Physicists keep faith in constants

For a long time, physicists took for granted that the fundamental numerical constants they plugged into their equations would remain unchanged throughout time. Some modern theories of matter's basic structure have suggested that these "constants" are chameleons. But now, events that happened long ago in a galaxy far away support the physicists' original faith.

In Friday's issue of Physical Review Letters, an international astronomical team describes how their measurements of these events put "very tight limits on changes" in some of those crucial constants. They appear to have had exactly the same values 6 billion years ago in a galaxy 6 billion light-years away that they have here on Earth today.

It's the latest report from the ongoing quest to test how sound the foundations of modern physics really are. The team was looking specifically at two of the basic constants: the ratio of the masses of the electron and the proton, and the so-called "fine structure constant," which characterizes the strength of electromagnetic interactions.

This may sound nerdy, but if their values 6 billion years ago were even slightly different from what they are today, it would shake up what physicists now consider their standard theory of matter.

The team got at the constants' values by analyzing four frequencies of radiation from hydroxyl molecules. These molecules are made up of an atom of oxygen and an atom of hydrogen. The result is that physicists can keep their faith in unchanging constants for now.

"This is the exciting frontier where astronomy meets particle physics," said Christopher Carilli, a team member at the National Radio Astronomy Observatory in Socorro, N.M. The team hopes to use its techniques to study the constants at other times in the past.

Meanwhile, Einstein's famous equation equating material mass with energy - another pillar of modern physics - has passed its most stringent test yet. A team at the Massachusetts Institute of Technology (MIT) and the National Institute of Standards and Technology (NIST) has tested Einstein's assertion that energy equals material mass multiplied by the square of the speed of light (E=mc2).

NIST team members measured the energy of gamma rays emitted by silicon and sulfur atoms. MIT researchers measured the mass of such atoms before and after the energy was emitted. They reported in the Dec. 22 issue of Nature that, to an accuracy of four-tenths of one part in a million, Einstein's mass-energy equivalence is correct. That's 55 times the accuracy of any previous test. Einstein once wrote that he considered this equation to be "the most important upshot of [his] special theory of relativity."

"If this equation were found to be even slightly incorrect, the impact would be enormous - given the degree to which [it] is woven into the theoretical basis of modern physics and everyday applications," said MIT physics professor David Pritchard. "This doesn't mean [the relation] has been proven to be completely correct. Future physicists will undoubtedly subject it to even more precise tests because accurate checks imply that our theory of the world is in fact more and more complete."

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