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Ring laser reveals subtle seismic motion

A laser gyroscope located deep beneath the Gran Sasso mountain in central Italy has made the first deep-underground measurements of the rotational motion that passing seismic waves generate in the Earth’s crust. The ability to make such measurements could boost our understanding of the strain that rocks undergo before an earthquake takes place, say the scientists who carried out the research.

Earthquakes release large amounts of pent-up energy in the form of seismic waves, which propagate in all directions from the quake’s epicentre. When those waves reach the Earth’s surface they can cause the ground to move along one or more orthogonal axes – up and down, back and forth, and side to side. But seismic waves can also generate much smaller rotational motions, in which the ground rotates around one or more of the three axes.

According to Gilberto Saccorotti of Italy’s National Institute for Geophysics and Volcanology (INGV), rotational motion is important to measure for a number of reasons. For one thing, seismologists can determine the speed of a seismic wave – and so better understand the kind of rock it propagates through – by comparing the magnitudes of the rotational and translational motions that it generates. In addition, better measurements of ground rotation during strong earthquakes would allow for more robust building regulations. “Circular motion, like horizontal motion, can be very dangerous,” he says. “Structures haven’t been designed with that in mind but are instead meant to resist vertical forces, i.e. their own weight.”

Circular motion, like horizontal motion, can be very dangerous
Gilberto Saccorotti, National Institute for Geophysics and Volcanology

Seismometers are not naturally suited to measuring this circular motion because they are based on pendulums or masses-on-a-spring, which respond in the same basic way, whether the devices’ housing moves up and down or is tilted. While arrays of seismometers can be used to measure circular motion, the relativity weak nature of these events means that only the strongest signals can be detected in this way.

Frequency shift

Ring-laser gyroscopes, on the other hand, are designed specifically to measure rotational motion. These devices record the very tiny differences in frequency between two laser beams sent in opposites directions around an optical circuit that is fixed rigidly to the ground. The frequency offset reflects the rate at which the ground rotates. Ring lasers in Germany, New Zealand and the US have been detecting earthquakes’ rotational ground movements for about the last two decades, but the fact that these instruments are located at or just below ground level exposes them to disturbances – be they of natural or human origin – that originate close to the Earth’s surface.

In the latest work, Saccorotti and colleagues at the INGV and Italy’s National Institute for Nuclear Physics (INFN) used a ring laser called GINGERino, consisting of four 3.6 m-long sides mounted on a block of granite. Housed 1400 m underground at the Gran Sasso National Laboratory, the device is largely shielded from the tiny variations in air pressure that can trouble ring lasers at shallower depths. It is the forerunner of an experiment called Gyroscopes in General Relativity (GINGER), which will use at least three large ring lasers arranged at right angles to one another to try and measure the very subtle “frame-dragging” effect predicted by Einstein’s general theory of relativity.

Using GINGERino, the INFN-INGV group was able to record a magnitude-seven earthquake that occurred under the Atlantic Ocean during a week of data-taking in June 2015. The researchers say that although their data exhibit a poor signal-to-noise-ratio, they were still able to detect rotational motion generated by the earthquake’s seismic waves in the rock surrounding the lab.

Potential earthquake precursors

According to Saccorotti, the result shows the feasibility of installing a long-term experiment in the Gran Sasso lab – be it GINGER or a single, larger ring laser. Such a device would systematically record rotational ground motions over a two- to four-year period. This would allow the detailed study of the elastic deformation of rock caused by the gradual build-up of energy across a geological fault ahead of an earthquake. “That deformation can include rotational motion, so having a very sensitive device in a low-noise environment opens up interesting possibilities for studying a potential earthquake precursor”, he says, pointing out that Gran Sasso is in one of the most seismically active regions of Italy.

Ulrich Schreiber of the Technical University of Munich, who collaborates with the Italian group, points out that the field of “rotational seismology” is now quite well established, thanks to the availability of improved ring-laser gyroscopes. But he nevertheless praises the latest work. “GINGERino is a prototype instrument that has still to mature a fair bit before reaching its full potential,” he says. “But being able to observe rotational motion from remote earthquakes in a deep-underground laboratory is an important step forward.”

The research is reported on the arXiv preprint server.

