Cosmologists at Perimeter Institute seek to help pin down the constituents and history of our universe, and the rules governing its origin and evolution. Many of the most interesting clues about physics beyond the standard model (e.g., dark matter, dark energy, the matter/anti-matter asymmetry, and the spectrum of primordial density perturbations], come from cosmological observations, and cosmological observations are often the best way to test or constrain a proposed modification of the laws of nature, since such observations can probe length scales, time scales, and energy scales that are beyond the reach of terrestrial laboratories.
Newton’s inferences from phenomena realize an ideal of
empirical success that’s richer than prediction. To realize Newton’s richer
conception of empirical success a theory needs to do more than to accurately
predict the phenomena it purports to explain: in addition it needs to have the
phenomena accurately measure parameters of the theory. Newton’s method aims to
turn theoretical questions into ones which can be empirically answered by
measurements from phenomena.
Propositions inferred from phenomena are provisionally
accepted as guides to further research.
Newton’s ideal of empirical success as agreeing
measurements from diverse phenomena is appealed to in support of the radical
inference to dark energy in cosmology today. Robert Kirshner (two of his PhDs
share one half of 2011’s Nobel Prize in physics) gave an account of the role of
cosmic microwave background measurements, to back up the supernova measurements
and measurements from galaxy clustering in supporting the transition of dark
energy from a wild hypothesis into an accepted background assumption that
guides further research in cosmology today. This illustrates a feature of
agreeing measurements from diverse phenomena that is especially important for
turning data into evidence. To the extent that the sources of systematic error
of the different measurements can be regarded as independent, their agreement
contributes additional support for counting them as accurate rather than as
mere artifacts of systematic error.
In the last few years there has been a burst of
progress in the field of massive gravity. The construction of consistent
theories in which the graviton has a small mass has in turn led to the
development a new family of compelling, consistent low-energy modifications of
General Relativity. These theories improve our understanding of the
interplay between gravity and particle physics and provide new approaches to
solving the cosmological constant problem. In this talk I will review
these recent developments. I will discuss the search among these new
theories for a symmetry that has the potential to address the cosmological
constant problem.
Gamma Rays at 130 GeV and How They Might Come from Dark
Matter"
I'll discuss the exciting (but somewhat controversial)
new discovery of a sharp gamma ray feature at 130 GeV from near the galactic
center and review some other evidence that might link it to annihilation of
dark matter. I will then explain the challenges in understanding how dark
matter might produce this signal and explain a model or two that overcome these
difficulties.