New test may provide 'smoking gun' for modified gravity

New test may provide 'smoking gun' for modified gravity: Now in a new paper published in Physical Review Letters, Wojciech A. Hellwing, et al., have proposed a new test of modified gravity that is based on measuring the tendency of well-separated galaxies to approach each other. This movement is called the galaxy pairwise velocity.
The physicists show that the galaxy pairwise velocity distribution of many galaxies with a wide range of masses is expected to deviate from the predictions of general relativity by significant amounts: between 5 and 10 standard deviations or higher, depending on the model. Due to these large deviations, this proposed test could potentially offer the strongest evidence in support of modified gravity to date.

Quantum Method Closes in on Gravitational Constant - Scientific American

Quantum Method Closes in on Gravitational Constant - Scientific American; Researchers have been unable to identify the source of errors causing the disagreement in the conventional measurements. The set-up of the latest measurement is unlikely to contain the same errors as the torque method...

In the experiment described by Tino’s team, pulses of laser light tickle a cloud of rubidium atoms cooled to nearly absolute zero, driving the atoms to rise and fall like a fountain under the influence of gravity. The pulses split the 'matter wave' associated with each atom into a superposition of two energy states, each of which has a different velocity and reaches a different height — 60 or 90 centimeters — before falling back. The matter wave that rises farthest has a greater separation from the tungsten cylinders, and thus senses a slightly different gravitational pull. The difference in force imparts a measurable shift in the final state of the two matter waves when they recombine, creating an interference pattern.

Turbulent black holes grow fractal skins as they feed - physics-math - 28 April 2014 - New Scientist

Turbulent black holes grow fractal skins as they feed - physics-math - 28 April 2014 - New Scientist: "We showed that when you throw stuff into a black hole, the surface of the black hole responds like a fluid – and in particular, it can become turbulent...  More precisely, the horizon itself becomes a fractal..."

To investigate what the horizon of a black hole looks like at mealtime, Adams took advantage of a mathematical duality between Einstein's equations of general relativity – which describe gravity near black holes – and fluid dynamics...

Led by Paul Chesler, who is a post-doc researcher at Harvard, the team first modelled a turbulent fluid system. They then translated it into the black hole regime and let it develop with time. When they looked again, the horizon of the black hole appeared to have developed an infinite surface area.

Curved Spacetime Mimicked on a Chip: Scientific American

Curved Spacetime Mimicked on a Chip: Scientific American: Liu and his collaborators simulated the gravitational lensing of a star on an integrated photonic chip. A layer of clear plastic on the chip acted as a waveguide, confining light to the chip’s surface. To change the index of refraction of the plastic, the researchers had to vary the plastic’s thickness. They did so by heating the plastic and adding polystyrene microspheres before the plastic cooled. Because the plastic rose upwards around the microspheres on cooling, the thickness of the waveguide increased near these miniature balls. The varying index of refraction the team achieved happens to be very similar to the bending of space-time geometry around a massive star...

“This is indeed the first time an exact solution of Einstein's equations was mimicked” using an optical model, says Leonhardt.

New Measurement of Gravitational Constant Comes Up Higher Than Expected - Wired Science

New Measurement of Gravitational Constant Comes Up Higher Than Expected - Wired Science: The team, led by Terry Quinn, the former director of the International Bureau of Weights and Measures in France, used an updated version of Cavendish’s setup for one experiment. But they conducted an additional experiment, using a servo to counteract the twisting of the wire and figuring out the gravitational constant based on the voltage required to keep their apparatus from moving. Taken together, their tests yielded a new G value of 6.67545 × 10−11 m3⁄kg s2, which is higher than the current accepted value by about 240 parts per million.

