Einstein's Theory of Gravity Waves Proven 100 Years Later!

[Peter Lemkin]

Gravitational waves detected 100 years after Einstein's prediction

February 11, 2016


An aerial view of the Laser Interferometer Gravitational-wave Observatory (LIGO) detector in Livingston, Louisiana. LIGO has two detectors: one in Livingston and the other in Hanaford, Washington. LIGO is funded by NSF; Caltech and MIT …moreFor the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at Earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein's 1915 general theory of relativity and opens an unprecedented new window to the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot be obtained from elsewhere. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.
The gravitational waves were detected on Sept. 14, 2015 at 5:51 a.m. EDT (09:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington. The LIGO observatories are funded by the National Science Foundation (NSF), and were conceived, built and are operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT). The discovery, accepted for publication in the journalPhysical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

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Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About three times the mass of the sun was converted into gravitational waves in a fraction of a secondwith a peak power output about 50 times that of the whole visible universe. By looking at the time of arrival of the signalsthe detector in Livingston recorded the event 7 milliseconds before the detector in Hanfordscientists can say that the source was located in the Southern Hemisphere.
Live stream of NSF press conference: You Tubewww.youtube.com/user/VideosatNSF/live and Onstreamwww.webcaster4.com/Webcast/Page/219/13131

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide at nearly half the speed of light and form a single more massive black hole, converting a portion of the combined black holes' mass to energy, according to Einstein's formula E=mc2. This energy is emitted as a final strong burst of gravitational waves. These are the gravitational waves that LIGO observed.
The existence of gravitational waves was first demonstrated in the 1970s and 1980s by Joseph Taylor, Jr., and colleagues. In 1974, Taylor and Russell Hulse discovered a binary system composed of a pulsar in orbit around a neutron star. Taylor and Joel M. Weisberg in 1982 found that the orbit of the pulsar was slowly shrinking over time because of the release of energy in the form of gravitational waves. For discovering the pulsar and showing that it would make possible this particular gravitational wave measurement, Hulse and Taylor were awarded the 1993 Nobel Prize in Physics.
The new LIGO discovery is the first observation of gravitational waves themselves, made by measuring the tiny disturbances the waves make to space and time as they pass through the earth.
"Our observation of gravitational waves accomplishes an ambitious goal set out over five decades ago to directly detect this elusive phenomenon and better understand the universe, and, fittingly, fulfills Einstein's legacy on the 100th anniversary of his general theory of relativity," says Caltech's David H. Reitze, executive director of the LIGO Laboratory.
The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probedand the discovery of gravitational waves during its first observation run. NSF is the lead financial supporter of Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project.
Several of the key technologies that made Advanced LIGO so much more sensitive were developed and tested by the German UK GEO collaboration. Significant computer resources were contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse University and the University of Wisconsin-Milwaukee. Several universities designed, built and tested key components for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Florida, Stanford University, Columbia University of the City of New York and Louisiana State University.
"In 1992, when LIGO's initial funding was approved, it represented the biggest investment NSF had ever made," says France Córdova, NSF director. "It was a big risk. But NSF is the agency that takes these kinds of risks. We support fundamental science and engineering at a point in the road to discovery where that path is anything but clear. We fund trailblazers. It's why the U.S. continues to be a global leader in advancing knowledge."
LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1,000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom and the University of the Balearic Islands in Spain.
"This detection is the beginning of a new era: The field of gravitational wave astronomy is now a reality," says Gabriela González, LSC spokesperson and professor of physics and astronomy at Louisiana State University.
LIGO was originally proposed as a means of detecting gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech's Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.
"The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein's face had we been able to tell him," says Weiss.
"With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universeobjects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples," says Thorne.
Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy.

