AUDIO: Peering into the quantum world, physicists use particle detectors and accelerators to probe matter on a nuclear scale. GLAST will use these high energy detector technologies to view the cosmos, recording gamma rays from immense particle accelerators that operate on scales far beyond anything achieved on planet Earth. But most cosmic gamma rays are blocked by the Earth's atmosphere, unable to reach detectors on the ground. So the GLAST mission must be carried out from space. When these gamma-ray photons interact with matter, they create pairs of oppositely charged particles. Light turns into matter and anti-matter, such as an electron and positron. The creation of particle pairs from purely energetic gamma rays is described by Einstein's famous equation, E=mc^2. VIDEO DESCRIPTION: Video of Stanford's Linear Accelerator, nuclear physicist working in a lab, artist concept of GLAST in orbit, artist concept of gamma rays being blocked by Earth's atmosphere, artist concept of photons interacting with matter.