Greene mentions a number of contemporary physicists—Gabriele Veneziano, Pierre Ramond, and Shing-Tung Yau among them—who have made important contributions to the advancement of string theory. The following list focuses primarily on the predecessors of string theory: scientists and mathematicians from earlier eras who laid the groundwork for what is now the cutting edge of physics.
A Danish physicist and contemporary of Einstein. Bohr developed quantum mechanics and was the first to apply the quantum theory to the problem of atomic structure. He received the Nobel Prize in 1922.
A German physicist. In 1926, Born introduced one of the most bizarre—but still experimentally verifiable—aspects of quantum theory: the idea that an electron wave must be interpreted from the standpoint of probability. Born’s reinterpretation of Schrödinger’s wave equation led to a new theory of quantum mechanics.
A French nobleman. In 1923, de Broglie suggested that Einstein’s conception of the wave-particle duality of light also applied to matter. For discovering the wave-nature of electrons, Broglie was awarded the 1929 Nobel Prize for Physics.
An English physicist. Eddington tested Einstein’s theory of general relativity during a 1919 total solar eclipse and found that the bending of light rays that Einstein predicted actually occurred. (Eddington’s conclusions were later called into question, but at the time they turned Einstein into an international celebrity.)
A German-American physicist. Einstein formulated both the theories of special and of general relativity. His theory of gravitation marked a profound revision of Newton’s ideas.
A Swiss mathematician and physicist. Euler is considered one of the founders of pure mathematics. His studies of strongly interacting particles influenced many physicists throughout the twentieth century.
An American theoretical physicist. Feynman reinvented quantum electrodynamics in the years following World War II. He advanced a powerful new way to think of Born’s probability theory, and many consider him the most important theoretical physicist since Einstein.
An American physicist. In 1969, Gell-Mann won the Nobel Prize for his classification systems of atomic and subatomic particles, and the ways in which they interact. It was Gell-Mann who coined the term quark, which he borrowed from James Joyce’s Finnegans Wake, to describe the building blocks of matter.
An American theoretical physicist. Glashow, along with Steven Weinberg and Abdus Salam, was awarded the 1979 Nobel Prize for Physics for his revolutionary formulation of electroweak theory, which explains the unity of electromagnetism and the weal force.
A Dutch-American physicist. Goudsmit, along with George Uhlenbeck, proposed the concept of electron spin, which posits that electrons rotate on an axis. This insight led to many revisions in theories about atomic structure and quantum mechanics.
An English theoretical physicist. Hawking’s black hole theory combines quantum mechanics and general relativity. Hawking is the author of the bestseller A Brief History of Time: From the Big Bang to Black Holes (1988), an explanation of the cosmos intended for the general public. He has also received the Albert Einstein Award, which is the most important award in theoretical physics.
The first proponent of the uncertainty principle, which has remained the key feature of quantum mechanics since its introduction in 1927.
A German physicist. In 1887, Hertz found that when electromagnetic radiation (light) shines on certain metals, they release electrons. From his studies of James Clerk Maxwell’s electromagnetic theory, Hertz established that light and heat are both electromagnetic forces.
An American astronomer. Hubble proved that the universe is expanding.
A German mathematician. In 1919, Kaluza proposed that the universe might contain more than three spatial dimensions. Kaluza’s theory was considered outlandish, and it took Einstein several years to consider Kaluza’s theory seriously, but string theorists today find it remarkably prescient.
A Swedish physicist. In 1926, Klein refined Theodor Kaluza’s notion of an extradimensional universe.
A French mathematician, astronomer, and physicist. Laplace is best known for applying Newton’s theory of gravitation to the solar system.
A Scottish physicist. Maxwell developed the set of four equations that became the basis of electromagnetic theory, the single force unifying electricity and magnetism. Maxwell’s work had a huge influence on twentieth-century physics, and he is ranked alongside Isaac Newton and Albert Einstein for the scope of his contributions. Maxwell’s field equations prompted Max Planck to formulate the quantum hypothesis—the theory that radiant-heat energy is emitted only in finite quantities, or quanta.
