TAT Blog interesting astrophysics stories

An atomic clock measured how general relativity warps time across a millimeter

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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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Event Horizon Telescope (EHT) tests of the strong-field regime of General Relativity

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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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Breathtaking 'Einstein Ring' Reveals Views of a Galaxy 9.4 Billion Light-Years Away

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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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The story behind Albert Einstein's most iconic photo

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The photo of Einstein sticking out his tongue is world-famous

It’s been 70 years since the genius physicist stuck out his tongue at pesky reporters. The photo turned him into an icon. But what's the story behind it?

It was March 14, 1951, the day Albert Einstein turned 72. The famous physicist, who was born in Ulm, Germany, had already been living in the United States for many years. At the time, he was working at the Institute for Advanced Study in Princeton, New Jersey. A birthday celebration was held in his honor at the research center.
The paparazzi were lurking outside the venue when he left, hoping to hear one of the world-famous professor's witty quips about the global political situation — and to take the perfect birthday photo.
Not a fan of media hype, and growing weary of being a spokesperson, Einsteinwas annoyed by their presence. Yet there he was, stuck in the back seat of a limousine, sandwiched between the institute's former director, Frank Aydelotte, and his wife, Marie, unable to escape the flashing bulbs. "Enough is enough..." he is said to have repeatedly shouted at the pushy reporters. "Hey, Professor, smile for a birthday photo, please," one shouts.

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Einstein’s theory of general relativity unveiled a dynamic and bizarre cosmos

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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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Nugget Galaxies Cross in the Sky

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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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Star orbiting the Milky Way’s giant black hole confirms Einstein was right

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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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Astronomers witness the dragging of space-time in stellar cosmic dance

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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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A century of correct predictions

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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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100 years on: the pictures that changed our view of the universe

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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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Ultraprecise atomic clocks put Einstein’s special relativity to the test

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WATCHING THE CLOCK Scientists monitored two atomic clocks for six months in order to test a tenet of Einstein’s special theory of relativity. Each clock, like the one shown, contained a single ion of ytterbium.

An experiment tested a foundational principle of physics known as Lorentz symmetry
BY EMILY CONOVER 2:00PM, MARCH 13, 2019

The ticktock of two ultraprecise clocks has proven Einstein right, once again.

A pair of atomic clocks made of single ions of ytterbium kept pace with one another over six months, scientists report March 13 in Nature. The timepieces’ reliability supports a principle known as Lorentz symmetry. That principle was the foundation for Einstein’s special theory of relativity, which describes the physics of voyagers dashing along at nearly the speed of light.

 

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Troubled Times for Alternatives to Einstein’s Theory of Gravity

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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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Galileo satellites prove Einstein's Relativity Theory to highest accuracy yet

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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

 

Mathematicians Disprove Conjecture Made to Save Black Holes

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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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What Is Spacetime?

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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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