Blog post: swansont: What…Do You…Mean by That? I…Have to Know!

Please Don’t Beam Me Up, Scotty

This is funny, and mostly right. But there's one physics error I spotted, and it's a whopper. As you might guess, it ties in with the details of quantum teleportation. It's unfortunate, too, because I think much of the story holds together without it.

What Spock should have said was that the answer is "no"; i.e. there's a superfluous "not" in there (a sign error, of sorts). Destruction of the state of the original is a requirement of quantum teleportation, which renders the rest of that section's argument moot. Perfect copying while retaining the original is cloning and there is something called the no-cloning theorem in quantum mechanics: basically, you can't make copies of an unknown quantum state (the wikipedia page on this gets technical pretty quickly). You can transfer that information from one particle to another, but the information in the original is destroyed.

The gory details of this bit of theory is tad outside of my wheelhouse, but as I understand it if you could clone, then you could measure the cloned state without disrupting the original. But there are a whole bunch of quantum effects that depend on a state being undetermined, rather than having some underlying reality — there must be more than one possible state in order to see interference. It's a reason that classical explanations for entanglement fail, because in classical physics you can have an unknown state (a coin you've flipped) and then measure it (look at the coin, see it's "heads"), and you will know that it was heads even before you looked at it. In QM, you don't know that it was heads until the moment of measurement — it was in a superposition of heads and tails before that, and that superposition will behave differently than a state that was secretly heads (or tails) the whole time.
Read and comment on the full post