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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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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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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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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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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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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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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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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