Quantum split: Particle this way, properties that way - physics-math - 23 July 2014 - New Scientist

Quantum split: Particle this way, properties that way - physics-math - 23 July 2014 - New Scientist: In Grenoble, the Vienna team used a feeble magnetic field and a weakly interacting neutron absorber to make the weak measurements. They found that when they put the absorber in one path of the interferometer (say left), there was a discernible effect at the output. But when they put it in the right path, it had no such effect. The neutrons were travelling in one path only.

Next, the experimenters introduced a weak magnetic field near each arm of the interferometer, to interact with the spin of the neutrons. When they did this in the left path, there was no change in the interferometer's output. If they introduced the magnetic field in the right path, though, there was a change: the magnetic field had interacted with the spin. In other words, they had confirmed that the spin had chosen the path not taken by the parent neutron...

White holes: Hunting the other side of a black hole - space - 20 July 2014 - New Scientist

White holes: Hunting the other side of a black hole - space - 20 July 2014 - New Scientist: Perhaps the fact that we have found no signs of a white hole, despite peering ever deeper into space, is a more fundamental problem. Enter a space telescope called RadioAstron whose wildly elongated orbit takes it out to a distance of 350,000 kilometres – nearly as far as the moon and 30 times wider than Earth's diameter. Launched from Kazakhstan's Baikonur Cosmodrome in 2011, its dish is only 10 metres across. But when its signals are combined with those from radio telescopes on Earth, the resulting images are as sharp as those from a dish 350,000 kilometres wide...

"...once we spot a gigantic powerful gamma-ray burst with a lot of radio radiation, we will take a close look with RadioAstron and try to determine its shape and size for the first time." That could provide important clues about its source. "It may be a white hole or a wormhole. Maybe the flashes are coming from another universe."

Is time moving forward or backward? Computers learn to spot the difference | Science/AAAS | News

Is time moving forward or backward? Computers learn to spot the difference | Science/AAAS | News: To find out, she and her collaborators broke down 180 YouTube videos into square patches of a few hundred pixels, which they further divided into four-by-four grids. Combining standard techniques for discovering objects in still photographs with motion detection algorithms, the researchers identified 4000 typical patterns of motion, or “flow words,” across a grid’s 16 cells. The gentle downward drifting of snowflakes, for example, would be one flow word. From those patterns, the team created flow word descriptions of each video along with three other versions—a time-reversed version, a mirror-image version, and a mirror-image and time-reversed version. Then, they made a computer program watch 120 of these clips, training it to identify which flow words best revealed whether a video ran forward or backward.

When they tested their program on the remaining 60 videos, the trained computers could correctly determine whether a video ran forward or backward 80% of the time...  A closer analysis found that flow words associated with divergence (water splashing outward as someone dives into a pool) or dissipation (a steam train’s exhaust spreading out in air) were especially good indicators of the direction in which time was moving.

Embrace the lumpiverse: How mess kills dark energy - physics-math - 25 June 2014 - New Scientist

Embrace the lumpiverse: How mess kills dark energy - physics-math - 25 June 2014 - New Scientist: Wiltshire takes issue with the last of the motions used to make the dipole anisotropy disappear: a movement at a speed of 635 kilometres per second of the entire Local Group towards a "great attractor" somewhere in the distant Hydra-Centaurus supercluster of galaxies...

They claim the galaxies' movements make most sense if the Local Group isn't moving at all. Instead, the greater density of matter towards Hydra-Centaurus is slowing the universe's expansion along our line of sight, giving us the impression of such a movement. A comparative void in the other direction, meanwhile, is producing the opposite effect, causing an area of faster expansion behind us. The effects of the inhomogeneities along this axis are comparatively local, occurring on scales up to about 300 million light years, and only alter the universe's expansion rate by some 0.5 per cent. But they are sufficient to account for nearly all of the dipole anisotropy – and so colour our view of the entire universe...

