Fatter, older and slower (and with a trigger)
The picture of the Universe has changed since the publication of the Planck results last March. One year earlier, the discovery of the Higgs boson had proved the existence of fundamental “scalar fields” – the most likely reason for why the Universe evolved from the Big Bang to what we observe today. At a workshop organized by the CERN Theory Unit, cosmologists and particle physicists discussed common issues and explored new avenues for better collaboration.
Planck enhanced anomalies. Photo: ESA and the Planck collaboration.
“Planck has not been kind to the Universe,” says Daniela Paoletti, a member of the Planck collaboration and a researcher at the Italian National Institute for Astrophysics in Bologna. “We know now that it is fatter because it contains more dark matter than what we had previously calculated; it is also a few hundred thousand years older and is expanding at a slower pace.”
What is the Universe really made of? Why are galaxies distributed the way they are? What did dark energy originate from? What is the role of the Higgs boson in the formation and evolution of the Universe? Will we be able to observe the primordial gravitational waves? These were some of the questions on the table for scientists participating in the “Cosmology and Fundamental Physics with Planck” workshop held at CERN from 17 to 28 June.
The venue might have seemed a bit unusual a few years ago when the two extremes – particle physics that studies the infinitely small using huge accelerators on Earth and cosmology that studies the infinitely large with satellites orbiting at a distance of over one million km from the Earth – were considered almost like different disciplines. “We observe Nature from two different angles and with different instruments but the recent results confirm that we are looking together in the same direction,” says Julien Lesgourgues of CERN’s Theory Unit who is a member of the Planck collaboration and was one of the workshop’s organisers. “The main goal of this initiative is to stimulate interaction between participants. To this end, the programme of talks is light, and several rooms and office space are made available for discussions.”
One of the main discussions concerned the role of the Higgs boson in the evolution of the Universe. The Planck results released last March confirmed that the most likely theory to describe the initial moments of the Universe is a model in which a scalar field – a field whose value is the same in whatever direction we measure it – triggers the very rapid and powerful expansion of the early Universe known as “inflation”. The Bulletin has already discussed the possibility of the Higgs boson – the first fundamental scalar field discovered in Nature – being the inflaton, and a large community of scientists is not new to this question. “The current data doesn’t allow us to figure out whether the Higgs boson and the inflaton are two distinct particles or the same one. But it is certainly compatible with the idea of Higgs inflation,” says Julien Lesgourgues.
The best of Planck’s results might still be to come in 2014 when, with the second data release, scientists will have also explored the polarisation properties of the Cosmic Microwave Background (CMB) radiation, the echo of the Big Bang. “The effects of the primordial gravitational waves, those that were generated during the first moments after the Big Bang, are imprinted in the radiation we observe today, and Planck could be able to detect them,” says Martin Kunz, a cosmologist at the University of Geneva and one of the participants in the workshop.
This intense workshop was an excellent opportunity for scientists from both extremes of the research spectrum to exchange their views and to plan future collaboration. The common enthusiastic feeling they took home with them was nicely expressed by Benjamin D. Wandelt, a researcher at the Institut d'Astrophysique de Paris, who said: “The last twelve months have been very exciting for cosmologists and particle physicists. We are actually experiencing what we were dreaming of when we were at university.”
