Clocks at different heights tick at different rates. An atomic clock has now revealed this key feature of the general theory of relativity on a scale of a millimeter. HIROSHI WATANABE/GETTY IMAGES PLUS

By Emily Conover -- OCTOBER 18, 2021

The record-breaking result reveals the incredible precision achievable by atomic clocks

A millimeter might not seem like much. But even a distance that small can alter the flow of time.

According to Einstein’s theory of gravity, general relativity, clocks tick faster the farther they are from Earth or another massive object (SN: 10/4/15). Theoretically, that should hold true even for very small differences in the heights of clocks. Now an incredibly sensitive atomic clock has spotted that speedup across a millimeter-sized sample of atoms, revealing the effect over a smaller height difference than ever before. Time moved slightly faster at the top of that sample than at the bottom, researchers report September 24 at arXiv.org.

“This is fantastic,” says theoretical physicist Marianna Safronova of the University of Delaware in Newark, who was not involved with the research. “I thought it would take much longer to get to this point.” The extreme precision of the atomic clock’s measurement suggests the potential to use the sensitive timepieces to test other fundamental concepts in physics.

An inherent property of atoms allows scientists to use them as timepieces. Atoms exist at different energy levels, and a specific frequency of light makes them jump from one level to another. That frequency — the rate of wiggling of the light’s waves — serves the same purpose as a clock’s regularly ticking second hand. For atoms farther from the ground, time runs faster, so a greater frequency of light will be needed to make the energy jump. Previously, scientists have measured this frequency shift, known as gravitational redshift, across a height difference of 33 centimeters (SN: 9/23/10).

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Credit: EHT Collaboration, [CC BY 4.0]

Written by Sebastian H. Völkel and Nicola Franchini

The name “black hole” describes the incredible phenomena that light cannot escape away from it. Here, the gravitational pull is beyond any measure, meaning that there is no emission at all. The boundary of this region is called the event horizon. On the other hand, the light that only approaches but never passes the event horizon is strongly deflected and eventually follows highly bent orbits around the black hole, until some of it can be observed on Earth.

Albert Einstein’s general theory of relativity predicts the existence of black holes. The mass of these objects can span from tens to millions or even billions of times the mass of the Sun. The latter is referred to by astrophysicists as supermassive black holes. These monsters have a lot of astrophysical relevance since they dwell in the centers of most galaxies, including the Milky Way.

According to scientists, black holes are surrounded by very hot gas in the shape of disks that are constantly rotating around the black hole. While some gas spirals inwards from far-out regions of the disk, other gas of the inner region falls into the black hole. These mechanisms produce light, which either fall in the black hole or escape from the system. The closest thing to a picture of a black hole (which itself does not emit light) is a detailed measurement of the shining gas being swallowed by it. Ongoing developments in radio astronomy, computer simulations, and data analysis techniques make it possible to take images of supermassive black holes, as demonstrated by the Event Horizon Telescope Collaboration in the last few years.

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The Molten Ring. (Saurabh Jha/Rutgers, The State University of New Jersey)

MICHELLE STARR

24 SEPTEMBER 2021

One of the most spectacular Einstein rings ever seen in space is enabling us to see what's happening in a galaxy almost at the dawn of time.

The smears of light called the Molten Ring, stretched out and warped by gravitational fields, are magnifications and duplications of a galaxy whose light has traveled a whopping 9.4 billion light-years. This magnification has given us a rare insight into the stellar 'baby boom' when the Universe was still in its infancy.

The early evolution of the Universe is a difficult time to understand. It blinked into existence as we understand it roughly 13.8 billion years ago, with the first light emerging (we think) around 1 billion years later. Light traveling for that amount of time is faint, the sources of it small, and dust obscures much of it.

Even the most intrinsically luminous objects are extraordinarily hard to see across that gulf of space-time, so there are large gaps in our understanding of how the Universe assembled itself from primordial soup.

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Neutron stars (one illustrated) squash the mass equivalent of the sun into the size of a city. CASEY REED/PENN STATE

By Elizabeth Quill FEBRUARY 3, 2021

The predictions were right about black holes, gravitational waves and universe expansion

Albert Einstein’s mind reinvented space and time, foretelling a universe so bizarre and grand that it has challenged the limits of human imagination. An idea born in a Swiss patent office that evolved into a mature theory in Berlin set forth a radical new picture of the cosmos, rooted in a new, deeper understanding of gravity.

Out was Newton’s idea, which had reigned for nearly two centuries, of masses that appeared to tug on one another. Instead, Einstein presented space and time as a unified fabric distorted by mass and energy. Objects warp the fabric of spacetime like a weight resting on a trampoline, and the fabric’s curvature guides their movements. With this insight, gravity was explained.

Einstein presented his general theory of relativity at the end of 1915 in a series of lectures in Berlin. But it wasn’t until a solar eclipse in 1919 that everyone took notice. His theory predicted that a massive object — say, the sun — could distort spacetime nearby enough to bend light from its straight-line course. Distant stars would thus appear not exactly where expected. Photographs taken during the eclipse verified that the position shift matched Einstein’s prediction. “Lights all askew in the heavens; men of science more or less agog,” declared a New York Times headline.

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Science and Nature  7.2.2021

You don’t have to know a whole lot about science to know that black holes normally suck things in, not spew things out. But NASA detected something mighty bizarre at the supermassive black hole Markarian 335. Two of NASA’s space telescopes, including the Nuclear Spectroscopic Telescope Array (NuSTAR), amazingly observed a black hole’s corona “launched” away from the supermassive black hole.

Then an enormous pulse of X-ray energy spewed out. This kind of phenomena has never been observed before.
“This is the first time we have been able to link the launching of the corona to a flare. This will help us comprehend how supermassive black holes power some of the brightest objects in the cosmos.” Dan Wilkins, of Saint Mary’s University, said. This is one of the most important discoveries so far.

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The canonical Einstein Cross, the quadruply lensed quasar Q2237+030, is seen in this Hubble image. A new study has found two additional Einstein Crosses created by the lensing of compact galaxies. [NASA, ESA, and STScI]

By Susanna Kohler on 9 December 2020

Seeing quadruple? In a rare phenomenon, some distant objects can appear as four copies arranged in an “Einstein cross”. A new study has found two more of these unusual sights — with an unexpected twist.

Searching for Rare Crosses

Gravitational lensing — the bending of light by the gravity of massive astronomical objects — can do some pretty strange things. One of lensing’s more striking creations is the Einstein cross, a configuration of four images of a distant, compact source created by the gravitational pull of a foreground object (which is usually visible in the center of the four images).

 The canonical example of this phenomenon is the Einstein Cross, a gravitationally lensed object called QSO 2237+0305, seen in the cover image above. In this case, as with the majority of known Einstein crosses, the background source is a distant quasar — the small and incredibly bright nucleus of an active galaxy. But other sources can be lensed into Einstein crosses as well, under the right circumstances.

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This year's Nobel Prize in Physics was awarded to Roger Penrose, Reinhard Genzel and Andrea Ghez.

By Emma Reynolds and Katie Hunt, CNN, October 6, 2020

(CNN)The 2020 Nobel Prize in Physics has been awarded to scientists Roger Penrose, Reinhard Genzel and Andrea Ghez for their discoveries about black holes.

Göran K. Hansson, secretary for the Royal Swedish Academy of Sciences, said at Tuesday's ceremony in Stockholm that this year's prize was about "the darkest secrets of universe."

Penrose, a professor at the University of Oxford who worked with Stephen Hawking, was awarded half of the prize "for the discovery that black hole formation is a robust prediction of the general theory of relativity." The other half was awarded jointly to Genzel and Ghez "for the discovery of a supermassive compact object at the center of our galaxy."

"Penrose, Genzel and Ghez together showed us that black holes are awe-inspiring, mathematically sublime, and actually exist," Tom McLeish, professor of natural philosophy at the University of York, told the Science Media Centre in London.

Ghez, born in New York City and a professor at the University of California, Los Angeles, is only the fourth woman to win a Nobel physics prize. It was awarded to a woman for the first time in 55 years in 2018, when Donna Strickland won for groundbreaking inventions in the field of laser physics.

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From the Royal Swedish Academy of Sciences

1  Original announcement

2  Scientific Background

3  Popular Science  Background

Snapshots of the appearance of M87 *, obtained with images and geometrical models and the EHT array between 2009 and 2017. The diameter of the rings is the same, but the location of the bright side varies. - (Image Credit: M. Wielgus, D. Pesce & the EHT Collaboration)

September 23, 2020

The Event Horizon Telescope is an array of telescopes that uses a technique called Very Long Baseline Interferometry (VLBI) to form a virtual radio telescope with a dish diameter similar to the size of Earth.

In the period between 2009-2013, M87* (the supermassive black hole in the galaxy M87) was observed with prototype EHT telescopes, at four different sites. Eventually, the entire EHT array came into operation in 2017, with seven telescopes located in five locations around the Earth.

