Sharper limits set on how much quantities so far considered to have a fixed value can vary

ANYONE even vaguely familiar with
equations of physics, would recall the
universal gravitational constant, denoted by the letter G. Besides G, there are
several other physical quantities which
govern the strength of interactions
between the elementary particles of
matter and are 'deemed to have a fixed
value. These are generally referred to as
fundamental constants. Paradoxically,
these fundamental constants could
show a variation.

Even as long ago as 1937, physicist P
A M Dirac noticed that these constants
could have a spatial and temporal variation with prof6und consequences. Now,
J D Prestage and his collaborators at the
Frequency Standards Laboratory at the
California Institute of Technology
report a new test - using clocks based
on the vibrations of different alkali
atoms (like cesium and mercury) and
H-maser (hydrogen maser) clocks -
which they claim has improved the laboratory limits on the time Yariation of a
fundamental constant - the fine structure constant - by about 100-fold over
the previous measurements (Physical
Review Letters, Vol 74, No 18).

Dirac had observed that the ratio of
the electric force to the gravitational
force between the electron and the pro-
ton (about 2000 million million million
million million million: 1) was remark-
ably similar to the age of the universe if
it were expressed in units of the time
taken by light to travel a distance called
the classical radius of the electron.
He conjectured that these 2 large quantities were proportional and thus the
fundamental constants characterising
these 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 Number
Hypothesis predicts a small variation for,
G and the fine structure constant; for a
universe which is 2 billion years old, the
fractional change in the fine structure
constant 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 to
the whole field. Changing gravitational
and fine structure constants will have
profound effects on our universe. For
instance, even a small departure from
the present value of G will make the
Earth inhospitable to life.

This has led some scientists to develop the anthropic cosmological principle, which states that the present values
of the constants is a small subset of the
possible values. Any other values for
these constants will lead to the universe
evolving in a completely different fashion - for instance, that universe could
be too young for life (and hence astronomers!) to evolve.

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