You are here:
Home >
Activities >
Physics >
Gravitational Constant
Gravitational Constant: Limits on Variations
Newton's gravitational constant G has been measured in the laboratory
with reasonable accuracy only for a limited range of distances. A
priori there is no guarantee that G has the same numerical value at
much larger distances, and neither is it clear that its value has
always been the same in the past. As long as we have no consistent
quantum theory of gravity, it is hard to find any theoretical argument
pro or con such variations. This makes it all the more important to
see to what extent observations can put limits on possible variations
of G in space and time.
Spatial Variations
Around 1980, the uncertainty in the comparison between the value of G
at laboratory scales and at astrophysical distances was estimated to
be roughly 40%. At that time, I realized that I could use white
dwarfs in order to further tighten this value. Even though neutron
stars have a much stronger gravitational field, there are far greater
uncertainties in the equation of state of a neutron star than in that
of a white dwarf. In the paper:
-
A Constraint on the Distance Dependence of the Gravitational Constant,
by Hut, P., 1981, Phys. Lett. 99B, 174-178.
I concluded that the two values of G were the same within 10%.
A few years later, these limits were further tightened at larger
scales through improved geophysical measurements in mine shafts, and
many years later at shorter scales through a set of ingenious
experiments in Seattle at the University of Washington to
distances
of less than 1 mm, and subsequently in Boulder, Colorado at even
smaller distances
around 0.1 mm; cf. J.C. Long et al., 2003, Nature 421, 922.
Temporal Variations
If the gravitational constant would be subject to variations in time,
as Dirac once speculated, any two bodies revolving around each other
in a gravitationally bound orbit would slowly change their orbital
parameters. We improved upon previous derivations of these changes,
generalizing those more limiting cases, in the paper:
For a much more recent paper on this topic, see
A new white dwarf
constraint on the rate of change of the gravitational constant, by
Marek Biesiada and Beata Malec.
Back to physics.
Back to activities
or to table of contents.
Back to Piet Hut's home page.