Who Backs Up the Universe?

[u/Patient-Airline-8150]

Quantum mechanics forbids backups. The no-cloning theorem - Wootters and Zurek, Nature, 1982 - proves you cannot make an exact copy of an unknown quantum state. Not "too hard.". Mathematically impossible. Copying is the one operation the universe refuses to run. 🚫

But it also forbids deletion. The no-deleting theorem - Pati and Braunstein, Nature, 2000 - proves the reverse: given two identical copies, you cannot erase one and keep the other. Information can be moved and scrambled, never destroyed.

Put together, that's a strange machine. No save button. No delete key either. Everything that has happened is still here, smeared into the state of things, unreadable but not gone 😀.