Guillermo Ballesteros

Institution: CEA

Lab: Institut de Physique Théorique IPhT

Year of Grant: 2015



Nationality: Spanish

Research : Cosmology, Particle

Mobility project

DEFT – Dark energy, non-linearites and effective theories

Did you know that the universe is expanding? Did you know that it expands ever faster as time goes by? As surprising as it might seem, all the galaxies scattered in the universe are being pulled apart. The universe is becoming larger and larger, faster and faster...  And, for all we know, it will never stop doing so.

Cosmologists call “dark energy” the force that produces the acceleration of the universe. It is too weak to be felt at short distances in our daily lives, but on cosmological scales its abundance drives the dynamics of the universe. In fact, the observations made with telescopes on Earth and orbiting around it indicate that about three quarters of the universe are actually composed of dark energy! This discovery, made in 1998, was awarded the Nobel Prize in Physics in 2011.

A constant term in Einstein's equations of General Relativity gives a remarkably simple description of the acceleration of the universe. However, the physical origin of dark energy remains poorly understood and constitutes one the biggest mysteries of fundamental physics. My project studies how to use the upcoming cosmological data to determine if this simple constant is all that hides behind the dark energy.

Academic Background & Research Field

I obtained a PhD in Physics at U. Autónoma de Madrid (Spain) and I have had postdoctoral positions in Italy (U. di Padova), Switzerlad (U. de Genève) and Germany (U. Heidelberg). As a theoretical cosmologist I am interested in the dynamics of the universe as a whole, its origin and evolution. I also work on specific open questions in the realm of the  microcosm of particle physics, which are intimately connected to the vast scales of the universe.

Publications and awards


ResearchGate profile: