I love taking walks, especially by the Leman Lake. I go there when I feel like stretching my legs and refreshing my brain. I’m there now, in company of swans, ducks and seagulls as they enjoy their life. A few of them are singing, others are flying, others are swimming. As they do so they leave trails behind them, ripples on the lake’s surface that gradually widen in aperture as they depart from their points of origin, the swimming birds. Every now and then a stronger wave reaches the shore where I am: tumultuous, with more pronounced ups and downs, I immediately suspect it coming from something a bit heftier than a swan. It’s a boat, carrying people and momentarily interrupting an otherwise perfect peace.
The situation I just observed is a poetic version of something right on spot in high end physics research: gravitational waves, the ripples in the cosmic sea of the Universe that are generated by mass and/or energy when in accelerated movement. Waves are ubiquitous in the Universe. They can be produced in a variety of ways, even familiar ones: with a musical instrument, that transfers its vibrations to our ears through air, switching on a lamp, thus provoking electron excitations in the filament, which then relax and release light, with an x-ray machine that sends high energy photons through our bodies.
Talking about relaxation, something that I’d like to do, other than walks, to give vent to the occasional pressure is playing a big drum with mallets. Waves again, yet in the form of sound, originated by the deformations I cause on the drum’s membrane by hitting it with the mallets. Probably less appealing to the ear than swans’ singing as I’m not gifted with musical capacity.
But I’m fond of Einstein and he was a very fine composer of the melodies of the Universe. He conceived one special symphony, a tale of massive bodies bumping into each other in the loneliness of the Universe, clinging to this encounter as the last one in their life and celebrating it with a dance that will bring them closer and closer, until they merge into one.
Listening to these melodies will allow us to reconstruct the furious dance that accompanied the bodies merger and infer a lot about a behavior of the Universe that we’re otherwise blind about. Or rather deaf.
This silence has finally been shattered now, by one of the most sensitive microphones ever built: LIGO, a machine that is capable of detecting a bulk vibration smaller than the size of an atom, should have heard the cosmic melody due to two black hole mallets hitting on the stiff membrane of spacetime.
Up until today we hadn’t been able to listen to any cosmic concert, we had only observed the movement of the percussionists: two very compact stars, approaching each other just as Einstein’s choreography dictates, a Nobel Prize discovery.
The difference between the two perspectives is fundamental … here comes another Nobel Prize! History really has a huge sense of humor, if all this happens a 100 years after Einstein wrote down the score of the symphony.
I’ve recently had the privilege to work on this animation about gravitational waves, together with the gifted Jorge Cham, artist and scientist, and Daniel Whiteson, a physicist who likes to do this type of outreach just as much as I do. There are both a video and a comic of this animation that you can find translated in many languages now. In what follows I would just like to mention a couple of things that didn’t fit in the narrative we adopted.
Visualizations and Sounds
If you’d like to see how you’d be changed by a (humongous) passing gravitational wave, go try this app!
To listen to the sounds corresponding to gravitational waves emitted by different sources, put your headphones on and head over to this website.
Supercomputers are crucial in gravitational wave research, for example to simulate black hole collisions. First in the ’60s and then in the ’80s, the need was recognized to develop and put together clusters of very powerful computing machines that would later bring about the first Internet browser and a physical infrastructure which is crucial to forecast weather, for example, or study the feasibility of molecules for medical and industrial purposes.
How can you be part of it?
Citizen science project Einstein@Home lets you contribute “to make the first direct detections of gravitational-wave emission from spinning neutron stars“, by running a useful screensaver on your personal computer. In fact, as we can read in LIGO Magazine #7, “searches for continuous GW signals are computationally limited and require relatively little data for very long processing times. This makes a volunteer computing project a very good match for the problem.”
Now go catch your wave from space!
Update following the announcement of the discovery
Did Einstein@Home play any role in this? No, it didn’t. The signal in the instrument lasted only about 1/4 of a second. It’s not a continuous-wave signal like the type that Einstein@Home has been searching for. But since the observing run ended in mid January, we have been preparing the data to start a new low-frequency all-sky search for continuous gravitational waves. We are now starting to run this on Einstein@Home, so please sign up your computers and disable their sleep mode! In the next months we will extend the frequency range of the continuous waves all-sky searches, target interesting point sources and we are also gearing up to perform broader surveys for binary black hole mergers.
The emotions of the first person to imagine LIGO
“I feel an enormous sense of relief and some joy, but mostly relief. There’s a monkey that’s been sitting on my shoulder for 40 years, and he’s been nattering in my ear and saying, “Ehhh, how do you know this is really going to work? You’ve gotten a whole bunch of people involved. Suppose it never works right?” And suddenly, he’s jumped off. It’s a huge relief.“
Read the rest at the MIT News bulletin.