In Defense of String Theory
Evaluating the Scientific Validity of the Theory of Everything
What sorts of standards determine the scientific status of a given theory? It is this question that is essential to our discussion of string theory as a valid/justified part of the scientific enterprise (as opposed to a theory of metaphysics, pseudo-science, or perhaps religion). Even a cursory historical analysis of string theory’s development can elicit the sense that there are countless factions that have arisen among astrophysicists in opposition to string theory’s legitimacy. Yet what evaluative standards do these physicists employ when they dismiss string theory as mere conjecture? Some call on the set of criteria laid out in Kuhn’s Objectivity, Value Judgment and Theory Choice and some employ Popper’s falsifiability criterion. In this paper, I will address each of the aforementioned works in an attempt to defend the scientific status of string theory, making use of the following structure:
I. I contend that string theory passes Popper’s falsifiability criterion.
II. I posit that string theory contains all the characteristics of a “good” scientific theory according to Thomas Kuhn’s aforementioned work.
Yet before we can properly evaluate string theory as a legitimate science, we must understand what is at stake, and why such an evaluation is necessary. If one were to empirically-evidentiate the accuracy of string theory, he would be able to attain what many refer to as the “Holy Grail” of physics—the ability to ascertain the Theory of Everything. According to physicist John Ellis, who introduced the term into technical literature, such a theory would “putatively explain and link together all known physical phenomena.” The promise of string theory is infinitely-great; it has the potential to quintessentially-explain the essence of all things: the keyboard upon which I am typing, the existence of elementary particles, and the origin of the universe we inhabit. Yet before we can even fathom justifying string theory as an accurate representation of the universe, we must first disprove those who immediately dismiss it as a theory of pseudo-science—a theory not to be taken seriously. At the very least, this paper aims to assign scientific relevance to string theory—a theory with far-too-much potential to wholly dismiss as unscientific.
Before progressing, we must first have an historical understanding of string theory and the development of its principle tenets. According to Michio Kaku, author of Parallel Worlds, the theory was “discovered quite by accident, applied to the wrong problem, relegated to obscurity, and suddenly resurrected as a theory of everything” (187). Unlike most theories where fundamental laws of quantum physics are used to perfect mathematical equations, physicists stumbled upon the mathematical Euler-Beta function—an equation that “seemed to describe the subatomic world” (188). This sub-atomic world was thought to be founded upon vibrating strings rather than upon particle-points, as current quantum theory posits. Each particle was merely a variation of a certain string-vibration, and each was accordingly assigned a “spin-value” of 0, 1, or 2 which explained inter-particle behavior.
However, many physicists take issue with string theory’s more-abstract principles that have developed more recently. The mathematical equations of the theory necessitate the existence of ten or twenty-six dimensions, as opposed to the mere four dimensions we know as length, width, depth, and time; nowhere else can physicists find a theory “that selects its own dimensionality” (192). Additionally, the divergences and anomalies found within the mathematical equations of string theory are answered by the concept of supersymmetry: the idea that all subatomic particles have partners invisible in nature. Finally, leading string theorists posit the existence of membranes—mysterious, eleven-dimensional entities that contain dimensions which fold upon themselves and necessitate the existence of a multiverse (i.e. parallel universes). For these seemingly scientifically-fictitious tenets, string theory has withstood various attacks that have threatened to undermine its potency as a scientific explanation since 1968. I argue that each challenge to string theory’s legitimacy is accompanied by a more innovative and promising counter—a few of which are subsequently explained.
In his Science: Conjectures and Refutations, Karl Popper seeks to draw the distinction between science and pseudo-science by employing the falsifiability criterion, a principle which is summed up by Popper himself: “The criterion of the scientific status of a theory is its falsifiability, or refutability, or testability” (179). Thus, if we are to establish string theory as legitimate according to Popper, we must prove that its theoretical mathematics can be tested in nature.
