The Cosmic Landscape: String Theory and the Illusion of Intelligent Design by Leonard Susskind (Little, Brown, and Company 2006) [B&T Books] QB981.S886 2005.

Leibniz famously concluded that this is the best of all possible worlds. Leonard Susskind (Father of String Theory, Bloch Professor of Theoretical Physics at Stanford, and grand nemesis of Stephen Hawking) would at least say that if not the best, this world is right up there with the best. From there the two part company in an infinity of right-angles. To begin, Leibniz would content that only one of the possible worlds (ours, aka "the best") is actually populated with actual concrete things. Susskind, on the other hand, will admit on the order of 10⁵⁰⁰ actual worlds and perhaps infinitely more (depending on where the inflation of space comes into play). For another, Leibniz contended that this world is the best because it was created by God, who--to put it very loosely--owed it to himself to create nothing but the best. Susskind, however, insists that with 10⁵⁰⁰ combinations, the physical constants required to maintain a universe that could support intelligent life were bound to arise, but I get ahead of myself. Besides, Susskind doesn't give Leibniz a single mention.

The Cosmic Landscape is Susskind's attempt to explain what string theory is, its history, its importance, and why his view is the most sensible. Here he joins company with Brian Greene of An Elegant Universe fame. Both try to explain general relativity, quantum mechanics and string theory to those of us for whom physics is an alien discipline and higher mathematics is a foreign language. Being among the benighted, I can't really say how accurately Susskind describes these theories, only that I feel more confident in the delusion that I have the gist of what string theory is all about than I had been.

There seem to be two factors make string theory so important to physicists today. First is the notorious fact that the two greatest physical theories of the twentieth century (general relativity and quantum mechanics) need each other to get a full sense of the universe but neither is compatible with the other. This acute embarrassment and has led to the quest of a "theory of everything." The other driving force is that the universe if filled with constants (such as the masses of elementary particles and the strength of certain forces) and these constants have most unintuitive values. Physicists know what these values are to a fair degree of accuracy, but there doesn't seem to be any reason why they should be what they are, other than the fact that the universe (or at least anything remotely like our universe) wouldn't exist without them. Such considerations have lead to something called the Anthropic Principle. The Principle states that the universe is the way it is in order that it may be observed (namely by us). Understandably, such notions drive most scientists nuts, but what are the options: (1) embrace the Anthropic Principle and admit that the universe is fine tuned for a purpose (2) play bait-and-switch by redefining the Anthropic Principle to be undeniably true for everyone, to the point of triviality, (3) show that the fine tuning that makes the universe possible is necessitated by more fundamental laws or (4) show that the fine tuning is the of dumb luck?

Early on in string theory, option (3) looked most promising. One can see this idea put forth by Brian Greene in An Elegant Universe. The embarrassment here was not the ten or eleven dimensions required to make everything work out or the mathematics--which by all accounts is devilish. No, apparently the problem with string theory was that while one could derive a universe with all the weird constants this one has, one can't exclude universes with different constants. The number of possibilities--for reasons you will just have to read about--is 10⁵⁰⁰. To make matters worse, there is a maxim in quantum mechanics that unless something can't happen it does. Consequently, there aren't 10⁵⁰⁰ possible universes, there are 10⁵⁰⁰ actual universes. So, although he protest to the contrary, Susskind has elected for dumb luck, but not just ordinary dumb luck. What was an embarrassment (10⁵⁰⁰ universes running about), is now an asset. With so many universes, at least one is bound wind up being "fine tuned." In fact, just so we don't miss the point, Susskind compares the universe not so much to Paley's watch but Rube Goldberg's machines (such as the game "Mouse Trap"). If you don't understand the reference, Susskind has provided an illustration. The choice is deliberate and provocative. One does not have to be a theist to appreciate elegance and simplicity. Scientists since the time of Aristotle (and before) have seen some connection between truth and beauty. Susskind seems to chalk all such sentiment to aesthetics, but I suspect there is something more fundamental to why we are drawn to simplicity. If nature is fundamentally diverse, that is to say that there are at least two aspect of existence that have nothing in common, then there is no basis on which they can interact. It is that commonality, that universal of universality on which simplicity derives and from it elegance.