NIST Ytterbium Atomic Clocks Set Record for Stability

NIST Ytterbium Atomic Clocks Set Record for Stability: The ytterbium clock ticks are stable to within less than two parts in 1 quintillion (1 followed by 18 zeros), roughly 10 times better than the previous best published results for other atomic clocks...
Each of NIST's ytterbium clocks relies on about 10,000 rare-earth atoms cooled to 10 microkelvin (10 millionths of a degree above absolute zero) and trapped in an optical lattice—a series of pancake-shaped wells made of laser light. Another laser that "ticks" 518 trillion times per second provokes a transition between two energy levels in the atoms. The large number of atoms is key to the clocks' high stability.
The ticks of any atomic clock must be averaged for some period to provide the best results. One key benefit of the very high stability of the ytterbium clocks is that precise results can be achieved very quickly. For example, the current U.S. civilian time standard, the NIST-F1 cesium fountain clock, must be averaged for about 400,000 seconds (about five days) to achieve its best performance. The new ytterbium clocks achieve that same result in about one second of averaging time.

What does mercury being liquid at room temperature have to do with Einstein’s theory of relativity? | The Curious Wavefunction, Scientific American Blog Network

What does mercury being liquid at room temperature have to do with Einstein’s theory of relativity? | The Curious Wavefunction, Scientific American Blog Network:  From Niels Bohr’s theory of atomic structure we know that the velocity of an electron is proportional to the atomic number of an element. For light elements like hydrogen (atomic number 1) the velocity is insignificant compared to the speed of light so relativity can be essentially ignored. But for the 1s electron of mercury (atomic number 80) this effect becomes significant; the electron approaches about 58% of the speed of light, and its mass increases to 1.23 times its rest mass. Relativity has kicked in. Since the radius of an electron orbit in the Bohr theory (orbital to be precise) goes inversely as the mass, this mass increase results in a 23% decrease in the orbital radius. This shrinkage makes a world of difference since it results in stronger attraction between the nucleus and the electrons, and this effect translates to the outermost 6s orbital as well as to other orbitals. The effect is compounded by the more diffuse d and f orbitals insufficiently shielding the s electrons. Combined with the filled nature of the 6s orbital, the relativistic shrinkage makes mercury very reluctant indeed to share its outermost electrons and form strong bonds with other mercury atoms.

The bonding between mercury atoms in small clusters thus mainly results from weak Van der Waals forces which arise from local charge fluctuations in neighboring atoms rather than the sharing of electrons.

Particles defy gravity, float upstream | Physics | Science News

Particles defy gravity, float upstream | Physics | Science News: Shinbrot set up two tanks side-by-side and elevated one of them, with water flowing down through a channel to bridge the 1-centimeter height gap. Sure enough, within seconds of adding chalk and mate tea to the bottom tank, particles began climbing up the channel to contaminate the upper tank.

Shinbrot’s experiments led him to the conclusion that Altshuler’s team had also reached: The particles overcome gravity and the current thanks to a property of water called surface tension.

Gravity-less toy black hole solves cosmic puzzles

Gravity-less toy black hole solves cosmic puzzles: His team modelled a minimal black hole, defined only by having an inside and an outside, using quantum theory. To their surprise, they found that this object reproduces a lot of the features of real black holes that are thought to rely on gravity, including Hawking radiation, which could occur via a process called quantum tunneling.

This chimes with suggestions that gravity is not a fundamental component of the universe but an emergent property of quantum mechanics, just as waves are an emergent property of water molecules.

Physicists Find a Backdoor Way to Do Experiments on Exotic Gravitational Physics

Physicists Find a Backdoor Way to Do Experiments on Exotic Gravitational Physics: But what about running the dualities in the other direction, using laboratory measurements of extreme materials to probe exotic gravitational physics?...
The experiments in question entail smashing gold or lead nuclei together to create plasmas of quarks and gluons...
The plasmas must actually be liquid...

They equated the viscosity of a fluid to gravitational waves caroming off a black hole in higher-dimensional space—which, even for a physicist, is not an analogy that springs to mind...

The answer: 1/4π, in the appropriate units. The viscosity measured by RHIC comes close. Water, some 400 times more viscous, is molasses in comparison.

