The sun shines because of fusion. It& #39;s in every middle school science book! So scientists must& #39;ve been 100% sure of this fact for a long time, right?

What if I told you that only a few decades ago, the Solar Neutrino Problem almost made us abandon this theory forever? https://abs.twimg.com/emoji/v2/... draggable="false" alt="🧵" title="Thread" aria-label="Emoji: Thread">
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🔴" title="Roter Kreis" aria-label="Emoji: Roter Kreis">Solar Energy Production
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟠" title="Orangefarbener Kreis" aria-label="Emoji: Orangefarbener Kreis">The Neutrino
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟡" title="Gelber Kreis" aria-label="Emoji: Gelber Kreis">Neutrinos in Matter
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟢" title="Grüner Kreis" aria-label="Emoji: Grüner Kreis">The Davis Experiment
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🔵" title="Blauer Kreis" aria-label="Emoji: Blauer Kreis">Trouble Brewing
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟣" title="Violetter Kreis" aria-label="Emoji: Violetter Kreis">Physicists Get Creative (and Momentarily Forget the Past Century of Stellar Astrophysics)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="⚪️" title="Weißer Kreis" aria-label="Emoji: Weißer Kreis">A Solution
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🔴" title="Roter Kreis" aria-label="Emoji: Roter Kreis">When we say the sun is powered by fusion, we are specifically referring to how lighter stars, like our sun, fuse hydrogen nuclei into Helium-4 nuclei in their core through a process theorized in the 1930s called the p-p chain (also known as the proton-proton chain).
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟠" title="Orangefarbener Kreis" aria-label="Emoji: Orangefarbener Kreis">What we REALLY care about for this thread are those tiny blue particles- neutrinos! Originally proposed by Wolfgang Pauli (and theoretically fleshed out by Enrico Fermi) to explain the energies of beta decays, the neutrino is a small, neutrally-charged lepton (like electrons).
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟡" title="Gelber Kreis" aria-label="Emoji: Gelber Kreis">The neutrinos bump into the nuclei in the detector volume. The matter-neutrino scattering cross section is extreeeemely tiny, so this happens rarely! As a result, the geometry of the detector volume doesn& #39;t even matter- a neutrino is equally likely to hit the front or back.
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟢" title="Grüner Kreis" aria-label="Emoji: Grüner Kreis">Now here& #39;s where things heat up. Now that neutrinos have been theorized (and a few even detected!), a physicist named Raymond Davis wanted to measure the flux of electron neutrinos generated by the sun through the p-p chain.
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟢" title="Grüner Kreis" aria-label="Emoji: Grüner Kreis">Davis would count the number of argon atoms in the detector during each flush, as argon is the byproduct of this specific chlorine-neutrino interaction. His results, which were swiftly duplicated by other types of detectors, suggested a baffling conclusion...
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🔵" title="Blauer Kreis" aria-label="Emoji: Blauer Kreis">The Sun wasn& #39;t releasing enough neutrinos! What?? The p-p chain is supposed to be the mechanism generating all of the energy in the sun- we know exactly how much energy is generated in a p-p event, and we know the luminosity (power) of the sun- so where are all the neutrinos?
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟣" title="Violetter Kreis" aria-label="Emoji: Violetter Kreis">Scientists began positing a number of creative theories as to why this could be the case. Stephen Hawking notably suggested that the energy from the sun could be from matter falling into a small black hole in its core, a callback to Lord Kelvin& #39;s famous theory of gravitational
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟣" title="Violetter Kreis" aria-label="Emoji: Violetter Kreis">contraction producing solar energy- though Lord Kelvin& #39;s calculations of the solar age were orders of magnitude too low and even precluded Darwin& #39;s theory of evolution from being possible!
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🟣" title="Violetter Kreis" aria-label="Emoji: Violetter Kreis">(Darwin was actually extremely nervous about Kelvin& #39;s paper on the subject and, as a result, struck his estimate for the timescales of evolution from future reproductions of his works)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="⚪️" title="Weißer Kreis" aria-label="Emoji: Weißer Kreis">In Pontecorvo& #39;s theory, neutrinos are NOT massless afterall. Instead, they have three mass states which are actually offset from their flavor states- meaning, electron neutrons don& #39;t have a mass, persay, but are instead a linear combination of the three mass states.
https://abs.twimg.com/emoji/v2/... draggable="false" alt="⚪️" title="Weißer Kreis" aria-label="Emoji: Weißer Kreis">The standard model is incomplete and neutrinos undergo oscillations due to their non-zero mass states. Today, neutrinos remain a heavily studied facet of particle physics, and there is much to learn about them- but, at last, we know for sure why the sun shines :)
Normally this is where& #39;d I& #39;d give reading materials- but instead I& #39;ll just tell you this is a preview thread for a more detailed thread on neutrino oscillations I& #39;m dropping on Saturday- so keep your eyes peeled! :)
Pic sources in order:
1) Me :)
2) https://en.wikipedia.org/wiki/Standard_Model
3)">https://en.wikipedia.org/wiki/Stan... https://www.insidescience.org/news/planned-neutrino-detector-may-also-reveal-details-earths-interior
4)">https://www.insidescience.org/news/plan... https://www.pbs.org/wgbh/nova/neutrino/dete-01.html
5)">https://www.pbs.org/wgbh/nova... https://www.cora.nwra.com/~werne/eos/text/neutrino.html
6)">https://www.cora.nwra.com/~werne/eo... https://ned.ipac.caltech.edu/level5/Sept05/Gondolo/Gondolo3.html
7)">https://ned.ipac.caltech.edu/level5/Se... https://www.businessinsider.com/super-kamiokande-neutrino-detector-is-unbelievably-beautiful-2018-6
8)">https://www.businessinsider.com/super-kam... https://www.italyonthisday.com/2019/08/bruno-pontecorvo-Italian-nuclear-physicist-soviet-spy-claim.html
9)">https://www.italyonthisday.com/2019/08/b... https://www.slideserve.com/rhona/1-neutrino-oscillation">https://www.slideserve.com/rhona/1-n...
Relevant companion thread! https://twitter.com/AstroYuki/status/1294252089112244224?s=20">https://twitter.com/AstroYuki...
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