The Failed Discussion of Quantum Gravity in Popular-Science

The Failed Discussion of Quantum Gravity in Popular-Science “String theory makes sense to me because the universe is a symphony that creates harmony with the vibration of our strings.” - Kamand Kojouri “Some string theorists prefer to believe that String Theory is too arcane to be understood by human beings, rather than consider the possibility that it might just be wrong.” - Lee Smolin Our understanding of gravity is based on the General Theory of Relativity as produced by Albert Einstein in 1915. Any candidate theory of quantum gravity must be able to reproduce Einstein's theory of General Relativity as a classical limit of a quantum theory. There have been a multitude of dedicated research programs and theories, such as asymptotically safe gravity, twistor theory, and non-commutative geometry. Though for several decades, two theories – Loop Quantum Gravity and String Theory – have dominated popular-science. This particular type of deliberation tends to create an impossible learning environment for everyone who’s not a professional. This is predominantly due to the fact that typical popular-science books on quantum gravity are authored by theorists who possess an innate bias towards their own field of study, portraying their personal interpretation as the singular truth. Consider the following scenario; two qualified scientists each author a book on the same theoretical discourse, however, each book offers mutually opposing assessments. How will the layman digest such contradictions? Its fairly obvious the public's interpretation won’t necessarily follow the most cogent argument. Instead it will likely be shaped by a range of publicity and marketing factors which ultimately coalesce as the number of book sales. For example, renowned physicist Michio Kaku (a major proponent of String Theory) probably sells more books than Roger Penrose, the mathematician responsible for the insight of LQG’s spin-networks. This may not be a threat to the general enlightenment of society. But popularity undoubtedly contributes to what future researchers choose to study. This is amplified by the politics inside academia itself. Many have described the cultural hostility towards anything outside of String Theory. And how hierarchy exacts too much control over what new PhDs spend their time researching. The manifestation of an over-hyped theory is exploited by publishers who expect scientists to write books making new and profound assertions that excite the imagination of their audience. A task to which String Theory is particularly well suited. Many have argued that these theories of quantum gravity (and String Theory more specifically) are in fact, not science. This is because neither String Theory or LQG make predictions which could be falsified using our present technology. String theory and Loop Quantum Gravity are individually very useful mathematical frameworks, however, good math doesn’t mean empirical science. That doesn’t discredit either theory, but strikes a blunt contrast to more traditional physical theories such as Quantum Mechanics and General Relativity. In spite of the fact that the various interpretations of Quantum Mechanics individually raise and resolve assorted paradoxes and philosophical speculation. QM is science, as it presents a set of axioms which can be experimentally verified, so too does General Relativity. At present neither of the leading theories of quantum gravity are formatted in a way that would be considered falsifiable, either experimentally or otherwise. Quantum gravity effects are notoriously difficult to measure due to the unimaginably small Planck length (10-35 m). In this regard, Loop Quantum Gravity has an advantage in its adherence to our macroscopic experience. This is in contrast to String theory, which makes many unverifiable predictions based on mathematical inference that expand beyond our perceivable reality. String Theory was born out of an era in physics which championed mathematical methods by the mantra 'Shut-up and Calculate'. But any student who's ever opened an introductory physics book knows the subject expects deeper insight than just rigorous math. In a related observation, an excerpt of The Feynman Lectures on Physics describes the failure of those who approach physics with an over dependence on their mathematical tools: “That is the difference between mathematics and physics. Mathematicians, or people who have very mathematical minds, are often led astray when ‘studying’ physics because they lose sight of the physics. They say: ‘Look, these differential equations – the Maxwell equations – are all there is to electrodynamics; it is admitted by the physicists that there is nothing which is not contained in the equations. The equations are complicated, but after all they are only mathematical equations and if I understand them mathematically inside out, I will understand the physics inside out.’ Only it doesn’t work that way. Mathematicians who study physics with that point of view – and there have been many of them – usually make little contribution to physics and, in fact, little to mathematics. They fail because the actual physical situations in the real world are so complicated that it is necessary to have a much broader understanding of the equations.” – The Feynman Lectures on Physics: Differential Calculus of Vector Fields The accompanying-post, Introductory Notes on Quantum Gravity, provides an unbiased, comparative outline of LQG and String Theory. This should be useful introducing students and laymen to the basic concepts. There's also a specific Wikipedia article on M-Theory intended for the novice. For readers looking for an introduction with more breadth, Lee Smolin – one of the founders of LQG – wrote an excellent book on the subject appropriately titled The Trouble with Physics. Being published in 2005, some of the general knowledge presented has fallen out of date, though it remains one of the most insightful analyses of the field in publication. Many of the themes in Smolin’s book are echoed in this post but the book provides a depth of history and detail that can’t be compressed into a single blog. In-spite of his influence on LQG, Smolin has done his share of work in String Theory as well, and The Trouble with Physics serves as a detailed lay-introduction to quantum gravity by an author who has managed to remain largely unbiased. The book also recounts several interesting stories from Smolin’s past which will be quite enjoyable to read for any aspiring scientist. Even if your field isn’t physics, this is one book every future scientist should read, especially those preparing to work in academia. “... String Theory needs to be developed in an open atmosphere, in which it is considered as one idea among several, without any presuppositions as to its ultimate success or failure. What the new spirit of physics cannot tolerate is a presumption that one idea has to succeed, whatever the evidence.” – Lee Smolin (The Trouble with Physics, 2005) For the record, the failures of popular-science aren't exclusive to quantum gravity. I recall a recent public television expo on current research in Dark Matter which focused it's hour entirely on Weakly Interacting Massive Particles, or WIMPS. The special noticeably neglected to acknowledge alternative resolutions such as Modified Newtonian Dynamics or Conformal Gravity. The issues pervading popular-science should be concerning to everyone. Every professional who has once been a student knows education doesn’t exist in the vacuum of textbooks and university faculty. Unfortunately a large sum of what determines our perception of science flows through channels controlled by marketing majors and business executives. PopSci authors must become more introspective and aware of the resonance of their opinion. And everyone must be aware of how ‘hard-science’ is ultimately being influenced by a debauched economy. Proceed to the Next Post: Introductory Notes on Quantum Gravity Have suggestions about future content or need help solving a physics/math problem? Tweet @ThePhysicsBlog