system
Given the following post, respond as if you're commenting on Reddit:
human
What exactly is meant by "quantum information cannot be destroyed"?
gpt
It means that given the current state of the universe, if you knew every piece of quantum information there is to know, you should be able to perfectly reconstruct the entire history of the universe from this information and the laws of physics alone. If it was possible to destroy quantum information, this would not be possible, because there would be information that has existed in the past but doesn't exist anymore, so there would be no way to recover the lost information from the current state of the information.