How LIGO will change our view of the universe

Results and data from the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) collaboration – which revealed last week that it had observed a gravitational wave for the first time – are already providing astronomers and cosmologists the world over with previously unknown information about our universe. While the current results have posed intriguing questions for astronomers regarding binary black-hole systems, gravitational-wave astronomy will also revolutionize our understanding of the universe during its infancy, according to cosmologist and Perimeter Institute director Neil Turok.

Many scientists, such as LIGO veteran Kip Thorne, have pointed out that the collaboration’s results have opened a new window onto the universe. Each time that this has happened in the past, unexpected phenomena have come to light – for example, the advent of radio astronomy revealed the universe’s most luminous objects in the form of quasars and pulsars.

Pristine objects

Turok told physicsworld.com that black holes – some of the most prolific producers of these ripples – are some of the simplest objects in the universe. He points out that when it comes to these “perfectly pristine objects”, there are “not too many parameters that need to be determined” because a black hole’s dynamics are mainly determined by its mass. Turok also points out that gravitational waves will provide even deeper insights, as they involve the fundamental force of gravity, which itself is still something of a puzzle.

Indeed, for Turok, this is what is most exciting about aLIGO’s discovery, which he says “may mark a bit of a transition as gravitational-wave observatories become the high-energy colliders of the future as we probe gravity and other extremely basic physics”. Gravitational waves can go to a time/place that, currently, we have very little information about – the early universe, which is opaque to all electromagnetic radiation.

Looking back in time

Thankfully, gravitational waves can travel freely through the hot plasma of the early universe and could be used “to look back to a trillionth of a second after the Big Bang”, according to Turok. For him, the discovery is very timely, as he is currently working with colleagues on a new theoretical proposal for “shockwaves” produced a millionth of a second after the Big Bang, which would have been present across all scales in the early universe. If these shockwaves exist, they would have an effect on the measured density variation that is seen in the cosmic microwave background, and could only be detected by gravitational radiation. Once they have a more complete theoretical description, Turok is convinced that LIGO and its successors such as the LISA Pathfinder and other space-based experiments could pick up the shockwave signal, if it exists.

Ultimately, Turok is delighted by LIGO’s discovery, and although he says that it is “much more important than any prize”, he is sure that it will win not only a Nobel prize, but also a slew of others, such as the Breakthrough prize.

A preprint of Turok’s paper on shockwaves is available on the arXiv server.

Waves of soup, spying on gravity and touring the solar system

Nathan Myrvold's gravity-inspired soup bowl (Courtesy: Modernist Cuisine). — Nathan Myhrvold’s gravity-inspired soup bowl. (Courtesy: Modernist Cuisine)

By Hamish Johnston

Nathan Myhrvold knows a lot about gravity (he worked with Stephen Hawking) and a lot about food (he wrote Modernist Cuisine) so it’s not really surprising that he has designed a soup bowl inspired by the collision of two black holes. Created in 2014, the bowl was made to hold two different types of soup in swirls of space–time. Now that the LIGO observatory has spotted a gravitational wave from the collision of two such black holes, I’m guessing sales of the bowl will be out of this world.

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Ultrathin lens is free of chromatic aberrations

A new type of flat, ultrathin lens designed to be free of chromatic aberrations has been developed by researchers in the US. The device has a variety of potential applications, from ultralight imaging systems for drone aircraft to more compact lenses for mobile-phone cameras.

Lenses for cameras, eyeglasses and other applications are traditionally based on refractive optics, which involves using curved lenses to bend light rays. The “optical power” of a conventional lens – how strongly it bends light – is proportional to its thickness, which means that a conventional refractive lens cannot be very thin. Refractive lenses also suffer from chromatic dispersion, wherein blue light bends more than red, and therefore multiple images are produced over a range of focal lengths. Multiple lenses can cancel out this dispersion, but this adds further to the weight, thickness and cost of a lens system.

Diffractive lenses offer a route to ultrathin lenses by redirecting light using the interference between light waves as they pass through a series of slits in a thin opaque material. Such lenses can be effectively flat, and therefore much lighter and thinner than refractive optics. However, diffractive lenses suffer from much larger dispersion. And to further complicate matters, this dispersion is anomalous with red light bending more than blue.

