Everybody was still at the window. It was all a bit strange, she conceded.

She set aside her coffee and, phone in hand, walked up to the window. She couldn’t see much past the shoulders of jostling cosmologists: a glimpse of green from the park, a washed-out blue sky. The window was sealed shut to allow the air-conditioning to work, but she thought she could hear a lot of traffic noise: the blaring of horns, sirens.

Toby Pitt spotted her at the back of the pack. A big, affable bear of a man with a strangulated Home Counties accent, Toby worked for the Royal Society; he was the manager of the conference today. “Siobhan! I won’t make jokes about the Astronomer Royal being the last to show any interest in the sky.”

She showed him her phone. “No need. My mother’s already been there.”

“It’s quite a view, though. Come and see.” He extended his massive arm around her shoulders and, with a skillful combination of physical presence and smiling tact, managed to shepherd her through the crowd to the window.

The City of London Rooms had a fine view of the Mall, and of St. James’ Park beyond. The grass of the park glowed lurid green, no longer a native specimen but a tough, thick-leaved drought-resistant breed imported from southern Texas, and the relentless sprinklers sent sprays of water shimmering into the air.

But the traffic in the Mall was jammed. The smart cars had calmly packed themselves up in an optimal queuing pattern, but their frustrated drivers were pounding at their horns, and heat haze rose in a shimmer in the humid air. Looking up the road Siobhan saw that the traffic control lights and lane guides were blinking, apparently at random: no wonder the traffic was snarled.