Friday, August 26, 2016

The Dark Side of Ghost Imaging

Displays of candy corn and costumes may soon be replacing sunscreen and beach towels, but this post isn’t meant to detract from what’s left of the summer. Ghost imaging is a technique for imaging something that you can’t see directly. It does seem a bit spooky—imagine getting detailed images of the ground from a satellite-based optical system even when clouds or smoke obscure the line-of-sight. However, ghost imaging isn’t a supernatural feat. It’s just another strange and mind-bending application of quantum mechanics.

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Thursday, August 25, 2016

In Combat and Car Accidents, Nanoparticles Could Fight Internal Bleeding

Injury is the number one cause of death in Americans ages 1-44. Resulting from violence and accidents, injuries claim nearly 200,000 lives per year in the United States alone. A team of researchers from the University of Maryland, Baltimore County is fighting back with a simple, nanoparticle-based technology to reduce blood loss from internal injuries.

Nanoparticles (green) help form clots in an injured liver. The researchers added color to the scanning electron microscopy image after it was taken.
Image Credit: Andrew Shoffstall, Ph.D

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Wednesday, August 24, 2016

Ballistic Fungi Use Surface Tension to Create Extraordinary Accelerations

Put a droplet of water on the table. Wet your finger and then, observing closely, touch your finger to that water droplet, and watch as the water on the table joins the droplet on your fingertip. It's a mundane process, but this humble mechanism is powerful enough to create some of the strongest accelerations on Earth.

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Friday, August 19, 2016

The Forces in Spilled Coffee Awaken

Like much of the world, scientists thrive on coffee. It’s not just because of the caffeine though, it turns out that even spilled coffee fuels research.

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Thursday, August 18, 2016

Captured Lightning: Electrons Follow Fractals Through Insulators

Fractals, shapes that look similar to their parts no matter how much you zoom in, are everywhere from broccoli to seashells. Now, a new study of an old physics problem has found more: Electrons inside some conductive materials may be hopping around atoms in fractal patterns.

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Monday, August 15, 2016

Escaping a Black Hole: Strongest Evidence Yet for Hawking Radiation

The exotic cosmic objects we call black holes aren’t truly holes, and it turns out that they may not be totally black either. In an article that appears today in the journal Nature Physics, Jeff Steinhauer from the Israel Institute of Technology (Technion) outlines the strongest experimental evidence yet that energy can escape from a black hole.

Professor Jeff Steinhauer in his lab.
Image Credit: Nitzan Zohar, Technion Spokesperson's Office
Black holes are extremely dense areas of space defined by an event horizon, a boundary beyond which nothing that gets sucked in can escape—not even light (hence the “black” in “black hole”). Theory predicts that black holes can be the size of an atom or millions of times as massive as the sun, although smaller ones are less stable. As strange and unique as they seem, there are likely millions of black holes in the universe, including at least one at the center of each galaxy.

Nearly 50 years ago, bold work by then-graduate student Jacob Bekenstein inspired black hole expert Stephen Hawking to take a closer look at the theoretical physics governing black holes. In the process, a surprised Hawking discovered that quantum mechanics enables some energy to escape from black holes. Hawking realized that over time this could cause black holes to shrink and evaporate.

Experimentally verifying or ruling out this “Hawking radiation” might seem like just a scientific curiosity, but it is actually an important test of our understanding of the universe and its behavior. Its existence would answer some questions, but raise others.

One of the biggest unsolved problems in physics is how general relativity merges with quantum mechanics. Gravitational effects and quantum effects meet head-on in black holes, so they are an ideal place to study this. However, the Hawking radiation escaping from a cosmic black hole is so small that we aren’t able to detect it directly, at least not yet.

If you can’t study Hawking radiation from a cosmic black hole, why not build your own black hole? Okay, how about a system with similar properties? The experiment reported in the Nature Physics article involved an analogous system called an acoustic black hole. Acoustic black holes don’t occur in nature, but they can be built out of a fluid whose flow changes from subsonic to supersonic. The idea was proposed in 1981 by William Unruh.