Thin metasurface

In 2015 Federico Capasso of Harvard University and colleagues showed that a flat lens can be made that focuses all of the colours of broadband light in the same plane. The team then unveiled a device that focused broadband infrared light onto a single line using a thin metasurface.

To be used in a camera, you need to be able to form good images, and that will require a little bit more work
Rajesh Menon, University of Utah

This device used dielectric resonators that interact directly with the electromagnetic field of light waves to impart any desired phase shift. However, this new technology brings its own challenges. Making the metasurfaces requires precision engineering because the resonators have to be smaller than the wavelength of the focussed light. Metasurfaces are also inherently polarization-sensitive, whereas a general-purpose camera lens needs to focus unpolarized light.

Now, Rajesh Menon of the University of Utah and colleagues have focused broadband visible light using a different approach that involves creating a series of grooves in a soda-lime glass surface. The height and width of each groove was selected using a computer algorithm that optimized focusing across the entire visible spectrum. This involved using the conventional dispersion of the glass material to compensate for the anomalous dispersion of the grating, such that waves would be focused on the same line irrespective of wavelength.

Less precision needed

To test their device, the researchers illuminated the lens with light at variable wavelengths, measuring the distances at which light of different wavelengths was focused. The difference was comparable with commercial “achromatic” refractive lenses, and rotating the polarization of the light made no detectable difference. Furthermore, creating the patterned surface does not require the same degree of precision engineering as resonators. The smallest feature size on the glass surface was 3 μm, whereas the researchers calculated that a metasurface to do the same job would need resonators just 39 nm in size.

Menon and colleagues are now working to develop their lens further. “What we have shown is only one function of the lens – focusing,” Menon says. “To be used in a camera, you need to be able to form good images, and that will require a little bit more work.”

“Both [Menon and Capasso] have contributed to an important advance in making diffractive lenses a practical proposition for broadband applications,” says John Pendry of Imperial College London. Pendry suspects the costs associated with mass production of Capasso’s design might be manageable. “The technologies used for making chips can get down to that sort of resolution for volume production,” he says. “Performance would be a better metric for comparison. It remains to be seen which solution wins in practical terms.”

The lens is described in Scientific Reports.

A big Lidl telescope in Belfast

Alan Fitzsimmons and his telescope — Not so Lidl: Alan Fitzsimmons and his bargain telescope.

By Hamish Johnston

There is an old joke in the UK about going to the discount supermarket Lidl for a pint of milk and coming home with a new set of power tools or ski-wear for the entire family. That’s because the retailer is famous for its seemingly random special offers. One week it could be car accessories and the following week the same shelves could be stocked with pyjamas or camping gear.

But Alan Fitzsimmons of Queen’s University Belfast deserves an award for best physics-related Lidl bargain with this huge telescope that he bought at the supermarket. It makes perfect sense to me – both Lidl and the telescope’s maker Bresser are German companies and, of course, Germany is famous for its optics.

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Chinese lab confirms antineutrino anomalies

Analysis of more than 300,000 electron antineutrinos emitted by nuclear reactors in China provides the best evidence yet that the flux and energy distribution of such particles do not agree with theoretical predictions. While the disparities could be caused by deficiencies in current models describing neutrino production and detection, a hitherto unknown fourth neutrino could also explain some of the disagreement with theory.

The data were obtained from the international Daya Bay Reactor Neutrino Experiment, which consists of eight antineutrino detectors that look for antineutrinos emitted by six nearby nuclear reactors. This latest measurement was done using six of these detectors, each containing 20 tonnes of a gadolinium-doped liquid scintillator that emits a tiny flash of light when an electron antineutrino interacts with a gadolinium nucleus.

Mysterious bump

Data were collected over 217 days, allowing the team to measure the energies of the antineutrinos to within 1% uncertainty – which the researchers claim is the most precise measurement to date. But instead of agreeing with current models of antineutrino production, the energy spectrum contained a large excess of antineutrinos at an energy of 4–6 MeV with a statistical significance of 4σ.

Although this is less than the 5σ normally required for a “discovery” in particle physics, the existence of this bump is backed up by two other reactor neutrino experiments – Double Chooz in France and RENO in Korea. Both have already seen excesses at 4–6 MeV, with significances of 3σ and 3.5σ, respectively.

