"But we would not allow the dissemination of any data. Only an inspection tour, at the highest level, would be acceptable."

"The highest level?"

"Perhaps you would care to visit the site yourself, Jack Raoul."

I laughed. "Perhaps... when I find out what the catch is."

The rolling accelerated. "We know each other too well. Jack, we would have to rebuild you."

There was no inflection in the artificial voice. The image of Earth rippled across Ghost skin.

I shivered.

"Ambassador, just give me one hint. You know I'm an inquisitive man."

"A hint?"

"What are you trying to do, with your quagma?"

The rolling stopped. "You have heard of the Uncertainty Principle..."

"Of course."

"We have violated it."

After my meeting with the Ambassador I returned to our New Bronx apartment, poured myself a malt, slumped on my favorite couch, and called up Eve.

One wall melted. Eve was heartbreakingly real, at least when she didn't move and the image stayed stable.

She looked around quickly, as if establishing where she was, then fixed me with an admonishing stare.

"You're looking good," I said, raising my glass at the wall.

She snorted, but pushed a hand through her grayed hair. "What do you want, Jack? You know this is bad for you."

"I want you to tell me about the Uncertainty Principle."

"Why?"

"I'll explain later."

She frowned. "The walls have plenty of popular science texts--"

"You know I can never understand a word of that stuff unless you explain it to me."

"Lethe, Jack; that's just sentimental--"

"Humor me. It's important."

She sighed and pulled at a stray lock of hair. "All right, damn it. But I'll keep it brief; and when it's over, that's it."

"It's a deal."

Now Eve changed, subtly, so that -- without any obvious reworking of the image -- she seemed younger, more comfortable on the couch. I guessed the wall was accessing an older part of her Notebooks. "To understand Heisenberg's Uncertainty Principle," she began, "you need to get a handle on quantum mechanics."

According to the quantum philosophy, particles like electrons don't exist as points of mass and charge. Instead each electron has a wave function which describes its position, velocity and other properties; it's as if the electron is spread over a small volume of space delimited by the wave function.

"So where does the Uncertainty Principle come in?"

Eve twisted my ring around her finger. "You can reduce the spread of an electron's position wave-volume -- perhaps by inspecting it using very high frequency photons. But the catch is that the wave-volume associated with another variable -- the electron's momentum -- expands enormously. And vice versa.

"So you can never know both the electron's position and momentum; you can never reduce both wave-volumes to zero."

"Okay. What's the size of these volumes?"