Physics: Principles and Problems


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A Changing Constant?
Posted January 2002

One of the first things that you learn in physics is that there are certain constants that never change (e.g., the speed of light, universal gravitation, Planck's constant). However, new evidence from a study conducted at the University of New South Wales in Australia points to the fact that one of these constants may have changed over the last few billion years.

The constant that was studied is called "alpha," named after the Greek symbol used to identify it in scientific calculations. It measures the electrical attraction between the fundamental particles -protons and electrons.

Evidence suggests that the alpha constant has grown stronger over the life of the universe. Of course, the possibility for change in the constant is incredibly small - only one part in 100,000 - but it is a change nonetheless. According to the evidence, between 8 and 11 billion years ago, the alpha constant was only slightly weaker than it is today.

One of the effects of a weaker alpha constant is that atoms may not be held together as tightly. In essence, the electrons orbiting the nucleus would be slightly less attracted to the protons inside. This would result in a different absorption pattern as light passed through ionized gas.

Physicist John K. Webb started studying this constant four years ago at the University of New South Wales. He and his team studied the behavior of quasars, which are objects that resemble stars but are very far away and have huge energy outputs.

By looking at these quasars, Webb and his team were, in a sense, looking into the past. Light travels only 186,000 miles every second, so it takes many years for the light to travel across the trillions of miles of the universe. The light from the quasars that Webb studied were billions of light years away. By studying the way the atoms in the quasars absorb the light, Webb and his colleagues were able to determine the alpha constant in these atoms.

Astrophysicists have been studying the alpha constant in distant quasars for about 40 years. However, Webb and his team were able to develop a new measuring system that determined alpha to a much more precise value.

The alpha constant has been considered one of the unshakable natural constants in the universe. It is the basis of the atomic clock, which is the most precise timepiece ever made, and it has also been verified by geologic records to have been constant as far back as 2 billion years ago.

"My gut feeling is that some other explanation will be discovered for this observation," says Robert J. Scherrer of Ohio State University. "Of course, I'd love to be proved wrong; that would be very exciting."

Use the Internet to research the alpha constant. In your Science Journal, explain how looking at very distant stars and other celestial bodies can help you learn about the past.



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Physics: Principles and Problems