Although the observations from 2009-2013 contained much less data than those from 2017 (lacking the capacity to provide a picture of the black hole at that point in time), the EHT team was able to identify changes in the appearance of M87* between 2009 and 2017 using statistical models.

The researchers concluded that the diameter of the black hole's shadow remains consistent with the predictions of Einstein's general theory of relativity for black holes of 6.5 billion solar masses. But they also found something unexpected: the crescent-shaped ring of hot plasma around M87* wobbles! It is the first time astronomers have glimpsed the dynamic accretion structure so close to the event horizon of a black hole, where gravity is extreme.

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Link to the publication 

See also

A star's rosette-shaped path around a black hole confirms Einstein's theory of gravity. Rather than tracing out a single ellipse (red), its orbit rotates over time (blue, rotation exaggerated in this illustration for emphasis). L. CALÇADA/ESO

Decades of observations revealed the rotation of the star’s elliptical orbit

Emily Conover - ScienceNews

The first sign that Albert Einstein’s theory of gravity was correct has made a repeat appearance, this time near a supermassive black hole.

In 1915, Einstein realized that his newly formulated general theory of relativity explained a weird quirk in the orbit of Mercury. Now, that same effect has been found in a star’s orbit of the enormous black hole at the heart of the Milky Way, researchers with the GRAVITY collaboration report April 16 in Astronomy & Astrophysics.

The star, called S2, is part of a stellar entourage that surrounds the Milky Way’s central black hole. For decades, researchers have tracked S2’s elliptical motion around the black hole. The researchers previously had used observations of S2 to identify a different effect of general relativity, the reddening of the star’s light due to what’s called gravitational redshift (SN: 7/26/18).

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Artist's depiction of 'frame-dragging': two spinning stars twisting space and time. Credit: Mark Myers, OzGrav ARC Centre of Excellence.

An international team of astrophysicists led by Australian Professor Matthew Bailes, from the ARC Centre of Excellence of Gravitational Wave Discovery (OzGrav), has shown exciting new evidence for 'frame-dragging'—how the spinning of a celestial body twists space and time—after tracking the orbit of an exotic stellar pair for almost two decades. The data, which is further evidence for Einstein's theory of General Relativity, is published today the journal Science.

More than a century ago, Albert Einstein published his iconic theory of General Relativity—that the force of gravity arises from the curvature of space and time and that objects, such as the Sun and the Earth, change this geometry. Advances in instrumentation have led to a flood of recent (Nobel prize-winning) science from phenomena further afield linked to General Relativity. The discovery of gravitational waves was announced in 2016; the first image of a black hole shadow and stars orbiting the supermassive black hole at the centre of our own galaxy was published just last year.

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An artist’s conception of two black holes entwined in a gravitational tango. Credit: NASA/JPL-Caltech/SwRI/MSSS/Christopher Go

Do supermassive black holes have friends? The nature of galaxy formation suggests that the answer is yes, and in fact, pairs of supermassive black holes should be common in the universe.

I am an astrophysicist and am interested in a wide range of theoretical problems in astrophysics, from the formation of the very first galaxies to the gravitational interactions of black holes, stars and even planets. Black holes are intriguing systems, and supermassive black holes and the dense stellar environments that surround them represent one of the most extreme places in our universe.

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Virginia Trimble at the University of California, Irvine, where she has been on the faculty since 1971. (Monica Almeida for Quanta Magazine)

Elizabeth Landau  November 11, 2019

How a young celebrity became one of the first female astronomers at Caltech, befriended Richard Feynman, and ended up the world’s foremost chronicler of the science of the night sky.

Beginning in 1991, Virginia Trimble read every single astronomy article published in 23 different journals. She would then write an annual “year in review” article, which astronomers everywhere used as a window into the rest of the field at large. Her characteristic dry humor came through even in the first installment: “Science, notoriously, progresses amoeba-like, thrusting out pseudopods in unpredictable directions and dragging in the rest of the body after or, occasionally, retreating in disorder.” She stopped in 2007, in part because, with online publishing, there were just too many articles to read.

This endeavor and others have given Trimble a perspective on the past half-century of astronomy that few others could claim.

Stardom was part of Trimble’s early years, and not just because she attended Hollywood High School. In 1962, while still an undergraduate at the University of California, Los Angeles, she achieved her first small measure of fame when Life magazine published an article about her titled “Behind a Lovely Face, a 180 I.Q.” Then in 1963, she became Miss Twilight Zone, the face of a publicity campaign to promote the popular sci-fi show with Rod Serling.

In college she immersed herself in the other kind of stars — the ones in the broader universe — and went on to become one of the first women to earn a doctorate in astrophysics at the California Institute of Technology. While she was there, she befriended Richard Feynman, who paid her $5.50 an hour to pose as a model.

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A black hole (one illustrated) with a mass equal to about 68 suns has been found in the Milky Way, researchers say. That dark mass is much heavier than other similar black holes. (NAOJ)

By Christopher Crockett 28.11.2019

A heavyweight black hole in our galaxy has some explaining to do.

With a mass of about 68 suns, it is far heftier than other stellar-mass black holes (those with masses below about 100 suns) in and around the Milky Way, scientists say. That’s not just a record, it’s also a conundrum. According to theory, black holes in our galaxy that form from the explosive deaths of massive stars — as this one likely did — shouldn’t be heavier than about 25 suns.

The black hole is locked in orbit with a young blue star dubbed LB-1, which sits about 13,800 light-years away in the constellation Gemini, researchers found. Combing through data from the LAMOST telescope in China, Jifeng Liu, an astrophysicist at the Chinese Academy of Sciences in Beijing, and colleagues noticed that LB-1 repeatedly moves toward and away from Earth with great speed — a sign that the star orbits something massive.

With additional observations from telescopes in Hawaii and the Canary Islands, the team mapped out the orbit and deduced that the star gets whipped around by a dark mass roughly 68 times as massive as the sun. Only a black hole fits that description, the team reports November 27 in Nature.

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Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. This long-sought image provides the strongest evidence to date for the existence of supermassive black holes and opens a new window onto the study of black holes, their event horizons, and gravity. Credit: Event Horizon Telescope Collaboration

https://www.youtube.com/watch?v=3QEPzP58neg&feature=youtu.be

2020 Breakthrough Prize in Fundamental Physics

The Event Horizon Telescope Collaboration

Collaboration Director Shep Doeleman of the Harvard-Smithsonian Center for Astrophysics will accept on behalf the collaboration. The $3 million prize will be shared equally with 347 scientists co-authoring any of the six papers published by the EHT on April 10, 2019, which can be found here. The names are also listed at the bottom of this page.
Citation: For the first image of a supermassive black hole, taken by means of an Earth-sized alliance of telescopes.
Description: Using eight sensitive radio telescopes strategically positioned around the world in Antarctica, Chile, Mexico, Hawaii, Arizona and Spain, a global collaboration of scientists at 60 institutions operating in 20 countries and regions captured an image of a black hole for the first time. By synchronizing each telescope using a network of atomic clocks, the team created a virtual telescope as large as the Earth, with a resolving power never before achieved from the surface of our planet. One of their first targets was the supermassive black hole at the center of the Messier 87 galaxy – its mass equivalent to 6.5 billion suns. After painstakingly analyzing the data with novel algorithms and techniques, the team produced an image of this galactic monster, silhouetted against hot gas swirling around the black hole, that matched expectations from Einstein's theory of gravity: a bright ring marking the point where light orbits the black hole, surrounding a dark region where light cannot escape the black hole's gravitational pull.

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Credit: Event Horizon Telescope Collaboration

Nature Physics 15, 415 (2019) -- Published: 02 May 2019

General relativity was first experimentally verified in 1919. On the centennial of this occasion, we celebrate the scientific progress fuelled by subsequent efforts at verifying its predictions, from time dilation to the observation of the shadow of a black hole.

When we think back to the beginnings of Einstein’s general theory of relativity, we consider the measurements obtained during the solar eclipse in 1919 as rock-solid proof. However, things weren’t as clear cut back then. In 1921, the editorial introducing the special issue on general relativity in Nature (https://go.nature.com/2uZCo4E) betrayed a certain level of caution: “In two cases predicted phenomena for which no satisfactory alternative explanation is forthcoming have been confirmed by observation, and the third is still a subject of inquiry.”

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Total solar eclipse, 29 May 1919. Glass positive photograph of the corona, taken at Sobral in Brazil, with a telescope of 4in in aperture and 19ft focal length. Photograph: Science & Society Picture Library/SSPL via Getty Images

Robin McKie
Sun 12 May 2019 

Arthur Eddington’s photographs of the 1919 solar eclipse proved Einstein right and ushered in a century where gravity was king

A hundred years ago this month, the British astronomer Arthur Eddington arrived at the remote west African island of Príncipe. He was there to witness and record one of the most spectacular events to occur in our heavens: a total solar eclipse that would pass over the little equatorial island on 29 May 1919.