A technician works on one of LIGO's optics. At each observatory, the 2 1/2-mile long L-shaped LIGO interferometer uses laser light split into two beams that travel back and forth down the arms. The beams are used to monitor the distance …moreFulvio Ricci, Virgo spokesperson, notes that: "This is a significant milestone for physics, but more importantly merely the start of many new and exciting astrophysical discoveries to come with LIGO and Virgo."
Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics adds: "Einstein thought gravitational waves were too weak to detect, and didn't believe in black holes. But I don't think he'd have minded being wrong!"
"The Advanced LIGO detectors are a tour de force of science and technology, made possible by a truly exceptional international team of technicians, engineers, and scientists," says David Shoemaker of MIT, the project leader for Advanced LIGO. "We are very proud that we finished this NSF-funded project on time and on budget."
At each observatory, the 2 1/2-mile (4-km) long, L-shaped LIGO interferometer uses laser light split into two beams that travel back and forth down the arms (four-foot diameter tubes kept under a near-perfect vacuum). The beams are used to monitor the distance between mirrors precisely positioned at the ends of the arms. According to Einstein's theory, the distance between the mirrors will change by an infinitesimal amount when a gravitational wave passes by the detector. A change in the lengths of the arms smaller than one-ten-thousandth the diameter of a proton (10-19 meter) can be detected.
"To make this fantastic milestone possible took a global collaboration of scientistslaser and suspension technology developed for our GEO600 detector was used to help make Advanced LIGO the most sophisticated gravitational wave detector ever created," says Sheila Rowan, professor of physics and astronomy at the University of Glasgow.
Independent and widely separated observatories are necessary to determine the direction of the event causing the gravitational waves, and also to verify that the signals come from space and are not from some other local phenomenon.
Toward this end, the LIGO Laboratory is working closely with scientists in India at the Inter-University Centre for Astronomy and Astrophysics, the Raja Ramanna Centre for Advanced Technology, and the Institute for Plasma to establish a third Advanced LIGO detector on the Indian subcontinent. Awaiting approval by the government of India, it could be operational early in the next decade. The additional detector will greatly improve the ability of the global detector network to localize gravitational-wave sources.
"Hopefully this first observation will accelerate the construction of a global network of detectors to enable accurate source location in the era of multi-messenger astronomy," says David McClelland, professor of physics and director of the Centre for Gravitational Physics at the Australian National University.

