Cosmology: the mysterious neutrino (Introduction)

by David Turell , Thursday, July 20, 2017, 18:51 (2682 days ago) @ David Turell

It can be three things at once:

https://aeon.co/essays/the-explosive-tale-of-a-spy-a-ghost-particle-and-a-new-physics?u...

"Neutrinos are fundamental to the construction of the Universe. They are tremendously abundant, outnumbering atoms by about a billion to one. They modulate the reactions that cause massive stars to explode as supernovas. Their properties provide clues about the laws governing particle physics. And yet neutrinos are among the most enigmatic particles, largely due to their reticent nature: they have no electric charge and practically no mass, so they interact only extremely weakly with ordinary matter. Some 65 billion of them stream through every square centimetre of your body – an area the size of a thumbnail – every second, without your ever noticing them. 

"Through elaborate sleuthing, physicists have identified three distinct types of neutrinos, which differ in their subtle interactions with other particles. Stranger still, the neutrinos can ‘oscillate’ between types, shedding one identity and adopting another as they travel through space. That discovery led to a significant expansion of the standard theory of how particles behave. Now neutrinos and their subtle oscillations have helped physicists prove an even deeper mystery of matter.

***

"The core of the Sun is a massive nuclear reactor, and theories of nuclear physics yielded a highly precise prediction of the neutrino flux that the Sun should produce. However, more sensitive follow-up experiments to the original Reines-Cowan test had found only about one third the expected number of solar neutrinos. During the early stirrings of US-USSR détente in the late 1960s, Pontecorvo was able to share his latest ideas directly with colleagues in the West. He now calculated that neutrinos should oscillate among three distinct flavours. If so, the solar neutrino detectors, which were only sensitive to one of the flavours, should register the readings of the neutrino flux that the experimentalists kept finding.

***

"The origin and nature of neutrino mass remains a major ongoing area of exploration. Physicists also continue to test whether only three flavours of neutrinos exist in nature. Any more than three would provide decisive evidence that the Standard Model of particle physics – a theory which has successfully described every experiment involving elementary particles for more than forty years – is incomplete.

***

"According to quantum theory, neutrinos’ flavour-changing ways are directly analogous to Schrödinger’s half-dead/half-alive cat, making neutrino oscillations a powerful way to explore the validity of superposition. My colleague Joe Formaggio realized that we could analyze how the mix of neutrino flavours changes as the particles travel, finally settling into a single flavour (equivalent to a definitive verdict of a ‘dead’ or ‘alive’ cat) when measured.

***

"Quantum effects like superposition are usually only manifest over incredibly short distances of tens or hundreds of nanometers, but our test demonstrated unmistakable quantum strangeness over a span of 735 kilometres. And that may be just the beginning. The world is awash in neutrinos that have traveled 150 million kilometres from the Sun, and cutting-edge experiments like the IceCube Neutrino Observatory at the South Pole can now detect primordial neutrinos that have been traveling through space for billions of years, ever since the Big Bang. Perhaps neutrinos like these can also be coaxed to reveal tell-tale signs of quantum superposition. Then we could test this central feature of quantum theory across the vastness of cosmic distances.

"In the meantime, by puzzling through the strange dance of oscillating neutrinos, my colleagues and I have found that, for all of the apparent fairytale strangeness of quantum mechanics, its predictions hold up at human scales. Perhaps it is fitting that the neutrinos’ journey from Fermilab to the Soudan mine is about the same distance that Pontecorvo himself traveled during his storied lifetime, bounding from Rome to Paris or sneaking from Helsinki to Moscow. Across distances like these, we can say with confidence that we really do live in a world of strange superpositions."

Comment: More evidence that the basis of the universe is quantum mechanics. What is more amazing is that big brained H. sapiens could predict the neutrino and then start to understand what they mean to the standard model. It takes the big brain, which started out 300,000 years ago not knowing what it did not know. Size first, obviously.