© 2016 EPFL/Jamani Caillet

12.02.16 - 1.3 billion years ago, two black holes collided in an enormous explosion of energy. The massive event sent gravitational waves across space-time. The waves finally passed through Earth last September, to be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States. EPFL astrophysicist Anaïs Rassat gives her thoughts about the discovery, and discusses its significance.

What was so exciting about yesterday's LIGO press announcement?

They announced that the LIGO-Virgo Consortium had made the first direct detection of gravitational waves using the Observatory’s advanced technology. Scientists have been trying to track down gravitational waves for decades. In the past, they have found hints of their presence, but through indirect methods of detection. We now have the first direct detection, which means we know for sure that gravitational waves exist. It is very exciting.

Science is about collaboration – and I find this to be a great aspect of the discovery. Like so many projects in physics today, the detection involved a a large international collaboration: over 1000 members representing 15 different countries have been working together since the beginning of the project in 1997. 

ARWhat are gravitational waves and why are they so difficult to detect?

Gravitational waves are “ripples” through space-time, which can be caused by violent events in the universe, e.g. the merging of two black holes, or could even be created in early times, just after the Big Bang. Gravitational waves were first proposed by Albert Einstein a hundred years ago, based on his theory of gravity – what is known as his theory of general relativity.

To detect gravitation waves, scientists use laser interferometers like LIGO’s. These systems bounce lasers over several kilometers and look for tiny, infinitesimal changes in the laser light across the length of the interferometer – think one part in 1021 (that is a 1 followed by 21 zeroes). That would be a sign that a gravitational wave passed through the instrument. It’s an amazing technological challenge, and extremely difficult to measure. 

What does the discovery mean for science? How does it change the way scientists observe the universe?

This is a breakthrough for science. Gravitational waves will help astrophysicists understand how gravity and black holes work. It also means we now have a whole new window in the universe: instead of observing the universe only with “standard” light (electromagnetic waves, which can be in the microwave, the infrared or the visible parts of the spectrum), we could hopefully now also use gravitational waves.

Will this affect your own research?

Gravitational waves might also exist in the very early universe, in which case they are called “primordial” gravitational waves. If we can observe these, we can learn more about the very early universe. My colleagues working on the very early universe are thrilled by this discovery.

We live in a very special time for science. A hundred years after Einstein worked out his famous theory of gravity, we finally have the technological tools to study the night sky and understand his theory better. There are many things about his theory that scientists are testing today, and its centennial is very exciting for scientists worldwide.

To spread the excitement of Einstein’s theory, I collaborated in making a 3-min animation narrated by former “Dr Who” David Tennant on Einstein's theory, with award-winning animator Eoin Duffy and the director Jamie Lochhead. You can watch it here:

Join in the conversation on #Einstein100 and #gravitationalwaves on social media too!