An artist’s rendering of the space-time ripples called gravitational waves. Image Credit: Jet Propulsion Laboratory

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!

Enter: the 21st century with more advanced technology, a vision to validate a key prediction made by General Relativity, Dr. Bruce Allen et al, and dedicated volunteers from the general public. The Einstein at Home project was conceived and implemented — a noteworthy effort to search for these telltale gravitational signals emitted by pulsars.

Einstein@Home uses computer time donated by computer owners all over the world to process data from gravitational wave detectors — the Laser Interferometer Gravitational Wave Observatory (LIGO), and the GEO 600 laser interferometer. Participants in E@H download software to their computers, which process gravitational wave data when not being used for other computer applications.

The sensitivity of the equipment used to make these observations is phenomenal — LIGO possesses the ability to measure changes in distance on the order of one-one hundred millionth the diameter of a hydrogen atom. For more detailed information, consult this overview.

We’ve now passed the one-year anniversary of the Einstein at Home distributed computing project having opened to the public, powered by the Berkeley Open Infastructure for Network Computing (BOINC). Talk about time flying — it seems like the Bad Astronomy / Universe Today team was just founded yesterday (our team’s page resides here). At the time of this entry, our team’s combined crunching efforts have earned well over 2,500,000 credits, and climbing.

If you’re interested in joining this project, visit the Einstein@Home portal at the University of Wisconsin-Milwaukee. This is a great opportunity for the average person (like me) to assist cutting-edge scientific efforts on the front lines. E@H is still in need of users to help process the wealth of data collected thus far, so if you’d like to donate extra CPU cycles, it’s not too late to sign up and crunch.