Despite the excess at 4–6 MeV, however, the total number of antineutrinos detected at Daya Bay with energies in the 1–7 MeV range was 6% less than predicted by theory. This deficiency was first identified in 2011 by Thierry Lasserre and colleagues at CEA Saclay in France, who evaluated data from a number of different reactor experiments.

According to Lasserre and colleagues, one explanation for the overall deficit of antineutrinos is that the missing particles have oscillated into a hypothetical fourth type of neutrino as they travel from reactor to detector. One candidate is the “sterile” neutrino, which is predicted by certain extensions of the Standard Model.

If they exist, sterile neutrinos would interact extremely weakly, if at all, with ordinary matter, and so would be even harder to detect than conventional neutrinos. However, the existence of sterile neutrinos could be inferred from discrepancies between measured and predicted neutrino fluxes.

More evidence needed

According to Lasserre, who is not part of the Daya Bay collaboration, physicists seeking sterile neutrinos will have to wait several years for better evidence. “We need new experiments dedicated to search for sterile neutrinos, and several of them are currently being realized,” he says. “We may expect new results within the next three years.”

As for the excess of antineutrinos at 4–6 MeV, Lasserre says this anomaly is relatively new, having first been identified in 2014. “Daya Bay now provides the most precise data, and this is a great result, but we don’t have yet any solid explanation of what it means exactly,” he explains.

However, Lasserre adds it is unlikely that the bump is related to sterile neutrinos, but could instead be related to limitations in our understanding of how antineutrinos are produced in reactors or of how the detectors work. Daya Bay Collaboration co-spokesperson Kam-Biu Luk of the University of California at Berkeley concurs. “This unexpected disagreement between our observation and predictions strongly suggested that the current calculations would need some refinement,” he says.

The Daya Bay measurement also provides important information for physicists studying how neutrinos from nuclear reactors oscillate between flavours as they travel long distances to remote detectors. According to the collaboration, such experiments may “need to revisit the models underlying their calculations”. This includes the JUNO detector, which is currently being built 200 km from Daya Bay.

The research is reported in Physical Review Letters.

Between the lines

Filling in the gaps

The story of astronomy has plenty of highlights. Galileo’s observations. Kepler’s calculations. Henrietta Leavitt’s Cepheid variables. Hubble’s receding galaxies. And so on, up through Arno Penzias and Robert Wilson’s puzzling detector noise (“the echo of the Big Bang”) and the still-mysterious discovery that the expansion of the universe is accelerating. All of these highlights could (and in most cases do) have entire books written about them, but it is rare to find all of them in a single volume, let alone one as accessible as Ethan Siegel’s Beyond the Galaxy. An astrophysicist and teacher, Siegel is best known for his blog Starts with a Bang (see October 2011 “Web life”), which has given him plenty of practice at explaining complex concepts to a general audience. This is fortunate, because the story he tells here is an intricate one, taking in elements of nuclear and atomic physics as well as astronomy and the history of science. In this methodical account, how we came to know things about cosmology is almost as important as the knowledge itself, and Siegel’s tale is distinguished by the respectful way he treats hypotheses that fell out of favour after new data emerged to discredit them. “When two explanations can account for the same phenomenon, it is not simply enough to choose the simpler one or the one that you feel better about,” he writes. “Instead, you need to look a little deeper, and find where the explanations differ from one another in their predictions for something you can then go and look for, either observationally or experimentally.” (Sometimes, of course, individual astronomers have clung to their preferred explanations even after the compass needle of evidence had swung in another direction; Siegel is much less forgiving of this.) The book is pitched at a level somewhere between popular science and beginners’ astronomy textbooks, and it contains few equations, but plenty of graphs containing real astrophysical data. It also offers detailed explanations of concepts such as the r-process, which describes how giant stars kick out huge quantities of heavy elements in their death throes. In the book’s later chapters, there are a few lapses; objects such as “cosmic strings” and “domain walls” play important roles in Siegel’s discussion of dark matter but are defined only briefly, while analyses of the three possible fates of our universe (a “big crunch”, limitless expansion in a “big freeze” or a finely balanced “Goldilocks” universe where expansion eventually slows to zero but never reverses) appear three separate times. Overall, though, Beyond the Galaxy is an excellent way for less cosmically minded physicists to fill in the gaps in their astronomy knowledge, and thereby transform “things I’ve vaguely heard about” into “things I actually know something about”.

