"But . . . the experiments?"

"The experiments were a sham. They could hardly have been performed on a visitor, on a physical brain -- could they?"

Paul shook his head, and whispered, "Abulafia."

No interface window appeared.

He gripped the couch and closed his eyes, then laughed. "You say I agreed to this? What kind of masochist would do that? I'm going out of my mind. I don't know what I am."

Elizabeth took hold of his arm again. "You're disoriented -- but that won't last long. And you know why you agreed. You were sick of Copies baling out on you. You had to come to terms with their experience. Spending a few days believing you were a Copy would make or break the project: you'd either end up psychologically prepared, at last, to give rise to a Copy who'd be able to cope with its fate -- or you'd gain enough sympathy for their plight to stop creating them.

"The plan was to tell you everything while you were still inside, after the third experiment. But when you went weird on me in there, I panicked. All I could think of was having the puppet playing your original tell you that it was going to pause you. I wasn't trying to frighten you. I didn't think you'd take it so badly."

A technician came into the room and removed the drip and catheter. Paul propped himself up and looked out through the windows of the room's swing doors; he could see half a dozen people in the corridor. He bellowed wordlessly at the top of his lungs; they all turned to stare in his direction. The technician said mildly, "Your penis might sting for an hour or two."

Paul slumped back onto the couch and turned to Elizabeth. "You wouldn't pay for reactive crowds. I wouldn't pay for reactive crowds. It looks like you're telling the truth."

+ + +

People, glorious people: thousands of strangers, meeting his eyes with suspicion or puzzlement, stepping out of his way on the street -- or, more often, clearly, consciously refusing to. The freedom of the city was so sweet. He walked the streets of Sydney for a full day, rediscovering every ugly shopping arcade, every piss-stinking litter-strewn park and alley, until, with aching feet, he squeezed his way home through the evening rush hour, to watch the real-time news.

There was no room for doubt: he was not in a virtual environment. Nobody in the world could have had reason to spend so much money, simply to deceive him.

When Elizabeth asked if his memories were back, he nodded and said of course. She didn't grill him on the details. In fact, having gone over her story so many times in his head, he could almost imagine the stages: his qualms after the fifth scan; repeatedly putting off running the model; confessing to Elizabeth about the project; accepting her challenge to experience for himself just what his Copies were suffering.

And if the suppressed memories hadn't actually reintegrated, well, he'd checked the literature, and there was a two point five percent risk of that happening; electronically censoring access to memories could sometimes permanently weaken the neural connections in which they were encoded.

He even had an account from the database service which showed that he'd consulted the very same articles before.

He reread and replayed the news reports that he'd accessed from inside -- and found no discrepancies. He flicked through encyclopedic databases -- spot-checking random facts of history, geography, astronomy -- and although he was surprised now and then by details which he'd never come across before, there were no startling contradictions. The continents hadn't moved. Stars and planets hadn't vanished. The same wars had been lost and won.

Everything was consistent. Everything was explicable.

And yet he couldn't stop wondering about the fate of a Copy who was shut down and never run again. A normal human death was one thing -- woven into a much vaster tapestry, it was a process which made perfect sense. From the internal point of view of a Copy whose model was simply halted, though, there was no explanation whatsoever for its demise -- just an edge where the pattern abruptly came to an end.

But if the insight he'd gained from the experiments was true (whether or not they'd ever really happened) -- if a Copy could assemble itself from dust scattered across the world, and bridge the gaps in its existence with dust from across the universe . . . then why should it ever come to an inconsistent end? Why shouldn't the pattern keep on finding itself?

Or find a larger pattern into which it could merge?

The dust theory implied a countless number of alternative worlds: billions of different possible histories spelled out from the same primordial alphabet soup. One history in which Durham did run Copy number five -- and one in which he didn't, but was persuaded to take its place as a visitor, instead.

But if the visitor had been perfectly deceived, and had experienced everything the Copy did . . . what set the two of them apart? So long as the flesh-and-blood man had no way of knowing the truth, it was meaningless to talk about "two different people" in "two different worlds." The two patterns of thoughts and perceptions had effectively merged into one.

If the Copy had been allowed to keep on running after the visitor had learned that he was flesh and blood, their two paths would have diverged again. But the Copy had been shut down; it had no future at all in its original world, no separate life to live.

So the two subjective histories remained as one. Paul had been a visitor believing he was a Copy. And he'd also been the Copy itself. The patterns had merged seamlessly; there could be no way of saying that one history was true and the other false. Both explanations were equally valid.

Once, preparing to be scanned, he'd had two futures.

Now he had two pasts.

+ + +

Paul woke in darkness, confused for a moment, then pulled his cramped left arm out from under the pillow and glanced at his watch. Low power infrared sensors in the watch face detected his gaze, and flashed up the time -- followed by a reminder: due at landau 7 a.m. It was barely after five, but it hardly seemed worth going back to sleep.

Memories of the night before came back to him. Elizabeth had finally confronted him, asking what decision he'd reached: to abandon his life's work, or to forge ahead, now that he knew, firsthand, what was involved.

His answer seemed to have disappointed her. He didn't expect to see her again.

How could he give up? He knew he could never be sure that he'd discovered the truth -- but that didn't mean that nobody else could.

If he made a Copy, ran it for a few virtual days, then terminated it abruptly . . . then at least that Copy would know if its own pattern of experience continued.

And if another Paul Durham in one of the countless billions of alternative worlds could provide a future for the terminated Copy -- a pattern into which it could merge -- then perhaps that flesh-and-blood Durham would repeat the whole process

And so on, again and again.

And although the seams would always be perfect, the "explanation" for the flesh-and-blood human believing that he had a second past as a Copy would necessarily grow ever more "contrived," less convincing . . . and the dust theory would become ever more compelling.

Paul lay in bed in the darkness, waiting for sunrise, staring into the future down this corridor of mirrors.

One thing nagged at him. He could have sworn he'd had a dream, just before he woke: an elaborate fable, conveying some kind of insight. That's all he knew -- or thought he knew. The details hovered maddeningly on the verge of recollection.