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LIGOThe Laser Interferometer Gravitational-Wave Observatory consists of two detectors in Hanford, Washington, and Livingston, Louisiana, built to observe gravitational waves produced by astronomical phenomena. Like ripples created by objects traveling along water, gravitational waves are ripples produced by objects moving through spacetime. Unlike light, which can be blocked by matter, gravitational waves travel at the speed of light unimpeded, allowing scientists to use LIGO to study otherwise invisible cosmic events (e.g., black holes).
Each detector has two 4-kilometer (2.5-mile) tunnels called arms, which form an "L" shape. During each experimental run, a continuous laser beam is split at the point where the arms connect, with each half sent down an arm. The beams reflect off mirrors—one at the end of the arm and one near where they connect—about 300 times before recombining. A passing gravitational wave will cause the recombined beam to produce a specific pattern, which is compared to those made in simulations to determine the characteristics of the cosmic event that created the waves.
Requiring extensive flat land, minimal seismic activity, and enough space between them to rule out false positives from the local environment, LIGO detectors were built 3,002 kilometers (1,865 miles) apart. Since going online in 2015 after a series of upgrades, LIGO has detected mergers involving black holes and neutron stars and validated predictions made by Albert Einstein and Stephen Hawking.Explore LIGO
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The construction of LIGO needed to compensate for Earth's curvatureAcross the 4-kilometer (2.5-mile) arms, the height of Earth's surface falls by almost a meter, preventing the lasers traveling within the arms from meeting the mirror at the end of each. Concrete slabs built beneath the arms help keep them level and provide structural support against seismic vibrations. LIGO Lab | CaltechWatch the director's cut of the award-winning documentary about LIGOProduction on the film began in August 2015, shortly before the facilities detected gravitational waves for the first time on September 14. Those interviewed, including future Nobel Laureates Kip Thorne and Barry Barish, provide their accounts of the discovery as events unfold in real time. Advanced LIGO Documentary ProjectHelp scientists at LIGO train AI to resolve glitches in observational dataVolunteers are provided with visual representations of signal abnormalities at various frequencies and tasked with categorizing them based on reference examples. Progressing through the tool unlocks more difficult images and additional features. Categorized images will be used to train machine learning algorithms for automated future classification. ZooniverseLIGO is part of the advanced gravitational wave detector networkLike the Laser Interferometer Gravitational-wave Observatory, Europe's Virgo Gravitational Wave Interferometer and Japan's Kamioka Gravitational Wave Detector reflect laser beams down perpendicular tunnels to detect gravitational waves in the patterns created by the recombined waves. Future observatories are expected to contribute to this network, further improving gravitational wave detections. NASASince 2017, Virgo has helped LIGO localize astronomical phenomenaThe detector near Pisa, Italy, coordinates its experimental runs with those in Hanford, Washington, and Livingston, Louisiana. Scientists can triangulate the locations of celestial events that generate gravitational waves using signal arrival times, just as earthquake locations can be determined from measurements at three seismic stations. American Physical SocietyBetween 2002 and 2025, upgrades have increased LIGO's detection range tenfoldAfter the construction of Initial LIGO was completed in 1999, no gravitational waves were detected during operations between 2002 and 2010. Instrument redesigns and significant technological improvements brought about Advanced LIGO, which began observations in 2015. Continued upgrades between continuous laser runs have improved detection sensitivity and stability. LIGO LabLIGO confirmed Stephen Hawking's theorem about black hole surface areasBlack holes are known to grow with increased mass but lose energy during mergers through the emission of gravitational waves. Amid these competing factors, the black hole area theorem—confirmed in 2021 using LIGO data—states that a merged black hole's size cannot be smaller than the combined surface area of its progenitors. Cornell UniversityLIGO boosts its signal sensitivity by manipulating quantum uncertaintyAccording to the uncertainty principle, the amplitude, or height of a wave's peak, and its phase—the point in time when the first peak is observed—are inversely linked. Based on the frequency of the gravitational waves of interest, scientists sacrifice precision in one optical property to reduce noise in another. CaltechLIGO can detect changes in spacetime one ten-thousandth the width of a protonGravity is the weakest of the fundamental forces in nature, meaning the length of objects only changes by minuscule amounts as gravitational waves ripple through space from distant, albeit massive, cosmic events. LIGO's sensitivity can measure an object shifting its position by one seven-hundred-trillionth