HISTORICAL AND PRESUPPOSITION ARGUMENTS FOR THE EXISTENCE OF A TOE

from macro systems to micro systems that comprise them (e.g., from gases, to molecules, to atoms, to nuclei, to protons, to quarks, to strings); and from a set of laws governing one system to more fundamental laws governing the more fun­damental system.

If history is any guide at all, it seems to me to suggest that there is a final theory.... Our deepest principles, although not yet final, have become steadily more simple and econom­ical.... It is very difficult to conceive of a regression of more and more fundamental theories becoming simpler and more unified, without the arrows of explanation having to converge somewhere.^[162]

Weinberg makes it clear that this final theory will contain fundamental principles that govern “elementary” particles.^[163]

One problem with this is that there are examples of sci­entific progressions in the opposite direction (e.g., going from macro-laws governing gases to even broader macro­generalizations in classical thermodynamics governing thermodynamic systems generally; or, as noted in the pre­vious chapters on simplicity, going from simple theories about the number of elements to complex ones). But let us ac­cept the idea that the history of science does contain (some) progressions from macro to micro, and some from com­plex to simple. Historically, when physicists have postulated some entity and claimed it to be simple, fundamental, and unanalyzable (whether molecules, atoms, nuclei, protons, or quarks), they have later postulated even simpler ones (now strings) of which it is composed. And when physicists have formulated laws and claimed them to be fundamental (whether at the micro or macro level), often new phenomena have been discovered showing that the laws are not funda­mental, or not even true, or at best approximately true or of limited applicability, or special cases of more fundamental ones (as happened with Newtonian mechanics).

Whatever support Weinberg's historical argument provides for the existence of fundamental objects and laws, it does not constitute what in chapter 1 I called “explanatory evidence” that such objects and laws exist. Given that there are some historical tendencies in science toward simpler and more fundamental theories, it is not probable that there is an explanatory connection between such tendencies and the fact, if it is one, that there are fundamental “atoms” (whatever they might be) and fundamental laws (whatever they might be). Perhaps the historical tendency of (some) physicists to proceed in a micro direction to simpler and more funda­mental theories suggests the idea, and produces the hope, that a “final” TOE will be found. Perhaps it makes it probable that (some) physicists will continue to search for one. But this does not provide evidence for the claim that there is one, or that if there is they will find it.

Finally, a proponent of a “historical argument” for the existence of a TOE has to show more than just that there is a theory describing fundamental entities subject to fun­damental laws. He must also show that such a theory is a “'1 Theory of Everything,” that it can unify and explain “every­thing.” But the history of science is full of examples in which a new theory, more fundamental and unifying than any pre­vious one, does not, its proponent admits, explain every­thing, even phenomena the theorizer would like to explain that are supposed to come under the rubric of the theory. Maxwell points out that his molecular theory does not ex­plain the known specific heat ratios of gases or their electrical conductivity. Newton points out that his mechanical theory does not explain why the planets move in the same direction on the same plane (see chapter 1).

A second argument, or at least claim, I will mention here is due to Thomas Nagel. The claim is not that a TOE exists but that its existence must be presupposed by science. Here are two passages from Nagel:

Science is driven by the assumption that the world is intelli­gible. That is, the world in which we find ourselves, and about which experience gives us some information, can be not only described but understood.

It seems to me that one cannot really understand the sci­entific world view unless one assumes that the intelligibility of the world, as described by the laws that science has uncovered, is itself part of the deepest explanation of why things are as they are.^[166]

Nagel's idea is that scientific inquiry itself (“the scientific worldview”) presupposes the “intelligibility of the world.”^[167] And, he goes on to argue, a necessary condition for the latter is that there is a TOE that explains everything at the most fundamental level.

This obviously does not establish, or give an epistemic reason for believing, that a TOE exists, only a pragmatic reason for presupposing that one does: you can't do sci­ence without presupposing this. But is it even true, as Nagel supposes, that scientists themselves generally assume or presuppose that the world is intelligible in the way that he imagines (intelligible in terms of fundamental “atoms” and laws)—even with respect to phenomena of a sort that fall within the scope of their inquiries? As noted earlier, Newton believed that certain physical properties of the planets, e.g., the fact that they revolve around the sun in the same direction and on the same plane, cannot be explained mechanically at any level, even an “atomic” one, but require God's inter­vention (not bodies subject to forces). Vitalists in biology, such as the early twentieth-century zoologist Hans Driesch, believed that biological processes, such as ones involving a two-celled egg forming a larva, cannot be explained in terms of the physical and chemical constituents of the pro­cess.

Is Nagel assuming that all scientists in fact subscribe to a worldview that presupposes what he says? Such an assumption is refuted by the history of science. Is he claiming that even if there are scientists who don't presuppose that the world is in­telligible in a sense requiring a TOE, scientists must presuppose this to do science at all? That claim is again refuted by the his­tory of science, unless we want to say scientists who engage in what we regard as scientific activities, but do not believe that everything is explainable by a TOE, aren't really engaging in activities that are scientific. Finally, perhaps Nagel is saying that it would be a very good thing for scientists to assume Nagelian “intelligibility”—good enough to be a requirement for doing good science. This claim is an important one, and I will discuss it in section 7.

5.