The myriad of universes (which he calls a megaverse, though I have more often heard it called a multiverse) rests in a Landscape. The Landscape is not actual, per se, but is instead the possible values within the vacuum (also known as dark energy). One might compare it (and here is where the imagery of a Landscape works) as peaks and valleys. Stable universes rest in valleys, less stable ones are on peaks where the vacuum eneries are more liable to change. I may have simplyy missed the point, but shouldn't there be some explanation to why the peaks and valleys that obtain with their given vacuum levels do so and not some others? The number 10⁵⁰⁰ impressive, but it surely does not cover all possible values, let alone whether these values exist as peaks, valleys or gentle slopes. Let us assume a megaverse, will future physicists really settle on random values? Since Susskind was not satisfied with the constants of the [this?] universe being a brute fact, I cannot see future physicsts stopping with a megaverse.

Susskind's theory is not without its problems. Most of which he deals with quite forthrightly. For instance, his theory depends (for reasons you will just have to read about) on space being negatively curved ever-so-slightly. As best as we can tell, it is not. However, just as the positive curve of the earth isn't apparent to the casual observer the curve of space may not be apparent even with our best attempts. This would especially true given the size of the universe and if (as Susskind states) the curve is very slight. More broadly, string theory depends on there being particles predicted by the Standard Model, but not yet observed. The Large Hadron Collider under development by CERN should be able to confirm the existence of such particles. If not, the universe is just a bit weirder than anyone has imagined. Physicists are use to this.

So, let us assume that this universe is as physicists describe it; that all the theoretical particles are found (likely enough) and that space does turn out to be negatively curved. Has Susskind made his case? For better or worse no, he hasn't and worse he avoids the most telling criticism by belittling it as so much philosophical ideology that is always one scientific discovery behind the times. That philosophical ideology is known as falsification--the doctrine that any scientific theory worth its salt must be able to make predictions that are (in principle) subject to disproof. For instance, Aristotle stated that elements find their natural level. This explained why solids sink and fire rises. A consequence of these theory was that heavier solids would find their level faster than lighters one. It made a testable prediction. One could never prove Aristotle right (after all if heavier solids did fall faster, there might be an alternative explanation). The best one could hope for was confirmation. The more a theory is confirmed, the stronger it becomes. Disproving (or falsifying) a theory is possible, at least in principle. Galileo falsified Aristotle's theory when he dropped to object of the same size but different weights from the Tower of Pisa. Unfortunately, Susskind confuses falsification with the doctrine of verification. Verification was something developed (and abandoned) by the Logical Positivists in the mid-twentieth century. Scientist and Philosophers of Science often talk past each other, ignoring the subtleties of the other, and it would appear that Susskind has done just that. It is particularly egregiously that he ignores the fact that the doctrine of falsification has always meant falsification in principle, even when he would admit that qualification.

However, even if theories are falsifiable in principle, one may never be able to do so in practice. The smaller the particle, the more constricted the force, the more energy it takes to parse them out. Big science may just be too expensive, which will leave us with the theoretical physicists. Susskind thinks that this may be enough, but I am not at convinced. In the eleventh century, physics seemed to have about come to its end. The position physics may find itself would be akin to where it was in the High Middle Ages. Physics then was highly unified. The thinkers of that time (for instance Aquinas, Averroes, and Maimonides) more or less agreed on how things moved, how they were composed, and how they arose and were maintained. The theories of the day were utterly consistent and could easily be confirmed (though not proven) by such observations as were available. Much of this physics--the physics of Aristotle--has, however, been falsified. A combination of technical break-throughs and original thinking started to break-down the old order. What would happen, however, if we have come to a point where physical theories are falsifiable in principle, but we will never have the resources to test the predictions made by such theories. Barring some experimental break-through, we may well come to the same point in the near future. Even if the Landscape and the megaverse are the only things we consistently image, existence may be weirder still.

Jimm Wetherbee

If The Cosmic Landscape looks good, here are some other interesting Baker and Taylor Books. . .

• Paralelle Worlds, by Michio Kaku.
  Call Number:QB981.K134 2004
• A Different Universe, by Robert B. Laughlin.
  Call Number: QC24.5. L38 2005

Updated August 14, 2008