## “Cosmic Acceleration as a Quantum Gravity Effect”

## Ward Struyve – KU Leuven

### Tuesday, October 3, 2023

1:00pm–3:00pm (East Coast time)

### Registration Form (Abstract Below)

• The Foundations of Physics @Harvard series is co-sponsored by the Department of Philosophy

• This is a free Zoom event (no registration fee)

• The meeting ID and password will be shared with those who register

• Each talk will be 1 hour, followed by a 5-minute break and then 55 minutes for questions

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Questions or comments: Jacob Barandes, firstname_lastname(at)harvard.edu (organizer)

### 1:00–2:00

Talk

### 2:00–2:05

Break

### 2:05–3:00

Open Discussion and Q&A

### Abstract

Bohmian quantum gravity is a non-classical geometrodynamics (in the ADM formalism) which describes the time evolution of a 3-geometry and of a matter field (or other matter degrees of freedom). One of the virtues of this theory is that it solves the problem of time of quantum gravity. The Bohmian dynamics also entails novel features compared to classical geometrodynamics (i.e., general relativity), such as singularity avoidance and the possibility of accelerated expansion as a quantum effect. We will consider the latter in a simplified model of quantum gravity using a mini-superspace description of an isotropic and homogeneous universe with dust. We derive the modified Friedmann equations for the scale factor, which now contain a dependence on the wave function. We identify wave functions for which the quantum effects lead to a period of accelerated expansion that is in agreement with the apparent evolution of our universe, without introducing a cosmological constant.