“Explain it to me again,” insisted Maria. Alex leaned forwards in his seat, elbows on knees, to narrow the gap between them across the tube carriage. He didn’t want to raise his voice. Around them people examined their phones.
“Are you just humouring me now ?” he asked. “I’m sure there’ll be things that explain it all when we get there.”
“No, I really want to try to understand it,” she replied. “And I like hearing you talk about it. I want you to humour me, not the other way round.”
The train slowed into its next station. Alex watched the blur through the window resolve itself into a platform, waiting people, a name. Camden Town. He always thought it was like watching a film slowing down into a series of still photographs and, finally, a single, framed shot. There was always a moment, even if it was just a fraction of a second, a heartbeat, when everything stopped before the train doors slid open and exhaled its passengers onto the platform. Mind the gap.
“Imagine the world and imagine a big line drawn all the way around the equator,” started Alex.
“I think I have this part,” said Maria. “I’m imagining parallel lines horizontally stacked on top of each other…”
“And underneath each other…”
“And underneath other other,” she continued. “Reaching to the North and South Poles. Take the equator as your start point and then you can measure how far north or south you are. Degrees of latitude. Seems straightforward enough.”
“Well, allowing for a certain degree of latitude in your explanation, you’re right,” acknowledged Alex with a smile. “But latitude was always the easy part because it works from a fixed physical point – the lines you draw north and south around the earth don’t move relative to the equator. And if you know your stars then you can work it out by looking at the sky. Longitude was where it got messy, all those imaginary lines are now running vertical and without a natural reference point.”
“This is where I lost you last time,” said Maria. “What do you mean there’s no natural reference point ?”
“Because the earth is spinning. Longitude is a distance in the Earth’s daily rotation. Unless you agree an arbitrary fixed point to measure against then no one will ever agree on where they are. It’s always moving. One degree every four minutes.”
“And so the good folks at Greenwich offered to be the fixed point of reference for measuring how far east or west you were ?”
“Well we’ve missed a bunch of stuff out about how they standardised solar time for everyone first so that you could always know what time it was in any given location but, yes, I guess you have it about right.”
“Not bad for an amateur,” smiled Maria with a satisfied nod of her head. “We can’t all be… what was it again ?”
“A physicist. Technically an astrophysicist I guess although I never finished my thesis.”
“Well, I don’t know about physics but I do know you’ll never find your way to where you want to go unless you know where you are now.”
The tannoy on the train interrupted them, announcing that there were suspensions on the Northern Line from the next stop in a tone that Alex recognised as more apologetic than Maria did. They changed at King’s Cross with a plan to skirt part of the circumference of the Circle Line and then take a boat up the Thames. It would take longer but Alex figured, on the plus side, that some time on the river would be a better way for Maria to see some of the sites and might give him a better chance to explain the intricacies of a system of navigation that had, after all, arisen to guide people lost on the waves. He wasn’t altogether sure why he’d agreed to the trip but Maria had suggested it and she’d been roundly supported by Sarah and Rob, the three of them nagging him through yesterday evening until he’d agreed to show her the Observatory at Greenwich. Despite himself the idea of it had gotten under his skin, sparked something of the curiousity he’d often felt from back when he was a post grad. He wasn’t booked out to a specific client this week so he’d taken a couple of days leave. He was long overdue holiday. It was a standing joke in the house that he had so many days in lieu stacked up that he could spend all of next year in Cornwall. It had taken Rob some time to explain this to Maria. Looe. It’s a place in Cornwall. In lieu. Oh never mind.
The disruption that had forced the change of route seemed to be causing problems across the network. They made halting progress on the Circle Line before the train stopped at Liverpool Street. Alex felt his phone vibrate in his pocket as it picked up the station wifi and he reflexively pulled it out to check his messages. Maria watched his expression change as he stared at the screen, the frown, the slight slump in his shoulders. He looked up and took a deep breath. She saved them both the awkwardness.
“Do you need to be somewhere else ?”
“I’m sorry. Really sorry. It’s a work thing. There’s a client audit that’s over running. They need an extra pair of hands to get it over the line by this evening. I don’t want to leave you in the lurch but..”
“Don’t worry about me,” said Maria. “I will find Greenwich just fine. 51 degrees north and zero degrees west, right ?”
“You were just humouring me,” said Alex. “How did you know that ?”
“I like to know where I am and where I’m going. Now, go on, go do whatever it is that your job needs you to do. Go count things. Just promise you’ll let me tell you all about it tonight.”
“Okay, that sounds good. Just stay on this train to Tower Hill and then you should be able to pick up the boat service.”
Alex left the train, left Maria, just as the doors slid shut again. He turned to wave and she lifted her arm in response, a brief flare of white as her watch caught the glare of an overhead light. Somewhere in the back of his mind he remembered Miller testily explaining relativity to them again, three of them sitting in his dusty study in Oxford, listening to the rain outside. He remembered listening for patterns and order in the rhythmic fall of water on pavement. Remembered debating the apparent randomness of rain with colleagues who went on to help discover gravitational waves. Discovered the universe’s pulse. Remembered letting his mind roam, untethered, to fathom the smallest particles and the largest spaces and the longest times. He knew, dimly, that he and Maria would observe that light on the train differently. Her from inside the carriage. He watching her move with the train from the platform. They would see light relative to their perspectives.
The train cleared the platform and, buffeted by the sudden back draught, Alex turned and headed for work.
Maria closed her eyes. The contrast was a little too bright when the carriage was plunged into the darkness of the tunnel. She felt the familiar, nagging tingle in her hands and rubbed them together until it faded.