When part of an atomic nucleus, neutrons are extremely stable, but 'free' neutrons (i.e. those outside of a nucleus) decay into a proton, an electron and an electron-antineutrino in about 15 minutes.

Two different methods have been used to measure the neutron's 'lifespan'.

The 'bottle' method and the 'in-beam' method (described in the links below) give different results. The bottle method puts the decay time at 878.5 seconds ±1 second. With the beam method it's 887.7 seconds ±1.9 seconds.

Not only do the results differ by more than 9 seconds, but also the 'margin of error' figures don't fit into the difference. So either the measurements are wrong, or the error margin is wrong, or both.

Although the 9 seconds difference may seem minimal, it has very far-reaching implications for calculations regarding the big bangplugin-autotooltip__plain plugin-autotooltip_bigBig Bang theory

There is now a large body of evidence (from different sources) to support the Big Bang Theory for the origin of the universe, but the problem remains as to the origin of the material or energy which initialised it.

As the UK’s Astronomer Royal Martin Rees has put it :, where neutrons and protons are believed to have been forming within 20 minutes or so of the event, and when the (lighter) elements were created.

See: Neutron death mystery Scientific American, May 2014

Further tech info :

Improved Determination of the Neutron Lifetime Phys. Rev. Lett. 111, 222501

Toward New Precision in Measuring the Neutron Lifetime NIST Center for Neutron Research

Also see Neutron CP problemplugin-autotooltip__plain plugin-autotooltip_bigNeutron CP problem

The neutron CP problem is a disparity between the Standard Model (SM) view of particle physics, and theoretical aspects of Quantum Chromo Dynamics (QCD).

The neutron (as the name implies) has a neutral electrical 'charge', because the three

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