Article/Document:

Speed of Light, Other Constants May Change

Space.com, 15 August 2001

original source | fair use notice

Summary: The speed of light and other fixed numbers (called constants) that scientists rely on to explain the universe and its formation mathematically may not be so constant, according to a new study conducted by an international team of researchers. The research was met with caution by many scientists, who also said that if it is accurate, then the adjustment to theories would be significant and far-reaching.

By Robert Roy Britt, Senior Science Writer

The speed of light and other fixed numbers (called constants) that scientists rely on to explain the universe and its formation mathematically may not be so constant, according to a new study conducted by an international team of researchers.

The finding involves what physicists and cosmologists have considered a basic law of nature involving the strength of attraction between electrically charged particles.

Studying how light was absorbed by metallic atoms in gas clouds some 12 billion light-years away, researchers found that the fine structure constant, as it is called, may be changing subtly as the universe grows older. The universe is thought to be roughly 13 billion years old, so the light observed in the new study was emitted when the universe was roughly a billion years old.

The research was met with caution by many scientists, who also said that if it is accurate, then the adjustment to theories would be significant and far-reaching.

A paper on the study, led by John K. Webb of the University of New South Wales in Sydney, Australia, will be published in the Aug. 27 issue of the journal Physical Review Letters. Webb and his colleagues reported similar but inconclusive evidence in 1999.

The apparent change in the fine structure constant, also called alpha, was very small, amounting to 1 part in 100,000. And the researchers calculated that there is a 1-in-10,000 chance that the result is a statistical fluke.

Alpha and the standard model

The fine structure constant explains how electromagnetic forces hold atoms together.

"This constant governs the structure of atoms, and it governs how light interacts with atoms," said Christopher Churchill, a member of the research team from Pennsylvania State University.

In a telephone interview, Churchill explained the physics of the finding. Imagine an atom as looking something like the solar system, he said, with the planets representing electrons orbiting around the nucleus. As light passes through an atom, certain wavelengths alter the positions of the electrons.

"It's like taking Earth's orbit and changing it to Mars' orbit," he said. The fine structure constant dictates that these interactions are precise. Certain wavelengths of light have predictable effects on each type of atom.

But when Churchill and his colleagues looked back in time at light passing through atoms in the young universe, they saw something else.

"What we've seen is that the structure of these atoms must be very slightly different, just so slightly, that the frequency of light that's involved in bumping the electrons from one orbit to the next is just a little bit different."

This implies that something in the early universe behaved differently. Because the speed of light is one factor in the fine structure constant equation, it might be it that has changed over time, Churchill said. Or it could be that unknown properties of the early universe forced atoms and electrons to behave in ways researchers don't understand.

That would change everything

"A variation of the fine structure constant would force a revision of the so-called standard model in particle physics," among other things, said Massimo Stiavelli, an astrophysicist at the Space Telescope Science Institute in Baltimore. He was not involved in the study.

This standard model is the basis for all assumptions about how the observable and microscopic physical worlds works, both now and in the past. But the standard model has withstood rigorous testing over several decades. It is considered successful because it adequately explains things that are plainly observable.

"The standard model has explained a large variety of phenomena and, although one must always be open to accept new evidence, it cannot be abandoned lightly," Stiavelli told SPACE.com. "Any new theory would have to repeat all the successes of the standard model in addition to incorporating the variation of the fine structure constant."

Stiavelli said that if the results hold up, it's likely that a new theory will have to be formulated that incorporates the existing standard model.

And there is precedent for this sort of evolution in scientific thinking. Both the theories of relativity and quantum mechanics were forced to incorporate classical mechanics as a special case.

Stiavelli added that the technique used to conduct the new study has probably been pushed to the limits of its capability, so in order to verify the results an independent measurement with a different technique will be needed.

Quasars yield more findings

The new study examined light emitted from distant quasars, powerful young galaxies powered by supermassive black holes. The researchers examined how atoms in giant gas clouds absorbed light back then compared to now. They found that the fine structure constant was smaller in the past.

Some exotic theories that currently are only on the fringes of cosmology could benefit by the possible change.

"There are many possibilities to incorporate a variation of the fine structure constant into existing theories, and there are some theories were the constants of nature are predicted to vary," Stiavelli said. "For the proponents of these theories this would become evidence that the theory is correct."

One of the ideas that might benefit is string theory, which holds that there are many more dimensions to the universe than just time and space. String theorists say that changes in these dimensions over time could force changes in the fine structure constant.

Several scientists told The New York Times that they were skeptical that the new finding would hold up under further scrutiny, saying that the very small difference found could be a slight statistical or observational flaw in the study. But these same scientists were also excited about the possible implications.

Churchill and his colleagues were also thrilled with the potential implications of their study, but they were careful not to overhype it.

The study was painstakingly checked for possible errors, Churchill said.

"If there is something that has fooled us, it absolutely must be a systematic effect," he said.

Such an effect could either be due to methods by which the data were collected or analyzed, Churchill said. To check the study's reliability, some 13 potential systematic errors were thoroughly investigated, and only two were found to be potential threats to the accuracy.

"Correcting for either of those actually enhances the measured change," he said.

Researchers at Cambridge University, the Carnegie Observatories and the University of California at San Diego also worked on the study. The observations were made using the Keck Telescope in Hawaii.