Interestingly enough, prominent astrophysicist Dr. Michio Kaku argues that a mechanism for testing string theory can be ascertained by a technology of the near-future. It turns out that ascertaining echoes from the eleventh dimension posited by the mathematics of string theory is not an unrealistic aspiration. If one is to experimentally validate string theory, he must generate empirical data that gives the theory credibility. There are a multitude of hereto-unobserved entities that string theory posits, some of which are listed below:
1. The tiny mass of the elusive neutrino particle
2. The decays of certain sub-atomic particles
3. New long-range forces
4. Dark matter particles
5. Einstein’s unit of gravity—the graviton
It is at this point in time when the skeptic may object, arguing that no technology fathomable to physicists today is capable of crediting the existence of such abstract and purely-theoretical entities. Yet there are a variety of technologies that are close to being able to do just that: “the device that may decisively settle many of these questions is the Large Hadron Collider (LHC), now nearing completion at the famed CERN laboratory” (Kaku, 276). With its ability to accelerate protons at a speed of 99.9999% the speed of light and its ability to collide those protons at energies exceeding 1.1 trillion volts, the LHC will have the ability to re-create a microcosm of the universe as it looked just moments after the Big Bang. More specifically; such a collision will free quarks into hot gluon plasma, allowing us to observe them through complex computer programs. The cosmology of string theory may “gradually become less a theoretical science and more an experimental science, with precise experiments on quark-gluon plasmas done right in the laboratory” (Kaku, 278). And while we may not be able to prove the accuracy of string theory just yet, its ability to be falsified does exist, as evidenced by the technology of the Large Hadron Collider.
Yet falsifying string theory may not be as complex an endeavor as one might think. Pierre Duhem contends that “the physicist who carries out an experiment implicitly recognizes the accuracy of a whole group of theories” (189). Therefore, we need not have to falsify the string theory as a whole as a means of satisfying the falsifiability criterion, but rather it suffices to falsify merely one of the theories it implicitly recognizes. Astrophysicist Joseph Polchinski argues that all string theory models are “Lorentz invariant, unitary, and contain Einstein’s General Relativity as a low energy limit” (Polchinski). Thus, if it is possible to falsify quantum mechanics, Lorentz invariance, or general relativity, it is possible to falsify string theory. Therefore, string theory can be considered to have legitimate scientific status according to the Popperian standard, as the aforementioned theories are considered to be testable and/or falsifiable.
Next, I will employ the criteria mentioned in Thomas Kuhn’s Objectivity, Value Judgment, and Theory Choice in an attempt to characterize string theory as a legitimate, scientific theory embodying the following characteristics:
1. Accurate: “Consequences deducible from a theory should be in demonstrated agreement with the results of existing experiments.”
2. Consistent: “A theory should be consistent, not only internally or with itself, but also with other currently accepted theories applicable to nature.”
3. Broadness: “A theory’s consequences should extend far beyond the particular observations or laws it was designed to explain.”
4. Simple: “A theory should bring order to phenomena that in its absence would be individually isolated and confused.”
5. Fruitful: “A theory should disclose new phenomena or previously unnoted relationships” (Kuhn, 213).
Accuracy and consistency must be analyzed together in the context of string theory, as each is inextricably linked to the other; consistency is dependent upon agreement with well-established theories and accuracy is dependent upon the experimental data used to confirm those theories. The principle tenets of string theory do concur with the most- accepted scientific theories of the recent past. We already know from Polchinski’s argument that string theory encompasses Einstein’s General Relativity, but according to Dr. Michio Kaku, string theory “can also offer solutions that are astonishingly close to the Standard Model of particle physics” (206). That is to say, the theory predicts the same “motley collection of bizarre subatomic particles” (207). Yet not only does string theory mathematically predict the same particles the Standard Model does, it also foretells the same mass and coupling strength of said particles. Some object that string theory is disconnected from the established principles of physics; Kaku argues that it actually embodies many of physics’ most fundamental theories.
