Is the Universe infinite in spatial extent? More generally: what is the topology of space?
We still don’t know, but in 2003 some important work was done on this issue: • Neil J. Cornish, David N. Spergel, Glenn D. Starkman and Eiichiro Komatsu, Constraining the Topology of the Universe. Briefly, the Wilkinson Microwave Anisotropy Probe (WMAP) was used to rule out nontrivial topology within a distance of 78,000 million light years–at least for a large class of models. For the precise details, you’ll have to read the article! • Why is there an arrow of time; that is, why is the future so much different from the past? Here are two pieces of required reading for anyone interested in this tough question: • Huw Price, Time’s Arrow and Archimedes’ Point: New Directions for a Physics of Time, Oxford University Press, Oxford, 1996. • H. D. Zeh, The Physical Basis of the Direction of Time, second edition, Springer Verlag, Berlin, 1992. • Will the future of the Universe go on forever or not? Will there be a “big crunch” at some future time, will the Universe keep on expanding forever,
