As if to make up for the departure of the glamorous Hale-Bopp comet, astronomers have re-
leased a flurry of reports on other celestial matters. Refined measurements of the ages of stars appear to be resolving the seeming paradox in which some stars appeared to be older than the universe it- self. A new observation offers the first concrete clues regarding the nature of the mysterious flashes of energetic radiation known as gammaray bursts.
But by far tile most startling and tentative finding is that the universe has a preferred orientation. Such directionality would challenge one of the basic tenets of physics and astronomy, taken for granted by Einstein, Newton and even Kepler. These giants all assumed that space possesses a property called rotational symmetry: spin a chunk of cosmos sideways or flip it upside down, and measurements of events within it yield precisely tile same results.
In the April 21, 1997 issue of physical Review Letters, however, Borge Nodland of the University of Rochestre and John P. Ealston of the University of Kausas present evidence that the principle of rotational symmetry may be violated on a cosmic scale. Measurements of light from distant galaxies, they say, vary depending on the galaxies' position in the sky.
Other theorists doubt whether the claim will stand up to close scrutiny; at least two critical analyses have already been posted on the Internet. For the moment, however, even the critics can savor the frisson of a tremor rocking their field' s foundations. "Nobody would be happier than me if they were right," says Sean M. Curroll of the University of California at Santa Barbara.
The surprising work on cosmic asymmetry began three years ago, while Nodland was working for his doctorate under Ralston's supervision. Ina search for signs of unconventional large - scale non - uniformity, the two researchers decided to investigate whether polarized light front remote galaxies changes with their direction or distance. (Polarized light typically swings within one plane rather than in all directions, ordinary sunlight does; it can be produced by a variety of phenomena. ) Polarized light often twists as it penetrates through space as a result of its encounters with electromagnetic fields; this well- understood phenomenon is called the Faraday effect. But Nodland and Raison wondered whether additional twisting effects might be at work.
To find out, they focused on studies of galaxies that emit large amounts of synchrotron radiation, a highly polarized form. of electromagnetism generated by charged particles passing through a strong electromagnetic field. After combing through the published literature, Nodland and Ralston compiled polarization data for 160 galaxies.
Their investigation involved a crucial assumption, that the initial angle of polarization of the light relative to the plane of each galaxy was the same for all 160 galaxies. Given this assumption and the estimated distances to the galaxies (inferred from their red shifts), Nodland and Ralslon could calculate whether the light underwent any twisting other than that caused by the Faraday effect.
The departure of the splendid Hale-Bopp comet is mentioned______.
A．to honor the contributions of Hale-Bopp.
B．to introduce to the topic of new report on cosmic matters.
C．to challenge the basic tenets of astronomy.
D．to recount the reactions of the public to the comet.
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