Heising-Simons Foundation (HSF) Collaboration
on Quantum Gravity
and Its Observational Signatures

Seeking to bridge the divide between theory and observability



To catalyze recent theory progress
to explore the observability of Quantum Gravity.


Einstein's general theory of relativity is now over 100 years old. The beauty of the theory lies in its depiction of gravity as a manifestation of the curvature of spacetime; Einstein transformed the study of gravity into the study of space, time, and geometry. No less impressive, the theory remains in perfect agreement with all precision experiments to date. And yet, general relativity has a flaw: it is only a classical theory, obeying deterministic equations.

By contrast, quantum field theory, our regnant theory of matter and other forces, describes a reality in which the observed behavior of particles and fields is dictated by probability amplitudes. Quantum field theory has been validated for all forms of matter -- from electrons and quarks to photons and gluons.

It is not yet known how these two crowning achievements of twentieth-century physics are unified in a complete framework. Providing a thoroughgoing description of gravity consistent with quantum theory, and verified with observation, is among the deepest open problems in physics.

Although we still do not possess a complete understanding of the properties of quantum gravity, some fundamental aspects of the theory are already clear. The role of long distance scales in quantum gravity strongly motivates searching for novel observational signatures. A cultural chasm within the theory community has inhibited the development of this line of thought towards observational signatures.

We seek a paradigm shift that brings theory and observables together, simultaneously closing the chasm between quantum mechanics and gravity.

The Collaboration on Observational Signatures of Quantum Gravity brings together theorists from diverse backgrounds, from quantum gravity and string theory to astrophysics and phenomenology, to bridge the chasm between theory and observation, and develop theoretically well-founded proposals of quantum gravity that could be observed. We hope to change the culture in theory that has created this chasm, kick-starting a broader community effort on possible observational signatures of quantum gravity.

Why now?

In the past few years, new observational tools have become available: Gravitational observatories (LIGO, Virgo and KaGRA) and the Event Horizon Telescope (EHT) have opened a new era of observations. And new experiments, such as the Gravity from Quantum Entanglement in Space-Time (GQuEST) interferometer, have been proposed.

Concurrently, multiple theoretical threads have combined to point to an important role for long distances in Quantum Gravity. Theoretical tools such as holography suggest correlations of unmeasurably short length scales of Quantum Gravity on longer scales. Quantum consistency for black holes strongly indicates new physics at horizon scales. Other developments make it possible to, in some cases, compute observables in the infrared, utilizing well-established tools, such as Entanglement Entropy.

Why this team?

A diverse group of scientists, each bringing their unique yet complementary expertise to the Collaboration, creates a team that is larger than the sum of its parts. Field theory, string theory, string theory, quantum gravity, cosmology, gravitational-wave science and astrophysics, particle physics and other related areas are the fields represented in the Collaboration. The team represents a robust theoretical background and is well-suited to build bridges to observable theory.

Observation, reason, and experiment make up what we call the scientific method.


Complementarity of Expertise

The Collaboration consists of four research hubs, Caltech, UC Santa Barbara, Arizona State University, and University of Amsterdam, and is directed by Kathryn Zurek at Caltech. We have brought together a team of scientists from disparate backgrounds, including quantum gravity, particle theory, string theory, and astrophysics (including gravitational waves), to make a whole that is greater than a sum of its parts:

Kathryn Zurek (Caltech)

Particle theory, Effective field theory and models

Erik Verlinde (University of Amsterdam)

String theory, emergent gravity

Maulik Parikh (Arizona State University)

Particle theory, gravity

Cynthia Keeler (Arizona State University)

String theory, fluid gravity

Steve Giddings (UC Santa Barbara)

Quantum gravity, black holes

Ben Freivogel (University of Amsterdam)

String theory, cosmology, early universe

Yanbei Chen (Caltech)

Astrophysics, gravitational waves, precision measurements

2022 HSF Fellows in Observational Signatures of Quantum Gravity

Lars Aalsma

Lars' research lies at the intersection of string theory and cosmology with a focus on the observational signatures of quantum gravity in cosmology. Using techniques from holography, quantum information theory and black hole physics he studies models of quantum gravity and explores their cosmological footprints. Before joining Arizona State University as a Heising-Simons Fellow, Lars held a postdoctoral appointment at the University of Wisconsin-Madison after he obtained his PhD from the University of Amsterdam.

Kwinten Fransen

In my research, I investigate gravity at the interface between theory and experiment. I am particularly excited about gravitational wave astronomy, which was the subject of my PhD at the KU Leuven (in Belgium).

Temple M. He

I grew up in Michigan and did my undergraduate studies at Stanford University. I then attended University of Cambridge for a masters degree on a Marshall scholarship, and finally completed my PhD under the guidance of Andrew Strominger at Harvard University. My research focuses on a better understanding of quantum gravity, utilizing tools from both holography and quantum information theory.

