In 2002, Leonard Susskind co-authored a paper in the Journal of High Energy Physics titled "Disturbing Implications of a Cosmological Constant". A recent New York Times article http://www.nytimes.com/2008/01/15/science/15brain.html) credited this paper with helping to set off a debate about the concept known as "Boltzmann brains": free-floating conscious entities arising from random fluctuations in energy. According to the Times article, the Boltzmann brain hypothesis "could be the weirdest and most embarrassing prediction in the history of cosmology, if not science. If true, it would mean that you yourself reading this article are more likely to be some momentary fluctuation in a field of matter and energy out in space than a person with a real past born through billions of years of evolution in an orderly star-spangled cosmos. Your memories and the world you think you see around you are illusions." In this talk, Professor Susskind, a who is also one of the fathers of string theory, will discuss the concept of Boltzmann brains and their role in contemporary physics.