LIGO: The strong belief

Twenty years of designing, building and testing a number of innovative technologies, with the strong belief that the endeavour would lead to a historic breakthrough. The Bulletin publishes an abstract of the Courier’s interview with Barry Barish, one of the founding fathers of LIGO.


The plots show the signals of gravitational waves detected by the twin LIGO observatories at Livingston, Louisiana, and Hanford, Washington. (Image: Caltech/MIT/LIGO Lab)

On 11 February, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo collaborations published a historic paper in which they showed a gravitational signal emitted by the merger of two black holes. These results come after 20 years of hard work by a large collaboration of scientists operating the two LIGO observatories in the US. Barry Barish, Linde Professor of Physics, Emeritus at the California Institute of Technology and former Director of the Global Design Effort for the International Linear Collider (ILC) led the LIGO endeavour from 1994 to 2005. On the day of the official announcement to the scientific community and the public, Barish was at CERN to give a historic seminar that captivated the whole audience, which had gathered in a packed Main Auditorium. We had the opportunity to interview him. A longer version of this interview will appear in the April issue of the CERN Courier.

Professor Barish, this achievement comes after 20 years of hard work, uncertainties and challenges. This is what research is all about, but what was the most challenging thing you had to overcome over this long period?

“It really was to do anything that takes 20 years and still be supported and have the energy to reach completion. LIGO is an incredible technical achievement. The experimental set-up we used to detect the gravitational signal is an enormous extrapolation from anything that was done before. The idea that you can take on high risk in such a scientific endeavour requires a lot of support, diligence and perseverance.”

The experimental confirmation of the existence of gravitational waves has a very profound impact on the future of astrophysics and gravitational physics. What do you think are the most important consequences of your discovery?

“The discovery opens two new areas of research for physics. One is on the general relativity theory itself. Gravitational waves are a powerful way of testing the heart of the theory by investigating the strong-field realm of gravitational physics. Even with just this first event – the merging of two black holes – we have created a true laboratory where you can study all this, and the understanding of general relativity at an absolutely fundamental level is now opening up.

The second huge consequence of the discovery is that we can now look at the Universe with a completely new “telescope”. So far, we have used and built all kinds of telescopes: infrared, ultraviolet, radio, optical… And the idea of recent years has been to look at the same things in different bandwidths.

However, no such previous instrument could have seen what we saw with the LIGO interferometers. Nature has been so generous to us that the very first event we have seen is new astrophysics. We have been really lucky. Over the next century, this field will provide a completely new way of doing an incredible amount of new science.”

What was your first feeling when you saw the event on your screen?

“We initially thought that it could be some instrumental crazy thing. We had to worry that somebody had done it on purpose. In order to carefully check the origin of the signal, we tracked back the formation of the event data from the two interferometers and we could see that the signal was recorded within 7 msec, exactly the time we expect for the same event to appear on the second interferometer. The two signals were perfectly consistent and this gave us total trust in our data.”

At the seminar at CERN you were welcomed and thanked like a star. It was a great honour for the CERN audience to have you in person giving the talk just after your colleagues had made the announcement in the US. What are you bringing back from this experience?

“I was very happy to be presenting this important achievement in the temple of science. The thing that made me feel that we made the case well was that people were interested in what we have done and are doing. In the packed audience, nobody seemed to question our methodology and our analysis. We have one single event but this was good enough to convince me and also my colleagues that it was a true discovery. I enjoyed receiving all the science questions from the audience, it was really a great moment for me.”

by Antonella Del Rosso