Constant inconsistency

ANYONE even vaguely familiar withequations of physics, would recall theuniversal gravitational constant, denoted by the letter G. Besides G, there areseveral other physical quantities

whichgovern the strength of interactionsbetween the elementary particles ofmatter and are 'deemed to have a fixedvalue. These are generally referred to asfundamental constants.

Paradoxically,these fundamental constants couldshow a variation. Even as long ago as 1937, physicist PA M Dirac noticed that these constantscould have a spatial and temporal variation with

prof6und consequences. Now,J D Prestage and his collaborators at theFrequency Standards Laboratory at theCalifornia Institute of Technologyreport a new test - using clocks basedon the

vibrations of different alkaliatoms (like cesium and mercury) andH-maser (hydrogen maser) clocks -which they claim has improved the laboratory limits on the time Yariation of afundamental

constant - the fine structure constant - by about 100-fold overthe previous measurements (PhysicalReview Letters, Vol 74, No 18). Dirac had observed that the ratio ofthe electric force to

the gravitationalforce between the electron and the pro-ton (about 2000 million million millionmillion million million: 1) was remark-ably similar to the age of the universe ifit were

expressed in units of the timetaken by light to travel a distance calledthe classical radius of the electron.He conjectured that these 2 large quantities were proportional and thus

thefundamental constants characterisingthese forces will vary with the age of the universe. The fine structure constant characterises the electric force and its Value is about 1/137.

Dirac's Large NumberHypothesis predicts a small variation for,G and the fine structure constant; for auniverse which is 2 billion years old, thefractional change in the fine

structureconstant is about 0.36 millionth millionth per year. JA Recently, some of the cosmic theories also predicted a varying fine structure constant, giving a fresh impetus tothe whole

field. Changing gravitationaland fine structure constants will haveprofound effects on our universe. Forinstance, even a small departure fromthe present value of G will make theEarth

inhospitable to life. This has led some scientists to develop the anthropic cosmological principle, which states that the present valuesof the constants is a small subset of thepossible

values. Any other values forthese constants will lead to the universeevolving in a completely different fashion - for instance, that universe couldbe too young for life (and hence

astronomers!) to evolve.