of the width of a human hair. Massachusetts Institute of TechnologyThe 2017 Nobel Prize in physics was awarded to LIGO's foundersRainer Weiss, Kip Thorne, and Barry Barish won the award for their contributions to the detector a year after the discovery of gravitational waves was announced. Acknowledging the Nobel statutes limited the prize to no more than three people, Thorne stated, "our marvelous discovery is the work of more than a thousand." CaltechLIGO made the first detection of gravitational wavesOn February 11, 2016, scientists at the Laser Interferometer Gravitational-Wave Observatory announced the confirmed detection of ripples in spacetime, which were produced from the collision of two black holes 36 and 29 times the mass of the sun. The detection confirmed that gravitational waves travel at the speed of light, as predicted by Albert Einstein in 1915. Physics WorldPotential LIGO sites were selected in pairs, approximately 3,000 kilometers apartThe 1,864-mile distance meant gravitational wave signals would be detected no more than 10 milliseconds apart, ruling out many background signals. The sites needed sufficient plots of nearly flat land, proximity to infrastructure (e.g., electricity), and adequate distance from urban areas and geologically active areas to reduce environmental noise. LIGO LabThe NSF funded the design and construction of LIGO by MIT and CaltechThe 1984 agreement between the National Science Foundation and both research institutions came four years after funding 1.5-meter (4.9-foot) and 40-meter (131-foot) prototypes. With an initial budget of $395M, LIGO was once one of the largest NSF-funded projects in history. Caltech LibraryIn LIGO's interferometers, light cancels itself out in the absence of gravitational wavesThe devices are designed so that a laser is split into two beams that later recombine, canceling each other out and producing no signal. Changes in the lengths of the arms due to passing gravitational waves result in an interference pattern whose properties reveal features of the objects that created the waves. SYFYGravitational waves are detected at LIGO by measuring shifts in interfering lasersThe instruments at each site send lasers down equally long arms, which should take the same amount of time to travel between suspended mirrors. Passing gravitational waves alter the shape of space—lengthening one arm and shrinking the other—altering how long it takes the lasers to complete their path, which scientists can measure. VeritasiumListen to the pair of colliding black holes detected by LIGOAs ripples in spacetime, gravitational waves do not produce sound, which is the perception of specific vibrations in matter (e.g., vocal cords vibrating air molecules). The "chirp" of gravitational waves comes instead from converting the spacetime ripples into sound waves that the human ear can hear. LIGO LabThe air around lightning can be five times hotter than the sun's surfaceAt that temperature, lightning can almost instantly boil all the water in a tree, causing it to explode! But how is that kind of energy created, and how do humans survive lightning strikes? Click the title of this resource to find out. 1440LIghter-colored eyes have heightened risks for macular degenerationPeople with blue eyes appear to be at elevated risk of developing the disorder, perhaps because more light can penetrate their eyes. But the most significant modifiable factor heightening the risk for macular degeneration is smoking. Docs Who LiftThe next generation of gravitational wave detectors may include a triangular designThe Einstein Telescope will use three pairs of underground detectors—each with arms separated by 60 degrees—arranged in an equilateral triangle. The European observatory will work alongside the Cosmic Explorer, a pair of new US detectors, to provide an eightfold increase in sensitivity over LIGO and extend the current detection frequency range. arXivBud Light was created to compete in the lower-calorie light beer marketArguably sparked by Miller Lite's successful 1975 launch, Anheuser-Busch rolled out Bud Light in 1982. The brand faced controversy in 2023 after a sponsorship deal with transgender influencer Dylan Mulvaney, sparking a Bud Light boycott. The Atlantic'Zeitgebers' like light are external cues for the circadian clockGerman for "time giver" or "time cues," common external zeitgebers include sunlight, food, and physical activity. The timing of these external influences can shift circadian clocks or lead to irregularities: A 2018 study, for example, found that later light exposure and meals were linked to later timing of peak activity and bedtimes. National Library of MedicineArtificial lighting and modern practices like working late are linked with sleep shiftsAn analysis of five adults participating in a German reality program that tasked them with living in a Stone-Age-like settlement for 2.5 months, provided some insights into how modern conditions may have shifted our circadian rhythms. The participants slept about 90 minutes more under these conditions, and went to bed earlier and rose earlier, raising questions about how circadian rhythms, sleep, and sleep quality are affected by modern lifestyles. Journal of Clinical Sleep MedicineArtificial lightning can improve the yield of shiitake mushroom growersResearchers have found that shockwaves