1. The Basic Building Blocks of Matter
In the past century, physicists have discovered new constituents of matter — quarks, gluons, neutrinos, and many others. These basic building blocks have been linked together into a well tested theoretical framework, the Standard Model of particle physics. But there are hints that the Standard Model is incomplete, and that a deeper theory lies behind it, waiting to be teased into the open. The work of scientists Bonnie Fleming and Mark Kruse, both at Fermilab in Batavia, IL is profiled. Go to this unit.
2. The Fundamental Interactions
The key to physicists' search for a new, underlying theory of the physical world is a better understanding of the fundamental interactions. One starting point is to investigate the microscopic description of forces: electromagnetism, gravity, and the two nuclear forces, strong and weak, with increasingly energetic collisions. The Large Hadron Collider (LHC) at CERN has achieved the highest energy yet in a particle accelerator, and also the highest luminosity — with events measured in millions of collisions per second. This presents a challenge for physicists Srini Rajagopalan to capture only the most interesting events and for Ayana Arce to find reliable ways to analyze these to reveal interactions that have never been seen before. Go to this unit.
The study of gravity has played a central role in the history of science — from Galileo and Newton to Einstein's 20th century theory of general relativity. Yet in spite of five centuries of study, many aspects of gravity remain a mystery. How can gravity, which in many ways is the dominant force in the universe, be at the same time, by far, the weakest of the four known forces in nature? See how physicists are approaching this question through two topics of intense research in gravitational physics today: short-scale measurements of gravity's inverse-square law at the University of Washington, and the search for ripples in space-time known as gravitational waves at MIT's LIGO facility. Go to this unit.
4. String Theory and Extra Dimensions
In the 20th century twin breakthroughs, quantum mechanics and general relativity provided fresh insight into phenomena at the sub-atomic and cosmological scales, respectively. Yet physicists are still struggling to develop a consistent theory that bridges quantum mechanics and gravity. One approach to "quantum gravity" is string theory: a mathematical description of particles and forces at scales 1031 times smaller than a proton. String theory attempts to link particle physics, the forces of nature, and the earliest moments of the universe into a fresh theoretical framework. Hard evidence remains elusive, but theorists are applying string theory to important problems: explaining the exponential growth of the early universe (Henry Tye of Cornell) and the paradoxes introduced to physics by the existence of black holes (Juan Maldacena of Princeton). Go to this unit.
5. The Quantum World
We are in a new quantum age in which the abstract concepts of the quantum revolution have become concrete thanks to rapid advances in controlling and manipulating atoms, molecules, and light. Find out how laser cooling and trapping, as shown in the lab of MIT's Martin Zwierlein, enables new laboratory experiments as models for disparate systems, providing insights into phenomena at scales from the atomic nucleus to neutron stars. Cooling and trapping atoms is also key to super-precise clocks like the atomic clocks at NIST Boulder — new tools that are being used to search for subtle changes over time in the fundamental constants of nature. Go to this unit.
6. Macroscopic Quantum Mechanics
Quantum mechanics provides a useful description of nature at the atomic and subatomic scale, but it also manifests itself in phenomena at macroscopic scales, including lasers, clouds of ultra-cold atoms, superfluids, and superconductivity. Among these phenomena, the recent discovery of new kinds of high-temperature superconducting materials holds the promise of many practical applications. See how researchers are developing ideas for how these materials work from two different directions: a "top-down" approach, closely examining the materials themselves (Jenny Hoffman of Harvard), and a "bottom-up" approach, looking at model systems that mimic the quantum interactions of the superconducting electrons inside the materials (Debbie Jin of JILA/NIST). Go to this unit.
7. Manipulating Light
Tools of quantum mechanics are opening new possibilities for controlling and manipulating light. Paul Kwiat is creating photons "to order" by carefully manipulating their quantum properties. In 2001, Lene Vestergaard Hau stopped a pulse of light in a cloud of atoms and then released it, along with the information it contained. Explore how light interacts with matter at the quantum level, and learn about the concepts of entanglement and action at a distance. These experiments with storing information in matter are building the groundwork for a new technology: quantum computers. Go to this unit.
8. Emergent Behavior in Quantum Matter
Reductionism — breaking things into their component parts to study how they work — is an effective tool in physics. But many real-world challenges resist this approach. All too often, large scale behavior emerges in ways that are difficult to predict from the behavior of individual components. When the computational requirements are too massive or the theories that govern the component parts are inadequate, many complex systems have yielded to the physics of emergence, which seeks organizing principles at the system level. Find out how many different phenomena — superconductors, hydrodynamics, and even the formation of structure in the universe — are all fruitful areas where the physics of emergence is leading to new understanding. The work of Piers Coleman of Rutgers and Paul Chaikin of NYU is featured. Go to this unit.
The broad, rapidly developing field of biophysics brings together many disciplines. The physics of biological systems provides new insights into how flowers explode into bloom and how bacteria travel. Computational biophysics works to develop designer drugs and a new understanding of neural networks in the brain. Molecular biophysics (Vinothan Manoharan of Harvard) opens the possibility of manipulating DNA and proteins, perhaps leading in the future to nanofabrication of biologically active molecules. And medical physics, as shown by Harald Paganetti at Mass General Hospital, is already providing novel ways of imaging living tissues, as well as curing disease through new uses for old accelerators with radiation therapy. Go to this unit.
10. Dark Matter
Since Swiss astrophysicist Fritz Zwicky first inferred its existence in 1933, dark matter has remained one of the greatest unsolved mysteries in cosmology. Invisible to telescopes, dark matter was detected through its effects on visible matter. Astronomical measurements have shown that dark matter is 3/4ths of all matter, but at present no one has yet directly observed a dark matter particle. See how astrophysicists are seeking evidence for dark matter at the center of the Milky Way galaxy (Doug Finkbeiner of Harvard) and how the LUX (Large Underground Xenon) detector almost a mile underground will look for dark matter particles (Rick Gaitskell of Brown). Go to this unit.
11. Dark Energy
Cosmologists have known that the universe is expanding in all directions since early in the 1920s. Later, they used new instruments to examine the question again. They assumed that — due to gravity — the rate of expansion of the universe today have slowed. Instead, measurements showed that the cosmic expansion has been speeding up. The expansion is attributed to "dark energy," a kind of springiness of empty space itself. Today's astronomical measurements show that dark energy makes up about 70% of the total mass-energy in the universe. See how Robert Kirshner's observations that measure the history of cosmic expansion more precisely, along with a more detailed look at the cosmic microwave background (by Princeton's David Spergel), are providing new clues about the nature of dark energy. Go to this unit.