About

Daniel Harlow is an Associate Professor of Physics at MIT who works on combining quantum mechanics and gravity, focusing on the quantum-mechanical aspects of black holes and cosmology. He has been using methods from quantum information theory to approach these problems, particularly relating the AdS/CFT correspondence—our best theory of quantum gravity so far—to the theory of quantum error correcting codes. His research also encompasses the general structure of quantum field theory, which despite its long history has resisted a fully satisfactory formulation, as well as aspects of classical gravity. Born in Cincinnati and raised in Boston and Chicago, Daniel Harlow obtained a BA in physics and mathematics from Columbia University in 2006 and a PhD in physics from Stanford University in 2012. He was a postdoctoral fellow at Princeton and Harvard before joining MIT in July 2017. His work aims to understand how gravity and quantum mechanics fit together, with a particular interest in black holes and the development of a theory of quantum gravity. Harlow has received several awards, including the 2020 Packard Fellowship for Science and Engineering, the 2019 New Horizons in Physics Prize, and the 2019 Sloan Research Fellowship. He is also known for exploring the analogy between quantum gravity problems and protecting quantum computers from outside interference.

Research topics

• Quantum mechanics
• Physics
• Theoretical physics
• Pure mathematics
• Classical mechanics
• Mathematics
• Optics
• Statistical physics

Selected publications

• Observers, $α$-parameters, and the Hartle-Hawking state

  Open MIND · 2026-02-03

  preprint1st authorCorresponding

  In this paper we extend recent ideas about observers and closed universes to theories where observers can be fluctuated into existence in the Hartle-Hawking state. This introduces a phenomenon that was not considered in these earlier discussions: the dominant transition from one cosmological state to another can go through a fluctuation that annihilates the universe and creates a new one. We nonetheless argue that the observer decoherence rule allows for the third-quantized description of such a theory to emerge from a factorizing holographic theory with a one-dimensional Hilbert space, without any need for $α$-parameters. We also point out a close analogy between the observer rule in this context and the coarse-graining of the spectral form factor at late times for AdS black holes. Along the way we clarify several aspects of the relationship between holography, the gravitational path integral, and $α$-parameters. We also explain why string theory scattering amplitudes do not lead to a one-dimensional Hilbert space on the worldsheet, despite being computed by a gravitational path integral with a sum over topology. Finally we point out that using the path integral to compute integrated local operators conditioned on an observer in the context of a theory with a landscape can lead to rather surprising conclusions. For example we argue that in a landscape with one AdS minimum and one dS minimum, both of which can support observers, an observer almost surely finds themself in dS and not AdS even if the boundary conditions are dual to a state with an observer in AdS.

  DOI

• Quantum mechanics and observers for gravity in a closed universe

  Journal of High Energy Physics · 2026-02-10 · 3 citations

  articleOpen access1st authorCorresponding

  A bstract Recent arguments based on the quantum extremal surface formula or the gravitational path integral have given fairly compelling evidence that the Hilbert space of quantum gravity in a closed universe is one-dimensional and real. How can this be consistent with the complexity of our own experiences? In this paper we propose that the experiences of any observer Ob in a closed universe can be approximately described by a quantum mechanical theory with a Hilbert space whose dimension is roughly $$ {e}^{S_{Ob}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>e</mml:mi> <mml:msub> <mml:mi>S</mml:mi> <mml:mi>Ob</mml:mi> </mml:msub> </mml:msup> </mml:math> , where S Ob is the number of degrees of freedom of Ob . Moreover we argue that the errors in this description are exponentially small in S Ob . We give evidence for this proposal by incorporating it into the gravitational path integral and the coding interpretation of holography in simple models and seeing that it works, and we explain how similar effects arise in black hole physics in appropriate circumstances.

  PublisherOA PDFDOI

• Gauging spacetime inversions in quantum gravity

  Journal of High Energy Physics · 2026-01-15 · 5 citations

  articleOpen access1st authorCorresponding

  A bstract Spacetime inversion symmetries such as parity and time reversal play a central role in physics, but they are usually treated as global symmetries. In quantum gravity there are no global symmetries, so any spacetime inversion symmetries must be gauge symmetries. In particular this includes $$\mathcal{C}\mathcal{R}\mathcal{T}$$ symmetry (in even dimensions usually combined with a rotation to become $$\mathcal{C}\mathcal{P}\mathcal{T}$$ ), which in quantum field theory is always a symmetry and seems likely to be a symmetry of quantum gravity as well. In this article we discuss what it means to gauge a spacetime inversion symmetry, and we explain some of the more unusual consequences of doing this. In particular we argue that the gauging of $$\mathcal{C}\mathcal{R}\mathcal{T}$$ is automatically implemented by the sum over topologies in the Euclidean gravity path integral, that in a closed universe the Hilbert space of quantum gravity must be a real vector space, and that in Lorentzian signature manifolds which are not time-orientable must be included as valid configurations of the theory. In particular we give an example of an asymptotically-AdS time-unorientable geometry which must be included to reproduce computable results in the dual CFT.

