“With the annihilation of space.”

She was silent a while. “Is that what you do?” she said in her mild, amused voice.

“No. It is not what I do! In the first place, I am not an inventor, an engineer. I am a theorist. What they want from me is a theory. A theory of the General Field in temporal physics. Do you know what that is?”

“Shevek, your Cetian physics, your Noble Science, is completely beyond my grasp. I am not trained in mathematics, in physics, in philosophy, and it seems to consist of all of those, and cosmology, and more besides. But I know what you mean when you say the Theory of Simultaneity, in the way I know what is meant by the Theory of Relativity; that is, I know that relativity theory led to certain great practical results; and so I gather that your temporal physics may make new technologies possible.”

He nodded. “What they want,” he said, “is the instantaneous transferral of matter across space. Transilience. Space travel, you see, without traversal of space or lapse of time. They may arrive at it yet; not from my equations, I think. But they can make the ansible, with my equations, if they want it. Men cannot leap the great gaps, but ideas can.”

“What is an ansible, Shevek?”

“An idea.” He smiled without much humor. “It will be a device that will permit communication without any time interval between two points in space. The device will not transmit messages, of course; simultaneity is identity. But to our perceptions, that simultaneity will function as a transmission, a sending. So we will be able to use it to talk between worlds, without the long waiting for the message to go and the reply to return that electromagnetic impulses require. It is really a very simple matter. Like a kind of telephone.”

Keng laughed. “The simplicity of physicists! So I could pick up the—ansible?—and talk with my son in Delhi? And with my granddaughter, who was five when I left, and who lived eleven years while I was traveling from Terra to Urras in a nearly light-speed ship. And I could find out what’s happening at home now, not eleven years ago. And decisions could be made, and agreements reached, and information shared. I could talk to diplomats on Chiffewar, you could talk to physicists on Hain, it wouldn’t take ideas a generation to get from world to world… Do you know, Shevek, I think your very simple matter might change the lives of all the billions of people in the nine Known Worlds?”

He nodded.

“It would make a league of worlds possible. A federation. We have been held apart by the years, the decades between leaving and arriving, between question and response. It’s as if you had invented human speech! We can talk—at last we can talk together.”

“And what will you say?”

His bitterness startled Keng. She looked at him and said nothing.