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The World as a Hologram

Professor Raphael Bousso
University of California , Berkeley

Physicists have come to recognize an unexpected, very general relation between Einstein's curved geometry of space and time, and the amount of information required to describe physical matter down to the smallest particles. This "holographic principle" is set to play a crucial role as we tackle the profound problem of unifying quantum mechanics with gravity. The session begins with the discussion of some everyday ways in which matter contains information, and how we can describe the state of matter by listing that information. It will be then explained what we have learned about the information content of black- holes, and how this knowledge has allowed us a first glimpse at the truly universal limits on information content that have since been discovered. Professor Bousso will emphasize in particular the counterintuitive nature of these limits: they imply that in a sense, the universe is only pretending to have 3 spatial dimensions, like a two-dimensional hologram on a credit card.      

Finding a Home in the Multiverse

Professor Anthony Aguirre
University of California, Santa Cruz

The history of cosmology over the past millennium has been that of an ever-widening view of the universe, from Earth surrounded by planets and "crystal spheres" of stars, to a solar system surrounded by thousands of distant stars, then to millions of stars, then to the realization that these millions comprise but one galaxy of millions in the observable universe. Over the past 20 years, several lines of thought have emerged suggesting that the universe may, in fact, be vastly larger yet -- it may in fact be a "Multiverse" of uncountable regions as large as all that we can observe, yet potentially with very different properties.  

Several lines of reasoning will be discussed -- from quantum mechanics, string theory, and observational and theoretical cosmology -- that both individually and in conjunction lead us to suspect that we may inhabit some sort of multiverse. Also, the following questions will be addressed: How likely are these different scenarios? How do we describe a mulitverse and what is its structure? Are other universes observable? Are multiverse theories testable, and how can they be tested if we only observe one universe?  

Extra Dimensions

Professor John Terning
University of California, Davis

There has been a revolution in our thinking about extra dimensions. A new understanding of the feasibility of localizing four dimensional gauge theories in higher dimensional spacetimes has led to a variety of phenomenologically viable models, and even to the possibility of localizing gravity. Unlike older theories of extra dimensions, much of the focus now is on extra dimensions with sizes on the order of one thousandth of a proton width or larger! Thus, there is a potential for discovery at current and soon-to-be-completed colliders, and in some cases table-top experiments. In addition there are tremendous implications for cosmology. The following topics will be covered:

• Einstein and the Fourth Dimension

• Waves in a Fifth Dimension

• String Theory and Branes

• Experimental Tests of Extra Dimensions

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