Observing such events is a straightforward business today, but a century ago the world was still recovering from the first world war. Scientific resources were meagre, photographic technology was relatively primitive, and the hot steamy weather would have made it difficult to focus instruments. For good measure, there was always a threat that clouds would blot out the eclipse.

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BLAST FROM COLLAPSE A collapsar occurs when a massive, spinning star collapses into a black hole, powering a blast of light known as a long gamma ray burst (illustrated) and exploding the star’s outer layers.

Spinning stellar objects collapsing into black holes could help explain heavy elements’ origins
BY EMILY CONOVER  MAY 8, 2019

The gold in your favorite jewelry could be the messy leftovers from a newborn black hole’s first meal.

Heavy elements such as gold, platinum and uranium might be formed in collapsars — rapidly spinning, massive stars that collapse into black holes as their outer layers explode in a rare type of supernova. A disk of material, swirling around the new black hole as it feeds, can create the conditions necessary for the astronomical alchemy, scientists report online May 8 in Nature.

“Black holes in these extreme environments are fussy eaters,” says astrophysicist Brian Metzger of Columbia University, a coauthor of the study. They can gulp down only so much matter at a time, and what they don’t swallow blows off in a wind that is rich in neutrons — just the right conditions for the creation of heavy elements, computer simulations reveal.

Astronomers have long puzzled over the origins of the heaviest elements in the universe. Lighter elements like carbon, oxygen and iron form inside stars, before being spewed out in stellar explosions called supernovas. But to create elements further down the periodic table, an extreme environment densely packed with neutrons is required. That’s where a chain of reactions known as the r-process can occur, in which atomic nuclei rapidly absorb neutrons and undergo radioactive decay to create new elements.

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EHT images of M87 on four different observing nights. In each panel, the white circle shows the resolution of the EHT. All four images are dominated by a bright ring with enhanced emission in the south. 

The Astrophysical Journal Letters

Shep Doeleman (EHT Director) on behalf of the EHT Collaboration -- April 2019

This Focus Issue shows ultra-high angular resolution images of radio emission from the supermassive black hole believed to lie at the heart of galaxy M87 (Figure 1). A defining feature of the images is an irregular but clear bright ring, whose size and shape agree closely with the expected lensed photon orbit of a 6.5 billion solar mass black hole. Soon after Einstein introduced general relativity, theorists derived the full analytic form of the photon orbit, and first simulated its lensed appearance in the 1970s. By the 2000s, it was possible to sketch the "shadow" formed in the image when synchrotron emission from an optically thin accretion flow is lensed in the black hole's gravity. During this time, observational evidence began to build for the existence of black holes at the centers of active galaxies, and in our own Milky Way. In particular, a steady progression in radio astronomy enabled very long baseline interferometry (VLBI) observations at ever-shorter wavelengths, targeting supermassive black holes with the largest apparent event horizons: M87, and Sgr A* in the Galactic Center. The compact sizes of these two sources were confirmed by studies at 1.3mm, first exploiting baselines that ran from Hawai'i to the mainland US, then with increased resolution on baselines to Spain and Chile.

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The most-visualized black hole of all, as illustrated in the movie Interstellar, shows a predicted event horizon fairly accurately for a very specific class of rotating black holes. Deep within the gravitational well, time passes at a different rate for observers than it does for us far outside of it. The Event Horizon Telescope is expected to reveal the emissions surrounding a black hole's event horizon, directly, for the first time. INTERSTELLAR / R. HURT / CALTECH

Ethan Siegel
Apr 2, 2019

In science, there's no moment more exciting than when you get to confront a longstanding theoretical prediction with the first observational or experimental results. Earlier this decade, the Large Hadron Collider revealed the existence of the Higgs boson, the last undiscovered fundamental particle in the Standard Model. A few years ago, the LIGO collaboration directly detected gravitational waves, confirming a longstanding prediction of Einstein's General Relativity.

And in just a few days, on April 10, 2019, the Event Horizon Telescope will make a much-anticipated announcement where they're expected to release the first-ever image of a black hole's event horizon. At the start of the 2010s, such an observation would have been technologically impossible. Yet not only are we about to see what a black hole actually looks like, but we're about to test some fundamental properties of space, time, and gravity as well.

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1 April 2019

The European Commission, European Research Council, and the Event Horizon Telescope (EHT) project will hold a press conference to present a groundbreaking result from the EHT.

When: On 10 April 2019 at 15:00 CEST

Where: The press conference will be held at the Berlaymont Building, Rue de la Loi (Wetstraat) 200, B-1049 Brussels, Belgium. The event will be introduced by European Commissioner for Research, Science and Innovation, Carlos Moedas, and will feature presentations by the researchers behind this result.

What: A press conference to present a groundbreaking result from the EHT.

Who: The European Commissioner for Research, Science and Innovation, Carlos Moedas, will deliver remarks. Anton Zensus, Chair of the EHT Collaboration Board will also make remarks and introduce a panel of EHT researchers who will explain the result and answer questions:
        Heino Falcke, Radboud University, Nijmegen, The Netherlands (Chair of the EHT Science Council)
        Monika Mościbrodzka, Radboud University, Nijmegen, The Netherlands (EHT Working Group Coordinator)
        Luciano Rezzolla, Goethe Universität, Frankfurt, Germany (EHT Board Member)
        Eduardo Ros, Max-Planck-Institut für Radioastronomie, Bonn, Germany, (EHT Board Secretary)

RSVP: This invitation is addressed to media representatives. To participate in the conference, members of the media must register by completing an online form before April 7 23:59 CEST. Please indicate whether you wish to attend in person or if you will participate online only. On-site journalists will have a question-and-answer session with panellists during the conference. In-person individual interviews immediately after the conference will also be possible.
The conference will be streamed online on the ESO website, by the ERC, and on social media. We will take a few questions from social media using the hashtag #AskEHTeu.

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Katia Moskvitch - Contributing Writer : April 30, 2018

New observations of extreme astrophysical systems have “brutally and pitilessly murdered” attempts to replace Einstein’s general theory of relativity.

Two white dwarfs and a pulsar orbit one another in a system that reveals how gravity behaves in extreme environments.

Miguel Zumalacárregui knows what it feels like when theories die. In September 2017, he was at the Institute for Theoretical Physics in Saclay, near Paris, to speak at a meeting about dark energy and modified gravity. The official news had not yet broken about an epochal astronomical measurement — the detection, by gravitational wave detectors as well as many other telescopes, of a collision between two neutron stars — but a controversial tweet had lit a firestorm of rumor in the astronomical community, and excited researchers were discussing the discovery in hushed tones.

Zumalacárregui, a theoretical physicist at the Berkeley Center for Cosmological Physics, had been studying how the discovery of a neutron-star collision would affect so-called “alternative” theories of gravity. These theories attempt to overcome what many researchers consider to be two enormous problems with our understanding of the universe. Observations going back decades have shown that the universe appears to be filled with unseen particles — dark matter — as well as an anti-gravitational force called dark energy. Alternative theories of gravity attempt to eliminate the need for these phantasms by modifying the force of gravity in such a way that it properly describes all known observations — no dark stuff required.

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The relativistic eccentricity of Galileo satellites 5 and 6 reaches a peak amplitude of approximately 370 nanoseconds (billionths of a second), driven by the shifting altitude, and hence changing gravity levels, of their elliptical orbits around Earth. A periodic modulation of this size is clearly discernible, given the relative frequency stability of the Passive Hydrogen Maser atomic clocks aboard the satellites. Credit: European Space Agency

December 5, 2018, European Space Agency

Europe's Galileo satellite navigation system – already serving users globally – has now provided a historic service to the physics community worldwide, enabling the most accurate measurement ever made of how shifts in gravity alter the passing of time, a key element of Einstein's Theory of General Relativity.

Two European fundamental physics teams working in parallel have independently achieved about a fivefold improvement in measuring accuracy of the gravity-driven time dilation effect known as 'gravitational redshift.'
The prestigious Physical Review Letters journal has just published the independent results obtained from both consortiums, gathered from more than a thousand days of data obtained from the pair of Galileo satellites in elongated orbits.
"It is hugely satisfying for ESA to see that our original expectation that such results might be theoretically possible have now been borne out in practical terms, providing the first reported improvement of the gravitational redshift test for more than 40 years," comments Javier Ventura-Traveset, Head of ESA's Galileo Navigation Science Office.
"These extraordinary results have been made possible thanks to the unique features of the Galileo satellites, notably the very high stabilities of their onboard atomic clocks, the accuracies attainable in their orbit determination and the presence of laser-retroreflectors, which allow for the performance of independent and very precise orbit measurements from the ground, key to disentangle clock and orbit errors."

