# Superstring Theory: The DNA of Reality

Overview

#### About

#### 01: The Macro/Micro/Mathematical Connection

Professor Gates opens with a survey of the goals of the series and introduces the concept of strings, which are incredibly tiny objects that may be the most fundamental objects in the universe. String theory is not yet experimental physics; it is theoretical physics, based on sophisticated mathematical ideas.

#### 02: Who Is Afraid of Music?

Mathematics will play an important role in this course because string theory is purely mathematical. But instead of studying equations, you will explore the mathematics of strings through computer images and animations. These are comparable to the music generated by notes on a musical score.

#### 03: Apropos Einstein's Perfect Brainstorm Year

This lecture explores Einstein's general theory of relativity, which led to a new understanding of gravity and sparked Einstein's quest for a "theory of everything." Building a mathematical theory of everything is like confronting a complicated toy on Christmas Eve, whose box states, "some assembly required."

#### 04: Honey, I Shrunk to the Quantum World—Part I

In the first of two lectures on the quantum world, you start at the level of the atom and dig deeper, discovering the following: leptons (electronlike objects); nuclear matter (protons, neutrons); quarks (subnuclear matter); and force carriers (photons, gluons, W and Z bosons, and gravitons).

#### 05: Honey, I Shrunk to the Quantum World—Part II

You investigate more properties of the quantum world, including spin, the Pauli exclusion principle, quantization, vacuum polarization, and quantum tunneling. You are also introduced to the Higgs boson, sometimes called the "God particle" for its apparent role in imparting mass to other particles.

#### 06: Dr. Hawking's Dilemma

Any object that possesses a temperature above absolute zero must give off thermal radiation. But how is this possible with a black hole, which is so massive that not even light can escape from it? In 1975, Stephen Hawking forced a crisis in theoretical physics with a stunning theory addressing this problem.

#### 07: I'd Like to See a Cosmos Sing in Perfect Harmony

In trying to explain black holes in a way consistent with Hawking's 1975 theory, scientists had to combine two pillars of physics—quantum theory and the general theory relativity. The resulting mathematics predicted a surprising form of matter: strings.

#### 08: Einstein's Hypotenuse and Strings—Part I

String theory may involve extra dimensions beyond the familiar three of space plus one of time. But how are physicists able to think about extra dimensions? The Pythagorean theorem provides a model, showing that it's possible to calculate the properties of objects in higher dimensions without having to visualize them.

#### 09: Einstein's Hypotenuse and Strings—Part II

Einstein incorporated the fourth dimension of time into the Pythagorean theorem and came up with an idea known as the Einstein hypotenuse. This led to the famous equation E = mc2, which can be interpreted as a statement about areas in a four-dimensional world. You see how Einstein's hypotenuse led to an object that could have destroyed the world of physics: the tachyon.

#### 10: Tying Up the Tachyon Monster with Spinning Strings

This lecture explores the phenomenon of spin, which is ubiquitous in the quantum world. Spin was well known to particle physicists in the 1970s, but it presented problems for the first generation of string theory. A new generation of spinning strings solved the problem and also dealt with the tachyon threat.

#### 11: The Invasion of the Anti-Commuting Numbers

Starting with the frustum (a truncated pyramid) on the back of a dollar bill, you explore some intriguing properties of numbers, including anti-commuting Grassman numbers. Anticommutivity is useful in quantum mechanics and manages to banish the tachyon from certain versions of string theory.

#### 12: It's a Bird—A Plane—No, It's Superstring!

In 1977 three physicists—Gliozzi, Sherk, and Olive—observed that it is supersymmetry (the equality of bosons and fermions) that kills the tachyon monster. Supersymmetry is the child of string theory and the parent of superstrings. But why are there five versions of superstrings.

#### 13: Gauge Theory—A Brief Return to the Real World

While working on supersymmetry around 1982, physicists Schwarz and Green found a solution that required 496 charges, implying a world in which there are 32 possible ways to rotate. The resulting string was called the SO(32) superstring, and was the world's first unified field theory, achieving a dream of Einstein.

#### 14: Princeton String Quartet Concerti—Part I

Circular polarization of light possesses a mathematical property useful in superstring theory. Standing waves, left-moving waves, and right-moving waves are introduced in this lecture. Recognition that all three exist in superstring theory led to a new "heterotic" string constructed by a group of four physicists at Princeton in 1984.

#### 15: Princeton String Quartet Concerti—Part II

The initial work of the "Princeton String Quartet" led to two strings from different dimensions: a left-moving superstring and the old bosonic right-moving string. But this work did not incorporate the requisite 496 charges. This lecture explores a new description of the heterotic string that produces that magic number.

#### 16: Extra Dimensions—Ether-like or Quark-like?

It is often said that string theory requires extra dimensions, but that's not quite true. The mathematics of the heterotic string can be interpreted with extra dimensions or without. What appear to be extra dimensions can be understood as angular variables associated with the change of force-carrying particles.

#### 17: The Fundamental Forces Strung Out

This lecture shows how superstring theory provides mathematical support for Hawking's theory of black-hole radiation, which was discussed earlier in the course. Observational proof of string theory may come not by looking at nature's smallest structures but by looking at its largest: the universe itself.

#### 18: Do-See-Do and Swing Your Superpartner—Part I

Why does the universe observe a dichotomy, in which beams of matter obey the Pauli exclusion principle but beams of energy do not? The universe may be more symmetrical than this model suggests. Here, you look at evidence for supersymmetry that points to the existence of superpartners for ordinary matter.

#### 19: Do-See-Do and Swing Your Superpartner—Part II

Supersymmetry implies that every known matter particle has a superpartner that has yet to be observed in the laboratory. In fact, it is much more likely that superpartners will be discovered indirectly than in the lab. This lecture covers a technique for detecting them.

#### 20: A Superpartner for Dr. Einstein's Graviton

Can physicists find a consistent way to introduce mass to the superpartners so that they become very heavy while ordinary matter remains very light? The Higgs mechanism is one such method and may offer an explanation for the mysterious dark matter that is key to the formation of galaxies.

#### 21: Can 4D Forces (without Gravity) Love Strings?

This lecture follows current attempts to use concepts from string theory to understand the forces and structures of matter inside the proton and neutron. You also visit the strange world of branes, and explore the type IIB string, which is one of five types of superstrings.

#### 22: If You Knew SUSY

If you were to pick up a physics journal from the last 20 years, you would likely come across the word SUSY, which means supersymmetric. In this lecture, you study an unusual aspect of SUSY, superspace, and learn how it accounts for the five types of superstrings.

#### 23: Can I Have that Extra Dimension in the Window?

Strings supposedly describe everything. But if that's true, how can there be five different "everythings"? This lecture investigates a possible solution in 11-dimensional supergravity, which may be part of a larger and even more mysterious construct, M-theory.

#### 24: Is String Theory the Theory of Our Universe?

String theory weaves together an amazing story with contributions by several generations of mathematicians and physicists. Professor Gates closes with a review of the current state of the field, and he looks at some denizens of the world of supersymmetry that he and his colleagues have recently identified.