13-5. The reason that massive neutrinos were considered as a candidate for solving the miss- ing mass problem is that, at the conclusion of the lepton era, the universe contained about equal numbers of photons and neutrinos. They are still here, for the most part. The former can be ob- served and their density is measured to be about 500 photons/cm³; thus, there must be about that number density of neutrinos in the universe, too. If neutrinos have a nonzero mass and if the cosmological expansion has reduced their average speed so that their energy is now pri- marily mass, what would be the individual neutrino mass (in eV/c²) necessary to account for the missing mass of the universe? Recall that the observed mass of the stars and galaxies (in- cluding the dust and gas) accounts for only about 4 percent of that needed to close the universe.

13-5. The reason that massive neutrinos were considered as a candidate for solving the miss- ing mass problem is that, at the conclusion of the lepton era, the universe contained about equal numbers of photons and neutrinos. They are still here, for the most part. The former can be ob- served and their density is measured to be about 500 photons/cm³; thus, there must be about that number density of neutrinos in the universe, too. If neutrinos have a nonzero mass and if the cosmological expansion has reduced their average speed so that their energy is now pri- marily mass, what would be the individual neutrino mass (in eV/c²) necessary to account for the missing mass of the universe? Recall that the observed mass of the stars and galaxies (in- cluding the dust and gas) accounts for only about 4 percent of that needed to close the universe.

College Physics

1st Edition

ISBN:9781938168000

Author:Paul Peter Urone, Roger Hinrichs

Publisher:Paul Peter Urone, Roger Hinrichs

Chapter31: Radioactivity And Nuclear Physics

Section: Chapter Questions

Problem 16CQ: Neutrinos are experimentally determined to have an extremer small mass. Huge numbers of neutrinos...

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