The Senior Official put a hand on Bai Bing’s shoulder. “Why don’t you move the time slider in the simulation farther forward?”

Bai Bing, Chen Xufeng, and Lu Wenming looked uncomprehendingly at the Senior Official.

“If we can accurately predict the future, we can change the present and control the course the future will take. We’d control everything—young man, don’t you think this is possible? Perhaps, together, we can shoulder the great duty of shaping the history to come.”

Bai Bing realized what he was saying and gave a pained smile, shaking his head. He stood and walked over to the computer. He clicked and dragged the time slider bar, extending its length beyond Now into the future. Then he said to the Senior Official, “Try it for yourself.”

INFINITE RECURSION

The Senior Official leapt toward the computer, quicker than anyone had ever seen him move, bringing to mind the dark image of a hungry eagle spotting a baby chick on the ground. He moved the mouse with practiced motions, sliding the time past the Now. In the instant that the slider entered the future, an error window popped up.

Stack Overflow

Bai Bing took the mouse from the Senior Official’s hand. “Let’s run a debugging program and trace that step by step.”

The simulation software returned to the state it had been in before the error and began to run line by line. When the real Bai Bing moved the slider past the present, the simulation Bai Bing in the digital mirror did the same. The debugging program immediately zoomed in on the digital mirror’s superstring computer display, allowing them to see that, on the simulated screen, the simulated simulated Bai Bing two layers down was also moving the slider past the present. Then the debugging program zoomed in on the superstring computer display in the third layer…. In this way the debugger progressed layer after layer deeper, each layer’s Bai Bing in the process of moving the slider past the present time, an infinite Droste image.

“This is recursion, a programming approach where a piece of code calls itself. Under normal circumstances, it finds its answer a finite number of layers down, after which the answer follows the chain of calls back to the surface. But here we see a function calling itself without end, forever unable to find an answer, in infinite recursion. Because it needs to store resources used by the previous layer on the stack at every call, it created the stack overflow we saw earlier. With infinite recursion, even a superstring computer’s ultimate capacity can be used up.”

“Ah.” The Senior Official nodded.

“As a result, even though the course of the universe was decided at the big bang, we still can’t know the future. For people who hate the determinist idea that everything comes from a chain of cause and effect, this probably provides some consolation.”

“Ah …” The Senior Official nodded again. He dragged out the sound for a long, long time.