On the morning of her twenty-fifth birthday, Clara Goldstein woke up in two beds, in two rooms, in two versions of New York City that existed side by side, touching but not touching, like the pages of a book pressed together. She did not know that there were two of her. She only knew that she felt strange, divided, as if a seam had been torn somewhere inside her chest and she could not find the thread to stitch it back together.

In the first version of the city, Clara Goldstein was married. She had married David Rosenberg in the spring of 1913, in a small ceremony at City Hall, and they lived in a three-room apartment on the Lower East Side with a view of the East River and a cat that David had found in the alley behind the Herald building. Clara worked at the Herald as a junior reporter, covering the same labor beat that David had covered before he was promoted to the city desk. She was good at her job—she had a way of listening to people that made them tell her things they had never told anyone else—and she was happy, or at least she told herself she was happy, because she had everything she had ever wanted. A job, a husband, an apartment with a view of the river. What more could a girl from the garment district ask for?

In the second version of the city, Clara Goldstein was alone. She had never married David Rosenberg, had never taken the job at the Herald, had never moved out of the tenement room on Orchard Street. After the Triangle fire, she had quit the newspaper and joined the Women's Trade Union League as a full-time organizer, and she had spent the last three years traveling across the country, speaking in factories and union halls and church basements, telling women what she had learned on a sidewalk in Greenwich Village: that the system was not broken, that the system was working exactly as designed, and that the design was death. She was not happy, but she was not unhappy either. She was something else, something that existed in the space between happiness and purpose, and she had learned to live there.

The two versions of Clara Goldstein did not know about each other, but they felt each other's presence. The married Clara sometimes woke in the middle of the night with a sense of loss that she could not explain, a feeling that she had given up something vital without knowing what it was. The solitary Clara sometimes felt a warmth in her chest, a phantom intimacy, as if someone she loved was standing just behind her, invisible but present. They were both incomplete, and they both knew it, and neither of them could say why.

The superposition held for twenty years. The married Clara had two children, a boy and a girl, and she raised them in an apartment in Brooklyn while David rose through the ranks of the Herald to become the managing editor. She stopped writing after the children were born, stopped attending union meetings, stopped reading the radical newspapers that had once filled her bookshelves. She told herself that she was still the same person, that motherhood was a different kind of organizing, that raising children was a different kind of revolution. But late at night, when the children were asleep and David was working late at the newspaper, she would sit at the kitchen table and stare at the typewriter that she had not touched in years, and she would feel the presence of the other Clara, the solitary one, the one who had chosen purpose over happiness and was out there somewhere, speaking in a union hall, making a difference, living the life that she had not lived.

The solitary Clara never married. She had lovers, briefly, but she never let them stay. She was too busy, she told herself, too committed to the cause, too needed by the women in the factories and the mills and the canneries who were depending on her to show them how to fight. She was famous, in certain circles—labor historians would later call her one of the most effective organizers of her generation—but fame is not the same as love, and late at night, when the speeches were done and the meetings were over and she was alone in a hotel room in some Midwestern city, she would feel the presence of the other Clara, the married one, the one who had chosen happiness over purpose and was out there somewhere, raising children and loving a man and living the life that she had not lived.

The two Claras met once, briefly, in 1933. It happened at a labor conference in Chicago, where the solitary Clara was giving the keynote address. The married Clara had come to the conference as a reporter for the Herald—she had started writing again, after the children were grown, and David had given her a column about women's issues. The married Clara sat in the back of the auditorium and watched the solitary Clara walk to the podium, and for a moment, for a single suspended second, their eyes met. The solitary Clara stopped speaking. The married Clara stopped breathing. And in that moment, the superposition collapsed.

They did not merge. They did not become one person. But they understood each other, finally, in a way that they had not understood before. The solitary Clara saw that the married Clara was not weak; she had made choices that were just as hard, just as brave, just as necessary as the choices she had made herself. The married Clara saw that the solitary Clara was not cold; she had loved and lost and kept going, and the love was still there, buried beneath the speeches and the organizing and the long nights in hotel rooms. They saw each other, and they forgave each other, and that was enough.

