Chris_Impey

THE LANDSCAPE

As the new century dawns we are at a watershed, a time that is likely to forever change our understanding of the universe. Something is happening that is much more than the discovery of new facts or new equations. Our entire outlook, our framework for thinking, and the whole epistemology of physics and cosmology are undergoing upheaval.

The narrow 20th century paradigm of a single universe, about ten billion years old and ten billion light years across, with a unique set of physical laws, is giving way to something much bigger and pregnant with new possibilities. Gradually physicists and cosmologists are coming to see our ten billion light years as an infinitesimal pocket of a stupendous megaverse. At the same time theoretical physicists are proposing theories which demote our ordinary laws of nature to a tiny corner of a gigantic landscape of mathematical possibilities. This landscape of possibilities is a mathematical space representing all of the possible environments that theory allows. Each possible environment has its own laws of physics, its own elementary particles and constants of nature. Some environments are similar to our own corner of the landscape but slightly different. They may have electrons, quarks and all the usual particles, but with gravity a billion times stronger than ours. Others have gravity like ours but electrons that are heavier than atomic nuclei. Still others may resemble our world except for a violent repulsive force (called the cosmological constant) that tears apart atoms, molecules and even galaxies. Not even the three dimensions of space are sacred; Regions of the landscape describe worlds of four, five, six and even more dimensions.

The diversity of the landscape is paralleled by a corresponding diversity in ordinary space. Inflationary cosmology, which is our best theory of the universe, is leading us, sometimes unwillingly, to a concept of a megaverse, filled with a prodigious number of what Alan Guth calls pocket universes. Some pockets are microscopically small and never get big. Others are big like ours but totally empty. And each lies in its own little valley of the landscape. The old 20th century question "what can you find in the universe?" is giving way to "what can you not find?"