When it was first introduced, String Theory (or M-Theory, as it has been renamed lately) seemed to have the promise to become a viable Theory of Everything (TOE). (I know that I was pretty excited.) TOE is the current name for the Grand Unification Theory (GUT) that Planck, Dr. Einstein and many, many others have sought after since the equations for the forces and particles started to converge after the discovery of Quantum Mechanics. The idea is simple: since there are only four known forces, it would be logical and seemingly appropriate if they could all and did all have the same origin in some super force that evolved immediately after the Big Bang. Or even if one could simply equilibrate each with the others. There was great excitement when Salam, Glashow and Weinberg, forged a binding between the electromagnetic force and the weak force to create the Electroweak equations in the 1970’s
And so, when the very early versions of String Theory seemed to show that both gravity and the electromagnetic forces evolved naturally from their equations, the excitement engendered was, in the physics community at least, quite palpable. The TOE was within reach!
String Theory is based on the assumption that at the heart of every force carrier or fundamental particle was a single vibrating string whose vibrations created the physical appearances that are characteristic of that object. This was a natural outgrowth of the Quantum definition that reduces all energetic phenomena to a wave function, which of course has a frequency and wavelength, and along the same line of thinking that Dr. Einstein used when he converted the theory of gravity into a geometrical solution. String Theory just extends those concepts to include all of the matter known and categorized by the Standard Model, and theorizes that the vibrating source for all of this is a set of single, small vibrating strings. Very, very small vibrating strings. Strings that are far below the size of a proton and only slightly above the observational limit imposed by the Planck length (10-35 meters). That seemed plausible enough.
But there were some problems that were immediately identified. First, and this is a problem that is rather causally dealt with even to this day, the theories all required extra dimensions, and not just one or two. The early, front running String Theories each required ten dimensions to create all of the required forces and particles, and there were at the time, four separate theories.
One theory required the existence of Tachyons, the mythical particles that can only go the speed of light or faster (not prohibited by Special Relativity) and that get more energetic as they slow down, the opposite of the way all other known matter reacts (and you thought that physicists lacked creativity). They might even be traveling backwards in time.
And then there’s the little problem of the hand picked parameters. You see, while String Theory is very good at predicting the known forces and subatomic particles, this is because the equations feature the constants and assumptions (laws) that will give the correct answers which are deliberately put into the equations by the physicist (convenient, no?).
Dr. Witten seemingly corrected the problem of the four competing theories by showing that, using 11 dimensions, you could derive and explain all of them. He called this, M-Theory where the M stands for Master, Mathematical, Mother, Mystery, Membrane, Magic or Matrix. Or Murky. Maybe, Muddlesome, Misguided and Mental might also apply. You pick, because Witten wouldn’t. And M-Theory seems to be the current leader.
Except that there’s another string theory that has 26 dimensions.
And then there’s the fact that String Theory is not solution specific, that is, it has been estimated that there may be as many as 10500 string theories (more than the number of particles in the known universe) that are all equally valid and internally consistent. The current thinking on this is that the set of equations that best describes our universe was somehow ‘chosen’ to promote the life that could understand it, the Anthropomorphic principle. Ahem.
So, like, what or where are these other dimensions? We all generally agree (well, with the exception of the author!) that there are four basic dimensions: length, width, height and time. So where are the other six or seven? And what are they, and how can we measure them? The answer from String Theory is that they are all too small to see and measure so they must be, erm, curled up in little balls or something attached to the dimensions that we otherwise recognize. We hope to find them someday, but since we don’t exactly know where they are or what they should look like, we don’t really know how to look for them, or what we must do to find them. It’s one of them paradoxes. And the String Theorists haven’t given anybody much help, since they have yet to give any clues as to where on the energy spectrum to look, or what external features that they might have.
String Theory has been added to this narrative not because it adds to the support for the theme of this book or because it provides any particular insights in that direction; it is included more in the interest of completeness and more importantly, as a Cautionary Tale.
You see, not only is String Theory very complex and delving into unknown mathematical territory, but it has completely divorced itself from the known and physical universe, and by doing so has lost any predictive capability, making it impossible to either prove or disprove.
At the turn of the 19th to the 20th century in the physics world, we had experimental evidence leading the theories, that is, new things were being discovered faster than the theoretical framework for them became established. The scientists at that time knew a whole lot about light and electromagnetic energy before Maxwell formed his famous equations that described the interdependence between magnetism and electricity, providing the theoretical background. The electron and the proton were discovered years before anyone had an inkling as to how to characterize their relationship.
The experiments were leading the theory.
That all changed when Paul Dirac used Quantum Mechanics to predict the existence of the positron. Suddenly, the theory was able to predict and, in a manner of speaking, propose, the experiment. Dr. Dirac gave the experimenters clear parameters that defined what they should be looking for, and don’t you know, he had explained exactly what they found, a positively charged electron.
Dr. Einstein’s famous theories can be seen in the same light. Both the Special and the General Theories of Relativity relied on known phenomena, made fundamental assumptions based on observed data and made testable predictions that could be verified by the experimenters.
But now, the theory was leading the experiments. This was not a bad thing, but it is a role reversal.
String Theory, however, has taken this relation one step further by declaring that the theory not only should lead the experiment, but that it need not require any experiments at all, and furthermore, that it can redefine reality based on a perceived mathematical need and the beauty of the formulation. With its unobservable strings that can have ends that may or may not be attached to themselves or to a higher order inter-dimensional surface (a Brane!) and a bevy of new ‘dimensions’ that are not explicitly defined and are outside of our ability to discern, String Theory has taken the world of theoretical physics down Lewis Carroll’s rabbit hole to a world only lightly tied to reality in which only those immersed in its culture can fully understand its rules, precepts and beauty.
The left turn initiated by Schrodinger has resulted in a decades long trip into Wonderland which has brought us no closer to a full understanding of the world in which we live.