The Cosmic Landscape (54 page)

There is a third context, after physics and biology, where the same two ingredients—a Landscape and a megaverse—are essential to our existence. Planets and other astronomical bodies come in a very large number of possible designs. Hot stars, cold asteroids, giant dust clouds are just a few. Once again the Landscape of possibilities is extremely rich. Just the variation in distance from the parent star gives great diversity to planets. As for the mechanism that turns possibilities into actualities, the Big Bang, and the subsequent clumping by means of gravity, created 10
²²
planets within the observable part of our universe alone.

In each of these cases the answers to the questions of our own existence are the same. There are many creatures/ planets/ pocket universes and many possible designs. The numbers are so big that, statistically, some of them will be intelligent or conducive to intelligent life. Most creatures/ universes/astro-bodies are dead ends from this point of view. We are just the lucky few. That is the meaning of the Anthropic Principle. There is no magic, no supernatural designer: just the laws of very large numbers.

My friend Steve Shenker, who is one of the wisest physicists I know, likes to reduce things to slogans. He feels that unless a big important idea can be encapsulated in a short phrase or two, its essence has not really been grasped. I think he is right. Here are some examples from the past.

From Newtonian mechanics:

Einstein and special relativity:

and

Einstein and general relativity:

Quantum mechanics:

Cosmology:

The best scientific slogans I know don’t come from physics or cosmology but from the theory of evolution:

If this book were to be reduced to a single thought, it would be that the grand organizing principle of both biology and cosmology is:

There is one frustrating difference between the biological or planetary mechanism and the Eternal Inflation that populates the Landscape. In the two former cases, we can directly observe the results of the prolific mechanism of creation. We see the diversity of bio-forms all around us. Astronomical objects are a little harder to observe, but even without telescopes we can see planets, moons, and stars. But the huge sea of pocket universes created by Eternal Inflation is hidden behind our cosmic event horizon. The problem is, of course, Einstein’s speed limit. If we could exceed the speed of light, there would be no problem traveling to distant pocket universes and back. We could navigate the entire megaverse. But, alas, punching a wormhole through space to a distant pocket universe is a fantasy that violates fundamental principles of physics. The existence of other pocket universes remains, and will remain, a conjecture, but a conjecture with explanatory power.

If the ideas that I have explained turn out to be correct, then our view of the world is about to expand far beyond the current provincial boundaries to something much grander: bigger in space, bigger in time, and bigger in possibilities. If correct, how long will it take for the paradigm to shift? Like the proverbial forest, paradigm shifts are easiest seen from a distance. While the ground is shifting, things are often too confusing, the waters too muddy, to see clearly, even a few years ahead. During those times it is almost impossible for outsiders to know whose ideas are serious and whose are fringe speculations. It’s even hard for the insiders to know. My main purpose in writing this book is not primarily to convince the reader of my own point of view; scientific arguments are best fought on the pages of technical journals and the blackboards of seminar rooms. My purpose is to explain the struggle of ideas that is about to take front-and-center place in the mainstream of science so that ordinary readers can follow the ideas as they unfold and experience the drama and excitement that I feel.

The history of scientific ideas has always fascinated me. I am as interested in how the great masters came to their insights as I am in the ideas themselves. But the great masters are not all dead. The present—right now—is a marvelous time to watch the Weinbergs, Wittens, ’t Hoofts, Polchinskis, Maldacenas, Lindes, Vilenkins… as they struggle toward a new paradigm. As far as I can make out, here is what my most distinguished colleagues think. I will address the physicists first and then the cosmologists.

Steven Weinberg, more than any other physicist, is responsible for the discovery of the Standard Model of particle physics. Steve is not a rash man and is likely to weigh the evidence at least as carefully as anyone. His writings and lectures clearly imply that he sees the evidence, if not as definitive, then as strongly suggesting that some version of the Anthropic Principle may play a role in determining the Laws of Physics. But his own writings express regret—regret for a “paradigm lost.” In his 1992 book,
Dreams of a Final Theory,
he writes:

Thus if such a cosmological constant is confirmed by observation, it will be reasonable to infer that our own existence plays an important role in explaining why the universe is the way it is.

For what it is worth, I hope that this is not the case. As a theoretical physicist, I would like to see us able to make precise predictions, not vague statements that certain constants have to be in a range that is more or less favorable to life. I hope that string theory really will provide a basis for a final theory and that this theory will turn out to have enough predictive power to be able to prescribe values for all the constants of nature including the cosmological constant. We shall see.

Weinberg wrote these words during the afterglow of the discoveries of Heterotic String Theory and Calabi Yau compactification. But he now knows that String Theory will not be the hoped-for alternative to the Anthropic Principle.

Ed Witten is one of the greatest mathematicians in the world and a Pythagorean at heart. He has built his career around the elegant and beautiful mathematics that came out of String Theory. His ability to plumb the mathematical depths of the subject is breathtaking. Not surprisingly he is one of the most reluctant of my colleagues to give up the search for a magic, mathematical silver bullet, a bullet that will pick out a unique, consistent set of physical laws for elementary particles. If such a bullet exists, Witten has the depth and power to find it. But he has been looking for a long time with no success. Although he has done more than anyone to create the tools that are needed to explore the Landscape, I don’t suppose he is at all happy about the current direction that the theory is taking.