An acoustic black hole is similar in many ways to a cosmic black hole, but it traps sound instead of matter and light. It turns out the equations that describe how gravity affects light are the same equations that describe how a flowing fluid affects phonons, which you can think of as a kind of particle that makes up sound waves.

Like the event horizon of a black hole, the event horizon of an acoustic black hole is the point of no return. Any sound that goes in will not come out—unless the hole emits the phonon equivalent of Hawking radiation. The systems are so similar that if you detect phonon radiation coming from an acoustical black hole, Hawking radiation most likely exists too.

Confirming Hawking radiation goes beyond detecting radiation outside of a black hole. The particles emitted by Hawking radiation are quantum mechanically connected or “entangled” with partner particles that are pulled into the black hole. Finding evidence of this is key to verifying its existence.

Steinhauer’s work is the first experimental evidence of such entangled particles. In 2009, he and his colleagues created the first acoustic black hole. They did so in a Bose Einstein condensate (BEC), a special, quantum state of matter in which many very cold atoms behave like a single atom. Using a laser, the researchers created an event horizon at which the flow of atoms in the BEC goes from subsonic to supersonic.

Since 2009, the researchers have improved the system and developed high-resolution imaging techniques for studying phonons and their partner particles. Today’s article presents their exciting results, which include observations of entangled phonons emitted by the acoustic black hole. The characteristics of these phonons are consistent with what you’d expect from Hawking radiation.

This isn’t the only experimental attempt to detect Hawking radiation. Through a variety of experiments based on several different analogous systems, scientists around the world are searching for signs of Hawking-like radiation even as you read this. Together with Steinhauer’s work, these experiments should help us build a more complete picture of just how “black” black holes are.

Kendra Redmond
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Friday, August 12, 2016

This is Your Brain on Physics

Like the physics engine in a video game that brings to life car crashes, nosedives, touchdown passes, and other physical events, humans may have a kind of “physics engine” in the brain that helps us survive. After all, even non-physicists quickly swerve to miss an oncoming car, duck to avoid being hit, and reflexively catch falling objects.

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Wednesday, August 10, 2016

PhysicsCentral Welcomes its Newest Contributor!

 Eran Moore Rea grew up in Sioux Falls, South Dakota and recently graduated from Yale University with a Bachelor’s degree in Physics (Intensive) and American Studies (Intensive, cultural history). At Yale, she researched with the ATLAS experiment at CERN, working on optimizing and implementing the Run 2 Monte Carlo simulation of the Higgs boson produced in association with a vector boson and decaying to a tau lepton pair. Always alert to the absurdity of life, she created the comic Midwestern Nerd at Yale for the Yale Daily News. She previously wrote for the University of Washington’s technology transfer department. At APS, she is excited to find the story (as well as the humor) in physics research, new technology and unexpected innovation. Currently melting in the DC heat, she eagerly waits for the winter again.

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Tuesday, August 09, 2016

Physicists Put "Backspin" on Laser Light

Like a pool shark developing trick shots, scientists are always finding ways to bend the rules. Now, physicists from the Shanghai Institute of Optics and Fine Mechanics (SIOM), part of the Chinese Academy of Sciences, have demonstrated a technique that lets them change the dynamics of reflection. By using an intense vortex beam—a special arrangement of photons superimposed on one another to create a rotating, hollow "tube" of light—the researchers coaxed the reflected beam out of the plane of incidence, a rather extraordinary trick. Their work is slated to appear soon in the American Physical Society's journal Physical Review Letters.

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Monday, August 08, 2016

Ghostly 4th Neutrino Most Likely Doesn't Exist

An international team of researchers from the IceCube Neutrino Observatory just announced with 99% certainty that a proposed particle called a sterile neutrino doesn’t exist. Why is the fact that something doesn’t exist big news? This ghost particle may have helped explain several mysteries of the universe, such as the origin of dark matter and why matter exists at all.

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