One of the major constituents of ordinary matter, the neutron, is unstable when it is isolated from the atomic nucleus. On average, a free neutron has a lifetime of about 15 minutes. This time defines the time scale during which the light elements (hydrogen, helium and lithium ...) were formed during the big bang creation of the universe. The abundance ratios of these light elements has changed very little in the subsequent evolution of the universe.
As a result, astronomical observations can be compared with theoretical predictions to provide a test of the big bang theory. A remarkable conclusion of such comparisons is the possibility that a substantial, perhaps dominant, portion of the mass of the universe is not in the form of ordinary matter.
The reasoning which leads to the possibility of such dark matter will be discussed. The talk will also describe some of the experimental work on the neutron lifetime which is currently in progress at the National Institute of Standards Cold Neutron Research Facility in Gaithersburg, Maryland.
Mr. Geoffrey Greene received his Ph.D from Harvard University in 1977. His research interests have focussed on tests of basic physical laws using very low energy neutrons. Mr. Greene was on the faculty of Yale University and came to the National Institute of Standards and Technology (NIST) in 1983 where he currently leads a group carrying out precision measurements at the NIST National Cold Neutron Research Facility in Gaithersburg, Maryland. He is the author of 80 scientific publications and edited the book The Investigation of Fundamental Interactions with Cold Neutrons.
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