Pseudorandom unitaries and black holes 💫

These complicated objects [black holes] function as natural information scramblers, so researchers have often modeled them using Haar-random unitaries. 

But the exponential complexity of these models doesn’t seem to conform with the behavior of black holes, which appear to scramble information very quickly. 

Physicists have therefore begun to wonder whether black holes might in fact just seem random, while actually emerging from a relatively simple process —in other words, they could be more like pseudorandom unitaries [PRUs]. 

Now that an explicit proof for the construction of PRUs exists, physicists can start probing that question more directly.

“The lines between physics and computation are becoming much more blurry,” said Poremba, who was a co-author on one of the early 2024 PRU papers.

For Kretschmer, the real significance of Ma and Huang’s proof is that it marks a step toward reconciling classical theory with quantum theory. 

“It’s telling us how to build pseudorandom unitaries, which are fundamentally quantum objects, from one-way functions, which are classical objects,” he said. “This is the bridge that’s being built.”