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Default Gallery: Einstein's Legacy: Inside the Quest for Gravity Waves

</img>: Photo: Dave Bullock/Wired.comPASADENA, California -- Like radio and gamma waves before them, the detection of gravity waves will likely expose a new layer of the universe and change the study of physics as we know it.
As Einstein predicted in 1912, gravity waves are emitted by massive bodies in space that don't necessarily leave visual evidence of their existence, such as black holes. Directly observing gravity waves, in a sense, would make these invisible phenomena visible.
On the forefront of the discovery of gravity waves is one of the largest projects ever funded by the National Science Foundation, the Laser Interferometer Gravitational-Wave Observatory (LIGO). The LIGO facilities house extremely long lasers that are sensitive to disturbances down to fractions of the width of a proton -- just sensitive enough to register the relatively weak gravity waves.
While the main LIGO data is generated from 2.5-mile-long laser beams in Washington and Louisiana, upgrades to increase the lasers' accuracy and sensitivity are developed on a smaller prototype at Caltech. Tour the LIGO labs at Caltech in this gallery.
Left: A pristinely ground and polished mirror hangs like a pendulum over a testing bench. Although transparent to visible light, this mirror reflects nearly 100 percent of the infrared light of the lasers inside the interferometer.
An interferometer is the device in which these lasers are contained. It uses the light from infrared laser beams to very accurately measure distance. The longer the laser beams, the more sensitive the interferometer can be. When a significantly strong gravity wave passes through an interferometer, it should change the length of the instrument only slightly due to the ripple in space and time that it causes.
</img>: Photo: Dave Bullock/Wired.comThe view from on top of the Caltech interferometer shows the "L" shape of the device, with each arm containing a laser beam that extends for 40 meters. These stainless steel chambers are emptied to roughly one-billionth of an atmosphere, creating an impressive and necessary vacuum for the beams.
This is a similar but smaller prototype of the interferometers in Washington and Louisiana which have arms measuring 2.5 miles each. Having these two similar facilities allows scientists to confirm that a detected anomaly is actually a gravity wave and not cars passing by the labs, waves crashing on distant shores or even the minute inconsistencies in the lasers themselves.
</img>: Photo: Dave Bullock/Wired.comInside the vacuum chamber, the beam-splitter sits at the intersection of the two arms of the interferometer (the joint of the "L"). This table is composed of an array of mirrors, prisms, filters and other optical devices. From here, the infrared laser beam is sent down each arm of the system.
Each laser beam is calibrated to the same, extremely precise resonance. If one beam has met with any interference it can be measured here against the other beam.
</img>: Photo: Dave Bullock/Wired.comThe problem with detecting gravity waves is that the changes they exert over the Earth are extremely small. The powerful waves generated by distant events are relatively weak by the time they reach Earth. For this reason, the instruments used to detect them must be extremely precise and elaborate.
At left, the end of one arm of the interferometer contains one of four main mirrors (center right) along with an assortment of smaller mirrors. All these mirrors are used to calibrate and align the laser. The main mirror reflects the laser beam back to the joint of the "L" for measurement.
</img>: Photo: Dave Bullock/Wired.comThe laser (before it splits) originates in the white tube on the right. This tube contains the elaborate and delicate instruments used to correct for as much signal noise as possible.
The amount of noise-correcting technology at work in the lab is mind-boggling, with layers and layers of isolation. The beam comes out of a 20-cm quartz tube suspended on a pendulum, which itself is on springs, on a seismic isolation stack, in a vacuum chamber. The chamber is temperature-controlled and insulated with fiberglass.
The photons bouncing back and forth inside the suspended cylinder stay resonant at the exact length at which the interferometer operates. Any shift in frequency or deviation in length of the laser beam causes the cavity to fall out of resonance and is detected by the system.
</img>: Photo: Dave Bullock/Wired.comAn optics bench at the end of one arm of the interferometer is used to monitor the intensity, position and angle of the laser beam.
</img>: Photo: Dave Bullock/Wired.comThis optic bench is used to sense light from various ports at the intersection of the interferometer arms, which is where the gravity waves may some day be detected. To do this, it's covered with LIGO-built detectors.
</img>: Photo: Dave Bullock/Wired.comThe three boxes in the center of this photo are quadrant photodiodes (QPDs), which are used to detect the precise position of the laser beam.

</img>: Photo: Dave Bullock/Wired.comThe LIGO prototype interferometer requires an extremely high vacuum of roughly one-billionth of an atmosphere, or about the level of vacuum found in low-Earth orbit. To attain this extreme level of emptiness, a vibration-free, magnetically levitated turbo-pump is employed. Pictured are a vacuum manifold and remote-controlled valves that help power the vacuum.
</img>: Photo: Dave Bullock/Wired.comThese expansion bellows allow the length of the interferometer arm to be adjusted to compensate for the temperature expansion of the stainless steel. Without these bellows the high-vacuum chamber would be pulled and dragged across the floor every time the ambient temperature changed.

</img>: Photo: Dave Bullock/Wired.comFrom left: Alan Weinstein, Steve Vass and Rob Ward next to the LIGO interferometer.

Weinstein is a professor of physics and applies his understanding of high-energy physics to studying the nature of dark energy and detecting gravitational waves. Vass has managed the LIGO prototype lab for over 20 years. Ward is a graduate student and one of the co-authors of a recent Nature article entitled A quantum-enhanced prototype gravitational-wave detector. The paper focuses on reducing the quantum-noise in the LIGO interferometer.
</img>: Image: NASAThough the direct detection of gravity has yet to be accomplished, last month information generated by LIGO helped diagnose the cause of the Crab Nebula's rapid energy loss.


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