All the information we will ever obtain from the early universe is imprinted in the spatial correlations of primordial fluctuations at the hot Big Bang. I will explain how an influx of ideas from various areas of fundamental physics is providing us with new conceptual and practical tools to decode the physics of these primordial fluctuations. A thorough understanding of the fluctuations will give us insight into particle physics at the highest energies and may provide a window into the nature of spacetime itself.

In these lectures I will review the current status of the theory and phenomenology of cosmological correlators — the observable which encodes the statistics of primordial fluctuations.

• I will give a broad overview of inflationary perturbation theory, the current observational status and future prospects for constraining inflation;
• Motivate the EFT perspective on primordial fluctuations, and propose “cosmological collider physics” as a way to probe the UV completion of inflation;
• Explain the various methods to compute cosmological correlators: the in-in formalism, the wavefunction of the universe, and the cosmological bootstrap;
• Give a survey of recent theoretical developments that draw inspiration from the scattering amplitude and conformal field theory literature.