Our home planet is young at heart. According to new calculations, Earth’s center is more than two years younger than its surface.

In Einstein’s general theory of relativity, massive objects warp the fabric of spacetime, creating a gravitational pull and slowing time nearby. So a clock placed at Earth’s center will tick ever-so-slightly slower than a clock at its surface. Such time shifts are determined by the gravitational potential, a measure of the amount of work it would take to move an object from one place to another. Since climbing up from Earth’s center would be a struggle against gravity, clocks down deep would run slow relative to surface timepieces.
Over the 4.5 billion years of Earth’s history, the gradual shaving off of fractions of a second adds up to a core that’s 2.5 years younger than the planet’s crust, researchers estimate in the May European Journal of Physics. Theoretical physicist Richard Feynman had suggested in the 1960s that the core was younger, but only by a few days.
The new calculation neglects geological processes, which have a larger impact on the planet’s age. For example, Earth’s core probably formed earlier than its crust. Instead, says study author Ulrik Uggerhøj of Aarhus University in Denmark, the calculation serves as an illustration of gravity’s influence on time — very close to home.

3-D Home TV Foreseen — The pace of new developments in the recently revived method of photography known as holography is so fast that three-dimensional television sets portraying life-size scenes could be a reality before 1984, as was predicted in George Orwell’s novel…. A hologram is a recording of an interference pattern reflected from an object. From this recording, the object can be reconstructed visually in a three-dimensional form. — Science News, June 11, 1966

UPDATE
Television viewers are still waiting for the 3-D revolution. Although 3-D TVs went on sale in the United States and elsewhere in 2010, they have yet to take off. Most sets require special glasses or have limited viewing angles, and none use holography to create the illusion of depth. Scientists haven’t given up, though. Using innovative plastic screens, researchers are projecting small holographic movies in real time (SN: 12/17/11, p. 18). The enormous bandwidth and processing power needed to transmit and display the images are still huge barriers to making Orwell’s vision a reality.

The green hairstreak butterfly (Callophrys rubi) gets its blue-green hue from complex nanoscale structures on its wings. The structures, called gyroids, are repeating patterns of spiral-shaped curls. Light waves bouncing off the patterned surface (top inset above) interfere with one another, amplifying green colors while washing out other shades (SN: 6/7/08, p. 26).

Scientists led by Min Gu of the Royal Melbourne Institute of Technology in Australia have now painstakingly re-created the gyroid structure by sculpting the shapes out of a special resin that solidifies when hit with laser light. The technique, called optical two-beam lithography, uses a pair of lasers to set the material in just the right pattern. Afterward, the remaining resin can be washed away, leaving only the gyroid structure. The fabricated version repeats its pattern every 360 nanometers, or billionths of a meter.

The gyroid structures determine more than just color. They also divvy up light that is circularly polarized — its electric fields spiral either clockwise or counterclockwise. In the butterfly, this effect is weak because of irregularities in the structure. But the artificial version sorts the light according to polarization, reflecting one type much more than the other, the researchers report May 13 in Science Advances.

The ability to control circular polarization of light with structures like these could allow scientists to increase the bandwidth of optical communications, the researchers say. The two polarizations of light could each carry different information, which could then be separated and decoded down the line.

The biggest ice shelf collapse on record was set in motion years earlier than previously thought, new research reveals.

Analyzing declassified images from spy satellites, researchers discovered that the downhill flow of ice on Antarctica’s Larsen B ice shelf was already accelerating as early as the 1960s and ’70s. By the late 1980s, the average ice velocity at the front of the shelf was around 20 percent faster than in the preceding decades, the researchers report in a paper to be published in Geophysical Research Letters.
Rising temperatures since the 1950s probably quickened the ice flow, which in turn put more strain on the ice and further weakened the shelf, says study coauthor Hongxing Liu, a geographer at the University of Cincinnati. Previous work had suggested that the ice shelf’s downward slide began only a few years before a Rhode Island-sized region of ice disintegrated into thousands of icebergs in 2002.

The new data will help scientists more confidently predict how Antarctic ice will fare in the coming decades, says Penn State glaciologist Richard Alley, who was not involved in the work. The early response of Larsen B to warming “is consistent with this ice shelf system being sensitive, and gives a target for future modeling studies to learn how sensitive, and for what reasons,” he says.

Ice shelves such as Larsen B line Antarctica’s coast and slow the flow of the continent’s glaciers and ice sheets into the sea. Rising temperatures are shrinking Antarctica’s ice, with several ice shelves on track to disappear completely within 100 years (SN Online: 3/26/15). Tracking the long-term decline of ice shelves is tricky, though. Scientific satellite images are sparse prior to the 1990s and next to nonexistent before the 1980s.

Liu and colleagues turned to another group that peered at Antarctica, a U.S. intelligence agency called the National Reconnaissance Office. In 1963, the agency photographed the continent as part of an intelligence-gathering mission. While these images were declassified in 1995, the photos were too distorted by effects such as the camera used and Earth’s curvature to use for ice flow measurements.

Making the photographs usable required identifying stationary landmarks for reference, a difficult task on a continent covered with shifting white ice. Comparing the spy photos with later scientific images, Liu and colleagues identified 44 potential landmarks. Then, using the locations as anchor points, the researchers unwarped the images. Along with additional satellite images snapped in 1979 and the 1980s, the modified images allowed the researchers to track Larsen B’s ice flow over time.
The ice on Larsen B’s front flowed at around 400 meters per year on average between 1963 and 1986, calculations using images from those years indicate. From 1986 to 1988, the average was 490 meters per year. That speed boost suggests that the ice flow accelerated between the 1963 to 1986 satellite images. Several glaciers that feed into Larsen B underwent similar accelerations, the researchers found.

Larsen B’s early acceleration hints that the ice shelf was already weakening well before the 1990s, says Ted Scambos, a polar scientist at the National Snow and Ice Data Center in Boulder, Colo., who was not involved in the study. Previous studies suggested that balmy surface temperatures caused Larsen B’s demise by forming meltwater pools on top of the ice shelf that forced open cracks in the ice (SN: 10/18/14, p. 9). The new satellite data suggest that this fracturing was a finishing blow following long-term weakening by forces such as relatively warm seawater eroding the ice shelf’s underside, Scambos says.