In this lecture Prof Susskind discusses the idea of Inflation. Inflation is one of the most important ideas on cosmology. At the root of much we know and suspect of cosmology.

Prof Susskind reviews what the presence of a cosmological constant does in Einstein’s equations. It is basically a term in the energy density parameter that does not dilute as the universe expands. Prof Susskind discusses the FRW Lemaitre equation for energy density. Prof Susskind discusses that in the general case the energy density dilutes upon expansion. We study the case of flat space and the equation for energy density. Prof Susskind discusses the case of matter dominated universe where r was mass energy based, and decreases due to expansion. We also study the early universe where the universe was radiation dominated and energy density was primarily radiation energy. Prof Susskind also discusses the idea of vacuum energy where energy density is constant. He presents the fact that the nature of vacuum energy is that it does not change over time, namely that only in the case of vacuum energy H (the Hubble’s constant) is truly a constant. Prof Susskind discusses the surface of last scattering and the microwave background radiation. Prof Susskind also discusses the primordial fluctuations and the imprinting of them on the microwave background radiation.