Latency as a physical quantity

Assembled from 18 blocks · 2 evidence · 19 related

1. Story
2. The delay between sending and receiving, and the property of the internet that is most stubbornly geographic. Light in silica glass travels at roughly two-thirds of its speed in vacuum — around 200,000 km per second — which works out at approximately 5 microseconds of delay for every kilometre of fibre. That number cannot be engineered away: no amount of capacity, compression or caching changes the transit time of a photon, so latency between two continents is set by the length of the cable between them and by nothing else. The consequences are visible and commercial. A New York–London route of about 6,000 km has a floor around 60 milliseconds round trip, which is why the Hibernia Express cable of 2015 was built and priced on being a few hundred microseconds shorter than its neighbours; financial trading firms pay for those microseconds because a market's price is a piece of information that arrives. Latency is also why detours matter after a break: when the Red Sea cables were cut in September 2025, cloud operators told customers that traffic previously crossing the Middle East would take longer, which is not a fault report but a statement about distance.
3. Knowledge
4. The submarine fibre-optic cable
5. Latency as a physical quantity
6. Connections
7. The submarine fibre-optic cable
8. A transatlantic cable is built to be short rather than large
9. SMW4 and IMEWE are cut near Jeddah
10. The cable landing station
11. The submarine optical repeater
12. The Convention for the Protection of Submarine Telegraph Cables
13. Latency as a physical quantity
14. Cables in the Luzon Strait break in sequence over nine hours
15. Cables and a power link are damaged in the Baltic Sea
16. Evidence
17. Supports the September 2015 entry into service of the first transatlantic cable optimised for low latency and the tested 58.95 ms round-trip figure between named data centres in New York and London. V55 verification basis: retrieved in summary, not opened. This is a commercial performance claim by the operator and its data-centre partner, measured between specific facilities, and is not an independent measurement of a route.
18. Supports the 2024 and 2025 Red Sea incidents as described here: the cables reported affected, the assessed anchor-drag mechanism in 2024 with ICPC comment, the 05:45 UTC start of the September 2025 latency effects, and Microsoft's statement that traffic previously routed through the Middle East would see higher latency. V55 verification basis: contemporaneous journalism retrieved in summary, not primary incident reports. Cause attribution for the 2024 damage is an assessment, not a finding; the Houthi movement denied involvement in the 2025 cuts and no cause has been established here.