The cosmic microwave background (CMB) is our most direct cosmological observable, encoding critical information about the evolution and development of the universe. The Wilkinson Microwave Anisotropy Probe (WMAP) has measured the angular power spectrum of the CMB temperature and temperature-polarization power spectra with unprecedented accuracy from its first year in flight. These recent observations along with developments in supernovae and galaxy surveys are generating critical challenges for theoretical physics, producing fundamental, intriguing questions in particle physics, cosmology and astrophysics that are as yet unresolved. We discuss in this seminar how the theoretical picture of the nature of dark matter and dark energy, and the origins of the universe, is being guided and modified by observations.
Perimeter Institute for Theoretical Physics
I explain what physicists mean when they say that space and time may be
relational and discuss the extent to which different of the contemporary
attempts at quantum gravity satisfy this criteria. I then discuss how
the current debates between advocates of background dependent and
background independent theories may be seen in the light of the
historical debate in philosophy between advocates of absolute and
relational notions of space and time.