COSMOLOGY is somewhat of an oddballamong the physical sciences. Experimental facts about the origin and theultimate fate of the universe are usuallyscarce, making cosmology a concoctionof theory, some facts and much speculation. However, the scenario has undergone a change in the recent past becauseof the availability of better equipment.The accurate measurement of microwave background radiation by theCosmic Background Explorer (com)satellite in 1993 has proved that cosmologists can have access to good and reliable experimental data (Science, Vol269, August 11, 1995).
One such cosmological aspectwhich has proved difficult to measurehas been the deceleration parameter q0.This is an extremely important cosmological quantity, being a measure of howfast the pull of gravity is slowing downthe expansion of the universe.
Applying different techniques, somegroups of astronomers working atCaltech in Pasadena, California, Lawrence Berkeley Labs in Berkeley,California and Harvard-SmithsonianCenter for Astrophysics in Cambridge,Massachusetts are now trying to mea-sure the value of the elusive decelerationparameter. The Berkeley group, forinstance, is using type IA supernovas,stars which are exploding with immenseenergies and having roughly the sameactual brightness. This point is crucialbecause to measure q0, "standardcandles" - sources whose apparent brightness can be taken as ameasure of their distance - areneeded. Comparing the distances ofthese objects with their redshifts(the change in the colour of thelight from them because of theirvelocity away from the earth) to seehow much the relation is distortedwill give hints of the presence ofcosmic deceleration.
Other methods of measuringthe deceleration parameter includeusing radio galaxies as standardcandles and looking at giant voidsin the distribution of galaxies. Forthe more ambitious, plans are afootto Use the LIGO gravity wave detector (aseries of wave detectors around theworld) when it will appear in 1999 tostudy pairs of neutron stars for measuring the q0. Astronomers, however,feel that conclusive data will be unavailable for quite some time. Till then, thefate of our universe will remain open tospeculation.