2015 World Scientific £29.00/$38.00pb 388pp

The Planck problem

For a physicist whose most important insight came in the year 1900 – and who by his own admission fell short of true scientific brilliance – Max Planck is remarkably well known. Physics students learn the value of his famous constant h (or its variant, ħ) by heart. Historians of science trace the quantum era back to Planck’s 1900 paper on black-body radiation, which suggested that light might exist in discrete packets. In Planck’s native Germany, his name is attached to a network of prestigious research institutions. And as Brandon Brown points out in his fine new biography Planck: Driven by Vision, Broken by War, this stern old-fashioned Prussian gentleman was also responsible for “Planck’s principle”, the darkly comic observation that a new scientific idea becomes accepted “because its opponents eventually die and a new generation grows up that is familiar with it”. Early in the book, Brown argues that Planck was an exception to this rule, pointing out that when Albert Einstein came on the scene, Planck (unlike most of his similarly middle-aged contemporaries) eagerly adopted the younger man’s revolutionary ideas about light and gravity. But Planck’s adaptability had limits. As the quantum revolution gathered pace, Brown writes, “Planck would play the role of a worried parent asking everyone to slow down, to be careful please”. Tragically, this innate conservatism also applied to Planck’s politics. In the opening weeks of the First World War, Planck was among the 93 Germans intellectuals who signed an “Appeal to the Cultured Peoples of the World” protesting against supposed “lies and calumnies” about the German army’s conduct in Belgium. His Dutch colleague Hendrik Lorentz (who Brown memorably describes as “the kindly papa bear of physics”) eventually managed to convince him that some of the atrocity stories were true, but he remained deeply patriotic. This stance led him, for the most part, to adopt a strategy of accommodation after the Nazis came to power in 1933. “Flanked by swastikas, he praised his Führer to start speeches [and] executed the Nazi salute,” Brown writes. “When asked to bar Jewish students from his classrooms and then fire Jewish staff, he did as he was told.” Planck’s chosen path, which Brown describes as “working within the new system, however deranged, and trying to make a positive difference, however small”, dealt a severe blow to his reputation. His sporadic attempts to ingratiate himself with the Nazis were also not enough to save his son Erwin, who was hanged for his alleged involvement in the 1944 plot to kill Adolf Hitler. After the war, some of his former colleagues forgave him; Brown quotes a postwar letter from Lise Meitner in which she writes of Planck’s “unusually pure disposition and inner rectitude”. Thanks to an Allied bombing raid that destroyed his home and library, there are big gaps in what we know about Planck; accordingly, Brown’s biography often strays from its central character. Many of these diversions are interesting in their own right, but the book’s nonlinear structure can be disorienting. In one especially jarring passage, Planck’s granddaughter survives a difficult birth on one page, then appears on the next page some 20 years later as a survivor of an apparent suicide attempt. Overall, though, Planck is an illuminating and thought-provoking book about one of physics’ near-greats and his troubled times.

2015 Oxford University Press £20.00/$29.95hb 280pp

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How black holes saved relativity

While there have been many popular science books on the historical and scientific legacy of Albert Einstein’s general theory of relativity, a gap exists in the literature for a definitive, accessible history of the theory’s most famous offshoot: black holes. When asked for a good introduction to the strange regions of space–time that nothing, not even light, can escape from, one might mention Stephen Hawking’s A Brief History of Time. However, while this text is highly accessible, it primarily focuses on the search for quantum gravity, with black holes playing a smaller role. Meanwhile, Kip Thorne’s Black Holes and Time Warps is all about black holes, but makes a rather demanding read; although it can be compelling for physicists or serious enthusiasts, it is perhaps too long and technical for a mainstream lay audience.

In Black Hole, the science writer Marcia Bartusiak aims for a discursive middle ground, writing solely about black holes at a level suitable for both high-school students and more mature readers while also giving some broader scientific context for black-hole research. Her text works harder than most to straddle the fence between popular-science exposition and history of science. Instead of simply developing the scientific theory and accessorizing it with historical facts, Bartusiak puts forward a thesis about the intimate relationship between the acceptance of general relativity and the acceptance of black holes by the physics mainstream.