produced from lightning strikes homogenously break internal filaments called hyphae, transitioning the mushrooms from a vegetative growth to a fruiting phase. Repeated minor shocks near mushroom logs mimicked this effect. Physics WorldLightning may kill as many as 320 million trees each yearIgnoring the effects of tree loss resulting from lightning-induced wildfires, researchers at the Technical University of Munich developed a quantitative model to estimate the loss of these organisms due to cloud-to-ground strikes, based on global lightning data and forest structure. They expect the estimate to rise due to increased strikes resulting from climate change. Yale e360Lightning bolts are about as thick as a garden hoseThe conductive filament ranges from about 2.5 to 5.0 centimeters (1 to 2 inches), though its extreme brightness makes it appear much thicker and visible from miles away. Scars on individuals who suffer a direct strike produce Lichtenberg figures with similar maximum thickness. Stuff You Should KnowLightning rods provide a conductive pathway to safely steer massive electric currentsThe device is positioned higher above the ground to "catch" one of the many branching filaments of electrons from clouds before they make contact with other surface structures, which have been induced to have a positive charge by overhead storm clouds. The current is then sent to a conductive grid buried underground. How Stuff WorksWatch lightning strike a building at 40,000 frames per secondWhen the built-up layer of negative charge at the bottom of clouds is sufficiently high, a network of charge filaments will emerge. If one of the filaments meets a rising strand of positively charged particles, a highly conductive path forms, and charges across all filaments move to the path, generating lightning AGULightning storms are more common in coastal and tropical regionsWater-abundant areas that receive increased solar radiation, such as those near the equator, experience increased rates of evaporation, which produce tall clouds as moisture rises, cools, and condenses. Mountain ranges can also steer air to higher altitudes, creating collisions between atmospheric particles that generate charge imbalances—the precursors to lightning. Ologies with Alie WardLightning forms when streams of rising and falling charged particles connectIn cloud-to-ground lightning, a buildup of negative charge at the bottom of clouds repels electrons on Earth's surface, leaving behind positively charged particles. When descending negatively charged air—the stepped leader—meets rising positively charged particles—the upward streamer—brightening runs up the connection, producing intense flashes known as return strokes. NOAALightning results from the rapid flow of charges through the atmosphereLightning in storm clouds forms from the collisions between graupel—small hail particles—and smaller ice particles, which transfer electrons. Layers of opposing charges form as these differently sized particles rise and fall. When air can no longer insulate these layers, electricity discharges, equalizing these regions. NOAA SciJinksBright light therapy involves basking in 10,000 lux of light for 30 minutes each morningNothing is better than going outside and soaking up real sunlight. However, this is harder in winter, especially in very cold and cloudy regions. SAD lamps are designed to project 10,000 lux—a unit of illuminance, or how much light actually hits a surface (rather than how much is produced, like watts). This video discusses product options and practical considerations. New York TimesInfrared light is most often associated with thermal radiation and cooking foodAlthough extensively used in remote controls for electronics, where LED lights send signals wirelessly, infrared cameras allow for night vision and thermography—imaging of heat patterns in the body to non-invasively reveal blood flow for supplementary diagnostics. Infrared radiation also provides heat in toasters, saunas, and other technologies. Geeks For GeeksLight can 3D print objects within rotating cylinders of resinComputed axial lithography involves using light to project 2D computerized tomography, or CT, scans of a figure onto photo-sensitive resin, which solidifies upon exposure. As the images and the cylinder are spun at the same rate, the object is volumetrically fabricated an order of magnitude faster than layer-by-layer methods. Nature VideoLight energy can be transformed into electricity in solar cells via the photovoltaic effectWhen light strikes semiconducting material, it can knock electrons out of atoms, creating a charge imbalance within the material. A wire connecting the oppositely charged regions can allow electrons to flow back, balancing the charges and producing an electric current that can be harnessed to power devices. The Engineering MindsetLight appears to slow down as it travels through different materialsAs electromagnetic waves interact with particles in a transparent medium, particles vibrate and generate their own electromagnetic waves. The interference of the original and generated waves, which are slightly delayed, results in ensemble light with an effective slower speed but unchanged color. Space.comLight waves can interfere and cancel each other outWhen light waves travel past one another, their peaks and valleys combine, just