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See also the 2015 announcement

Galileo satellites set for year-long Einstein experiment

Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole's accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results.GRMHD SIMULATIONS OF VISIBILITY AMPLITUDE VARIABILITY FOR EVENT HORIZON TELESCOPE IMAGES OF SGR A*, L. MEDEIROS ET AL., ARXIV:1601.06799

Oct 3, 2018

Ethan Siegel & Starts With A Bang

What does a black hole actually look like? For generations, scientists argued over whether black holes actually existed or not. Sure, there were mathematical solutions in General Relativity that indicated they were possible, but not every mathematical solution corresponds to our physical reality. It took observational evidence to settle that issue.

Owing to matter orbiting and infalling around black holes, both stellar-mass versions and the supermassive versions, we've detected the X-ray emissions characteristic of their existences. We found and measured the motions of individual stars that orbit suspected black holes, confirming the existence of massive objects at the centers of galaxies. If only we could directly image these objects that emit no light themselves, right? Amazingly, that time is here.

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A 1998 illustration of a spacecraft using negative energy to warp space-time and travel faster than light (digital art by Les Bossinas (Cortez III Service Corp.), 1998)

Dave Mosher May 24, 2018

• The US Department of Defense funded a series of studies on advanced aerospace technologies, including warp drives.
• The studies came out of a program that also funded research into UFO sightings.
• One report describes the possibility of using dark energy to warp space and effectively travel faster than light.
• However, a theoretical physicist says there's "zero chance that anyone within our lifetimes or the next 1,000 years" will see it happen.

Sometime after August 2008, the US Department of Defense contracted dozens of researchers to look into some very, very out-there aerospace technologies, including never-before-seen methods of propulsion, lift, and stealth.

Two researchers came back with a 34-page report for the propulsion category, titled "Warp Drive, Dark Energy, and the Manipulation of Extra Dimensions."

The document is dated April 2, 2010, though it was only recently released by the Defense Intelligence Agency. (Business Insider first learned about in a post by Paul Szoldra at Task & Purpose.)

The authors suggest we may not be too far away from cracking the mysteries of higher, unseen dimensions and negative or "dark energy," a repulsive force that physicists believe is pushing the universe apart at ever-faster speeds.

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Mathematicians have disproved the strong cosmic censorship conjecture. Their work answers one of the most important questions in the study of general relativity and changes the way we think about space-time.

Kevin Hartnet   May 17, 2018

Nearly 60 years after it was proposed, mathematicians have settled one of the most profound questions in the study of general relativity. In a paper posted online last fall, mathematicians Mihalis Dafermos and Jonathan Luk have proven that the strong cosmic censorship conjecture, which concerns the strange inner workings of black holes, is false.

“I personally view this work as a tremendous achievement — a qualitative jump in our understanding of general relativity,” emailed Igor Rodnianski, a mathematician at Princeton University.

The strong cosmic censorship conjecture was proposed in 1979 by the influential physicist Roger Penrose. It was meant as a way out of a trap. For decades, Albert Einstein’s theory of general relativity had reigned as the best scientific description of large-scale phenomena in the universe. Yet mathematical advances in the 1960s showed that Einstein’s equations lapsed into troubling inconsistencies when applied to black holes. Penrose believed that if his strong cosmic censorship conjecture were true, this lack of predictability could be disregarded as a mathematical novelty rather than as a sincere statement about the physical world.

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Physicists believe that at the tiniest scales, space emerges from quanta. What might these building blocks look like?

George Musser  09 MAY 2018

People have always taken space for granted. It is just emptiness, after all—a backdrop to everything else. Time, likewise, simply ticks on incessantly. But if physicists have learned anything from the long slog to unify their theories, it is that space and time form a system of such staggering complexity that it may defy our most ardent efforts to understand.

Albert Einstein saw what was coming as early as November 1916. A year earlier he had formulated his general theory of relativity, which postulates that gravity is not a force that propagates through space but a feature of spacetime itself. When you throw a ball high into the air, it arcs back to the ground because Earth distorts the spacetime around it, so that the paths of the ball and the ground intersect again. In a letter to a friend, Einstein contemplated the challenge of merging general relativity with his other brainchild, the nascent theory of quantum mechanics. That would not merely distort space but dismantle it. Mathematically, he hardly knew where to begin. “How much have I already plagued myself in this way!” he wrote.

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FREE-FALLIN’ Scientists compared the acceleration of two objects in free fall in a satellite orbiting 710 kilometers above Earth (illustrated)

Equivalence principle holds up inside an orbiting satellite
BY EMILY CONOVER 6:00AM, DECEMBER 4, 2017

Galileo’s most famous experiment has taken a trip to outer space. The result? Einstein was right yet again. The experiment confirms a tenet of Einstein’s theory of gravity with greater precision than ever before.

According to science lore, Galileo dropped two balls from the Leaning Tower of Pisa to show that they fell at the same rate no matter their composition. Although it seems unlikely that Galileo actually carried out this experiment, scientists have performed a similar, but much more sensitive experiment in a satellite orbiting Earth. Two hollow cylinders within the satellite fell at the same rate over 120 orbits, or about eight days’ worth of free-fall time, researchers with the MICROSCOPE experiment report December 4 in Physical Review Letters. The cylinders’ accelerations match within two-trillionths of a percent.

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RUSSELL MCLENDON -- November 20, 2017

From explaining the mysteries of nature to proving the power of daydreams, Albert Einstein gave the world a lot to be grateful for.

On Thanksgiving Day in 1915, a 36-year-old physicist named Albert Einstein submitted a paper to the Proceedings of the Prussian Academy of Sciences in Berlin. That paper — titled "Die Feldgleichungen der Gravitation," or "The Field Equations of Gravity" — was a scientific blockbuster, unveiling equations that govern the universe.

Einstein was in Germany at the time, so the U.S. holiday of Thanksgiving may not have been top of mind. (Also, he was probably a bit distracted by revolutionizing modern physics and astronomy.) Yet even if Einstein wasn't thinking of Thanksgiving on that fateful November day, it was one of many moments in his life that would inspire gratitude from people around the world, even a century later.

Physicists and astronomers are understandably thankful for Einstein's work, as are many other scientists whose careers hinge on his game-changing equations. But Einstein isn't just an esoteric hero for scholars — he's one of the most famous scientists of all time, serving as a global icon and synonym for ingenuity itself.

Hyperbole is common when describing the impact of historical figures, yet in Einstein's case, the superlatives are generally apt. He really was a rare genius who transformed our understanding of space, time and gravity, and his discoveries really did enable a wide array of modern technology. He also left a rich cultural legacy, proving the power of daydreams and independent thought, among other things.

So, in the seasonal spirit of thankfulness — or just because gratitude is good for you any time of year — here are a few brief reasons to appreciate Einstein:

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Until recently, simulations of the universe haven’t given its lumps their due

BY EMILY CONOVER 3:30PM, NOVEMBER 14, 2017

Magazine issue: Vol. 192 No. 9, November 25, 2017, p. 22

If the universe were a soup, it would be more of a chunky minestrone than a silky-smooth tomato bisque.

Sprinkled with matter that clumps together due to the insatiable pull of gravity, the universe is a network of dense galaxy clusters and filaments — the hearty beans and vegetables of the cosmic stew. Meanwhile, relatively desolate pockets of the cosmos, known as voids, make up a thin, watery broth in between.

Until recently, simulations of the cosmos’s history haven’t given the lumps their due. The physics of those lumps is described by general relativity, Albert Einstein’s theory of gravity. But that theory’s equations are devilishly complicated to solve. To simulate how the universe’s clumps grow and change, scientists have fallen back on approximations, such as the simpler but less accurate theory of gravity devised by Isaac Newton.

Relying on such approximations, some physicists suggest, could be mucking with measurements, resulting in a not-quite-right inventory of the cosmos’s contents. A rogue band of physicists suggests that a proper accounting of the universe’s clumps could explain one of the deepest mysteries in physics: Why is the universe expanding at an increasingly rapid rate?

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Natalie Wolchover -- June 20, 2017

Recent calculations tie together two conjectures about gravity, potentially revealing new truths about its elusive quantum nature.

Physicists have wondered for decades whether infinitely dense points known as singularities can ever exist outside black holes, which would expose the mysteries of quantum gravity for all to see. Singularities — snags in the otherwise smooth fabric of space and time where Albert Einstein’s classical gravity theory breaks down and the unknown quantum theory of gravity is needed — seem to always come cloaked in darkness, hiding from view behind the event horizons of black holes. The British physicist and mathematician Sir Roger Penrose conjectured in 1969 that visible or “naked” singularities are actually forbidden from forming in nature, in a kind of cosmic censorship. But why should quantum gravity censor itself?