One of the pleasures of Bartusiak’s book is her careful word choice and the exquisitely clear explanations of the science involved at every point in the story. Bartusiak holds a faculty appointment in a science writing programme, and this is strongly reflected in Black Hole. Her words are a powerful riposte to the suggestion that writing for a popular audience requires specious oversimplifications of the science at play or repeated use of the same analogies over and over again. Bartusiak invents some novel ways to describe physics, which is a helpful contribution not only for lay readers but also for scientists looking for new ways to communicate their research. I enjoyed her penchant for unusual phrasing – for example, in describing black holes as “wackily weird” in the preface.

Though the first few chapters on the early history of the idea of black holes are somewhat lethargic, the writing bursts into life when she introduces supernovae – stars that have exploded at the end of their lives – to the story. Her account of Fritz Zwicky’s thought process as he developed the first rudimentary understanding of how a supernova might occur provides a useful lesson about how creativity – an often-ignored quality – is required to succeed in science. By connecting ideas from two seemingly disparate areas of physics, Zwicky used imagination rather than algorithm to develop a new and ultimately profound idea.

In some ways, Black Hole succeeds as a history of science book. The main text de-emphasizes dates, improving the book’s accessibility, while Bartusiak has added a helpful timeline at the back for the curious reader. However, her dedication to readability can prove frustrating for readers looking for a more open interpretation of historical events. For example, in describing a famous incident where the British astronomer Arthur Eddington rejected Subramanyan Chandrashekar’s proposed minimum mass for white-dwarf stars, Bartusiak’s account of what happened between Eddington and the Punjabi-born “Chandra” significantly neuters the story in a way that seems designed to make readers comfortable, at the expense of truly capturing what happened. This part of the story is best read in tandem with Arthur I Miller’s book Empire of the Stars, which describes Chandra’s feeling that racism was a factor in Eddington’s behaviour, and also shows the extreme impact that this rejection had on Chandra’s psychological wellbeing for the rest of his life.

Bartusiak does, ultimately, wonder whether things might have been different if Eddington had championed Chandra’s idea instead of eviscerating it. She answers in the form of a quote from the physicist Werner Israel, who says that the culture was simply not ready to accept black holes. But there’s another question that Bartusiak fails to ask, which is this: What compelling discovery might Chandra have made had he not felt so discouraged that he stopped working on black holes for decades? Einstein himself was a staunch anti-racist, so I doubt he would object to us asking this question 100 years after the advent of general relativity, in an era when “diversity” has become a buzzword. Bartusiak misses an opportunity to reflect on the lessons old mistakes ought to teach us about the impact of discrimination on the scientific mission today.

More broadly, Black Hole was, at times, an uncomfortable read for a theoretical cosmologist. One of the book’s central theses is that acceptance of general relativity was predicated entirely on the community’s belief that black holes were a phenomenon worth investigating. In this particular telling of general relativity’s history, the dramatic competition to accurately measure Hubble’s constant (which lasted for more than half a century) never figures into the conversation, even though it happened simultaneously in some of the same research centres as the black-hole story.

Perhaps Bartusiak is correct, and general relativity would have died out as a research area had it not been for the renewed interest generated by black-hole-related discoveries. But Black Hole never makes a truly compelling case for this idea, in part because Bartusiak circumscribes the storytelling to leave out any true mention of cosmology research. Had this been properly accounted for, the thesis that black holes were simply more important to the theory’s long-term viability might be more believable.

Black Hole ends without fully moving into the modern era of black-hole exploration, where intersections with other areas of research, such as cosmology and galaxy formation, are ever-growing. The community has changed, too, with more members of under-represented groups participating in black hole research, although almost none are mentioned in the book. Ultimately, though, Bartusiak’s work fills a much-needed gap in the popular-science literature and provides an excellent introduction for non-experts to the science of black holes, even if it does not completely succeed at capturing the historical arc of black-hole exploration.

