# super string theory

## why Did sheldon leave it?

### Margie sanchez, contributing science writer

**L**ike many of you, I revel in the weekly antics of Sheldon, Leonard, Penny, and the rest of the cast of *The Big Bang Theory*. This is truly one of the most humorous shows ever conceived in the history of television. Until recently, it seems I took my science background for granted, as far as the science references in the show. That is, until my nephew expressed an interest in understanding more about String Theory and other topics that routinely surface during the plot development or in the conversation among the main characters, especially when Sheldon is involved. String theory, quantum mechanics, dark matter, quantum singularities, general relativity, tachyons, gravitons, leptons, the Higg’s boson, ad infinitum… I am fairly familiar with most of the concepts included in the show since my background is in molecular biology, which includes a lot of chemistry as well as some physics. The motivation here is to attempt to explain and define, in simple language and terms, a few concepts of particle, quantum, and other main fields of physics.

Let’s start with string theory, the bane of Sheldon’s existence. String Theory, also known as Super String Theory or M-Theory, is based on the concept that all matter is made up of infinitely small filaments of vibrating energy. **I’m talking about a scale beyond the subatomic level, smaller than quarks**. (Yeah, yeah, I know you Trekkie fans are quite familiar with a character named Quark from DS 9, but I’m not talking about a diminutive, enterprising alien right now.) String theory bears the nickname “the DNA of Reality” because of its significant relevance in the search for the ultimate nature of physical reality. For scientists, especially the great physicists- Newton, Tesla, Einstein, Schrodinger, Hawking, Weinberg, Higgs, and Fineman, the ultimate quest is to find the fundamental units that make up the physical world around us.

String theory is just one of the theories of unification, also known as the unified theory of nature. According to unification theory, fundamental forces like electromagnetism, weak nuclear force, and strong nuclear force comprise the prevailing explanation of the material world around us. I’m not just talking about the world immediately visible to us, but the entire cosmos from the microcosm to the macrocosm. Why is string theory such a big thing? You see, string theory includes gravity as the fourth force to account for our physical world. By changing the way we think about gravity, string theory may be able to solve some of the most elusive mysteries in the cosmos.

So why does the very mention of string theory now raise objections from Sheldon since he abandoned his work on the subject in Season 7 of BBT, often setting up an episode for hilarious hijinks and conflicts? Well….

does the very mention of String Theory raise Sheldon’s hackles, often setting up an episode for hilarious hijinks and conflicts? Well….

There are two major sides in the community of physicists. On one side is **cosmology and general relativity**. If you don’t recognize the term general relativity, you really did nap during high school science classes. Bueller, Bueller, anyone???? Remember Albert Einstein? Yeah, the guy that created the term general relativity when he achieved his greatest contribution to the world of science and humanity. Ok, so what is general relativity and why is it significant to the explanation of the physical world? Well, it’s a rather elegant way to explain that matter or energy cause spacetime to curve, and that this curvature is what deflects the path of particles, such as the ones in a gravitational field. Remember, we live in a visible reality of three spatial dimensions- up and down, left and right, forward and backward. Then we add time, resulting in a four dimensional blending of space and time we refer to as spacetime, or for Trekkies like me, my brothers, Sheldon, Leonard, Howard, and Raj- the spacetime continuum.

So, general relativity is a way to account for the location of things, anything from planets to atoms, and everything has a definite location and velocity. In addition, general relativity is probably still the best theory for gravity. So, you can plug in those locations, velocities, and even the masses of objects into the general relativity equations to calculate the curvature of spacetime, and then conclude the effects of gravity on the objects’ trajectories. Yeah, I know, some of you have already zoned out by now. But for those of you who haven’t, let’s examine the other main cadre of physicists, those on the side of **particle physics and quantum theory.**

** **About 90 years ago, quantum mechanics was introduced to explain the behavior of particles and forces at the atomic and subatomic levels. These tiny scales make quantum effects particularly relevant in the physical world. ** **At the scale of atoms and electrons, quantum theory states that particles do not necessarily have definite locations and velocities. This quantum version is a paradigm shift from general relativity which places everything at a fixed location with a definite velocity. Therefore, a quantum version of gravity has to be fundamentally different than the general relativity theory of gravity. To complicate things even further, at even the tiniest scale determined by the Planck length (10 -33 centimeter), quantum theory implies that spacetime itself is more like a sea of virtual particles filling empty space everywhere.

Think of dark matter and dark energy. Sounds like science fiction, right? But I assure you this is very active, current research. In the quantum version, everything is in a constant state of flux, even “empty” space, which isn’t really empty at all, but filled with the aforementioned virtual particles that move in and out of existence continuously. This version of spacetime is markedly different from the smooth field of spacetime curvature defined by general relativity. In other words, if we say that matter follows laws of quantum theory, but adhere to general relativity’s version of gravity, the result is mathematical contradictions. Therefore, a quantum theory of gravity has been like the proverbial Holy Grail for a new breed of physicists because all physical forces can be described by quantum laws, EXCEPT for gravity.

This is why string theory and other unification theories are so important. New developments constantly bring new theories to the table, each attempting to bridge the gap between general relativity and quantum forces, and to further our understanding of the world around us.

You see, most of the time these differences and contradictions between quantum theory and general relativity are insignificant because the effects of calculations for either are so small that they can either be dismissed or approximated. However, calculations performed when the curvature of spacetime is immense causes the quantum aspects of gravity to suddenly become extremely relevant. We’re talking about things like the center of a black hole or the beginning of the big bang – situations where a quantum theory of gravity must be considered, as well as a theory of quantum spacetime since the spacetime curvature includes the effects of gravity. And this, ladies and gentlemen, is where we interject string theory.

Since the 1970s, theoretical physicists have utilized string theory in an attempt to overcome some of the problems inherent to formulating a quantum version of gravity.

So, why did Sheldon abandon string theory after devoting much of his life to its pursuit? Unfortunately, although string theorists have developed some approximations, they do not yet have true exact equations, so string theory is still evolving. And they do not even know some of the principles that explain the form of the equations. Nevertheless, even some of the most renowned and respected physicists still see string theory as the possible unification theory because it is a way of addressing the infinities in the quantum version of gravity. And a quantum theory of gravity is absolutely necessary to unite all the forces of nature in any attempt to explain or describe the material world around us, the visible as well as the invisible. Including the really cool stuff like dark matter and dark energy. What is dark matter, you ask? Well, let’s reserve that topic for another time in the spacetime continuum…..