May 25 2012

Speed of Light

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Study: Light Speed May Have Changed
By MATT CRENSON, AP National Writer

New observations from the world’s biggest telescope indicate that one of nature’s supposedly immutable constants has changed over the 15 billion-year history of the universe.

Physicists were shocked at the discovery, but pleasantly so because it suggests that new theories about how the universe works on the subatomic scale may be correct.

“This has fundamental implications for our understanding of physics,” said John Webb, a professor at the University of New South Wales in Sydney, Australia.

Webb led the research team that made the discovery, which is described in a paper to be published August 27 in Physical Review Letters.

The team found that the fine structure constant – a number that determines the strength of electromagnetic force and thus the speed of light – may have been ever so slightly smaller billions of years ago. If true, then current theories are incorrect because they maintain that light’s speed and other fundamental properties do not change in either space or time.

This is actually good news to physicists, because proposed theories can accommodate changes in the fine structure constant over time. Known as string theories, they allow either a 10- or 26-dimensional universe, rather than a 4-D one containing the three spatial dimensions plus time. The extra dimensions would be curled or folded, so they would be impossible to detect in everyday life – or even in any physics experiment yet conducted.

“This would be a clue to help guide how you convert string theories into something relevant,” said Gordon Kane, a physicist at the University of Michigan. “It’s just a very nice piece of information, if it stands up.”

That is a big if, said John Bahcall of the Institute for Advanced Study in Princeton, N.J.

“I’m quite cautious about whether to believe this result,” Bahcall said.

The physicists used the world’s most powerful telescope to peer at some of the most distant objects in the universe. They aimed the Keck telescope atop Hawaii’s Mauna Kea at 17 different quasars, which are extremely bright objects probably associated with black holes.

The quasars are so far away – about 12 billion light-years – that light they produced at the dawn of the universe is only now reaching Earth.

During its long journey, the light has passed through clouds of intergalactic gas, where some of it has been absorbed. The patterns of absorption tell scientists something about the gas, and something about the light as well – including its speed and the fine structure constant that determines how fast it goes.

“It’s like a car headlight on a foggy night. The headlight shines through the fog … and you can see the change on the background light because of the presence of the fog,” Webb said.

The scientists hope to confirm their results using a different telescope, perhaps the Very Large Telescope at the European Southern Observatory in Chile.

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