BIG BANG NO 4
The Big Bang, that primordial explosion more than 13 million years ago provides the accepted description of our universe’s beginning. We can trace with exquisite precision what happened during the expansion and cooling that followed that cataclysm, but the presence of neutrinos in the earliest phase continues to elude direct experimental confirmation.
Neutrinos, once they were in thermal equilibrium, were supposedly freed of their bonds to other particles about 2 seconds after the bang. Since then they have been roaming undisturbed in intergalactic space, Some 200 of them in every cubic centimetre of our universe; altogether a billion of them for every single atom.
Their presence is noted indirectly in the universe’s expansion: However, though they are presumably by far the most numerous type of material particle in existence, not a single one of those primordial neutrinos has ever been detected. It is not for want of trying, but the necessary experiments are almost unimaginably difficult. And yet those neutrinos must be there. If they are not, our picture of the early universe will have to be totally reconfigured.
Wolfgang Pauli’s original proposal of the neutrino’s existence was so daring he did not publish it. Enrico Fermi’s brilliant 1934 theory of how neutrinos are produced in nuclear reactors and soon afterwards in particle accelerators.
Starting in the 1960’s an experimental tour de force revealed their existence in the solar core. Finally in 1987 a 10 second burst of neutrinos was observed radiating outwards from a supernova that occurred almost 200*000 years ago. When they reached earth and observed, one prominent physicist quipped that extra solar neutrino astronomy: “Has gone in 10 seconds from science fiction to science fact.” These are some of the milestones of 20th century neutrino physics.
In the 21st century we eagerly await another milestone - the observation of neutrino0s in the first seconds after the Big Bang. We have been able to infer their presence, but will we be able to actually detect these minute and elusive particles.
They must be somewhere around us, even though we cannot prove it.
Acknowledgements Gino Segre Noted theoretical physicist, prof in depart.and astronomy : university of Pennsylvania.
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