, in the LIGO Laboratory, developed an ambitious program for Advanced LIGO that incorporated a new suspension system to stabilize the mirrors and an active seismic isolation system to sense and correct for ground motions," says Barish.
The active seismic isolation system developed for Advanced LIGO works in a similar fashion to noise-canceling headphones, except it can measure and cancel out ground vibrations coming from many directions. In conjunction with this system, a new "quieter" way to suspend LIGO's mirrors was developed with the help of the Glasgow group, which involved hanging the mirrors with a four-stage pendulum. The combination of these two advances gave LIGO a huge improvement in sensitivity to lower frequencies of gravitational waves, which was ultimately what was needed to detect the crashing of two black holes.
Barish also created the LIGO of today: a collaboration of approximately 1,200 scientists and engineers at about 100 institutions in 19 nations called the LIGO Scientific Collaboration (LSC).
"In addition to picking the right technologies and developing them, and securing funding, we needed to build a collaboration of the absolute best people possible for this almost impossible project," says Barish. "Forming an international collaboration, the LSC, enabled this. We attracted the best people from other universities and countries, creating an 'equal opportunity' collaboration, where there was no advantage to being at Caltech or MIT." The LSC conducted the scientific searches and analysis that led to the LIGO discovery.
While this experimental work was taking place, theorists outside Caltech, MIT, and the LIGO project were developing computer codes to simulate the massive collisions of black holes and other sources of gravitational waves that LIGO might detect. These simulations are essential to LIGO; by comparing the shapes of the waves that LIGO observes with the simulations' predicted wave shapes, LIGO scientists can figure out what produces the observed waves. In the early 2000s, Thorne became alarmed at the slow progress on simulations and so with then-Caltech physicist Lee Lindblom, he created a research group at Caltech in collaboration with a group at Cornell University led by his former student Saul Teukolsky (PhD '74), who is now jointly the Robinson Professor of Theoretical Astrophysics at Caltech and Hans A. Bethe Professor of Physics and Astrophysics at Cornell University. By 2015, this SXS (Simulating eXtreme Spacetimes) project was simulating the collisions of black holes with ease, as were several other research groups.
On September 14, 2015, just after the Advanced LIGO interferometers began their first search for gravitational waves, they captured a strong signal. Comparison with the SXS simulations revealed that the signal was from the collision of two hefty black holes 29 and 36 times more massive than the sun and located 1.3 billion light-years from Earth. The waves carried away as much energy as would be produced by annihilating three suns. After intense scrutiny of the results, the LIGO scientists announced this discovery to the world on February 11, 2016.
"I'm positively delighted that the Nobel Committee has recognized the LIGO discovery and its profound impact on the way we view the cosmos," says Reitze. "This prize rewards not just Kip, Barry, and Rai but also the large number of very smart and dedicated scientists and engineers who worked tirelessly over the past decades to make LIGO a reality."
"LIGO was a huge technical and scientific gamble," says Fiona Harrison, the Benjamin M. Rosen Professor of Physics and the Kent and Joyce Kresa Leadership Chair in Caltech's Division of Physics, Mathematics and Astronomy. "But it paid off in spades with one of the most dramatic discoveries in decades. The entire LIGO team should be celebrating today."
The 2017 Nobel Prize in Physics represents the 37th and 38th Nobel Prizes awarded to Caltech faculty and alumni. Current Caltech faculty with Nobel Prizes include: Robert Grubbs, winner of the 2005 Nobel Prize in Chemistry with Yves 