OTHER POSSIBLE ARGUMENT STRATEGIES

If the previous arguments do not establish or even give some reason to believe that a TOE exists, what sort would? Various strategies might be tried, some empirical, some a priori.

Empirical strategy 1: (a) Start with a potential TOE (or at least a part of one) and provide some empirical reason to think that the allegedly fundamental objects postulated exist and that the allegedly fundamental laws invoked are true; (b) show how this potential TOE in fact explains a wide variety of phenomena in terms of the laws governing these objects; (c) argue inductively that the allegedly funda­mental objects and laws are genuinely fundamental since no known objects and laws are more fundamental and since the explanations in (b) do not, and do not need to, introduce any more fundamental objects and laws to explain what they do; (d) argue, again inductively, from (a)-(c), that probably “all” other phenomena, known and unknown, can be explained by reference to the objects and laws in question, and require no more fundamental objects and laws to be explained.^[174]

Empirical strategy 2: (i) Start with a non-TOE, appealing to objects, laws, and phenomena that have been discovered and are not claimed to be fundamental; (ii) argue that the partic­ular physical characteristics of these discovered objects, laws, and phenomena constitute some reason to believe that there are underlying objects and laws that can explain the behav­ior of the discovered objects and other phenomena as well; (iii) extend this type of reasoning until objects and laws are inferred from the evidence that explain a large range of phe­nomena, where no more fundamental objects and laws are known or required for the explanations; (iv) proceed induc­tively in the manner of (c) and (d) above to the conclusion that the objects and laws are fundamental and that “all” phe­nomena can be explained by reference to them.

'1 These empirical strategies do not appeal to the history of sci­ence, or to what scientists presuppose, or to the very gen­eral idea that everything interacts with everything else. Both strategies involve the construction of a particular TOE. In the first, we start with a potential TOE and argue that it re­ally is a TOE. In the second, we start with something that is not a TOE and argue to the existence of a particular TOE. Neither task has been accomplished by any of the TOE proponents mentioned. With respect to the first strategy, as noted in section 4, the “fundamental” objects TOE theorists have postulated (now or in the past) have not been shown to be fundamental. And in the case of strings, or Nagel's panpsychic “atoms,” they have not even been shown to exist. Nor (in the case of Nagel and Chalmers) have laws been formulated, or if they have (as with the mechanical philos­ophy), they are either false (as with Newton's law of gravity) or else not shown to be true or to have empirical support (as with string theory). Even if steps (a) and (b) of strategy 1 are somehow accomplished, some empirical reasons are needed in defense of the grand inductive generalizations in (c) and (d).

In the case of the second strategy, (i) and (ii) are familiar moves. (For example, they are employed by Perrin in arguing from the existence of Brownian motion to the existence of molecules that explain such motion and other phenomena as well.^[175]) It is (iii) and (iv)—producing arguments for fun­damentally and for universal explanatory power—that have yet to be accomplished. As in the case of string theory, or molecular theory in the nineteenth century, there are (or were) known phenomena (e.g., dark matter and “arbitrary” constants in the case of string theory, electrical properties of gases for molecular theory) that resist or have resisted ex­planation in terms of the objects and laws postulated. What is also needed is an empirical defense for the idea that these micro-objects and the laws governing them are fundamental (that they themselves have no further explanation) and that they can explain “everything.”

It is not my claim that these defenses are impossible to mount, only that they represent very ambitious programs that have never been carried out successfully in the history of science.

A Priori Strategies: TOE enthusiasts may want to construe the claim that a TOE exists not as empirical but as a priori. One approach is to understand this claim as an a priori meta­physical one about the universe to the effect that the universe must contain fundamental objects subject to fundamental laws that explain “everything.” TOE enthusiasts such as Weinberg, Greene, Nagel, and Chalmers present no reasons for supposing that this is so.^[176] Earlier, I noted Weinberg's claim that a TOE is a “final” theory in the sense that such a theory states that the world must contain the fundamental laws and objects it postulates that explain “everything.” (I then said that for the purposes of the discussion, I would not make this a requirement for “finality.”) But even if a TOE is to state that the world must be this way, and even if the “must” is construed metaphysically, it doesn't follow that such a (correct) TOE in fact exists and that the world must be (and hence is) that way. All that follows is that if such a TOE exists (one stating that the world must be that way), then the world must be that way. Nagel claims that scientists do, and perhaps must, assume that the world is that way. But even if Nagel were right, it doesn't follow that the world is or must be that way.

Perhaps, then, the claim that a TOE exists is supposed to reflect an a priori metaphysical truth that requires no argu­ment because it is self-evident. It doesn't look self-evident. (If it were self-evident, why would physicists such as Weinberg and Smolin try to present arguments for it?) Indeed, various scientists have thought it is false. I have already mentioned Newton, who invoked God, rather than bodies and forces, to explain certain facts about planetary motion, which he believed could not be explained in mechanical terms; and Driesch, who invoked emergent, non-reductive vital forces to do an analogous thing in biology. Even some more recent physicists such as Prigogine^[177] and Laughlin and Pines^[178] re­ject the idea that all physical phenomena are reducible to “fundamental” entities and laws.^[179] These scientists may be importantly mistaken in their views, but if their mistake is a priori, that should be demonstrated. Appeals to a priori self­evidence are notoriously suspect.

There is another a priori strategy. Rather than attempting to show a priori that a TOE exists, it seeks to defend an a priori evaluative claim to the effect that it would be desir­able for science if one did exist, whether or not it does and whether or not scientists could discover it. I turn to this claim next.

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