Have I celebrated the discovery of gravitational waves too much?
I can’t see straight! 😉
While I’m at it, let me post the coolest car plate I’ve found so far: it belongs to one of LIGO scientists but you’re welcome to get inspiration by her.
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.
Yesterday the European Space Agency launched a new satellite: called LISA Pathfinder, its role is to pave the way for the ambitious LISA mission by conducting crucial tests of its technology.
LISA stands for Laser Interferometer Space Antenna and basically is an open mike for Einstein, who imagined the universe as a very lively Sunday market, where people go by or bump into each other, they salute by a mere gesture or take time to exchange about their condition. Much in the same way as the market conveners can talk softly or loudly, if at all, the universe is filled with tales of stars grazing each other, exploding, fusing into one, falling into black holes or witnessing them merge in an even stronger monster.
The convener of this universal market is not Sunday, it’s gravity: so LISA will listen to the story gravity has to tell. The stories that this exquisitely sophisticated microphone will be sensitive to sound like this symphony.
If listening to it makes you want to shake your body a bit, I invite you over to this other post of mine, where I describe gravity as the dance of space and time.
Don’t know what a black hole is? Don’t worry: not even Hawking does. Not completely at least. Of course he’s among the best positioned to have a quite detailed picture but, as you might have noticed from recent press, the (in)famous black hole monster is still an open research problem for the whole scientific community who’s been working on it for the past 40 years! Yeah: that’s how difficult the problem is, so don’t feel too small.
Black holes stare at us with their load of secrets as they sit at the crossroad of physics’ most comprehensive theories. The first one is Einstein’s theory of gravity, called General Relativity, which accounts for the movement of very large objects in the universe and even the history of the cosmos itself; the second theory is called Quantum Mechanics and describes the very small and quirky realm of infinitesimal particles. Both theories were heavily influenced by Einstein, who helped jumpstart the quantum revolution and completely molded General Relativity. Hawking & Co. are right in Einstein’s tracks, as black holes find themselves at the convergence of Quantum Mechanics and General Relativity: understanding them fully is poised to bring a revolution in physics.
The problem physicists have been working on since the 60’s is called the black hole information loss paradox and can be encapsulated in one very simple question “what happens if you pour a cup of tea on a black hole“? This is an example of how physicists work: they ask “what if … ?” and embark in the ensuing adventure.
Just so I clear the doubt once for all: most of the times these questions are explored by scientists in collaboration and, even if a single one makes great strides and becomes famous, like Einstein and Hawking, at least they rely on previous hard work by other smart people. So the reason why I take Hawking here as representative of the endeavor is just because, as Einstein, he’s an iconic character.
Back to business, what happens if you pour a cup of tea on a black hole? The tea itself would disappear because black holes suck everything, as you might already know, even though this only happens in their proximity: so, unless you go poke the bear, a black hole is not dangerous.
What about the heat of the tea? is it gone, too? is there a way from the outside to reconstruct the characteristics of what went in the black hole? had it been a cup of equally hot milk, would we be able to tell the difference by inspecting the black hole? or, in current physics parlance, can we retrieve information from a black hole?
Notice that I said that, in order to know what happens to the cup of tea, we would “inspect” the black hole, I didn’t say we’d ”look at it” for a very precise reason: black holes do not reflect the light impinging on them, as do objects we can see. If you have never thought about the ability of seeing in these terms, try for a moment to picture yourself at night, shining a torch ON objects so that they can bounce light back at your eyes.
Hawking has already contributed a smart idea to the problem of how reticent black holes can be about what they have hidden in their interiors. Forty years ago, he figured black holes can sweat! He did not use these exact words though; so far I haven’t heard anyone else using them but that’s a way I think can ease the understanding of Hawking radiation, as his proposal came to be known.
It turns out that calling space empty is a misnomer: even when devoid of matter particles, space is full of other stuff we do not see other than through its effects. Imagine you are on the top of a mountain, contemplating the panorama around you, especially the mountains summits framing your horizon; between the mountain you’re sitting on and the mountains at the horizon there’s no other mountain: there’s an emptiness of mountains. However, there might be fields in between, covering the valleys hidden by the clouds: lavender fields, corn fields, etc. That’s the closest I can go to the situation in space: between Earth and the Moon, and between us and the Sun, there does not seem to be anything but in reality there are so-called fields, such as the electromagnetic field and the gravitational field.
