I finished reading Brian Greene’s *The Elegant Universe*, which indeed is the best written and most comprehensible introduction-to-string-theory-for-the-mathematically-challenged (such as myself) that I have yet come across. But still, I found myself underwhelmed and far from convinced.

It’s partly John Horgan’s objection, which I have mentioned before: the fact that almost nothing about string theory can be empirically verified/falsified, since the theory deals with entities that remain forever out of the range of experimental investigation. (Indeed, Greene’s chapter on the possible future empirical verification of string theory is by far the lamest part of the the book. He basically says that, if more powerful atom smashers and space telescopes are built, then within a decade or two we might discover some new stuff that isn’t incompatible with string theory. In no other branch of science would this qualify as “proof”).

The physicists would probably answer Horgan that even if strings can never be actually detected (in the ways that, remember, protons and electrons and photons and even quarks *can* be actually detected) they are still the universe at its most basic, being what quarks and photons and electrons are *made of*. And this *has* to be the case, they would say, because the equations work. String theorist Edward Witten is quoted by both Horgan and Greene as saying that the proof of string theory is that it correctly predicts the existence of gravity.

That is to say, string theory is justified mainly on the basis that its *consequences* are the very “laws of nature” that we already know without it. It claims to unify general relativity (the theory of gravity) with quantum mechanics (the theory of elementary particles and the other forces in the universe aside from gravity, i.e. electromagnetism and the strong and weak nuclear forces). But the only real “proof” it offers of this unification is that the equations of relativity and quantum mechanics can be derived from the string equations (or could be, if the string theory equations were more fully worked out).

It strikes me that the lack of empirical verification that Horgan points to is really a consequence of a deeper problem, that of what Whitehead called the Fallacy of Misplaced Concreteness: the “error of mistaking the abstract for the concrete.” The wondrous equations of string theory are abstractions. They are artificially isolated simplifications of a concrete reality that is more complex and more complete. This, in itself, is not a problem. All science, indeed all knowledge, works by a process of abstraction. “You cannot think without abstractions,” Whitehead says; but that is why, he adds, “it is of the utmost importance to be vigilant in critically revising your *modes* of abstraction.”

That is to say, the problem comes when abstractions are mistaken for ultimates. In order to make the mathematics of string theory work, physicists need to postulate a whole group of “supersymmetric” subatomic particles that have never been observed (and I mean this in strong contrast to the ways in which protons and electrons and photons and neutrinos *have* in fact been observed). They also need to postulate six (or seven) “curled up” spatial dimensions, ones that are entirely, and necessarily, outside experience, in addition to the three spatial dimensions that are the core of our experience. This is supposed to make for an “elegant universe,” because of how well the equations fit together (though if your sense of aesthetics. or logic, includes Occam’s Razor, you are not likely to find these assumptions “elegant”).

Now, mathematical requirements have in fact led to what Tom Siegfried, in his rah-rah-science book *Strange Matters*, calls “prediscoveries.” Things like neutrinos, and antimatter, were predicted theoretically long before they were actually observed. The theories gave experimentalists strong hints on what to look for, and where; and their predictions were borne out. It’s also worth noting that proto-positivists like Ernst Mach regarded atoms as merely as necessary fictions; something which, I think, is refuted by the fact that we can now actually see atoms in electron scanning microscopes. It has been a losing proposition, for the past century, to bet against the actuality of scientific abstractions.

But it’s hard to see how additional, unobservable spatial dimensions, or a “multiverse” in which different “universes” had different physical parameters, could move from “prediscovery” to empirical verification in the same way that atoms and neutrinos have. And not for positivist, epistemological reasons, but for more profoundly metaphysical ones. The string theorists’ assumptions that science can not only explain *how* physical forces work, but positively *account for them* (as in the sense of explaining *why* physical constants have the particular values they do, which is one thing string theorists hope to accomplish) does seem to be mistaking the explanatory abstractions for the things they have been abstracted from.

Another quote from Whitehead: “Speculative Philosophy is the endeavor to frame a coherent, logical, necessary system of general ideas in terms of which every element of our experience can be interpreted.” By this criterion, string theory fails as speculative philosophy, because its mathematical abstractions fail to be ideas of sufficient generality. But if string theory also fails as empirical science, because it is too purely speculative, where does that leave us?

