Archive for January, 2014

Jellyfish-Like Flying Machines

Jellyfish-;ike robot

Credit: Dr. Leif Ristroph / NYU

Researchers have built a small vehicle whose flying motion resembles the movements of a Jellyfish.

inventor Dr. Leif Ristroph, a postdoctoral researcher at New York University, wanted to determine if he could invent a winged flying machine that was inherently stable, with no sensors or artificial nervous system needed. After trying several designs, he ended up creating a cone-like machine made of four wings that are hinged at the top approximately 3 inches (8 centimeters) long, surrounding a small motor, a commercially available component about the size of the vibrator in a cell phone and which accounts for about half the mass of the device. The motor, located at the at the top, opens and closes the wings together not-quite-simultaneously at a rate of 20 times a second.

Other flying robots, like the tiny robotic bee built at Harvard’s Wyss Institute, or the H2bird flapping-wing drone built at a lab at Berkeley, sense the direction and location and adjust their movements to stay in the air. But the lightweight, electrically powered flyer keeps itself right side up without the benefit of sensors or any righting mechanism. Instead, the stability is a result of the shape and the movement of the wings.

Dr. Ristroph and his colleagues detailed their invention in the January 15th in the Journal of the Royal Society. They also presented the robot at the 66th Annual Meeting of the APS Division of Fluid Dynamics last November. In addition to showing that the flying device is stable, Ristroph and Stephen Childress, also at NYU, found that the size of the machine mainly depends on the weight and power of the motor.

“What’s cool is you can actually build these flying things yourself,” Ristroph told LiveScience. “All the components I used to make this, they cost about $15 and they’re available on hobby airplane websites.”

The top figures illustrate the body and wing design; the bottom figures detail the motor assembly (left), and the wingspan assembly (right).

The top figures illustrate the body and wing design; the bottom figures detail the motor assembly (left), and the wingspan assembly (right). Images © Journal of The Royal Society

The prototype doesn’t include a battery, so the ornithopter, as they call it, requires a wire for power. More engineering work is necessary to get power and a radio receiver onboard so that an operator can control the ornithopter from a distance. It also can’t steer, either autonomously or via remote control.

You can view a YouTube video of the ornithopter in action here.

Is The Universe A Hologram?


The holographic principle is a property of quantum gravity and string theories which states that the description of a volume of space can be thought of as encoded on a boundary to the region—preferably a light-like boundary like a gravitational horizon. In other words, all of three-dimensional reality can be described as a two-dimensional sheet or surface of information that extends to the limits of the observable universe – what theoretical physicist and string theorist Raphael Bousso calls “a universal relation between geometry [surface area] and information” in space-time.

So what makes at least some theoretical physicists think that the universe may be a hologram, or at least be best described as a hologram.

It all starts with black hole physics. When an object becomes part of a black hole, two things happen. First, information about that object is lost. Second, the surface area of the black hole’s event horizon (the point at which the gravitational pull becomes so great as to make escape by both matter and energy impossible) grows. The first fact appears to violate the second law of thermodynamics, since one of the lost details was the object’s entropy, or the information describing its microscopic parts. But the second fact offered a way out: if entropy must always grow, and a black hole’s surface area must too, perhaps for the black hole they’re one and the same, and information is somehow stored on the horizon.

The beginning of the attempt to resolve the black hole information paradox within the framework of string theory, Charles Thorn in 1978 developed an approach to string theory based on the idea of string bits, observing that string theory admits a lower-dimensional description in which gravity emerges from it in what would now be called a holographic way. Then in 1993, Gerard t’Hooft proposed what is now known as the holographic principle. Quantum mechanics starts with the assumption that information is stored in every volume of space. But any patch of space can become a black hole, nature’s densest file cabinet, which stores information in bits of area. Perhaps, then, all that’s needed to describe a patch of space, black hole or no, is that area’s worth of information. t’Hooft argued exactly that – that the information contained within a region of space can be determined by the information at the surface that contains it. Mathematically, the space can be represented as a hologram of the surface that contains it.

In 1995, Leonard Susskind a Professor of Theoretical Physics at Stanford University, combined his ideas with previous ones of ‘t Hooft and Charles Thorn in a paper suggesting that the entire universe might be a hologram in which people are just seeing a projection of the real thing. Susskind suggested that the entire universe could be seen as a two-dimensional information structure “painted” on the cosmological horizon, such that the three dimensions we observe are only an effective description at macroscopic scales and low energies.

In 1997, theoretical physicist Juan Maldacena proposed a model of the Universe in which gravity arises from infinitesimally thin, vibrating strings could be reinterpreted in terms of well-established physics. Called the anti-de Sitter/conformal field theory correspondence, or AdS/CFT correspondence In this model, the mathematically intricate world of strings, which exist in nine dimensions of space plus one of time, would be merely a hologram: the real action would play out in a simpler, flatter cosmos where there is no gravity.

Maldacen’s model did two things: it solved apparent inconsistencies between quantum mechanics and general relativity, and it provided a way to translate back and forth between the two. Unfortunately, while Maldacena made a compelling argument, it was a conjecture, not a formal proof.

Now, two papers have come out demonstrating that the conjecture works for a particular theoretical case. In two papers posted on the arXiv repository, Yoshifumi Hyakutake of Ibaraki University in Japan and his colleagues now provide, if not an actual proof, at least compelling evidence that Maldacena’s conjecture is true.

In the first paper, Hyakutake computes the internal energy of a black hole, the position of its event horizon (the boundary between the black hole and the rest of the Universe), its entropy and other properties based on the predictions of string theory as well as the effects of so-called virtual particles that continuously pop into and out of existence. In the second, Hyakutake and his collaborators calculated the internal energy of the corresponding lower-dimensional cosmos with no gravity. The two computer calculations match.

It’s important to note that the papers don’t suggest that our universe is a hologram. The computations describe a universe with ten dimensions in the realm of the black hole and a single dimension universe when calculating characteristics of a gravity free two-dimensional universe. It does, however, suggest that what can be calculated using different dimensional universes could one day be calculated for our own, and is one more step showing that the holographic principle could be useful in understanding the universe.


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