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AdS/CFT equates a string theory with gravity to a particle theory without gravity.
Black Holes
One of the strangest predictions of general relativity is that space-time can bend so much that it will produce a hole in the middle of space.
Brane Annihilation
In one model, two branes moving towards each other drove inflation. Their collision ended inflation and resulted in the formation of strings.
String theory contains more than just strings: it includes multi-dimensional objects, or "branes." Our universe is made up of a 3-dimensional brane.
Extra Dimensions
Above each point in our visible dimensions, a small extra-dimensional space may be hidden.
Fundamental Strings
String Theory proposes that the building blocks of matter are not point like particles, but instead are vibrating "strings."
Gravitational Lensing
Gravitational lensing occurs when a dense object bends space-time and causes the path of a light ray to be deflected around it, producing a distorted image.
Hawking Radiation
According to quantum mechanics, black holes are actually continuously emitting tiny amounts of matter. This is known as Hawking radiation.
In its first fraction of a second, our universe expanded by a factor of 1030, growiing by a greater percentage than it has in the 14 billion years since.
String Theory and Extra Dimensions
String theory proposes as many as seven extra spatial dimensions.


Cosmic String Lensing
A cosmic string could produce a double image of a galaxy behind it.
Einstein, Albert
Some of Einstein's great insights began in thought experiments.
Kaluza and Klein
Theodor Kaluza (left) and Oskar Klein (right) made a remarkable theoretical description of gravity in a fifth dimension.
Large Hadron Collider
The LHC creates the highest-energy collisions on Earth, but these are irrelevant to Planck-scale physics.
The weakness of gravity is difficult to maintain in quantum mechanical theory, much as it is difficult to balance a pencil on its tip.
30 Doradus in the large magellanic cloud
Structure in the Cosmos
While the universe appears approximately uniform, we see varied and beautiful structure on smaller scales.

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artist's rendition of a black hole
Accreting Black Hole
Artist's conception of a black hole accreting matter from a companion star.
AdS/CFT duality
AdS/CFT Duality
The AdS/CFT duality relates a theory on the boundary of a region to a theory with gravity in the interior.
branes and antibranes
Brane Inflation
A brane and an antibrane moving toward one another and colliding could have caused inflation and the Big Bang.
p branes
Branes and Strings
Strings can break open and end on a brane.
Compactified Extra Dimension
String theorists generally believe that extra dimensions are compactified, or curled up.
Cosmic Microwave Background
Map of the temperature variations in the cosmic microwave background measured by the WMAP satellite.
Equivalent String Configurations
The consequences of strings winding around a larger extra dimension are the same as strings moving around a smaller extra dimension.
expanding universe graphic
Expanding Universe
General relativity is consistent with all the cosmological data that characterizes our visible universe.
Expanding Universe
If we run time backwards, the entire universe collapses into a single, infinitely dense point.
Extra-Dimensional Space
A depiction of one of the six-dimensional spaces that seem promising for string compactification.
Gravitational Field Lines
The gravitational field lines spread out radially from a massive particle.
Graviton Exchange
Gravitons arise naturally in string theory, leading to Feynman diagrams like the one on the right.
Gravity and Extra Dimensions
Gravity leaking into extra dimensions could explain the hierarchy problem.
Hawking radiation graphic
Hawking Radiation
Black holes radiate by a quantum mechanical process.
horizon problem
Horizon Problem
Both sides of the universe look the same, although light could not have traveled from one side to the other.
cosmic inflation
During the period of inflation, the universe grew by a factor of at least 1025.
inflaton potential
Inflaton Potential
A potential like the one shown above for the inflaton field could have caused inflation.
Length Scale
Quantum effects meet general relativity somewhere near the center of this length scale.
giant plastic ball in valley
Origin of Particles
All the Standard Model particles could have been produced by the inflaton oscillating around its ground state like a ball rolling around in a valley.
planck satellite
Planck Satellite
The Planck satellite will make precise measurements of fluctuations in the CMB.
Quark Flux Tubes
Quark Flux Tubes
As quarks are pulled apart, eventually new quarks appear.
Star image
Quark-Gluon Plasma
The aftermath of a heavy ion collision at RHIC, the Relativistic Heavy Ion Collider.
Riemann Surfaces
These objects are Riemann surfaces with genus 0, 1, and 2.
simulated LHC collision
Simulated LHC Collision
The rules of quantum gravity must predict the probability of different collision fragments forming at the LHC, such as the miniature black hole simulated here.
Standard Model
The Standard Model of particle physics.
String Collision
String collisions are softer than particle collisions.
String Landscape
Typical string theories or supersymmetric field theories have many candidate scalar field inflatons.
String on a Double Torus
Strings can wind around a double torus in many distinct ways.
Structure Formation
Small fluctuations in density in the leftmost box collapse into large structures on the right in this computer simulation of the universe.
The fundamental units of matter may be minuscule bits of string.
Temperatures, Energies, and Lengths
Changes in short-distance physics—at the Planck scale—can produce profound changes in cosmology, at the largest imaginable distances.
Waves on a Circle
If a particle is constrained to move on a circle, its wave must resemble the left drawing rather than the right.