Near-perfect physics

Using better instruments and more powerful computers, scientists are demonstrating key aspects of physics with unprecedented precision.

Three weeks ago, an international team showed how observations of an unusual double star system verify an effect predicted by Einstein's general relativity to an accuracy of 99.95 percent. That leaves little wiggle room for doubts about Einstein's theory of gravity. Thursday, another group reports a significant advance in laboratory experiments in teleportation. Quantum theory predicts that a particle can transfer – teleport – some of its properties to another particle when there is no discernable physical link between them. Highly precise experiments are turning that weird prediction, which was considered fiction only a decade ago, into observable fact.

Physicists don't consider general relativity or quantum theory the last word on how nature works. They can't even get the two theories to work together in one overarching scheme. They hope that the insights gained by their high precision studies will point the way toward better theoretical concepts.

Quantum teleportation has already been demonstrated between particles of the same kind, such as two light photons or two matter particles. Jacob Sherson at the Neils Bohr Institute in Copenhagen and colleagues explain in Thursday's issue of Nature how, for the first time, they have achieved teleportation between particles of different types. In this case, it is between photons and cesium atoms. That's an important step closer to using teleportation in future communications and computer technologies.

Einstein's gravity theory has its own exotic aspects. Stars don't exert gravitational force on a planet, he said. Instead, they bend space and warp time. The path a planet takes through curved space around a star just looks like gravitational attraction to us.

The theory predicts effects that don't arise in Newton's theory, which treats gravity as an attractive force. Using Einstein's theory, scientists can calculate the orbits of planets and other orbiting bodies correctly, when Newton doesn't get things quite right.

These effects show up best where gravity is strong. So Michael Kramer at the University of Manchester in England and colleagues on three continents have been studying them in a system where two very compact, very massive stars are orbiting each other 2,000 light-years from Earth in the constellation Puppis. The stars are called pulsars because they emit radio beams that sweep repeatedly over Earth as the stars rotate.

These very regular lighthouselike pulses can be used to probe the star system. Dr. Kramer's team tracks them with radio telescopes in Australia, England, and North America. Commenting on their report Sept. 14 in Science, Kramer says that all the relativistic phenomena that can be observed in this way are confirmed to new levels of precision. He calls it "the most stringent test ever made of General Relativity" under conditions of strong gravity. One effect – delay in the radio signals as the stars move through curved space – now is verified with 99.95 percent certainty.

The theory also predicts that the stars will spiral toward each other as they radiate energy in gravitational waves, which are ripples in space-time. The team reports the stars are losing orbital energy precisely as Einstein says they should.

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