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Since 1967 the SI second has been defined by the radiation frequency of the caesium-133 atom, 9,192,631,770 cycles, and not by the rotation of the Earth.

the verdict
SUPPORTED
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Recorded sources
3 sources for · 0 against

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Is it true that since 1967 the SI second has been defined by the radiation frequency of the caesium-133 atom, 9,192,631,770 cycles, and not by the rotation of the Earth?

Yes. A Wikipedia reference on the caesium standard states that the BIPM's 1967 definition fixed the second as 9,192,631,770 periods of caesium-133 radiation, and a NIST page confirms the second equals that many caesium cycles, replacing astronomical timekeeping.

Verdict: SUPPORTED · 3 sources for, 0 against · Last checked

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Evidence for · 3
Beams of Atoms: The First Atomic Clocks | NISTLock
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Beams of Atoms: The First Atomic Clocks | NISTLock. (n.d.). nist.gov. https://www.nist.gov/atomic-clocks/how-atomic-clocks-work/beams-atoms-first-atomic-clocks

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More for · 2
Caesium standard - Wikipedia
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Caesium standard - Wikipedia. (n.d.). en.wikipedia.org. https://en.wikipedia.org/wiki/Caesium_standard

When should we change the definition of the second?
2011
Get citation
Gill, P. R. (2011). When should we change the definition of the second?. doi.org. https://doi.org/10.1098/rsta.2011.0237

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