IS THERE A TOE ON THE HORIZON?
successful string theory has been in unifying the basic forces of nature is controversial among physicists themselves. Even its proponents recognize its limitations and that it is still a work in progress.[157] Smolin, a critic, claims that of the five basic problems of physics cited earlier, string theory has solved, or pointed in the direction of, only two (the unification of particles and forces, and the problem of quantum gravity).
He writes:At the present time, string theory does not solve any of the three remaining problems. It appears incapable of explaining the parameters of the standard models of physics and cosmology. It provides a list of possible candidates for the dark matter and energy but doesn't uniquely predict or explain anything about them. And so far, string theory has nothing to say about the greatest mystery of all, which is the meaning of quantum theory.[158]
Even if string theory is (or could be developed into) a TOE, there are no experiments showing that the postulated strings and 10-dimensional spacetime exist and satisfy the claims of the theory.[159] (The energies required to produce string effects are too great for current experiments.) Moreover, even its proponents admit that the exact equations of the theory are not yet known.[160] '1 he other potential TOEs mentioned earlier fare even worse. '1 he seventeenth-century mechanical philosophy has been abandoned. Nagel provides only a bare outline of the kind of TOE he seeks. And Chalmers presents very general ideas on how a TOE should be constructed, without even beginning the construction of one.
This, however, will not discourage TOE theorists. What they believe is: (i) that such a theory exists, whether or not it is ever constructed; (ii) that constructing such a theory is an “ideal” toward which science and scientists should aim; and (iii) that it is “in principle” possible to construct such a theory.
Given (i)-(iii), they assert that searching for a 'lheory of Everything is a good and reasonable thing to do. What does “in principle” mean in (iii)? At least that it is not a logical contradiction to assert that such a theory will be constructed. Possibly, it is supposed to mean more, viz. that the construction of such a theory (and hence its existence) is not incompatible with established scientific laws, or with any laws that govern the universe, whether established or not. Or perhaps it is supposed to mean something epistemic, viz. that on the basis of all the evidence we now have, there is no reason for us to believe that such a theory will not be constructed.That it is not a logical, or nomological, or epistemic contradiction to assert that a TOE will be constructed is no reason to think that one will be. Nor, more important, is the fact that it is not a logical, nomological, or epistemic contradiction to assert that such a theory exists any reason to think that one does. (To borrow an example used by Daniel Dennett in discussions about God, that there is a teacup on Mars is not a logical, physical, or epistemic impossibility, but is no reason to think there is one.) Without asking about evidence for any particular theory that claims to be a TOE, is there any reason to believe the general claim that the search for a TOE will not be in vain?
In the next two sections, I consider some very general arguments. Each focuses on one or more aspects of what a TOE is supposed to provide. If none by itself provides evidence for the existence or constructability of a TOE, perhaps together they do so, and thereby demonstrate that it is not a speculation. Or, for those such as the present author who consider the idea of a TOE to be a speculation, perhaps the arguments show at least that it is a good speculation— one worth pursuing. The arguments I consider are not ones for believing that some particular TOE exists and can be constructed, such as string theory or Nagel's panpsychic theory. They do not purport to show, e.g., that strings or panpsychic “atoms” exist. Rather, they are supposed to provide at least some reason to think that some TOE or other exists and can be constructed, or at least that scientists must presuppose that this is so.[161]
4.