Experiment

Key Einstein principle survives quantum test

warping space
EINSTEIN ENDURES According to Einstein’s general theory of relativity, massive objects warp space (illustrated above), producing gravitational attraction. Scientists don’t understand how general relativity interfaces with quantum mechanics, but a pillar of general relativity, the equivalence principle, has withstood a new quantum test.

Particles with mind-bending quantum properties still follow a standard gravitational rule, at least as far as scientists can tell.

The equivalence principle — one of the central tenets of Einstein’s theory of gravity — survived a quantum test, scientists report online April 7 at arXiv.org.

In Einstein’s gravity theory — the general theory of relativity — gravity and acceleration are two sides of the same coin. According to the equivalence principle, the gravitational mass of an object, which determines the strength of gravity’s pull, is the same as its inertial mass, which determines how much an object accelerates when given a push (SN: 10/17/15, p. 16). As a result, two objects dropped on Earth’s surface should accelerate at the same rate (neglecting air resistance), even if they have different masses or are made of different materials.

One of the first reported tests of the equivalence principle — well before it was understood in the framework of general relativity — was Galileo’s apocryphal experiment in which he is said to have dropped weights from the Leaning Tower of Pisa. Scientists have since adapted that test to smaller scales, swapping out the weights for atoms. In the new study, physicists went a step further, putting atoms into…

Collider data hint at unexpected new subatomic particles

LHCb experiment
WEIRD DECAYS Something funny may be going on in certain particle decays measured in the LHCb experiment in Geneva (above). A new measurement has now added to scientists’ suspicions.

A handful of measurements of decaying particles has seemed slightly off-kilter for years, intriguing physicists. Now a new decay measurement at the Large Hadron Collider in Geneva has amplified that interest into tentative enthusiasm, with theoretical physicists proposing that weird new particles could explain the results. Scientists with the LHCb experiment reported the new result on April 18 in a seminar at the European particle physics lab CERN, which hosts the LHC.

“It’s incredibly exciting,” says theoretical physicist Benjamin Grinstein of the University of California, San Diego. The new measurement is “a further hint that there’s something new and unexpected happening in very fundamental interactions.”

Other physicists, however, are more cautious, betting that the series of hints will not lead to a new discovery. “One should always remain suspicious of an effect that does not show up in a clear way” in any individual measurement, Carlos Wagner of the University of Chicago wrote in an e-mail.

Taken in isolation, none of the measurements rise beyond the level that can be explained by a statistical fluctuation, meaning that the discrepancies could easily disappear with more data. But, says theoretical physicist David London of the University of Montreal, there are multiple independent hints, “and they all seem to be pointing at something.”

The measurements all involve a class of particle called a B meson, which can be produced when protons are smashed together in the LHC. When a B meson decays, it can produce a type of particle called a kaon that is accompanied either by…

New particle probably can’t explain nuclear reactor neutrino mystery

neutrino
NO NEW NEUTRINO Scientists with the Daya Bay experiment in China, shown above, have determined that a shortage of neutrinos from nuclear reactors is probably due to a miscalculation, not a new type of neutrino.

A puzzling neutrino shortfall seems to be due to faulty predictions, not a new particle.

In experiments at nuclear reactors, scientists have consistently found about 6 percent fewer antineutrinos, the antimatter form of neutrinos, than expected. That deficit could hint that the lightweight particles are morphing into undetectable new particles called sterile neutrinos (SN: 3/19/16, p. 14)….

Earth’s mantle may be hotter than thought

Earth's mantle
HOT STUFF Temperatures in Earth’s mantle are higher than previously thought, results from a new experiment suggest.

Temperatures across Earth’s mantle are about 60 degrees Celsius higher than previously thought, a new experiment suggests. Such toasty temperatures would make the mantle runnier than earlier research suggested, a development that could help explain the details of how tectonic plates glide on top of the mantle, geophysicists report in the March 3 Science.

“Scientists have been arguing over the mantle temperature for decades,” says study coauthor Emily Sarafian, a geophysicist at the Woods Hole Oceanographic Institution in Massachusetts and at MIT. “Scientists will argue over 10 degree changes, so changing it by 60 degrees is quite a large jump.”

The mostly solid mantle sits between Earth’s crust and core and makes up around 84 percent of Earth’s volume. Heat from the mantle fuels volcanic eruptions and drives plate tectonics, but taking the mantle’s temperature is trickier than dropping a thermometer down a hole.

Scientists know from the paths of earthquake waves and from measures of how electrical charge moves through Earth that a boundary in the mantle exists a few dozen kilometers below Earth’s surface. Above that boundary, mantle rock can begin melting on its way up to the surface. By mimicking the extreme conditions in the deep Earth — squeezing and heating bits of mantle that erupt from undersea volcanoes or similar rocks synthesized in the lab — scientist can also determine the melting temperature of mantle rock. Using these two facts, scientists have estimated that temperatures at the boundary depth below Earth’s oceans are around 1314° C to…