A German theoretical physicist. Planck pioneered quantum theory. Planck’s constant,Planck tension, and Planck mass are all named after him. His work revolutionized physicists’ understanding of atomic and subatomic particles. Planck won the Nobel Prize in 1918.
A German mathematician. Riemann’s geometrical studies were foundational to Einstein’s theory of relativity.
A Pakistani physicist. Salam was awarded the 1979 Nobel Prize, along with Sheldon Glashow and Steven Weinberg, for his work developing electroweak theory.
An Austrian physicist. Schrödinger argued that waves were really “smeared” electrons. He objected to the then-universally accepted description of matter in terms of waves and particles, and instead advanced a quantum mechanical wave equation. Schrödinger shared the Nobel Prize of 1933.
A German astronomer and physicist. Schwarzchild worked out Einstein’s field equations of general relativity while stationed on the Russian front during World War I.
A Dutch physicist. Uhlenbeck, along with Samuel Goudsmit, proposed the concept of electron spin, which posits that electrons rotate on an axis. This insight led to many revisions in theories about atomic structure and quantum mechanics.
An American nuclear physicist. Weinberg shared the 1979 Nobel Prize with Sheldon Glashow and Abdus Salam for the formulation of electroweak theory. Weinberg showed that photons and bosons actually belong to the same particle family.
An American physicist. Witten instigated the second superstring revolution in 1995. It was Witten who first proposed that the five versions of string theory were really just five interpretations of the same theory. He also introduced the important possibility that string theory encompasses far more than just strings.
An English physicist. Young disproved Newton’s conception of light as a stream of particles. By allowing light to pass through two pinholes onto a screen, he found that the light beams spread apart and overlapped. In the area of overlap, Young saw bands of bright light alternating with bands of darkness. With this demonstration, he revived the century-old wave theory of light and established the principle of interference of light.
Matter with the same gravitational properties as regular matter, but with an opposite electric charge and opposite nuclear force charges.
A particle of antimatter.
The widely accepted theory concerning the origin of the universe. The big bang theory posits that the universe evolved approximately 10 to 15 billion years ago from the explosion of an incredibly dense, hot substance that was contained at one point. The universe has been expanding since the first fraction of a second after the big bang occurred.
The term referring to what some physicists believe will happen when the expanding universe stops and implodes. When the big crunch occurs, according to the theory, all space and matter will collapse together.
A region of space formed when a giant star collapses and all of its mass compresses to a single point, forming a gravitational field so overpowering that it traps anything that comes close to it, including light.
A pattern of string vibration with an amount of spin measurable in whole numbers. A boson is most often a messenger particle.
The first version of string theory. Bosonic string theory, which dealt with string’s vibrational patterns, emerged in the 1970s. This version was later revised and replaced by supersymmetrical string theory.
A theoretical configuration that many physicists believe might contain the additional dimension string theory requires. Many thousands of such possible configurations exist, but string theory has yet to verify the correct one.
One of the four fundamental forces, along with gravity, the strong force, and the weak force. Electromagnetism determines all types of electromagnetic radiation, including light, X-rays, and radio waves.
A relativistic quantum field theory that describes the weak force and the electromagnetic force within a single framework.
To Greene, string theory defines elegance because it is extremely simple, but it may explain every event in the universe.
The indivisible or “uncuttable” unit found in all matter and forces. Elementary particles are now categorized by quarks and leptons, and their antimatter counterparts.
The basic tenet of general relativity. The equivalence principle states that accelerated motion is indistinguishable from gravity. It generalizes the theory of relativity by showing that all observers, regardless of their state of motion, can say that they are at rest, provided they take the presence of a gravitational field into account.
Also called topography-changing transitions. Flop transitions are the act of Calabi-Yau space ripping and repairing itself.
A particle that transmits one of the four fundamental forces. The strong force is associated with gluon; electromagnetism with the photon; the weak force with W and Z; and graviton (which hasn’t yet been discovered) with gravity.
There are four fundamental forces : electromagnetism, strong force, weak force, and gravity.