When we employ broadness and fruitfulness as evaluative standards of string theory, we can conclude that it is a “good scientific theory” according to Kuhnian criteria. Rather than merely positing rules that govern a subject’s particular behavior, string theory has the potential to unify sets of principles that span across multiple scientific disciplines. According to Brian Greene, author of The Elegant Universe, the triumph of string theory is “its natural incorporation of quantum mechanics and gravity” (379). The ability of string theory to universally explain quantum mechanics refers to its ability to provide us with an explanation of all behavior on the atomic level (i.e. the behavior of molecules, atoms, electrons, protons, and other sub-atomic particles). The ability of string theory to explain gravity refers to its ability to incorporate quantum laws with Einstein’s General Relativity, which includes gravitation. If string theory can successfully combine quantum mechanics and gravity into a unified theory, its broadness in scope is infinite; it will explain all the physical phenomena of our universe, allowing us to ascertain new phenomena and new scientific relationships yet to be discovered.
Moreover, a unified string theory would be the most simple and elegant theory known to science. Einstein once said that “if a theory did not offer a physical picture that even a child could understand, then it was probably useless” (Einstein qtd. in Kaku, 196). Fortunately, string theory paints an exceedingly “simple physical picture” which underlies its mathematics—“a picture based on music” (Kaku, 196). According to string theory, strings no larger than Planck length (10-33) can vibrate to produce sub-atomic particles. Imagine the strings on a guitar: if we pluck the 3rd string on the first fret, we may produce a graviton; however, if we pluck the 4th string on the third fret, we may produce a beta particle. The beauty of string theory lies within its ability to reduce order from chaos in the form of “cosmic music.”
Yet despite its scientific appeal, string theory has produced a vocal faction of skepticism among astrophysicists. These skeptics argue that string theory is riddled with theoretical entities that can never be empirically-validated by experimental data, regardless of the potential for technological advancement. They would have us believe that even the technology of the LHC can only work in theory, as opposed to in reality.
Yet opponents of string theory fail to realize that astrophysicists are only beginning to scratch the surface of string theory’s complex nature. The skeptics fail to realize that most string theorists do not claim that string theory is accurate; rather, they claim that it is scientifically-relevant and may be evidentiated in the future. Kaku reflects on this in Parallel Worlds: “String theory may very well be the theory of everything, but I believe that it is far from finished. The theory has been evolving backwards since 1968, and its final equations have not yet been found” (238). Those who automatically dismiss string theory are engaging in blatant oversight; they would have us believe that the investigation is over, and that string theory as it stands now is representative of “the theory of everything.” Such a notion could not be further from the truth. The mathematics of string theory have not yet been perfected, and even if the LHC can not empirically-produce string theory’s theoretical entities now, the possibility exists in the future as we continue to add to our arsenal of scientific knowledge.
Some physicists are also skeptical of the five self-consistent superstring theories that undermine string theory’s unifying potential. How can astrophysicists claim to have found a unified field theory if there are five of them? But in 1994, Edward Witten mathematically proved that these ten-dimensional superstring theories were merely “approximations of a higher, mysterious, eleven-dimensional theory of unknown origin” (Kaku, 212).
In an interview with the Public Broadcasting Service, Edward Witten proclaimed:
I feel we are so close with string theory that—in my moments of greatest optimism—I imagine that any day, the final form of the theory might drop out of the sky and land in someone’s lap (
If we are to infer one thing from
Works Cited
Duhem, Pierre. The Aim and Structure of Physical Theory. Princeton:
Greene, Brian. The Elegant Universe.
Kaku, Michio. Parallel Worlds.
Kuhn, Thomas. "Objectivity, Value Judgment, and Theory Choice." The Essential Tension (1977): 320-39.
Polchinski, Joseph. String Theory.
Popper, Karl. Conjectures and Refutations: The Growth of Scientific Knowledge. 1965.
