A lightweight universe?

Neta A. Bahcall, Xiaohui Fan

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


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 ~20-30% of the critical density. Thus, the universe may expand forever.

Original languageEnglish (US)
Pages (from-to)5956-5959
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number11
StatePublished - May 26 1998

All Science Journal Classification (ASJC) codes

  • General


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