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This computer simulation shows the collision of two black holes, a tremendously powerful event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, which detected gravitational waves as the black holes …moreLIGO Livingston FAQ
[B]What do we know about this first-ever detected gravitational wave?[/B]
[B]LIGO has made the first-ever observations of gravitational waves arriving on Earth from space, and the first detection of two black holes colliding.[/B]
[B]The gravitational wave signal was detected in Livingston and seven milliseconds later, the instrument at the LIGO observatory in Hanford, Washington detected the same gravitational wave. It confirms that black holes exist in binary systems with solar masses. It confirms aspects of Einstein's Theory of General Relativity.][/B]
[B]From this, we will be able to learn more about gravity near a black hole, where space-time is warped, that would not be possible to learn in other ways.[/B]
[B][B]How do the LIGO instruments work?[/B][/B]
[B][B]The LIGO detectors are interferometers that shine a laser through a vacuum down two arms in the shape of an L that are each 4 kilometers in length. The light from the laser bounces back and forth between mirrors on each end of the L. Scientists measure the length of both arms using the light.[/B][/B]
[B][B]If there's a disturbance in space-time, such as a gravitational wave, the time the light takes to travel 4 kilometers will be slightly different in each arm making one arm look longer than the other. LIGO scientists measure the interference in the two beams of light when they come back to meet, which reveals information on the space-time disturbance.[/B][/B]
[B][B]The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first-generation LIGO detectors, enabling a large increase in the volume of the universe probed and the discovery of gravitational waves during its first observational run.[/B][/B]
[B][B][B]How do we know it's a black hole?[/B][/B][/B]
[B][B]The scientists compared the observation with Einstein's prediction to identify that black holes produced this gravitational wave, how far they were, what the masses were and how large the final black hole was because of the energy emitted.[/B][/B]
[B][B][B]What is the LIGO Scientific Collaboration?[/B][/B][/B]
[B][B]LIGO research is carried out by the LIGO Scientific Collaboration, or LSC, a group of more than1,000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration.[/B][/B]
[B][B]The LSC detector network includes the LIGO interferometers and the GEO600 detector. It includes matching LIGO facilities in Livingston, LA and Hanford, WA. The location of the two observatories with another one in Europe creates a triangle that can verify astronomical observations.[/B][/B]
[B][B]LSU Physics & Astronomy Professor Gabriela Gonzalez is the elected spokesperson for the LIGO Scientific Collaboration, a post she has held for five years. LSU Physics & AstronoProfessor Joe Giaime is the Observatory Head of LIGO Livingston.[/B][/B]
[B][B][B]What is LIGO Livingston?[/B][/B][/B]
[B][B]LIGO Livingston is one of two laser interferometer observatories built to detectgravitational waves. About 40 people work at LIGO Livingston, which is about 36 miles north-east of Baton Rouge, Louisiana, where LSU is located. LIGO Livingston employs engineers, scientists and staff who support facilities, outreach and information technology to run the observatory. It is funded completely by the National Science Foundation, or NSF, and managed by the California Institute of Technology, or Caltech, and the Massachusetts Institute of Technology, or MIT. LSU owns the land, which is 180 acres, leased to the NSF until 2044.[/B][/B]
[B][B]LIGO Livingston began collecting data in 2005. In 2015, it received a major upgrade. The Advanced LIGO configurations increased the sensitivity of the instrumentation ten-fold. LIGO Livingston's annual budget is $6-9 million per year.[/B][/B]
[B][B]About 17,000 people from the general public visit LIGO Livingston's Science Education Center each year. Free hands-on educational activities are available for school groups as well as professional development training for educators.[/B][/B]
[B][B][B]What's next?[/B][/B][/B]
[B][B]This is only the beginning of the field of gravitational wave astronomy. LIGO Scientific Collaboration scientists continue to conduct research on the existing data and expect to detect more astronomical events as the LIGO detectors and technology become more sensitive, and the French-Italian gravitational wave detector, VIRGO, located in Cascina, Italy begins to collect data this year.[/B][/B]
[B][B]Scientists anticipate detecting other events including neutron stars in our galaxy, otherblack holes and supernova explosions.[/B][/B]
[B][B] [B]Explore further: Gravitational waves: Why the fuss? (Update)[/B][/B][/B]
[B][B][B]More information: PRL:journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102#fulltext[/B][/B][/B]

[Drew Phipps]

Now all we need is Halpern's Truth Machine, Roddenberry's warp drive, the ability to 3d print food (other than chocolate), and we're good to go.

[Peter Lemkin]

The First Sounds of Merging Black Holes

Published 11 February 2016

Viewpoint: The First Sounds of Merging Black Holes

• Emanuele Berti, Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677, USA and CENTRA, Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais 1, 1049 Lisboa, Portugal
  

February 11, 2016 Physics 9, 17
Gravitational waves emitted by the merger of two black holes have been detected, setting the course for a new era of observational astrophysics.