A field is like The Force, not the physics concept but the Star Wars one, an entity that permeates space and that you do not see directly with your eyes but it has visible effects, such as Yoda lifting a spaceship. In the case of physics the electromagnetic field is responsible for magnets feeling each other’s presence and for connecting you with the world through a mobile phone.
As much as flower fields can wave in the wind, physical fields oscillate, too: instead of setting daisies free in the air, they liberate particles, sometimes in entangled couples, letting them exist for a blink of an eye before they disappear again in the expanse of the field. Hawking understood that for fields around black holes the reabsorption of the particle pairs would not go as unnoticed as the emission: if one of them were sucked by the black hole, the other would be able to fly away, free from its former binding companion.
The particle ending up inside the black hole is such that, by swallowing it, the black hole takes a loss in energy, thus reducing its own mass. The particle escaping to infinity instead has a temperature, so from afar it looks like the black hole emitted heat, which cost it work: in due time (a very large one) the black hole would sweat itself away or, as Hawking and Co. say, it would evaporate.
Unfortunately, the energy regurgitated in this way by the black hole carries no information about what its meal has been. It would seem there’s no way to know what made the black hole sweat, hence the information loss paradox: information should not be destroyed but just transformed, like energy (if you understand French there’s a science poem of mine about energy I’d like to suggest).
If information is not destroyed, where does the black hole hide it then? Hawking has just proposed something in accordance to others before him, that information is stored on the black hole horizon, the surface of no return if you incidentally crossed it. This is a big deal for a very good reason that we can all understand. Imagine you were at the library and you were wondering how many interesting stories and theories and facts were written inside those thick books, on their millions of pages. You’d be surprised if the librarian, some Jacob Bekenstein, came to you and said that, in his library, books wear their stories on their jackets only: they do not need pages for storing their tales. That’s exactly what the late Prof. Bekenstein had found about black holes’ storage habits in the ’60s, before Hawking contributed his pieces to the puzzle.
I think this account is enough to give you an idea of what is keeping Hawking and colleagues’ mind in check; if you want to deal with the matter further see the “Backreaction” blog. Last but not least, in case you had other metaphors useful to convey a sense of the many weird features of black holes, do not hesitate to let me know, either in private or through the comments.
At the end of 2012, before leaving the University of Maryland, I took part in an initiative that blended science with performing arts: that was “Gravity: the dance of space and time” and it was developed in collaboration with the School of Dance Instructor Adriane Fang and Astronomy Professor Cole Miller.
In this post I would like to present the performance in detail, by pointing at the background scientific concepts and how they got translated artistically into the show, which you can see in its final form here.
Inspired by the “Dance your PhD” contest, Adriane was interested in bringing some science into dance and that’s where Cole and I came to the rescue: though we did not end up dancing in the show as it is required to the contest participants, we got actively involved in the rehearsals, not only building a conversation with the artists but also trying some moves out. I hope my following description will convey the feelings of emotion and satisfaction that I experienced during all the stages of the project.
Even though gravity might sound like something obvious and a completely figured out concept it is actually among the most intriguing domains of current investigations in both theoretical and experimental physics. Just think about the mysterious dark matter and dark energy and the fact that they account for as much as 96% of the total mass-energy density of the universe. In our everyday life we only have one chance to appreciate how gravity is far from evident, when we use the GPS antenna in our navigator or smartphone: if Einstein had not improved on Newton’s grasp of gravity the GPS could not exist or work. In Newton’s description gravity is a force that propagates instantaneously, for example from the Sun to the Earth: if one could make the Sun disappear we would immediately realize the absence of its gravitational pull on Earth (see for example a video from Brian Greene’s documentary “The Elegant Universe”- Episode 1, 9:30 into it). The set in which this happens is as static as a fixed stage, where every actor experiences things in the same way, most notably for what concerns time. Then came Einstein. In his picture gravity is still due to the presence of mass but there is something more profound to it: mass deforms space in a way similar to how a heavy ball acts on a trampoline or to when we sit on a couch pillow; objects put in the vicinity of the deformation fall towards the mass responsible for that, just as we see them falling toward the Earth when we release them to the pull of its gravity. What does this have to do with GPS? The answer lies in the fact that, with Einstein, space is no longer a static stage with one given universal time: there exists a single entity called spacetime, which is a dynamic stage that can do stuff and participates to the acting.
