Bahcall N A, Fan X
Princeton University Observatory, Princeton, NJ 08544, USA.
Proc Natl Acad Sci U S A. 1998 May 26;95(11):5956-9. doi: 10.1073/pnas.95.11.5956.
How much matter is there in the universe? Does the universe have the critical density needed to stop its expansion, or is the universe underweight and destined to expand forever? We show that several independent measures, especially those utilizing the largest bound systems known-clusters of galaxies-all indicate that the mass-density of the universe is insufficient to halt the expansion. A promising new method, the evolution of the number density of clusters with time, provides the most powerful indication so far that the universe has a subcritical density. We show that different techniques reveal a consistent picture of a lightweight universe with only approximately 20-30% of the critical density. Thus, the universe may expand forever.
宇宙中有多少物质？宇宙是否具有阻止其膨胀所需的临界密度，或者宇宙质量不足注定要永远膨胀下去？我们表明，几种独立的测量方法，尤其是那些利用已知的最大束缚系统——星系团——的方法，都表明宇宙的质量密度不足以阻止膨胀。一种有前景的新方法，即星系团数量密度随时间的演化，提供了迄今为止最有力的迹象，表明宇宙具有亚临界密度。我们表明，不同的技术揭示了一个质量轻的宇宙的一致图景，其质量仅约为临界密度的20% - 30%。因此，宇宙可能会永远膨胀下去。
