“So that was what happened to Jupiter,” Pirius said.

“Yes. Quite a monument!”

“But if they could make black-hole cannons, if they could go back in time, why not just fly out to the Qax home world and wipe them out?”

Nilis smiled. “Spoken like a true pragmatist! But the Friends’ objective was more philosophical. . . .”

The first Friends of Wigner had taken their name from an ancient philosopher who had pondered the mysteries of quantum physics. Beneath the world perceived by humans was a scaffolding of uncertainty. Quantum functions pervaded space, each a description of the probability governing a particle or system; it was only when an observation was made that a particle could be pinned down to a particular place, or to a definite speed.

“But this ancient philosopher, Wigner, took that logic a step further,” Nilis said. “Any observer is herself a quantum object—everything is, we all are—and therefore herself subject to quantum uncertainty. You need a second observer to make her real, and thence to make her observation real. If Wigner is the first observer, his friend is the second.”

Pirius thought that over. “But what about the friend’s quantum function? That isn’t made definite until a third observer makes an observation of her.”

“You have it,” said Nilis approvingly. “And then you need a fourth, and a fifth.”

Pirius’s head was swimming with infinities. “But no matter how many observers you have, how many friends of Wigner you line up, you always need one more. So nothing can be real.”

“This was called the paradox of Wigner’s friends,” Nilis said. “But the Friends believed they had a resolution.”

The chains of unresolved quantum states will build on and on, growing like flowers, extending into the future. At last the great chains of quantum functions would finally merge at the last boundary of the universe, at timelike infinity.

“And there, argued the Friends, will reside the Ultimate Observer, the last sentient being of all. All quantum functions, all world lines, must terminate in the Observer—for otherwise, she would not be the last. The Observer will make a single climactic Observation—”

“And the chains of observations will collapse.”

“History will be made real at last, but only at its very end.”

Pirius said, “But I don’t see how this was going to help the Friends get rid of the Qax.”

The Friends had come to believe that the Ultimate Observer might not be a passive eye, but that this final being might have a choice: that she might be able to exert an influence on how the chains of quantum functions were collapsed, on which cosmic history out of the many possible was selected.

“And if a being has such power,” Nilis said, “perhaps she can be lobbied. And that was what the Friends intended to do. They were going to send the Ultimate Observer a message.”

“How? With Jupiter?”