Nima Arkani-Hamed

Our current description of the basic interactions in nature, based on the standard model of particle physics and general relativity, is in spectacular agreement with all known experiments. However, it is almost certainly fundamentally incomplete. In addition to purely theoretical difficulties associated with constructing a sensible quantum-mechanical theory of gravity, two striking experimental clues suggest that something is amiss in our current understanding of nature. The extreme weakness of gravity relative to the other forces, as well as the extraordinary flatness of our observable universe, appear to require absurdly finely tuned choices for the parameters of the theory. It is highly implausible that nature works this way. Instead, we expect that new physical principles will be revealed that address these puzzles, known as the “hierarchy problem” and the “cosmological constant problem”. Fortuitously, these mysteries are associated with length scales – the electroweak scale and the Hubble scale – which will be probed experimentally in the near future with particle accelerators and cosmological observations. Therefore theories which address these puzzles are likely to have experimental consequences that will be checked in the near future.

Nima Arkani-Hamed’s research in theoretical physics is driven by attempting to address these mysteries. Much of his work has centred around addressing the hierarchy problem. Together with Savas Dimopoulos and Gia Dvali, he suggested that the extreme weakness of gravity can be attributed to the existence of large extra dimensions of space, perhaps as large as 100 microns in size, with the scale of quantum gravity lowered to the electroweak scale. This opens up the possibility that quantum gravitational effects can be probed at accelerators and even in table-top experiments. More recently, in an orthogonal direction, together with Andy Cohen and Howard Georgi he has constructed models where (non-gravitational) extra dimensions are generated dynamically from purely four-dimensional models. This has also led to new approaches to the hierarchy problem. The cosmological constant problem is far thornier, and remains a deep conceptual problem in physics. Arkani-Hamed plans to continue exploring possible avenues of attack on this problem.