Now, new theoretical calculations provide a possible explanation for why naked singularities do not exist — in a particular model universe, at least. The findings indicate that a second, newer conjecture about gravity, if it is true, reinforces Penrose’s cosmic censorship conjecture by preventing naked singularities from forming in this model universe. Some experts say the mutually supportive relationship between the two conjectures increases the chances that both are correct. And while this would mean singularities do stay frustratingly hidden, it would also reveal an important feature of the quantum gravity theory that eludes us.

“It’s pleasing that there’s a connection” between the two conjectures, said John Preskill of the California Institute of Technology, who in 1991 bet Stephen Hawking that the cosmic censorship conjecture would fail (though he actually thinks it’s probably true).

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Physicists have gathered evidence that space-time can behave like a fluid. Is space not as immaterial as we thought?

Tuesday 03rd October
Sabine Hossenfelder | Research fellow at the Frankfurt Institute for Advanced Studies and author of blog Backreaction

Physicists have gathered evidence that space-time can behave like a fluid. Mathematical evidence, that is, but still evidence. If this relation isn’t a coincidence, then space-time – like a fluid – may have a substructure.

We shouldn’t speak of space and time as if the two were distant cousins. We have known at least since Einstein that space and time are inseparable, two hemispheres of the same cosmic brain, joined to a single entity: space-time. Einstein also taught us that space-time isn’t flat, like paper, but bent and wiggly, like a rubber sheet. Space-time curves around mass and energy and this gives rise to the effect we call gravity.

That’s what Einstein said. But turns out if you write down the equations for small wiggles in a medium – such as soundwaves in a fluid – then the equations look exactly like those of waves in a curved background.

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A fundamental challenge
Bill Saxton/NRAO/AUI/NSF

By Joshua Sokol

Imagine you’re an astronomer with bright ideas about the hidden laws of the cosmos. Like any good scientist, you craft an experiment to test your hypothesis.

Then comes bad news – there’s no way to carry it out, except maybe in a computer simulation. For cosmic objects are way too unwieldy for us to grow them in Petri dishes or smash them together as we do with subatomic particles.

Thankfully, though, there are rare places in space where nature has thrown together experiments of its own – like PSR J0337+1715. First observed in 2012 and announced in 2014, this triple system is 4200 light years away in the constellation Taurus.

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This illustration reveals how the gravity of a white dwarf star warps space and bends the light of a distant star behind it. Credit: NASA, ESA, and A. Feild (STScI)

June 7, 2017

Albert Einstein predicted that whenever light from a distant star passes by a closer object, gravity acts as a kind of magnifying lens, brightening and bending the distant starlight. Yet, in a 1936 article in the journal Science, he added that because stars are so far apart "there is no hope of observing this phenomenon directly."

Now, an international research team directed by Kailash C. Sahu has done just that, as described in their June 9, 2017 article in Science. The study is believed to be the first report of a particular type of Einstein's "gravitational microlensing" by a star other than the sun.

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Using a massive telescope network, scientists have data in hand that could open new frontiers in our understanding of gravity.

Westford, MassachusettsFor the monster at the Milky Way’s heart, it’s a wrap.

After completing five nights of observations, today astronomers may finally have captured the first-ever image of the famous gravitational sinkhole known as a black hole.

More precisely, the hoped-for portrait is of a mysterious region that surrounds the black hole. Called the event horizon, this is the boundary beyond which nothing, not even light, can escape the object’s gargantuan grasp.

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Extra dimensions hiding here

Signatures of extra dimensions that don’t normally affect the four dimensions we can observe could show up in the way they warp ripples in space-time

By Leah Crane

HIDDEN dimensions could cause ripples through reality by modifying gravitational waves – and spotting such signatures of extra dimensions could help solve some of the biggest mysteries of the universe.

Physicists have long wondered why gravity is so weak compared with the other fundamental forces. This may be because some of it is leaking away into extra dimensions beyond the three spatial dimensions we experience.

Some theories that seek to explain how gravity and quantum effects mesh together, including string theory, require extra dimensions, often with gravity propagating through them. Finding evidence of such exotic dimensions could therefore help to characterise gravity, or find a way to unite gravity and quantum mechanics – it could also hint at an explanation for why the universe’s expansion is accelerating.

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HEART OF THE MATTER An illustration of the supermassive black hole at the center of the Milky Way.
PHOTOGRAPH BY NRAO, AUI, NSF

By Ron Cowen
PUBLISHED APRIL 11, 2017
WESTFORD, MASSACHUSETTS For the monster at the Milky Way’s heart, it’s a wrap.

After completing five nights of observations, today astronomers may finally have captured the first-ever image of the famous gravitational sinkhole known as a black hole.

More precisely, the hoped-for portrait is of a mysterious region that surrounds the black hole. Called the event horizon, this is the boundary beyond which nothing, not even light, can escape the object’s gargantuan grasp.

As the final observing run ended at 11:22 a.m. ET, team member Vincent Fish sat contentedly in his office at the MIT Haystack Observatory in Westford, Massachusetts. For the past week, Fish had been on call 24/7, sleeping fitfully with his cell phone next to him, the ringer set loud.

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Now we wait to see it.

FIONA MACDONALD 12 APR 2017

Scientists around the world have spent five sleepless nights staring into the abyss, and are hoping they've been rewarded with something that could change physics forever - the first photo of the event horizon at the edge of a black hole.

If their efforts were successful, we might be on the verge of actually seeing the edge of an elusive black hole, allowing us to see if the fundamentals of general relativity hold fast under some pretty extreme conditions. If Einstein was alive, we're sure he'd be excitedly freaking out right now.

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Upholding Einstein, so far
Andrew Brookes, National Physical Laboratory/SPL

By Anil Ananthaswamy

22 March 2017

OUR most accurate clocks are probing a key tenet of Einstein’s theory of relativity: the idea that time isn’t absolute. Any violation of this principle could point us to a long-sought theory that would unite Einstein’s ideas with quantum mechanics.

Special relativity established that the laws of physics are the same for any two observers moving at a constant speed relative to each other, a symmetry called Lorentz invariance. One consequence is that they would observe each other’s clocks running at different rates. Each observer would regard themselves as stationary and see the other observer’s clock as ticking slowly – an effect called time dilation.

Einstein’s general relativity compounds the effect. It says that the clocks would run differently if they experience different gravitational forces.

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Virgo stretches its 3-kilometer arms across the Tuscan plain near Pisa, Italy.
Virgo Collaboration/N. Baldocchi

By Daniel Clery

Feb. 16, 2017 , 2:00 PM

On 20 February, dignitaries will descend on Virgo, Europe’s premier gravitational wave detector near Pisa, Italy, for a dedication ceremony to celebrate a 5-year, €24 million upgrade. But the pomp will belie nagging problems that are likely to keep Virgo from joining its U.S. counterpart, the Laser Interferometer Gravitational-Wave Observatory (LIGO), in a hunt for gravitational wave sources that was meant to start next month. What has hobbled the 3-kilometer-long observatory: glass threads just 0.4 millimeters thick, which have proved unexpectedly fragile. The delay, which could last a year, is “very frustrating for everyone,” says LIGO team member Bruce Allen, director of the Max Planck Institute for Gravitational Physics in Hannover, Germany.

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LISA would use three spacecraft linked by lasers to detect passing gravitational waves. Credit: AEI/MM/exozet 

by Jeff Foust — February 7, 2017

WASHINGTON — A combination of scientific breakthroughs and technical accomplishments are making astronomers optimistic the European Space Agency will proceed with development of a space-based gravitational wave observatory.

A European consortium submitted to ESA in January a proposal for the development of the Laser Interferometer Space Antenna (LISA) mission for ESA’s third large mission, or L3, competition. LISA is widely considered the leading candidate to be selected for that mission for launch likely in the early 2030s.

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 LIGO Detection: Behind the scenes of the discovery of the decade

To celebrate the one-year anniversary of a discovery that changed the face of astronomy, on 7 February we feature the exclusive world premiere of a new documentary.

LIGO Detection reveals what unfolded behind the scenes between the detection of merging black holes on 14 September 2015, and five months later when LIGO announced it to the world

Click here to sign up to our newsletter and find out about exclusive content like this before anyone else.

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Figure 1: Both the LUX and PandaX-II experiments look for dark matter particles (𝜒) by sensing their interaction with xenon atoms. The detector in each experiment consists of a large tank of ultrapure liquid xenon (dark purple) topped with xenon gas (light purple). An interaction produces two light signals, one from photons, S1, and another, S2, from electrons when they drift into the gas. The signals are detected by photomultiplier tubes at the top and bottom of the tank (yellow cylinders). 

Jodi A. Cooley, Department of Physics, Southern Methodist University, 3215 Daniel Ave., Dallas, TX 75205, USA

January 11, 2017• Physics 10, 3

No dark matter particles have been observed by two of the world’s most sensitive direct-detection experiments, casting doubt on a favored dark matter model.

