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in apparently senseless behavior. She made him so greedy that he destroyed his own habitat against all reason—all this with the aim of driving him into outer space. When Earth was dying, Man had just managed to jump off to other planets and their moons. Instead of learning from old mistakes—something he never did—Man once again bit down tightly on the outermost tip of a blade of grass: Again he destroyed his now extremely meager biotope and at last had to settle other star systems, then the whole galaxy. Here, Man, lacking other energy sources, learned the cultivation and manipulation of black holes. Thus he came to influence the universe itself and push it, as the last blade of grass, to its collapse and the renewed quantum bath for a resurrected Quman.

Was all this done with foresight, with Man as plaything of a more intelligent life-form? Quman does not follow any plan, any more than did the lancet liver fluke. She settles in the universe and accepts its every turn and swing. Worries she never has, for well she knows that all happens as is writ—in the wave function of the universe.

10. THEORY OF EVERYTHING?

PHYSICS AND HUBRIS

For if he once, by chance, uttered the most perfect thought, he would not know so himself. For only delusion is given to all.

—XENOPHANES OF KOLOPHON, Fragment

In the preceding chapter our topic was the status of unique solutions of a given theory and its laws. A whole other question is that of the uniqueness of the laws themselves. Since a unique theory would have to describe all that is observable in the world, it is often termed the “theory of everything.”

PRINCIPLES:

SCIENCE FOUNDATION

Strictly speaking, there is no “presuppositionless” knowledge; the thought of such a thing is unthinkable, paralogical: A philosophy, a “faith” always has to be there first, for knowledge to win from it a direction, a meaning, a limit, a method, a right to exist.

—FRIEDRICH NIETZSCHE, On the Genealogy of Morality

The question of the uniqueness of a theory is of a very different quality from that of the uniqueness of solutions within a theory. For a set of equations, it may be difficult to decide about the uniqueness of its solutions, but the decision is based on a clear mathematical procedure. Physically, a unique solution, if it exists, has irrevocable meaning by a comparison of the properties it implies with observations. Whether a mathematically unique solution is also physically relevant can thus be tested in principle. But how does one define the uniqueness of a theory, and how would one perform physical tests to confirm the relevance of its uniqueness? That such questions have now come to be asked in physics is another sign of its immense progress, realized in large part thanks to quantum theories of gravity, in particular string theory.

In all aspects of uniqueness of a whole theory there is always a degree of arbitrariness. Constructions of theories most often start from physically motivated and general principles that one would like to see incorporated. General relativity, for instance, makes use of principles realized so successfully in special relativity, and tries to extend them to the gravitational force. General relativity is not the only possibility for accomplishing this; thus the theory is not unique in this sense. But among all comparable theories, it is the most successful in its agreement with observations, the most elegant in comparison to theories of similar success; it is therefore concretely elected by experiments, not by a purely mathematical uniqueness proof. Still, the use of the term “elegance”—a high degree of mathematical economy, for instance, in the length of resulting equations—already indicates that willfulness may enter the decision.

When desired principles become strong and precise enough, a mathematical treatment of the uniqueness question can come into reach. How, then, does one arrive at those principles, strong enough to put fantasy in a straitjacket? Since theoretical physics, like all science, grows historically, principles initially