2015 Yale University Press £14.99/$27.50hb 240pp

Indian gravitational-wave observatory wins governmental approval

Hot on the heels of last week’s monumental discovery of gravitational waves – made by researchers working on the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) in the US – India’s Union Cabinet has given its “in-principle” approval for a similar observatory, dubbed LIGO-India, to be built in the country. The project will be led by the Indian Initiative in Gravitational-wave Observations (IndIGO), which has been a member of the international LIGO collaboration since 2011 and contributed towards last week’s discovery. Once built, LIGO-India will join the global network of LIGO observatories, which currently includes the US, Germany, Italy and Japan.

LIGO-India will be backed by the government’s Department of Atomic Energy (DAE) and the Department of Science and Technology (DST), together with its US counterparts. Indeed, Indian prime minister Narendra Modi gave his approval this morning via a series of tweets, saying that the “LIGO-India project will establish a state-of-the-art gravitational-wave observatory in collaboration with LIGO Laboratory run by Caltech and MIT”. Modi added that LIGO-India will also bring “considerable opportunities” in cutting-edge technology for Indian industry. “The project will motivate Indian students and scientists to explore newer frontiers of knowledge and will add impetus to scientific research,” he tweeted.

Global eye on the sky

The aLIGO collaboration last week announced that it had detected gravitational waves produced from the collision of two black holes of 36 and 29 solar masses some 1.3 billion light-years from Earth. The holes had merged to form a spinning, 62 solar-mass black hole, in an event dubbed GW150914. The signal revealed the characteristic “chirp” waveform of such an event, and LIGO collaborators in India, including Bala Iyer from the Raman Research Institute in Bengaluru and Sanjeev Dhurandhar at the Inter University Campus for Astronomy and Astrophysics in Pune, were instrumental in calculating and simulating such waveforms.

“It is heartening to see the involvement of many young scientists in India in this discovery”, says LIGO member B S Sathyaprakash, from Cardiff University in the UK.

For GW109914, a signal was picked up by both of LIGO’s US observatories, in Hanford, Washington, and in Livingston, Louisiana, which are separated by 3002 km. But researchers are keen to refine their observations and improve their measurement sensitivity by having a global network of detectors, which would simultaneously detect incoming gravitational-wave signals and reveal more about where they come from.

A map showing the global gravitational-wave observatory network — **Across the globe – gravitational-wave observatory network** Current operating facilities in the global network include the twin LIGO detectors – in Hanford, Washington, and Livingston, Louisiana – and GEO600 in Germany. The Virgo detector in Italy and the Kamioka Gravitational Wave Detector (KAGRA) in Japan are undergoing upgrades and are expected to begin operations in 2016 and 2018, respectively. LIGO-India has just received its first approval from the government. (Courtesy: LIGO)

Worldwide network

With each added observatory, the researchers can pick up even more signals, boosting the chances of a confirmed wave. Such a network would also let researchers narrow and localize the gravitational-wave’s source in the sky – with two detectors, LIGO can currently only gauge the general direction from which the waves have come. Pinpointing a fixed location requires data to be combined from geographically separated detectors.

Apart from the two LIGO observatories in the US, astronomers have access to data from the GEO600 detector in Germany, which is currently online, while the Virgo detector in Italy (HHLV) and the KAGRA detector in Japan are both currently being upgraded (see map above). According to the IndIGO collaboration, adding a new detector in India a long way from existing detectors would “dramatically improve the source-localization accuracies (five to 10 times), thus enabling us to use gravitational-wave observations as an excellent astronomical tool”.

It is still, however, early days for LIGO-India, despite the positive global reaction to last week’s discovery of gravitational waves. Although Satyaprakash says he is “absolutely delighted, as this is what our Indian colleagues were seeking”, he told physicsworld.com that the government should now release funds for exploratory work and submit a “detailed project report” for full approval. “In a way, the real work starts now,” he says. “When the full approval comes this will be a new chapter in Indian science but we need to wait until then.”

What’s so super about superconductivity?

The fascinating phenomenon of superconductivity was discovered in Leiden in 1911 by the Dutch physicist Heike Kamerlingh Onnes. In this video from our 100 Second Science series, Catherine Pépin of CEA Saclay, France, describes how Onnes was surprised to see the electrical resistance of mercury drop to zero when the metal was chilled to a temperature of about 4 K. Pépin describes some of the unexpected consequences of this discovery and how it triggered a hunt for room-temperature superconductors that could lead to transformational applications.

If you enjoyed this video explainer, then check out more from our 100 Second Science series.

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