The SI second is defined by hyperfine atomic transition oscillations

the verdict

SUPPORTED

the evidence backs this

Recorded sources

2 sources for · 0 against

Counts group repeated records of the same source within each side. They do not measure evidence strength or source independence.

The SI second is officially defined by the hyperfine transition frequency of the cesium-133 atom.

The analysis

The claim is a well-established scientific fact regarding the definition of the SI second, which is supported by literature describing primary cesium standards and microwave hyperfine transitions.

Evidence for · 2

Towards the optical second: verifying optical clocks at the SI limit.

Recorded source metadata

McGrew WF, Zhang X, Leopardi H, Fasano RJ, Nicolodi D, Beloy K, Yao J, Sherman JA, Schäffer SA, Savory J, Brown RC, Römisch S, Oates CW, Parker TE, Fortier TM, Ludlow AD. Towards the optical second: verifying optical clocks at the SI limit.. 2019. https://doi.org/10.1364/optica.6.000448

This paper notes that the current SI definition of the second is based on the microwave hyperfine transition in 133Cs.

Source citation format

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More for · 1

Search for Ultralight Dark Matter from Long-Term Frequency Comparisons of Optical and Microwave Atomic Clocks.

Recorded source metadata

Kobayashi T, Takamizawa A, Akamatsu D, Kawasaki A, Nishiyama A, Hosaka K, Hisai Y, Wada M, Inaba H, Tanabe T, Yasuda M. Search for Ultralight Dark Matter from Long-Term Frequency Comparisons of Optical and Microwave Atomic Clocks.. 2022. https://doi.org/10.1103/physrevlett.129.241301

This paper discusses frequency comparisons involving 133Cs fountain microwave clocks in the context of the SI second definition.

Source citation format

The paper trail · every fact has a biography

first checked01 Aug 2026

judged → SUPPORTED · 8301 Aug 2026

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