The street was called Hanover Mews, a narrow lane in a part of London that had survived two world wars and the Blitz and the postwar reconstruction and the Thatcher years and the new millennium, and though the buildings had changed and the people had changed and the purpose of the street had shifted from artisans' workshops to something that resembled a tourist destination without quite achieving it, the street itself had remained constant, and two women who lived at opposite ends of its history stood at two different points in its timeline, both right in their own reference frame, and the gap between their perspectives was not a matter of truth versus falsehood but a Doppler shift, the change in frequency caused by relative motion through the medium of shared space.

1925: Eleanor Price lived at number fourteen, a Georgian townhouse that had been divided into flats in 1890 and divided again in 1920, and she occupied the second floor, a room with a window that faced east toward the street and a view of the chimney pots across the alley. Eleanor was sixty-two years old and had been living at number fourteen for forty-one years, since she had moved here with her husband, Thomas, who had been a clockmaker and who had died three years ago.

The street in 1925 was a living thing to Eleanor. She knew the sound of each door when it was opened: the heavy thud of number three, the sharp crack of number seven, the soft sigh of number eleven. She knew the rhythm of the street through the day: the milkman at six, the newspaper boy at seven, the butcher's boy at eight with the paper-wrapped parcels that smelled of salt and meat. She knew the faces of the people who lived here and the people who worked here—the seamstress at number nine, the printer at number five, the widow at number seventeen who grew geraniums in every window box.

Eleanor moved through the street at a certain speed, the speed of a woman who had established her routine forty years ago and had adjusted it only gradually as the world changed around her. The motor cars had appeared fifteen years ago and were still novel enough that she stopped in her doorway to watch them pass, the way she had once stopped to watch the horse-drawn carriages. The electric lights had replaced gas two decades ago, and the change had been so gradual that she could not remember the last night when gas had lit the street.

Her information network was the street itself. She received information through the same channels that had served her since 1884: conversations at the corner shop, notes pinned to the church bulletin board, the gossip of the women who gathered at the washhouse on Tuesday mornings. Information traveled through this network at the speed of human speech, which was slow by modern standards but was the only speed that existed in 1925, and Eleanor understood this speed completely, the way a fish understands water, because it was the medium in which her entire life had been immersed.

A message from her daughter in Australia took six weeks to arrive by ship, and Eleanor read each letter three times and then folded it and placed it in a drawer with the other letters, a collection that represented the complete information history of her relationship with her daughter, measured not in words but in the distance those words had traveled.

1975: Margaret Price lived at number fourteen, and she was Eleanor's granddaughter, though she had never known her grandmother, who had died before Margaret was born. Margaret was thirty-four years old and had moved to number fourteen because it was cheap and central and she needed a place to live while she worked as a librarian at the British Museum.

The street in 1975 was unrecognizable to anyone who knew it in 1925. The Georgian townhouses had been converted into offices and small businesses. The butcher's shop was now a record store. The seamstress at number nine had been replaced by a taxi dispatcher. The church had become a gallery. The washhouse had been demolished for a parking lot.

Margaret moved through the street at a different speed, the speed of a woman who had arrived only three months ago and was still mapping the territory. She did not know the sound of each door. She did not know the faces of her neighbors. She received information through channels that Eleanor would not have recognized: telephone calls that connected her to anywhere in the world instantly, newspapers that reported events on every continent within hours, television broadcasts that brought images into her living room in real time.

Her information network was global and instantaneous. She received information through the telephone, the newspaper, the television, and conversations with colleagues at the museum who brought her news from London and Paris and New York, cities she had never visited but which felt close through the immediacy of the information that flowed between them.

A message to her friend in Australia took minutes to arrive by telephone, and Margaret spoke the words aloud and heard the reply instantly, and the distance between London and Australia, which had separated her grandmother from her daughter by weeks of ocean travel, was compressed into a conversation of forty-five minutes that ended with a promise to visit and a knowledge that the promise could be kept whenever either of them decided.

The Doppler shift between Eleanor's experience and Margaret's experience was determined by the relative velocity of their information environments. Eleanor's information moved at the speed of the milk truck and the walking postman and the sailing ship. Margaret's information moved at the speed of the telephone wire and the jet plane and the television signal. The frequency of Eleanor's information was low—few messages, long intervals, deep meaning compressed into each one. The frequency of Margaret's information was high—many messages, short intervals, shallow meaning distributed across a vast network.

Both were right. Both were experiencing the information flow of their reference frame accurately. Neither was experiencing the other's frame, and the gap between them was not a gap in understanding but a gap in velocity, the way a sound appears lower in pitch to a listener who is moving away from the source and higher to a listener who is moving toward it.

On a Sunday afternoon in October 1975, Margaret sat in the drawing room of number fourteen and found a drawer full of letters tied with ribbon, and she read the first one, addressed in a hand that was elegant and precise, from a daughter to her mother, describing a day in Sydney Harbor, and as she read, Margaret felt the Doppler shift between the two women, the change in frequency caused by the century of acceleration between Eleanor's world and her own, and she understood that both worlds were real, both were valid, and the difference between them was not a matter of better or worse but a matter of speed, and the street outside the window had carried both speeds without changing its name, without changing its location, without acknowledging that two women who had lived in the same room at opposite ends of its history had experienced it as two entirely different universes.