Surprisingly, the minimum value is the same for all fluids, whatever they are made of. Through the logic of duality, this universality has a simple explanation: Viscosity is equivalent to a gravitational phenomenon, and according to Einstein’s general theory of relativity, gravitation is blind to compositional details.

Higgs boson continues to be maddeningly well-behaved

Higgs boson continues to be maddeningly well-behaved: Today, experimentalists from CMS and the other main LHC detector ATLAS, armed with twice as much data as they had in July, told the Hadron Collider Physics symposium in Kyoto, Japan, that the number of tau particles detected has crept up. The new data can't yet rule out a deviation from the standard model but they do remove the main reason for thinking there was one in the first place...
...direct searches for new physics at the LHC have turned up empty too. Physicists presented searches for dozens of particles that would exist in a world governed by some of these new theories...
"The results really tell us that we're either not looking in the right place, or we're not looking in the right way, or maybe both..."

The surprise theory of everything

The surprise theory of everything: The question is whether we can express the whole of physics simply by enumerating possible and impossible processes in a given situation. This is very different from how physics is usually phrased, in both the classical and quantum regimes, in terms of states of systems and equations that describe how those states change in time. The blind alleys down which the standard approach can lead are easiest to understand in classical physics, where the dynamical equations we derive allow a whole host of processes that patently do not occur - the ones we have to conjure up the laws of thermodynamics expressly to forbid, such as dye molecules reclumping spontaneously in water...

Apply this logic more generally, and time ceases to exist as an independent, fundamental entity, but one whose flow is determined purely in terms of allowed and disallowed processes. With it go problems such as that I alluded to earlier, of why the universe started in a state of low entropy. If states and their dynamical evolution over time cease to be the question, then anything that does not break any transformational rules becomes a valid answer.

Dark matter underpinnings of cosmic web found

Dark matter underpinnings of cosmic web found: The massive filament's gravity focuses the light travelling towards Earth from more distant background galaxies. The team used this light to calculate the filament's mass and shape. X-rays from the hot gas of normal matter in the vicinity showed that this matter lined up with the filament but made up only about 10 per cent of its mass. The rest must be dark matter...

Revolutionary 'DNA Tracking Chamber' Could Detect Dark Matter� - Technology Review

Revolutionary 'DNA Tracking Chamber' Could Detect Dark Matter� - Technology Review: The dark matter headwind should be coming from the direction of Cygnus, so a suitable detector should see the direction change as the Earth rotates each day...
...Its basic detecting unit consists of a thin gold sheet with many strands of single-strand DNA hanging from it, like bead curtains or a hanging forest. Each strand of DNA is identical except for a label at the free hanging end, which identifies where on the gold sheet it sits.

The idea is that a dark matter particle smashes into a heavy gold nucleus in the sheet, sending it careering out of the gold foil and through the DNA forest.  The gold nucleus then severs DNA strands as it travels, cutting a swathe through the forest.
These strands fall onto a collecting tray below, which is removed every hour or so. The segments can then be copied many times using a polymerase chain reaction, thereby amplifying the signal a billion times over...
The entire detector consists of hundreds or thousands of these sheets sandwiched between mylar sheets, like pages in a book. In total, a detector the size of a tea chest would require about a kilogram of gold and about 100 grams of single-strand DNA.

Dark matter, dark energy, dark… magnetism?

Dark matter, dark energy, dark… magnetism?:   In 2008 at the Complutense University of Madrid, Spain, they were playing with a particular version of a mutant gravity model called a vector-tensor theory, which they had found could mimic dark energy. Then came a sudden realisation. The new theory was supposed to be describing a strange version of gravity, but its equations bore an uncanny resemblance to some of the mathematics underlying another force. "They looked like electromagnetism," says Beltrán, now based at the University of Geneva in Switzerland. "We started to think there could be a connection."

So they decided to see what would happen if their mathematics described not masses and space-time, but magnets and voltages...

