Editing Speed of light (section)

=== Large distances on Earth ===
[[File:Light world trip.ogg|thumb|Acoustic representation of the speed of light: in the period between beeps, light travels the circumference of Earth at the equator.]]
Given that the equatorial circumference of the Earth is about {{val|40075|u=km}} and that ''c'' is about {{val|300000|u=km/s}}, the theoretical shortest time for a piece of information to travel half the globe along the surface is about 67 milliseconds. When light is traveling in [[optical fibre]] (a [[Transparency and translucency|transparent material]]) the actual transit time is longer, in part because the speed of light is slower by about 35% in optical fibre with an refractive index ''n'' around 1.52.<ref name=Midwinter>
{{Cite book
 | last = Midwinter |first=J. E.
 | year = 1991
 | title = Optical Fibers for Transmission
 | edition = 2
 | publisher = Krieger
 | isbn = 978-0-89464-595-2
}}</ref> Straight lines are rare in global communications and the travel time increases when signals pass through electronic switches or signal regenerators.<ref>
{{Cite web
 |date=June 2007
 |title=Theoretical vs real-world speed limit of Ping
 |url=http://royal.pingdom.com/2007/06/01/theoretical-vs-real-world-speed-limit-of-ping/
 |website=Pingdom
 |access-date=5 May 2010
 |archive-date=2 September 2010
 |archive-url=https://web.archive.org/web/20100902224536/http://royal.pingdom.com/2007/06/01/theoretical-vs-real-world-speed-limit-of-ping/
 |url-status=dead
}}</ref>

Although this distance is largely irrelevant for most applications, latency becomes important in fields such as [[high-frequency trading]], where traders seek to gain minute advantages by delivering their trades to exchanges fractions of a second ahead of other traders. For example, traders have been switching to [[microwave]] communications between trading hubs, because of the advantage which radio waves travelling at near to the speed of light through air have over comparatively slower [[fibre optic]] signals.<ref>{{Cite journal |last1=Buchanan |first1=Mark |date=11 February 2015 |title=Physics in finance: Trading at the speed of light |journal=Nature |volume=518 |issue=7538 |pages=161–163 |bibcode=2015Natur.518..161B |doi=10.1038/518161a |pmid=25673397 |doi-access=free}}</ref><ref>{{Cite news |date=10 May 2013 |title=Time is money when it comes to microwaves |newspaper=Financial Times |url=http://www.ft.com/cms/s/2/2bf37898-b775-11e2-841e-00144feabdc0.html |archive-url=https://ghostarchive.org/archive/20221210211258/https://www.ft.com/content/2bf37898-b775-11e2-841e-00144feabdc0 |archive-date=10 December 2022 |url-access=subscription |access-date=25 April 2014 |url-status=live }}</ref>