A dream comes true

GW150914 observed in LIGO Hanford left and LIGO Livingston on the right. Over 0.25 seconds, the ‘chirp’ signal increases frequency and amplitude.

More than a decade before becoming Director of the newly forming Global Design Effort (GDE) for the ILC in 2005, I took on the task of directing the Laser Interferometer Gravitational-wave Observatory (LIGO) project. Like the ILC, LIGO was an incredibly challenging project with potentially a fantastic scientific payoff.

Of course, we had our critics on LIGO: they said the science could not be guaranteed, the project was too hard technically and it would cost too much money. Nevertheless, we doggedly persisted and had unwavering support from the National Science Foundation, and from our two lead institutions, Caltech and MIT. From the beginning, we knew it would be a long hard road. We proposed to build LIGO in two steps: first, Initial LIGO, that used tested technologies and was designed to have a sensitivity where we could “possibly” detect gravitational waves, and a second phase, Advanced LIGO, where we would use more advanced technologies that would significantly improve our sensitivity to where detections would be “probable.”

We completed Initial LIGO and were well into data taking and limit setting when, in 2005, I was asked to direct the GDE. I agreed to take on that task for the period of developing a Technical Design Report and before we upgraded to Advanced LIGO. During that period, I continued a part-time involvement in LIGO, as we set ever-improving limits for gravitational waves. Despite our lack of success at detecting gravitational waves, the NSF supported our ambitious Advanced LIGO upgrade project.

Since the ILC TDR was completed, I have once again concentrated my efforts on LIGO. We successfully commissioned Advanced LIGO last year, and began our first data run this past September. On 14 September, we recorded a spectacular “eureka” event simultaneously in our two LIGO interferometers separated by some 3000 kilometres. After months of detailed analysis, background studies, physics interpretations, we submitted our discovery paper to Physical Review Letters, where it has now been refereed and accepted for publication.

This event, GW150914, corresponds to the first direct detection of gravitational waves, predicted by Einstein 100 years ago. What did we detect? Our analysis has convincingly concluded that the observed gravitational waves come from the merger of two approximately 30 solar-mass black holes. Such heavy stellar black holes have never been observed and the merger of a pair of black holes is completely new.  This single observation is giving us new insights into astrophysics, in order to explain the formation of such heavy stellar black holes, as well as their existence as binary pairs that merge within the lifetime of our Universe. In addition, this event is enabling new tests of the theory of general relativity in what is called the strong field limit that agree beautifully with the best formulations begun by Einstein.

This discovery is very exciting, and as we continue to take data and improve LIGO sensitivity, we will be effectively opening a new window on the Universe. I hope and believe that the ILC will follow a similar exciting path. The ILC also has its detractors, technological challenges and will cost a lot of money. Nevertheless, great experimental science follows from great ideas. It just takes lots of perseverance, patience, support, and sometimes a little good luck!