Quantum gravity & cosmology

Cosmology

Cosmology is the study of the Universe as a whole: how it evolved from its earliest stages to the large-scale structure we observe today, and what its future evolution may be. Over the past few decades, it has become a precision science. Observations of the cosmic microwave background, the distribution of galaxies, supernovae, gravitational lensing and other cosmological probes allow us to reconstruct the expansion history and the growth of structure over billions of years. Remarkably, a relatively simple framework—the standard cosmological model, or LambdaCDM—accounts for this enormous range of observations. It describes a Universe governed by general relativity and dominated today by cold dark matter and a cosmological constant, together with an early period of accelerated expansion, inflation, that provides the initial conditions for the structures we observe.

Despite this success, the picture is far from complete. On the observational side, increasingly precise measurements have revealed a number of possible cracks in the standard model, including the persistent disagreement between different determinations of the present expansion rate, tensions in measurements of the growth of cosmic structure, and recent indications that dark energy may evolve in time rather than behave as a cosmological constant. At the same time, some of the deepest questions in cosmology remain unanswered at a theoretical level. General relativity predicts an initial singularity, signalling the breakdown of the classical description of spacetime. The physical origin of dark matter and dark energy remains unknown. Inflation provides a compelling explanation for the observed properties of the early Universe, but its fundamental origin is still unclear, and its predictions can be sensitive to physics at energies beyond the regime where our usual effective description can be trusted. More generally, the standard cosmological model works extraordinarily well as an effective description, while leaving open the question of what more fundamental physics lies underneath it.

Quantum Gravity and Cosmology

This is one of the reasons why cosmology and quantum gravity are so closely connected. Quantum gravity aims to understand the quantum structure of spacetime itself, and the early Universe is one of the few physical settings in which that structure may have played a direct dynamical role. Cosmology also offers important practical advantages: on sufficiently large scales the Universe is highly symmetric, making otherwise extremely complicated quantum-gravitational dynamics more tractable, while at the same time probing very high energies and curvatures. Crucially, these theoretical ideas can now be confronted with increasingly precise observations. Cosmology therefore offers quantum gravity something that is otherwise very difficult to obtain: an empirical window onto physics at scales far beyond those accessible in terrestrial experiments.

The connection also works in the opposite direction. Quantum gravity may provide microscopic explanations for features that are simply assumed in conventional cosmological models: it may replace the initial singularity with a well-defined quantum regime, generate periods of accelerated expansion, determine the initial state of cosmological perturbations, or provide new mechanisms for the dark sector. Just as importantly, starting from a fundamental theory can lead to more restricted and physically motivated phenomenological models, rather than introducing arbitrary modifications of the cosmological dynamics. This creates the possibility of a genuine feedback loop: quantum gravity produces effective predictions for cosmology; observations constrain those predictions; and the resulting constraints can then be used to guide the construction of the underlying quantum-gravity theory.

Current Research

My research lies precisely at this interface. In particular, I study cosmological physics emerging from Group Field Theories, a class of non-perturbative quantum-gravity models in which spacetime is built from fundamental quantum degrees of freedom associated with elementary building blocks of geometry (see here for more). From these microscopic theories, I derive effective descriptions of cosmological dynamics and identify possible observational signatures—for example, mechanisms for early- or late-time cosmic acceleration. I then confront these models with cosmological observations. The aim is therefore not only to ask what quantum gravity might predict for the Universe, but also to use the Universe itself to constrain quantum gravity and help determine which microscopic models can describe our world.

Selected work

Related publications