C. Henze/NASA Ames Research Center

Figure 1: Numerical simulations of the gravitational waves emitted by the inspiral and merger of two black holes. The colored contours around each black hole represent the amplitude of the gravitational radiation; the blue lines represent the orbits of the bla... Show moreFor decades, scientists have hoped they could "listen in" on violent astrophysical events by detecting their emission of gravitational waves. The waves, which can be described as oscillating distortions in the geometry of spacetime, were first predicted to exist by Einstein in 1916, but they have never been observed directly. Now, in an extraordinary paper, scientists report that they have detected the waves at the Laser Interferometer Gravitational-wave Observatory (LIGO) [1]. From an analysis of the signal, researchers from LIGO in the US, and their collaborators from the Virgo interferometer in Italy, infer that the gravitational waves were produced by the inspiral and merger of two black holes (Fig. 1), each with a mass that is more than 25 times greater than that of our Sun. Their finding provides the first observational evidence that black hole binary systems can form and merge in the Universe.
Gravitational waves are produced by moving masses, and like electromagnetic waves, they travel at the speed of light. As they travel, the waves squash and stretch spacetime in the plane perpendicular to their direction of propagation (see inset, Video 1). Detecting them, however, is exceptionally hard because they induce very small distortions: even the strongest gravitational waves from astrophysical events are only expected to produce relative length variations of order 10−2110−21.
"Advanced" LIGO, as the recently upgraded version of the experiment is called, consists of two detectors, one in Hanford, Washington, and one in Livingston, Louisiana. Each detector is a Michelson interferometer, consisting of two 4-km-long optical cavities, or "arms," that are arranged in an L shape. The interferometer is designed so that, in the absence of gravitational waves, laser beams traveling in the two arms arrive at a photodetector exactly 180° out of phase, yielding no signal. A gravitational wave propagating perpendicular to the detector plane disrupts this perfect destructive interference. During its first half-cycle, the wave will lengthen one arm and shorten the other; during its second half-cycle, these changes are reversed (see Video 1). These length variations alter the phase difference between the laser beams, allowing optical powera signalto reach the photodetector. With two such interferometers, LIGO can rule out spurious signals (from, say, a local seismic wave) that appear in one detector but not in the other.
LIGO's sensitivity is exceptional: it can detect length differences between the arms that are smaller than the size of an atomic nucleus. The biggest challenge for LIGO is detector noise, primarily from seismic waves, thermal motion, and photon shot noise. These disturbances can easily mask the small signal expected from gravitational waves. The upgrade, completed in 2015, improved the detector's sensitivity by a factor of 35 for waves in the 100300 Hz frequency band and by more than a factor of 10 below 60 Hz. These improvements have enhanced the detector's sensitivity to more distant sources and were crucial to the discovery of gravitational waves.

APS/Alan Stonebraker

Video 1: (Animation appears online only.) A schematic depiction of LIGO's interferometric gravitational wave detector. Light from a laser is split in two by a beam splitter; one half travels down the vertical arm of the interferometer, the other half travels down the horizontal arm. The detector is designed so that in the absence of gravitational waves (top left) the light takes the same time to travel back and forth along the two arms and interferes destructively at the photodetector, producing no signal. As the wave passes (moving clockwise from top right) the travel times for the lasers change, and a signal appears in the photodetector. (The actual distortions are extremely small, but are exaggerated here for easier viewing.) Inset: The elongations in a ring of particles show the effects of a gravitational wave on spacetime.On September 14, 2015, within the first two days of Advanced LIGO's operation, the researchers detected a signal so strong that it could be seen by eye (Fig. 2). The most intense portion of the signal lasted for about 0.2 s and was observed in both detectors, with a combined signal-to-noise ratio of 24. Fittingly, this first gravitational wave signal, dubbed GW150914, arrived less than two months before the 100-year anniversary of the publication of Einstein's general relativity theory.
Up until a few decades ago, detecting gravitational waves was considered an impossible task. In fact, in the 1950s, physicists were still heatedly debating whether the waves were actual physical entities and whether they could carry energy. The turning point was a 1957 conference in Chapel Hill, North Carolina [2, 3]. There, the theorist Felix Pirani pointed out a connection between Newton's second law and the equation of geodesic deviation, which describes the effect of tidal forces in general relativity. This connection allowed him to show that the relative accelerations of neighboring particles in the presence of a gravitational wave provide a physically meaningfuland measurableway to observe it. Sadly, Pirani, who laid the groundwork for our modern thinking about gravitational waves and how to detect them, passed away on December 31, 2015, just weeks before the LIGO scientists announced their discovery.
Other prominent physicists at the meeting, including Joseph Weber, Richard Feynman, and Hermann Bondi, were instrumental in pushing Pirani's ideas forward. Feynman and Bondi, in particular, developed Pirani's observation into what is now known as the "sticky bead" thought experiment. They argued that if beads sliding on a sticky rod accelerated under the effect of a passing gravitational wave, then they must surely also transfer heat to the rod by friction. This heat transfer is proof that gravitational waves must indeed carry energy, and are therefore, in principle, detectable.
Interest in carrying out such experiments wasn't immediate. As Pirani noted in his 1964 lectures on gravitational radiation [4], Weber thought that meaningful laboratory experiments were "impossible by several orders of magnitude." At about the same time, William Fowler (the future Nobel laureate) suggested that a large fraction of the energy emitted by so-called massive double quasarswhat we now know as black hole binariesmight be in the form of gravitational radiation. Pirani, however, felt that the direct observation of gravitational waves was not "necessary or sufficient" to justify a corresponding theory, arguing that unless physicists figured out a way to quantize gravity, such a theory would not "have much to do with physics" [4].