When our GPS antenna talks to the GPS satellite fleet to establish its position relative to the satellites’, an exchange of signals is involved in the process; the situation is reminiscent of clock synchronization among people: if everyone’s watch shows a different time there are very few chances to recombine all together on time. In the case of GPS satellites communicating to our antenna, synchronization is not so easy: for starters time does not flow at the same pace for everyone! that’s what a dynamical spacetime stage entails. If mass can deform space, and space is a whole with time, mass affects time: the closer you are to the source of deformation, the slower time flows for your watch as compared to one which is at a larger distant from the mass. Finally, there’s one more source of difference between the pace of satellites’ time and the one of clocks on Earth’s surface, speed effects: the faster you move the slower time flows for your watch as compared to one which is at rest. It wouldn’t be worthy of Einstein if things were not so rich!
|I find Salvador Dali’s “The Persistence of Memory” a powerful visual handle to grasp the concept of mutable time.|
This was kind of a long introduction but it will allow you to better appreciate the dance show, especially its second part: in fact, while the first act represents the motion of astrophysical objects in spacetime, the second is devoted to spacetime itself. For this reason, I’m going to talk about the final half of the show first.
In collaboration with costume designer Kate Fulop, we chose black stretchy costumes to be used in the second act: they were meant to represent spacetime as an elastic deformable cosmic fabric. The moves the dancers perform are both artistically pleasant and scientifically suggestive: they alternate between slow and fast, just as we said time can flow in a specific region of space according to the proximity of this region to a heavy astrophysical mass.
Of course, we did not want the dance performance to be just descriptive: that’s what I meant earlier on when I said that the entire collaboration has been the result of a conversation around a scientific theme. Adriane proposed her graduate students to perform their moves according to an interesting interpretation of the scientific concepts: in pairs, the artists would stimulate their partner’s movement by transmitting them their own energy through a flow without contact; then the partners would react either by affinity or contrast, that is to say moving towards or against the source of energy, respectively. I personally took part in the rehearsals in which the dancers were exploring this part of their “phrase”, as it is called in their jargon: for me it was both new and challenging to try and bring formulae alive in this way. Another distinctive type of the grad students’ moves inspired by science was the “stretch and squeeze”. In order to explain it let me go back to the trampoline analogy I used to depict how spacetime gets deformed in the presence of mass. Imagine moving the mass around on the surface of the trampoline: you can picture ripples forming on the elastic membrane, just like waves on the surface of a pond. This might make you think of yet another type of waves coming from a perturbed membrane: the ones coming from a drum hit by mallets, that is to say sound waves. Like a buoy is carried up and down by the tide a device probing spacetime ripples would experience two peculiar effects: the aforementioned stretch and squeeze.
The sound you hear at the end of the first act is the melody played by two huge cosmic mallets hitting on the spacetime drum, a couple of merging black holes. This is the result of a simulation where the astrophysical signal expected from the coalescence has been treated in such a way as to shift its frequency to the region audible to our ears: in fact, these gravitational waves do not bring any type of light by themselves, so we will not “see” them but rather “listen” to them with our instruments. Given the variety of astrophysical sources and configurations, scientists expect to listen to a sort of very peculiar concert of gravitational waves: in the next few years instruments will be upgraded to the necessary sensitivity and we could hear as many as a hundred of different “music pieces” per year.
On scene the sound simulation accompanies the evolutions of the last two dancers in the first act: they represent two black holes orbiting around each other in a spiraling shrinking motion dictated by Einstein’s equations; the very last stage of the evolution, the merger of the two bodies, is described by the powerful moment of a hug between the two dancers. One of them is still carrying her veil. This element of the costumes is instrumental to the science too. When an astrophysical object passes by another its companion experiences a varying gravitational field, thus the companion deforms its shape. This is fancy talk to refer to Earth’s tides; due to the varying distance of the Moon our planet gets periodically deformed on two sides: the one closer to the Moon, which is feeling its gravitational pull more strongly, and the other farther from the Moon, which is feeling its gravitational pull less strongly. At a more quantitative level such tidal deformations, and their physical effects, are nicely represented by simulations such as this one from Caltech.
The first act of the performance is then a joyful succession of star and black hole encounters, something that cannot happen in our astronomical neighborhood because it is not very populated. While this is good for the survival of the human race on Earth it is kind of boring for the curious scientists. Soon they will be able to add yet more information to their comprehension of astronomy by opening a new observation window on the Universe: this is what scientists such as Cole and I call gravitational wave astronomy; together with Adriane, her amazing students and her friendly colleagues we happily participated in building a representation of the subject that could be attractive to non-scientists. We hope we succeeded. Now watch the video of the performance again and see if you think likewise.
Head of Humanities, ex-VSO and Teacher of History. Left wing politically, conservative pedagogically.
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