During the last three weeks, we were visited by an impressive list of cosmologists trying to make sense of what is driving the present accelerated expansion of the Universe. The return of De Sitter, this is the name of the NORDITA workshop organized by OKC members Fawad Hassan and Ariel Goobar, together with Stefan Hofmann from LMU in Munich.
I asked Ariel Goobar, professor at OKC, and Stefan Sjörs, a PhD student in the Cosmology, Astroparticle Physics and String Theory group, to tell us about the conference.
Stefan For students and other apt minds, the “Return of de Sitter” conference at Nordita started one week earlier with a preparatory school. Already at the prep school the theme for the conference was clear: the course was set for the interplay between observation and theory. I had the honor and privilege to both give and attend lectures at the school, coming from the theory side, and I hope people learned as much from my lectures as I did from others.
Ariel: Recent observations suggest that we are approaching a de Sitter phase, similar to the Inflationary era of the early universe. Thus, we may indeed be experiencing a return of de Sitter, as indicated by the name of the NORDITA workshop.
Stefan:The questions raised during the conference were often refreshingly honest. What are the interesting observations to be made and where should we point our telescopes tomorrow? These questions are very much inspiring for a young novice, with his or her own predictions for cosmology and astrophysics.
Ariel: The tantalizing possibility that gravity is carried by a massive particle was adressed by several speakers, including Greg Gabadadze from New York University, who concluded that such a scenario leads to a prediction about either inhomogeneity or anisotropy of the universe at very large scales, clearly an exciting prospect for observers searching for evidence for deviations from the current vanilla model:lambda-CDM.
The notion that we are experiencing a golden age of precision cosmology was reinforced by Adam Riess, who described his team’s recent estimate of the Hubble constant, now known with 3% accuracy, as well as OKC’s Rahman Amanullah (in the picture as Rahman The Sitter Amanullah) who reviewed the status of the combined analysis of Type Ia supernova distances, cosmic microwave background anisotropies and baryon acoustic oscillations resulting in a 10% measurement of the w, the equation of state parameter of dark energy.
Looking into the future, Berkeley’s Eric Linder explained how several physically motivated dark energy models would naturally lead to a value of w very close to -1, i.e., resembling a cosmological constant, but distinguishable with starting or planned surveys.
The next breakthrough in cosmology may be yet closer: Andreas Albrecht from UC Davis gave an intriguing talk about the de Sitter phase as being an equilibrium state of the universe. His formalism leads to a prediction for global curvature in the universe within the precision range for ESA’s Planck mission, launched almost 2 years ago.
Similarly, Ignatios Antoniadis, head of the CERN theory division, proposed a model of dark energy which may be tested through a potential detection non-Gaussianity in the CMB sky.
Thus, whether de Sitter is indeed back or not, observations may tell before too long!
Stefan:These discussions were often continued after the daily seminars, next to the coffee machine, in front of black boards or over dinner. Also at the conference dinner, a classical Swedish Smörgåsbord at Grand Hotel, the physics discussions continued, though I think it is safe to say that the discussions got a little bit more “philosophical” after a pint of mead at a medieval pub in Gamla Stan, after the conference dinner.
After three weeks of conference one is now pretty much done for, but it is with new inspiration we eagerly return to understanding de Sitter.