Albert Einstein’s formulation that gravity results from the warping of spacetime. Through this curvature, space and time communicate the gravitational force.
Physicists believe that graviton—which has not yet been proven to exist—is the particle carrier of the gravitational force.
The weakest and most mysterious of the four fundamental forces. Gravity acts over an infinite range, and gravitation describes the force of attraction between objects containing either mass or energy.
The theory under which all five previous versions of string theory fall. The most recent synthesis of string theory ideas, M-theory predicts eleven spacetime dimensions and describes “membranes” as a fundamental element in nature.
A precept of string theory that demonstrates how two different Calabi-Yau shapes have identical physics.
Laws of motion based on an absolute and unchanging notion of space and time. Newton’s laws of motion were later replaced by Einstein’s theory of special relativity.
A machine that speeds up the movement of particles and then either shoots them out at a fixed target or makes them collide. Particle accelerators allow physicists to study the movement of particles in extreme conditions.
A formal framework for making approximate calculations. Perturbation theory is a linchpin of string theory in its current form. The approximate solution will be refined later as more details fall into place.
The smallest bundle of light. Photons are the messenger particles of the electromagnetic force.
The action of electrons shooting from a metallic surface when light is shone onto that surface.
The energy required to probe Planck-length-scale distances.
Planck length—approximately 10–33 centimeters—is the scale at which quantum fluctuations occur. Planck length is also the size of a typical string.
Planck mass is roughly equal to the mass of a grain of dust, or ten billion billion times the mass of a proton.
Planck’s constant is also known (and written) as the “h-bar.” It is a fundamental component of quantum mechanics.
About 10 (to the 39th power) tons. Planck tension is equal to the tension of a typical string.
According to the laws of quantum mechanics, the smallest physical unit that something can be broken into. Photons are the quanta of the electromagnetic field.
Also known as relativistic quantum field theory. Quantum field theory describes particles in terms of fields, as well as how particles can be created or annihilated, and how they scatter.
Also known as spacetime foam. Quantum foam is the violent turbulence of spatial fabric at an ultramicroscopic scale. Its existence is one of the chief reasons that quantum mechanics is incompatible with general relativity.
The framework of laws that describe matter on atomic and subatomic scales. The uncertainty principle is a pillar of quantum mechanics.
A family of elementary particles (matter or antimatter) that make up protons and neutrons. There are many types of quarks: up, charm, top, down, strange, and bottom. Quarks are acted upon by the strong force. Murray Gell-Mann named quarks after he read James Joyce’s Finnegans Wake.
Einstein’s description of particle motion, which hinges on the constancy of the speed of light. The theory of relativity states that even if an observer is moving, the speed of light never changes. Distance, time, and mass, however, all depend on the observer’s relative motion.
The theory that all particles have an intrinsic amount of spin in either whole- or half-integer denominations.
A quantum model that explains three of the fundamental forces—electromagnetism, the strong force, and the weak force—but does not take gravity into consideration.
Miniscule one-dimensional vibrating strands of energy. String theories posit that these filaments are the basis of all elementary particles. The length of a string is 10–33 cm; strings have no width.
So called because it is the strongest of the four fundamental forces. It holds quarks together and keeps protons and neutrons in the nuclei of atoms.
A theory that describes resonant strings as the most elementary units in nature.
A principle of symmetry relating the properties of particles with a whole-number quantity of spin (bosons) to those with half a whole number of spin (fermions). Supersymmetry posits that all elementary matter particles have corresponding superpartner force carrier particles. No one has yet observed these theoretical superpartners, which are thought to be even larger than their counterparts.
A particle that has a negative mass when squared. The existence of a tachyon usually indicates a problem with a theory.
The study of geometric figures’ properties that exhibit ongoing transformations and are unchanged by stretching or bending.
Heisenberg’s uncertainty principle is the crux of quantum mechanics. It proclaims that you can never know both the position and the velocity of a particle simultaneously. To isolate one, you must somehow blur the other.
A theory describing all four fundamental forces and all of matter within a single framework.
One of the four fundamental forces. Weak force operates over a short range.