What if the Sun vanished?

At exactly noon, the Sun stopped existing. Kabir, an apprentice at the Hanle Observatory high in Ladakh, was eating Maggi outside the dome. Nothing happened. The snow peaks glittered. His shadow lay crisp on the ground.

Nothing could happen yet. The sunlight already on its way was still arriving, and so was the Sun's gravity: changes in gravity travel at the speed of light too. For 8 minutes and 20 seconds, Earth carried on curving round an empty point in space, lit by a star that was no longer there.

At 12:08:20 the day switched off. Not a sunset, no orange glow, just black. Kabir's colleague screamed. The Moon, which had been a pale half-disc in the afternoon sky, vanished too; it had only ever shone by reflected sunlight. So did Venus and Jupiter.

And at that same moment, with nothing to curve round, Earth stopped turning its corner and shot off in a straight line along its old orbit, at nearly 30 kilometres a second, into the dark.

The first week was the worst. With no sunlight, average temperatures dropped below freezing within days. Plants stopped making food, and the crops in the fields went limp and then black. The government announced heat rationing: one warm room per family, powered by whatever the nuclear plants could give.

Kabir's family moved to Puga, where hot springs bubble out of the ground. Geothermal heat became the most valuable thing on Earth. People who had never thought about the planet's hot interior now built their lives around it.

A year on, the surface was colder than Antarctica. The oceans froze over at the top, but the ice acted like a blanket and the water beneath stayed liquid for a very long time.

Kabir watched a documentary, broadcast from a deep-sea station, about the creatures around volcanic vents on the ocean floor. They had never needed sunlight. They fed on chemicals from the Earth's crust, and they didn't even know anything had happened. 'They're the lucky ones,' his sister said. Kabir wasn't sure anyone was.