# Physics 3: String Theory

I finished reading Brian Greene’s *The Elegant Universe*, which indeed is the best written and most comprehensible introduction-to-string-theory-for-the-mathematically-challenged (such as myself) that I have yet come across. But still, I found myself underwhelmed and far from convinced.

It’s partly John Horgan’s objection, which I have mentioned before: the fact that almost nothing about string theory can be empirically verified/falsified, since the theory deals with entities that remain forever out of the range of experimental investigation. (Indeed, Greene’s chapter on the possible future empirical verification of string theory is by far the lamest part of the the book. He basically says that, if more powerful atom smashers and space telescopes are built, then within a decade or two we might discover some new stuff that isn’t incompatible with string theory. In no other branch of science would this qualify as “proof”).

The physicists would probably answer Horgan that even if strings can never be actually detected (in the ways that, remember, protons and electrons and photons and even quarks *can* be actually detected) they are still the universe at its most basic, being what quarks and photons and electrons are *made of*. And this *has* to be the case, they would say, because the equations work. String theorist Edward Witten is quoted by both Horgan and Greene as saying that the proof of string theory is that it correctly predicts the existence of gravity.

That is to say, string theory is justified mainly on the basis that its *consequences* are the very “laws of nature” that we already know without it. It claims to unify general relativity (the theory of gravity) with quantum mechanics (the theory of elementary particles and the other forces in the universe aside from gravity, i.e. electromagnetism and the strong and weak nuclear forces). But the only real “proof” it offers of this unification is that the equations of relativity and quantum mechanics can be derived from the string equations (or could be, if the string theory equations were more fully worked out).

It strikes me that the lack of empirical verification that Horgan points to is really a consequence of a deeper problem, that of what Whitehead called the Fallacy of Misplaced Concreteness: the “error of mistaking the abstract for the concrete.” The wondrous equations of string theory are abstractions. They are artificially isolated simplifications of a concrete reality that is more complex and more complete. This, in itself, is not a problem. All science, indeed all knowledge, works by a process of abstraction. “You cannot think without abstractions,” Whitehead says; but that is why, he adds, “it is of the utmost importance to be vigilant in critically revising your *modes* of abstraction.”

That is to say, the problem comes when abstractions are mistaken for ultimates. In order to make the mathematics of string theory work, physicists need to postulate a whole group of “supersymmetric” subatomic particles that have never been observed (and I mean this in strong contrast to the ways in which protons and electrons and photons and neutrinos *have* in fact been observed). They also need to postulate six (or seven) “curled up” spatial dimensions, ones that are entirely, and necessarily, outside experience, in addition to the three spatial dimensions that are the core of our experience. This is supposed to make for an “elegant universe,” because of how well the equations fit together (though if your sense of aesthetics. or logic, includes Occam’s Razor, you are not likely to find these assumptions “elegant”).

Now, mathematical requirements have in fact led to what Tom Siegfried, in his rah-rah-science book *Strange Matters*, calls “prediscoveries.” Things like neutrinos, and antimatter, were predicted theoretically long before they were actually observed. The theories gave experimentalists strong hints on what to look for, and where; and their predictions were borne out. It’s also worth noting that proto-positivists like Ernst Mach regarded atoms as merely as necessary fictions; something which, I think, is refuted by the fact that we can now actually see atoms in electron scanning microscopes. It has been a losing proposition, for the past century, to bet against the actuality of scientific abstractions.

But it’s hard to see how additional, unobservable spatial dimensions, or a “multiverse” in which different “universes” had different physical parameters, could move from “prediscovery” to empirical verification in the same way that atoms and neutrinos have. And not for positivist, epistemological reasons, but for more profoundly metaphysical ones. The string theorists’ assumptions that science can not only explain *how* physical forces work, but positively *account for them* (as in the sense of explaining *why* physical constants have the particular values they do, which is one thing string theorists hope to accomplish) does seem to be mistaking the explanatory abstractions for the things they have been abstracted from.

Another quote from Whitehead: “Speculative Philosophy is the endeavor to frame a coherent, logical, necessary system of general ideas in terms of which every element of our experience can be interpreted.” By this criterion, string theory fails as speculative philosophy, because its mathematical abstractions fail to be ideas of sufficient generality. But if string theory also fails as empirical science, because it is too purely speculative, where does that leave us?