NATO is ready to help Finland and Estonia as Finnish authorities probe an oil tanker that sailed from a Russian port over the possible "sabotage" of a power cable linking the two member countries, alliance chief Mark Rutte has said.
"Spoke with (Estonian Prime Minister) Kristen Michal about reported possible sabotage of Baltic Sea cables. NATO stands in solidarity with Allies and condemns any attacks on critical infrastructure.
"We are following investigations by Estonia and Finland, and we stand ready to provide further support," Mr Rutte said on X.
Earlier, Finnish authorities said they were investigating an oil tanker that sailed from a Russian port for the "sabotage" of a power cable linking Finland and Estonia that was damaged the previous day.
The Cook Islands-registered ship, named by authorities as the Eagle S, was boarded by a Finnish coast guard crew which took command in the Baltic Sea and sailed the vessel to Finnish waters, a coast guard official told a press conference.
"From our side we are investigating grave sabotage," Robin Lardot, Director of the Finnish National Bureau of Investigation, said.
"According to our understanding an anchor of the vessel that is under investigation has caused the damage," he added.
In addition to the curvature of the Earth as mentioned by @[email protected], there is also atmospheric dispersion (implied by @[email protected] answer) and... geological movement.
Land moves slowly due to geological faults, thermal expansion, the gravitational influence of the Moon, ground vibrations (such as those caused by cars and trucks rolling over the ground), among other reasons. This is not a short-term problem for fiber optic cables (because fiber optic cables have some extra length to compensate if the distance becomes slightly longer or shorter), but it is a problem for lasers, because they need to be precisely aimed at a receiver area.
Just micrometers (less than 1 mm) of displacement are enough to mess with the phase of the light. In fact, this is a well-known phenomenon and has been well-exploited in optical interferometry experiments (such as LIGO, which observes small fluctuations in alignment to detect gravitational waves).
Air movement (wind and convection currents) also provokes slight light displacement, enough for laser misalignment.