By VALERIE HOPKINS and RICHARD PÉREZ-PEÑAAn old dispute between the Balkan neighbors over power supplies made residents of countries like Portugal and Poland late.
PRISTINA, Kosovo — Physicists tell us that time expands and contracts because of relativity. Poets and philosophers tell us that time alters with love and age. And, across Europe, microwave ovens tell us that time changes with tussles between Balkan nations.
A dispute between Serbia and Kosovo has disrupted the electric power grid for most of the Continent, making certain kinds of clocks — many of those on ovens, in heating systems and on radios — run up to six minutes slow.
It is one of the stranger examples of technology binding together far-flung parts of the world, and one quirky effect of more than two decades of conflict in the former Yugoslavia.
The slowdown began in mid-January, and since then clocks in 25 countries, from Poland to Portugal and Denmark to Turkey, have lost time. The fluctuation in the power supply is infinitesimally small — not nearly enough to make a meaningful difference for most powered devices — and if it were a brief disturbance, the effect on clocks might be too little to worry about.
But millions of people run the risk of showing up late for work or missing appointments.
The organization that runs the continental grid, the European Network of Transmission System Operators for Electricity, disclosed the problem on Tuesday, saying that it had never seen anything like it before. It announced on Thursday that it had reached an agreement with Serb and Kosovar authorities to end the disruption, for now. It offered no further details.
But the group cautioned that it would take some time to fully stabilize the grid after seven weeks of volatility, and that a long-term solution was still needed to prevent similar problems in the future.
“Misbehavior of both countries” caused the disturbance, Susanne Nies, a spokeswoman for the system operators’ group, said in an interview. “There are some ongoing conflicts that urgently need to be resolved so that we never face such a situation again.”
In technical terms, power systems in Europe, and much of Asia and Africa, run on alternating current at 50 hertz, meaning that the flow of electricity changes directions 50 times per second. (In the United States and most of the Americas, the standard is 60 hertz.)
Because of the disruption in the Balkans, the grid for most of Europe has run since January at an average of 49.996 hertz. (Britain, Ireland, Norway, Sweden and the nations of the former Soviet Union, which are not as tightly linked to the continental system, have not been affected.)
Most clocks tell time using internal mechanisms or, like cellphones, get the time from a radio signal, and those have been fine. But clocks that measure time by that alternating current have been fooled by the drop in frequency.
Major systems like train networks and nuclear reactors were not affected.
The problem began when a power plant in Kosovo, a former province of Serbia, went down for repairs, causing a shortfall in the power supply. Serbia, which still controls Kosovo’s transmission system, has refused to make up the difference, despite an agreement to do so.
But the roots of their dispute run much deeper.
They fought a war in Kosovo, whose population is mostly ethnic Albanian and Muslim, in 1998 and 1999; it ended only after a NATO bombing campaign forced Serbia to withdraw its forces. Kosovo became largely autonomous, and it declared independence in 2008.
The European Union has brokered negotiations for years to normalize relations between the two countries, but many ethnic Serbs in the northern part of the country — and many of their allies in Serbia — do not recognize the authority of the Kosovo government.
That includes refusing to pay for electricity supplied by the Kosovo utility, costing it tens of millions of dollars per year. Under a 2015 agreement that was supposed to ensure a reliable flow of power across the border, Belgrade, the Serbian capital, created companies to supply ethnic Serbs who wanted to pay their bills to a Serb utility.
But a paperwork dispute has kept the new companies from being registered in Kosovo, and each country has accused the other of being the obstruction.
Serbian officials declined to comment this week, instead referring to a report they released in November that blamed Kosovo.
According to Kosovo officials, documents for the companies do not recognize the existence of their country. To them, the underlying problem is that Serbia’s state-owned utility, EPS, owns and profits from much of Kosovo’s grid.
“By biding time, they are getting richer,” said Fadil Ismajli, a former head of Kosovo’s power company, which he said is running out of money. “All this time, we were patient; we wanted to solve this problem at the table.”
Whether Europe’s clocks will lose more time before that happens is unclear.