After the conference, the two Claras did not speak again. They went back to their separate lives, their separate cities, their separate versions of the world. But something had changed. The married Clara started writing more seriously, started using her column to advocate for the same causes that the solitary Clara had spent her life fighting for. The solitary Clara started taking more time for herself, started reading novels and going to concerts and allowing herself to feel the things she had been suppressing for twenty years. They were still divided, still incomplete, still two halves of a whole that could never be reunited. But they were less alone than they had been before.

Clara Goldstein died at the age of eighty-three, in a hospital bed in Brooklyn. Or she died at the age of eighty-three in a hotel room in Chicago. Or she died in both places at the same time, and the two deaths were really one death, and the one death was really two, and the truth existed in the space between them, which is where the truth always exists.

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The collapse of the superposition, when it came, was not dramatic. There was no flash of light, no sudden merging of two separate lives into one. Clara simply understood, in a moment that was no different from any other moment, that the choice she had made—to marry David or not to marry him, to stay at the Herald or to leave—was not the only choice she could have made, and that the alternative choice had been just as real, just as possible, just as alive as the choice she had lived. The other Clara, the one who had not married David, the one who had spent her life on the road organizing strikes and giving speeches—she was not a ghost, not a fantasy, not a regret. She was a parallel reality, a quantum state that had never been observed but had never ceased to exist.

The understanding did not make Clara's life easier. If anything, it made it harder, because it meant that every choice she made was a kind of death—the death of the alternative, the death of the life she had not lived. But it also made her life richer, fuller, more meaningful, because it meant that every choice was also a kind of birth—the birth of a specific reality, a specific path, a specific version of herself that would not have existed if she had chosen differently.

Clara began to think of her life not as a single line but as a branching tree, with every decision creating a new branch, every branch creating new possibilities, every possibility creating a new version of herself. The tree was infinite, and most of the branches were invisible, but they were real. They existed in the same quantum space that had held the two Claras for twenty years, the space of possibilities that had not been observed but had not been destroyed. The tree grew as she aged, and the branches multiplied, and by the time she was eighty years old the tree was as large as a forest. She could not see all the branches, but she could feel them, could feel the lives she had not lived pressing against the life she had lived like water against a dam.

When she died, at the age of eighty-three, all the possible Claras died with her. The wave function collapsed, finally and completely, and the superposition resolved into a single state: a woman named Clara Goldstein-Rosenberg, who had been a garment worker and a reporter and an organizer and a mother and a wife and a revolutionary. The other Claras—the one who had stayed at the Herald, the one who had moved to Paris, the one who had never left the Lower East Side—faded into the quantum noise from which they had come. But they had been real, for a time. They had existed, in the space between observation and reality, and the woman who died in the hospital bed in Brooklyn had been all of them, simultaneously, undivided at last.

There was a third Clara, too—not the married one and not the solitary one, but a third version that existed only in the imagination of the people who knew about the other two. This Clara was a myth, a legend, a figure that activists invoked when they needed courage and journalists invoked when they needed a story. She was not real, but she was true—true in the way that myths are true, which is different from the way that facts are true. The myth of Clara Goldstein was the myth of the woman who could have been anything, who had chosen one path but carried all the others inside her, who represented the infinite possibilities that every woman contained. The myth was more powerful than the reality, because the reality was limited—a human being can only live one life—but the myth was unlimited. The myth contained all the Claras that had ever been imagined, and all the Claras that would ever be imagined, and its power came from its refusal to choose among them.

David Rosenberg, who had known both the real Claras and the myth, understood this better than anyone. In his memoirs, which he wrote in the 1950s and which were published after his death, he described Clara not as a person but as a principle. She was the principle of possibility, he wrote, the living proof that a woman could be more than the world expected her to be. And the proof was not in what she did—though she did extraordinary things—but in what she contained. She contained multitudes, and she never let the world reduce her to a single one.