Lorentz Center - Non-Linear Structure in the Modified Universe from 14 Jul 2014 through 18 Jul 2014
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    Non-Linear Structure in the Modified Universe
    from 14 Jul 2014 through 18 Jul 2014


Description and aim

The future of cosmology lies in understanding the late time universe. The accelerated expansion happening today is still a mystery. Since gravity is the only force we know that acts on scales as large as the entire universe, it seems obvious to consider modifications of gravity in order to understand the accelerated expansion. Gravity however acts on all cosmological scales, varying from the radius of the entire universe to the size of planets. Modifications that explain the accelerated expansion, could therefore potentially be distinguished from the General theory of Relativity in the history of the growth of structures.

The aim of the workshop was therefore: "Constructing a road map for testing modified gravity through linear and non-linear cosmological structures."



Following the advise of the Lorentz Center, we opted for a programme with more time allocated for discussions than for talks. In the plenary sessions, we chose to let two speakers who represent potentially opposite approaches speak directly after each other, followed by a discussion lead by a third expert. The format proved to be a very successful way to provoke discussion. With renowned scientists as discussion leaders rather than speakers, discussions immediately focussed on fundamental questions.



Prior to the workshop, we stated that the workshop would be a success if N-body simulators learned about the key aspects of modified gravity in late time structure formation, and if gravity theorists learned in which regimes modifications of gravity can matter at all. Given this condition, the workshop was more than a success.

The exchange of knowledge between various experts was tremendous. However, as with all progress in science, the number of questions raised grows faster than the number of questions answered.


Throughout the workshop there were many `aha'-moments, most of them in the category of an extra degree of uncertainty on (or lack of understanding of) one phenomenon or another, about which people had not worried enough. For example, an important step forward is the acknowledgement of the fact that baryonic physics does play a crucial and not well-understood role on the formation of structure, on much larger scales than what many of the participants assumed. Vice versa, modifications of gravity can play significant roles on much smaller scales then assumed, depending on the type of screening, and the possibility of the absence of Birkhoff's theorem.


Participants and acknowledgements

The workshop was attended by 49 participants from 11 countries. Practically each of them thanked the organizers for an exceptionally fruitful workshop, but most of their gratitude must be forwarded to the Lorentz Center, which made the workshop an extremely smooth experience. The organising committee could fully focus on the scientific content of the workshop, and even there, the help from the Lorentz Center with the design of the programme certainly had great positive impact on its success. The workshop received additional support from the “Leiden University Fund” (LUF).



Anne Christine Davis (Cambridge, UK)

Claudia de Rham (Cleveland, USA)

Alessandra Silvestri (Leiden, Netherlands)

Wessel Valkenburg (Leiden, Netherlands)