Over 80 years ago astronomers and astrophysicists began to inventory the amount of matter in the Universe. In doing so, they stumbled into an incredible discovery: the motion of stars within galaxies, and of galaxies within galaxy clusters, could not be explained by the gravitational tug of visible matter alone [1]. So to rectify the situation, they suggested the presence of a large amount of invisible, or “dark,” matter. We now know that dark matter makes up 84% of the matter in the Universe [2], but its composition—the type of particle or particles it’s made from—remains a mystery. Researchers have pursued a myriad of theoretical candidates, but none of these “suspects” have been apprehended. The lack of detection has helped better define the parameters, such as masses and interaction strengths, that could characterize the particles. For the most compelling dark matter candidate, WIMPs, the viable parameter space has recently become smaller with the announcement in September 2016 by the PandaX-II Collaboration [3] and now by the Large Underground Xenon (LUX) Collaboration [4] that a search for the particles has come up empty.

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Following their discovery, the US White House Committee on Science, Space, and Technology asked LIGO Scientific Collaboration members to testify on the discovery, its meaning for science and society, and what the future may hold. From left to right: assistant director of the NSF's Directorate of Mathematical and Physical Sciences, Fleming Crim; LIGO lab director David Reitze; LIGO spokesperson Gabriela Gonzalez; and LIGO MIT director David Shoemaker. (Courtesy: LIGO Collaboration)

The Physics World 2016 Breakthrough of the Year goes to "the LIGO Scientific Collaboration for its revolutionary, first-ever direct observations of gravitational waves". Nine other achievements are highly commended and cover topics ranging from nuclear physics to material science and more.

Almost exactly 100 years after they were first postulated by Albert Einstein in his general theory of relativity, gravitational waves hit the headlines in 2016 as the US-based LIGO collaboration detected two separate gravitational-wave events using the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO). The first observation was made on 14 September 2015 and was announced in February this year. A second set of gravitational waves rolled through LIGO's detectors on 26 December 2015, and this so-called "Boxing Day event" was announced in June this year. Gravitational waves are ripples in the fabric of space–time, and these observations mark the end of a decades-long hunt for these interstellar undulations.

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Nicolle R. Fuller/Science Photo Library

Black hole mergers captured by LIGO offer a chance to explore new physics.

Gravitational-wave data show tentative signs of firewalls or other exotic physics.

Zeeya Merali
09 December 2016

It was hailed as an elegant confirmation of Einstein’s general theory of relativity — but ironically the discovery of gravitational waves earlier this year could herald the first evidence that the theory breaks down at the edge of black holes. Physicists have analysed the publicly released data from the Laser Interferometer Gravitational-Wave Observatory (LIGO), and claim to have found “echoes” of the waves that seem to contradict general relativity’s predictions1.

The echoes could yet disappear with more data. If they persist, the finding would be extraordinary. Physicists have predicted that Einstein’s hugely successful theory could break down in extreme scenarios, such as at the centre of black holes. The echoes would indicate the even more dramatic possibility that relativity fails at the black hole’s edge, far from its core.

If the echoes go away, then general relativity will have withstood a test of its power — previously, it wasn’t clear that physicists would be able to test their non-standard predictions.

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The newborn universe may have glowed with light beams moving much faster than they do today, according to a theory that overturns Einstein’s century-old claim that the speed of light is a constant.

João Magueijo, of Imperial College London, and Niayesh Afshordi, of the University of Waterloo in Canada, propose that light tore along at infinite speed at the birth of the universe when the temperature of the cosmos was a staggering ten thousand trillion trillion celsius.

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A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by invoking dark matter. Prof. Erik Verlinde, renowned expert in string theory at the University of Amsterdam and the Delta Institute for Theoretical Physics, published a new research paper today in which he expands his groundbreaking views on the nature of gravity.

In 2010, Erik Verlinde surprised the world with a completely new theory of gravity. According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.

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By Nola Taylor Redd

Sometimes, a flaw in your magnifying glass can be a good thing; in the case of some new research, it can even reveal invisible dark matter galaxies.

Astronomers probing the sky used the gravity of a massive galaxy as a natural magnifying glass, and they found a strange distortion on its edge. That distortion proved to be a smaller, invisible galaxy composed of dark matter. The discovery, explained in a new video, could pave the way to finding more of these unusual objects, providing a better understanding of the mysterious material that makes up most of the matter in the universe.

"We can find these invisible objects in the same way that you can see rain droplets on a window," lead author Yashar Hezaveh said in a statement. Like raindrops, the massive clumps of matter warp objects seen through them. Hezaveh, an astronomer at Stanford University in California, worked with a team of scientists that used a massive radio telescope, the Atacama Large Millimeter/submillimeter Array (ALMA) inChile, to find a clump of missing matter in the outer rim of a larger galaxy that.

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Einstein's theory of general relativity is to be put to the test by a newly launched satellite in an experiment that could upend our understanding of physics.

The French "Microscope" orbiter will try to poke a hole in one of Einstein's most famous theories, which provides the basis for our modern understanding of gravity.
Scientists will use the kit to measure how two different pieces of metal—one titanium and the other a platinum-rhodium alloy—behave in orbit.
"In space, it is possible to study the relative motion of two bodies in almost perfect and permanent free fall aboard an orbiting satellite, shielded from perturbations encountered on Earth," said Arianespace, which put the satellite into orbit on Monday.
Einstein's theory suggests that in perfect free-fall, the two objects should move in exactly the same way. But if they are shown to behave differently "the principle will be violated: an event that would shake the foundations of physics", Arianespace added.

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Successful test drive for space-based gravitational-wave detector
Mission paves the way for planned €1-billion space observatory.

Elizabeth Gibney
25 February 2016

Scientists have long dreamed of launching a constellation of detectors into space to observe gravitational waves — the ripples in space-time predicted by Albert Einstein and observed for the first time earlier this month.

That dream is now a step closer to reality. Researchers working on a €400-million (US$440-million) mission to try out the necessary technology in space for the first time — involving firing lasers between metal cubes in free fall — have told Nature that the initial test drive is performing just as well as they had hoped.

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NASA, ESA, D. Coe, G. Bacon (STScI)
A black hole, visualized here in the M60-UCD1 galaxy, was thought to lose information as it disappears.

Some welcome his latest report as a fresh way to solve a black-hole conundrum; others are unsure of its merits.

Davide Castelvecchi
27 January 2016

Almost a month after Stephen Hawking and his colleagues posted a paper about black holes online1, physicists still cannot agree on what it means.

Some support the preprint’s claim — that it provides a promising way to tackle a conundrum known as the black hole information paradox, which Hawking identified more than 40 years ago. “I think there is a general sense of excitement that we have a new way of looking at things that may get us out of the logjam,” says Andrew Strominger, a physicist at Harvard University in Cambridge, Massachusetts, and a co-author of the latest paper.

Strominger presented the results on 18 January at a crowded talk at the University of Cambridge, UK, where Hawking is based.

Others are not so sure that the approach can solve the paradox, although some say that the work illuminates various problems in physics. In the mid-1970s, Hawking discovered that black holes are not truly black, and in fact emit some radiation2. According to quantum physics, pairs of particles must appear out of quantum fluctuations just outside the event horizon — the black hole’s point of no return. Some of these particles escape the pull of the black hole but take a portion of its mass with them, causing the black hole to slowly shrink and eventually disappear.

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Successful commissioning of GRAVITY at the VLTI
13 January 2016

Zooming in on black holes is the main mission for the newly installed instrument GRAVITY at ESO’s Very Large Telescope in Chile. During its first observations, GRAVITY successfully combined starlight using all four Auxiliary Telescopes. The large team of European astronomers and engineers, led by the Max Planck Institute for Extraterrestrial Physics in Garching, who designed and built GRAVITY, are thrilled with the performance. During these initial tests, the instrument has already achieved a number of notable firsts. This is the most powerful VLT Interferometer instrument yet installed.

The GRAVITY instrument combines the light from multiple telescopes to form a virtual telescope up to 200 metres across, using a technique called interferometry. This enables the astronomers to detect much finer detail in astronomical objects than is possible with a single telescope.

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The Crafoord Prize in Astronomy and Mathematics 2016
ON, JAN 13, 2016 19:00 EST

The Royal Swedish Academy of Sciences has decided to award

the 2016 Crafoord Prize in Mathematics to

Yakov Eliashberg, Stanford University, Stanford, California, USA

“for the development of contact and symplectic topology and groundbreaking discoveries of rigidity and flexibility phenomena.”

and the 2016 Crafoord Prize in Astronomy to

Roy Kerr, University of Canterbury, Christchurch, New Zealand

Roger Blandford, Stanford University, Stanford, California, USA

“ for fundamental work on rotating black holes and their astrophysical consequences”

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IF TRUE, THE DISCOVERY WOULD SUPPORT ONE OF EINSTEIN'S MAJOR PREDICTIONS.
By Sarah Fecht Posted Yesterday at 11:10pm

In September, the Caltech theoretical physicist Lawrence Krauss tweeted:

@LKrauss1 amazing if true, but as scientists shouldn't we avoid spreading rumors, especially in a public space, and wait to know the facts?
1:31 PM - 26 Sep 2015

The folks on the LIGO experiment neither confirmed nor denied the rumor, and in Krauss's rumor-mongering raised hackles in the astrophysics community.

