String theory

**String theory** tries to use math to explain the four known fundamental forces—gravitation, electromagnetism, strong nuclear force, weak nuclear force—together in one theory. This tries to solve the problems of having both classical physics and quantum physics.  

Einstein wanted a unified field theory, a single theory to explain the fundamental forces. Today's scientists want a unified field theory that also explains matter.  This is called the search for a theory of everything (TOE). The most famous theory used as a TOE is called superstring theory. It says there are 6 higher dimensions as well as the four dimensions of Height, Length, Width and Time).

Some superstring theories think that it is about the geometry of space. This idea is a big part of a theory called M-theory. Many string theorists believe that M-theory explains the universe and might explain how other universes, if they exist, are as part of the  "multiverse". M theory/supergravity theory has 7 higher dimensions and the four dimensions of Height, Length, Width and Time. 

## Background 
Introductions to string theory that are designed for the general public must first explain physics.  Some of the controversies over string theory are because of people not understanding physics. A common misunderstanding even is the idea that a theory is proven true whenever something it says will happen happens.  Another misunderstanding is that earlier physical scientists, including chemists, have already explained the world. This leads to the misunderstanding that string theorists began making up new ideas after they became "set free from truth".  There are many versions of string theory, none quite successfully predicting the observational data explained by the Standard Model.  M theory is now known to have countless solutions, often predicting things strange and unknown to exist.  Some allege that string theorists select only the desired predictions.

The allegation that string theory makes no testable predictions is false, as it makes many.  No theory—a predictive and perhaps explanatory model of some domain of natural phenomena—is verifiable.  All conventional physical theories until the Standard Model have made claims about unobservable aspects of the natural world.  Even the Standard Model has various interpretations as to the natural world.  When the Standard Model is operated, it is often made a version with supersymmetry, doubling the number of particle species so far identified by particle physicists.

None can literally measure space, yet Newton postulated absolute space and time, and Newton's theory made explicit predictions, highly testable and predictively successful for 200 years, but the theory was still falsified as explanatory of nature.  Physicists accept that there exists no such attractive force directly attracting matter to matter, let alone that the force traverses the universe instantly.  Nevertheless, Newton's theory is still paradigmatic of science.

### Hidden dimensions? 
The idea of hidden dimensionality of space can seem occult.  Some theorists of loop quantum gravity—a contender for quantum gravity—regard string theory as fundamentally misguided by presuming that space even has a shape until particles shape it.  That is, they do not doubt that space takes various shapes, simply regard the particles as determining space's shape, not the other way around.  The spacetime vortex predicted by general relativity is apparently confirmed.

If interpreted as naturally true, the Standard Model, representing a quantum particle as a 0D point, already indicates that spacetime is a sea of roiling shapes, quantum foam.  String theorists tend to believe nature more elegant, a belief that loop theorist Lee Smolin dismisses as romantic while using biology's Modern Synthesis as a rhetorical device.  Experiments to detect added spatial dimensions have so far failed, yet there is still the possibility that signs of them can emerge.  Leonard Susskind, a leader of string theory, interprets string theory's plasticity of solutions as paradoxical support resolving the mystery of why *this* universe exists, as M theory shows it but a variant of a general pattern that always approximately results.

In 1957 Hugh Everett described his "Relative state" interpretation.  Everett maintained that the wavefunction does not collapse, and since all matter and interactions are presumed to be built up from quantum waveparticles, all possible variations of the quantum field—indicated by the mathematical equations—are *real* and simultaneously occurring but different courses of history. or that our universe is both—a black hole and dark energy.  The Schwarzschild solution of Einstein's equations can be maximally extended to predict a black hole having a flip side—another universe emerging from a white hole.  Perhaps our universe's big bang was half of a *big bounce*, something's collapse down to a black hole, and our universe popping out its other side as a white hole.

### Particles are strings? 
Physicists widely doubt that quantum particles are truly 0D points as represented in Standard Model, which offers *formalism*—mathematical devices whose strokes predict phenomena of interest upon input of data—not *interpretation* of the mechanisms determining those phenomena.  Yet string theorists do tend to optimistically conjecture that the strings are both real and explanatory, not merely predictive devices.  It is far beyond the capacity of today's particle accelerators to propel any probing particles at energy levels high enough to overcome a quantum particle's own energy and determine whether it is a string.  Yet this limitation also exists on testing other theories of quantum gravity.  Instead, when two particles, each of a certain mass—measured in terms of *energy* as electronvolts—are collided, they can combine into a particle of that combined mass/energy, and the generated particle is "observed" for correspondence with the prediction.  Matter's being a special variant of energy was a consequence of Einstein's special theory of relativity, and thereupon Einstein formalized the mass-energy equivalence, E=mc2.  When sufficiently energetic photons collide, they can combine and generate matter—matter creation.  All particles have antiparticles, and atoms of matter have antiatoms of antimatter, whose union annihilates the particles and matter while leaving energy.

## Developments 
An inspiring development is discovery of mirror symmetry, whereby Calabi-Yau spaces tend to come in pairs such that solutions previously difficult within the extreme vibrational mode of one string can be solved by through the mirror Calabi-Yau space's geometry in its opposite range.

String theory is usually solved through conformal field theory, a quantum field theory on 2D space.  It is confirmed that molecules can collapse to 2D.  And the electron, long presumed an elementary particle, apparently splits into three entities separately carrying the electron's three degrees of freedom when the molecules that contain the electrons are channeled through a 1D pathway.

## Related pages
*M-theory

## Notes