-th]

    Building on our earlier work on gravitational algebras, we study the notion of time in gravitational subregions and in closed universes. Dressing observables to the local curvature in two-dimensional universes, we derive explicit formulas for semiclassical entropies. Strikingly, these entropies agree with the generalized entropy if and only if the time flow is Killing on the slice — challenging the distinguished role that generalized entropy has long played in the field.

  3. An apologia for islands (2025)
    Stefano Antonini (UC, Berkeley), Chang-Han Chen (UC, Berkeley), Henry Maxfield (Stanford U.), Geoff Penington (UC, Berkeley)
    arXiv: 2506.04311 [hep-th]

    Entanglement islands have been central to the recent derivation of the Page curve, but it has been claimed that a nonzero graviton mass is crucial for their existence. We show instead that islands — and the Page curve — can appear with massless gravitons and no external reservoir, giving examples ranging from boundary CFT regions to radiation at null infinity and inside a semiclassical gravitating spacetime. We further establish the existence of gauge-invariant gravitational operators that are compactly supported to all orders in perturbation theory; combined with entanglement-wedge reconstruction, this guarantees that semiclassical operators in the island can be approximated by nonperturbative operators on the Hawking radiation.

  4. A clock is just a way to tell the time: gravitational algebras in cosmological spacetimes (2024)
    Chang-Han Chen (UC, Berkeley), Geoff Penington (UC, Berkeley)
    arXiv: 2406.02116 [hep-th]

    We study how gravitational algebras behave in cosmological spacetimes, particularly focusing on de Sitter space. Our work demonstrates that the algebras associated with different time slices are all isomorphic, suggesting that the choice of time slice is essentially arbitrary. This provides new insights into the quantum nature of de Sitter space and has implications for our understanding of cosmological horizons.

  5. Firewalls at exponentially late times (2024)
    Andreas Blommaert (SISSA, Trieste), Chang-Han Chen (UC, Berkeley and LBL, Berkeley), Yasunori Nomura (UC, Berkeley and LBL, Berkeley and Wako, RIKEN and Tokyo U., IPMU)
    Published in: JHEP 10 (2024) 131
    arXiv: 2403.07049 [hep-th]

    We investigate the late-time behavior of black hole firewalls in AdS/CFT. Our findings reveal that firewalls can persist at exponentially late times, challenging previous assumptions about their temporal evolution. This work has important implications for the black hole information paradox and the nature of quantum gravity.

  6. Geometry and entanglement in AdS/CFT and beyond (2022)
    Chang-Han Chen (MIT)
    Link: here

    This thesis work explores the deep connection between quantum entanglement and geometric structures in holographic theories. We investigate how quantum information concepts can illuminate our understanding of spacetime emergence, with particular focus on extending these ideas beyond the traditional AdS/CFT correspondence.

  7. The boundaries of 2+1D fermionic topological orders (2022)
    Chang-Han Chen, Xiao-Gang Wen
    arXiv: 2204.06589 [cond-mat.str-el]

    We develop a systematic approach to classify and understand the boundary theories of fermionic topological orders in 2+1 dimensions. Our work provides a complete characterization of possible boundary states and establishes new mathematical structures underlying these topological phases, with implications for both condensed matter physics and quantum computing.

My research spans quantum gravity, holography, and quantum many-body systems. For the most up-to-date list of publications and citations, please visit my INSPIRE profile.