The Cosmic Landscape
By Leonard Susskind
It is gradually becoming accepted, by many theoretical physicists, that the Laws of Physics may not only be variable but are almost always deadly. In a sense the laws of nature are like East Coast weather: tremendously variable, almost always awful, but on rare occasions, perfectly lovely. Like deadly storms, bubbles of extremely hostile environments may propagate through the universe causing destruction in their wake. But in rare and special places, we find Laws of Physics perfectly suited to our existence. In order to understand how it came to pass that we find ourselves in such an exceptional place, we have to understand the reasons for the variability of the Laws of Physics, just how large the range of possibilities is, and how a region of space can suddenly change its character from lethal to benign. This brings us to the central concern of this book, the Landscape.
As I have said, the Landscape is a space of possibilities. It has geography and topography with hills, valleys, flat plains, deep trenches, mountains, and mountain passes. But unlike an ordinary landscape, it isn't three-dimensional. The Landscape has hundreds, maybe thousands, of dimensions. Almost all of the Landscape describes environments that are lethal to life, but a few of the low-lying valleys are habitable. The Landscape is not a real place. It doesn't exist as a real location on the earth or anywhere else. It doesn't exist in space and time at all. It's a mathematical construct, each of whose points represents a possible environment or, as a physicist would say, a possible vacuum .
In common usage the word vacuum means empty space, space from which all air, water vapor, and other material has been sucked out. That's also what it means to an experimental physicist who deals in vacuum tubes, vacuum chambers, and vacuum pumps. But to a theoretical physicist, the term vacuum connotes much more. It means a kind of background in which the rest of physics takes place. The vacuum represents potential for all the things that can happen in that background. It means a list of all the elementary particles as well as the constants of nature that would be revealed by experiments in that vacuum. In short, it means an environment in which the Laws of Physics take a particular form. We say of our vacuum that it can contain electrons, positrons, photons, and the rest of the usual elementary particles. In our vacuum the electron has a mass of .51 Mev 2 , the photon's mass is zero, and the fine structure constant is 0.007297351. Some other vacuum might have electrons with no mass, a photon with mass 10 Mev, and no quarks but forty different kinds of neutrinos and a fine structure constant equal to 15.003571. A different vacuum means different Laws of Physics; each point on the Landscape represents a set of laws that are, most likely, very different from our own but which are, nonetheless, entirely consistent possibilities. The Standard Model is merely one point in the Landscape of possibilities.
And if the Laws of Physics can be different in other vacuums, so can all of science. A world with much lighter electrons but heavier photons would have no atoms. No atoms means no chemistry, no periodic table, no molecules, no acids, no bases, no organic substances, and of course, no biology.
Ultimately the Laws of Physics are variable because they are determined by fields, and fields can vary. Switching on magnetic and electric fields is one way to change the laws, but it is by no means the only way to modify the vacuum, or even the most interesting way. The second half of the twentieth century was a time of discovery of new elementary particles, new forces, and above all, new fields. Einstein's gravitational field was one, but there were many others. Space can be filled with a wide variety of invisible influences that have all sorts of effects on ordinary matter.
Leonard Susskind is one of the pioneers of string theory. He has been the Felix Bloch Professor in theoretical physics at Stanford University since 1978 and is a member of the National Academy of Sciences and the American Academy of Arts and Sciences.
