# String Theory

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### String Theory and Calabi-Yau Manifolds

The problem of extra dimensions continued to plague string theory, but these were solved by introducing the idea of compactification, in which the extra dimensions curl up around each other, growing so

### String Theory: Duality

The core of M-theory is the idea that each of the five string theories is actually a variation on one theory. This new theory — M-theory — is an 11-dimensional theory that allows for each of the existing

### Two Dualities to Unite Five Superstring Theories

Both T-duality and S-duality relate different string theories together. String theory skeptics aren’t convinced that these dualities in some specific states of the theories relate to a more fundamental

### The Second Superstring Revolution: The 11-Dimensional Theory

The period immediately following the proposal of M-theory has been called the “second superstring revolution,” because it once again inspired a flurry of research into superstring theory. The research

### String Theory: A History of Cosmology

Before string theory, there was Einstein’s relativity, and before that was Newton’s gravity, and for about two centuries before Newton, the laws governing the universe were believed, by most of the Western

### History of String Theory: The Enlightened Universe

The history of string theory includes the history of cosmology and astrology. In the 1500s, the geosynchronous model was replaced with the heliocentric

### String Theory and the Idea of an Expanding Universe

Before string theory, Albert Einstein was strongly influenced by the concept of an unchanging universe. His general theory of relativity predicted a dynamic universe — one that changed substantially over

### String Theory and The Big Bang

String theory will hopefully help physicists understand more precisely what happened in those early moments of the universe, so understanding the big bang theory is a key component of string theory's cosmological

### String Theory and the Steady State Theory

Though we know much more than ever about what makes up the heavens, the black space between the stars still holds many mysteries — and string theory is at the heart of the search for the answers to many

### String Theory and Inflation

Today, the principles at the heart of inflation theory have a profound impact on the way that string theory is viewed by many physicists. In trying to understand the universe, two major problems remained

### String Theory: Variations of the Inflation Model

Some variations and alternatives to the inflation model are posed by string theorists and other physicists. Two creators of inflation theory, Andreas Albrecht and Paul J. Steinhart, have worked on alternative

### String Theory and the History of Dark Matter

Physicists have calculated that throughout the universe, there’s approximately six times as much dark matter as normal visible matter — and string theory may explain where it comes from!

### String Theory: The History of Dark Energy

Recent findings have indicated that the expansion rate of the universe is actually increasing, meaning that the cosmological constant has a positive value. This repulsive gravity — or

### Bosonic String Theory: The First String Theory

The first string theory has become known as bosonic string theory, and it said that all the particles that physicists have observed are actually the vibration of multidimensional “strings.” But the theory

### String Theory: The First Physical Model

The basic physical interpretation of string theory was as vibrating strings. As the strings, each representing a particle, collided with each other, the S-matrix described the result.

### Why Bosonic String Theory Doesn’t Describe Our Universe

The early string theorists had therefore spent a lot of time giving meaning to a theory that seemed to (almost) accurately predict the S-matrix, only to find that the majority of particle physicists weren’t

### String Theory and Massless Particles

One side effect of creating a consistent string theory is that it had to contain certain objects that can never be brought to rest. Because mass is a measure of an object while it’s at rest, these sorts

### String Theory and Tachyons

A bigger problem than massless particles for string theory in the 1970's was the tachyon, a particle predicted by bosonic string theory that travels faster than the speed of light. Under a consistent bosonic

### Bosonic String Theory: 25 Space Dimensions

In 1974, Claude Lovelace discovered that bosonic string theory could only be physically consistent if it were formulated in 25 spatial dimensions, but so far as anyone knows, we only have three spatial

### The History of Superstring Theory

Despite bosonic string theory’s apparent failures, some brave physicists stayed committed to their work. Why? Well, physicists can be a passionate bunch

### String Theory: Fermions and Bosons

The notion of symmetry was picked up by Pierre Ramond in 1970, followed by the work of John Schwarz and Andre Neveu in 1971, to give hope to string theorists. Symmetries exist throughout physics. A

### String Theory: Supersymmetry Hypothesizes Superpartners

Under supersymmetry, the corresponding bosons and fermions are called superpartners. The superpartner of a standard particle is called a sparticle.

Because none of the existing particles are superpartners

### String Theory: The History of Supersymmetry

As a consequence of the Standard Model’s success, string theory wasn’t needed to explain particle physics. Instead, almost by accident, string theorists began to realize that string theory might just be

### String Theory: Five Theories

In the wake of 1984’s superstring revolution, work on string theory reached a fever pitch. If anything, it proved a little too successful. It turned out that instead of one superstring theory to explain

### String Theory and The Hierarchy Problem in Physics

Many physicists feel that string theory will ultimately be successful at resolving the hierarchy problem of the Standard Model of particle physics. Although it is an astounding success, the Standard Model

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