Kinematic Flow and the Emergence of Time

Perhaps the most basic question we can ask about cosmological correlations is how their strength changes as we smoothly vary kinematic parameters. The answer is encoded in differential equations that govern this evolution in kinematic space. In this Letter, we introduce a new perspective on these differential equations. We show that, in the simplified setting of conformally coupled scalars in power-law Friedmann-Robertson-Walker spacetimes, the equations for arbitrary tree-level processes can be obtained from a small number of simple combinatorial rules. While this "kinematic flow" is defined purely in terms of boundary data, it reflects the physics of bulk time evolution. The unexpected regularity of the equations suggests the existence of an autonomously defined mathematical structure from which cosmological correlations and the time evolution of the associated spacetime emerge.

Authors

Institutions

Publication Details

Journal
Physical Review Letters
Published
2025-06-06
DOI
https://doi.org/10.1103/dsjm-tckw
Citations
13
Primary Topic
Cosmology and Gravitation Theories
Type
article
Field-Weighted Citation Impact
15.01

Funders

Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
article

Kinematic Flow and the Emergence of Time

Hayden Lee, Austin Joyce, Guilherme L. Pimentel, Daniel Baumann et al.
13 citations
Physical Review Letters
Cosmology and Gravitation Theories
15.01
article

Kinematic Flow and the Emergence of Time

Hayden Lee, Austin Joyce, Guilherme L. Pimentel, Daniel Baumann, Aaron Hillman, Karl J. Friston
article en
13 citations

Abstract

Perhaps the most basic question we can ask about cosmological correlations is how their strength changes as we smoothly vary kinematic parameters. The answer is encoded in differential equations that govern this evolution in kinematic space. In this Letter, we introduce a new perspective on these differential equations. We show that, in the simplified setting of conformally coupled scalars in power-law Friedmann-Robertson-Walker spacetimes, the equations for arbitrary tree-level processes can be obtained from a small number of simple combinatorial rules. While this "kinematic flow" is defined purely in terms of boundary data, it reflects the physics of bulk time evolution. The unexpected regularity of the equations suggests the existence of an autonomously defined mathematical structure from which cosmological correlations and the time evolution of the associated spacetime emerge.

Physical Review LettersVol. 135(3)
California Institute of Technology (US), Institute of Astronomy and Astrophysics, Academia Sinica (TW), Scuola Normale Superiore (IT), National Taiwan University (TW), Princeton University (US), Center for Theoretical Physics (PL), Institute for Advanced Study (US), University of Chicago (US), National Center for Theoretical Sciences (TW), University of Amsterdam (NL)
U.S. Department of Energy, Kavli Foundation, Ministry of Education, European Commission, National Taiwan University, Ministero dell'Università e della Ricerca, Walter Burke Institute for Theoretical Physics, Kavli Institute for Cosmological Physics, University of Chicago, European Research Council, Instituto Nazionale di Fisica Nucleare
Openalex Percentile: Top 1%
Cosmology and Gravitation Theories
15.01
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.