Crucially, inflation could also have boosted the new electromagnetic waves. Beltrán and Maroto found that this process would leave behind vast temporal modes: waves of electric potential with wavelengths many orders of magnitude larger than the observable universe. These waves contain some energy but because they are so vast we do not perceive them as waves at all.

Astrophile: The case of the disappearing pulsar - New Scientist - New Scientist

Astrophile: The case of the disappearing pulsar: The star was a spectacular find: unlike every other pulsar ever observed, this one was in a close binary orbit with another pulsar. Together, the pair provided a precise laboratory to test Einstein's theory of general relativity, and a means of detailing how pulsars behave.
But in March 2008, Pulsar B went dark...
No one snuffed out Pulsar B – it just rotated out of view...

"We can see the light from one pulsar being bent as it travels through the gravitational well of the other pulsar," she says. "It's really neat. We have proof that one of these objects is distorting spacetime."
The eclipsing pulsars also provided a test of "spin precession", the idea that the pulsars' axes should wobble around like a top as they spin.

Nearby dark-matter-free zone poses cosmic conundrum

Nearby dark-matter-free zone poses cosmic conundrum: ...until now most velocity measurements considered only stars zipping around the Milky Way radially, like an ant sitting on a vinyl record. By contrast, Moni Bidin's team looked outward from the plane of the galaxy, perpendicular to the galactic disc. Using historical survey data and new observations from telescopes at the La Silla Observatory and the Las Campanas Observatory, both in Chile, the researchers mapped the motions of more than 400 stars up to 13,000 light-years from the sun.

They used those measurements to calculate the mass of matter in a volume four times larger than had been considered before at this level of precision. Under the standard dark matter theory, there should be at least as much dark matter as visible matter in this region. "Contrary to our expectations, there is none," Moni Bidin says. "The result matches the visible mass strongly."

Largest dark matter map holds clues to dark energy

Largest dark matter map holds clues to dark energy: Heymans's team used the Canada-France-Hawaii Telescope to observe 10 million galaxies, each about 6 billion light years away. The researchers analysed the images to build a map of dark matter spanning 10 billion light years, the first direct glimpse of dark matter on such a large scale.
The map shows a great cosmic web, with scattered clumps of dark matter linked by wispy filaments...
The map also reaffirms the need for dark energy to account for the accelerating expansion of the universe. Some proposed alternatives say that, instead of invoking a whole new entity, physicists might simply need to tweak Einstein's theory of general relativity on very large scales. But the new map, which spans very large scales yet is consistent with general relativity, lets the air out of those theories. "So far," says Miller, "there is no observational evidence for any departure from Einstein's theory."

Fire Burns Differently in Space, Space Station Experiment Shows | NASA & International Space Station Science | Fire & Microgravity Research | Space.com

Fire Burns Differently in Space, Space Station Experiment Shows: To study fires in space, FLEX researchers ignite a small drop of heptane or methanol fuel in a special experiment rack aboard the space station. As the droplet burns, a spherical flame engulfs it, and cameras record the whole process.

So far, researchers have observed some unexpected phenomena.

"Thus far, the most surprising thing we've observed is continued apparent burning of heptane droplets after flame extinction under certain conditions," Williams said. "Currently, this is entirely unexplained."

Blog - How Superconductors Can Detect Gravitational Waves

Blog - How Superconductors Can Detect Gravitational Waves: They imagine a bar of superconducting metal being hit by a gravitational wave. The waves act on all masses within the bar but the resulting movement of the metallic lattice, which is bound in place, will be very different from the movement of superconducting electrons, which are entirely unbound and free to move...
Next, they place another superconducting bar at the end of the first but at right angles to it. While the first bar is squeezed by a gravitational wave, the second will be stretched. So the electrons in this bar will oscillate too, albeit shifted by half a period relative to the first.
Finally, if these bars are connected by a superconducting wire, an oscillating current should flow through it.