The Cosmic Landscape: String Theory and the Illusion of Intelligent Design [Englisch] [Taschenbuch]

Unlike the physicists who wrote the first two reviews, I don't know much 'bout string theory. Which is why I turn to books like this, or Greene's _The Elegant Universe_. Let me try to explain what this book is trying to do, and how, for one proverbial intelligent layman, it stacks up.

Susskind is a man with a mission. What he's describing here is not settled science, but his own view of the direction fundamental physics should be trying to go. In order to describe that properly, of course, he has to explain a good deal of settled physics along the way. He does this engagingly and fairly clearly, though he doesn't have the truly remarkable expository gifts of Brian Greene, and I strongly recommend that anyone who wants to tackle this book should read _Elegant Universe_ first.

The book has two tightly intertwined main theses. The first has to do with the Anthropic Principle: the observation that a large number of physical constants are required to fall within a surprisingly narrow range of values, in order for the apparatus of biology ever to appear. Slight tweaks to any of them would make galaxies, stars, atoms, chemical elements heavier than helium, to say nothing of carbon based life forms, impossible. Susskind's thesis here is that the AP is neither, as many theists would like to claim, evidence for a Designer who tailored the universe to make us possible; nor, as secular physicists would like to claim, an uninteresting tautology requiring no explanation. Rather, its explanation is to be found in the last decades' developments in string theory.

His second thesis is that these developments - especially the way in which string theory, which was originally hoped could prove mathematically that the various physical constants could have only one uniquely determined set of values, turned out to be a family of five, then many, then mind bogglingly many, distinct theories - are not the intellectual catastrophe some have felt them to be. Rather they are an argument in favor of the truth of string theory, because the innumerable variations in the laws of physics permitted by the various string theories provides a naturalistic explanation for the Anthropic Principle. To wit: cosmic inflation creates innumerable new universes all the time, each with its own set of physical constants, and it is not surprising that some of them should have laws (and in particular a value for Einstein's cosmological constant, which is more extremely constrained than any of the others) which permit life to arise. The collection of all these possible universes, by analogy with the "fitness landscapes" of evolutionary theory in biology, is what Susskind designates as "the cosmic landscape" of the title.

There are a lot of problems with this point of view. Susskind considers them, and argues enthusiastically, subtly and fairly that none of them is a show stopper. In the end, I felt he failed to close the sale. Until someone solves what he calls the "measure problem", the whole scheme is dead in the water. Further, we are never given a positive reason to believe in the truth of string theory, other than the fact that no other consistent theory unifying gravity and quantum mechanics has surfaced yet.

In his final chapter, Susskind tries to summarize the disparate attitudes of a dozen major living theorists toward this emerging Landscape picture. The two most telling criticisms come from physicist David Gross. The book gives them a pretty fair hearing , and doesn't claim to dispose of them.First, if we adopt the idea that the physical constants have randomly created values, the enterprise of trying to explain why they have the particular values they do comes to a dead halt - perhaps prematurely. "Quantum fluctuations did it" puts the kibosh on further inquiry as surely as "God did it" would. Second, we don't really know how wide a range of physical constants could produce life and intelligence in *some* form.

Those who are looking for a primer on string theory, or on the latest truths that scientists have learned and agreed on, won't find it here. But if you are interested in the Anthropic Principle, or in the ferment of controversies at the edge of the presently knowable, you won't have to agree with Susskind to take delight, as I did, in colorfully articulated, intriguing, and frequently illuminating read.

Is this book just what I wanted? Well, what I think I really wanted was for Einstein to return to us today and write a book on the philosophy of modern physics based on today's understanding of things. Yes, that would have been just great! But Einstein is dead. Luckily, of course, there are some excellent physicists around, such as the author of this book.

This book, written by an eminent String Theorist, has some fine explanations for the layman of some topics in modern physics, including String Theory. But the most interesting part is advertised in the title, namely the nature of the cosmic landscape.

