YOUR BASIC TOE

I suggest constraints that will, I hope, reflect some basic ones shared by TOE theorists.

First, a search for a TOE is a search for a theory that not only purports to explain everything (perhaps some theo­logical theories do) but also is true—one that offers correct explanations.^[150] I will consider such a theory to consist not just in its central and distinctive assumptions but also, since it is supposed to explain everything, in the explanations it offers.

Following what I take to be the views of TOE theorists in section 1, I will suppose: (1) that a TOE is to correctly explain by appeal to a set of laws for which no further ex­planation exists—“fundamental” laws—not just ones for which no further explanation has been or will be discov­ered; (2) that, according to a TOE, there are (“fundamental”) objects (e.g., strings, or Nagel's panpsychic “atoms,” or fun­damental physical and phenomenal entities in Chalmers' “scrutability” base, or some fundamental forces or fields or other ontological beings) that are not further analyzable and that are governed by the laws in the “fundamental” set; and (3) that “everything” that happens is correctly explained by the properties and states of these basic objects and the laws that govern them.

What sorts of laws and explanations in suppositions (1)— (3) are allowed by TOE theorists? Must the laws be universal, or can they be probabilistic? If the latter are permitted, must a TOE explanation make what is explained highly probable (as Nagel, who seems to be following Hempel's “inductive- statistical” model of explanation, requires)? Or, in accord­ance with models of explanation proposed by Railton^[151] and Salmon,^[152] does it suffice that the fundamental laws give what is to be explained a probability that may be high or low? Or, as Chalmers seems to do, shall we require that a TOE explana­tion deductively entail the phenomenon explained? Different TOE theorists have different views on these issues (or none at all).

There is another idea invoked by some TOE theorists, viz. “finality.” This may simply involve the thought that no further (deeper, more comprehensive) explanation exists than one provided by a TOE. If so, then the idea is captured by suppositions (1)-(3). But perhaps there is more to it than that. For example, Steven Weinberg writes that a TOE would declare that things are the way they are because they have to be that way. Any and all variations, no matter how small, lead to a theory that—like the phrase “'I liis sentence is a lie”—sows the seeds of its own destruction.^[153]

A “final” theory should not just say what the fundamental laws and entities of the world are in terms of which “eve­rything” can be explained; it should also make a claim to the effect that the world must be such as to contain these entities subject to these laws. (And since we are requiring truth for a TOE, the world must indeed contain these entities and laws.)

What sort of “must” is this? If the Liar paradox analogy is to be taken seriously, is it a logical “must?” Or, by analogy with Kant's defense of Newton's laws of motion plus gravity,^[154] is it a metaphysical one? Or is it perhaps an epistemic “must” to the effect that all the evidence known at a given moment should strongly support the theory in question and discon­firm any contrary, or perhaps any known contrary? Weinberg does not elaborate.^[155] In any case, not all TOE theorists appeal to “finality,” or if they do, it is not clear that they mean more than is conveyed by suppositions (1)-(3).^[156] In what follows, I will simply understand “finality” in the latter sense, without the requirement of logical, metaphysical, or epistemic neces­sity. This means that a TOE, if one exists, satisfies (1)-(3) in our world, though not in all logically, metaphysically, or ep- istemically possible worlds.

What does “everything” encompass? We cannot impose the constraint that a TOE must provide a correct answer to literally every question that might be asked about anything at all, since according to TOE advocates, the fundamental laws governing fundamental objects have no explanation; they are simply fundamental. But given this exception, there is a lot of leeway. String theorists and mechanical philosophers do not have to claim that “everything” includes facts about mental phenomena, even though Nagel and Chalmers impose such a constraint on a TOE of the sort they want. Still, “everything” should be construed quite broadly, perhaps to include all facts about physical phenomena, or mental phenomena, or both, assuming they are nonfundamental, rather than nar­rowly to include just facts about certain types of physical or mental phenomena. A TOE of the sort string theorists seek will explain physical micro-phenomena covered by quantum mechanics, as well as physical macro-phenomena covered by general relativity. The broader the better, but we don't have to take “everything” to include all nonfundamental facts about all phenomena, even if some TOE advocates seem to (in­cluding Nagel, Chalmers, and some string theorists).

TOE theorists emphasize that a TOE provides “unifica­tion,” although they do not attempt to define this idea. From the examples they offer, one may infer that at least part of what they mean is that a TOE unifies because it correctly explains a remarkably large and diverse range of phenomena (a unifi­cation of phenomena—an idea related to William Whewells concept of “consilience”). But there seems to be more to their idea than this. A TOE should unify ontologically by reducing more complex objects to simpler ones governed by a set of laws; and it should explain phenomena at the more complex level by appeal to these simpler objects and laws (ontological reduction). Finally, although this is a bit fuzzier, perhaps TOE theorists will say that the assumptions of a TOE should them­selves be unified: they should “hang together” (unification of assumptions—an idea quite similar to Whewells concept of “coherence”). They should not just be a set each member of which explains something different, but one whose members together explain the phenomena they do. Newton's gravita­tional theory of mechanics might be said to unify in all three ways. It unifies celestial and terrestrial phenomena. It unifies ontologically by reducing the various postulated forces of gravity for each planet to just one, the universal force of gravity. And it does these things using a set of laws, viz. Newton's three laws of motion, plus gravity, that “hang together.”

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