The SI second is defined by a specific hyperfine transition frequency of cesium-133

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 retrieved literature consistently confirms that the current International System of Units (SI) definition of the second is based on the microwave hyperfine transition of cesium-133.

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 definition of the second in the SI is based on the microwave hyperfine transition in cesium-133 (133Cs).

Source citation format

See more details

More for · 1

A Historical Review of U.S. Contributions to the Atomic Redefinition of the SI Second in 1967.

Recorded source metadata

Lombardi MA. A Historical Review of U.S. Contributions to the Atomic Redefinition of the SI Second in 1967.. 2017. https://doi.org/10.6028/jres.122.029

This historical review discusses the atomic redefinition of the SI second.

Source citation format

The paper trail · every fact has a biography

first checked01 Aug 2026

judged → SUPPORTED · 8301 Aug 2026

More receipts

Is it true that Phonological evolution involves regular processes of phoneme elision, vowel nasalization, and tonogenesis?Is it true that Hemangiomas are treatable with medication?Is it true that Research identifies forms of intelligence that diverge from standard IQ measures?

Random receipt →The Trust Wiki →

Anyone with this link can read the claim and its public receipt, including any personal information in that text. Open permanent receipt.

Check your own claim

Challenge the receipt

I have a source that contradicts this verdict I have a source that supports it No source: request a receipt review Requests are recorded for review. This does not start an automatic check or guarantee a response time.

trust me, bro: win the argument, pass the class, survive peer review.

Citation formatting by citeproc-js (Frank Bennett) and the Citation Style Language project. Source and licenses.

This receipt is an automated verdict against our published method · not an opinion about any author or publication.
Terms · Privacy · How verdicts work · Dispute this receipt