This suggests that the age of the universe could be as much as 18.6 billion years in places where a low density of matter means the clock has ticked particularly fast. Our own smaller estimate of the universe's age is a natural consequence of sitting in an area of unusually high density: a galaxy.

Clingy dark matter may slow the spin of corpse stars - physics-math - 23 June 2014 - New Scientist

Clingy dark matter may slow the spin of corpse stars - physics-math - 23 June 2014 - New Scientist: Their strong magnetic fields gradually slow their spin, but over the past 15 years, astronomers have noticed that many pulsars are slowing more than we would expect.

Chris Kouvaris at the University of Southern Denmark thinks a form of dark matter with a tiny electric charge may be putting on the brakes.

Quantum theory reveals puzzling pattern in how people respond to some surveys

Quantum theory reveals puzzling pattern in how people respond to some surveys: The survey changed the order in which these questions were asked between respondents and, as expected, there were question-order effects found. When respondents were asked about Clinton first, 49 percent said that both Clinton and Gore were trustworthy. But when respondents were asked about Gore first, 56 percent said that both were trustworthy.

The pattern that quantum theory predicted – and that the researchers found – was that the number of people who switch from "yes-yes" to "no-no" when the question order is reversed must be offset by the number of people who switch in the opposite direction...

The researchers called this phenomenon "quantum question equality." They found it in every one of the surveys studied.

Create the ultimate world clock with a quantum link - physics-math - 15 June 2014 - New Scientist

Create the ultimate world clock with a quantum link - physics-math - 15 June 2014 - New Scientist: Timekeeping institutes around the world each have their own caesium clocks. They submit their time signal measurements to the International Bureau of Weights and Measures in Paris, France, which averages them and publishes a monthly newsletter that sets Coordinated Universal Time (UTC). But that means there is no real-time measure of a universally agreed standard time...

...The team calculates that a global quantum clock network would be about 100 times more precise than any individual clock...

Quantum Entanglement Drives the Arrow of Time, Scientists Say | Simons Foundation

Quantum Entanglement Drives the Arrow of Time, Scientists Say | Simons Foundation: Using an obscure approach to quantum mechanics that treated units of information as its basic building blocks, Lloyd spent several years studying the evolution of particles in terms of shuffling 1s and 0s. He found that as the particles became increasingly entangled with one another, the information that originally described them (a “1” for clockwise spin and a “0” for counterclockwise, for example) would shift to describe the system of entangled particles as a whole. It was as though the particles gradually lost their individual autonomy and became pawns of the collective state. Eventually, the correlations contained all the information, and the individual particles contained none. At that point, Lloyd discovered, particles arrived at a state of equilibrium, and their states stopped changing, like coffee that has cooled to room temperature.

“What’s really going on is things are becoming more correlated with each other,” Lloyd recalls realizing. “The arrow of time is an arrow of increasing correlations.”

How the U.S. Built the World’s Most Ridiculously Accurate Atomic Clock | Science | WIRED

How the U.S. Built the World’s Most Ridiculously Accurate Atomic Clock | Science | WIRED: Both NIST-F2 and the standard it replaces, NIST-F1, are known as cesium-based atomic fountain clocks...

The previous generation of atomic clock was already quite good at figuring out the length of a second but had a few small sources of error. NIST-F1 operates at room temperature and so the walls of the chamber in which the cesium atom ball is tossed heat up, emitting a small amount of radiation. This interferes with the atoms, causing them to shift ever so slightly in their energy levels. By cooling NIST-F2 with liquid nitrogen, the new timepiece reaches temperatures of – 316 degrees Fahrenheit, virtually eliminating this excess radiation and reducing the shifting 100-fold.

The Astounding Link Between the P≠NP Problem and the Quantum Nature of Universe — The Physics arXiv Blog — Medium

The Astounding Link Between the P≠NP Problem and the Quantum Nature of Universe — The Physics arXiv Blog — Medium: ...He says the key is to think of Schrodinger’s cat as a problem of computational complexity theory...

