The Dark Side

Chapter 6 deals with the remaining mysteries in cosmology—dark matter, dark energy, and inflationary expansion—and the experiments aimed at solving them. It reviews the evidence for dark matter, and experiments to detect the microscopic particles proposed as its constituents: weakly interacting massive particles and invisible axions. Contrasts are drawn between the failure to understand the scale of dark energy theoretically and the ambitious new survey telescopes, such as the Large Synoptic Survey Telescope (or LSST), that aim to constrain its equation of state. The theoretical concepts and possible experimental signatures of cosmic inflation are described. Searches for possible imprints from primordial inflation-induced gravitational waves on the polarization of the cosmic microwave background (CMB polarization) are discussed in the context of the pioneering first detection by the Laser Interferometer Gravitational-Wave Observatory (or LIGO) of gravitational waves from distant black-hole mergers. Philosophical questions regarding the falsifiability of inflation are raised.