SOME (POTENTIAL) THEORIES OF EVERYTHING
a. String Theory
I begin with string theory, one of the examples of a speculation I noted in chapter 1. Its proponents are enthusiastic and believe it is or will be developed into a TOE.[136] Lee Smolin, a theoretical physicist who is admittedly a critic of the theory, characterizes its aim as one of solving what he calls “the five great problems in theoretical physics.”[137] They are:
1.
Combine general relativity and quantum theory into a single theory that can claim to be the complete theory of nature. This is called the “problem of quantum gravity.”2. Resolve the problems in the foundations of quantum mechanics, either by making sense of the theory as it stands or by inventing a new theory that does make sense.
3. Determine whether or not the various particles and forces can be unified in a theory that explains them all as a manifestation of a single, fundamental entity.
4. Explain how the values of the free constants in the standard model of particle physics are chosen in nature.
5. Explain dark matter and dark energy.
String theory, which seeks to solve these problems, postulates that all the particles and forces of nature arise from strings that vibrate in 10-dimensional spacetime and are subject to a set of simple laws specified in the theory. The strings, which can be open with endpoints or closed loops, vibrate in different patterns, giving rise to particles such as electrons and quarks. The equations governing the interactions of forces and particles are to be derived from the basic idea that the vibrations of strings are propagated so as to minimize the area of propagation in spacetime.
What counts as “everything” on this theory? The most straightforward answer is that the theory attempts to explain issues of the sort mentioned in Smolin's “five problems.” No doubt there are other problems physicists would cite, and as the theory is further worked out, new problems will arise that call for explanations.
But these are ones that would normally be treated by physicists, not by experts in other sciences. As Brian Greene notes, however, string theorists tend to have reductionist ideals and would like to be able to use the theory to explain a lot more, or at least believe that the theory could “in principle” explain a lot more, including psychological phenomena such as joy and sorrow, as well as complex physical phenomena such as tornados.[138] The matter is controversial, and not all string theorists have such vaulting ambitions.b. Seventeenth-Century Mechanical Philosophy
Its defenders had a different physics in mind, but it is also quite general.[139] The greatest of the mechanical philosophers, of course, was Isaac Newton. In his introduction to the first edition of the Principia, he writes:
our present work sets forth mathematical principles of natural philosophy. For the basic problem of philosophy seems to be to discover the forces of nature from the phenomena of motions and then to demonstrate the other phenomena from these forces.[140]
Newton goes on to develop his three laws of motion mathematically, and finally, using these, together with theorems he derives from them and six observed phenomena pertaining to the motions of the planets and their satellites, he proves the law of gravity. He uses the latter to “demonstrate” other celestial and terrestrial phenomena.[141] Newton does not claim that all phenomena can be so demonstrated. But the class of physical phenomena he intends is quite broad. The central idea is that physical phenomena are explainable by reference to bodies (a basic ontological category) that are in motion and are subject to forces governed by fundamental laws.
The mechanical philosophy extended well into the nineteenth century, when James Clerk Maxwell, e.g., attempted to provide mechanical explanations for heat, light, electricity, and magnetism. He claimed that no more basic explanation of physical phenomena can be given.[142] There are those who thought that the program of the mechanical philosophy, whether expressed in terms of Newton's laws or later variations or additions (e.g., Maxwell's electromagnetic laws and the concept of a field), could be extended to areas well beyond those mentioned, such as chemistry, biology, and even psychology.11 But neither Newton nor Maxwell had such ambitions. “Explaining everything” for Newton and Maxwell meant explaining physical phenomena of a sort they described in their works and other physical phenomena that may come to be discovered.
But neither scientist had the ambition to apply the theories they produced beyond the physical sciences.[143] [144]c. Thomas Nagel’s Grand Unification
Nagel writes:
This, then, is what a theory of everything has to explain: not only the emergence from a lifeless universe of reproducing organisms and their development by evolution to greater and greater functional complexity; not only the consciousness of some of those organisms and its central role in their lives; but also the development of consciousness into an instrument of transcendence that can grasp objective reality and objective value.[145]
Nagel does not produce an actual theory of this sort, though he does make an outline of the kind of theory he has in mind. It will contain non-teleological, non-deterministic laws of physics “governing the ultimate elements of the universe, whatever they are.” It will also contain teleological laws governing states of the universe that assign certain successor states higher probabilities than those assigned by the laws of physics. These teleological laws ascribe to the ultimate elements of the universe basic (“panpsychic”) tendencies to achieve certain outcomes or “end-states,” including mental ones. Nagel says it is up to scientists to provide the actual “theory of everything.” His job is to state the direction that should be taken and the problems to be solved.[146]
What does Nagel have in mind by “everything”? He certainly wants a theory to explain all the phenomena explained by physics and biology. But he also wants that theory to explain “mental” phenomena, including consciousness, cognition, and value, since he believes that physics and biology are incapable of doing so.
d. Chalmers’ “Construction of the World”
David Chalmers defends the idea that there is a small class of basic truths from which all the other truths of the world can be determined. He calls this idea a “scrutability thesis”:
It says that the world is in a certain sense comprehensible, at least given a certain class of basic truths about the world.
In particular it says that all truths about the world are scrutable from some basic truths.[147]Unlike string theorists, mechanical philosophers, and Nagel, however, Chalmers is not out to present, or even point in the direction of, a particular scientific theory that explains, or can explain, everything. On his view, there are various types of “scrutability bases” and various senses that can be given to the “scrutability” relation. His aim is to characterize these different types, and tell us what general type he personally prefers and why. He seeks to provide a general framework for any TOE, not to construct a particular one. I classify him as a “theorist of everything” because he believes that there is a class of basic truths from which all others are “scrutable,” and he believes that this makes the world comprehensible.
The “scrutability” relation Chalmers favors is “a priori entailment,” rather than some sort of empirical-inductive relationship. And his favored class of basic truths “includes both truths of physics and phenomenal truths, as well as certain indexical truths.” The class of physical truths, he writes, will include
microphysical truths (truths about fundamental physical entities in the language of a completed fundamental physics) and macrophysical truths (truths about any entities, including macroscopic entities, in the language of classical physics).[148]
There will also be “phenomenal” truths about phenomenal properties (what it is like to see red or feel pain), and index- ical truths of the form “I am X” and “now is Y” Chalmers claims that “all ordinary macroscopic truths are a priori entailed” by such a class.[149] Although he does not use the expression “theory of everything,” he really does seem to mean “everything.” All truths whatever are to be either in the class of basic truths or are to be derivable from such a class.
In what follows I will not focus on the details of any of these theories or programs but only on some general ideas they share and the basis for them.
2.