...He says there is an implicit assumption when physicists say that Schrödinger’s equation can describe macroscopic systems. This assumption is that the equations can be solved in a reasonable amount of time to produce an answer...

If P ≠ NP and there is no efficient algorithm for solving Schrödinger’s equation, then there is only one way of finding a solution, which is a brute force search...

So the number of elementary operations needed to exactly solve this equation would be equal to 2^10^24...

...this time scale is considerably shorter than the Planck timescale, which is roughly equal to 10^-43 seconds.

Can matter cycle through shapes eternally? : Nature News & Comment

Can matter cycle through shapes eternally? : Nature News & Comment: Wilczek's latest paper outlines another, perhaps simpler, scheme for making a time crystal. It starts with two chunks of superconductor connected by a nonsuperconductor. This device,called a Josephson junction, can create fluctuations in currents if an external voltage is applied. Wilczek argues that merely breaking the contact between the superconductors could create the type of fluctuations that characterize a time crystal.

Physicist proves impossibility of quantum time crystals

Physicist proves impossibility of quantum time crystals: Bruno explains that this proof should not come as a surprise, since a 1964 theory by another Nobel Laureate, Walter Kohn, shows that an insulator is completely insensitive to a magnetic flux. Since quantum time crystals are modeled as ring-shaped Wigner crystals, and Wigner crystals are insulators, attempting to show that a magnetic flux can cause such a system to rotate is, as Bruno writes, "a hopelessly doomed endeavor."

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.

How to Build a Time Cloak with Mirrors | MIT Technology Review

How to Build a Time Cloak with Mirrors | MIT Technology Review:  His idea is to use one set of mirrors to divert light through an extra distance before it reaches the clock and another set of mirrors that diverts light through a similar distance after it has hit the clock.

This extra distance essentially slows down the lights before it hits the clock. After it has been reflected, the light can be speeded up by avoiding the diversion so that it does not travel the extra distance.

Super-accurate atomic clock doubles up as quantum sim - physics-math - 08 August 2013 - New Scientist

Super-accurate atomic clock doubles up as quantum sim - physics-math - 08 August 2013 - New Scientist: Electrons' behaviour inside solids can be physically modelled using networks of atoms cooled to trillionths of a degree above absolute zero...

...she and her colleagues have stumbled upon a way to mimic quantum behaviour in a system several orders of magnitude warmer: an atomic clock...

Rey says that the strontium atoms in the ground state can be used to simulate spin-down electrons, and the excited atoms, spin-up electrons. Tracking the emergence and details of the interactions between the atoms could then shed light on the nature of the quantum interactions between electrons in magnets.

Physicists freeze motion of light for a minute

Physicists freeze motion of light for a minute: To stop the light, the physicists used a glass-like crystal that contains a low concentration of ions – electrically charged atoms – of the element praseodymium. The experimental setup also includes two laser beams. One is part of the deceleration unit, while the other is to be stopped. The first light beam, called the "control beam", changes the optical properties of the crystal: the ions then change the speed of light to a high degree. The second beam, the one to be stopped, now comes into contact with this new medium of crystal and laser light and is slowed down within it. When the physicists switch off the control beam at the same moment that the other beam is within the crystal, the decelerated beam comes to a stop.


More precisely, the light turns into a kind of wave trapped in the crystal lattice. This can be explained in greatly simplified form as follows. The praseodymium ions are orbited by electrons. These behave similarly to a chain of magnets: if you put one into motion, the movement – mediated by magnetic forces – propagates in the chain like a wave. Since physicists call the magnetism of electrons "spin", a "spin wave" forms in the same manner when freezing the laser beam. This is a reflection of the laser's light wave. In this way, the Darmstadt researchers were able to store images, such as a striped pattern, made of laser light within the crystal. The information can be read out again by turning the control laser beam on again.

