http://einstein.phys.uwm.edu/ Thank you for your interest in Einstein@home! Einstein@home is a program that uses your computer's idle time to search for spinning neutron stars (also called pulsars) using data from the LIGO and GEO gravitational wave detectors. Einstein@home is a World Year of Physics 2005 project supported by the American Physical Society (APS) and by a number of international organizations. After several months of testing, we are now 'throwing open the doors' for general participation. If you would like to take part, please use the Create account link to create an account, and follow the instructions. Einstein@home is available for Windows, Linux and MacOS X computers. This first production run of Einstein@home carries out a search for pulsars over the entire sky, using the most sensitive 600 hours of data from LIGO's third science run, S3. Bruce Allen, Professor of Physics, U. of Wisconsin - Milwaukee Einstein@home Leader for the LIGO Scientific Collaboration _________________________________________________________________ http://www.ligo.caltech.edu/ The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a facility dedicated to the detection of cosmic gravitational waves and the harnessing of these waves for scientific research. It consists of two widely separated installations within the United States one in Hanford Washington and the other in Livingston, Louisiana operated in unison as a single observatory. Gravitational Waves: Ripples in the Fabric of Space Time Albert Einstein predicted the existence of gravitational waves in 1916 as part of the theory of general relativity. Einstein described space and time as different aspects of our reality, in which matter and energy are ultimately the same thing. Space-time can be thought of as a "fabric" defined by the measuring of distances by rulers and the measuring of time by clocks. The presence of large amounts of mass or energy distort space-time--in essence causing the fabric to become curved, or "warped"--and we observe this as gravity. Freely falling objects-whether a soccer ball, a satellite, or a beam of starlight-simply follow the most direct path in this curved space-time. When large masses move suddenly, some of this space-time curvature ripples outward, the ripples spreading much the way ripples do on the surface of a pond after a stone has been thrown into the water. Imagine two neutron stars orbiting each other. A neutron star is the burned-out core that can be left behind after a star explodes. It is an incredibly dense object that can carry about as much mass as a star like our sun, in a ball only a few miles wide. When two such dense objects orbit each other, space-time is stirred by their motion, and gravitational energy ripples outward into the universe. In 1974 Joseph Taylor and Russell Hulse found such a pair of neutron stars in our own galaxy. One of the neutron stars is a pulsar, meaning that it beams regular pulses of radio waves toward Earth. Taylor and his colleagues were able to use these radio pulses, like the ticks of a very precise clock, to study the orbiting neutron stars. Over two decades, they watched for and found the tell-tale shift in timing of these pulses, which indicated the loss of energy from the stars-energy that had been carried away as gravitational waves. The result was just what Einstein had predicted it would be! LIGO will detect the ripples in space-time by using a device called a laser interferometer, in which the time it takes light to travel between suspended mirrors is measured with high precision using controlled laser light. Two mirrors hang very far apart, forming an "arm" of the interferometer, and two more mirrors make a second arm perpendicular to the first arm. When viewed from above, the two arms form an L shape. Laser light enters the arms through a beam splitter located at the corner of the L, dividing the light between the arms. The light is allowed to bounce back and forth between the mirrors many times before it returns to the beam splitter. If the two arms have identical lengths, then interference between the light beams returning to the beam splitter will direct all of the light back toward the laser. But if there is any difference between the lengths of the two arms, some light will travel to where it can be recorded by a photodetector. The space-time ripples cause the distance measured by a light beam to change as the gravitational wave passes by, causing the amount of light falling on the photodetector to vary. The photodetector then produces a signal telling how the light falling on it changes over time. The laser interferometer is like a microphone that converts gravitational waves into electrical signals. Two interferometers of this kind are being built for LIGO one near Richland, Washington, and the other near Baton Rouge, Louisiana. LIGO must have two widely separated detectors, operated in unison, in order to rule out false signals and confirm that a gravitational wave has passed through Earth.