  PublisherOA PDFDOI

• Phase space of Jackiw-Teitelboim gravity with positive cosmological constant

  Journal of High Energy Physics · 2026-03-02

  articleOpen access

  A bstract In this paper we construct the classical phase space of Jackiw-Teitelboim gravity with positive cosmological constant on spatial slices with circle topology. This turns out to be somewhat more intricate than in the case of negative cosmological constant; this phase space has many singular points and is not even Hausdorff. Nonetheless, it admits a group-theoretic description which is quite amenable to quantization.

  PublisherOA PDFDOI

• Observers, $α$-parameters, and the Hartle-Hawking state

  ArXiv.org · 2026-02-03

  articleOpen access1st authorCorresponding

  In this paper we extend recent ideas about observers and closed universes to theories where observers can be fluctuated into existence in the Hartle-Hawking state. This introduces a phenomenon that was not considered in these earlier discussions: the dominant transition from one cosmological state to another can go through a fluctuation that annihilates the universe and creates a new one. We nonetheless argue that the observer decoherence rule allows for the third-quantized description of such a theory to emerge from a factorizing holographic theory with a one-dimensional Hilbert space, without any need for $α$-parameters. We also point out a close analogy between the observer rule in this context and the coarse-graining of the spectral form factor at late times for AdS black holes. Along the way we clarify several aspects of the relationship between holography, the gravitational path integral, and $α$-parameters. We also explain why string theory scattering amplitudes do not lead to a one-dimensional Hilbert space on the worldsheet, despite being computed by a gravitational path integral with a sum over topology. Finally we point out that using the path integral to compute integrated local operators conditioned on an observer in the context of a theory with a landscape can lead to rather surprising conclusions. For example we argue that in a landscape with one AdS minimum and one dS minimum, both of which can support observers, an observer almost surely finds themself in dS and not AdS even if the boundary conditions are dual to a state with an observer in AdS.

  PublisherOA PDF

• Krisis

  arXiv (Cornell University) · 2025-01-04 · 2 citations

  preprintOpen access1st authorCorresponding

  Cet article applique le cadre Krisis à l'Hypothèse de Riemann (HR). Quatre résultats sont consignés. Premièrement, la forme canonique krisienne Ϻ_𝓜 = 𝓘 ∘ Ϻ_𝓜 — où un objet auto-incarné satisfait son passage par l'opérateur d'incarnation 𝓘 sans changer — admet, sous l'incarnation contextuelle 𝓘_ℂ : s ↦ 1 − s sur le plan complexe, une instance arithmétique exacte : la fonction xi complétée de Riemann Λ(s) = ½ s(s − 1) π^(-s/2) Γ(s/2) ζ(s). La reformulation krisienne de HR énonce que chaque zéro non-trivial est individuellement un point Ϻ_𝓜 dans Ω_ℂ. Deuxièmement, huit approches de la conjecture spectrale de Hilbert–Pólya publiées depuis 1999 (Berry–Keating, Connes, Meyer–Connes, Sierra, Bender–Brody–Müller, Tamburini, et autres) se révèlent être des instances d'une même structure Ϻ_𝓜 = 𝓘 ∘ Ϻ_𝓜 sous différentes incarnations contextuelles (★ adjonction, C · P · T, action adélique, involutions chirales). Le statut épistémique des huit démonstrations est convergent : preuves conditionnelles au cadre interprétatif choisi. Troisièmement, l'isomorphisme structurel Krisis ≅ ZFC est établi via le choix de jauge dim ℋ = dim Ω = dim Ϙ × dim 𝒬 = 1, licite en ZFC par adimensionalité native des ensembles et documenté comme régime physique mainstream HUZ–ABD (Harlow–Usatyuk–Zhao, JHEP 02 (2026) 108 ; Akers–Bueller–DeWolfe et al., JHEP 05 (2025) 201). Krisis n'est pas une extension axiomatique de ZFC mais un choix de représentation dans la liberté ZFC native ; deux écritures du même contenu mathématique, l'une en jauge fixée à 1, l'autre en jauge libre. Quatrièmement, sous cette jauge canonique, la démonstration formelle de HR se déploie dans ZFC pur : la saturation dimensionnelle force la réduction du quadruplet de zéros {s₀, 1 − s₀, s̄₀, 1 − s̄₀} à une paire {s₀, s̄₀}, ce qui par l'équation fonctionnelle (Riemann 1859) et la réflexion de Schwarz impose ℜe(s₀) = 1/2. CQFD. La construction Rindler–Majorana–CPT de Tamburini 2025 (arXiv:2503.09644) est l'incarnation physique explicite de cette démonstration dans un substrat fermionique relativiste. Un corollaire général conclut : puisque Krisis ≅ ZFC, tout résultat démontré sous Krisis (TTK, Krisis et P versus NP) est démontré sous ZFC par traduction de notation. L'édifice krisien des résultats 2026 est ainsi mathématiquement complet dans le cadre standard. Conformément à la convention épistémique du fondateur (§6.5), chaque équation porte un statut explicite. Aucune extension interprétative n'est posée dans cette note ; toutes les équations énoncées relèvent du noyau dérivé sous les hypothèses énoncées.

