Physicists live with the never-ending threat that new data will puncture cherished assumptions. That's the way it is with the fundamental constants of nature. These are numerical factors that make the mathematical equations for nature's laws work. Their numerical values are found by laboratory measurement. Physicists assume, without proof, that these numbers are the same throughout the universe and remain constant throughout all time.

New research indicates that this may not be so.

If further research were to confirm that any of the constants is variable, physicists would face the stark realization that their understanding of how the physical universe works is fundamentally flawed. These latest results are uncertain. But they show that the tedious effort to refine what already are highly precise measurements is worthwhile.

The constants in question include: the speed of light in empty space, a constant that's used to determine gravitational force; the fine-structure constant that fixes the strength of electromagnetic forces; and the ratio of the mass of a proton to the mass of an electron.

This last one relates to the strength of the force that holds atomic nuclei together. In the April 21 issue of Physics Review Letters, Wim Ubachs at Vrije Universiteit in Amsterdam and an international group of colleagues explained why they think that this atomic mass ratio may have decreased by 0.002 percent over the past 12 billion years. They have compared the ratio as measured in the laboratory with the value derived from light coming from distant objects as observed at the European Southern Observatory in Chile.

It took a lot of arcane analysis to winkle that deduction out of the team's data. Its authors admit that, while it is suggestive, it does not rise to the level of proof. What's remarkable about their work is it demonstrates techniques that promise to raise the laboratory measurement of the mass ratio to a much higher level of precision. On its website, Dr. Ubachs's group says such precision promises "the possibility of searching for temporal variations of fundamental constants only based on laboratory measurements." It adds that this "is the goal of a new research programme." If successful, the group will look for variability in the mass ratio right here on Earth over time periods of a decade or less. There would be no need to look at distant astronomical objects to see what the ratio was billions of years ago.

Meanwhile, the National Institute of Standards and Technology says that physicists at an institute it shares with the University of Colorado in Boulder have boosted the precision of measuring energy levels in molecules 10 to 25 times. Also, they can, for the first time, make two such measurements simultaneously on a given molecule. When such laboratory measurements are compared with similar measurements of the same type of molecule in distant astronomical objects, physicists can get a tighter grip on whether or not the fine structure constant changes over time. Some unpersuasive observations in recent years have indicated that it does vary. The implications of changeable fundamental "constants" are so profound that any hint that this might be proved true makes news. But the real news is the dramatic increase in precision of the relevant measurements. That is going on in laboratories around the world right now.

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