Professor Bailyn offers a review of what is known so far about the expansion of the universe from observing galaxies, supernovae, and other celestial phenomena. The rate of the expansion of the universe is discussed along with the Big Rip theory and the balance of dark energy and dark matter in the universe over time. The point at which the universe shifts from accelerating to decelerating is examined. Worries related to the brightness of high redshift supernovae and the effects of gravitational lensing are explained.

This lecture introduces an important concept related to the past and future of the universe: the Scale factor, which is a function of time. With reference to a graph whose coordinates are the Scale factor and time, the problem of dark matter is addressed again. Cosmological redshifts are measured to determine the scale of the universe. The discovery of the repulsive, anti-gravitational force of dark energy is explained. The lecture concludes with discussion of Einstein’s biggest mistake: the invention of the cosmological constant to balance gravity.

Professor Bailyn returns to the subject of the expansion of the universe to offer explanations that do not require belief in the Big Bang theory. One alternative is a theory that, in the past, the entire universe was reduced to an “initial singularity,” in which everything was much closer, and therefore denser and hotter. Since the universe is in constant flux, however, it follows that in the future things will drift apart. The Steady State explanation for the expansion of the universe is then explained.

The third and final part of the course begins, consisting of a series of lectures on cosmology. A brief history of how cosmology developed into a scientific subject is offered. The discovery of dark energy, along with dark matter, played a crucial role in the development of cosmology. The lecture then discusses the discovery of spiral nebulae in 1920, as well as the “Great Debate” over what they were. Hubble’s famous redshift diagram is presented as the basis for Hubble’s Constant and Big Bang cosmology.

The lecture begins with a question-and-answer session about black holes. Topics include the extent to which we are sure black holes exist in the center of all galaxies, how massive they are, and how we can observe them. The lecture then turns to strong-field relativity: relativistic effects that are unrelated to Newtonian theory. The possibility of testing predictions of the existence of black holes is discussed in the context of strong-field relativity. One way we might learn about black holes is through observation of the orbit of the companion star in an X-ray binary star system.