The Wraparound Universe
AK PETERS: 2008. 400 pp. $39.
Is space finite or infinite? This question has perplexed scientists and driven astronomical observations for generations. When found to be incompatible with observations and consequent new understanding of physical law, early models of a finite cosmos were replaced with that of a static, infinite universe. Such a model dominated scientific thinking until the twentieth century, when Milton Humason and Edwin Hubble discovered that extragalactic objects were receding away from us in every direction at speeds proportional to their distance. After this discovery, a radical notion began to take hold, in which the Universe was better explained by the non-static, expanding solutions of general relativity found by Alexander Friedman, Georges Lemaître, Howard Percy Robertson and Arthur Geoffrey Walker. The discovery of the cosmic microwave background radiation by Arno Penzias and Robert Wilson in 1965 provided further evidence that our Universe had expanded from an initial hot dense state. Recent observations of the cosmic microwave background by the Wilkinson Microwave Anisotropy Probe have culminated in the choice of a certain expanding solution, called the concordance model, as the one describing our Universe. Although its parameters are set by astronomical observations, the concordance model incorporates certain assumptions. In particular, although it is manifestly non-static, the Universe is still taken to be spatially infinite, an assumption tied to the hypothesis that it underwent an extended period of exponential expansion, called inflation. But is this assumption supported by observation?
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