But now he's back at it again:

My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting.
4:46 PM - 11 Jan 2016

There's plenty of reason to remain skeptical--we won't know for sure whether the rumor is true until we hear from the researchers on the experiment. If it does turn out to be true, it would be a very exciting finding.

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December 30, 2015

Limits on the differences of the γ values for three FRB observations. Credit: Phys. Rev. Lett. 115, 261101 – Published 23 December 2015. DOI: 10.1103/PhysRevLett.115.261101

dx.doi.org/10.1103/PhysRevLett.115.261101

A new way to test one of the basic principles underlying Einstein's theory of General Relativity using brief blasts of rare radio signals from space called Fast Radio Bursts is ten times, to one-hundred times better than previous testing methods that used gamma-ray bursts, according to a paper just published in the journal Physical Review Letters. The paper received additional highlighting as an "Editor's Suggestion" due to "its particular importance, innovation, and broad appeal," according to the journal's editors.

The new method is considered to be a significant tribute to Einstein on the 100th anniversary of his first formulation of the Equivalence Principle, which is a key component of Einstein's theory of General Relativity. More broadly, it also is a key component of the concept that the geometry of spacetime is curved by the mass density of individual galaxies, stars, planets, and other objects.

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Image credit: CPEP (Contemporary Physics Education Project), NSF/DOE/LBNL.

The Universe we know and love — with Einstein’s General Relativity as our theory of gravity and quantum field theories of the other three forces — has a problem that we don’t often talk about: it’s incomplete, and we know it. Einstein’s theory on its own is just fine, describing how matter-and-energy relate to the curvature of space-and-time. Quantum field theories on their own are fine as well, describing how particles interact and experience forces. Normally, the quantum field theory calculations are done in flat space, where spacetime isn’t curved. We can do them in the curved space described by Einstein’s theory of gravity as well (although they’re harder — but not impossible — to do), which is known as semi-classical gravity. This is how we calculate things like Hawking radiation and black hole decay.

But even that semi-classical treatment is only valid near and outside the black hole’s event horizon, not at the location where gravity is truly at its strongest: at the singularities (or the mathematically nonsensical predictions) theorized to be at the center. There are multiple physical instances where we need a quantum theory of gravity, all having to do with strong gravitational physics on the smallest of scales: at tiny, quantum distances. Important questions, such as:

What happens to the gravitational field of an electron when it passes through a double slit?
What happens to the information of the particles that form a black hole, if the black hole’s eventual state is thermal radiation?
And what is the behavior of a gravitational field/force at and around a singularity?

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5 March 2015

Astronomers using the NASA/ESA Hubble Space Telescope have, for the first time, spotted four images of a distant exploding star. The images are arranged in a cross-shaped pattern by the powerful gravity of a foreground galaxy embedded in a massive cluster of galaxies. The supernova discovery paper will appear on 6 March 2015 in a special issue of Science celebrating the centenary of Albert Einstein’s theory of general relativity.

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03 December 2015

ESA's LISA Pathfinder lifted off earlier today on a Vega rocket from Europe's spaceport in Kourou, French Guiana, on its way to demonstrate technology for observing gravitational waves from space.

Gravitational waves are ripples in the fabric of spacetime, predicted a century ago by Albert Einstein's General Theory of Relativity, published on 2 December 1915.
Einstein's theory predicts that these fluctuations should be universal, generated by accelerating massive objects. However, they have not been directly detected to date because they are so tiny. For example, the ripples emitted by a pair of orbiting black holes would stretch a million kilometre-long ruler by less than the size of an atom.

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15. November 2015 von Markus Pössel in Astronomie, Kosmologie

Dieser Tage befinden wir uns mitten im 100jährigen Jubiläum von Albert Einsteins Allgemeiner Relativitätstheorie, also von Einsteins Theorie von Raum, Zeit und Gravitation. Wer meinen Jubiläumsvortrag dazu noch mitbekommen möchte, hat am 25. November in Berlin im Planetarium am Insulaner dazu Gelegenheit; in Heidelberg habe ich ihn letzte Woche bereits zweimal gehalten, und eine Hauptbotschaft bei meinem Überblick über die letzten hundert relativistischen Jahre lautet: Wo sich die Beobachter und Experimentatoren anfangs sehr abmühen mussten, um die von Einstein vorhergesagten Effekte wie Lichtablenkung im Schwerefeld oder Gravitations-Rotverschiebung nachzuweisen, sind dieselben Effekte heutzutage längst entweder Störeffekte bei anderen Messungen oder aber Werkzeuge, die sich beispielsweise für astronomische Messungen nutzen lassen.

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Relativity is one of the most successful theories that Albert Einstein ever came up with. It shook the world by altering the way that we think of space and time.

One of the effects that come out of the theory of relativity is that different observers, traveling at different speeds, may take completely different measurements of the same event. However, all the measurements are technically correct. It's all relative. For example, a period of time for someone on Earth that lasts for hundreds of years may only be a couple of hours for someone zooming around in a rocket at close to the speed of light. One person may measure a stationary car to be one length, but when that same car starts racing along a track, its length appears shorter to a stationary person. These two effects are known as time dilation and length contraction.

You may be aware of the effects of relativity at insanely fast speeds: near the speed of light. It may surprise you to hear, then, that relativity is something that we experience every day. It's found in the most technical of places, and some places that may never even have occurred to you as being out of the ordinary. Since it's 100 years since Einstein published his paper on general relativity, it seems like the perfect occasion to find out how relativity affects us day-to-day.

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ABOUT THIS IMAGE:
This artistic illustration is of a binary black hole found in the center of the nearest quasar host galaxy to Earth, Markarian 231. Like a pair of whirling skaters, the black-hole duo generates tremendous amounts of energy that makes the core of the host galaxy outshine the glow of the galaxy's population of billions of stars. Quasars have the most luminous cores of active galaxies and are often fueled by galaxy collisions.

Hubble observations of the ultraviolet light emitted from the nucleus of the galaxy were used to deduce the geometry of the disk, and astronomers were surprised to see light diminishing close to the central black hole. They deduced that a smaller companion black hole has cleared out a donut hole in the accretion disk, and the smaller black hole has its own mini-disk with an ultraviolet glow.

Astronomers using NASA's Hubble Space Telescope have found that Markarian 231 (Mrk 231), the nearest galaxy to Earth that hosts a quasar, is powered by two central black holes furiously whirling about each other.

The finding suggests that quasars — the brilliant cores of active galaxies — may commonly host two central supermassive black holes that fall into orbit about one another as a result of the merger between two galaxies. Like a pair of whirling skaters, the black-hole duo generates tremendous amounts of energy that makes the core of the host galaxy outshine the glow of the galaxy's population of billions of stars, which scientists then identify as quasars.

Scientists looked at Hubble archival observations of ultraviolet radiation emitted from the center of Mrk 231 to discover what they describe as "extreme and surprising properties."

If only one black hole were present in the center of the quasar, the whole accretion disk made of surrounding hot gas would glow in ultraviolet rays. Instead, the ultraviolet glow of the dusty disk abruptly drops off towards the center. This provides observational evidence that the disk has a big donut hole encircling the central black hole. The best explanation for the observational data, based on dynamical models, is that the center of the disk is carved out by the action of two black holes orbiting each other. The second, smaller black hole orbits in the inner edge of the accretion disk, and has its own mini-disk with an ultraviolet glow.

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RECORDED IN LIGHT A ring of light surrounds the boundary of a black hole in this artist illustration. Stephen Hawking theorizes that light on this boundary encodes information about everything that falls into the black hole.

Light sliding along the outside of a black hole is the key to understanding what’s inside, Stephen Hawking says.

The proposal from the world’s most famous living physicist, presented August 25 at a conference in Stockholm, is the latest attempt to explain what happens to information that falls into the abyss of a black hole. Losing that information would violate a key principle of quantum mechanics, leading to what’s known as the information paradox.

Hawking and two collaborators claim that the contents of a black hole are inventoried on a hologram on its boundary, the event horizon. Unlike previous descriptions of this hologram, the researchers say, their proposal lays out a specific mechanism for storing information that applies to every black hole in the universe. “This resolves the information paradox,” Hawking said in his presentation at the Hawking Radiation conference at the KTH Royal Institute of Technology.

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So I’m at this black hole conference in Stockholm, and at his public lecture yesterday evening, Stephen Hawking announced that he has figured out how information escapes from black holes, and he will tell us today at the conference at 11am.

