Fundamental constant didn’t vary after all

A few years ago, observations of distant quasars rocked the scientific community by indicating that one of the constants of nature—the strength of the electromagnetic force—hasn’t been constant throughout the universe’s history. Now, an analysis of new quasar observations suggests that that constant has been unwavering after all.

In such studies, scientists investigate which wavelengths of light are absent from quasar spectra because they had been absorbed by clouds of gas lying between the quasars and Earth. The radiation passed through some of these clouds billions of years ago.

Researchers know that the constant under scrutiny, called the fine-structure constant or alpha, determines the wavelengths of light that atoms can absorb.

John K. Webb of the University of New South Wales in Sydney, Australia, and his colleagues have been investigating differences between wavelengths absorbed by clouds and wavelengths soaked up by atoms in a laboratory. In 2001, Webb’s group interpreted quasar spectra recorded at the Keck I telescope in Hawaii as evidence that alpha was slightly smaller in the early universe than it is today (SN: 10/6/01, p. 222: Constant Changes).

In the new study, Patrick Petitjean of the Institut d’Astrophysique de Paris and his colleagues collected spectra at the European Southern Observatory’s Very Large Telescope in Chile. They purged their data of components that were hard to interpret.

While the team’s analysis of the remaining data can’t rule out extremely small variations of alpha, it suggests that the constant has not changed over the past 12 billion years, Petitjean says. He and his colleagues describe their new result in the March 26 Physical Review Letters.