B. P. Abbott et al. [1].

Figure 2: On September 14, 2015, similar signals were observed in both of LIGO's interferometers. The top panels show the measured signal in the Hanford (top left) and Livingston (top right) detectors. The bottom panels show the expected signal produced by the... Show moreWhat galvanized the field was a 1969 paper from Weber, who claimed he had detected gravitational radiation with a resonant bar detector (see 22 December 2005 Focus story). The finding was controversialphysicists could not duplicate it and by the mid-1970s, most agreed that Weber had likely been incorrect. However, a few years later a young professor at the Massachusetts Institute of Technology named Rainer Weiss was preparing for his course on relativity when he came across a proposal by Pirani for detecting gravitational waves. Pirani had suggested using light signals to see the variations in the positions of neighboring particles when a wave passed. His idea, with one key modification, led to the genesis of LIGO: rather than using the timing of short light pulses, Weiss proposed to make phase measurements in a Michelson interferometer [5]. Ronald Drever, Kip Thorne, and many others made crucial contributions to developing this idea into what LIGO is today. (See Ref. [2] for a historical account.)
Now, what was once considered "impossible by several orders of magnitude" is a reality. To confirm the gravitational-wave nature of their signal, the researchers used two different data analysis methods. The first was to determine whether the excess power in the photodetector could be caused by a signal, given their best estimate of the noise, but without any assumptions about the origin of the signal itself. From this analysis, they could say that a transient, "unmodeled" signal was observed with a statistical significance greater than 4.6σ4.6𝜎. The second method involved comparing the instrumental output (signal plus noise) with a theoretical signal from numerical simulations of merging black holes using general relativity. From this so-called matched-filtering search, the researchers concluded that the significance of the observation was greater than 5.1σ5.1𝜎.
The most exciting conclusions come from comparing the observed signal's amplitude and phase with numerical relativity predictions, which allows the LIGO researchers to estimate parameters describing the gravitational-wave source. The waveform is consistent with a black hole binary system whose component masses are 36 and 29 times the mass of the Sun. These stellar-mass black holesso named because they likely formed from collapsing starsare the largest of their kind to have been observed. Moreover, no binary system other than black holes can have component masses large enough to explain the observed signal. (The most plausible competitors would be two neutron stars, or a black hole and a neutron star.) The binary is approximately 1.3 billion light years from Earth, or equivalently, at a luminosity distance of 400 megaparsecs (redshift of z∼0.1z∼0.1). The researchers estimate that about 4.6% of the binary's energy was radiated in gravitational waves, leading to a rotating black hole remnant with mass 62 times the mass of the Sun and dimensionless spin of 0.67.
From the signal, the researchers were also able to perform two consistency tests of general relativity and put a bound on the mass of the gravitonthe hypothetical quantum particle that mediates gravity. In the first test, they used general relativity to estimate the black hole remnant's mass and spin from the pre-merger parameters. They then also determined the remnant's mass and spin from the oscillations in the wave produced by the final black hole [6]. They found that the values inferred from these oscillations agreed with those they had calculated. The second test was to analyze the phase of the wave generated by the black holes as they spiraled inward towards one another. This phase can be written as a series expansion in v∕cv∕c, where vv is the speed of the orbiting black holes, and the authors verified that the coefficients of this expansion were consistent with the predictions of general relativity. By assuming that a graviton with mass would modify the phase of the waves, they determined an upper bound on the particle's mass of 1.2×10−22eV∕c21.2×10−22eV∕c2, improving the bounds from measurements in our Solar System and from observations of binary pulsars. These findings will be discussed in detail in later papers.