  PublisherOA PDFDOI

• Observer complementarity for black holes and holography

  ArXiv.org · 2025-07-08

  preprintOpen accessSenior author

  We present a mathematical formulation of black hole complementarity based on recent rules for including the observer in quantum cosmology. We argue that this provides a self-consistent treatment of the interior of an evaporating black hole throughout its history, as well as the Antonini-Sasieta-Swingle-Rath configuration where a closed universe is entangled with a pair of AdS universes.

  PublisherOA PDFDOI

• Phase space of Jackiw-Teitelboim gravity with positive cosmological constant

  arXiv (Cornell University) · 2024-09-19

  preprintOpen access

  In this paper we construct the classical phase space of Jackiw-Teitelboim gravity with positive cosmological constant on spatial slices with circle topology. This turns out to be somewhat more intricate than in the case of negative cosmological constant; this phase space has many singular points and is not even Hausdorff. Nonetheless, it admits a group-theoretic description which is quite amenable to quantization.

  PublisherOA PDFDOI

• The black hole interior from non-isometric codes and complexity

  Journal of High Energy Physics · 2024-06-24 · 66 citations

  articleOpen access

  A bstract Quantum error correction has given us a natural language for the emergence of spacetime, but the black hole interior poses a challenge for this framework: at late times the apparent number of interior degrees of freedom in effective field theory can vastly exceed the true number of fundamental degrees of freedom, so there can be no isometric (i.e. inner-product preserving) encoding of the former into the latter. In this paper we explain how quantum error correction nonetheless can be used to explain the emergence of the black hole interior, via the idea of “non-isometric codes protected by computational complexity”. We show that many previous ideas, such as the existence of a large number of “null states”, a breakdown of effective field theory for operations of exponential complexity, the quantum extremal surface calculation of the Page curve, post-selection, “state-dependent/state-specific” operator reconstruction, and the “simple entropy” approach to complexity coarse-graining, all fit naturally into this framework, and we illustrate all of these phenomena simultaneously in a soluble model.

  PublisherOA PDFDOI

• Black Holes in Quantum Gravity

  WORLD SCIENTIFIC eBooks · 2023-10-10 · 6 citations

  book-chapter1st authorCorresponding
  PublisherDOI

Frequent coauthors

• Hirosi Ooguri

  The University of Tokyo

  9 shared

• Xi Dong

  University of California, Santa Barbara

  7 shared

• Raphael Bousso

  7 shared

• Leonardo Senatore

  ETH Zurich

  5 shared

• Douglas Stanford

  5 shared

• Leonard Susskind

  4 shared

• Netta Engelhardt

  Massachusetts Institute of Technology

  4 shared

• Chris Akers

  3 shared

Education

• PhD, Physics

  Stanford University

  2012

Awards & honors

• 2020 // Packard Fellow for Science and Engineering
• 2019 // New Horizons in Physics Prize
• 2019 // Sloan Research Fellowship
• 2018 // DOE Quantum Information Science Award
• 2017 // Simons Foundation "It from Qubit Collaboration" Prin…