as overlapping ripples in water can combine to form a larger ripple. When the peak of a light wave meets the valley of another of the same wavelength and brightness, the waves combine to produce no light. VeritasiumLight has been modeled as a wave and a stream of particles throughout historyIsaac Newton first identified white light as composed of a spectrum of colors, which he believed consisted of particles of different hues. Various light phenomena, including refraction, led Christiaan Huygens to develop an alternative wave model. Quantum mechanics validated both models through the concept of wave-particle duality. Be SmartLichtenberg figures capture lightning-like patterns within insulatorsWhen high-energy electrons from particle accelerators are fired into materials like acrylic, they form a charged plane before discharging into scarred patterns within the material. By evenly charging a cylindrical bottle through rotation during the irradiation process, a 3D figure of lightning in a bottle can be created. Electron ImpressionsWhen they merge, black holes release multiple solar masses of energyThe energy emanates outward in the form of gravitational waves, which can be detected at observatories like LIGO. After merging, it is impossible to determine the characteristics of the two black holes that merged to create it. NOVA PBS OfficialLight echoes are expanding shells of reflected starlightJust as sound waves reveal the location of obstacles by reflecting off them, pulses of light emitted by stars illuminate rings of interstellar dust, giving the appearance of ejected material as the light travels outward. NASA Science‘Guiding Light’ was the longest-running scripted drama in broadcast historyThe show ran for 72 years, starting as a radio program in 1937, and eventually transitioning to television in 1952. Along the way, it launched several Hollywood stars, like Kevin Bacon, James Earl Jones, and Christopher Walken. CBS canceled the show in 2009. NPRLight can be used to slow the motion of atomsWhile photons possess energy, they also have momentum, which allows them to collide with other particles, much like billiard balls, thereby slowing them down and reducing their kinetic energy, or temperature. Using multiple lasers from different directions, particles can be cooled to within one degree of absolute zero. Physics GirlCannes Lions winners, after the awardsRather than focusing on the brands or agencies behind winning campaigns, this list highlights the people who earned Cannes Lions. It’s a fascinating look at what wins awards and what those awards can do for the recipients. ZappiCannes Lions features over 30 different awardsWhile the classic track is limited to audio and radio, film, outdoor, and print and publishing, Cannes Lions’ many other awards embrace the broad spectrum of the creative fields. Cannes LionsThe light sleep stages of the sleep cycleEach night as we sleep, we progress through a predictable pattern of brain activity known as the “sleep cycle.” The sleep cycle consists of four distinct parts, and the early portion of this cycle is often referred to as “light sleep.” This helpful page written by journalist Lisa L. Lewis helps clarify what exactly “light” sleep means and why it perhaps doesn’t get the credit it deserves. After all, we spend about half the night in this stage, which researchers have discovered is critical for memory consolidation and learning. Sleep.comLighting the menorah is viewed as the most important Hanukkah ritualThis short video guides viewers through the process, from the supplies required to the order in which the candles are lit. It also covers the prayers that are recited nightly and associated blessings for each individual night. HowcastA new logo helped the NBA stay relevant in the '70sIn 1967, the American Basketball Association was formed, featuring a flashier style of offense. The competition caused player salaries to rise in both leagues. After watching Major League Baseball unveil its new logo, the NBA decided to use the same designer to create an iconic logo for the league. It debuted in 1971 and reignited basketball fans' interest. Creative BloqLight pollution is giving oysters insomniaOysters, bivalve mollusks that have light-detecting cells along their skin, can't sleep with all this artificial light. According to a 2022 study, oysters' sleep cycles are disturbed by light dimmer than that provided by the full moon. As with humans, it's possible that these bouts of insomnia could have adverse health effects and contribute to the development of disease over time. Hakai MagazineElectrical discharge from stressed rocks may produce lightningAlthough flashes of light in the sky likely result from storms or damaged transformers and power lines coinciding with geological events, some scientists theorize that fracto-luminescence, or earthquake lights, may be caused by discharged built-up static electricity. NOVA PBS OfficialLego stop motion reenacts the longest battle in World War IOne of the longest and bloodiest battles of World War I, the Battler of Verdun was a deadly conflict between French and German forces for 10 months in 1916. Some 300,000 lives were lost, but ultimately the French triumphed. This video provides a stop-motion reenactment of the battle in Lego bricks. YouTube
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