String Theory

String Theory predicts the existence of more than the 3 space dimensions and 1 time dimension we are all familiar with. According to string theory, there are additional dimensions that we are unfamiliar with because they are curled up into tiny complicated shapes that can only be seen on tiny scales. If we could shrink to this tiny, Planck-sized scale we could see that at every 3D point in space, we can also explore 6 additional dimensions. This animation shows a Calabi-Yau surface which is a projection of these higher dimensions into the more familiar dimensions we are aware of.

In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. In string theory, the different types of observed elementary particles arise from the different quantum states of these strings. In addition to the types of particles postulated by the standard model of particle physics, string theory naturally incorporates gravity, and is therefore a candidate for a theory of everything, a self-contained mathematical model that describes all fundamental forces and forms of matter. Aside from this hypothesized role in particle physics, string theory is now widely used as a theoretical tool in physics, and it has shed light on many aspects of quantum field theory and quantum gravity.

The earliest version of string theory, called bosonic string theory, incorporated only the class of particles known as bosons, although this theory developed into superstring theory, which posits that a connection (a "supersymmetry") exists between bosons and the class of particles called fermions. String theory requires the existence of extra spatial dimensions for its mathematical consistency. In realistic physical models constructed from string theory, these extra dimensions are typically compactified to extremely small scales.

String theory was first studied in the late 1960s as a theory of the strong nuclear force before being abandoned in favor of the theory of quantum chromodynamics. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it an outstanding candidate for a quantum theory of gravity. Five consistent versions of string theory were developed before it was realized in the mid-1990s that these theories could be obtained as different limits of a conjectured eleven-dimensional theory called M-theory.

Many theoretical physicists (among them Stephen Hawking, Edward Witten, and Juan Maldacena) believe that string theory is a step towards the correct fundamental description of nature. This is because string theory allows for the consistent combination of quantum field theory and general relativity, agrees with general insights in quantum gravity such as the holographic principle and black hole thermodynamics, and because it has passed many non-trivial checks of its internal consistency. According to Hawking in particular, "M-theory is the only candidate for a complete theory of the universe." Other physicists, such as Richard Feynman, Roger Penrose, and Sheldon Lee Glashow, have criticized string theory for not providing novel experimental predictions at accessible energy scales and say that it is a failure as a theory of everything. Read more ...

In theoretical physics, M-theory is an extension of string theory in which 11 dimensions of spacetime are identified as 7 higher-dimensions plus the 4 common dimensions (11D st = 7 hd + 4D). Proponents believe that the 11-dimensional theory unites all five 10 dimensional string theories (10D st = 6 hd + 4D) and supersedes them. Though a full description of the theory is not known, the low-entropy dynamics are known to be supergravity interacting with 2- and 5-dimensional membranes.

In the News ...

String field theory could be the foundation of quantum mechanics: Connection could be huge boost to string theory   Science Daily - November 4, 2014

Scientists propose a link between string field theory and quantum mechanics that could open the door to using string field theory as the basis of all physics. Their calculations "could solve the mystery of where quantum mechanics comes from," said a co-author.

String field theory could be the foundation of quantum mechanics   PhysOrg - November 4, 2014

Two USC researchers have proposed a link between string field theory and quantum mechanics that could open the door to using string field theory - or a broader version of it, called M-theory - as the basis of all physics. M-Theory

Scientists find a practical test for string theory   PhysOrg - January 6, 2014

Scientists at Towson University in Towson, Maryland, have identified a practical, yet overlooked, test of string theory based on the motions of planets, moons and asteroids, reminiscent of Galileo's famed test of gravity by dropping balls from the Tower of Pisa. String theory is infamous as an eloquent theoretical framework to understand all forces in the universe - a so-called "theory of everything" that can't be tested with current instrumentation because the energy level and size scale to see the effects of string theory are too extreme.

A 40-year-old puzzle of superstring theory solved by supercomputer   PhysOrg - December 23, 2011
A group of three researchers from KEK, Shizuoka University and Osaka University has for the first time revealed the way our universe was born with 3 spatial dimensions from 10-dimensional superstring theory in which space-time has 9 spatial directions and 1 temporal direction. This result was obtained by numerical simulation on a supercomputer. According to Big Bang cosmology, the universe originated in an explosion from an invisibly tiny point. This theory is strongly supported by observation of the cosmic microwave background and the relative abundance of elements. However, a situation in which the whole universe is a tiny point exceeds the reach of Einstein's general theory of relativity, and for that reason it has not been possible to clarify how the universe actually originated.

In superstring theory, which is considered to be the "theory of everything", all the elementary particles are represented as various oscillation modes of very tiny strings. Among those oscillation modes, there is one that corresponds to a particle that mediates gravity, and thus the general theory of relativity can be naturally extended to the scale of elementary particles. Therefore, it is expected that superstring theory allows the investigation of the birth of the universe. However, actual calculation has been intractable because the interaction between strings is strong, so all investigation thus far has been restricted to discussing various models or scenarios. Read more at:

String Theorists Simulate the Big Bang   Live Science - December 14, 2011
Japanese physicists have created a string theory model that simulates the birth of the universe. In their model, the Big Bang was a "symmetry-breaking event" - a fluctuation that caused three spatial dimensions to break free from the other six dimensions of string theory, then rapidly unfurl to produce our universe's observed 3D structure. String theory - a proposed "theory of everything" that unites quantum mechanics and general relativity together in one complete picture - models elementary particles as oscillating lines ("strings") rather than dimensionless points. In order for the math to work, string theory requires that there be 10 dimensions: nine of space and one of time. Our universe only appears to have three spatial dimensions, string theorists say, because the other six are curled up in undetectably tiny bundles called Calabi-Yau manifolds, which are a minuscule 10^-33 centimeters across.

Physicists use offshoot of string theory to describe puzzling behavior of superconductors   PhysOrg - August 9, 2010

Physicists are divided on whether string theory is a viable theory of everything, but many agree that it offers a new way to look at physical phenomena that have otherwise proven difficult to describe. In the past decade, physicists have used string theory to build a connection between quantum and gravitational mechanics, known as gauge/gravity duality.

Multiple Dimensions: Between Superstrings and Parallel Worlds   Epoch Times - March 26, 2009

Every minute, billions of particles traveling from the sun pass through our bodies, and their trajectory continues—passing right through the planet as if solid matter didn’t exist. These are, of course, neutrinos, the particles “without mass.” While recent studies have revealed that these neutrally charged particles actually do possess mass, neutrinos remain the most difficult subatomic particles for modern physicists to study, mainly because they make so little of an impact on atomic structures as they wander about. Due to their tiny size they pass through everything, as though they were ghosts. What’s more, thanks to a few neutrinos that have actually been able to be observed through special detectors set up in a lab at the South Pole, scientists may have confirmed the existence of other dimensions.