The Quantum Zeno Effect actually does stop the world

The Quantum Zeno Effect actually does stop the world: Let's say an atom is very likely to have decayed after three seconds, but very unlikely to have decayed after one. Check on it after three seconds, and it probably will have decayed. But, Misra and Sudarshan argue, check on it three times in one second intervals, and it will most likely not have decayed. Every time you check on it, it will revert to its "original" measured state, and the clock will start over. Amazingly, this actually does happen. Researchers observing sodium atoms observed that, "Depending on the frequency of measurements we observe a decay that is suppressed or enhanced as compared to the unperturbed system." The "enhanced" decay is the result of the Quantum Anti-Zeno Effect. Time your measurements just right and you can actually push a system to decay faster than it would if it were unobserved.

Precise atomic clock may redefine time : Nature News & Comment

Precise atomic clock may redefine time : Nature News: First, like trapped-ion clocks, they measure the frequency of visible light, with a frequency tens of thousands of times higher than that of microwaves. Second, they measure the average emission frequency from several thousand trapped atoms rather than just one, and so the measurement statistics are better. The atoms are trapped in an optical lattice, rather like an electromagnetic egg box for holding atoms.

If OLCs are to succeed, however, researchers must show that one such clock ticks at exactly the same rate as another prepared in an identical way. This is what Lodewyck and colleagues have shown. They prepared optical lattices that each held about 10,000 atoms of the isotope strontium-87, and have shown that the two clocks stay in synchrony to within a precision of at least 1.5 × 10−16, which is as accurately as the experiment could measure.

Time cloak hides events by splicing them movie style

Time cloak hides events by splicing them movie style: Time cloaks work by slowing down light in an optical fibre, creating a gap in the beam. Any outside light that enters the hole becomes cloaked when the original beam is sped up...

A diffraction grating stretches out a laser beam, producing a series of gaps. Pulses of light sent along the fibre at the same time slot into these. A second grating then closes the holes, hiding the pulses from the intended receiver. There is now no record that the pulses ever traversed the fibre... This string of cloaks can hide up to 1.5 gigabytes per second.

Physicists Create Quantum Link Between Photons That Don't Exist at the Same Time

Physicists Create Quantum Link Between Photons That Don't Exist at the Same Time: They start with a scheme known as entanglement swapping. To begin, researchers zap a special crystal with laser light a couple of times to create two entangled pairs of photons, pair 1 and 2 and pair 3 and 4. At the start, photons 1 and 4 are not tangled. But they can be if physicists play the right trick with 2 and 3.

The key is that a measurement "projects" a particle into a definite state -- just as the measurement of a photon collapses it into either vertical or horizontal polarization. So even though photons 2 and 3 start out unentangled, physicists can set up a "projective measurement" that asks, are the two in one of two distinct entangled states or the other? That measurement entangles the photons, even as it absorbs and destroys them. If the researchers select only the events in which photons 2 and 3 end up in, say, the first entangled state, then the measurement also entangles photons 1 and 4. (See diagram, top.) The effect is a bit like joining two pairs of gears to form a four-gear chain: Enmeshing to inner two gears establishes a link between the outer two.

In recent years, physicists have played with the timing in the scheme. For example, last year a team showed that entanglement swapping still works even if they make the projective measurement after they've already measured the polarizations of photons 1 and 4. Now, Eisenberg and colleagues have shown that photons 1 and 4 don't even have to exist at the same time, as they report in a paper in press at Physical Review Letters.

To do that, they first create entangled pair 1 and 2 and measure the polarization of 1 right away. Only after that do they create entangled pair 3 and 4 and perform the key projective measurement. Finally, they measure the polarization of photon 4. And even though photons 1 and 4 never coexist, the measurements show that their polarizations still end up entangled. Eisenberg emphasizes that even though in relativity, time measured differently by observers traveling at different speeds, no observer would ever see the two photons as coexisting.