Editing Second (section)

===Optical lattice clock===
{{Main|Optical lattice clock}}

While they are not yet part of any timekeeping standard, optical lattice clocks with frequencies in the visible light spectrum now exist and are the most accurate timekeepers of all.  A [[strontium]] clock with frequency 430&nbsp;[[Terahertz (unit)|THz]], in the red range of visible light, during the 2010s held the accuracy record: it gains or loses less than a second in 15 billion years, which is longer than the estimated age of the universe. Such a clock can measure a change in its elevation of as little as 2&nbsp;cm by the change in its rate due to [[gravitational time dilation]].<ref>{{cite web|last1=Vincent|first1=James|title=The most accurate clock ever built only loses one second every 15 billion years|url=https://www.theverge.com/2015/4/22/8466681/most-accurate-atomic-clock-optical-lattice-strontium|website=TheVerge|date=April 22, 2015|access-date=January 26, 2018|archive-url=https://web.archive.org/web/20180127084115/https://www.theverge.com/2015/4/22/8466681/most-accurate-atomic-clock-optical-lattice-strontium|archive-date=January 27, 2018|url-status=live}}</ref>