As your blogger at location I feel a certain duty to leak information ;)

Extrapolating from the previous paper and some rumors, it’s something with AdS/CFT and work with Andrew Strominger, so likely to have some strings attached.

30 minutes to 11, and the press has arrived. They're clustering in my back, so they're going to watch me type away, fun.

10 minutes to 11, some more information emerges. There's a third person involved in this work, besides Andrew Strominger also Malcom Perry who is sitting in the row in front of me. They started their collaboration at a workshop in Hereforshire Easter 2015.

10 past 11. The Awaited is late. We're told it will be another 10 minutes.

11 past 11. Here he comes.

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Inspired by Scientific American’s terrific September issue, which celebrates the 100th anniversary of Einstein’s theory of general relativity [see Addendum], I’ve dusted off an essay I wrote for The New York Times a decade ago. Here is an edited, updated version. —John Horgan

When Stevens Institute of Technology hired me a decade ago, it installed me for several months in the department of physics, which had a spare office. Down the hall from me, Albert Einstein's electric-haired visage beamed from a poster for the "World Year of Physics 2005." The poster celebrated the centennial of the "miraculous year" when a young patent clerk in Bern, Switzerland, revolutionized physics with five papers on relativity, quantum mechanics and thermodynamics. "Help make 2005 another Miraculous Year!" the poster exclaimed.

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Alternative gravity theories would result in “bumpy black holes,” which might be identifiable in x-ray observations.

Just before being gobbled up by a black hole, in-falling matter may emit an x-ray signal that could tell us about the black hole’s gravitational field. That’s the assumption of a new theoretical study of matter-accretion disks that form around black holes. The researchers show that alternative gravity models—characterized by “bumps” in the spacetime fabric around the black hole—produce slightly different x-ray emission from the disks. But identifying this signal will be challenging.

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Einstein Rings are more than just an incredible novelty. It’s also a very rare phenomenon that can offer insights into dark matter, dark energy, the nature of distant galaxies, and the curvature of the Universe itself. The phenomenon, called gravitational lensing, occurs when a massive galaxy in the foreground bends the light rays from a distant galaxy behind it, in much the same way as a magnifying glass would. When both galaxies are perfectly lined up, the light forms a circle, called an “Einstein ring”, around the foreground galaxy. If another more distant galaxy lies precisely on the same sightline, a second, larger ring will appear.

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The film Interstellar should be shown in school science lessons, a scientific journal has urged.
They say their call follows a new insight gained into black holes as a result of producing the visual effects for the Hollywood film.
Experts have also confirmed that the portrayal of "wormholes" is scientifically accurate.
Scientific papers have been published in the American Journal of Physics and in Classical and Quantum Gravity.

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Albert Einstein ... a voice for the oppressed. Photograph: Corbis

From his radical thinking to his radical politics, his disavowal of celebrity to his wild hairstyle, the great physicist’s significance endures, argues his biographer

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Being in two places at the same time isn't easy for mere humans (Image: Chen Liu/EyeEm/Getty)

The same quirk of general relativity that means your head ages faster than your feet may mean we have to go to space to see large-scale quantum mechanics in action

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Aiming to make the first portrait of the hungry monster at the center of our galaxy, astronomers built “a telescope as big as the world.”

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The supermassive black hole in NGC 5813 has erupted at least three times, with the latest still occurring.

Chandra data show the supermassive black hole at the center of NGC 5813 has erupted multiple times over 50 million years. NGC 5813 is the central component of a group of galaxies called the NGC 5813 Group that is immersed in an enormous reservoir of hot gas.

 Scientists discovered this history of black hole eruptions by studying the NGC 5813 Group, a group of galaxies about 105 million light-years from Earth. These Chandra observations are the longest ever obtained of a galaxy group, lasting for just over a week. The Chandra data are shown in this new composite image where the X-rays from Chandra (purple) have been combined with visible-light data (red, green, and blue).

Galaxy groups are like their larger cousins, galaxy clusters, but instead of containing hundreds or even thousands of galaxies like clusters do, galaxy groups are typically composed of 50 or fewer galaxies. Like galaxy clusters, groups of galaxies are enveloped by giant amounts of hot gas that emit X-rays.

The erupting supermassive black hole is located in the central galaxy of the NGC 5813 Group. The black hole’s spin, coupled with gas spiraling toward the black hole, can produce a rotating, tightly wound vertical tower of magnetic field that flings a large fraction of the inflowing gas away from the vicinity of the black hole in an energetic high-speed jet.

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An interview with theoretical physicist Lee Smolin.

In this book, Lee — always the optimist — made the prediction that

“We shall have the basic framework of the quantum theory of gravity by 2010, 2015 at the outside.”

When I visited Perimeter Institute some weeks ago I figured time had come to revisit this prediction.

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Sharpest View Ever of Star Formation in the Distant Universe

ALMA’s Long Baseline Campaign has produced a spectacular image of a distant galaxy being gravitationally lensed. The image shows a magnified view of the galaxy’s star-forming regions, the likes of which have never been seen before at this level of detail in a galaxy so remote. The new observations are far sharper than those made using the NASA/ESA Hubble Space Telescope, and reveal star-forming clumps in the galaxy equivalent to giant versions of the Orion Nebula in the Milky Way.

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Some physicists think they can explain why the universe first formed. If they are right, our entire cosmos may have sprung out of nothing at all.

People have wrestled with the mystery of why the universe exists for thousands of years. Pretty much every ancient culture came up with its own creation story - most of them leaving the matter in the hands of the gods - and philosophers have written reams on the subject. But science has had little to say about this ultimate question.

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Why is it you can break an egg, but not make the pieces spring back together again? To find out, we have to go back to the birth of the universe

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Physicists want to find a single theory that describes the entire universe, but to do so they must solve some of the hardest problems in science

The recent film The Theory of Everything tells the story of Stephen Hawking, who managed to become a world-famous physicist despite being confined to a wheelchair by a degenerative disease. It's mostly about his relationship with his ex-wife Jane, but it does find a bit of time to explain what Hawking has spent his career doing.

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(a) Scheme of the experiment. (b) Gravitational acceleration along the symmetry axis (az) produced by the source masses and the Earth’s gravity gradient. Credit: Phys. Rev. Lett. 114, 013001

A team of researchers working in Italy has successfully conducted an experiment to directly measure gravity's curvature for the first time. In their paper published in the journal Physical Review Letters, the team describes their work and note that what they have accomplished could lead to an improvement in G, the Newtonian constant of gravity.

Over many years, scientists have developed more sophisticated ways to measure gravity, one of the latest is to use atom interferometry—it enables distance measurement with very high precision and works by exploiting the quantum-mechanical wavelike nature of atoms. Up till now researchers have been able to measure the changes in gravity as altitude increases, for heights as little as a few feet, creating a gradient. In this new research the team has found a way to measure the change in gravity that is produced by a large mass. This change in the gradient is known as gravity's curvature.

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ONE of the defining anniversaries in 2015 will be the centenary of general relativity. In 1915, Einstein published a set of equations that changed our understanding of the universe. Out went the Newtonian notion of gravity as a force between massive objects; in came the counter-intuitive idea that gravity is a property of the universe, with massive objects curving space-time.

A century on, gravity continues to challenge us. The equations predict that cataclysmic cosmic events should send ripples through space-time, but we have yet to observe any. This year will see two projects aimed at sorting this out: the resumption of a gravitational-wave experiment called LIGOMovie Camera and the launch of a spacecraft called LISA Pathfinder that will test technology for catching the waves in space.

We may even see progress on the biggest unresolved issue of all – the incompatibility of relativity and quantum theory. At the atomic scale, gravity is so weak we routinely ignore it. Now it seems we are wrong to do so (see "Gravity's secret: How relativity meets quantum physicsMovie Camera"). Gravity might play a crucial role in the quantum world. It might be the secret ingredient of reality. We won't get full answers this year, but relativity's greatest remaining puzzle looks to be on its way to being solved, at last.

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 Black holes create and destroy galaxies, like this spiral galaxy in the constellation Dorado. (Roberto Colombari/Stocktrek Images/Corbis)

Much has been made of the mind-bending visual effects in Interstellar. But the methods created by the film’s Oscar-nominated visual effects team may have more serious applications than wowing movie audiences—they could actually be useful to scientists, too. A new paper in Classical and Quantum Gravity tells how the Interstellar team turned science fiction towards the service of scientific fact and produced a whole new picture of what it might look like to orbit around a spinning black hole.

Director Christopher Nolan and executive producer (and theoretical physicist) Kip Thorne wanted to create a visual experience that was immersive and credible. When they began to construct images of a black hole within an accretion disk, they realized that existing visual effects technology wouldn’t cut it—it created a flickering effect that would have looked bad in IMAX theaters. So the team turned to physics to create something different.

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