"The 1967 General Conference on Weights and Measures defined the of time, the second, based on an atomic transition—specifically, between two hyperfine levels of the ground state of cesium-133. (See Physics Today, August 1968, page 60.) Although Cs atomic clocks remain the standard, their time might be running out. Their underlying atomic transition is excited by radiation with a microwave frequency around 9 × 109 Hz, and after decades of advances, a Cs clock’s frequency can be measured with a fractional uncertainty Δν/ν0 of about one part in 1016. But clocks based on optical transitions operate at frequencies around 1014 Hz, which gives them an advantage in the push for lower uncertainty. (See the article by James Bergquist, Steven Jefferts, and David Wineland, Physics Today, March 2001, page 37.) The current record, 9.4 × 10−19, was set in 2019 by an aluminum ion–based optical atomic clock at ."
Quote Details
Added by wikiquote-import-bot
Unverified quote
0 likes
Original Language: English
Available Languages (1)
Sources
Christine Middleton,
https://en.wikiquote.org/wiki/Clock
Revision History
No revisions have been submitted for this quote.
Categories
Clock
8 quotes on TrueQuotesView all quotes by Clock →
Related Quotes
"The simplest and perhaps earliest consisted of an earthen vessel with a small hole in the bottom. This was filled wit…"
"... Early clocks were inaccurate by as much as half an hour a day, and had to be reset frequently with the aid of a ;…"
"The invention of the mechanical clock, and the significant perceptual shift that attended it, provides rich and under…"
"By a clock we understand anything characterized by a phenomenon passing periodically through identical phases so that…"
"… We are accustomed to regard as real those sense perceptions which are common to different individuals, and which th…"
"The clock, not the steam-engine, is the key-machine of the modern industrial age. For every phase of its development …"
"We do not know when men first began to use instruments which were at all similar to modern sundials. A stone fragment…"
"Carbonization drives off moisture... with... low molecular weight organic compounds... from extractives and... pyroly…"
"has not been generally used as a feedstock in simple thermal cracking... because the decomposition temperature is too…"
"[A]n overall model for the simulation of pyrolysis reactors should... include the heat, momentum, s differential equa…"