The First GLAST Symposium

Public Lecture by Andrei Linde

"The Origin and Fate of the Universe"

For a long time scientists believed that our universe was born as an expanding spherically symmetric ball of fire. If the universe expands fast enough, it will expand forever, whereas if its expansion is slow, it will collapse and disappear. This scenario dramatically changed during the last 25 years. Now we think that initially the universe was rapidly inflating, being in an unstable energetic vacuum-like state. It became hot only later, when this vacuum-like state decayed. Quantum fluctuations produced during inflation are responsible for galaxy formation. In some places, these quantum fluctuations are so large that they can produce new rapidly expanding parts of the universe. This process transforms the universe into a huge fractal consisting of many exponentially large parts with different laws of low-energy physics operating in each of them. This picture became even more unusual lately, when string theory predicted that the total number of different laws of low-energy physics operating in different parts of the universe can also be exponentially large. According to string theory, each part of the cosmic fractal may eventually collapse into a huge black hole, or become 10 dimensional. However, the universe as a whole is immortal.