The cosmic landscape refers to the mathematical space which has as its elements the values of the "fields" that constitute the physical laws and constants which apply to a particular "universe" (with a small u) or "pocket universe" if one prefers that term. The idea is that there may be many possible sets of physical laws and constants. The more we discover about physics, the more it seems that there are plenty of possible universes. But do they really exist? That is, is the landscape populated by more than our known universe? Is it heavily populated? The author argues that it is. And that certainly makes sense to me.

We're told about the anthropic principle. At its simplest, this principle merely states that we have to live in a universe that permits intelligent life. That's not very profound. But this principle also suggests that there is indeed a landscape of possible universes, and it encourages us to verify that only a very small fraction of them would permit the kind of complexity required for intelligent life. And in fact, Susskind gives us a good example of this. It turns out that the Cosmological Constant (which causes a universal repulsive force, sort of the opposite of gravity) we observe is about 120 orders of magnitude less than an unsophisticated theory might predict. That leaves us with a very tiny number to explain, a number which is fundamental to the laws of our universe. Well, sure enough, there appears to be an anthropic reason. Susskind tells us that Steven Weinberg calculated that a constant even ten times bigger would result in enough repulsion so that the clumpiness of the early universe would have been reduced so much that no galaxies, stars, or planets would have formed. Similarly, a large cosmological constant with the opposite sign would have caused our early universe to collapse.

Given that there may be a large multiplicity of actual universes, how do they originate? Since we appear to be in a rather unusual universe, it is tempting to hypothesize that there's some sort of selection principle at work. But what? We get into questions about a possible evolution of universes. But this could be quite different than evolution in biology. Are there incremental changes between generations of universes, and if so, how? Susskind doubts that changes are incremental. Are there universes that produce large numbers of other universes, given that there are no obvious selection benefits to having fewer offspring? As Susskind says, we see no mechanism to cause competition for resources. Are we in a produced universe, a producing universe, or both? If our universe is a producer, do miscellaneous black holes each produce new universes? Well, according to Susskind, they don't: the production mechanism he suspects is dominant is the cloning of space due to the metastability of the vacuum.

I think it helps to remind ourselves that if there is a large system of pretty much random entitites, that system will be dominated by the biggest ones. If time exists, that system will soon be dominated by not just the biggest, but the most stable and longest-lived ones. And those objects that produce, get produced, or are reproducing (or even better, reproducing in a manner than permits improvements) have a huge advantage. That applies to the Earth's biosphere, and presumably it applies to Reality as a whole.

Susskind discusses the "many-worlds" interpretation of quantum mechanics. In this version, when there is a random choice of polarizations for a particle (or a random choice of which slit a photon traveled through), both possibilities actually occur, but in different aspects of reality! That works mathematically, although it does produce a truly huge number of alternate realities. Susskind does say that this is a little like the huge number of alternate realities of the cosmic landscape. But there is a difference which he admits. The many-worlds alternatives all have the same physical laws, while the cosmic landscape does not.

The book includes a very good discussion of the question about possible information loss in a black hole. Stephen Hawking used to argue that such an information loss actually occurs. Susskind and `t Hooft argued that information has to be conserved, and that it must somehow be stored outside the black hole, and Hawking now has conceded this point. And we also learn about black hole complimentarity, which helps explain all this by making it clear that information has no definite location in space.

I truly enjoyed this book, and I strongly recommend it.

I a bit mystified as to why so many book reviews center around God. This is a book about physics, about using the scientific method to find out how our universe works. Indeed, it even discusses our latest tentative views about many possible universes (an infinite number of them?) might work.

This book does touch on religion at one major point. Most traditional theists, including Jews, Christians and Muslims, assume that this is the only possible universe, created by God. Modern day science - which physicists fully admit is incomplete - shows that our particular universe has a number of constants, a change of which would likely make life as we know it impossible. This has been seized upon by theists as proof of God's existence and creation of the universe. Unfortunately, this is both bad science and bad theology. I don't have time to fully explain why, but I can summarize the problem: It is a "God of the Gaps" argument, which makes God smaller and more inconsequential with every subsequent discovery.

As for the actual physics content of the book, it is great. It is not meant to focus on string theory alone (for that see "The Elegant Universe" by Brian Greene), but it does discuss string theory in some detail, with useful diagrams. Susskind also discusses cosmology, branes, M-theory and other related ideas.