The good news is that thanks to research by an international group of scientists and published in the August 20, 2010 issue of Science [Cosmological Constraints from Strong Gravitational Lensing in Clusters of Galaxies] we have a much more precise idea of the amount of dark energy in the universe and a fix on the geometry of the universe as well. The bad news is according to the study, some previous notions are probably right: The universe is flat and will expand forever, leading to terminal entropy. (Translation: In some 10100 years, give or take, the universe will be so expanded that there will be no more energy for heat, in short, the death of the universe.)
This is not a new idea; the precursors go back to the 1850’s and discussions about the laws of thermodynamics. The total entropy (heat-death) of the universe has always been one of the ‘logical’ options and is often contrasted with the infinitely recurring universe (sort of Big-Bang cycle). There are other cosmological variants about the fate of the universe. However, new evidence that provides confirmation of one variant or another is important – if not necessarily conclusive.
The paper is based on work with data from the Kepler Space Telescope and ground-based telescopes that measure the effects on the light coming from distant galaxies as it passes through Abel 1689, the largest cluster of galaxies in the known universe. The gravitational pull of this cluster is so massive that light from the distant galaxies is bent (or refracted) in much the same way as light passing through an optical lens like a magnifying glass. By measuring the properties of this refraction and plugging the data into complex mathematical models, a great deal can be learned:
“The precise effects of lensing depend on the mass of the lens, the structure of space-time, and the relative distance between us, the lens and the distant object behind it,” explains Priyamvada Natarajan, a co-author of the paper. “It’s like a magnifying glass, where the image you get depends on the shape of the lens and how far you hold it from the object you’re looking at. If you know the shape of the lens and the image you get, you can work out the path that light followed between the object and your eye.”
Looking at the distorted images allows astronomers to reconstruct the path that light from distant galaxies takes to make its long journey to Earth. It also lets them study the effect of dark energy on the geometry of space in the light path from the distant objects to the lensing cluster and then from the cluster to us. As dark energy pushes the Universe to expand ever faster, the precise path that the light beams follow as they travel through space and are bent by the lens is subtly altered. This means that the distorted images from the lens encapsulate information about the underlying cosmology, as well as about the lens itself.
To produce the kind of refraction of light seen in the models, the elusive quantity known as dark energy – and the universe – must be expanding in a single plane – a flat universe. Dark energy is considered to be the driving force behind the expansion. Without some other kind of dynamic (which also requires evidence), the expansion of the universe will continue to accelerate and go on indefinitely. However at some point, the materials of the universe including matter, dark matter, and dark energy are so pulled-apart that they no longer exhibit gravitational attraction. They are devoid of all energy and are therefore at terminal cold (absolute zero temperature). This is known as the ‘heat death’ of the universe.
It’s a bleak outcome, if impossibly remote from the human perspective of time. The research may be one more nail in this cold-coffin theory.