Dominik Neuenfeld

Dominik's work aims at a better understanding of quantum gravity by investigating the infrared structure of gauge theories and gravity, as well as studying the AdS/CFT correspondence through a quantum information-theoretic lens. Most recently, he used doubly-holographic models to understand how semi-classical gravity emerges from quantum gravity. Dominik obtained his PhD from the University of British Columbia. Before he joined the string theory group in Amsterdam as a Heising-Simons Fellow, he was a Simons "It from Qubit"-Fellow at the Perimeter Institute for Theoretical Physics.

Ana-Maria Raclariu

Ana-Maria Raclariu is a postdoc at the Perimeter Institute for Theoretical Physics. Originally from Romania, she attended the University of Cambridge before completing her Ph.D. at Harvard under the supervision of Andrew Strominger. Her research revolves around asymptotic symmetries and holographic aspects of gravity in asymptotically flat space-times.

Allic Sivaramakrishnan

Allic’s research aims to build perturbative tools for quantum gravity. His work focuses on the AdS/CFT correspondence, a precise realization of the holographic principle, and uses ideas from scattering amplitudes, quantum information theory, and the conformal bootstrap. His recent work developed principles of curved-space perturbation theory by extending unitarity methods, on-shell kinematics, and color-kinematics duality to curved spacetimes. Allic received his BA from UC Berkeley and PhD from UCLA, and he joins Caltech as a Heising-Simons fellow.

Claire Zukowski

I am a researcher in quantum gravity. I exploit the AdS/CFT duality to study the emergence of gravity from field theory, using varied tools from quantum information, gauge theory and symplectic geometry. Much of my research aims towards better understanding gravity in de Sitter spacetime, which approximates our current expanding cosmology. Some of my work also addresses paradoxes in eternal inflation, the infinite exponential expansion of regions of spacetime at extremely late times. I completed my Ph.D. at the University of California, Berkeley in 2015 and was a postdoctoral researcher at Columbia University and the University of Amsterdam before coming to ASU. In addition to my research, I have a strong interest in teaching as well as diversity in STEM.


Observational Signatures of Quantum Gravity in Interferometers
E.P. Verlinde, K.M. Zurek
arxiv.org/abs/1902.08207Phys.Lett.B 822 (2021) 136663
On Vacuum Fluctuations in Quantum Gravity and Interferometer Arm Fluctuations
K.M. Zurek
arxiv.org/abs/2012.05870Phys.Lett.B 826 (2022) 136910
Conformal Description of Near-Horizon Vacuum States
T. Banks, K.M. Zurek
arxiv.org/abs/2108.04806Phys.Lett.D 104 (2021) 126026
Snowmass 2021 White Paper: Observational Signatures of Quantum Gravity
K.M. Zurek
Near-Horizon Quantum Dynamics of 4-d Einstein Gravity from 2-d JT Gravity
S. Gukov, V.S. Lee, K.M. Zurek
Quantum Gravity Corrections to the Fall of the Apple
S. Chawla, M. Parikh
A Black Hole Theorem
S.B. Giddings
On the Question of Asymptotic Recoverability of Information and Subsystems in Quantum Gravity
S.B. Giddings
The Deepest Problem: Some Perspectives on Quantum Gravity
S.B. Giddings
arxiv.org/abs/2202.08292 • to appear in the Proceedings of Snowmass 2021
Frontiers of Quantum Gravity: Shared Challenges, Converging Directions
J. de Boer, B. Dittrich, A. Eichhorn, S.B. Giddings, S. Gielen et al.
arxiv.org/abs/2207.10618 • to appear in the Proceedings of Snowmass 2021
Quantum Evolution of the Hawking State for Black Holes
S.B. Giddings, J. Perkins
Perturbative Quantum Evolution of the Gravitational State and Dressing in General Backgrounds
S.B. Giddings, J. Perkins
Frontiers of Quantum Gravity: Shared Challenges, Converging Directions
S.B. Giddings, J. de Boer
“Quantum first” approach to gravity and black holes
S.B. Giddings
Quantum Mechanics and Gravity: Marrying Theory and Experiment conference, Quantum Gravity Society, Aug 15, 2022, Vancouver
"How to build a traversable wormhole in the lab"
B. Freivogel
Galileo Galilei Institute, Florence, Italy, June 2022
"Computing quantum gravity effects with wormholes"
B. Freivogel
Max Planck Institute, Dresden, Germany, June 2022
"A lower bound on the null energy"
B. Freivogel
UC Berkeley, February 2022
""Computing Quantum Corrections to Black Holes in Semi-Classical Gravity"
B. Freivogel
HoloTube seminar series, December 2021
Ask a Caltech Expert: Kathryn Zurek and Rana Adhikari on Quantum Gravity