In physics, we live and breathe for discoveries like the one reported by LIGO, but the best is yet to come. As Kip Thorne recently said in a BBC interview, recording a gravitational wave for the first time was never LIGO's main goal. The motivation was always to open a new window onto the Universe.
Gravitational wave detection will allow new and more precise measurements of astrophysical sources. For example, the spins of two merging black holes hold clues to their formation mechanism. Although Advanced LIGO wasn't able to measure the magnitude of these spins very accurately, better measurements might be possible with improved models of the signal, better data analysis techniques, or more sensitive detectors. Once Advanced LIGO reaches design sensitivity, it should be capable of detecting binaries like the one that produced GW150914 with 3 times its current signal-to-noise ratio, allowing more accurate determinations of source parameters such as mass and spin.
The upcoming network of Earth-based detectors, comprising Advanced Virgo, KAGRA in Japan, and possibly a third LIGO detector in India, will help scientists determine the locations of sources in the sky. This would tell us where to aim "traditional" telescopes that collect electromagnetic radiation or neutrinos. Combining observational tools in this way would be the basis for a new research field, sometimes referred to as "multimessenger astronomy" [7]. Soon we will also collect the first results from LISA Pathfinder, a spacecraft experiment serving as a testbed foreLISA, a space-based interferometer. eLISA will enable us to peer deeper into the cosmos than ground-based detectors, allowing studies of the formation of more massive black holes and investigations of the strong-field behavior of gravity at cosmological distances [8].
With Advanced LIGO's result, we are entering the dawn of the age of gravitational wave astronomy: with this new tool, it is as though we are able to hear, when before we could only see. It is very significant that the first "sound" picked up by Advanced LIGO came from the merger of two black holes. These are objects we can't see with electromagnetic radiation. The implications of gravitational-wave astronomy for astrophysics in the near future are dazzling. Multiple detections will allow us to study how often black holes merge in the cosmos and to test astrophysical models that describe the formation of binary systems [9, 10]. In this respect, it's encouraging to note that LIGO may have already detected a second event; a very preliminary analysis suggests that if this event proves to have an astrophysical origin, then it is likely to also be from a black hole binary system. The detection of strong signals will also allow physicists to test the so-called no-hair theorem, which says that a black hole's structure and dynamics depend only on its mass and spin. Observing gravitational waves from black holes might also tell us about the nature of gravity. Does gravity really behave as predicted by Einstein in the vicinity of black holes, where the fields are very strong? Can dark energy and the acceleration of the Universe be explained if we modify Einstein's gravity? We are only just beginning to answer these questions [11, 12].

[Magda Hassan]

Now all we need is Halpern's Truth Machine, Roddenberry's warp drive, the ability to 3d print food (other than chocolate), and we're good to go.

No it only needs to print chocolate thank you! It is the most important food group.
I loved that this came out on Darwin Day. Or was it the day before? Anyway science is good stuff! Scientists on the other hand come in a variety of flavours.