Alia walked past John, who flinched back.

And now, at last, she came to me. She was a creature the size of a ten-year-old child, her fur shining where it lay in layers over her flesh. I could hardly read the expression in her squashed-up face, she was too alien for that. But I thought I saw warmth in her eyes.

I said, “I suppose you’re wondering why I asked you here today.”

John snorted. “Christ, Michael. How can you joke?”

“I like your humor, Michael Poole,” Alia said. “Not that I always understood it.”

“You did?” My head was spinning; I tried to make sense of this. “You’ve, uh, studied me?”

“We say Witnessing, ” she said. “I’ve Witnessed you, Michael Poole, all of your life. All of my life.”

“Then you really are from the future,” Tom said. There was an edge to his voice. “My father is dead to you, isn’t he? He’s a fossil you dug up. You can read his whole life the way you can read a book. From birth to death. We are all dead to you—”

John touched his arm. “Tom, take it easy.”

“It isn’t like that,” Alia said. “Thomas George Poole, to Witness isn’t just to watch. It is to appreciate. To share. Michael Poole, I have shared your life, your triumphs, your woes. And now I meet you at last. It is more than an honor. It is — fulfillment.”

Rosa pursed her lips and nodded. That I was being watched by the future was one of the possibilities she had guessed at. She looked almost satisfied, the puzzle resolved.

But I felt deeply uneasy. It was more than self-consciousness. I was a bug trapped beneath a microscope slide, my whole life had been splayed open for inspection. I snapped, “And what about Morag?”

Alia’s smile faded. “I stand before you, and you ask for Morag?”

I couldn’t believe it. She sounded hurt.

Rosa spoke, for the first time since this new apparition had come to us. “Tom is right, isn’t he? That you are from the future?”

Alia turned to her. Her small face was creased, comically quizzical. “It depends what you mean. Can you rephrase the question?”

Tom asked cautiously, “Were you born on Earth?…” His nerve seemed to fail him. “Oh, hell. I can’t believe I even asked a question like that! This is like something from that old stuff you used to read, Dad, it’s a clichй—”

Sonia touched his arm. “Tom, it’s OK.”

I said, “This is difficult for all of us.” So it was. I was calmer than Tom or John, but inside I was screaming at the idiotic strangeness of the whole setup.

Tom took a breath, and tried again. “OK. So were you born on Earth?”

Alia snorted. “Do I look like I was born on Earth?… Sorry. I was born on a ship, called the Nord. ” She hesitated. At times it seemed to take her a while to find the right word, as if she was accessing some nested data store. “Umm, a starship.”

“Ah,” said Rosa.

John turned on her. “What do you mean, ah?”

“That explains the long arms, the high chest. Like our primate ancestors, Alia is evolved for climbing — or for low gravity.” She smiled. “Our ancestors were apes, and so will our descendants be. Bishop Wilberforce must be turning in his grave.”

“Descendants?” That was too big a leap for me. “Alia — are you human?”

“Of course I’m human.” Again she seemed hurt, upset I’d even asked.

Oddly, at times she seemed very young, even adolescent, and easily rebuffed, especially by me. I decided I was going to have to be very gentle, tactful. Or as tactful as you can be with an ape-girl from the future. What a mess, I thought.

Alia said, “But in my time it’s different. Humans have spread out. We have become a family.”

“Across the stars?” Gea asked.

“Across the Galaxy.”

“This is the Expansion you mentioned,” I said. “Or Expansions. ”

“In a human Galaxy, there are lots of different sorts of humans. Just as there are in your time.” She frowned. “Or not. Are there? I’m sorry, I should know.”

Rosa said gently, “It’s some thirty thousand years since the last nonhuman hominid died. Homo sapiens sapiens is alone on Earth.”

“Thirty thousand years? Oh, well.” Alia said this in a flip way, as if thirty thousand years was nothing, her mistake forgivable. Her manner was playful, almost coquettish. But there was a bleak, chilling perspective behind her words, a vastness of empty time.

I said, “All right. Then you are from the future. What date are you from?”

“I can’t say.”

“What date were you born?”

“I can’t say!” She flapped her hands, agitated. “These are slippery concepts. I want to give you answers, but you have to ask the right questions!”

Gea said, “Of course she can’t answer questions about dates.”

John growled, “What are you getting at?”

“Relativity.”

It is a strange consequence of Einstein’s special relativity that time is fragmented. Information cannot travel faster than light, and that finiteness makes it impossible to establish true simultaneity, a universal “now.” And so there is a sort of uncertainty in time, which increases the further you travel. If Alia was born halfway across the Galaxy, that uncertainty could be significant indeed.

“How strange,” Rosa said, “to live in a geography so expansive that such effects become important.”

“Oh, for Christ’s sake,” John snapped.

Gea said to Alia, “Suppose your ancestors had stayed on Earth.”

“Yes?”

“That would eliminate relativity ambiguities. In that case, how long would have elapsed, on Earth, between Michael Poole’s birth and your own? Do you know that?”

Alia said, “Round numbers—”

“That will do.”

“Half a million years.”

There was another stunned moment, a shocked silence. The human race in my day, as I now had to think of it — was only, only, maybe a hundred thousand years old. Alia was remote from me indeed, the species itself many times older than in my time. It was hard to take in such a perspective.

Tom said, “So how did you get here? Did you travel in time?”

Alia cocked her head. “I hate to be boring. Here we go again! Can you rephrase the question?…”

With Gea giving us the lead, we managed to extract a little more.

The universe was finite. It was folded over on itself in spatial dimensions — modern cosmologists knew that much — but also in time,so that the future somehow merged with the past. So to get to the past, you would think, all you had to do was travel far enough into the future — just as Columbus had once tried to find a new route to the east by traveling far enough west around the curve of the Earth.

It wasn’t as simple as that, however, as Alia tried to tell us. “It is a question of information,” she said. “Spacetime is discrete, it comes in small packages, particles. Therefore a given volume can only store a finite amount of information. And that information can be fully described by information stored on the bounding surface of the volume.” She frowned at me. “Is that clear?”

Not to me. But Gea said, “Like a hologram. You have a two-dimensional surface that contains information about a three-dimensional object, the hologram, which is reconstructed when you shine laser light on it.”

“Or like Plato,” John said. “We are prisoners in a cave and all we perceive is shadows cast on the wall outside, shadows of reality.”

“Yes,” I said. “But now Alia is saying the shadows are the reality. I think.”

Gea said to me, “This is like the holographic principle. An early attempt at quantum gravity theory.”

“Never heard of it.”

“It was abandoned, decades ago.”

“Maybe that was a mistake…”

Alia’s time was like a surface bounding the past — bounding all of history, including our own long-vanished time. And everything that could be known about the past was contained in her time, in each successive instant. That wasn’t so hard to grasp; geologists, paleontologists and historians, even detectives, have to believe that the past can be reconstructed from traces stored in the present.